diff --git a/compiler/testData/asJava/lightClassStructure/Declared.kt b/compiler/testData/asJava/lightClassStructure/Declared.kt
index f8dbe82eafa..e09d095bfe4 100644
--- a/compiler/testData/asJava/lightClassStructure/Declared.kt
+++ b/compiler/testData/asJava/lightClassStructure/Declared.kt
@@ -23,7 +23,7 @@ final class Final
 // Special
 annotation class Annotation
 enum class Enum
-trait Trait
+interface Trait
 
 // Deprecation
 deprecated("") class Deprecated
diff --git a/compiler/testData/asJava/lightClassStructure/DeclaredWithGenerics.kt b/compiler/testData/asJava/lightClassStructure/DeclaredWithGenerics.kt
index 70e2c5e47e5..440a2203f1e 100644
--- a/compiler/testData/asJava/lightClassStructure/DeclaredWithGenerics.kt
+++ b/compiler/testData/asJava/lightClassStructure/DeclaredWithGenerics.kt
@@ -7,5 +7,5 @@ class Generic2<A, B>
 class Generic2WithBounds<A, B> where A: Bound1, A: Bound2, B: Generic1<A>
 
 class Bound1
-trait Bound2
+interface Bound2
 
diff --git a/compiler/testData/asJava/lightClasses/delegation/Function.kt b/compiler/testData/asJava/lightClasses/delegation/Function.kt
index 9fda4a47c45..2b0a72c3c32 100644
--- a/compiler/testData/asJava/lightClasses/delegation/Function.kt
+++ b/compiler/testData/asJava/lightClasses/delegation/Function.kt
@@ -1,6 +1,6 @@
 // Derived
 
-trait Base {
+interface Base {
     fun baz(s: String): String
 }
 
diff --git a/compiler/testData/asJava/lightClasses/delegation/Property.kt b/compiler/testData/asJava/lightClasses/delegation/Property.kt
index ce590bfa050..7b2c815ace1 100644
--- a/compiler/testData/asJava/lightClasses/delegation/Property.kt
+++ b/compiler/testData/asJava/lightClasses/delegation/Property.kt
@@ -1,6 +1,6 @@
 // Derived
 
-trait Base {
+interface Base {
     val boo: String
 }
 
diff --git a/compiler/testData/asJava/lightClasses/nullabilityAnnotations/Generic.kt b/compiler/testData/asJava/lightClasses/nullabilityAnnotations/Generic.kt
index 2541b473c8e..a1b5772cb8b 100644
--- a/compiler/testData/asJava/lightClasses/nullabilityAnnotations/Generic.kt
+++ b/compiler/testData/asJava/lightClasses/nullabilityAnnotations/Generic.kt
@@ -1,6 +1,6 @@
 // Generic
 
-trait Generic<N, NN: Any> {
+interface Generic<N, NN: Any> {
     fun a(n: N): N
     fun b(nn: NN): NN
 
diff --git a/compiler/testData/asJava/lightClasses/nullabilityAnnotations/IntOverridesAny.kt b/compiler/testData/asJava/lightClasses/nullabilityAnnotations/IntOverridesAny.kt
index 274a682a4f6..0bc3e928ac2 100644
--- a/compiler/testData/asJava/lightClasses/nullabilityAnnotations/IntOverridesAny.kt
+++ b/compiler/testData/asJava/lightClasses/nullabilityAnnotations/IntOverridesAny.kt
@@ -1,6 +1,6 @@
 // C
 
-trait Tr {
+interface Tr {
     fun foo(): Any
     val v: Any
 }
diff --git a/compiler/testData/asJava/lightClasses/nullabilityAnnotations/OverrideAnyWithUnit.kt b/compiler/testData/asJava/lightClasses/nullabilityAnnotations/OverrideAnyWithUnit.kt
index 1efb58ec710..9915f6225bd 100644
--- a/compiler/testData/asJava/lightClasses/nullabilityAnnotations/OverrideAnyWithUnit.kt
+++ b/compiler/testData/asJava/lightClasses/nullabilityAnnotations/OverrideAnyWithUnit.kt
@@ -1,6 +1,6 @@
 // C
 
-trait Base {
+interface Base {
     fun foo(): Any
 }
 
diff --git a/compiler/testData/asJava/lightClasses/nullabilityAnnotations/Primitives.kt b/compiler/testData/asJava/lightClasses/nullabilityAnnotations/Primitives.kt
index 7efecda0ad5..b586c4344c1 100644
--- a/compiler/testData/asJava/lightClasses/nullabilityAnnotations/Primitives.kt
+++ b/compiler/testData/asJava/lightClasses/nullabilityAnnotations/Primitives.kt
@@ -1,6 +1,6 @@
 // Primitives
 
-trait Primitives {
+interface Primitives {
     fun int(x: Int): Int
 
     val nullableBool: Boolean?
diff --git a/compiler/testData/asJava/lightClasses/nullabilityAnnotations/PrivateInTrait.kt b/compiler/testData/asJava/lightClasses/nullabilityAnnotations/PrivateInTrait.kt
index f15c852a545..3b69e0a805c 100644
--- a/compiler/testData/asJava/lightClasses/nullabilityAnnotations/PrivateInTrait.kt
+++ b/compiler/testData/asJava/lightClasses/nullabilityAnnotations/PrivateInTrait.kt
@@ -1,6 +1,6 @@
 // PrivateInTrait
 
-trait PrivateInTrait {
+interface PrivateInTrait {
     private var nn: String
         get() = ""
         set(value) {}
diff --git a/compiler/testData/asJava/lightClasses/nullabilityAnnotations/Trait.kt b/compiler/testData/asJava/lightClasses/nullabilityAnnotations/Trait.kt
index ebced47d04e..11d7f619b95 100644
--- a/compiler/testData/asJava/lightClasses/nullabilityAnnotations/Trait.kt
+++ b/compiler/testData/asJava/lightClasses/nullabilityAnnotations/Trait.kt
@@ -3,7 +3,7 @@
 import org.jetbrains.annotations.NotNull
 import org.jetbrains.annotations.Nullable
 
-trait Trait {
+interface Trait {
     fun notNull(a: String): String
     fun nullable(a: String?): String?
 
diff --git a/compiler/testData/asJava/lightClasses/nullabilityAnnotations/TraitClassObjectField.kt b/compiler/testData/asJava/lightClasses/nullabilityAnnotations/TraitClassObjectField.kt
index 73598d0f805..18550ad7fc4 100644
--- a/compiler/testData/asJava/lightClasses/nullabilityAnnotations/TraitClassObjectField.kt
+++ b/compiler/testData/asJava/lightClasses/nullabilityAnnotations/TraitClassObjectField.kt
@@ -1,6 +1,6 @@
 // TraitClassObjectField
 
-trait TraitClassObjectField {
+interface TraitClassObjectField {
     companion object {
         val x: String? = ""
         private val y: String? = ""
diff --git a/compiler/testData/asJava/lightClasses/nullabilityAnnotations/UnitAsGenericArgument.kt b/compiler/testData/asJava/lightClasses/nullabilityAnnotations/UnitAsGenericArgument.kt
index be4e460f616..a4ecf3d1916 100644
--- a/compiler/testData/asJava/lightClasses/nullabilityAnnotations/UnitAsGenericArgument.kt
+++ b/compiler/testData/asJava/lightClasses/nullabilityAnnotations/UnitAsGenericArgument.kt
@@ -1,6 +1,6 @@
 // C
 
-trait Base<T> {
+interface Base<T> {
     fun foo(t: T): T
 }
 
diff --git a/compiler/testData/cfg-variables/basic/VariablesInitialization.instructions b/compiler/testData/cfg-variables/basic/VariablesInitialization.instructions
index 28c356a8d57..8aa81131cf1 100644
--- a/compiler/testData/cfg-variables/basic/VariablesInitialization.instructions
+++ b/compiler/testData/cfg-variables/basic/VariablesInitialization.instructions
@@ -51,7 +51,7 @@ sink:
     <SINK>                                       INIT: in: {foo=ID} out: {foo=ID}    USE: in: {} out: {}
 =====================
 == Foo ==
-trait Foo {
+interface Foo {
     var c: Int
 }
 ---------------------
diff --git a/compiler/testData/cfg-variables/basic/VariablesInitialization.kt b/compiler/testData/cfg-variables/basic/VariablesInitialization.kt
index ae78a8a15e1..58f7e678bef 100644
--- a/compiler/testData/cfg-variables/basic/VariablesInitialization.kt
+++ b/compiler/testData/cfg-variables/basic/VariablesInitialization.kt
@@ -11,6 +11,6 @@ fun bar(foo: Foo) {
     42
 }
 
-trait Foo {
+interface Foo {
     var c: Int
 }
\ No newline at end of file
diff --git a/compiler/testData/cfg-variables/basic/VariablesInitialization.values b/compiler/testData/cfg-variables/basic/VariablesInitialization.values
index 9401bee010c..9a9d3f560be 100644
--- a/compiler/testData/cfg-variables/basic/VariablesInitialization.values
+++ b/compiler/testData/cfg-variables/basic/VariablesInitialization.values
@@ -28,7 +28,7 @@ foo                      <v3>: {<: Foo}   NEW: r(foo) -> <v3>
 { foo.c foo.c = 2 42 }   <v5>: *          COPY                                          
 =====================
 == Foo ==
-trait Foo {
+interface Foo {
     var c: Int
 }
 ---------------------
diff --git a/compiler/testData/cfg/declarations/classesAndObjects/delegationByExpression.instructions b/compiler/testData/cfg/declarations/classesAndObjects/delegationByExpression.instructions
index b2917e4afd8..53d4756dcaf 100644
--- a/compiler/testData/cfg/declarations/classesAndObjects/delegationByExpression.instructions
+++ b/compiler/testData/cfg/declarations/classesAndObjects/delegationByExpression.instructions
@@ -1,5 +1,5 @@
 == T ==
-trait T
+interface T
 ---------------------
 L0:
   1 <START>
diff --git a/compiler/testData/cfg/declarations/classesAndObjects/delegationByExpression.kt b/compiler/testData/cfg/declarations/classesAndObjects/delegationByExpression.kt
index 8071281842b..36d898f091b 100644
--- a/compiler/testData/cfg/declarations/classesAndObjects/delegationByExpression.kt
+++ b/compiler/testData/cfg/declarations/classesAndObjects/delegationByExpression.kt
@@ -1,4 +1,4 @@
-trait T
+interface T
 
 class A(a: Int, b: Int): T
 
diff --git a/compiler/testData/cfg/declarations/classesAndObjects/delegationByExpression.values b/compiler/testData/cfg/declarations/classesAndObjects/delegationByExpression.values
index c5f4dbea26c..c6d2ab9a9d1 100644
--- a/compiler/testData/cfg/declarations/classesAndObjects/delegationByExpression.values
+++ b/compiler/testData/cfg/declarations/classesAndObjects/delegationByExpression.values
@@ -1,5 +1,5 @@
 == T ==
-trait T
+interface T
 ---------------------
 =====================
 == A ==
diff --git a/compiler/testData/cfg/declarations/local/ObjectExpression.instructions b/compiler/testData/cfg/declarations/local/ObjectExpression.instructions
index 33e977e7794..3bb05196aa5 100644
--- a/compiler/testData/cfg/declarations/local/ObjectExpression.instructions
+++ b/compiler/testData/cfg/declarations/local/ObjectExpression.instructions
@@ -1,5 +1,5 @@
 == A ==
-trait A {
+interface A {
     fun foo() : Int
 }
 ---------------------
diff --git a/compiler/testData/cfg/declarations/local/ObjectExpression.kt b/compiler/testData/cfg/declarations/local/ObjectExpression.kt
index cf5ba96f594..cac81104548 100644
--- a/compiler/testData/cfg/declarations/local/ObjectExpression.kt
+++ b/compiler/testData/cfg/declarations/local/ObjectExpression.kt
@@ -1,4 +1,4 @@
-trait A {
+interface A {
     fun foo() : Int
 }
 
diff --git a/compiler/testData/cfg/declarations/local/ObjectExpression.values b/compiler/testData/cfg/declarations/local/ObjectExpression.values
index 9f3d26b4b75..d9e98bf93d8 100644
--- a/compiler/testData/cfg/declarations/local/ObjectExpression.values
+++ b/compiler/testData/cfg/declarations/local/ObjectExpression.values
@@ -1,5 +1,5 @@
 == A ==
-trait A {
+interface A {
     fun foo() : Int
 }
 ---------------------
diff --git a/compiler/testData/cli/jvm/multipleTextRangesInDiagnosticsOrder.kt b/compiler/testData/cli/jvm/multipleTextRangesInDiagnosticsOrder.kt
index 7340ff8a25d..29e26a1bf18 100644
--- a/compiler/testData/cli/jvm/multipleTextRangesInDiagnosticsOrder.kt
+++ b/compiler/testData/cli/jvm/multipleTextRangesInDiagnosticsOrder.kt
@@ -1,7 +1,7 @@
-trait A {
+interface A {
     public val c: Int
 }
 
-trait B: A {
+interface B: A {
     override protected private val c: Int
 }
diff --git a/compiler/testData/cli/jvm/signatureClash.kt b/compiler/testData/cli/jvm/signatureClash.kt
index e7e5eafa6d1..7dbda49c9db 100644
--- a/compiler/testData/cli/jvm/signatureClash.kt
+++ b/compiler/testData/cli/jvm/signatureClash.kt
@@ -12,7 +12,7 @@ class A : B() {
 fun getB(): Int = 1
 val b: Int = 1
 
-trait Tr {
+interface Tr {
     fun getTr() = 1
 }
 
diff --git a/compiler/testData/cli/jvm/wrongAbiVersionLib/src/TraitWithDefault.kt b/compiler/testData/cli/jvm/wrongAbiVersionLib/src/TraitWithDefault.kt
index df593504f3d..4c81a02698d 100644
--- a/compiler/testData/cli/jvm/wrongAbiVersionLib/src/TraitWithDefault.kt
+++ b/compiler/testData/cli/jvm/wrongAbiVersionLib/src/TraitWithDefault.kt
@@ -1,5 +1,5 @@
 package wrong
 
-trait TraitWithDefault {
+interface TraitWithDefault {
     fun foo() = 1
 }
\ No newline at end of file
diff --git a/compiler/testData/cli/warnings.kt b/compiler/testData/cli/warnings.kt
index ad276976b28..7a459c181d4 100644
--- a/compiler/testData/cli/warnings.kt
+++ b/compiler/testData/cli/warnings.kt
@@ -5,6 +5,6 @@ fun foo(p: Int??) {
 
 }
 
-trait T {
+interface T {
     abstract fun foo()
 }
\ No newline at end of file
diff --git a/compiler/testData/codegen/box/bridges/complexMultiInheritance.kt b/compiler/testData/codegen/box/bridges/complexMultiInheritance.kt
index cce9635c317..2128aa8fab4 100644
--- a/compiler/testData/codegen/box/bridges/complexMultiInheritance.kt
+++ b/compiler/testData/codegen/box/bridges/complexMultiInheritance.kt
@@ -2,13 +2,13 @@ open class A {
     open fun foo(): Any = "A"
 }
 
-trait B : A
+interface B : A
 
 open class C : A() {
     override fun foo(): Int = 222
 }
 
-trait D {
+interface D {
     fun foo(): Number
 }
 
diff --git a/compiler/testData/codegen/box/bridges/complexTraitImpl.kt b/compiler/testData/codegen/box/bridges/complexTraitImpl.kt
index 18f692013e5..ce91d13f080 100644
--- a/compiler/testData/codegen/box/bridges/complexTraitImpl.kt
+++ b/compiler/testData/codegen/box/bridges/complexTraitImpl.kt
@@ -5,13 +5,13 @@ abstract class A {
     abstract fun foo(): List<String>
 }
 
-trait B {
+interface B {
     fun foo(): ArrayList<String> = ArrayList(Arrays.asList("B"))
 }
 
 open class C : A(), B
 
-trait D {
+interface D {
     fun foo(): Collection<String>
 }
 
diff --git a/compiler/testData/codegen/box/bridges/delegation.kt b/compiler/testData/codegen/box/bridges/delegation.kt
index 41c3ddd3470..d0dd7aa00f0 100644
--- a/compiler/testData/codegen/box/bridges/delegation.kt
+++ b/compiler/testData/codegen/box/bridges/delegation.kt
@@ -1,4 +1,4 @@
-trait A<T> {
+interface A<T> {
     fun foo(): T
 }
 
diff --git a/compiler/testData/codegen/box/bridges/delegationProperty.kt b/compiler/testData/codegen/box/bridges/delegationProperty.kt
index 5ffd4270b87..768f010140f 100644
--- a/compiler/testData/codegen/box/bridges/delegationProperty.kt
+++ b/compiler/testData/codegen/box/bridges/delegationProperty.kt
@@ -1,4 +1,4 @@
-trait A<T> {
+interface A<T> {
     var result: T
 }
 
diff --git a/compiler/testData/codegen/box/bridges/diamond.kt b/compiler/testData/codegen/box/bridges/diamond.kt
index 2e798707253..b1ea60973a5 100644
--- a/compiler/testData/codegen/box/bridges/diamond.kt
+++ b/compiler/testData/codegen/box/bridges/diamond.kt
@@ -1,10 +1,10 @@
-trait A<T, U> {
+interface A<T, U> {
     fun foo(t: T, u: U) = "A"
 }
 
-trait B<U> : A<String, U>
+interface B<U> : A<String, U>
 
-trait C<T> : A<T, Int>
+interface C<T> : A<T, Int>
 
 class Z : B<Int>, C<String> {
     override fun foo(t: String, u: Int) = "Z"
diff --git a/compiler/testData/codegen/box/bridges/fakeCovariantOverride.kt b/compiler/testData/codegen/box/bridges/fakeCovariantOverride.kt
index bb93071f603..e62de29d55a 100644
--- a/compiler/testData/codegen/box/bridges/fakeCovariantOverride.kt
+++ b/compiler/testData/codegen/box/bridges/fakeCovariantOverride.kt
@@ -1,6 +1,6 @@
 // KT-4145
 
-trait A {
+interface A {
     fun foo(): Any
 }
 
diff --git a/compiler/testData/codegen/box/bridges/fakeGenericContravariantOverride1.kt b/compiler/testData/codegen/box/bridges/fakeGenericContravariantOverride1.kt
index 78b90f2fe89..822954327ea 100644
--- a/compiler/testData/codegen/box/bridges/fakeGenericContravariantOverride1.kt
+++ b/compiler/testData/codegen/box/bridges/fakeGenericContravariantOverride1.kt
@@ -1,8 +1,8 @@
-trait A<T> {
+interface A<T> {
     fun foo(t: T): String
 }
 
-trait B {
+interface B {
     fun foo(t: Int) = "B"
 }
 
diff --git a/compiler/testData/codegen/box/bridges/fakeGenericContravariantOverride2.kt b/compiler/testData/codegen/box/bridges/fakeGenericContravariantOverride2.kt
index 2a946f96200..73a3d93682b 100644
--- a/compiler/testData/codegen/box/bridges/fakeGenericContravariantOverride2.kt
+++ b/compiler/testData/codegen/box/bridges/fakeGenericContravariantOverride2.kt
@@ -1,8 +1,8 @@
-trait A<T> {
+interface A<T> {
     fun foo(t: T): String
 }
 
-trait B<T : Number> {
+interface B<T : Number> {
     fun foo(a: T) = "B"
 }
 
diff --git a/compiler/testData/codegen/box/bridges/fakeGenericCovariantOverride.kt b/compiler/testData/codegen/box/bridges/fakeGenericCovariantOverride.kt
index 0225c55c686..584d1ce3da3 100644
--- a/compiler/testData/codegen/box/bridges/fakeGenericCovariantOverride.kt
+++ b/compiler/testData/codegen/box/bridges/fakeGenericCovariantOverride.kt
@@ -1,6 +1,6 @@
 // KT-3985
 
-trait Trait<T> {
+interface Trait<T> {
     fun f(): T
 }
 
diff --git a/compiler/testData/codegen/box/bridges/fakeGenericCovariantOverrideWithDelegation.kt b/compiler/testData/codegen/box/bridges/fakeGenericCovariantOverrideWithDelegation.kt
index 4fa2cc018a8..e794fa46083 100644
--- a/compiler/testData/codegen/box/bridges/fakeGenericCovariantOverrideWithDelegation.kt
+++ b/compiler/testData/codegen/box/bridges/fakeGenericCovariantOverrideWithDelegation.kt
@@ -1,8 +1,8 @@
-trait A<T> {
+interface A<T> {
     fun foo(t: T): String
 }
 
-trait B {
+interface B {
     fun foo(t: Int) = "B"
 }
 
diff --git a/compiler/testData/codegen/box/bridges/fakeOverrideInTraitWithRequiredFromTraitImpl.kt b/compiler/testData/codegen/box/bridges/fakeOverrideInTraitWithRequiredFromTraitImpl.kt
index ba0b79cbdda..fee76a53e9c 100644
--- a/compiler/testData/codegen/box/bridges/fakeOverrideInTraitWithRequiredFromTraitImpl.kt
+++ b/compiler/testData/codegen/box/bridges/fakeOverrideInTraitWithRequiredFromTraitImpl.kt
@@ -2,11 +2,11 @@ abstract class A {
     abstract fun foo(): Any
 }
 
-trait B {
+interface B {
     fun foo(): String = "B"
 }
 
-trait C : A, B
+interface C : A, B
 
 class D : A(), C
 
diff --git a/compiler/testData/codegen/box/bridges/fakeOverrideOfPropertySetterInTraitImpl.kt b/compiler/testData/codegen/box/bridges/fakeOverrideOfPropertySetterInTraitImpl.kt
index 4a6a4a9e2fa..78126d2ac93 100644
--- a/compiler/testData/codegen/box/bridges/fakeOverrideOfPropertySetterInTraitImpl.kt
+++ b/compiler/testData/codegen/box/bridges/fakeOverrideOfPropertySetterInTraitImpl.kt
@@ -1,6 +1,6 @@
 var result = ""
 
-trait A {
+interface A {
     var foo: String
         get() = result
         set(value) {
diff --git a/compiler/testData/codegen/box/bridges/fakeOverrideOfTraitImpl.kt b/compiler/testData/codegen/box/bridges/fakeOverrideOfTraitImpl.kt
index f8850de7c2b..1f023aad5ba 100644
--- a/compiler/testData/codegen/box/bridges/fakeOverrideOfTraitImpl.kt
+++ b/compiler/testData/codegen/box/bridges/fakeOverrideOfTraitImpl.kt
@@ -1,15 +1,15 @@
 var result = ""
 
-trait D1 {
+interface D1 {
     fun foo(): D1 {
         result += "D1"
         return this
     }
 }
 
-trait F2 : D1
+interface F2 : D1
 
-trait D3 : F2 {
+interface D3 : F2 {
     override fun foo(): D3 {
         result += "D3"
         return this
diff --git a/compiler/testData/codegen/box/bridges/fakeOverrideWithImplementationInTrait.kt b/compiler/testData/codegen/box/bridges/fakeOverrideWithImplementationInTrait.kt
index 3f3a0750cf1..843f133922b 100644
--- a/compiler/testData/codegen/box/bridges/fakeOverrideWithImplementationInTrait.kt
+++ b/compiler/testData/codegen/box/bridges/fakeOverrideWithImplementationInTrait.kt
@@ -1,8 +1,8 @@
-trait A {
+interface A {
     fun foo(): String = "A"
 }
 
-trait B {
+interface B {
     fun foo(): Any
 }
 
diff --git a/compiler/testData/codegen/box/bridges/fakeOverrideWithSeveralSuperDeclarations.kt b/compiler/testData/codegen/box/bridges/fakeOverrideWithSeveralSuperDeclarations.kt
index 04a752cf905..461f1b25c8b 100644
--- a/compiler/testData/codegen/box/bridges/fakeOverrideWithSeveralSuperDeclarations.kt
+++ b/compiler/testData/codegen/box/bridges/fakeOverrideWithSeveralSuperDeclarations.kt
@@ -1,12 +1,12 @@
-trait D1 {
+interface D1 {
     fun foo(): Any
 }
 
-trait D2 {
+interface D2 {
     fun foo(): Number
 }
 
-trait F3 : D1, D2
+interface F3 : D1, D2
 
 open class D4 {
     fun foo(): Int = 42
diff --git a/compiler/testData/codegen/box/bridges/fakeOverrideWithSynthesizedImplementation.kt b/compiler/testData/codegen/box/bridges/fakeOverrideWithSynthesizedImplementation.kt
index a4d0a21e5f9..13b87b448a2 100644
--- a/compiler/testData/codegen/box/bridges/fakeOverrideWithSynthesizedImplementation.kt
+++ b/compiler/testData/codegen/box/bridges/fakeOverrideWithSynthesizedImplementation.kt
@@ -1,6 +1,6 @@
 open data class A(val value: String)
 
-trait B {
+interface B {
     fun component1(): Any
 }
 
diff --git a/compiler/testData/codegen/box/bridges/kt1939.kt b/compiler/testData/codegen/box/bridges/kt1939.kt
index 81cc023ddaa..ff7e345fdde 100644
--- a/compiler/testData/codegen/box/bridges/kt1939.kt
+++ b/compiler/testData/codegen/box/bridges/kt1939.kt
@@ -2,7 +2,7 @@ abstract class Foo<T> {
     fun hello(id: T) = "Hi $id"
 }
 
-trait Tr {
+interface Tr {
     fun hello(s : String)
 }
 
diff --git a/compiler/testData/codegen/box/bridges/kt2833.kt b/compiler/testData/codegen/box/bridges/kt2833.kt
index c5d90cbede8..50a2989d904 100644
--- a/compiler/testData/codegen/box/bridges/kt2833.kt
+++ b/compiler/testData/codegen/box/bridges/kt2833.kt
@@ -1,10 +1,10 @@
 package test
 
-public trait FunDependencyEdge {
+public interface FunDependencyEdge {
     val from: FunctionNode
 }
 
-public trait FunctionNode
+public interface FunctionNode
 
 public class FunctionNodeImpl : FunctionNode
 
diff --git a/compiler/testData/codegen/box/bridges/kt2920.kt b/compiler/testData/codegen/box/bridges/kt2920.kt
index 07802cbaad3..0f71953ba12 100644
--- a/compiler/testData/codegen/box/bridges/kt2920.kt
+++ b/compiler/testData/codegen/box/bridges/kt2920.kt
@@ -1,4 +1,4 @@
-trait Tr<T> {
+interface Tr<T> {
     val v: T
 }
 
diff --git a/compiler/testData/codegen/box/bridges/kt318.kt b/compiler/testData/codegen/box/bridges/kt318.kt
index c1929b1d81a..f454d01992d 100644
--- a/compiler/testData/codegen/box/bridges/kt318.kt
+++ b/compiler/testData/codegen/box/bridges/kt318.kt
@@ -1,9 +1,9 @@
 var result = ""
 
-trait Base
+interface Base
 open class Child : Base
 
-trait A<T : Base> {
+interface A<T : Base> {
     fun <E : T> foo(a : E) {
         result += "A"
     }
diff --git a/compiler/testData/codegen/box/bridges/methodFromTrait.kt b/compiler/testData/codegen/box/bridges/methodFromTrait.kt
index 95c87724b52..46bbf4e80fb 100644
--- a/compiler/testData/codegen/box/bridges/methodFromTrait.kt
+++ b/compiler/testData/codegen/box/bridges/methodFromTrait.kt
@@ -1,4 +1,4 @@
-trait A<T, U> {
+interface A<T, U> {
     fun foo(t: T, u: U) = "A"
 }
 
diff --git a/compiler/testData/codegen/box/bridges/noBridgeOnMutableCollectionInheritance.kt b/compiler/testData/codegen/box/bridges/noBridgeOnMutableCollectionInheritance.kt
index 46ea079d779..6a4fa135a71 100644
--- a/compiler/testData/codegen/box/bridges/noBridgeOnMutableCollectionInheritance.kt
+++ b/compiler/testData/codegen/box/bridges/noBridgeOnMutableCollectionInheritance.kt
@@ -1,11 +1,11 @@
 import java.util.ArrayList
 import java.util.Arrays
 
-trait A {
+interface A {
     fun foo(): Collection<String>
 }
 
-trait B : A {
+interface B : A {
     override fun foo(): MutableCollection<String>
 }
 
diff --git a/compiler/testData/codegen/box/bridges/objectClone.kt b/compiler/testData/codegen/box/bridges/objectClone.kt
index 359cacc6764..266bd90f610 100644
--- a/compiler/testData/codegen/box/bridges/objectClone.kt
+++ b/compiler/testData/codegen/box/bridges/objectClone.kt
@@ -1,7 +1,7 @@
 // TARGET_BACKEND: JVM
 import java.util.HashSet
 
-trait A : Set<String>
+interface A : Set<String>
 
 class B : A, HashSet<String>() {
     override fun clone(): B = throw AssertionError()
diff --git a/compiler/testData/codegen/box/bridges/propertyDiamond.kt b/compiler/testData/codegen/box/bridges/propertyDiamond.kt
index 5f8a54a1588..802f6f77932 100644
--- a/compiler/testData/codegen/box/bridges/propertyDiamond.kt
+++ b/compiler/testData/codegen/box/bridges/propertyDiamond.kt
@@ -1,11 +1,11 @@
-trait A<O, K> {
+interface A<O, K> {
     val o: O
     val k: K
 }
 
-trait B<K> : A<String, K>
+interface B<K> : A<String, K>
 
-trait C<O> : A<O, String>
+interface C<O> : A<O, String>
 
 class D : B<String>, C<String> {
     override val o = "O"
diff --git a/compiler/testData/codegen/box/bridges/propertyInConstructor.kt b/compiler/testData/codegen/box/bridges/propertyInConstructor.kt
index 1bc200b1b5c..9ca1e8bf8f5 100644
--- a/compiler/testData/codegen/box/bridges/propertyInConstructor.kt
+++ b/compiler/testData/codegen/box/bridges/propertyInConstructor.kt
@@ -1,4 +1,4 @@
-trait A<T> {
+interface A<T> {
     var x: T
 }
 
diff --git a/compiler/testData/codegen/box/bridges/propertySetter.kt b/compiler/testData/codegen/box/bridges/propertySetter.kt
index b26bed9f0fb..a258dc85346 100644
--- a/compiler/testData/codegen/box/bridges/propertySetter.kt
+++ b/compiler/testData/codegen/box/bridges/propertySetter.kt
@@ -1,4 +1,4 @@
-trait A<T> {
+interface A<T> {
     var v: T
 }
 
diff --git a/compiler/testData/codegen/box/bridges/simpleEnum.kt b/compiler/testData/codegen/box/bridges/simpleEnum.kt
index b4f682850ac..11b715d6c18 100644
--- a/compiler/testData/codegen/box/bridges/simpleEnum.kt
+++ b/compiler/testData/codegen/box/bridges/simpleEnum.kt
@@ -1,4 +1,4 @@
-trait A<T> {
+interface A<T> {
     open fun foo(t: T) = "A"
 }
 
diff --git a/compiler/testData/codegen/box/bridges/simpleTraitImpl.kt b/compiler/testData/codegen/box/bridges/simpleTraitImpl.kt
index 9cd6c1d6b5f..4d2a723aaad 100644
--- a/compiler/testData/codegen/box/bridges/simpleTraitImpl.kt
+++ b/compiler/testData/codegen/box/bridges/simpleTraitImpl.kt
@@ -1,4 +1,4 @@
-trait A<T> {
+interface A<T> {
     fun foo(t: T) = "A"
 }
 
diff --git a/compiler/testData/codegen/box/bridges/substitutionInSuperClass/delegation.kt b/compiler/testData/codegen/box/bridges/substitutionInSuperClass/delegation.kt
index d469bf5d7f6..ae0d6317dfe 100644
--- a/compiler/testData/codegen/box/bridges/substitutionInSuperClass/delegation.kt
+++ b/compiler/testData/codegen/box/bridges/substitutionInSuperClass/delegation.kt
@@ -1,4 +1,4 @@
-trait A<T> {
+interface A<T> {
     fun id(t: T): T
 }
 
diff --git a/compiler/testData/codegen/box/bridges/substitutionInSuperClass/enum.kt b/compiler/testData/codegen/box/bridges/substitutionInSuperClass/enum.kt
index 747ca7f6549..ac9d01f3797 100644
--- a/compiler/testData/codegen/box/bridges/substitutionInSuperClass/enum.kt
+++ b/compiler/testData/codegen/box/bridges/substitutionInSuperClass/enum.kt
@@ -1,8 +1,8 @@
-trait A<T> {
+interface A<T> {
     open fun foo(t: T) = "A"
 }
 
-trait B : A<String>
+interface B : A<String>
 
 enum class Z(val name: String) : B {
     Z1 : Z("Z1")
diff --git a/compiler/testData/codegen/box/bridges/traitImplInheritsTraitImpl.kt b/compiler/testData/codegen/box/bridges/traitImplInheritsTraitImpl.kt
index 1e5a588a0ab..93d02c7fa93 100644
--- a/compiler/testData/codegen/box/bridges/traitImplInheritsTraitImpl.kt
+++ b/compiler/testData/codegen/box/bridges/traitImplInheritsTraitImpl.kt
@@ -1,8 +1,8 @@
-trait A {
+interface A {
     fun foo(): Any = "A"
 }
 
-trait B : A {
+interface B : A {
     override fun foo(): String = "B"
 }
 
diff --git a/compiler/testData/codegen/box/bridges/traitWithRequiredCovariantOverride.kt b/compiler/testData/codegen/box/bridges/traitWithRequiredCovariantOverride.kt
index 35e0c38a30c..997a5c33760 100644
--- a/compiler/testData/codegen/box/bridges/traitWithRequiredCovariantOverride.kt
+++ b/compiler/testData/codegen/box/bridges/traitWithRequiredCovariantOverride.kt
@@ -2,7 +2,7 @@ open class A {
     open fun foo(): Any = "A"
 }
 
-trait B : A {
+interface B : A {
     override fun foo(): String = "B"
 }
 
diff --git a/compiler/testData/codegen/box/bridges/twoParentsWithDifferentMethodsTwoBridges.kt b/compiler/testData/codegen/box/bridges/twoParentsWithDifferentMethodsTwoBridges.kt
index 8edaa868640..ba08200e6f2 100644
--- a/compiler/testData/codegen/box/bridges/twoParentsWithDifferentMethodsTwoBridges.kt
+++ b/compiler/testData/codegen/box/bridges/twoParentsWithDifferentMethodsTwoBridges.kt
@@ -1,8 +1,8 @@
-trait A<T> {
+interface A<T> {
     fun foo(t: T, u: Int) = "A"
 }
 
-trait B<T, U> {
+interface B<T, U> {
     fun foo(t: T, u: U) = "B"
 }
 
diff --git a/compiler/testData/codegen/box/bridges/twoParentsWithTheSameMethodOneBridge.kt b/compiler/testData/codegen/box/bridges/twoParentsWithTheSameMethodOneBridge.kt
index 22163c367ef..21ffaa75e18 100644
--- a/compiler/testData/codegen/box/bridges/twoParentsWithTheSameMethodOneBridge.kt
+++ b/compiler/testData/codegen/box/bridges/twoParentsWithTheSameMethodOneBridge.kt
@@ -1,8 +1,8 @@
-trait A<T> {
+interface A<T> {
     fun foo(t: T) = "A"
 }
 
-trait B<T> {
+interface B<T> {
     fun foo(t: T) = "B"
 }
 
diff --git a/compiler/testData/codegen/box/builtinStubMethods/dontGenerateBodyInTrait.kt b/compiler/testData/codegen/box/builtinStubMethods/dontGenerateBodyInTrait.kt
index 900d979832f..65cfb766528 100644
--- a/compiler/testData/codegen/box/builtinStubMethods/dontGenerateBodyInTrait.kt
+++ b/compiler/testData/codegen/box/builtinStubMethods/dontGenerateBodyInTrait.kt
@@ -1,10 +1,10 @@
-trait A : Collection<String>
-trait B : List<String>
-trait C : Map<Long, Double>
-trait D : Map.Entry<Any, Nothing>
-trait E : Iterator<Int>
+interface A : Collection<String>
+interface B : List<String>
+interface C : Map<Long, Double>
+interface D : Map.Entry<Any, Nothing>
+interface E : Iterator<Int>
 
 fun box(): String {
-    trait F : A, B, C, D, E
+    interface F : A, B, C, D, E
     return "OK"
 }
diff --git a/compiler/testData/codegen/box/builtinStubMethods/implementationInTrait.kt b/compiler/testData/codegen/box/builtinStubMethods/implementationInTrait.kt
index d08887a8854..7baaa46e2f8 100644
--- a/compiler/testData/codegen/box/builtinStubMethods/implementationInTrait.kt
+++ b/compiler/testData/codegen/box/builtinStubMethods/implementationInTrait.kt
@@ -1,4 +1,4 @@
-trait Addable {
+interface Addable {
     fun add(s: String): Boolean = true
 }
 
diff --git a/compiler/testData/codegen/box/classes/classObjectInTrait.kt b/compiler/testData/codegen/box/classes/classObjectInTrait.kt
index cff3e374654..e34f5622a3e 100644
--- a/compiler/testData/codegen/box/classes/classObjectInTrait.kt
+++ b/compiler/testData/codegen/box/classes/classObjectInTrait.kt
@@ -1,6 +1,6 @@
 // EA-38323 - Illegal field modifiers in class: classObject field in C must be static and final 
 
-trait C {
+interface C {
   companion object {
     public val FOO: String = "OK"
   }
diff --git a/compiler/testData/codegen/box/classes/delegation2.kt b/compiler/testData/codegen/box/classes/delegation2.kt
index 83a4028d53e..81b8b0fb47e 100644
--- a/compiler/testData/codegen/box/classes/delegation2.kt
+++ b/compiler/testData/codegen/box/classes/delegation2.kt
@@ -1,8 +1,8 @@
-trait Trait1 {
+interface Trait1 {
     fun foo() : String
 }
 
-trait Trait2  {
+interface Trait2  {
     fun bar() : String
 }
 
diff --git a/compiler/testData/codegen/box/classes/delegation3.kt b/compiler/testData/codegen/box/classes/delegation3.kt
index 33d2ed5b9e0..fd4f07800a2 100644
--- a/compiler/testData/codegen/box/classes/delegation3.kt
+++ b/compiler/testData/codegen/box/classes/delegation3.kt
@@ -1,8 +1,8 @@
-trait One {
+interface One {
   public open fun foo() : Int
   public open fun faz() : Int = 10
 }
-trait Two {
+interface Two {
   public open fun foo() : Int
   public open fun quux() : Int = 100
 }
diff --git a/compiler/testData/codegen/box/classes/delegation4.kt b/compiler/testData/codegen/box/classes/delegation4.kt
index a37cb061d7c..d29ddb16c89 100644
--- a/compiler/testData/codegen/box/classes/delegation4.kt
+++ b/compiler/testData/codegen/box/classes/delegation4.kt
@@ -1,8 +1,8 @@
-open trait First {
+open interface First {
   public open fun foo() : Int
 }
 
-open trait Second : First {
+open interface Second : First {
   public open fun bar() : Int
 }
 
diff --git a/compiler/testData/codegen/box/classes/delegationGenericArg.kt b/compiler/testData/codegen/box/classes/delegationGenericArg.kt
index fed9f214dd8..f298e834f79 100644
--- a/compiler/testData/codegen/box/classes/delegationGenericArg.kt
+++ b/compiler/testData/codegen/box/classes/delegationGenericArg.kt
@@ -1,4 +1,4 @@
-trait A<T> {
+interface A<T> {
     fun foo(t: T): String
 }
 
diff --git a/compiler/testData/codegen/box/classes/delegationGenericArgUpperBound.kt b/compiler/testData/codegen/box/classes/delegationGenericArgUpperBound.kt
index b5da8aaffee..72e541b7f3b 100644
--- a/compiler/testData/codegen/box/classes/delegationGenericArgUpperBound.kt
+++ b/compiler/testData/codegen/box/classes/delegationGenericArgUpperBound.kt
@@ -1,4 +1,4 @@
-trait A<T: Number> {
+interface A<T: Number> {
     fun foo(t: T): String
 }
 
diff --git a/compiler/testData/codegen/box/classes/delegationGenericLongArg.kt b/compiler/testData/codegen/box/classes/delegationGenericLongArg.kt
index df80d1064e6..8bd117f9fa1 100644
--- a/compiler/testData/codegen/box/classes/delegationGenericLongArg.kt
+++ b/compiler/testData/codegen/box/classes/delegationGenericLongArg.kt
@@ -1,4 +1,4 @@
-trait A<T, U> {
+interface A<T, U> {
     fun foo(t: T, u: U): String
 }
 
diff --git a/compiler/testData/codegen/box/classes/delegationMethodsWithArgs.kt b/compiler/testData/codegen/box/classes/delegationMethodsWithArgs.kt
index dc84a1ed194..a8c0e37230c 100644
--- a/compiler/testData/codegen/box/classes/delegationMethodsWithArgs.kt
+++ b/compiler/testData/codegen/box/classes/delegationMethodsWithArgs.kt
@@ -1,14 +1,14 @@
 package test
 
-trait TextField {
+interface TextField {
     fun getText(): String
 }
 
-trait InputTextField : TextField {
+interface InputTextField : TextField {
     fun setText(text: String)
 }
 
-trait MooableTextField : InputTextField {
+interface MooableTextField : InputTextField {
     fun moo(a: Int, b: Int, c: Int): Int
 }
 
diff --git a/compiler/testData/codegen/box/classes/diamondInheritance.kt b/compiler/testData/codegen/box/classes/diamondInheritance.kt
index 447036bf49b..f20f33ab2cd 100644
--- a/compiler/testData/codegen/box/classes/diamondInheritance.kt
+++ b/compiler/testData/codegen/box/classes/diamondInheritance.kt
@@ -5,7 +5,7 @@ open class Base() {
 }
 
 open class Left() : Base() {}
-trait Right : Base {}
+interface Right : Base {}
 
 class D() : Left(), Right
 
diff --git a/compiler/testData/codegen/box/classes/funDelegation.kt b/compiler/testData/codegen/box/classes/funDelegation.kt
index f940e8e16c9..2a75f698109 100644
--- a/compiler/testData/codegen/box/classes/funDelegation.kt
+++ b/compiler/testData/codegen/box/classes/funDelegation.kt
@@ -2,7 +2,7 @@ open class Base() {
     fun n(n : Int) : Int = n + 1
 }
 
-trait Abstract {}
+interface Abstract {}
 
 class Derived1() : Base(), Abstract {}
 class Derived2() : Abstract, Base() {}
diff --git a/compiler/testData/codegen/box/classes/inheritSetAndHashSet.kt b/compiler/testData/codegen/box/classes/inheritSetAndHashSet.kt
index b7711f77748..dce4e5da005 100644
--- a/compiler/testData/codegen/box/classes/inheritSetAndHashSet.kt
+++ b/compiler/testData/codegen/box/classes/inheritSetAndHashSet.kt
@@ -1,6 +1,6 @@
 import java.util.HashSet
 
-trait A : Set<String>
+interface A : Set<String>
 
 class B : A, HashSet<String>()
 
diff --git a/compiler/testData/codegen/box/classes/inheritance.kt b/compiler/testData/codegen/box/classes/inheritance.kt
index 1b919497b5c..78d6d58fa3b 100644
--- a/compiler/testData/codegen/box/classes/inheritance.kt
+++ b/compiler/testData/codegen/box/classes/inheritance.kt
@@ -1,7 +1,7 @@
 // Changed when traits were introduced. May not make sense any more
 
 open class X(val x : Int) {}
-trait Y {
+interface Y {
     abstract val y : Int
 }
 
@@ -11,7 +11,7 @@ class Point(x : Int, yy : Int) : X(x) , Y {
     override val y : Int = yy
 }
 
-trait Abstract {}
+interface Abstract {}
 
 class P1(x : Int, yy : Y) : Abstract, X(x), Y by yy {}
 class P2(x : Int, yy : Y) : X(x), Abstract, Y by yy {}
diff --git a/compiler/testData/codegen/box/classes/kt1345.kt b/compiler/testData/codegen/box/classes/kt1345.kt
index 28d9467076a..3933f9c552e 100644
--- a/compiler/testData/codegen/box/classes/kt1345.kt
+++ b/compiler/testData/codegen/box/classes/kt1345.kt
@@ -1,10 +1,10 @@
-trait Creator<T> {
+interface Creator<T> {
     fun create() : T
 }
 
 class Actor(val code: String = "OK")
 
-trait Factory : Creator<Actor>
+interface Factory : Creator<Actor>
 
 class MyFactory() : Factory {
     override fun create(): Actor = Actor()
diff --git a/compiler/testData/codegen/box/classes/kt1918.kt b/compiler/testData/codegen/box/classes/kt1918.kt
index 7dabde92a46..1da1471e2d3 100644
--- a/compiler/testData/codegen/box/classes/kt1918.kt
+++ b/compiler/testData/codegen/box/classes/kt1918.kt
@@ -1,7 +1,7 @@
 class Bar {
 }
 
-trait Foo {
+interface Foo {
     fun xyzzy(x: Any?): String
 }
 
diff --git a/compiler/testData/codegen/box/classes/kt2224.kt b/compiler/testData/codegen/box/classes/kt2224.kt
index 83c8cb44b86..fe6d9bcbe48 100644
--- a/compiler/testData/codegen/box/classes/kt2224.kt
+++ b/compiler/testData/codegen/box/classes/kt2224.kt
@@ -1,4 +1,4 @@
-trait A {
+interface A {
     fun foo(): Int
 }
 
diff --git a/compiler/testData/codegen/box/classes/kt2390.kt b/compiler/testData/codegen/box/classes/kt2390.kt
index 18366e5222f..9d664ee825d 100644
--- a/compiler/testData/codegen/box/classes/kt2390.kt
+++ b/compiler/testData/codegen/box/classes/kt2390.kt
@@ -5,18 +5,18 @@ class JsonObject() {
 class JsonArray() {
 }
 
-public trait Formatter<in IN: Any, out OUT: Any> {
+public interface Formatter<in IN: Any, out OUT: Any> {
     public fun format(source: IN?): OUT
 }
 
-public trait MultiFormatter <in IN: Any, out OUT: Any> {
+public interface MultiFormatter <in IN: Any, out OUT: Any> {
     public fun format(source: Collection<IN>): OUT
 }
 
 public class Project() {
 }
 
-public trait JsonFormatter<in IN: Any>: Formatter<IN, JsonObject>, MultiFormatter<IN, JsonArray> {
+public interface JsonFormatter<in IN: Any>: Formatter<IN, JsonObject>, MultiFormatter<IN, JsonArray> {
     public override fun format(source: Collection<IN>): JsonArray {
         return JsonArray();
     }
diff --git a/compiler/testData/codegen/box/classes/kt2391.kt b/compiler/testData/codegen/box/classes/kt2391.kt
index 005c5715d29..2176c01b98e 100644
--- a/compiler/testData/codegen/box/classes/kt2391.kt
+++ b/compiler/testData/codegen/box/classes/kt2391.kt
@@ -1,4 +1,4 @@
-public trait LoggerAware {
+public interface LoggerAware {
     public val logger: StringBuilder
 }
 
diff --git a/compiler/testData/codegen/box/classes/kt2477.kt b/compiler/testData/codegen/box/classes/kt2477.kt
index a18e8731ab6..bd449eefb43 100644
--- a/compiler/testData/codegen/box/classes/kt2477.kt
+++ b/compiler/testData/codegen/box/classes/kt2477.kt
@@ -1,11 +1,11 @@
 package test
 
-trait A {
+interface A {
     public val c: String
         get() = "OK"
 }
 
-trait B {
+interface B {
     protected val c: String
 }
 
diff --git a/compiler/testData/codegen/box/classes/kt2532.kt b/compiler/testData/codegen/box/classes/kt2532.kt
index a3a0a4a0d35..24d12e9f884 100644
--- a/compiler/testData/codegen/box/classes/kt2532.kt
+++ b/compiler/testData/codegen/box/classes/kt2532.kt
@@ -1,6 +1,6 @@
 package foo
 
-trait B {
+interface B {
     val c: Int
         get() = 2
 }
diff --git a/compiler/testData/codegen/box/classes/kt2566.kt b/compiler/testData/codegen/box/classes/kt2566.kt
index fff411738e8..6a134feb84f 100644
--- a/compiler/testData/codegen/box/classes/kt2566.kt
+++ b/compiler/testData/codegen/box/classes/kt2566.kt
@@ -6,7 +6,7 @@ open class B : A() {
     override fun foo() = super.foo()
 }
 
-trait I
+interface I
 
 class C : I, B() {
     override fun foo() = super<B>.foo()
diff --git a/compiler/testData/codegen/box/classes/kt285.kt b/compiler/testData/codegen/box/classes/kt285.kt
index 4c47239d8ae..514d086e8d3 100644
--- a/compiler/testData/codegen/box/classes/kt285.kt
+++ b/compiler/testData/codegen/box/classes/kt285.kt
@@ -1,4 +1,4 @@
-trait Trait {
+interface Trait {
     fun foo() = "O"
     override fun toString() = "K"
 }
diff --git a/compiler/testData/codegen/box/classes/kt3001.kt b/compiler/testData/codegen/box/classes/kt3001.kt
index 35925eade05..0524528ca1e 100644
--- a/compiler/testData/codegen/box/classes/kt3001.kt
+++ b/compiler/testData/codegen/box/classes/kt3001.kt
@@ -1,4 +1,4 @@
-trait A {
+interface A {
     val result: String
 }
 
diff --git a/compiler/testData/codegen/box/classes/kt3414.kt b/compiler/testData/codegen/box/classes/kt3414.kt
index 6770d466086..6b4a083eda9 100644
--- a/compiler/testData/codegen/box/classes/kt3414.kt
+++ b/compiler/testData/codegen/box/classes/kt3414.kt
@@ -1,8 +1,8 @@
-trait A {
+interface A {
     fun foo(): Int
 }
 
-trait B {
+interface B {
     fun foo(): Int
 }
 
diff --git a/compiler/testData/codegen/box/classes/kt3546.kt b/compiler/testData/codegen/box/classes/kt3546.kt
index 4fb5ce41dd3..b4d36c1f3e6 100644
--- a/compiler/testData/codegen/box/classes/kt3546.kt
+++ b/compiler/testData/codegen/box/classes/kt3546.kt
@@ -1,12 +1,12 @@
-trait A {
+interface A {
     fun test(): String
 }
 
-trait B {
+interface B {
     fun test(): String
 }
 
-trait C: A, B
+interface C: A, B
 
 class Z(val param: String): C {
 
diff --git a/compiler/testData/codegen/box/classes/kt3862.kt b/compiler/testData/codegen/box/classes/kt3862.kt
index c6d52a45fc4..6f020ac8ab0 100644
--- a/compiler/testData/codegen/box/classes/kt3862.kt
+++ b/compiler/testData/codegen/box/classes/kt3862.kt
@@ -2,7 +2,7 @@ open class A<T> {
     open fun foo(a: T): Int = 2
 }
 
-trait B<T> : A<T> {
+interface B<T> : A<T> {
     override fun foo(a: T): Int = 1
 }
 
diff --git a/compiler/testData/codegen/box/classes/propertyDelegation.kt b/compiler/testData/codegen/box/classes/propertyDelegation.kt
index fcf720a21ba..5af5516c859 100644
--- a/compiler/testData/codegen/box/classes/propertyDelegation.kt
+++ b/compiler/testData/codegen/box/classes/propertyDelegation.kt
@@ -10,7 +10,7 @@ open class Base() {
       }
 }
 
-trait Abstract {}
+interface Abstract {}
 
 class Derived1() : Base(), Abstract {}
 class Derived2() : Abstract, Base() {}
diff --git a/compiler/testData/codegen/box/classes/rightHandOverride.kt b/compiler/testData/codegen/box/classes/rightHandOverride.kt
index 987da6bd6b0..2c5af2c9927 100644
--- a/compiler/testData/codegen/box/classes/rightHandOverride.kt
+++ b/compiler/testData/codegen/box/classes/rightHandOverride.kt
@@ -1,6 +1,6 @@
 // Changed when traits were introduced. May not make sense any more
 
-trait Left {}
+interface Left {}
 open class Right() {
     open fun f() = 42
 }
diff --git a/compiler/testData/codegen/box/classes/typedDelegation.kt b/compiler/testData/codegen/box/classes/typedDelegation.kt
index 0ffd3265146..e0b1241a6aa 100644
--- a/compiler/testData/codegen/box/classes/typedDelegation.kt
+++ b/compiler/testData/codegen/box/classes/typedDelegation.kt
@@ -1,4 +1,4 @@
-trait A<T> {
+interface A<T> {
   var zzzValue : T
   fun zzz() : T
 }
diff --git a/compiler/testData/codegen/box/closures/captureOuterProperty/captureFunctionInProperty.kt b/compiler/testData/codegen/box/closures/captureOuterProperty/captureFunctionInProperty.kt
index 57d93cb270a..e2c507f3b28 100644
--- a/compiler/testData/codegen/box/closures/captureOuterProperty/captureFunctionInProperty.kt
+++ b/compiler/testData/codegen/box/closures/captureOuterProperty/captureFunctionInProperty.kt
@@ -1,4 +1,4 @@
-trait T {
+interface T {
     fun result(): String
 }
 
diff --git a/compiler/testData/codegen/box/closures/captureOuterProperty/inFunction.kt b/compiler/testData/codegen/box/closures/captureOuterProperty/inFunction.kt
index 03bdb3b499a..7b4828fa7b5 100644
--- a/compiler/testData/codegen/box/closures/captureOuterProperty/inFunction.kt
+++ b/compiler/testData/codegen/box/closures/captureOuterProperty/inFunction.kt
@@ -1,4 +1,4 @@
-trait T {
+interface T {
     fun result(): String
 }
 
diff --git a/compiler/testData/codegen/box/closures/captureOuterProperty/inProperty.kt b/compiler/testData/codegen/box/closures/captureOuterProperty/inProperty.kt
index 15769f77148..8f1846f7cfb 100644
--- a/compiler/testData/codegen/box/closures/captureOuterProperty/inProperty.kt
+++ b/compiler/testData/codegen/box/closures/captureOuterProperty/inProperty.kt
@@ -1,4 +1,4 @@
-trait T {
+interface T {
     fun result(): String
 }
 
diff --git a/compiler/testData/codegen/box/closures/captureOuterProperty/inPropertyDeepObjectChain.kt b/compiler/testData/codegen/box/closures/captureOuterProperty/inPropertyDeepObjectChain.kt
index 2dfd7949ca6..0bb07f581b9 100644
--- a/compiler/testData/codegen/box/closures/captureOuterProperty/inPropertyDeepObjectChain.kt
+++ b/compiler/testData/codegen/box/closures/captureOuterProperty/inPropertyDeepObjectChain.kt
@@ -1,4 +1,4 @@
-trait T {
+interface T {
     fun result(): String
 }
 
diff --git a/compiler/testData/codegen/box/closures/captureOuterProperty/inPropertyFromSuperClass.kt b/compiler/testData/codegen/box/closures/captureOuterProperty/inPropertyFromSuperClass.kt
index 934d0b58ec7..2f7ff86a10c 100644
--- a/compiler/testData/codegen/box/closures/captureOuterProperty/inPropertyFromSuperClass.kt
+++ b/compiler/testData/codegen/box/closures/captureOuterProperty/inPropertyFromSuperClass.kt
@@ -1,4 +1,4 @@
-trait T {
+interface T {
     fun result(): String
 }
 
diff --git a/compiler/testData/codegen/box/closures/captureOuterProperty/inPropertyFromSuperSuperClass.kt b/compiler/testData/codegen/box/closures/captureOuterProperty/inPropertyFromSuperSuperClass.kt
index 4dc735a2bf7..3d600017d08 100644
--- a/compiler/testData/codegen/box/closures/captureOuterProperty/inPropertyFromSuperSuperClass.kt
+++ b/compiler/testData/codegen/box/closures/captureOuterProperty/inPropertyFromSuperSuperClass.kt
@@ -1,4 +1,4 @@
-trait T {
+interface T {
     fun result(): String
 }
 
diff --git a/compiler/testData/codegen/box/closures/closureInsideClosure/propertyAndFunctionNameClash.kt b/compiler/testData/codegen/box/closures/closureInsideClosure/propertyAndFunctionNameClash.kt
index 0133c48cc07..b19e4b61b0d 100644
--- a/compiler/testData/codegen/box/closures/closureInsideClosure/propertyAndFunctionNameClash.kt
+++ b/compiler/testData/codegen/box/closures/closureInsideClosure/propertyAndFunctionNameClash.kt
@@ -24,7 +24,7 @@ class LI : ListTag() {}
 public fun ListTag.item(body: LI.() -> Unit): Unit {}
 fun HtmlTag.a(contents: A.() -> Unit) {}
 
-trait A : HtmlTag {
+interface A : HtmlTag {
     public var text: String
 }
 
diff --git a/compiler/testData/codegen/box/controlStructures/emptyFor.kt b/compiler/testData/codegen/box/controlStructures/emptyFor.kt
index fc3f6332871..e39e3997923 100644
--- a/compiler/testData/codegen/box/controlStructures/emptyFor.kt
+++ b/compiler/testData/codegen/box/controlStructures/emptyFor.kt
@@ -1,6 +1,6 @@
 var index = 0
 
-trait IterableIterator : Iterator<Int> {
+interface IterableIterator : Iterator<Int> {
     fun iterator(): Iterator<Int> = this
 }
 
diff --git a/compiler/testData/codegen/box/defaultArguments/function/funInTrait.kt b/compiler/testData/codegen/box/defaultArguments/function/funInTrait.kt
index ba7df2c9e0b..06b181e10b6 100644
--- a/compiler/testData/codegen/box/defaultArguments/function/funInTrait.kt
+++ b/compiler/testData/codegen/box/defaultArguments/function/funInTrait.kt
@@ -1,4 +1,4 @@
-trait Foo {
+interface Foo {
     fun foo(a: Double = 1.0): Double
 }
 
diff --git a/compiler/testData/codegen/box/defaultArguments/function/trait.kt b/compiler/testData/codegen/box/defaultArguments/function/trait.kt
index b986362f653..91bafe072f3 100644
--- a/compiler/testData/codegen/box/defaultArguments/function/trait.kt
+++ b/compiler/testData/codegen/box/defaultArguments/function/trait.kt
@@ -1,5 +1,5 @@
-trait Base {
-    fun bar(a: String = "abc"): String = a + " from trait"
+interface Base {
+    fun bar(a: String = "abc"): String = a + " from interface"
 }
 
 class Derived: Base {
diff --git a/compiler/testData/codegen/box/delegatedProperty/inTrait.kt b/compiler/testData/codegen/box/delegatedProperty/inTrait.kt
index f9802ba1e3f..1f5e64731a9 100644
--- a/compiler/testData/codegen/box/delegatedProperty/inTrait.kt
+++ b/compiler/testData/codegen/box/delegatedProperty/inTrait.kt
@@ -2,7 +2,7 @@ class Delegate {
     fun get(t: Any?, p: PropertyMetadata): Int = 1
 }
 
-trait A {
+interface A {
     val prop: Int
 }
 
diff --git a/compiler/testData/codegen/box/delegatedProperty/kt4138.kt b/compiler/testData/codegen/box/delegatedProperty/kt4138.kt
index d4e52b824b5..f1f85eeaee1 100644
--- a/compiler/testData/codegen/box/delegatedProperty/kt4138.kt
+++ b/compiler/testData/codegen/box/delegatedProperty/kt4138.kt
@@ -11,7 +11,7 @@ class Foo (val f: Int) {
     }
 }
 
-trait FooTrait {
+interface FooTrait {
     companion object {
         val A: Foo by Delegate(Foo(11))
         var B: Foo by Delegate(Foo(11))
diff --git a/compiler/testData/codegen/box/delegatedProperty/propertyDelegatedMethod/inTrait.kt b/compiler/testData/codegen/box/delegatedProperty/propertyDelegatedMethod/inTrait.kt
index c721d6b81b9..370b3ec7275 100644
--- a/compiler/testData/codegen/box/delegatedProperty/propertyDelegatedMethod/inTrait.kt
+++ b/compiler/testData/codegen/box/delegatedProperty/propertyDelegatedMethod/inTrait.kt
@@ -4,7 +4,7 @@ class Delegate {
     fun propertyDelegated(p: PropertyMetadata) { name = p.name }
 }
 
-trait A {
+interface A {
     val prop: String
 }
 
diff --git a/compiler/testData/codegen/box/diagnostics/functions/invoke/onObjects/invokeOnClassObject2.kt b/compiler/testData/codegen/box/diagnostics/functions/invoke/onObjects/invokeOnClassObject2.kt
index 74cb9e4c24e..45495ff0179 100644
--- a/compiler/testData/codegen/box/diagnostics/functions/invoke/onObjects/invokeOnClassObject2.kt
+++ b/compiler/testData/codegen/box/diagnostics/functions/invoke/onObjects/invokeOnClassObject2.kt
@@ -1,4 +1,4 @@
-trait B
+interface B
 
 fun B.invoke(i: Int) = i
 
diff --git a/compiler/testData/codegen/box/enum/enumInheritedFromTrait.kt b/compiler/testData/codegen/box/enum/enumInheritedFromTrait.kt
index a371c7e27ae..7659029d2b6 100644
--- a/compiler/testData/codegen/box/enum/enumInheritedFromTrait.kt
+++ b/compiler/testData/codegen/box/enum/enumInheritedFromTrait.kt
@@ -11,6 +11,6 @@ enum class MyEnum : T {
     }
 }
 
-trait T {
+interface T {
     fun f(): String
 }
\ No newline at end of file
diff --git a/compiler/testData/codegen/box/extensionFunctions/kt1776.kt b/compiler/testData/codegen/box/extensionFunctions/kt1776.kt
index 2e742d78312..5174d4cc374 100644
--- a/compiler/testData/codegen/box/extensionFunctions/kt1776.kt
+++ b/compiler/testData/codegen/box/extensionFunctions/kt1776.kt
@@ -1,4 +1,4 @@
-trait Expr {
+interface Expr {
     public fun ttFun() : Int = 12
 }
 
diff --git a/compiler/testData/codegen/box/extensionFunctions/kt606.kt b/compiler/testData/codegen/box/extensionFunctions/kt606.kt
index ed62435c2c9..5e1de696f70 100644
--- a/compiler/testData/codegen/box/extensionFunctions/kt606.kt
+++ b/compiler/testData/codegen/box/extensionFunctions/kt606.kt
@@ -10,7 +10,7 @@ class StandardPipelineFactory(val config : ChannelPipeline.() -> Unit) : Channel
     }
 }
 
-trait ChannelPipeline  {
+interface ChannelPipeline  {
   fun print(any: Any)
 }
 
@@ -19,7 +19,7 @@ class DefaultChannelPipeline : ChannelPipeline {
 
 }
 
-trait ChannelPipelineFactory {
+interface ChannelPipelineFactory {
     fun getPipeline() : ChannelPipeline
 }
 
diff --git a/compiler/testData/codegen/box/fakeOverride/diamondFunction.kt b/compiler/testData/codegen/box/fakeOverride/diamondFunction.kt
index 7c150aaaa7b..da73cd28d7f 100644
--- a/compiler/testData/codegen/box/fakeOverride/diamondFunction.kt
+++ b/compiler/testData/codegen/box/fakeOverride/diamondFunction.kt
@@ -1,4 +1,4 @@
-trait T {
+interface T {
     fun foo(): Unit
 }
 
@@ -6,7 +6,7 @@ open class A : T {
     override fun foo() {}
 }
 
-trait B : T
+interface B : T
 
 class C : A(), B
 class D : B, A()
diff --git a/compiler/testData/codegen/box/fakeOverride/function.kt b/compiler/testData/codegen/box/fakeOverride/function.kt
index 1158cddb0c9..af0e02f4f49 100644
--- a/compiler/testData/codegen/box/fakeOverride/function.kt
+++ b/compiler/testData/codegen/box/fakeOverride/function.kt
@@ -1,4 +1,4 @@
-trait T {
+interface T {
     fun foo(): Unit
 }
 
@@ -9,7 +9,7 @@ open class A : T {
 class B : A(), T
 class C : T, A()
 
-trait U : T
+interface U : T
 class D : U, A()
 class E : A(), U
 class F : U, T, A()
diff --git a/compiler/testData/codegen/box/fakeOverride/propertyGetter.kt b/compiler/testData/codegen/box/fakeOverride/propertyGetter.kt
index 0c86e6eacab..c032e3ab837 100644
--- a/compiler/testData/codegen/box/fakeOverride/propertyGetter.kt
+++ b/compiler/testData/codegen/box/fakeOverride/propertyGetter.kt
@@ -1,4 +1,4 @@
-trait T {
+interface T {
     val foo: String
 }
 
@@ -9,7 +9,7 @@ open class A : T {
 class B : A(), T
 class C : T, A()
 
-trait U : T
+interface U : T
 
 class D : U, A()
 class E : A(), U
diff --git a/compiler/testData/codegen/box/fakeOverride/propertySetter.kt b/compiler/testData/codegen/box/fakeOverride/propertySetter.kt
index 2103491b1ad..c2f623ba448 100644
--- a/compiler/testData/codegen/box/fakeOverride/propertySetter.kt
+++ b/compiler/testData/codegen/box/fakeOverride/propertySetter.kt
@@ -1,4 +1,4 @@
-trait T {
+interface T {
     var result: String
 }
 
diff --git a/compiler/testData/codegen/box/functions/defaultargs4.kt b/compiler/testData/codegen/box/functions/defaultargs4.kt
index 045f17be11f..b98b9a95d64 100644
--- a/compiler/testData/codegen/box/functions/defaultargs4.kt
+++ b/compiler/testData/codegen/box/functions/defaultargs4.kt
@@ -1,4 +1,4 @@
-trait A {
+interface A {
     fun bar2(arg: Int = 239) : Int
 
     fun bar(arg: Int = 240) : Int = bar2(arg/2)
diff --git a/compiler/testData/codegen/box/functions/defaultargs6.kt b/compiler/testData/codegen/box/functions/defaultargs6.kt
index 21a9faeae3f..90c4e943d5d 100644
--- a/compiler/testData/codegen/box/functions/defaultargs6.kt
+++ b/compiler/testData/codegen/box/functions/defaultargs6.kt
@@ -1,4 +1,4 @@
-trait A {
+interface A {
     fun foo(x: Int, y: Int = x + 20, z: Int = y * 2) = z
 }
 
diff --git a/compiler/testData/codegen/box/functions/fakeDescriptorWithSeveralOverridenOne.kt b/compiler/testData/codegen/box/functions/fakeDescriptorWithSeveralOverridenOne.kt
index 862108d8b89..0086f8ab719 100644
--- a/compiler/testData/codegen/box/functions/fakeDescriptorWithSeveralOverridenOne.kt
+++ b/compiler/testData/codegen/box/functions/fakeDescriptorWithSeveralOverridenOne.kt
@@ -1,12 +1,12 @@
-trait Named {
+interface Named {
     abstract fun getName() : String;
 }
 
-trait MemberDescriptor : Named {}
+interface MemberDescriptor : Named {}
 
-trait ClassifierDescriptor : Named {}
+interface ClassifierDescriptor : Named {}
 
-trait ClassDescriptor : MemberDescriptor, ClassifierDescriptor {}
+interface ClassDescriptor : MemberDescriptor, ClassifierDescriptor {}
 
 class ClassDescriptorImpl : ClassDescriptor {
     override fun getName(): String {
diff --git a/compiler/testData/codegen/box/functions/kt1199.kt b/compiler/testData/codegen/box/functions/kt1199.kt
index 0d1899c549e..b29953c4862 100644
--- a/compiler/testData/codegen/box/functions/kt1199.kt
+++ b/compiler/testData/codegen/box/functions/kt1199.kt
@@ -1,5 +1,5 @@
 
-trait MyIterator<T> {
+interface MyIterator<T> {
     fun hasNext() : Boolean
     fun next() : T
 }
diff --git a/compiler/testData/codegen/box/functions/kt1413.kt b/compiler/testData/codegen/box/functions/kt1413.kt
index 6cc787850e1..15b496fb9b9 100644
--- a/compiler/testData/codegen/box/functions/kt1413.kt
+++ b/compiler/testData/codegen/box/functions/kt1413.kt
@@ -1,6 +1,6 @@
 package t
 
-trait I{
+interface I{
     fun f()
 }
 
diff --git a/compiler/testData/codegen/box/functions/kt1649_1.kt b/compiler/testData/codegen/box/functions/kt1649_1.kt
index ef16a4645a6..849bf5525ff 100644
--- a/compiler/testData/codegen/box/functions/kt1649_1.kt
+++ b/compiler/testData/codegen/box/functions/kt1649_1.kt
@@ -1,4 +1,4 @@
-trait A {
+interface A {
     val method : (() -> Unit)?
 }
 
diff --git a/compiler/testData/codegen/box/functions/kt1649_2.kt b/compiler/testData/codegen/box/functions/kt1649_2.kt
index e75d9cb4b62..33f420dc3f9 100644
--- a/compiler/testData/codegen/box/functions/kt1649_2.kt
+++ b/compiler/testData/codegen/box/functions/kt1649_2.kt
@@ -1,4 +1,4 @@
-trait A {
+interface A {
     val method : () -> Unit?
 }
 
diff --git a/compiler/testData/codegen/box/innerNested/kt3132.kt b/compiler/testData/codegen/box/innerNested/kt3132.kt
index 9428d2d7fe7..afcee1c6ca1 100644
--- a/compiler/testData/codegen/box/innerNested/kt3132.kt
+++ b/compiler/testData/codegen/box/innerNested/kt3132.kt
@@ -1,5 +1,5 @@
 class Test {
-    trait Foo { }
+    interface Foo { }
 
     class FooImplNested: Foo { }
     
diff --git a/compiler/testData/codegen/box/labels/propertyAccessorObject.kt b/compiler/testData/codegen/box/labels/propertyAccessorObject.kt
index 3459ad58cce..1fc9f25aa82 100644
--- a/compiler/testData/codegen/box/labels/propertyAccessorObject.kt
+++ b/compiler/testData/codegen/box/labels/propertyAccessorObject.kt
@@ -1,4 +1,4 @@
-trait Base {
+interface Base {
     fun foo(): Int
 }
 
diff --git a/compiler/testData/codegen/box/localClasses/kt2700.kt b/compiler/testData/codegen/box/localClasses/kt2700.kt
index f6964fb8e1e..3baacf0b21f 100644
--- a/compiler/testData/codegen/box/localClasses/kt2700.kt
+++ b/compiler/testData/codegen/box/localClasses/kt2700.kt
@@ -1,6 +1,6 @@
 package a.b
 
-trait Test {
+interface Test {
     fun invoke(): String {
         return "OK"
     }
diff --git a/compiler/testData/codegen/box/localClasses/kt3210.kt b/compiler/testData/codegen/box/localClasses/kt3210.kt
index da90a52d584..12c9b1cba6e 100644
--- a/compiler/testData/codegen/box/localClasses/kt3210.kt
+++ b/compiler/testData/codegen/box/localClasses/kt3210.kt
@@ -1,12 +1,12 @@
 package org.example
 
-trait SomeTrait {}
+interface SomeTrait {}
 
-trait KotlinProcessor<T> {
+interface KotlinProcessor<T> {
     fun execute(callback: KotlinCallback<T>?);
 }
 
-trait KotlinCallback<T> {
+interface KotlinCallback<T> {
     fun on(t : T);
 }
 
diff --git a/compiler/testData/codegen/box/objects/anonymousObjectPropertyInitialization.kt b/compiler/testData/codegen/box/objects/anonymousObjectPropertyInitialization.kt
index a46db9d4e66..4765e8858ba 100644
--- a/compiler/testData/codegen/box/objects/anonymousObjectPropertyInitialization.kt
+++ b/compiler/testData/codegen/box/objects/anonymousObjectPropertyInitialization.kt
@@ -1,4 +1,4 @@
-trait T {
+interface T {
     fun foo(): String
 }
 
diff --git a/compiler/testData/codegen/box/objects/kt4086.kt b/compiler/testData/codegen/box/objects/kt4086.kt
index e28c8e5fca4..2aa1ca343d8 100644
--- a/compiler/testData/codegen/box/objects/kt4086.kt
+++ b/compiler/testData/codegen/box/objects/kt4086.kt
@@ -1,4 +1,4 @@
-trait N
+interface N
 
 open class Base(n: N)
 
diff --git a/compiler/testData/codegen/box/objects/objectWithSuperclassAndTrait.kt b/compiler/testData/codegen/box/objects/objectWithSuperclassAndTrait.kt
index ad0d2513d01..c239a3eff27 100644
--- a/compiler/testData/codegen/box/objects/objectWithSuperclassAndTrait.kt
+++ b/compiler/testData/codegen/box/objects/objectWithSuperclassAndTrait.kt
@@ -4,7 +4,7 @@ open class A {
     }
 }
 
-trait T {
+interface T {
     open fun foo(): Int {
         return 3
     }
diff --git a/compiler/testData/codegen/box/objects/privateFunctionFromClosureInInitializer_kt5582.kt b/compiler/testData/codegen/box/objects/privateFunctionFromClosureInInitializer_kt5582.kt
index 833336b325c..5b71ab435fe 100644
--- a/compiler/testData/codegen/box/objects/privateFunctionFromClosureInInitializer_kt5582.kt
+++ b/compiler/testData/codegen/box/objects/privateFunctionFromClosureInInitializer_kt5582.kt
@@ -1,4 +1,4 @@
-trait T
+interface T
 
 object Foo {
     private fun foo(p: T) = p
diff --git a/compiler/testData/codegen/box/operatorConventions/compareTo/comparable.kt b/compiler/testData/codegen/box/operatorConventions/compareTo/comparable.kt
index fec5ac5bfa0..957816c8974 100644
--- a/compiler/testData/codegen/box/operatorConventions/compareTo/comparable.kt
+++ b/compiler/testData/codegen/box/operatorConventions/compareTo/comparable.kt
@@ -1,4 +1,4 @@
-trait A : Comparable<A>
+interface A : Comparable<A>
 
 class B(val x: Int) : A {
     override fun compareTo(other: A) = x.compareTo((other as B).x)
diff --git a/compiler/testData/codegen/box/properties/kt1714.kt b/compiler/testData/codegen/box/properties/kt1714.kt
index 655312cc2b7..87696e39e7f 100644
--- a/compiler/testData/codegen/box/properties/kt1714.kt
+++ b/compiler/testData/codegen/box/properties/kt1714.kt
@@ -1,4 +1,4 @@
-trait A {
+interface A {
     val method : (() -> Unit )?
     val test : Integer
 }
diff --git a/compiler/testData/codegen/box/properties/kt1714_minimal.kt b/compiler/testData/codegen/box/properties/kt1714_minimal.kt
index dd255aa79f7..e453069c4ad 100644
--- a/compiler/testData/codegen/box/properties/kt1714_minimal.kt
+++ b/compiler/testData/codegen/box/properties/kt1714_minimal.kt
@@ -1,4 +1,4 @@
-trait A {
+interface A {
     val v: Int
 }
 
diff --git a/compiler/testData/codegen/box/properties/kt2655.kt b/compiler/testData/codegen/box/properties/kt2655.kt
index 36244dcee3f..3956fb3a17d 100644
--- a/compiler/testData/codegen/box/properties/kt2655.kt
+++ b/compiler/testData/codegen/box/properties/kt2655.kt
@@ -1,4 +1,4 @@
-trait TextField {
+interface TextField {
     fun getText(): String
     fun setText(text: String)
 }
diff --git a/compiler/testData/codegen/box/properties/kt2786.kt b/compiler/testData/codegen/box/properties/kt2786.kt
index 7b813217918..003ca536275 100644
--- a/compiler/testData/codegen/box/properties/kt2786.kt
+++ b/compiler/testData/codegen/box/properties/kt2786.kt
@@ -1,4 +1,4 @@
-trait FooTrait {
+interface FooTrait {
         val propertyTest: String
 }
 
diff --git a/compiler/testData/codegen/box/properties/kt4373.kt b/compiler/testData/codegen/box/properties/kt4373.kt
index 74d2ae00485..41b781f2cfc 100644
--- a/compiler/testData/codegen/box/properties/kt4373.kt
+++ b/compiler/testData/codegen/box/properties/kt4373.kt
@@ -1,4 +1,4 @@
-trait Tr<T> {
+interface Tr<T> {
     val prop: T
 }
 
diff --git a/compiler/testData/codegen/box/properties/primitiveOverrideDefaultAccessor.kt b/compiler/testData/codegen/box/properties/primitiveOverrideDefaultAccessor.kt
index eabdf4c4050..e8039fa4cc7 100644
--- a/compiler/testData/codegen/box/properties/primitiveOverrideDefaultAccessor.kt
+++ b/compiler/testData/codegen/box/properties/primitiveOverrideDefaultAccessor.kt
@@ -1,4 +1,4 @@
-trait R<T: Comparable<T>> {
+interface R<T: Comparable<T>> {
     var value: T
 }
 
diff --git a/compiler/testData/codegen/box/properties/primitiveOverrideDelegateAccessor.kt b/compiler/testData/codegen/box/properties/primitiveOverrideDelegateAccessor.kt
index c757476551a..315732f3f1f 100644
--- a/compiler/testData/codegen/box/properties/primitiveOverrideDelegateAccessor.kt
+++ b/compiler/testData/codegen/box/properties/primitiveOverrideDelegateAccessor.kt
@@ -3,7 +3,7 @@ class Holder(var value: Int) {
     fun set(that: Any?, desc: PropertyMetadata, newValue: Int) { value = newValue }
 }
 
-trait R<T: Comparable<T>> {
+interface R<T: Comparable<T>> {
     var value: T
 }
 
diff --git a/compiler/testData/codegen/box/properties/traitExtendsClass.kt b/compiler/testData/codegen/box/properties/traitExtendsClass.kt
index 96726168446..d1aa10bec1a 100644
--- a/compiler/testData/codegen/box/properties/traitExtendsClass.kt
+++ b/compiler/testData/codegen/box/properties/traitExtendsClass.kt
@@ -2,7 +2,7 @@ open class Base {
     val pr : String = "OK"
 }
 
-trait Trait : Base {
+interface Trait : Base {
     fun f() : String {
         return this.pr
     }
diff --git a/compiler/testData/codegen/box/secondaryConstructors/delegationWithPrimary.kt b/compiler/testData/codegen/box/secondaryConstructors/delegationWithPrimary.kt
index 2ab364d1d71..16f433527f9 100644
--- a/compiler/testData/codegen/box/secondaryConstructors/delegationWithPrimary.kt
+++ b/compiler/testData/codegen/box/secondaryConstructors/delegationWithPrimary.kt
@@ -1,4 +1,4 @@
-trait A {
+interface A {
     fun foo(): String
 }
 
diff --git a/compiler/testData/codegen/box/super/basicmethodSuperTrait.kt b/compiler/testData/codegen/box/super/basicmethodSuperTrait.kt
index 29d7cbd13ec..c147c0b8b1c 100644
--- a/compiler/testData/codegen/box/super/basicmethodSuperTrait.kt
+++ b/compiler/testData/codegen/box/super/basicmethodSuperTrait.kt
@@ -1,6 +1,6 @@
 import java.util.ArrayList
 
-trait Tr {
+interface Tr {
    fun extra() : String = "_"
 }
 
diff --git a/compiler/testData/codegen/box/super/enclosedFun.kt b/compiler/testData/codegen/box/super/enclosedFun.kt
index 1bc7a0a7640..5f317b46f77 100644
--- a/compiler/testData/codegen/box/super/enclosedFun.kt
+++ b/compiler/testData/codegen/box/super/enclosedFun.kt
@@ -1,8 +1,8 @@
-trait BK {
+interface BK {
     fun x() : Int = 50
 }
 
-trait K : BK {
+interface K : BK {
     override fun x() : Int = super.x() * 2
 }
 
diff --git a/compiler/testData/codegen/box/super/innerClassLabeledSuper.kt b/compiler/testData/codegen/box/super/innerClassLabeledSuper.kt
index 9d405bd2317..cbb0a875df9 100644
--- a/compiler/testData/codegen/box/super/innerClassLabeledSuper.kt
+++ b/compiler/testData/codegen/box/super/innerClassLabeledSuper.kt
@@ -1,9 +1,9 @@
-trait BK {
+interface BK {
     fun foo(): String
     fun bar(): String
 }
 
-trait K : BK {
+interface K : BK {
     override fun foo() = bar()
 }
 
diff --git a/compiler/testData/codegen/box/super/innerClassLabeledSuper2.kt b/compiler/testData/codegen/box/super/innerClassLabeledSuper2.kt
index f7681e7e67e..1a0bca8c437 100644
--- a/compiler/testData/codegen/box/super/innerClassLabeledSuper2.kt
+++ b/compiler/testData/codegen/box/super/innerClassLabeledSuper2.kt
@@ -1,10 +1,10 @@
 //inspired by kt3492
-trait BK {
+interface BK {
     fun foo(): String
     fun bar(): String
 }
 
-trait KTrait: BK {
+interface KTrait: BK {
     override fun foo() = bar()
 }
 
diff --git a/compiler/testData/codegen/box/super/innerClassLabeledSuperProperty.kt b/compiler/testData/codegen/box/super/innerClassLabeledSuperProperty.kt
index 4f4a62f8850..bb8098564f6 100644
--- a/compiler/testData/codegen/box/super/innerClassLabeledSuperProperty.kt
+++ b/compiler/testData/codegen/box/super/innerClassLabeledSuperProperty.kt
@@ -1,4 +1,4 @@
-trait Base {
+interface Base {
     val foo: String
     fun bar(): String
 }
diff --git a/compiler/testData/codegen/box/super/innerClassLabeledSuperProperty2.kt b/compiler/testData/codegen/box/super/innerClassLabeledSuperProperty2.kt
index ad6f8ddf94c..effc71e7925 100644
--- a/compiler/testData/codegen/box/super/innerClassLabeledSuperProperty2.kt
+++ b/compiler/testData/codegen/box/super/innerClassLabeledSuperProperty2.kt
@@ -1,5 +1,5 @@
 //inspired by kt3492
-trait Base {
+interface Base {
     val foo: String
     fun bar(): String
 }
diff --git a/compiler/testData/codegen/box/super/kt3492TraitFun.kt b/compiler/testData/codegen/box/super/kt3492TraitFun.kt
index 19c9a2920c0..144e86036a3 100644
--- a/compiler/testData/codegen/box/super/kt3492TraitFun.kt
+++ b/compiler/testData/codegen/box/super/kt3492TraitFun.kt
@@ -1,4 +1,4 @@
-trait ATrait {
+interface ATrait {
     open fun foo2(): String = "OK"
 }
 
diff --git a/compiler/testData/codegen/box/super/kt3492TraitProperty.kt b/compiler/testData/codegen/box/super/kt3492TraitProperty.kt
index bfd7859f19f..c4c3298afcb 100644
--- a/compiler/testData/codegen/box/super/kt3492TraitProperty.kt
+++ b/compiler/testData/codegen/box/super/kt3492TraitProperty.kt
@@ -1,4 +1,4 @@
-trait A {
+interface A {
     open val foo: String
       get() = "OK"
 }
diff --git a/compiler/testData/codegen/box/super/kt3538.kt b/compiler/testData/codegen/box/super/kt3538.kt
index 47656e7b4df..7186da045ec 100644
--- a/compiler/testData/codegen/box/super/kt3538.kt
+++ b/compiler/testData/codegen/box/super/kt3538.kt
@@ -4,7 +4,7 @@ open class Base {
     }
 }
 
-trait Trait: Base {
+interface Trait: Base {
     override fun sayHello(): String {
         return "K"
     }
diff --git a/compiler/testData/codegen/box/super/multipleSuperTraits.kt b/compiler/testData/codegen/box/super/multipleSuperTraits.kt
index 2312888b2fa..2ddb25d35b9 100644
--- a/compiler/testData/codegen/box/super/multipleSuperTraits.kt
+++ b/compiler/testData/codegen/box/super/multipleSuperTraits.kt
@@ -1,8 +1,8 @@
-trait T1 {
+interface T1 {
     fun foo() = "O"
 }
 
-trait T2 {
+interface T2 {
     fun foo() = "K"
 }
 
diff --git a/compiler/testData/codegen/box/super/traitproperty.kt b/compiler/testData/codegen/box/super/traitproperty.kt
index 820d99402a7..a5de71c24eb 100644
--- a/compiler/testData/codegen/box/super/traitproperty.kt
+++ b/compiler/testData/codegen/box/super/traitproperty.kt
@@ -1,4 +1,4 @@
-trait M {
+interface M {
     var backingB : Int
     var b : Int
         get() = backingB
diff --git a/compiler/testData/codegen/box/superConstructorCall/deepLocalHierarchy.kt b/compiler/testData/codegen/box/superConstructorCall/deepLocalHierarchy.kt
index 51a059cb0a3..534370e134e 100644
--- a/compiler/testData/codegen/box/superConstructorCall/deepLocalHierarchy.kt
+++ b/compiler/testData/codegen/box/superConstructorCall/deepLocalHierarchy.kt
@@ -1,5 +1,5 @@
 fun box(): String {
-    open trait L1 {
+    open interface L1 {
         fun foo(): String
     }
 
diff --git a/compiler/testData/codegen/box/traits/finalMethod.kt b/compiler/testData/codegen/box/traits/finalMethod.kt
index 1469b0e10fb..443d02c1cf4 100644
--- a/compiler/testData/codegen/box/traits/finalMethod.kt
+++ b/compiler/testData/codegen/box/traits/finalMethod.kt
@@ -1,6 +1,6 @@
 //KT-2382
 
-trait T {
+interface T {
     final fun foo() = "OK"
 }
 
diff --git a/compiler/testData/codegen/box/traits/genericMethod.kt b/compiler/testData/codegen/box/traits/genericMethod.kt
index 06fa2f35a31..e3d47b24181 100644
--- a/compiler/testData/codegen/box/traits/genericMethod.kt
+++ b/compiler/testData/codegen/box/traits/genericMethod.kt
@@ -1,4 +1,4 @@
-trait A<T> {
+interface A<T> {
     val property : T
 
     open  fun a() : T {
diff --git a/compiler/testData/codegen/box/traits/inheritedFun.kt b/compiler/testData/codegen/box/traits/inheritedFun.kt
index 1262b29ba06..756aed226c7 100644
--- a/compiler/testData/codegen/box/traits/inheritedFun.kt
+++ b/compiler/testData/codegen/box/traits/inheritedFun.kt
@@ -1,5 +1,5 @@
 //KT-2206
-trait A {
+interface A {
     fun f():Int = 239
 }
 
diff --git a/compiler/testData/codegen/box/traits/inheritedVar.kt b/compiler/testData/codegen/box/traits/inheritedVar.kt
index f1aa0ab825b..887f33c2178 100644
--- a/compiler/testData/codegen/box/traits/inheritedVar.kt
+++ b/compiler/testData/codegen/box/traits/inheritedVar.kt
@@ -1,6 +1,6 @@
 //KT-2206
 
-trait A {
+interface A {
     var a:Int
         get() = 239
         set(value) {
diff --git a/compiler/testData/codegen/box/traits/kt1936.kt b/compiler/testData/codegen/box/traits/kt1936.kt
index 7361d996893..0764dca3de4 100644
--- a/compiler/testData/codegen/box/traits/kt1936.kt
+++ b/compiler/testData/codegen/box/traits/kt1936.kt
@@ -1,6 +1,6 @@
 var result = "Fail"
 
-trait MyTrait
+interface MyTrait
 {
     var property : String
     fun foo()  {
diff --git a/compiler/testData/codegen/box/traits/kt1936_1.kt b/compiler/testData/codegen/box/traits/kt1936_1.kt
index b79da2cf44e..c3c6ef815f6 100644
--- a/compiler/testData/codegen/box/traits/kt1936_1.kt
+++ b/compiler/testData/codegen/box/traits/kt1936_1.kt
@@ -1,4 +1,4 @@
-trait MyTrait
+interface MyTrait
 {
     var property : String
     fun foo() = property
diff --git a/compiler/testData/codegen/box/traits/kt2260.kt b/compiler/testData/codegen/box/traits/kt2260.kt
index b3f39f8234c..f63a2220542 100644
--- a/compiler/testData/codegen/box/traits/kt2260.kt
+++ b/compiler/testData/codegen/box/traits/kt2260.kt
@@ -1,4 +1,4 @@
-trait Flusher {
+interface Flusher {
     fun flush() = "OK"
 }
 
diff --git a/compiler/testData/codegen/box/traits/kt2399.kt b/compiler/testData/codegen/box/traits/kt2399.kt
index d53fc22bf53..6d26c72c134 100644
--- a/compiler/testData/codegen/box/traits/kt2399.kt
+++ b/compiler/testData/codegen/box/traits/kt2399.kt
@@ -10,15 +10,15 @@ class ProjectInfo {
     override fun toString(): String = "OK"
 }
 
-public trait Parser<in IN: Any, out OUT: Any> {
+public interface Parser<in IN: Any, out OUT: Any> {
     public fun parse(source: IN): OUT
 }
 
-public trait MultiParser<in IN: Any, out OUT: Any> {
+public interface MultiParser<in IN: Any, out OUT: Any> {
     public fun parse(source: IN): Collection<OUT>
 }
 
-public trait JsonParser<T: Any>: Parser<JsonObject, T>, MultiParser<JsonArray, T> {
+public interface JsonParser<T: Any>: Parser<JsonObject, T>, MultiParser<JsonArray, T> {
     public override fun parse(source: JsonArray): Collection<T> {
         return ArrayList<T>()
     }
diff --git a/compiler/testData/codegen/box/traits/kt2541.kt b/compiler/testData/codegen/box/traits/kt2541.kt
index c054d5fbadc..5be4abf0272 100644
--- a/compiler/testData/codegen/box/traits/kt2541.kt
+++ b/compiler/testData/codegen/box/traits/kt2541.kt
@@ -1,4 +1,4 @@
-trait A<T, U> {
+interface A<T, U> {
     fun foo(t: T, u: U) = "OK"
 }
 
diff --git a/compiler/testData/codegen/box/traits/kt3315.kt b/compiler/testData/codegen/box/traits/kt3315.kt
index 7a0e3262554..91f7f81a489 100644
--- a/compiler/testData/codegen/box/traits/kt3315.kt
+++ b/compiler/testData/codegen/box/traits/kt3315.kt
@@ -1,4 +1,4 @@
-trait B<T> {
+interface B<T> {
     fun foo(dd: T): T = dd
 }
 
diff --git a/compiler/testData/codegen/box/traits/kt3500.kt b/compiler/testData/codegen/box/traits/kt3500.kt
index ba3e63ce5ca..18433df514a 100644
--- a/compiler/testData/codegen/box/traits/kt3500.kt
+++ b/compiler/testData/codegen/box/traits/kt3500.kt
@@ -1,8 +1,8 @@
-trait BK {
+interface BK {
     fun foo(): String = 10.toString()
 }
 
-trait KTrait: BK {
+interface KTrait: BK {
     override fun foo() = 30.toString()
 }
 
diff --git a/compiler/testData/codegen/box/traits/kt5495.kt b/compiler/testData/codegen/box/traits/kt5495.kt
index 7a78baa0b9b..5d541929589 100644
--- a/compiler/testData/codegen/box/traits/kt5495.kt
+++ b/compiler/testData/codegen/box/traits/kt5495.kt
@@ -1,5 +1,5 @@
 fun box(): String {
-    trait A {
+    interface A {
         fun foo() = "OK"
     }
 
diff --git a/compiler/testData/codegen/box/traits/multiple.kt b/compiler/testData/codegen/box/traits/multiple.kt
index da0c9da4a36..bc6470c0d6b 100644
--- a/compiler/testData/codegen/box/traits/multiple.kt
+++ b/compiler/testData/codegen/box/traits/multiple.kt
@@ -1,8 +1,8 @@
-trait AL {
+interface AL {
     fun get(index: Int) : Any? = null
 }
 
-trait ALE<T> : AL {
+interface ALE<T> : AL {
     fun getOrNull(index: Int, value: T) : T {
         val r = get(index) as? T
         return r ?: value
diff --git a/compiler/testData/codegen/box/traits/traitWithPrivateExtension.kt b/compiler/testData/codegen/box/traits/traitWithPrivateExtension.kt
index 64b307eb1f9..5dee33c0792 100644
--- a/compiler/testData/codegen/box/traits/traitWithPrivateExtension.kt
+++ b/compiler/testData/codegen/box/traits/traitWithPrivateExtension.kt
@@ -4,7 +4,7 @@ open class B {
 
 class BB : B()
 
-trait Z<T :B > {
+interface Z<T :B > {
     fun T.getString() : String {
         return p
     }
diff --git a/compiler/testData/codegen/box/traits/withRequired/generic.kt b/compiler/testData/codegen/box/traits/withRequired/generic.kt
index bb5f05817b9..75d26e62299 100644
--- a/compiler/testData/codegen/box/traits/withRequired/generic.kt
+++ b/compiler/testData/codegen/box/traits/withRequired/generic.kt
@@ -2,7 +2,7 @@ open class AL<T> {
     fun get(index: Int) : T? = null
 }
 
-trait ALE<T> : AL<T> {
+interface ALE<T> : AL<T> {
     fun getOrValue(index: Int, value : T) : T = get(index) ?: value
 }
 
diff --git a/compiler/testData/codegen/box/traits/withRequired/genericProperty.kt b/compiler/testData/codegen/box/traits/withRequired/genericProperty.kt
index 23019a5e84b..2579ef900b5 100644
--- a/compiler/testData/codegen/box/traits/withRequired/genericProperty.kt
+++ b/compiler/testData/codegen/box/traits/withRequired/genericProperty.kt
@@ -2,7 +2,7 @@ abstract class Base<T> {
     abstract var s: T
 }
 
-trait Trait<T> : Base<T> {
+interface Trait<T> : Base<T> {
     var value : T
         get() = s
         set(value) { s = value }
diff --git a/compiler/testData/codegen/box/traits/withRequired/kt1936_2.kt b/compiler/testData/codegen/box/traits/withRequired/kt1936_2.kt
index d892033bb6b..8c17c464421 100644
--- a/compiler/testData/codegen/box/traits/withRequired/kt1936_2.kt
+++ b/compiler/testData/codegen/box/traits/withRequired/kt1936_2.kt
@@ -2,7 +2,7 @@ open class MyClass(param : String) {
     var propterty = param
 }
 
-trait MyTrait : MyClass
+interface MyTrait : MyClass
 {
     fun foo()  = propterty
 }
diff --git a/compiler/testData/codegen/box/traits/withRequired/kt2963.kt b/compiler/testData/codegen/box/traits/withRequired/kt2963.kt
index 03b1d72120b..2d463906975 100644
--- a/compiler/testData/codegen/box/traits/withRequired/kt2963.kt
+++ b/compiler/testData/codegen/box/traits/withRequired/kt2963.kt
@@ -1,6 +1,6 @@
 open class Base
 
-trait Derived : Base {
+interface Derived : Base {
     fun foo(): String {
         return object {
             fun bar() = baz(this@Derived)
diff --git a/compiler/testData/codegen/box/traits/withRequired/kt3413.kt b/compiler/testData/codegen/box/traits/withRequired/kt3413.kt
index 30cefd6fa2c..a27f370230f 100644
--- a/compiler/testData/codegen/box/traits/withRequired/kt3413.kt
+++ b/compiler/testData/codegen/box/traits/withRequired/kt3413.kt
@@ -1,4 +1,4 @@
-trait Trait<T : Enum<T>> : Enum<T> {
+interface Trait<T : Enum<T>> : Enum<T> {
     val value : String get() = name()
 }
 
diff --git a/compiler/testData/codegen/box/traits/withRequired/kt3429.kt b/compiler/testData/codegen/box/traits/withRequired/kt3429.kt
index f865200c56c..18a55c90083 100644
--- a/compiler/testData/codegen/box/traits/withRequired/kt3429.kt
+++ b/compiler/testData/codegen/box/traits/withRequired/kt3429.kt
@@ -4,7 +4,7 @@ open class Base {
     }
 }
 
-trait Trait: Base {
+interface Trait: Base {
     override fun sayHello(): String {
         return "OK"
     }
diff --git a/compiler/testData/codegen/box/traits/withRequired/property.kt b/compiler/testData/codegen/box/traits/withRequired/property.kt
index 8aac0835791..f6945f36518 100644
--- a/compiler/testData/codegen/box/traits/withRequired/property.kt
+++ b/compiler/testData/codegen/box/traits/withRequired/property.kt
@@ -2,7 +2,7 @@ open class Base {
     var s = "Fail"
 }
 
-trait Trait : Base {
+interface Trait : Base {
     var value : String
         get() = s
         set(value) { s = value }
diff --git a/compiler/testData/codegen/box/traits/withRequired/propertyViaBridge.kt b/compiler/testData/codegen/box/traits/withRequired/propertyViaBridge.kt
index c07ce9735f9..96ed04b4aa6 100644
--- a/compiler/testData/codegen/box/traits/withRequired/propertyViaBridge.kt
+++ b/compiler/testData/codegen/box/traits/withRequired/propertyViaBridge.kt
@@ -1,6 +1,6 @@
 open class Base
 
-trait Trait : Base {
+interface Trait : Base {
     private val value : String
         get() = "OK"
         
diff --git a/compiler/testData/codegen/box/traits/withRequired/simple.kt b/compiler/testData/codegen/box/traits/withRequired/simple.kt
index 580498cbb68..2a4b89e189d 100644
--- a/compiler/testData/codegen/box/traits/withRequired/simple.kt
+++ b/compiler/testData/codegen/box/traits/withRequired/simple.kt
@@ -1,4 +1,4 @@
-trait Trait : java.lang.Object {
+interface Trait : java.lang.Object {
     fun foo(): String = "239 " + toString()
 }
 
diff --git a/compiler/testData/codegen/box/traits/withRequired/super.kt b/compiler/testData/codegen/box/traits/withRequired/super.kt
index ac4d1f89cc3..064084c26ba 100644
--- a/compiler/testData/codegen/box/traits/withRequired/super.kt
+++ b/compiler/testData/codegen/box/traits/withRequired/super.kt
@@ -4,7 +4,7 @@ open class Base {
     }
 }
 
-trait Derived : Base {
+interface Derived : Base {
     override fun foo() : String {
         //super.foo()
         return "OK"
diff --git a/compiler/testData/codegen/box/traits/withRequired/superViaBridge.kt b/compiler/testData/codegen/box/traits/withRequired/superViaBridge.kt
index a00ac37c3d1..7bd8a552608 100644
--- a/compiler/testData/codegen/box/traits/withRequired/superViaBridge.kt
+++ b/compiler/testData/codegen/box/traits/withRequired/superViaBridge.kt
@@ -3,7 +3,7 @@ open class Base {
     open fun foo2() { }
 }
 
-trait Derived : Base {
+interface Derived : Base {
     override fun foo() {
         object {
             fun bar() {
diff --git a/compiler/testData/codegen/box/traits/withRequired/traitFuncCall.kt b/compiler/testData/codegen/box/traits/withRequired/traitFuncCall.kt
index e84d7931c56..b704ceb9e2d 100644
--- a/compiler/testData/codegen/box/traits/withRequired/traitFuncCall.kt
+++ b/compiler/testData/codegen/box/traits/withRequired/traitFuncCall.kt
@@ -3,7 +3,7 @@ open class Foo() {
 }
 
 
-trait T: Foo {
+interface T: Foo {
     public fun xyzzy(): String = o() + k()
     public fun o(): String
 }
diff --git a/compiler/testData/codegen/boxAgainstJava/notNullAssertions/Delegation.kt b/compiler/testData/codegen/boxAgainstJava/notNullAssertions/Delegation.kt
index 29b0e162a71..3dc0d38d534 100644
--- a/compiler/testData/codegen/boxAgainstJava/notNullAssertions/Delegation.kt
+++ b/compiler/testData/codegen/boxAgainstJava/notNullAssertions/Delegation.kt
@@ -1,4 +1,4 @@
-trait Tr { 
+interface Tr {
     fun foo(): String
 }
 
diff --git a/compiler/testData/codegen/boxAgainstJava/property/fieldAccessFromExtensionInTraitImpl.kt b/compiler/testData/codegen/boxAgainstJava/property/fieldAccessFromExtensionInTraitImpl.kt
index ccd336f24d1..9b423f9a325 100644
--- a/compiler/testData/codegen/boxAgainstJava/property/fieldAccessFromExtensionInTraitImpl.kt
+++ b/compiler/testData/codegen/boxAgainstJava/property/fieldAccessFromExtensionInTraitImpl.kt
@@ -2,7 +2,7 @@
 
 import fieldAccessFromExtensionInTraitImpl as D
 
-trait T {
+interface T {
     fun Int.foo(d: D) = d.result!!
 }
 
diff --git a/compiler/testData/codegen/boxInline/anonymousObject/capturedLambdaInInlineObject.2.kt b/compiler/testData/codegen/boxInline/anonymousObject/capturedLambdaInInlineObject.2.kt
index a3ff909d1c5..f54f014b2bf 100644
--- a/compiler/testData/codegen/boxInline/anonymousObject/capturedLambdaInInlineObject.2.kt
+++ b/compiler/testData/codegen/boxInline/anonymousObject/capturedLambdaInInlineObject.2.kt
@@ -1,6 +1,6 @@
 package test
 
-trait A<T> {
+interface A<T> {
     fun run(): T;
 }
 
diff --git a/compiler/testData/codegen/boxInline/builders/builders.2.kt b/compiler/testData/codegen/boxInline/builders/builders.2.kt
index f2c29052b97..cb4bc6eac25 100644
--- a/compiler/testData/codegen/boxInline/builders/builders.2.kt
+++ b/compiler/testData/codegen/boxInline/builders/builders.2.kt
@@ -3,7 +3,7 @@ package builders
 import java.util.ArrayList
 import java.util.HashMap
 
-trait Element {
+interface Element {
     fun render(builder: StringBuilder, indent: String)
 
     override fun toString(): String {
diff --git a/compiler/testData/codegen/boxInline/builders/buildersAndLambdaCapturing.2.kt b/compiler/testData/codegen/boxInline/builders/buildersAndLambdaCapturing.2.kt
index c19b0284c3b..2fc26f262e8 100644
--- a/compiler/testData/codegen/boxInline/builders/buildersAndLambdaCapturing.2.kt
+++ b/compiler/testData/codegen/boxInline/builders/buildersAndLambdaCapturing.2.kt
@@ -3,7 +3,7 @@ package builders
 import java.util.ArrayList
 import java.util.HashMap
 
-trait Element {
+interface Element {
     fun render(builder: StringBuilder, indent: String)
 
     override fun toString(): String {
diff --git a/compiler/testData/codegen/boxInline/complex/use.2.kt b/compiler/testData/codegen/boxInline/complex/use.2.kt
index 0c74af1e7b2..c2a6ac78683 100644
--- a/compiler/testData/codegen/boxInline/complex/use.2.kt
+++ b/compiler/testData/codegen/boxInline/complex/use.2.kt
@@ -9,7 +9,7 @@ public  class Output(val d: Data) : Closeable {
     public fun doOutput(data: Int): Int = data
 }
 
-public open trait Closeable {
+public open interface Closeable {
     open public fun close() {}
 }
 
diff --git a/compiler/testData/codegen/boxInline/complex/with.2.kt b/compiler/testData/codegen/boxInline/complex/with.2.kt
index 0684df6c177..a4ac07cfd41 100644
--- a/compiler/testData/codegen/boxInline/complex/with.2.kt
+++ b/compiler/testData/codegen/boxInline/complex/with.2.kt
@@ -11,7 +11,7 @@ public  class Output(val d: Data) : Closeable {
     public fun doOutput(data: Int): Int = data
 }
 
-public open trait Closeable {
+public open interface Closeable {
     open public fun close() {}
 }
 
diff --git a/compiler/testData/codegen/boxInline/nonLocalReturns/tryFinally/exceptionTable/exceptionInFinally.2.kt b/compiler/testData/codegen/boxInline/nonLocalReturns/tryFinally/exceptionTable/exceptionInFinally.2.kt
index 8e0745401c9..436c9974338 100644
--- a/compiler/testData/codegen/boxInline/nonLocalReturns/tryFinally/exceptionTable/exceptionInFinally.2.kt
+++ b/compiler/testData/codegen/boxInline/nonLocalReturns/tryFinally/exceptionTable/exceptionInFinally.2.kt
@@ -1,6 +1,6 @@
 package test
 
-public trait MCloseable {
+public interface MCloseable {
     public open fun close()
 }
 
diff --git a/compiler/testData/codegen/boxInline/trait/trait.2.kt b/compiler/testData/codegen/boxInline/trait/trait.2.kt
index d7a9b4e33c1..ed56b295051 100644
--- a/compiler/testData/codegen/boxInline/trait/trait.2.kt
+++ b/compiler/testData/codegen/boxInline/trait/trait.2.kt
@@ -1,6 +1,6 @@
 package test
 
-trait InlineTrait {
+interface InlineTrait {
 
     inline final fun finalInline(s: () -> String): String {
         return s()
diff --git a/compiler/testData/codegen/boxWithJava/builtinStubMethods/substitutedIterable/substitutedIterable.kt b/compiler/testData/codegen/boxWithJava/builtinStubMethods/substitutedIterable/substitutedIterable.kt
index f1812b3e4f7..0a6c159ccb2 100644
--- a/compiler/testData/codegen/boxWithJava/builtinStubMethods/substitutedIterable/substitutedIterable.kt
+++ b/compiler/testData/codegen/boxWithJava/builtinStubMethods/substitutedIterable/substitutedIterable.kt
@@ -1,4 +1,4 @@
-trait MyIterable<T> : Iterable<T>
+interface MyIterable<T> : Iterable<T>
 
 class E : RuntimeException()
 fun foo(): MyIterable<String> = throw E()
diff --git a/compiler/testData/codegen/boxWithJava/properties/classObjectProperties/Test.java b/compiler/testData/codegen/boxWithJava/properties/classObjectProperties/Test.java
index eef03d83106..28cf20463a5 100644
--- a/compiler/testData/codegen/boxWithJava/properties/classObjectProperties/Test.java
+++ b/compiler/testData/codegen/boxWithJava/properties/classObjectProperties/Test.java
@@ -6,7 +6,7 @@ class Test {
         if (!s.equals("Klass")) throw new AssertionError("Fail class: " + s);
 
         s = Trait.NAME;
-        if (!s.equals("Trait")) throw new AssertionError("Fail trait: " + s);
+        if (!s.equals("Trait")) throw new AssertionError("Fail interface: " + s);
 
         s = Enoom.NAME;
         if (!s.equals("Enoom")) throw new AssertionError("Fail enum: " + s);
diff --git a/compiler/testData/codegen/boxWithJava/properties/classObjectProperties/classObjectProperties.kt b/compiler/testData/codegen/boxWithJava/properties/classObjectProperties/classObjectProperties.kt
index 00c287d105d..395e96670e0 100644
--- a/compiler/testData/codegen/boxWithJava/properties/classObjectProperties/classObjectProperties.kt
+++ b/compiler/testData/codegen/boxWithJava/properties/classObjectProperties/classObjectProperties.kt
@@ -4,7 +4,7 @@ class Klass {
     }
 }
 
-trait Trait {
+interface Trait {
     companion object {
         val NAME = "Trait"
     }
diff --git a/compiler/testData/codegen/boxWithJava/trait/interfaceInheritance.kt b/compiler/testData/codegen/boxWithJava/trait/interfaceInheritance.kt
index 7e1dd4e1527..bceff8b3b05 100644
--- a/compiler/testData/codegen/boxWithJava/trait/interfaceInheritance.kt
+++ b/compiler/testData/codegen/boxWithJava/trait/interfaceInheritance.kt
@@ -1,4 +1,4 @@
-trait A : MyInt {
+interface A : MyInt {
     override public fun test(): String? {
         return "OK"
     }
diff --git a/compiler/testData/codegen/boxWithStdlib/arrays/stdlib.kt b/compiler/testData/codegen/boxWithStdlib/arrays/stdlib.kt
index 58b5bcbb584..e7ff20e0b62 100644
--- a/compiler/testData/codegen/boxWithStdlib/arrays/stdlib.kt
+++ b/compiler/testData/codegen/boxWithStdlib/arrays/stdlib.kt
@@ -1,8 +1,8 @@
-trait ISized {
+interface ISized {
     val size : Int
 }
 
-trait javaUtilIterator<T> : Iterator<T> {
+interface javaUtilIterator<T> : Iterator<T> {
     fun remove() : Unit {
         throw UnsupportedOperationException()
     }
@@ -16,13 +16,13 @@ class MyIterator<T>(val array : ReadOnlyArray<T>) : javaUtilIterator<T> {
     override fun next() : T = array.get(index++)
 }
 
-trait ReadOnlyArray<out T> : ISized, Iterable<T> {
+interface ReadOnlyArray<out T> : ISized, Iterable<T> {
   fun get(index : Int) : T
 
   override fun iterator() : Iterator<T> = MyIterator<T>(this)
 }
 
-trait WriteOnlyArray<in T> : ISized {
+interface WriteOnlyArray<in T> : ISized {
   fun set(index : Int, value : T) : Unit
 
   fun set(from: Int, count: Int, value: T) {
diff --git a/compiler/testData/codegen/boxWithStdlib/callableReference/function/local/enumExtendsTrait.kt b/compiler/testData/codegen/boxWithStdlib/callableReference/function/local/enumExtendsTrait.kt
index 36954fb8250..5b28434e19c 100644
--- a/compiler/testData/codegen/boxWithStdlib/callableReference/function/local/enumExtendsTrait.kt
+++ b/compiler/testData/codegen/boxWithStdlib/callableReference/function/local/enumExtendsTrait.kt
@@ -1,4 +1,4 @@
-trait Named {
+interface Named {
     fun name(): String
 }
 
diff --git a/compiler/testData/codegen/boxWithStdlib/callableReference/function/traitImplMethodWithClassReceiver.kt b/compiler/testData/codegen/boxWithStdlib/callableReference/function/traitImplMethodWithClassReceiver.kt
index 27f8a407fb9..b47561d9d03 100644
--- a/compiler/testData/codegen/boxWithStdlib/callableReference/function/traitImplMethodWithClassReceiver.kt
+++ b/compiler/testData/codegen/boxWithStdlib/callableReference/function/traitImplMethodWithClassReceiver.kt
@@ -1,4 +1,4 @@
-trait T {
+interface T {
     fun foo() = "OK"
 }
 
diff --git a/compiler/testData/codegen/boxWithStdlib/callableReference/function/traitMember.kt b/compiler/testData/codegen/boxWithStdlib/callableReference/function/traitMember.kt
index 8b278fb0ebb..619220ff65f 100644
--- a/compiler/testData/codegen/boxWithStdlib/callableReference/function/traitMember.kt
+++ b/compiler/testData/codegen/boxWithStdlib/callableReference/function/traitMember.kt
@@ -1,4 +1,4 @@
-trait A {
+interface A {
     fun foo(): String
 }
 
diff --git a/compiler/testData/codegen/boxWithStdlib/dataClasses/tostring/alreadyInherited.kt b/compiler/testData/codegen/boxWithStdlib/dataClasses/tostring/alreadyInherited.kt
index b91111255d8..52cefe0fa66 100644
--- a/compiler/testData/codegen/boxWithStdlib/dataClasses/tostring/alreadyInherited.kt
+++ b/compiler/testData/codegen/boxWithStdlib/dataClasses/tostring/alreadyInherited.kt
@@ -1,4 +1,4 @@
-trait SuperTrait {
+interface SuperTrait {
   override fun toString(): String = "!"
 }
 
diff --git a/compiler/testData/codegen/boxWithStdlib/fullJdk/regressions/kt1202.kt b/compiler/testData/codegen/boxWithStdlib/fullJdk/regressions/kt1202.kt
index deaa57f525c..b95c0cb3fd9 100644
--- a/compiler/testData/codegen/boxWithStdlib/fullJdk/regressions/kt1202.kt
+++ b/compiler/testData/codegen/boxWithStdlib/fullJdk/regressions/kt1202.kt
@@ -2,7 +2,7 @@ package testeval
 
 import java.util.*
 
-trait Expression
+interface Expression
 class Num(val value : Int) : Expression
 class Sum(val left : Expression, val right : Expression) : Expression
 class Mult(val left : Expression, val right : Expression) : Expression
@@ -16,7 +16,7 @@ fun eval(e : Expression) : Int {
     }
 }
 
-trait ParseResult<out T> {
+interface ParseResult<out T> {
     val success : Boolean
     val value : T
 }
diff --git a/compiler/testData/codegen/boxWithStdlib/reflection/enclosing/anonymousObjectInInlinedLambda.kt b/compiler/testData/codegen/boxWithStdlib/reflection/enclosing/anonymousObjectInInlinedLambda.kt
index 6744ff747e3..a1d3c1b512b 100644
--- a/compiler/testData/codegen/boxWithStdlib/reflection/enclosing/anonymousObjectInInlinedLambda.kt
+++ b/compiler/testData/codegen/boxWithStdlib/reflection/enclosing/anonymousObjectInInlinedLambda.kt
@@ -1,4 +1,4 @@
-trait A {
+interface A {
     fun f(): String
 }
 
diff --git a/compiler/testData/codegen/boxWithStdlib/reflection/enclosing/kt6368.kt b/compiler/testData/codegen/boxWithStdlib/reflection/enclosing/kt6368.kt
index 92ed2f45efe..16d226f3c0d 100644
--- a/compiler/testData/codegen/boxWithStdlib/reflection/enclosing/kt6368.kt
+++ b/compiler/testData/codegen/boxWithStdlib/reflection/enclosing/kt6368.kt
@@ -1,7 +1,7 @@
 import kotlin.properties.Delegates
 import java.util.HashMap
 
-trait R {
+interface R {
     fun result(): String
 }
 
diff --git a/compiler/testData/codegen/boxWithStdlib/reflection/enclosing/lambdaInObjectExpression.kt b/compiler/testData/codegen/boxWithStdlib/reflection/enclosing/lambdaInObjectExpression.kt
index dc13bfe9571..0e04ffaa04b 100644
--- a/compiler/testData/codegen/boxWithStdlib/reflection/enclosing/lambdaInObjectExpression.kt
+++ b/compiler/testData/codegen/boxWithStdlib/reflection/enclosing/lambdaInObjectExpression.kt
@@ -1,4 +1,4 @@
-trait C {
+interface C {
     val a: Any
 }
 
diff --git a/compiler/testData/codegen/boxWithStdlib/reflection/genericSignature/kt5112.kt b/compiler/testData/codegen/boxWithStdlib/reflection/genericSignature/kt5112.kt
index 4be92ec9f51..c1a8e0d47f4 100644
--- a/compiler/testData/codegen/boxWithStdlib/reflection/genericSignature/kt5112.kt
+++ b/compiler/testData/codegen/boxWithStdlib/reflection/genericSignature/kt5112.kt
@@ -4,7 +4,7 @@ class G<T>(val s: T) {
 
 }
 
-public trait ErrorsJvmTrait {
+public interface ErrorsJvmTrait {
     companion object {
         public val param : G<String> = G("STRING")
     }
diff --git a/compiler/testData/codegen/boxWithStdlib/regressions/Kt1149.kt b/compiler/testData/codegen/boxWithStdlib/regressions/Kt1149.kt
index 1abb4b7ec6f..7738799710e 100644
--- a/compiler/testData/codegen/boxWithStdlib/regressions/Kt1149.kt
+++ b/compiler/testData/codegen/boxWithStdlib/regressions/Kt1149.kt
@@ -3,7 +3,7 @@ package test.regressions.kt1149
 import java.util.ArrayList
 import kotlin.util.*
 
-public trait SomeTrait {
+public interface SomeTrait {
     fun foo()
 }
 
diff --git a/compiler/testData/codegen/boxWithStdlib/regressions/kt4142.kt b/compiler/testData/codegen/boxWithStdlib/regressions/kt4142.kt
index e02b05f37bb..d7fe122fda7 100644
--- a/compiler/testData/codegen/boxWithStdlib/regressions/kt4142.kt
+++ b/compiler/testData/codegen/boxWithStdlib/regressions/kt4142.kt
@@ -3,7 +3,7 @@ open class B {
         get() = "OK"
 }
 
-trait A {
+interface A {
     val name: String
 }
 
diff --git a/compiler/testData/codegen/boxWithStdlib/regressions/objectCaptureOuterConstructorProperty.kt b/compiler/testData/codegen/boxWithStdlib/regressions/objectCaptureOuterConstructorProperty.kt
index c25d8948d60..dd3315896ec 100644
--- a/compiler/testData/codegen/boxWithStdlib/regressions/objectCaptureOuterConstructorProperty.kt
+++ b/compiler/testData/codegen/boxWithStdlib/regressions/objectCaptureOuterConstructorProperty.kt
@@ -1,6 +1,6 @@
 import kotlin.support.*
 
-trait Stream<T> {
+interface Stream<T> {
     fun iterator(): Iterator<T>
 }
 
diff --git a/compiler/testData/codegen/boxWithStdlib/reified/anonymousObjectNoPropagate.kt b/compiler/testData/codegen/boxWithStdlib/reified/anonymousObjectNoPropagate.kt
index b405666b768..b9ff3a1cd9a 100644
--- a/compiler/testData/codegen/boxWithStdlib/reified/anonymousObjectNoPropagate.kt
+++ b/compiler/testData/codegen/boxWithStdlib/reified/anonymousObjectNoPropagate.kt
@@ -1,6 +1,6 @@
 import kotlin.test.assertEquals
 
-trait A {
+interface A {
     fun f1(): String
     fun f2(): String
     fun f3(): String
diff --git a/compiler/testData/codegen/boxWithStdlib/reified/reifiedInlineFunOfObject.kt b/compiler/testData/codegen/boxWithStdlib/reified/reifiedInlineFunOfObject.kt
index 339a09dd4a4..610af457377 100644
--- a/compiler/testData/codegen/boxWithStdlib/reified/reifiedInlineFunOfObject.kt
+++ b/compiler/testData/codegen/boxWithStdlib/reified/reifiedInlineFunOfObject.kt
@@ -2,7 +2,7 @@ import kotlin.test.assertEquals
 
 fun foo(block: () -> String) = block()
 
-trait A {
+interface A {
     fun f(): String
     fun g(): String
 }
diff --git a/compiler/testData/codegen/boxWithStdlib/reified/reifiedInlineFunOfObjectWithinReified.kt b/compiler/testData/codegen/boxWithStdlib/reified/reifiedInlineFunOfObjectWithinReified.kt
index 94335af2b62..0796b64399e 100644
--- a/compiler/testData/codegen/boxWithStdlib/reified/reifiedInlineFunOfObjectWithinReified.kt
+++ b/compiler/testData/codegen/boxWithStdlib/reified/reifiedInlineFunOfObjectWithinReified.kt
@@ -6,7 +6,7 @@ inline fun <reified T> className(): String = javaClass<T>().getName()
 
 inline fun <reified T> lambdaShouldBeReified(): String = foo { className<T>() }
 
-trait A {
+interface A {
     fun f(): String
     fun g(): String
 }
diff --git a/compiler/testData/codegen/boxWithStdlib/reified/reifiedInlineIntoNonInlineableLambda.kt b/compiler/testData/codegen/boxWithStdlib/reified/reifiedInlineIntoNonInlineableLambda.kt
index ce25ba54f75..542b658441a 100644
--- a/compiler/testData/codegen/boxWithStdlib/reified/reifiedInlineIntoNonInlineableLambda.kt
+++ b/compiler/testData/codegen/boxWithStdlib/reified/reifiedInlineIntoNonInlineableLambda.kt
@@ -4,7 +4,7 @@ fun foo(block: () -> String) = block()
 
 inline fun<reified T> className(): String = javaClass<T>().getName()
 
-trait A {
+interface A {
     fun f(): String
     fun g(): String
 }
diff --git a/compiler/testData/codegen/bytecodeText/bridgeForFakeOverride.kt b/compiler/testData/codegen/bytecodeText/bridgeForFakeOverride.kt
index 1b9a31ed573..2f481c74fc3 100644
--- a/compiler/testData/codegen/bytecodeText/bridgeForFakeOverride.kt
+++ b/compiler/testData/codegen/bytecodeText/bridgeForFakeOverride.kt
@@ -1,4 +1,4 @@
-trait A {
+interface A {
     fun foo(): Any
 }
 
diff --git a/compiler/testData/codegen/bytecodeText/traitImplGeneratedOnce.kt b/compiler/testData/codegen/bytecodeText/traitImplGeneratedOnce.kt
index 51ce275d99e..234a276c49d 100644
--- a/compiler/testData/codegen/bytecodeText/traitImplGeneratedOnce.kt
+++ b/compiler/testData/codegen/bytecodeText/traitImplGeneratedOnce.kt
@@ -1,4 +1,4 @@
-trait A {
+interface A {
     fun foo() = 42
 }
 
diff --git a/compiler/testData/codegen/classes/delegationToVal.kt b/compiler/testData/codegen/classes/delegationToVal.kt
index ec6242f5d16..0a4558ae4b7 100644
--- a/compiler/testData/codegen/classes/delegationToVal.kt
+++ b/compiler/testData/codegen/classes/delegationToVal.kt
@@ -1,4 +1,4 @@
-trait IActing {
+interface IActing {
   fun act(): String
 }
 
diff --git a/compiler/testData/codegen/innerClassInfo/innerAccessFlags.kt b/compiler/testData/codegen/innerClassInfo/innerAccessFlags.kt
index b902284e2b8..a96744e9995 100644
--- a/compiler/testData/codegen/innerClassInfo/innerAccessFlags.kt
+++ b/compiler/testData/codegen/innerClassInfo/innerAccessFlags.kt
@@ -2,7 +2,7 @@ class A {
     // Kind
     annotation class Annotation
     enum class Enum
-    trait Trait
+    interface Trait
 
     // Modality
     open class OpenStaticClass
diff --git a/compiler/testData/codegen/java8/boxWithJava/defaultMethodCallViaTrait/defaultMethodCallViaTrait.kt b/compiler/testData/codegen/java8/boxWithJava/defaultMethodCallViaTrait/defaultMethodCallViaTrait.kt
index 77c2a40cf45..e7ba10889c2 100644
--- a/compiler/testData/codegen/java8/boxWithJava/defaultMethodCallViaTrait/defaultMethodCallViaTrait.kt
+++ b/compiler/testData/codegen/java8/boxWithJava/defaultMethodCallViaTrait/defaultMethodCallViaTrait.kt
@@ -1,4 +1,4 @@
-trait TestTrait : Simple {}
+interface TestTrait : Simple {}
 class Test : TestTrait {}
 
 fun box(): String {
diff --git a/compiler/testData/codegen/notNullAssertions/AssertionChecker.kt b/compiler/testData/codegen/notNullAssertions/AssertionChecker.kt
index 40eb76742af..d3643218d1d 100644
--- a/compiler/testData/codegen/notNullAssertions/AssertionChecker.kt
+++ b/compiler/testData/codegen/notNullAssertions/AssertionChecker.kt
@@ -11,7 +11,7 @@ class AssertionChecker(val illegalStateExpected: Boolean) {
 }
 
 
-trait Tr { 
+interface Tr {
     fun foo(): String
 }
 
diff --git a/compiler/testData/codegen/properties/syntheticMethod/inTrait.kt b/compiler/testData/codegen/properties/syntheticMethod/inTrait.kt
index 4baa7786d3b..7f11e0e4012 100644
--- a/compiler/testData/codegen/properties/syntheticMethod/inTrait.kt
+++ b/compiler/testData/codegen/properties/syntheticMethod/inTrait.kt
@@ -2,6 +2,6 @@ import java.lang.annotation.*
 
 Retention(RetentionPolicy.RUNTIME) annotation class SomeAnnotation(val value: String)
 
-trait T {
+interface T {
     [SomeAnnotation("OK")] val property: Int
 }
diff --git a/compiler/testData/codegen/regressions/kt297.kt b/compiler/testData/codegen/regressions/kt297.kt
index 0a6ad8f82a5..169d061c6de 100644
--- a/compiler/testData/codegen/regressions/kt297.kt
+++ b/compiler/testData/codegen/regressions/kt297.kt
@@ -1,4 +1,4 @@
-// KT-297 Overload resolution ambiguity with required in trait
-trait ALE<T> : java.util.ArrayList<T> {
+// KT-297 Overload resolution ambiguity with required in interface
+interface ALE<T> : java.util.ArrayList<T> {
    fun getOrValue(index: Int, value : T) : T = if(index >= 0 && index < size()) get(index) else value
 }
\ No newline at end of file
diff --git a/compiler/testData/compileJavaAgainstKotlin/method/Delegation.kt b/compiler/testData/compileJavaAgainstKotlin/method/Delegation.kt
index 81c402f355b..880b3c9ad0f 100644
--- a/compiler/testData/compileJavaAgainstKotlin/method/Delegation.kt
+++ b/compiler/testData/compileJavaAgainstKotlin/method/Delegation.kt
@@ -1,6 +1,6 @@
 package test
 
-trait Trait {
+interface Trait {
     fun foo()
     val bar: Int
 }
diff --git a/compiler/testData/compileJavaAgainstKotlin/method/TraitImpl.kt b/compiler/testData/compileJavaAgainstKotlin/method/TraitImpl.kt
index 8f12a0bf590..14d5affe430 100644
--- a/compiler/testData/compileJavaAgainstKotlin/method/TraitImpl.kt
+++ b/compiler/testData/compileJavaAgainstKotlin/method/TraitImpl.kt
@@ -1,6 +1,6 @@
 package test
 
-trait Trait {
+interface Trait {
     fun simple() {
     }
 
diff --git a/compiler/testData/compileJavaAgainstKotlin/method/primitiveOverride/ByteOverridesObject.kt b/compiler/testData/compileJavaAgainstKotlin/method/primitiveOverride/ByteOverridesObject.kt
index 230e0d16013..ca45627f88a 100644
--- a/compiler/testData/compileJavaAgainstKotlin/method/primitiveOverride/ByteOverridesObject.kt
+++ b/compiler/testData/compileJavaAgainstKotlin/method/primitiveOverride/ByteOverridesObject.kt
@@ -1,6 +1,6 @@
 package test
 
-trait A<T> {
+interface A<T> {
     fun foo(): T
 }
 
diff --git a/compiler/testData/compileJavaAgainstKotlin/method/primitiveOverride/CallFinalNotInSubclass.kt b/compiler/testData/compileJavaAgainstKotlin/method/primitiveOverride/CallFinalNotInSubclass.kt
index 918943a1ab1..db977673289 100644
--- a/compiler/testData/compileJavaAgainstKotlin/method/primitiveOverride/CallFinalNotInSubclass.kt
+++ b/compiler/testData/compileJavaAgainstKotlin/method/primitiveOverride/CallFinalNotInSubclass.kt
@@ -1,6 +1,6 @@
 package test
 
-trait A<T> {
+interface A<T> {
     fun foo(): T
 }
 
diff --git a/compiler/testData/compileJavaAgainstKotlin/method/primitiveOverride/CallNotInSubclass.kt b/compiler/testData/compileJavaAgainstKotlin/method/primitiveOverride/CallNotInSubclass.kt
index 3bba95749b3..9e76fbf5f05 100644
--- a/compiler/testData/compileJavaAgainstKotlin/method/primitiveOverride/CallNotInSubclass.kt
+++ b/compiler/testData/compileJavaAgainstKotlin/method/primitiveOverride/CallNotInSubclass.kt
@@ -1,6 +1,6 @@
 package test
 
-trait A<T> {
+interface A<T> {
     fun foo(): T
 }
 
diff --git a/compiler/testData/compileJavaAgainstKotlin/method/primitiveOverride/CovariantReturnTypeOverride.kt b/compiler/testData/compileJavaAgainstKotlin/method/primitiveOverride/CovariantReturnTypeOverride.kt
index 795637eaa7b..edb53697a90 100644
--- a/compiler/testData/compileJavaAgainstKotlin/method/primitiveOverride/CovariantReturnTypeOverride.kt
+++ b/compiler/testData/compileJavaAgainstKotlin/method/primitiveOverride/CovariantReturnTypeOverride.kt
@@ -1,6 +1,6 @@
 package test
 
-trait A {
+interface A {
     fun foo(): Any
 }
 
diff --git a/compiler/testData/compileJavaAgainstKotlin/method/primitiveOverride/FinalOverride.kt b/compiler/testData/compileJavaAgainstKotlin/method/primitiveOverride/FinalOverride.kt
index f2f8226a9bc..d05e0c28918 100644
--- a/compiler/testData/compileJavaAgainstKotlin/method/primitiveOverride/FinalOverride.kt
+++ b/compiler/testData/compileJavaAgainstKotlin/method/primitiveOverride/FinalOverride.kt
@@ -1,6 +1,6 @@
 package test
 
-trait A<T> {
+interface A<T> {
     fun foo(): T
 }
 
diff --git a/compiler/testData/compileJavaAgainstKotlin/method/primitiveOverride/IntOverridesComparable.kt b/compiler/testData/compileJavaAgainstKotlin/method/primitiveOverride/IntOverridesComparable.kt
index 227271d3d74..4825976da81 100644
--- a/compiler/testData/compileJavaAgainstKotlin/method/primitiveOverride/IntOverridesComparable.kt
+++ b/compiler/testData/compileJavaAgainstKotlin/method/primitiveOverride/IntOverridesComparable.kt
@@ -1,6 +1,6 @@
 package test
 
-trait A<T : Comparable<T>> {
+interface A<T : Comparable<T>> {
     fun foo(): T
 }
 
diff --git a/compiler/testData/compileJavaAgainstKotlin/method/primitiveOverride/IntOverridesNumber.kt b/compiler/testData/compileJavaAgainstKotlin/method/primitiveOverride/IntOverridesNumber.kt
index 69d6c4796a4..4e59e10e679 100644
--- a/compiler/testData/compileJavaAgainstKotlin/method/primitiveOverride/IntOverridesNumber.kt
+++ b/compiler/testData/compileJavaAgainstKotlin/method/primitiveOverride/IntOverridesNumber.kt
@@ -1,6 +1,6 @@
 package test
 
-trait A<T : Number> {
+interface A<T : Number> {
     fun foo(): T
 }
 
diff --git a/compiler/testData/compileJavaAgainstKotlin/method/primitiveOverride/IntOverridesObject.kt b/compiler/testData/compileJavaAgainstKotlin/method/primitiveOverride/IntOverridesObject.kt
index 185be0adc22..97b8a7540f1 100644
--- a/compiler/testData/compileJavaAgainstKotlin/method/primitiveOverride/IntOverridesObject.kt
+++ b/compiler/testData/compileJavaAgainstKotlin/method/primitiveOverride/IntOverridesObject.kt
@@ -1,6 +1,6 @@
 package test
 
-trait A<T> {
+interface A<T> {
     fun foo(): T
 }
 
diff --git a/compiler/testData/compileJavaAgainstKotlin/method/primitiveOverride/ManyClassesHierarchy.kt b/compiler/testData/compileJavaAgainstKotlin/method/primitiveOverride/ManyClassesHierarchy.kt
index 825917181d6..404576a1c11 100644
--- a/compiler/testData/compileJavaAgainstKotlin/method/primitiveOverride/ManyClassesHierarchy.kt
+++ b/compiler/testData/compileJavaAgainstKotlin/method/primitiveOverride/ManyClassesHierarchy.kt
@@ -1,10 +1,10 @@
 package test
 
-trait A<T> {
+interface A<T> {
     fun foo(): T
 }
 
-trait B : A<Int>
+interface B : A<Int>
 
 abstract class C : B
 
diff --git a/compiler/testData/compileJavaAgainstKotlin/method/primitiveOverride/NullableIntOverridesObject.kt b/compiler/testData/compileJavaAgainstKotlin/method/primitiveOverride/NullableIntOverridesObject.kt
index 816a6c0b288..642fdaf23df 100644
--- a/compiler/testData/compileJavaAgainstKotlin/method/primitiveOverride/NullableIntOverridesObject.kt
+++ b/compiler/testData/compileJavaAgainstKotlin/method/primitiveOverride/NullableIntOverridesObject.kt
@@ -1,6 +1,6 @@
 package test
 
-trait A<T> {
+interface A<T> {
     fun foo(): T
 }
 
diff --git a/compiler/testData/compileJavaAgainstKotlin/method/primitiveOverride/OverrideInJava.kt b/compiler/testData/compileJavaAgainstKotlin/method/primitiveOverride/OverrideInJava.kt
index d1e5e86a8ef..8438becf723 100644
--- a/compiler/testData/compileJavaAgainstKotlin/method/primitiveOverride/OverrideInJava.kt
+++ b/compiler/testData/compileJavaAgainstKotlin/method/primitiveOverride/OverrideInJava.kt
@@ -1,6 +1,6 @@
 package test
 
-trait A<T> {
+interface A<T> {
     fun foo(): T
 }
 
diff --git a/compiler/testData/compileJavaAgainstKotlin/method/throws/Delegation.kt b/compiler/testData/compileJavaAgainstKotlin/method/throws/Delegation.kt
index 6d11ab9149d..9399efe1aa5 100644
--- a/compiler/testData/compileJavaAgainstKotlin/method/throws/Delegation.kt
+++ b/compiler/testData/compileJavaAgainstKotlin/method/throws/Delegation.kt
@@ -3,7 +3,7 @@ package test
 class E1: Exception()
 class E2: Exception()
 
-trait Trait {
+interface Trait {
     throws()
     fun none()
 
diff --git a/compiler/testData/compileJavaAgainstKotlin/method/throws/GenericSubstitution.kt b/compiler/testData/compileJavaAgainstKotlin/method/throws/GenericSubstitution.kt
index 27154abdc6e..befd95233be 100644
--- a/compiler/testData/compileJavaAgainstKotlin/method/throws/GenericSubstitution.kt
+++ b/compiler/testData/compileJavaAgainstKotlin/method/throws/GenericSubstitution.kt
@@ -2,7 +2,7 @@ package test
 
 class E1: Exception()
 
-trait Base<T> {
+interface Base<T> {
     throws(E1::class)
     fun one(t: T) {}
 }
diff --git a/compiler/testData/compileJavaAgainstKotlin/method/throws/TraitMembers.kt b/compiler/testData/compileJavaAgainstKotlin/method/throws/TraitMembers.kt
index 58f97b762dc..cb242d3c5c7 100644
--- a/compiler/testData/compileJavaAgainstKotlin/method/throws/TraitMembers.kt
+++ b/compiler/testData/compileJavaAgainstKotlin/method/throws/TraitMembers.kt
@@ -3,7 +3,7 @@ package test
 class E1: Exception()
 class E2: Exception()
 
-trait Trait {
+interface Trait {
     throws()
     fun none() {}
 
diff --git a/compiler/testData/compileJavaAgainstKotlin/staticFields/AnnotationTrait.kt b/compiler/testData/compileJavaAgainstKotlin/staticFields/AnnotationTrait.kt
index 9c0944a7948..06aed71a05a 100644
--- a/compiler/testData/compileJavaAgainstKotlin/staticFields/AnnotationTrait.kt
+++ b/compiler/testData/compileJavaAgainstKotlin/staticFields/AnnotationTrait.kt
@@ -8,7 +8,7 @@ annotation class ALong(val value: Long)
 annotation class ADouble(val value: Double)
 annotation class AFloat(val value: Float)
 
-trait Test {
+interface Test {
 
     companion object {
         val vstring: String = "Test"
diff --git a/compiler/testData/compileJavaAgainstKotlin/staticFields/staticTraitProperty.kt b/compiler/testData/compileJavaAgainstKotlin/staticFields/staticTraitProperty.kt
index 9d8b9a15fbe..b1958bb1156 100644
--- a/compiler/testData/compileJavaAgainstKotlin/staticFields/staticTraitProperty.kt
+++ b/compiler/testData/compileJavaAgainstKotlin/staticFields/staticTraitProperty.kt
@@ -1,6 +1,6 @@
 package test
 
-trait Test {
+interface Test {
 
   companion object {
     public val valProp: Int = 10
diff --git a/compiler/testData/compileKotlinAgainstCustomBinaries/noWarningsOnJavaKotlinInheritance/noWarningsOnJavaKotlinInheritance.kt b/compiler/testData/compileKotlinAgainstCustomBinaries/noWarningsOnJavaKotlinInheritance/noWarningsOnJavaKotlinInheritance.kt
index 11f0f17de03..bc617c7f74c 100644
--- a/compiler/testData/compileKotlinAgainstCustomBinaries/noWarningsOnJavaKotlinInheritance/noWarningsOnJavaKotlinInheritance.kt
+++ b/compiler/testData/compileKotlinAgainstCustomBinaries/noWarningsOnJavaKotlinInheritance/noWarningsOnJavaKotlinInheritance.kt
@@ -7,7 +7,7 @@ class SimpleSubclass : JavaInterface {
 
 // Class extends both Java and Kotlin traits. Checks that there's no DIFFERENT_NAMES_FOR_THE_SAME_PARAMETER_IN_SUPERTYPES warning
 
-trait KotlinTrait {
+interface KotlinTrait {
     public fun foo(someOtherName: Int) {}
 }
 
diff --git a/compiler/testData/compileKotlinAgainstKotlin/AnnotationInTrait.A.kt b/compiler/testData/compileKotlinAgainstKotlin/AnnotationInTrait.A.kt
index dc872ab7fd2..a04ee6dda50 100644
--- a/compiler/testData/compileKotlinAgainstKotlin/AnnotationInTrait.A.kt
+++ b/compiler/testData/compileKotlinAgainstKotlin/AnnotationInTrait.A.kt
@@ -5,7 +5,7 @@ import java.lang.annotation.*
 Retention(RetentionPolicy.RUNTIME)
 annotation class Ann
 
-trait Tr {
+interface Tr {
     Ann
     fun foo() {}
 }
\ No newline at end of file
diff --git a/compiler/testData/compileKotlinAgainstKotlin/RecursiveGeneric.A.kt b/compiler/testData/compileKotlinAgainstKotlin/RecursiveGeneric.A.kt
index 3c7973fdbdc..15e0b1766fb 100644
--- a/compiler/testData/compileKotlinAgainstKotlin/RecursiveGeneric.A.kt
+++ b/compiler/testData/compileKotlinAgainstKotlin/RecursiveGeneric.A.kt
@@ -1,9 +1,9 @@
 package a
 
-trait Rec<R, out T: Rec<R, T>> {
+interface Rec<R, out T: Rec<R, T>> {
     fun t(): T
 }
 
-trait Super {
+interface Super {
     fun foo(p: Rec<*, *>) = p.t()
 }
\ No newline at end of file
diff --git a/compiler/testData/constraintSystem/declarations/declarations.kt b/compiler/testData/constraintSystem/declarations/declarations.kt
index d4dc77f5df6..832e99dd7f9 100644
--- a/compiler/testData/constraintSystem/declarations/declarations.kt
+++ b/compiler/testData/constraintSystem/declarations/declarations.kt
@@ -1,10 +1,10 @@
 fun foo<T, P: T>() = 42
 
-trait A
-trait B : A
-trait C : B
+interface A
+interface B : A
+interface C : B
 
-trait Consumer<in T>
-trait Producer<out T>
+interface Consumer<in T>
+interface Producer<out T>
 
-trait My<T>
\ No newline at end of file
+interface My<T>
\ No newline at end of file
diff --git a/compiler/testData/diagnostics/checkerTestUtil/test_with_diagnostic.kt b/compiler/testData/diagnostics/checkerTestUtil/test_with_diagnostic.kt
index 781f16efae5..5842af1f97d 100644
--- a/compiler/testData/diagnostics/checkerTestUtil/test_with_diagnostic.kt
+++ b/compiler/testData/diagnostics/checkerTestUtil/test_with_diagnostic.kt
@@ -1,4 +1,4 @@
-trait Pa<X, Y>
+interface Pa<X, Y>
 
 fun foo(<!UNUSED_PARAMETER(IGNORE)!>u<!> : Unit) : Int = 1
 fun bas(<!UNUSED_PARAMETER!>u<!> : Pa<Int, String>) = 3
diff --git a/compiler/testData/diagnostics/tests/AbstractInTrait.kt b/compiler/testData/diagnostics/tests/AbstractInTrait.kt
index 777898b1f12..dca6ca1344e 100644
--- a/compiler/testData/diagnostics/tests/AbstractInTrait.kt
+++ b/compiler/testData/diagnostics/tests/AbstractInTrait.kt
@@ -1,6 +1,6 @@
 package abstract
 
-trait MyTrait {
+interface MyTrait {
     //properties
     val a: Int
     val a1: Int = <!PROPERTY_INITIALIZER_IN_TRAIT!>1<!>
diff --git a/compiler/testData/diagnostics/tests/AnonymousInitializers.kt b/compiler/testData/diagnostics/tests/AnonymousInitializers.kt
index 69df0631f6b..c139a55789f 100644
--- a/compiler/testData/diagnostics/tests/AnonymousInitializers.kt
+++ b/compiler/testData/diagnostics/tests/AnonymousInitializers.kt
@@ -1,4 +1,4 @@
-trait NoC {
+interface NoC {
   <!ANONYMOUS_INITIALIZER_IN_TRAIT!>init {
 
   }<!>
diff --git a/compiler/testData/diagnostics/tests/Builders.kt b/compiler/testData/diagnostics/tests/Builders.kt
index d2a0fa788b6..2f334cd72d5 100644
--- a/compiler/testData/diagnostics/tests/Builders.kt
+++ b/compiler/testData/diagnostics/tests/Builders.kt
@@ -49,7 +49,7 @@ fun main(args : Array<String>) {
   println(result)
 }
 
-trait Element {
+interface Element {
   fun render(builder : StringBuilder, indent : String)
 
   override fun toString() : String {
diff --git a/compiler/testData/diagnostics/tests/CovariantOverrideType.kt b/compiler/testData/diagnostics/tests/CovariantOverrideType.kt
index 94e0624b2f4..b3cfc4ff9be 100644
--- a/compiler/testData/diagnostics/tests/CovariantOverrideType.kt
+++ b/compiler/testData/diagnostics/tests/CovariantOverrideType.kt
@@ -1,4 +1,4 @@
-trait A {
+interface A {
     fun foo() : Int = 1
     fun foo2() : Int = 1
     fun foo1() : Int = 1
diff --git a/compiler/testData/diagnostics/tests/DeferredTypes.kt b/compiler/testData/diagnostics/tests/DeferredTypes.kt
index 01524cefbfd..107a25ea17b 100644
--- a/compiler/testData/diagnostics/tests/DeferredTypes.kt
+++ b/compiler/testData/diagnostics/tests/DeferredTypes.kt
@@ -1,3 +1,3 @@
-trait T {
+interface T {
   val a = <!PROPERTY_INITIALIZER_IN_TRAIT!><!UNRESOLVED_REFERENCE!>Foo<!>.<!DEBUG_INFO_ELEMENT_WITH_ERROR_TYPE!>bar<!>()<!>
 }
\ No newline at end of file
diff --git a/compiler/testData/diagnostics/tests/DiamondFunction.kt b/compiler/testData/diagnostics/tests/DiamondFunction.kt
index 9e171ba1dc1..0d8b9a77755 100644
--- a/compiler/testData/diagnostics/tests/DiamondFunction.kt
+++ b/compiler/testData/diagnostics/tests/DiamondFunction.kt
@@ -1,9 +1,9 @@
-trait Base {
+interface Base {
     fun f() = 1
 }
     
 open class Left() : Base
 
-trait Right : Base
+interface Right : Base
 
 class Diamond() : Left(), Right
diff --git a/compiler/testData/diagnostics/tests/DiamondFunctionGeneric.kt b/compiler/testData/diagnostics/tests/DiamondFunctionGeneric.kt
index 3fe4f3a0c26..d84e34a40a8 100644
--- a/compiler/testData/diagnostics/tests/DiamondFunctionGeneric.kt
+++ b/compiler/testData/diagnostics/tests/DiamondFunctionGeneric.kt
@@ -1,9 +1,9 @@
-trait Base<P> {
+interface Base<P> {
     fun f() = 1
 }
     
 open class Left<P>() : Base<P>
 
-trait Right<P> : Base<P>
+interface Right<P> : Base<P>
 
 class Diamond<P>() : Left<P>(), Right<P>
diff --git a/compiler/testData/diagnostics/tests/DiamondProperty.kt b/compiler/testData/diagnostics/tests/DiamondProperty.kt
index fcc8bc39372..5a93ad88daa 100644
--- a/compiler/testData/diagnostics/tests/DiamondProperty.kt
+++ b/compiler/testData/diagnostics/tests/DiamondProperty.kt
@@ -1,4 +1,4 @@
-trait Base {
+interface Base {
     var v : Int
         get() = 1
         set(v) {}
@@ -6,6 +6,6 @@ trait Base {
     
 open class Left() : Base
 
-trait Right : Base
+interface Right : Base
 
 class Diamond() : Left(), Right
diff --git a/compiler/testData/diagnostics/tests/GenericArgumentConsistency.kt b/compiler/testData/diagnostics/tests/GenericArgumentConsistency.kt
index d95b35b7eec..29bb7ee8614 100644
--- a/compiler/testData/diagnostics/tests/GenericArgumentConsistency.kt
+++ b/compiler/testData/diagnostics/tests/GenericArgumentConsistency.kt
@@ -1,43 +1,43 @@
 // FILE: b.kt
-trait A<in T> {}
-trait B<T> : A<Int> {}
-trait C<T> : <!INCONSISTENT_TYPE_PARAMETER_VALUES!>B<T>, A<T><!> {}
-trait C1<T> : <!INCONSISTENT_TYPE_PARAMETER_VALUES!>B<T>, A<Any><!> {}
-trait D : <!INCONSISTENT_TYPE_PARAMETER_VALUES, INCONSISTENT_TYPE_PARAMETER_VALUES!>C<Boolean>, B<Double><!>{}
+interface A<in T> {}
+interface B<T> : A<Int> {}
+interface C<T> : <!INCONSISTENT_TYPE_PARAMETER_VALUES!>B<T>, A<T><!> {}
+interface C1<T> : <!INCONSISTENT_TYPE_PARAMETER_VALUES!>B<T>, A<Any><!> {}
+interface D : <!INCONSISTENT_TYPE_PARAMETER_VALUES, INCONSISTENT_TYPE_PARAMETER_VALUES!>C<Boolean>, B<Double><!>{}
 
-trait A1<out T> {}
-trait B1 : A1<Int> {}
-trait B2 : <!INCONSISTENT_TYPE_PARAMETER_VALUES!>A1<Any>, B1<!> {}
+interface A1<out T> {}
+interface B1 : A1<Int> {}
+interface B2 : <!INCONSISTENT_TYPE_PARAMETER_VALUES!>A1<Any>, B1<!> {}
 
-trait BA1<T> {}
-trait BB1 : BA1<Int> {}
-trait BB2 : <!INCONSISTENT_TYPE_PARAMETER_VALUES!>BA1<Any>, BB1<!> {}
+interface BA1<T> {}
+interface BB1 : BA1<Int> {}
+interface BB2 : <!INCONSISTENT_TYPE_PARAMETER_VALUES!>BA1<Any>, BB1<!> {}
 
 
 // FILE: b.kt
 package x
-    trait AA1<out T> {}
-    trait AB1 : AA1<Int> {}
-    trait AB3 : AA1<Comparable<Int>> {}
-    trait AB2 : <!INCONSISTENT_TYPE_PARAMETER_VALUES!>AA1<Number>, AB1, AB3<!> {}
+    interface AA1<out T> {}
+    interface AB1 : AA1<Int> {}
+    interface AB3 : AA1<Comparable<Int>> {}
+    interface AB2 : <!INCONSISTENT_TYPE_PARAMETER_VALUES!>AA1<Number>, AB1, AB3<!> {}
 
 // FILE: b.kt
 package x2
-    trait AA1<out T> {}
-    trait AB1 : AA1<Any> {}
-    trait AB3 : AA1<Comparable<Int>> {}
-    trait AB2 : <!INCONSISTENT_TYPE_PARAMETER_VALUES!>AA1<Number>, AB1, AB3<!> {}
+    interface AA1<out T> {}
+    interface AB1 : AA1<Any> {}
+    interface AB3 : AA1<Comparable<Int>> {}
+    interface AB2 : <!INCONSISTENT_TYPE_PARAMETER_VALUES!>AA1<Number>, AB1, AB3<!> {}
 
 // FILE: b.kt
 package x3
-    trait AA1<in T> {}
-    trait AB1 : AA1<Any> {}
-    trait AB3 : AA1<Comparable<Int>> {}
-    trait AB2 : <!INCONSISTENT_TYPE_PARAMETER_VALUES!>AA1<Number>, AB1, AB3<!> {}
+    interface AA1<in T> {}
+    interface AB1 : AA1<Any> {}
+    interface AB3 : AA1<Comparable<Int>> {}
+    interface AB2 : <!INCONSISTENT_TYPE_PARAMETER_VALUES!>AA1<Number>, AB1, AB3<!> {}
 
 // FILE: b.kt
 package sx2
-    trait AA1<in T> {}
-    trait AB1 : AA1<Int> {}
-    trait AB3 : AA1<Comparable<Int>> {}
-    trait AB2 : <!INCONSISTENT_TYPE_PARAMETER_VALUES!>AA1<Number>, AB1, AB3<!> {}
\ No newline at end of file
+    interface AA1<in T> {}
+    interface AB1 : AA1<Int> {}
+    interface AB3 : AA1<Comparable<Int>> {}
+    interface AB2 : <!INCONSISTENT_TYPE_PARAMETER_VALUES!>AA1<Number>, AB1, AB3<!> {}
\ No newline at end of file
diff --git a/compiler/testData/diagnostics/tests/MultipleBounds.kt b/compiler/testData/diagnostics/tests/MultipleBounds.kt
index 0fcd73ad2fe..243940985b5 100644
--- a/compiler/testData/diagnostics/tests/MultipleBounds.kt
+++ b/compiler/testData/diagnostics/tests/MultipleBounds.kt
@@ -4,11 +4,11 @@ open class A() {
   fun foo() : Int = 1
 }
 
-trait B {
+interface B {
   fun bar() : Double = 1.0;
 }
 
-trait G<X> {
+interface G<X> {
     val <X : A> boo: Double  where X : B
     val <A> bal: Double  where A : B
     val <Y : B> bas: Double where <!NAME_IN_CONSTRAINT_IS_NOT_A_TYPE_PARAMETER!>X<!> : B
diff --git a/compiler/testData/diagnostics/tests/OverridenFunctionAndSpecifiedTypeParameter.kt b/compiler/testData/diagnostics/tests/OverridenFunctionAndSpecifiedTypeParameter.kt
index 297eb3aefff..95d4fdcc9c8 100644
--- a/compiler/testData/diagnostics/tests/OverridenFunctionAndSpecifiedTypeParameter.kt
+++ b/compiler/testData/diagnostics/tests/OverridenFunctionAndSpecifiedTypeParameter.kt
@@ -1,5 +1,5 @@
 
-trait Aaa<T> {
+interface Aaa<T> {
   fun zzz(value: T): Unit
 }
 
diff --git a/compiler/testData/diagnostics/tests/OverridingVarByVal.kt b/compiler/testData/diagnostics/tests/OverridingVarByVal.kt
index e14eef6b41e..c18a525c9e6 100644
--- a/compiler/testData/diagnostics/tests/OverridingVarByVal.kt
+++ b/compiler/testData/diagnostics/tests/OverridingVarByVal.kt
@@ -2,7 +2,7 @@ open class Var() {
   open var v : Int = 1
 }
 
-trait VarT {
+interface VarT {
   var v : Int
 }
 
diff --git a/compiler/testData/diagnostics/tests/ProjectionsInSupertypes.kt b/compiler/testData/diagnostics/tests/ProjectionsInSupertypes.kt
index 03b68107997..2a428d0261d 100644
--- a/compiler/testData/diagnostics/tests/ProjectionsInSupertypes.kt
+++ b/compiler/testData/diagnostics/tests/ProjectionsInSupertypes.kt
@@ -1,6 +1,6 @@
-trait A<T> {}
-trait B<T> {}
-trait C<T> {}
-trait D<T> {}
+interface A<T> {}
+interface B<T> {}
+interface C<T> {}
+interface D<T> {}
 
-trait Test : A<<!PROJECTION_IN_IMMEDIATE_ARGUMENT_TO_SUPERTYPE!>in<!> Int>, B<<!PROJECTION_IN_IMMEDIATE_ARGUMENT_TO_SUPERTYPE!>out<!> Int>, C<<!PROJECTION_IN_IMMEDIATE_ARGUMENT_TO_SUPERTYPE!>*<!>><!NULLABLE_SUPERTYPE!>?<!><!REDUNDANT_NULLABLE!>?<!><!REDUNDANT_NULLABLE!>?<!>, D<Int> {}
\ No newline at end of file
+interface Test : A<<!PROJECTION_IN_IMMEDIATE_ARGUMENT_TO_SUPERTYPE!>in<!> Int>, B<<!PROJECTION_IN_IMMEDIATE_ARGUMENT_TO_SUPERTYPE!>out<!> Int>, C<<!PROJECTION_IN_IMMEDIATE_ARGUMENT_TO_SUPERTYPE!>*<!>><!NULLABLE_SUPERTYPE!>?<!><!REDUNDANT_NULLABLE!>?<!><!REDUNDANT_NULLABLE!>?<!>, D<Int> {}
\ No newline at end of file
diff --git a/compiler/testData/diagnostics/tests/SelfTypesUnsupported.kt b/compiler/testData/diagnostics/tests/SelfTypesUnsupported.kt
index 43c2f651488..e137d8399ec 100644
--- a/compiler/testData/diagnostics/tests/SelfTypesUnsupported.kt
+++ b/compiler/testData/diagnostics/tests/SelfTypesUnsupported.kt
@@ -2,7 +2,7 @@
 
 fun foo(f: <!UNSUPPORTED!>This<!>) {}
 
-trait C<T: C<<!UNSUPPORTED!>This<!>>> {
+interface C<T: C<<!UNSUPPORTED!>This<!>>> {
     val x: <!UNSUPPORTED!>This<!>
     val y: <!UNSUPPORTED!>This<!>?
 }
\ No newline at end of file
diff --git a/compiler/testData/diagnostics/tests/SupertypeListChecks.kt b/compiler/testData/diagnostics/tests/SupertypeListChecks.kt
index 3ef95fb2b33..fc282ff139c 100644
--- a/compiler/testData/diagnostics/tests/SupertypeListChecks.kt
+++ b/compiler/testData/diagnostics/tests/SupertypeListChecks.kt
@@ -4,7 +4,7 @@
 In a supertype list:
  Same type should not be mentioned twice
  Same type should not be indirectly mentioned with incoherent type arguments
- Every trait's required dependencies should be satisfied
+ Every interface's required dependencies should be satisfied
  No final types should appear
  Only one class is allowed
 */
@@ -17,24 +17,24 @@ open class C2 {}
 
 open class C3 {}
 
-trait T1 {}
+interface T1 {}
 
-trait T2<T> {}
+interface T2<T> {}
 
-trait Test<!CONSTRUCTOR_IN_TRAIT!>()<!> {
+interface Test<!CONSTRUCTOR_IN_TRAIT!>()<!> {
 }
 
-trait Test1 : <!TRAIT_WITH_SUPERCLASS!>C2<!><!SUPERTYPE_INITIALIZED_IN_TRAIT!>()<!> {}
+interface Test1 : <!TRAIT_WITH_SUPERCLASS!>C2<!><!SUPERTYPE_INITIALIZED_IN_TRAIT!>()<!> {}
 
-trait Test2 : <!TRAIT_WITH_SUPERCLASS!>C2<!> {}
+interface Test2 : <!TRAIT_WITH_SUPERCLASS!>C2<!> {}
 
-trait Test3 : <!TRAIT_WITH_SUPERCLASS!>C2<!>, <!MANY_CLASSES_IN_SUPERTYPE_LIST!>C3<!> {}
+interface Test3 : <!TRAIT_WITH_SUPERCLASS!>C2<!>, <!MANY_CLASSES_IN_SUPERTYPE_LIST!>C3<!> {}
 
-trait Test4 : T1 {}
+interface Test4 : T1 {}
 
-trait Test5 : T1, <!SUPERTYPE_APPEARS_TWICE!>T1<!> {}
+interface Test5 : T1, <!SUPERTYPE_APPEARS_TWICE!>T1<!> {}
 
-trait Test6 : <!TRAIT_WITH_SUPERCLASS, FINAL_SUPERTYPE!>C1<!> {}
+interface Test6 : <!TRAIT_WITH_SUPERCLASS, FINAL_SUPERTYPE!>C1<!> {}
 
 class CTest1() : OC1() {}
 
diff --git a/compiler/testData/diagnostics/tests/TraitOverrideObjectMethods.kt b/compiler/testData/diagnostics/tests/TraitOverrideObjectMethods.kt
index 7361b31d2d3..d49911c5101 100644
--- a/compiler/testData/diagnostics/tests/TraitOverrideObjectMethods.kt
+++ b/compiler/testData/diagnostics/tests/TraitOverrideObjectMethods.kt
@@ -1,4 +1,4 @@
-trait MyTrait: <!PLATFORM_CLASS_MAPPED_TO_KOTLIN, TRAIT_WITH_SUPERCLASS!>Object<!> {
+interface MyTrait: <!PLATFORM_CLASS_MAPPED_TO_KOTLIN, TRAIT_WITH_SUPERCLASS!>Object<!> {
     override fun toString(): String
     public override fun finalize()
     public <!OVERRIDING_FINAL_MEMBER!>override<!> fun wait()
diff --git a/compiler/testData/diagnostics/tests/TraitWithConstructor.kt b/compiler/testData/diagnostics/tests/TraitWithConstructor.kt
index 325d5b83e9e..92374c88b6a 100644
--- a/compiler/testData/diagnostics/tests/TraitWithConstructor.kt
+++ b/compiler/testData/diagnostics/tests/TraitWithConstructor.kt
@@ -1,12 +1,12 @@
 class C(val a: String) {}
 
-trait T1<!CONSTRUCTOR_IN_TRAIT!>(val x: String)<!> {}
+interface T1<!CONSTRUCTOR_IN_TRAIT!>(val x: String)<!> {}
 
-trait T2<!CONSTRUCTOR_IN_TRAIT!>()<!> {}
+interface T2<!CONSTRUCTOR_IN_TRAIT!>()<!> {}
 
-trait T3<!CONSTRUCTOR_IN_TRAIT!>(<!UNUSED_PARAMETER!>a<!>: Int)<!> {}
+interface T3<!CONSTRUCTOR_IN_TRAIT!>(<!UNUSED_PARAMETER!>a<!>: Int)<!> {}
 
-trait T4 {
+interface T4 {
     <!CONSTRUCTOR_IN_TRAIT!>constructor(a: <!DEBUG_INFO_MISSING_UNRESOLVED!>Int<!>) {
         val b: <!DEBUG_INFO_MISSING_UNRESOLVED!>Int<!> = 1
     }<!>
diff --git a/compiler/testData/diagnostics/tests/UnusedVariables.kt b/compiler/testData/diagnostics/tests/UnusedVariables.kt
index 7ad929ffd38..e8106fe91b7 100644
--- a/compiler/testData/diagnostics/tests/UnusedVariables.kt
+++ b/compiler/testData/diagnostics/tests/UnusedVariables.kt
@@ -112,7 +112,7 @@ fun testFunctionLiterals() {
     }
 }
 
-trait Trait {
+interface Trait {
     fun foo()
 }
 
diff --git a/compiler/testData/diagnostics/tests/annotations/annotationInheritance.kt b/compiler/testData/diagnostics/tests/annotations/annotationInheritance.kt
index 62870d6b0ab..4fc4167de8a 100644
--- a/compiler/testData/diagnostics/tests/annotations/annotationInheritance.kt
+++ b/compiler/testData/diagnostics/tests/annotations/annotationInheritance.kt
@@ -1,6 +1,6 @@
 val a = object: T {}
 open class C
-trait T
+interface T
 
 annotation class Ann: <!SUPERTYPES_FOR_ANNOTATION_CLASS!>C()<!>
 annotation class Ann2: <!SUPERTYPES_FOR_ANNOTATION_CLASS!>T<!>
diff --git a/compiler/testData/diagnostics/tests/annotations/annotationModifier.kt b/compiler/testData/diagnostics/tests/annotations/annotationModifier.kt
index 35d4889f7a9..8c5e211eead 100644
--- a/compiler/testData/diagnostics/tests/annotations/annotationModifier.kt
+++ b/compiler/testData/diagnostics/tests/annotations/annotationModifier.kt
@@ -6,7 +6,7 @@ class A {
 
 <!ILLEGAL_ANNOTATION_KEYWORD!>annotation<!> object O {}
 
-<!ILLEGAL_ANNOTATION_KEYWORD!>annotation<!> trait T {}
+<!ILLEGAL_ANNOTATION_KEYWORD!>annotation<!> interface T {}
 
 <!ILLEGAL_ANNOTATION_KEYWORD!>annotation<!> fun f() = 0
 
diff --git a/compiler/testData/diagnostics/tests/annotations/bracketsDeprecation.kt b/compiler/testData/diagnostics/tests/annotations/bracketsDeprecation.kt
index 488f8e505c0..b3a9d8eda97 100644
--- a/compiler/testData/diagnostics/tests/annotations/bracketsDeprecation.kt
+++ b/compiler/testData/diagnostics/tests/annotations/bracketsDeprecation.kt
@@ -28,7 +28,7 @@ fun bar2(): Array<Q> = null!!
 
 val y: Array<[<!DEBUG_INFO_MISSING_UNRESOLVED!>Ann<!>] String?> = arrayOfNulls(1)
 val block: ([<!DEBUG_INFO_MISSING_UNRESOLVED!>Ann<!>] x: <!DEPRECATED_ANNOTATION_SYNTAX!>[Ann]<!> String) -> <!DEPRECATED_ANNOTATION_SYNTAX!>[Ann]<!> String = { "" }
-trait B
-trait D : [<!DEBUG_INFO_MISSING_UNRESOLVED!>Ann<!>] B
+interface B
+interface D : [<!DEBUG_INFO_MISSING_UNRESOLVED!>Ann<!>] B
 
 Ann(<!ANNOTATION_PARAMETER_MUST_BE_CONST!><!DEPRECATED_ANNOTATION_SYNTAX!>[Ann]<!> 1<!>) class MyClass
diff --git a/compiler/testData/diagnostics/tests/annotations/onInitializer.kt b/compiler/testData/diagnostics/tests/annotations/onInitializer.kt
index 0cf9234c4e7..94e69bbf308 100644
--- a/compiler/testData/diagnostics/tests/annotations/onInitializer.kt
+++ b/compiler/testData/diagnostics/tests/annotations/onInitializer.kt
@@ -5,7 +5,7 @@ class A {
     <!UNRESOLVED_REFERENCE!>@aaa<!> init {}
 }
 
-trait T {
+interface T {
     <!ANONYMOUS_INITIALIZER_IN_TRAIT!>ann init {}<!>
     <!ANONYMOUS_INITIALIZER_IN_TRAIT!>@ann init {}<!>
     <!ANONYMOUS_INITIALIZER_IN_TRAIT!><!UNRESOLVED_REFERENCE!>aaa<!> init {}<!>
diff --git a/compiler/testData/diagnostics/tests/cast/DowncastMap.kt b/compiler/testData/diagnostics/tests/cast/DowncastMap.kt
index 02a4fcc04ca..7bf0df122ee 100644
--- a/compiler/testData/diagnostics/tests/cast/DowncastMap.kt
+++ b/compiler/testData/diagnostics/tests/cast/DowncastMap.kt
@@ -1,5 +1,5 @@
-trait Map<K, out V>
-trait MutableMap<K, V>: Map<K, V> {
+interface Map<K, out V>
+interface MutableMap<K, V>: Map<K, V> {
   fun set(k: K, v: V)
 }
 
diff --git a/compiler/testData/diagnostics/tests/cast/IsErasedAllowForTypeWithIrrelevantMixin.kt b/compiler/testData/diagnostics/tests/cast/IsErasedAllowForTypeWithIrrelevantMixin.kt
index 81074b9ac86..296ae7582aa 100644
--- a/compiler/testData/diagnostics/tests/cast/IsErasedAllowForTypeWithIrrelevantMixin.kt
+++ b/compiler/testData/diagnostics/tests/cast/IsErasedAllowForTypeWithIrrelevantMixin.kt
@@ -1,9 +1,9 @@
-trait A
-trait B: A
-trait D
+interface A
+interface B: A
+interface D
 
-trait BaseSuper<out T>
-trait BaseImpl: BaseSuper<D>
-trait DerivedSuper<out S>: <!INCONSISTENT_TYPE_PARAMETER_VALUES!>BaseSuper<S>, BaseImpl<!>
+interface BaseSuper<out T>
+interface BaseImpl: BaseSuper<D>
+interface DerivedSuper<out S>: <!INCONSISTENT_TYPE_PARAMETER_VALUES!>BaseSuper<S>, BaseImpl<!>
 
 fun test(t: BaseSuper<B>) = t is DerivedSuper<A>
\ No newline at end of file
diff --git a/compiler/testData/diagnostics/tests/cast/IsErasedDisallowForTypeWithConstraints.kt b/compiler/testData/diagnostics/tests/cast/IsErasedDisallowForTypeWithConstraints.kt
index be45dbe7036..a82c71eafef 100644
--- a/compiler/testData/diagnostics/tests/cast/IsErasedDisallowForTypeWithConstraints.kt
+++ b/compiler/testData/diagnostics/tests/cast/IsErasedDisallowForTypeWithConstraints.kt
@@ -1,6 +1,6 @@
-trait A
-trait B: A
+interface A
+interface B: A
 
-trait Base<T>
+interface Base<T>
 
 fun <T> test(a: Base<B>) where T: Base<A> = a is <!CANNOT_CHECK_FOR_ERASED!>T<!>
\ No newline at end of file
diff --git a/compiler/testData/diagnostics/tests/cast/IsErasedNonGeneric.kt b/compiler/testData/diagnostics/tests/cast/IsErasedNonGeneric.kt
index 97387f2bdef..a27a5165198 100644
--- a/compiler/testData/diagnostics/tests/cast/IsErasedNonGeneric.kt
+++ b/compiler/testData/diagnostics/tests/cast/IsErasedNonGeneric.kt
@@ -1,3 +1,3 @@
-trait A
-trait B
+interface A
+interface B
 fun testing(a: A) = a as B
diff --git a/compiler/testData/diagnostics/tests/cast/IsTraits.kt b/compiler/testData/diagnostics/tests/cast/IsTraits.kt
index 99656c2ab24..defcbfb3bc9 100644
--- a/compiler/testData/diagnostics/tests/cast/IsTraits.kt
+++ b/compiler/testData/diagnostics/tests/cast/IsTraits.kt
@@ -1,4 +1,4 @@
-trait Aaa
-trait Bbb
+interface Aaa
+interface Bbb
 
 fun f(a: Aaa) = a is Bbb
diff --git a/compiler/testData/diagnostics/tests/cast/bare/AsNestedBare.kt b/compiler/testData/diagnostics/tests/cast/bare/AsNestedBare.kt
index c7f76721598..9f04ed15dbb 100644
--- a/compiler/testData/diagnostics/tests/cast/bare/AsNestedBare.kt
+++ b/compiler/testData/diagnostics/tests/cast/bare/AsNestedBare.kt
@@ -1,5 +1,5 @@
-trait Tr
-trait G<T>
+interface Tr
+interface G<T>
 
 fun test(tr: Tr): Any {
     return tr as G<<!WRONG_NUMBER_OF_TYPE_ARGUMENTS!>G<!>>
diff --git a/compiler/testData/diagnostics/tests/cast/bare/AsNullable.kt b/compiler/testData/diagnostics/tests/cast/bare/AsNullable.kt
index 87602183923..48f5318520a 100644
--- a/compiler/testData/diagnostics/tests/cast/bare/AsNullable.kt
+++ b/compiler/testData/diagnostics/tests/cast/bare/AsNullable.kt
@@ -1,7 +1,7 @@
 // !CHECK_TYPE
 
-trait Tr<T>
-trait G<T> : Tr<T>
+interface Tr<T>
+interface G<T> : Tr<T>
 
 fun test(tr: Tr<String>) {
     val v = tr as G?
diff --git a/compiler/testData/diagnostics/tests/cast/bare/AsNullableNotEnough.kt b/compiler/testData/diagnostics/tests/cast/bare/AsNullableNotEnough.kt
index 9069dbbbe10..ff5111e66af 100644
--- a/compiler/testData/diagnostics/tests/cast/bare/AsNullableNotEnough.kt
+++ b/compiler/testData/diagnostics/tests/cast/bare/AsNullableNotEnough.kt
@@ -1,7 +1,7 @@
 // !CHECK_TYPE
 
-trait Tr
-trait G<T>
+interface Tr
+interface G<T>
 
 fun test(tr: Tr) {
     val v = tr as <!NO_TYPE_ARGUMENTS_ON_RHS!>G?<!>
diff --git a/compiler/testData/diagnostics/tests/cast/bare/EitherAs.kt b/compiler/testData/diagnostics/tests/cast/bare/EitherAs.kt
index 4aa276049bd..d3c22b7fa60 100644
--- a/compiler/testData/diagnostics/tests/cast/bare/EitherAs.kt
+++ b/compiler/testData/diagnostics/tests/cast/bare/EitherAs.kt
@@ -1,8 +1,8 @@
 // !CHECK_TYPE
 
-trait Either<out A, out B>
-trait Left<out A>: Either<A, Nothing>
-trait Right<out B>: Either<Nothing, B>
+interface Either<out A, out B>
+interface Left<out A>: Either<A, Nothing>
+interface Right<out B>: Either<Nothing, B>
 
 class C1(val v1: Int)
 class C2(val v2: Int)
diff --git a/compiler/testData/diagnostics/tests/cast/bare/EitherIs.kt b/compiler/testData/diagnostics/tests/cast/bare/EitherIs.kt
index fd19005bde2..29725127b34 100644
--- a/compiler/testData/diagnostics/tests/cast/bare/EitherIs.kt
+++ b/compiler/testData/diagnostics/tests/cast/bare/EitherIs.kt
@@ -1,9 +1,9 @@
 // !DIAGNOSTICS: -DEBUG_INFO_SMARTCAST
-trait Either<out A, out B>
-trait Left<out A>: Either<A, Nothing> {
+interface Either<out A, out B>
+interface Left<out A>: Either<A, Nothing> {
     val value: A
 }
-trait Right<out B>: Either<Nothing, B> {
+interface Right<out B>: Either<Nothing, B> {
     val value: B
 }
 
diff --git a/compiler/testData/diagnostics/tests/cast/bare/EitherNotIs.kt b/compiler/testData/diagnostics/tests/cast/bare/EitherNotIs.kt
index fd623e2a19e..a07e46eb9c3 100644
--- a/compiler/testData/diagnostics/tests/cast/bare/EitherNotIs.kt
+++ b/compiler/testData/diagnostics/tests/cast/bare/EitherNotIs.kt
@@ -1,9 +1,9 @@
 // !DIAGNOSTICS: -DEBUG_INFO_SMARTCAST
-trait Either<out A, out B>
-trait Left<out A>: Either<A, Nothing> {
+interface Either<out A, out B>
+interface Left<out A>: Either<A, Nothing> {
     val value: A
 }
-trait Right<out B>: Either<Nothing, B> {
+interface Right<out B>: Either<Nothing, B> {
     val value: B
 }
 
diff --git a/compiler/testData/diagnostics/tests/cast/bare/EitherSafeAs.kt b/compiler/testData/diagnostics/tests/cast/bare/EitherSafeAs.kt
index 3d018404418..ff8660f2698 100644
--- a/compiler/testData/diagnostics/tests/cast/bare/EitherSafeAs.kt
+++ b/compiler/testData/diagnostics/tests/cast/bare/EitherSafeAs.kt
@@ -1,8 +1,8 @@
 // !CHECK_TYPE
 
-trait Either<out A, out B>
-trait Left<out A>: Either<A, Nothing>
-trait Right<out B>: Either<Nothing, B>
+interface Either<out A, out B>
+interface Left<out A>: Either<A, Nothing>
+interface Right<out B>: Either<Nothing, B>
 
 class C1(val v1: Int)
 class C2(val v2: Int)
diff --git a/compiler/testData/diagnostics/tests/cast/bare/EitherWhen.kt b/compiler/testData/diagnostics/tests/cast/bare/EitherWhen.kt
index 61f862dbc1b..ca683c6efda 100644
--- a/compiler/testData/diagnostics/tests/cast/bare/EitherWhen.kt
+++ b/compiler/testData/diagnostics/tests/cast/bare/EitherWhen.kt
@@ -1,9 +1,9 @@
 // !DIAGNOSTICS: -DEBUG_INFO_SMARTCAST
-trait Either<out A, out B>
-trait Left<out A>: Either<A, Nothing> {
+interface Either<out A, out B>
+interface Left<out A>: Either<A, Nothing> {
     val value: A
 }
-trait Right<out B>: Either<Nothing, B> {
+interface Right<out B>: Either<Nothing, B> {
     val value: B
 }
 
diff --git a/compiler/testData/diagnostics/tests/cast/bare/ErrorsInSubstitution.kt b/compiler/testData/diagnostics/tests/cast/bare/ErrorsInSubstitution.kt
index 7ab2e12040e..043002d60f2 100644
--- a/compiler/testData/diagnostics/tests/cast/bare/ErrorsInSubstitution.kt
+++ b/compiler/testData/diagnostics/tests/cast/bare/ErrorsInSubstitution.kt
@@ -1,7 +1,7 @@
 // !CHECK_TYPE
 
-trait B<T>
-trait G<T>: B<T>
+interface B<T>
+interface G<T>: B<T>
 
 fun f(p: B<<!UNRESOLVED_REFERENCE!>Foo<!>>): Any {
     val v = <!DEBUG_INFO_ELEMENT_WITH_ERROR_TYPE!>p<!> as G
diff --git a/compiler/testData/diagnostics/tests/cast/bare/NullableAs.kt b/compiler/testData/diagnostics/tests/cast/bare/NullableAs.kt
index 6b629938e4b..85d624a9139 100644
--- a/compiler/testData/diagnostics/tests/cast/bare/NullableAs.kt
+++ b/compiler/testData/diagnostics/tests/cast/bare/NullableAs.kt
@@ -1,7 +1,7 @@
 // !CHECK_TYPE
 
-trait Tr<T>
-trait G<T> : Tr<T>
+interface Tr<T>
+interface G<T> : Tr<T>
 
 fun test(tr: Tr<String>?) {
     val v = tr as G
diff --git a/compiler/testData/diagnostics/tests/cast/bare/NullableAsNotEnough.kt b/compiler/testData/diagnostics/tests/cast/bare/NullableAsNotEnough.kt
index 97245e159ee..a2bd99fae2f 100644
--- a/compiler/testData/diagnostics/tests/cast/bare/NullableAsNotEnough.kt
+++ b/compiler/testData/diagnostics/tests/cast/bare/NullableAsNotEnough.kt
@@ -1,7 +1,7 @@
 // !CHECK_TYPE
 
-trait Tr
-trait G<T>
+interface Tr
+interface G<T>
 
 fun test(tr: Tr?) {
     val v = tr as <!NO_TYPE_ARGUMENTS_ON_RHS!>G<!>
diff --git a/compiler/testData/diagnostics/tests/cast/bare/NullableAsNullable.kt b/compiler/testData/diagnostics/tests/cast/bare/NullableAsNullable.kt
index fad623e937b..3914084b7cb 100644
--- a/compiler/testData/diagnostics/tests/cast/bare/NullableAsNullable.kt
+++ b/compiler/testData/diagnostics/tests/cast/bare/NullableAsNullable.kt
@@ -1,7 +1,7 @@
 // !CHECK_TYPE
 
-trait Tr<T>
-trait G<T> : Tr<T>
+interface Tr<T>
+interface G<T> : Tr<T>
 
 fun test(tr: Tr<String>?) {
     val v = tr as G?
diff --git a/compiler/testData/diagnostics/tests/cast/bare/NullableAsNullableNotEnough.kt b/compiler/testData/diagnostics/tests/cast/bare/NullableAsNullableNotEnough.kt
index e144b0b6e0d..01797878cb2 100644
--- a/compiler/testData/diagnostics/tests/cast/bare/NullableAsNullableNotEnough.kt
+++ b/compiler/testData/diagnostics/tests/cast/bare/NullableAsNullableNotEnough.kt
@@ -1,7 +1,7 @@
 // !CHECK_TYPE
 
-trait Tr
-trait G<T>
+interface Tr
+interface G<T>
 
 fun test(tr: Tr?) {
     val v = tr as <!NO_TYPE_ARGUMENTS_ON_RHS!>G?<!>
diff --git a/compiler/testData/diagnostics/tests/cast/bare/RedundantNullable.kt b/compiler/testData/diagnostics/tests/cast/bare/RedundantNullable.kt
index 77933e0545a..4e526bada9b 100644
--- a/compiler/testData/diagnostics/tests/cast/bare/RedundantNullable.kt
+++ b/compiler/testData/diagnostics/tests/cast/bare/RedundantNullable.kt
@@ -1,4 +1,4 @@
-trait B<T>
+interface B<T>
 class G<T>: B<T>
 
 fun f(b: B<String>?) = b is G?<!REDUNDANT_NULLABLE!>?<!>
\ No newline at end of file
diff --git a/compiler/testData/diagnostics/tests/cast/bare/UnrelatedAs.kt b/compiler/testData/diagnostics/tests/cast/bare/UnrelatedAs.kt
index 540732d157f..4fee2d2b298 100644
--- a/compiler/testData/diagnostics/tests/cast/bare/UnrelatedAs.kt
+++ b/compiler/testData/diagnostics/tests/cast/bare/UnrelatedAs.kt
@@ -1,7 +1,7 @@
 // !CHECK_TYPE
 
-trait Tr
-trait G<T>
+interface Tr
+interface G<T>
 
 fun test(tr: Tr) {
     val v = tr as <!NO_TYPE_ARGUMENTS_ON_RHS!>G<!>
diff --git a/compiler/testData/diagnostics/tests/cast/bare/UnrelatedColon.kt b/compiler/testData/diagnostics/tests/cast/bare/UnrelatedColon.kt
index de85372d101..06abe2bc01c 100644
--- a/compiler/testData/diagnostics/tests/cast/bare/UnrelatedColon.kt
+++ b/compiler/testData/diagnostics/tests/cast/bare/UnrelatedColon.kt
@@ -1,6 +1,6 @@
 // !CHECK_TYPE
 
-trait Tr
-trait G<T>
+interface Tr
+interface G<T>
 
 fun test(tr: Tr) = checkSubtype<<!WRONG_NUMBER_OF_TYPE_ARGUMENTS!>G<!>>(tr)
\ No newline at end of file
diff --git a/compiler/testData/diagnostics/tests/cast/bare/UnrelatedIs.kt b/compiler/testData/diagnostics/tests/cast/bare/UnrelatedIs.kt
index bf51d82c30c..a9b9a061eb8 100644
--- a/compiler/testData/diagnostics/tests/cast/bare/UnrelatedIs.kt
+++ b/compiler/testData/diagnostics/tests/cast/bare/UnrelatedIs.kt
@@ -1,4 +1,4 @@
-trait Tr
-trait G<T>
+interface Tr
+interface G<T>
 
 fun test(tr: Tr) = tr is <!NO_TYPE_ARGUMENTS_ON_RHS!>G<!>
\ No newline at end of file
diff --git a/compiler/testData/diagnostics/tests/cast/isErasedUnrelatedAndStarred.kt b/compiler/testData/diagnostics/tests/cast/isErasedUnrelatedAndStarred.kt
index 4c93d96d241..f53785c40c6 100644
--- a/compiler/testData/diagnostics/tests/cast/isErasedUnrelatedAndStarred.kt
+++ b/compiler/testData/diagnostics/tests/cast/isErasedUnrelatedAndStarred.kt
@@ -1,4 +1,4 @@
 class G<T>
-trait Tr
+interface Tr
 
 fun f(q: Tr) = q is G<*>
\ No newline at end of file
diff --git a/compiler/testData/diagnostics/tests/cast/neverSucceeds/NoGenericsRelated.kt b/compiler/testData/diagnostics/tests/cast/neverSucceeds/NoGenericsRelated.kt
index f1f4577abcf..83a09248321 100644
--- a/compiler/testData/diagnostics/tests/cast/neverSucceeds/NoGenericsRelated.kt
+++ b/compiler/testData/diagnostics/tests/cast/neverSucceeds/NoGenericsRelated.kt
@@ -1,12 +1,12 @@
 // !DIAGNOSTICS: -WARNING +CAST_NEVER_SUCCEEDS
-trait T1
-trait T2
-trait T3
+interface T1
+interface T2
+interface T3
 open class OC1: T1
 open class OC2: OC1(), T2
 class FC1: OC2(), T3
-trait T4: OC1
-trait T5: T2
+interface T4: OC1
+interface T5: T2
 
 fun test<TP1: OC1, TP2: T2, TP3: OC2>(
     t2: T2,
diff --git a/compiler/testData/diagnostics/tests/cast/neverSucceeds/NoGenericsUnrelated.kt b/compiler/testData/diagnostics/tests/cast/neverSucceeds/NoGenericsUnrelated.kt
index 897080f40ea..6c84314fb27 100644
--- a/compiler/testData/diagnostics/tests/cast/neverSucceeds/NoGenericsUnrelated.kt
+++ b/compiler/testData/diagnostics/tests/cast/neverSucceeds/NoGenericsUnrelated.kt
@@ -1,6 +1,6 @@
 // !DIAGNOSTICS: -WARNING +CAST_NEVER_SUCCEEDS
-trait Trait1
-trait Trait2
+interface Trait1
+interface Trait2
 open class OClass1
 open class OClass2
 class FClass1
diff --git a/compiler/testData/diagnostics/tests/checkType.kt b/compiler/testData/diagnostics/tests/checkType.kt
index fb9ef7ae1e6..7b01f120491 100644
--- a/compiler/testData/diagnostics/tests/checkType.kt
+++ b/compiler/testData/diagnostics/tests/checkType.kt
@@ -1,8 +1,8 @@
 // !CHECK_TYPE
 
-trait A
-trait B : A
-trait C : B
+interface A
+interface B : A
+interface C : B
 
 fun test(b: B) {
     b checkType { _<B>() }
diff --git a/compiler/testData/diagnostics/tests/controlFlowAnalysis/definiteReturn/ReturnFromFunctionInObject.kt b/compiler/testData/diagnostics/tests/controlFlowAnalysis/definiteReturn/ReturnFromFunctionInObject.kt
index 04f9bff6ade..16948d1b94c 100644
--- a/compiler/testData/diagnostics/tests/controlFlowAnalysis/definiteReturn/ReturnFromFunctionInObject.kt
+++ b/compiler/testData/diagnostics/tests/controlFlowAnalysis/definiteReturn/ReturnFromFunctionInObject.kt
@@ -1,4 +1,4 @@
-trait X {
+interface X {
     fun f(): Boolean
 }
 
diff --git a/compiler/testData/diagnostics/tests/controlFlowAnalysis/definiteReturn/kt4034.kt b/compiler/testData/diagnostics/tests/controlFlowAnalysis/definiteReturn/kt4034.kt
index 284a07bffc3..40c2f3f5871 100644
--- a/compiler/testData/diagnostics/tests/controlFlowAnalysis/definiteReturn/kt4034.kt
+++ b/compiler/testData/diagnostics/tests/controlFlowAnalysis/definiteReturn/kt4034.kt
@@ -2,9 +2,9 @@
 
 // KT-4034 An expression of type Nothing may not affect 'definite return' analysis
 
-trait JavaClassifierType
-trait TypeUsage
-trait JetType
+interface JavaClassifierType
+interface TypeUsage
+interface JetType
 
 private fun transformClassifierType(classifierType: JavaClassifierType, howThisTypeIsUsed: TypeUsage): JetType? {
     null!!
diff --git a/compiler/testData/diagnostics/tests/controlFlowAnalysis/kt1191.kt b/compiler/testData/diagnostics/tests/controlFlowAnalysis/kt1191.kt
index 9f6f690387b..b4fef753131 100644
--- a/compiler/testData/diagnostics/tests/controlFlowAnalysis/kt1191.kt
+++ b/compiler/testData/diagnostics/tests/controlFlowAnalysis/kt1191.kt
@@ -1,7 +1,7 @@
 //KT-1191 Wrong detection of unused parameters
 package kt1191
 
-trait FunctionalList<T> {
+interface FunctionalList<T> {
     val size: Int
     val head: T
     val tail: FunctionalList<T>
diff --git a/compiler/testData/diagnostics/tests/controlFlowAnalysis/kt2226.kt b/compiler/testData/diagnostics/tests/controlFlowAnalysis/kt2226.kt
index a846732a18d..f326ec0a926 100644
--- a/compiler/testData/diagnostics/tests/controlFlowAnalysis/kt2226.kt
+++ b/compiler/testData/diagnostics/tests/controlFlowAnalysis/kt2226.kt
@@ -1,7 +1,7 @@
 //KT-2226 Parameter used as delegation by object marked as unused
 package a
 
-trait A {
+interface A {
     fun foo() : Int
 }
 
diff --git a/compiler/testData/diagnostics/tests/controlFlowAnalysis/kt3444.kt b/compiler/testData/diagnostics/tests/controlFlowAnalysis/kt3444.kt
index 9d3dfc994d6..a72db64ced4 100644
--- a/compiler/testData/diagnostics/tests/controlFlowAnalysis/kt3444.kt
+++ b/compiler/testData/diagnostics/tests/controlFlowAnalysis/kt3444.kt
@@ -3,7 +3,7 @@ fun box() {
     <!NO_RETURN_IN_FUNCTION_WITH_BLOCK_BODY!>}<!>
 }
 
-trait X {
+interface X {
     fun f(): Boolean
 }
 
diff --git a/compiler/testData/diagnostics/tests/controlStructures/commonSupertypeOfT.kt b/compiler/testData/diagnostics/tests/controlStructures/commonSupertypeOfT.kt
index 7e959f31192..b6c4f6021ac 100644
--- a/compiler/testData/diagnostics/tests/controlStructures/commonSupertypeOfT.kt
+++ b/compiler/testData/diagnostics/tests/controlStructures/commonSupertypeOfT.kt
@@ -16,7 +16,7 @@ fun <T: Any> fn(t1: T, t2: T?) {
     y.hashCode()
 }
 
-trait Tr {
+interface Tr {
     fun foo()
 }
 
diff --git a/compiler/testData/diagnostics/tests/cyclicHierarchy/cyclicHierarchy.kt b/compiler/testData/diagnostics/tests/cyclicHierarchy/cyclicHierarchy.kt
index 318d67fd867..1069f78978e 100644
--- a/compiler/testData/diagnostics/tests/cyclicHierarchy/cyclicHierarchy.kt
+++ b/compiler/testData/diagnostics/tests/cyclicHierarchy/cyclicHierarchy.kt
@@ -1,13 +1,13 @@
-trait A {
+interface A {
     fun foo() {}
 }
-trait B : A, <!CYCLIC_INHERITANCE_HIERARCHY!>E<!> {}
-trait C : <!CYCLIC_INHERITANCE_HIERARCHY!>B<!> {}
-trait D : <!CYCLIC_INHERITANCE_HIERARCHY!>B<!> {}
-trait E : <!CYCLIC_INHERITANCE_HIERARCHY!>F<!> {}
-trait F : <!CYCLIC_INHERITANCE_HIERARCHY!>D<!>, <!CYCLIC_INHERITANCE_HIERARCHY!>C<!> {}
-trait G : F {}
-trait H : F {}
+interface B : A, <!CYCLIC_INHERITANCE_HIERARCHY!>E<!> {}
+interface C : <!CYCLIC_INHERITANCE_HIERARCHY!>B<!> {}
+interface D : <!CYCLIC_INHERITANCE_HIERARCHY!>B<!> {}
+interface E : <!CYCLIC_INHERITANCE_HIERARCHY!>F<!> {}
+interface F : <!CYCLIC_INHERITANCE_HIERARCHY!>D<!>, <!CYCLIC_INHERITANCE_HIERARCHY!>C<!> {}
+interface G : F {}
+interface H : F {}
 
 val a : A? = null
 val b : B? = null
diff --git a/compiler/testData/diagnostics/tests/cyclicHierarchy/javaKotlinJavaCycle.kt b/compiler/testData/diagnostics/tests/cyclicHierarchy/javaKotlinJavaCycle.kt
index de8b50c27e4..5ad56e7b4c6 100644
--- a/compiler/testData/diagnostics/tests/cyclicHierarchy/javaKotlinJavaCycle.kt
+++ b/compiler/testData/diagnostics/tests/cyclicHierarchy/javaKotlinJavaCycle.kt
@@ -6,7 +6,7 @@ interface A extends C {
 
 // FILE: B.kt
 
-trait B : <!CYCLIC_INHERITANCE_HIERARCHY!>A<!> {
+interface B : <!CYCLIC_INHERITANCE_HIERARCHY!>A<!> {
     fun bar()
 }
 
diff --git a/compiler/testData/diagnostics/tests/cyclicHierarchy/kotlinJavaNestedCycle.kt b/compiler/testData/diagnostics/tests/cyclicHierarchy/kotlinJavaNestedCycle.kt
index 0d587c7913e..1edd2e30e6d 100644
--- a/compiler/testData/diagnostics/tests/cyclicHierarchy/kotlinJavaNestedCycle.kt
+++ b/compiler/testData/diagnostics/tests/cyclicHierarchy/kotlinJavaNestedCycle.kt
@@ -1,11 +1,11 @@
 // FILE: ExceptionTracker.kt
 
-trait ExceptionTracker : <!CYCLIC_INHERITANCE_HIERARCHY!>LockBasedStorageManager.ExceptionHandlingStrategy<!> {
+interface ExceptionTracker : <!CYCLIC_INHERITANCE_HIERARCHY!>LockBasedStorageManager.ExceptionHandlingStrategy<!> {
 }
 
 // FILE: StorageManager.kt
 
-trait StorageManager : <!CYCLIC_INHERITANCE_HIERARCHY!>ExceptionTracker<!> {
+interface StorageManager : <!CYCLIC_INHERITANCE_HIERARCHY!>ExceptionTracker<!> {
     fun foo()
 }
 
diff --git a/compiler/testData/diagnostics/tests/dataClasses/implementTraitWhichHasComponent1.kt b/compiler/testData/diagnostics/tests/dataClasses/implementTraitWhichHasComponent1.kt
index 144286c58ed..7cb40548632 100644
--- a/compiler/testData/diagnostics/tests/dataClasses/implementTraitWhichHasComponent1.kt
+++ b/compiler/testData/diagnostics/tests/dataClasses/implementTraitWhichHasComponent1.kt
@@ -1,4 +1,4 @@
-trait T {
+interface T {
     fun component1(): Int
 }
 
diff --git a/compiler/testData/diagnostics/tests/dataClasses/implementTraitWhichHasFinalComponent1.kt b/compiler/testData/diagnostics/tests/dataClasses/implementTraitWhichHasFinalComponent1.kt
index 4e46de1163f..8efc12249f6 100644
--- a/compiler/testData/diagnostics/tests/dataClasses/implementTraitWhichHasFinalComponent1.kt
+++ b/compiler/testData/diagnostics/tests/dataClasses/implementTraitWhichHasFinalComponent1.kt
@@ -1,4 +1,4 @@
-trait T {
+interface T {
     final fun component1(): Int = 42
 }
 
diff --git a/compiler/testData/diagnostics/tests/dataFlow/WhenSubject.kt b/compiler/testData/diagnostics/tests/dataFlow/WhenSubject.kt
index 5a667cac7b0..e6cd7eab473 100644
--- a/compiler/testData/diagnostics/tests/dataFlow/WhenSubject.kt
+++ b/compiler/testData/diagnostics/tests/dataFlow/WhenSubject.kt
@@ -1,4 +1,4 @@
-trait Expr
+interface Expr
 class BinOp(val operator : String) : Expr
 
 fun test(e : Expr) {
diff --git a/compiler/testData/diagnostics/tests/dataFlow/local/LocalClassDelegation.kt b/compiler/testData/diagnostics/tests/dataFlow/local/LocalClassDelegation.kt
index bf2293bb328..cd28f9b0ecc 100644
--- a/compiler/testData/diagnostics/tests/dataFlow/local/LocalClassDelegation.kt
+++ b/compiler/testData/diagnostics/tests/dataFlow/local/LocalClassDelegation.kt
@@ -1,4 +1,4 @@
-trait D {
+interface D {
   fun foo() {}
 }
 
diff --git a/compiler/testData/diagnostics/tests/dataFlow/local/LocalClassFunctions.kt b/compiler/testData/diagnostics/tests/dataFlow/local/LocalClassFunctions.kt
index 41708ae9e57..5a828797628 100644
--- a/compiler/testData/diagnostics/tests/dataFlow/local/LocalClassFunctions.kt
+++ b/compiler/testData/diagnostics/tests/dataFlow/local/LocalClassFunctions.kt
@@ -1,4 +1,4 @@
-trait D {
+interface D {
   fun foo(): String = ""
 }
 
diff --git a/compiler/testData/diagnostics/tests/dataFlow/local/LocalClassInitializer.kt b/compiler/testData/diagnostics/tests/dataFlow/local/LocalClassInitializer.kt
index b9cfcd6c29e..38b9340f85a 100644
--- a/compiler/testData/diagnostics/tests/dataFlow/local/LocalClassInitializer.kt
+++ b/compiler/testData/diagnostics/tests/dataFlow/local/LocalClassInitializer.kt
@@ -10,7 +10,7 @@ fun f(a: Any?) {
   }
 }
 
-trait B {
+interface B {
   fun foo() {}
 }
 open class X(<!UNUSED_PARAMETER!>b<!>: B)
\ No newline at end of file
diff --git a/compiler/testData/diagnostics/tests/dataFlow/local/LocalObjectDelegation.kt b/compiler/testData/diagnostics/tests/dataFlow/local/LocalObjectDelegation.kt
index 32f5d1b1af7..a937c8bdb11 100644
--- a/compiler/testData/diagnostics/tests/dataFlow/local/LocalObjectDelegation.kt
+++ b/compiler/testData/diagnostics/tests/dataFlow/local/LocalObjectDelegation.kt
@@ -1,6 +1,6 @@
 // KT-2225 Object expression delegation parameter should be checked with data flow info
 
-trait A {
+interface A {
     fun foo() : Int
 }
 
diff --git a/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/ArrayGetSetConvention.kt b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/ArrayGetSetConvention.kt
index d1ed5a0eb2f..ea5e8ede713 100644
--- a/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/ArrayGetSetConvention.kt
+++ b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/ArrayGetSetConvention.kt
@@ -1,6 +1,6 @@
 // !CHECK_TYPE
 
-trait G {
+interface G {
     fun get(x: Int, y: Int): Int = x + y
     fun set(x: Int, y: Int, value: Int) {}
 }
diff --git a/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/Assignment.kt b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/Assignment.kt
index 02f061d7ba4..09563b897f7 100644
--- a/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/Assignment.kt
+++ b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/Assignment.kt
@@ -1,5 +1,5 @@
-trait A
-trait B : A {
+interface A
+interface B : A {
     fun foo()
 }
 
diff --git a/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/AssignmentInInitializer.kt b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/AssignmentInInitializer.kt
index 36bae29e745..5197a621d68 100644
--- a/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/AssignmentInInitializer.kt
+++ b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/AssignmentInInitializer.kt
@@ -1,8 +1,8 @@
 // KT-2825  DataFlowInfo is not retained after assignment
 
-trait A
+interface A
 
-trait B : A {
+interface B : A {
     fun foo()
 }
 
diff --git a/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/BinaryExpressionCompareToConvention.kt b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/BinaryExpressionCompareToConvention.kt
index e4d901c387f..68e9e099cf9 100644
--- a/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/BinaryExpressionCompareToConvention.kt
+++ b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/BinaryExpressionCompareToConvention.kt
@@ -1,8 +1,8 @@
 // !CHECK_TYPE
 
-trait A
+interface A
 
-trait B : A
+interface B : A
 fun B.compareTo(b: B) = if (this == b) 0 else 1
 
 fun foo(a: A): Boolean {
diff --git a/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/BinaryExpressionEqualsConvention.kt b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/BinaryExpressionEqualsConvention.kt
index 312009ea0a0..ca529d1337d 100644
--- a/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/BinaryExpressionEqualsConvention.kt
+++ b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/BinaryExpressionEqualsConvention.kt
@@ -1,7 +1,7 @@
 // !CHECK_TYPE
 
-trait A
-trait B : A
+interface A
+interface B : A
 
 fun foo1(a: A, b: B): Boolean {
     val result = (a as B) == b
diff --git a/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/BinaryExpressionPlusConvention.kt b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/BinaryExpressionPlusConvention.kt
index 36551a1ca38..d6e0f6ac247 100644
--- a/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/BinaryExpressionPlusConvention.kt
+++ b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/BinaryExpressionPlusConvention.kt
@@ -1,8 +1,8 @@
 // !CHECK_TYPE
 
-trait A
+interface A
 
-trait B : A
+interface B : A
 fun B.plus(b: B) = if (this == b) b else this
 
 fun foo(a: A): B {
diff --git a/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/smartcasts/SmartcastAmbiguitites.kt b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/smartcasts/SmartcastAmbiguitites.kt
index 93097f4489d..74e7f6924e8 100644
--- a/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/smartcasts/SmartcastAmbiguitites.kt
+++ b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/smartcasts/SmartcastAmbiguitites.kt
@@ -1,4 +1,4 @@
-trait B {
+interface B {
   fun bar() {}
 }
 
diff --git a/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/smartcasts/SmartcastsForStableIdentifiers.kt b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/smartcasts/SmartcastsForStableIdentifiers.kt
index ab3cfab05fc..e41ee3cd045 100644
--- a/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/smartcasts/SmartcastsForStableIdentifiers.kt
+++ b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/smartcasts/SmartcastsForStableIdentifiers.kt
@@ -74,7 +74,7 @@ fun Any?.foo() : Int {
 }
 
 
-trait T {}
+interface T {}
 
 open class C {
     fun foo() {
diff --git a/compiler/testData/diagnostics/tests/declarationChecks/FunctionWithMissingNames.kt b/compiler/testData/diagnostics/tests/declarationChecks/FunctionWithMissingNames.kt
index 70c6bd895de..4451972d529 100644
--- a/compiler/testData/diagnostics/tests/declarationChecks/FunctionWithMissingNames.kt
+++ b/compiler/testData/diagnostics/tests/declarationChecks/FunctionWithMissingNames.kt
@@ -1,6 +1,6 @@
 annotation class a
-trait A
-trait B
+interface A
+interface B
 
 <!FUNCTION_DECLARATION_WITH_NO_NAME, CONFLICTING_OVERLOADS!>fun ()<!> {}
 <!FUNCTION_DECLARATION_WITH_NO_NAME, CONFLICTING_OVERLOADS!>fun A.()<!> {}
diff --git a/compiler/testData/diagnostics/tests/declarationChecks/ambiguousObjectExpressionType.kt b/compiler/testData/diagnostics/tests/declarationChecks/ambiguousObjectExpressionType.kt
index eaf60600357..34d002fe049 100644
--- a/compiler/testData/diagnostics/tests/declarationChecks/ambiguousObjectExpressionType.kt
+++ b/compiler/testData/diagnostics/tests/declarationChecks/ambiguousObjectExpressionType.kt
@@ -1,4 +1,4 @@
-trait MyTrait {
+interface MyTrait {
   fun f1() {}
 }
 
diff --git a/compiler/testData/diagnostics/tests/declarationChecks/illegalModifiersOnClass.kt b/compiler/testData/diagnostics/tests/declarationChecks/illegalModifiersOnClass.kt
index b940b6d1a44..8a5deec1784 100644
--- a/compiler/testData/diagnostics/tests/declarationChecks/illegalModifiersOnClass.kt
+++ b/compiler/testData/diagnostics/tests/declarationChecks/illegalModifiersOnClass.kt
@@ -15,5 +15,5 @@
 <!ILLEGAL_MODIFIER!>final<!> object B4 {}
 
 <!ILLEGAL_MODIFIER!>override<!> enum class C {}
-<!ILLEGAL_MODIFIER!>override<!> trait D {}
+<!ILLEGAL_MODIFIER!>override<!> interface D {}
 <!ILLEGAL_MODIFIER!>override<!> annotation class E
diff --git a/compiler/testData/diagnostics/tests/declarationChecks/kt1141.kt b/compiler/testData/diagnostics/tests/declarationChecks/kt1141.kt
index 3106a880fc5..8ff4388f74e 100644
--- a/compiler/testData/diagnostics/tests/declarationChecks/kt1141.kt
+++ b/compiler/testData/diagnostics/tests/declarationChecks/kt1141.kt
@@ -2,7 +2,7 @@
 
 package kt1141
 
-public trait SomeTrait {
+public interface SomeTrait {
     fun foo()
 }
 
diff --git a/compiler/testData/diagnostics/tests/declarationChecks/kt2397.kt b/compiler/testData/diagnostics/tests/declarationChecks/kt2397.kt
index 0b5e602d432..7149a9f90fb 100644
--- a/compiler/testData/diagnostics/tests/declarationChecks/kt2397.kt
+++ b/compiler/testData/diagnostics/tests/declarationChecks/kt2397.kt
@@ -1,7 +1,7 @@
 //KT-2397 Prohibit final methods in traits with no implementation
 package a
 
-trait T {
+interface T {
     <!FINAL_FUNCTION_WITH_NO_BODY!>final<!> fun foo()
     <!FINAL_PROPERTY_IN_TRAIT!>final<!> val b : Int
 
diff --git a/compiler/testData/diagnostics/tests/delegatedProperty/delegatedPropertyOverridedInTrait.kt b/compiler/testData/diagnostics/tests/delegatedProperty/delegatedPropertyOverridedInTrait.kt
index 4ec29930810..0560f15cf9d 100644
--- a/compiler/testData/diagnostics/tests/delegatedProperty/delegatedPropertyOverridedInTrait.kt
+++ b/compiler/testData/diagnostics/tests/delegatedProperty/delegatedPropertyOverridedInTrait.kt
@@ -1,6 +1,6 @@
 // !DIAGNOSTICS: -UNUSED_PARAMETER
 
-trait A {
+interface A {
     val prop: Int
 }
 
diff --git a/compiler/testData/diagnostics/tests/delegatedProperty/delegatedPropertyOverridedInTraitTypeMismatch.kt b/compiler/testData/diagnostics/tests/delegatedProperty/delegatedPropertyOverridedInTraitTypeMismatch.kt
index 236edfde773..ca7cb09ce06 100644
--- a/compiler/testData/diagnostics/tests/delegatedProperty/delegatedPropertyOverridedInTraitTypeMismatch.kt
+++ b/compiler/testData/diagnostics/tests/delegatedProperty/delegatedPropertyOverridedInTraitTypeMismatch.kt
@@ -1,6 +1,6 @@
 // !DIAGNOSTICS: -UNUSED_PARAMETER
 
-trait A {
+interface A {
     val prop: Int
 }
 
diff --git a/compiler/testData/diagnostics/tests/delegatedProperty/inTrait.kt b/compiler/testData/diagnostics/tests/delegatedProperty/inTrait.kt
index fb10ae2726f..eef69f71f7b 100644
--- a/compiler/testData/diagnostics/tests/delegatedProperty/inTrait.kt
+++ b/compiler/testData/diagnostics/tests/delegatedProperty/inTrait.kt
@@ -1,6 +1,6 @@
 // !DIAGNOSTICS: -UNUSED_PARAMETER
 
-trait T {
+interface T {
   val a: Int <!DELEGATED_PROPERTY_IN_TRAIT!>by Delegate()<!>
 }
 
diff --git a/compiler/testData/diagnostics/tests/delegatedProperty/inference/differentDelegatedExpressions.kt b/compiler/testData/diagnostics/tests/delegatedProperty/inference/differentDelegatedExpressions.kt
index 786ef8dab41..d8bf1eaf054 100644
--- a/compiler/testData/diagnostics/tests/delegatedProperty/inference/differentDelegatedExpressions.kt
+++ b/compiler/testData/diagnostics/tests/delegatedProperty/inference/differentDelegatedExpressions.kt
@@ -38,11 +38,11 @@ object O {
     fun getMyProperty<A, B>() = MyProperty<A, B>()
 }
 
-trait MyPropertyContainer {
+interface MyPropertyContainer {
     fun <R, T> getMyProperty(): MyProperty<R, T>
 }
 
-trait Outer {
+interface Outer {
     fun getContainer(): MyPropertyContainer
 }
 
diff --git a/compiler/testData/diagnostics/tests/delegation/DelegationAndOverriding.kt b/compiler/testData/diagnostics/tests/delegation/DelegationAndOverriding.kt
index 9777d79cb0e..51859a91f2b 100644
--- a/compiler/testData/diagnostics/tests/delegation/DelegationAndOverriding.kt
+++ b/compiler/testData/diagnostics/tests/delegation/DelegationAndOverriding.kt
@@ -1,6 +1,6 @@
 package override
 
-trait T {
+interface T {
     fun foo()
     val v : Int
 }
@@ -21,7 +21,7 @@ class Br2(t : T) : Br1(t) {
 
 }
 
-trait G<T> {
+interface G<T> {
     fun foo(t : T) : T
 }
 
diff --git a/compiler/testData/diagnostics/tests/delegation/DelegationExpectedType.kt b/compiler/testData/diagnostics/tests/delegation/DelegationExpectedType.kt
index d795d700bfe..98255091ab1 100644
--- a/compiler/testData/diagnostics/tests/delegation/DelegationExpectedType.kt
+++ b/compiler/testData/diagnostics/tests/delegation/DelegationExpectedType.kt
@@ -1,6 +1,6 @@
 // !DIAGNOSTICS: -UNUSED_PARAMETER
 
-trait A<T> {
+interface A<T> {
     fun foo(): Int
 }
 
diff --git a/compiler/testData/diagnostics/tests/delegation/DelegationNotTotrait.kt b/compiler/testData/diagnostics/tests/delegation/DelegationNotTotrait.kt
index a6ee551a1e8..044c92ed23a 100644
--- a/compiler/testData/diagnostics/tests/delegation/DelegationNotTotrait.kt
+++ b/compiler/testData/diagnostics/tests/delegation/DelegationNotTotrait.kt
@@ -4,7 +4,7 @@ open class Foo() {
 
 class Barrr() : <!DELEGATION_NOT_TO_TRAIT!>Foo<!> by Foo() {}
 
-trait T {}
+interface T {}
 
 class Br(t : T) : T by t {}
 
diff --git a/compiler/testData/diagnostics/tests/delegation/Delegation_ClashingFunctions.kt b/compiler/testData/diagnostics/tests/delegation/Delegation_ClashingFunctions.kt
index 5dc08ebb127..906b40675ab 100644
--- a/compiler/testData/diagnostics/tests/delegation/Delegation_ClashingFunctions.kt
+++ b/compiler/testData/diagnostics/tests/delegation/Delegation_ClashingFunctions.kt
@@ -1,12 +1,12 @@
 // !DIAGNOSTICS: -CONFLICTING_JVM_DECLARATIONS
-trait One {
+interface One {
     public fun foo(): Any?
 }
-trait Two {
+interface Two {
     public fun foo(): String?
 }
 
-trait Three {
+interface Three {
     public fun foo(): String
 }
 
diff --git a/compiler/testData/diagnostics/tests/delegation/Delegation_Hierarchy.kt b/compiler/testData/diagnostics/tests/delegation/Delegation_Hierarchy.kt
index 46fc4d424f8..a92b0861c9f 100644
--- a/compiler/testData/diagnostics/tests/delegation/Delegation_Hierarchy.kt
+++ b/compiler/testData/diagnostics/tests/delegation/Delegation_Hierarchy.kt
@@ -1,4 +1,4 @@
-trait A {
+interface A {
     fun foo() {}
 }
 
diff --git a/compiler/testData/diagnostics/tests/delegation/Delegation_MultipleDelegates.kt b/compiler/testData/diagnostics/tests/delegation/Delegation_MultipleDelegates.kt
index bb5209747a9..26501f0de2e 100644
--- a/compiler/testData/diagnostics/tests/delegation/Delegation_MultipleDelegates.kt
+++ b/compiler/testData/diagnostics/tests/delegation/Delegation_MultipleDelegates.kt
@@ -1,16 +1,16 @@
 // !DIAGNOSTICS: -CONFLICTING_JVM_DECLARATIONS
-trait One {
+interface One {
   public open fun foo() : Int
   private fun boo() = 10
 }
-trait Two {
+interface Two {
   public open fun foo() : Int
 }
 
-trait OneImpl : One {
+interface OneImpl : One {
   public override fun foo() = 1
 }
-trait TwoImpl : Two {
+interface TwoImpl : Two {
   public override fun foo() = 2
 }
 
diff --git a/compiler/testData/diagnostics/tests/delegation/Delegation_ScopeInitializationOrder.kt b/compiler/testData/diagnostics/tests/delegation/Delegation_ScopeInitializationOrder.kt
index d4255d31081..269d5360436 100644
--- a/compiler/testData/diagnostics/tests/delegation/Delegation_ScopeInitializationOrder.kt
+++ b/compiler/testData/diagnostics/tests/delegation/Delegation_ScopeInitializationOrder.kt
@@ -1,8 +1,8 @@
-trait A {
+interface A {
   fun foo() {}
 }
 
-trait B : A {}
+interface B : A {}
 
 class C(b : B) : B by b {
 
diff --git a/compiler/testData/diagnostics/tests/deprecated/typeUsage.kt b/compiler/testData/diagnostics/tests/deprecated/typeUsage.kt
index a53c3b48d9e..a8765891d4c 100644
--- a/compiler/testData/diagnostics/tests/deprecated/typeUsage.kt
+++ b/compiler/testData/diagnostics/tests/deprecated/typeUsage.kt
@@ -8,7 +8,7 @@ open class Obsolete2 [deprecated("Constructor")]() {
     fun use() {}
 }
 
-trait Generic<T>
+interface Generic<T>
 
 open class Derived() : <!DEPRECATED_SYMBOL_WITH_MESSAGE!>Obsolete<!>()
 
diff --git a/compiler/testData/diagnostics/tests/duplicateJvmSignature/accidentalOverrides/delegatedFunctionOverriddenByProperty.kt b/compiler/testData/diagnostics/tests/duplicateJvmSignature/accidentalOverrides/delegatedFunctionOverriddenByProperty.kt
index 69ae81fea64..c0f7cfff409 100644
--- a/compiler/testData/diagnostics/tests/duplicateJvmSignature/accidentalOverrides/delegatedFunctionOverriddenByProperty.kt
+++ b/compiler/testData/diagnostics/tests/duplicateJvmSignature/accidentalOverrides/delegatedFunctionOverriddenByProperty.kt
@@ -1,8 +1,8 @@
-trait B {
+interface B {
     fun getX() = 1
 }
 
-trait D {
+interface D {
     val x: Int
 }
 
diff --git a/compiler/testData/diagnostics/tests/duplicateJvmSignature/accidentalOverrides/overridesNothing.kt b/compiler/testData/diagnostics/tests/duplicateJvmSignature/accidentalOverrides/overridesNothing.kt
index 6c012b7706a..a40245e86d7 100644
--- a/compiler/testData/diagnostics/tests/duplicateJvmSignature/accidentalOverrides/overridesNothing.kt
+++ b/compiler/testData/diagnostics/tests/duplicateJvmSignature/accidentalOverrides/overridesNothing.kt
@@ -1,4 +1,4 @@
-trait B {
+interface B {
     fun getX() = 1
 }
 
diff --git a/compiler/testData/diagnostics/tests/duplicateJvmSignature/accidentalOverrides/require.kt b/compiler/testData/diagnostics/tests/duplicateJvmSignature/accidentalOverrides/require.kt
index 77a52be51e5..9c8dc4b1f62 100644
--- a/compiler/testData/diagnostics/tests/duplicateJvmSignature/accidentalOverrides/require.kt
+++ b/compiler/testData/diagnostics/tests/duplicateJvmSignature/accidentalOverrides/require.kt
@@ -2,6 +2,6 @@ open class C {
     val x = 1
 }
 
-trait Tr : <!TRAIT_WITH_SUPERCLASS!>C<!> {
+interface Tr : <!TRAIT_WITH_SUPERCLASS!>C<!> {
     <!ACCIDENTAL_OVERRIDE!>fun getX()<!> = 1
 }
\ No newline at end of file
diff --git a/compiler/testData/diagnostics/tests/duplicateJvmSignature/accidentalOverrides/traitFunctionOverriddenByProperty.kt b/compiler/testData/diagnostics/tests/duplicateJvmSignature/accidentalOverrides/traitFunctionOverriddenByProperty.kt
index 51c5ab88129..64fc7a27d37 100644
--- a/compiler/testData/diagnostics/tests/duplicateJvmSignature/accidentalOverrides/traitFunctionOverriddenByProperty.kt
+++ b/compiler/testData/diagnostics/tests/duplicateJvmSignature/accidentalOverrides/traitFunctionOverriddenByProperty.kt
@@ -1,4 +1,4 @@
-trait T {
+interface T {
     fun getX() = 1
 }
 
diff --git a/compiler/testData/diagnostics/tests/duplicateJvmSignature/accidentalOverrides/traitFunctionOverriddenByPropertyInTrait.kt b/compiler/testData/diagnostics/tests/duplicateJvmSignature/accidentalOverrides/traitFunctionOverriddenByPropertyInTrait.kt
index 7ac61cb4db6..0500cd621d7 100644
--- a/compiler/testData/diagnostics/tests/duplicateJvmSignature/accidentalOverrides/traitFunctionOverriddenByPropertyInTrait.kt
+++ b/compiler/testData/diagnostics/tests/duplicateJvmSignature/accidentalOverrides/traitFunctionOverriddenByPropertyInTrait.kt
@@ -1,8 +1,8 @@
-trait T {
+interface T {
     fun getX() = 1
 }
 
-trait C : T {
+interface C : T {
     val x: Int
         <!ACCIDENTAL_OVERRIDE!>get()<!> = 1
 }
\ No newline at end of file
diff --git a/compiler/testData/diagnostics/tests/duplicateJvmSignature/accidentalOverrides/traitFunctionOverriddenByPropertyNoImpl.kt b/compiler/testData/diagnostics/tests/duplicateJvmSignature/accidentalOverrides/traitFunctionOverriddenByPropertyNoImpl.kt
index fd6f97455e4..428eaedd188 100644
--- a/compiler/testData/diagnostics/tests/duplicateJvmSignature/accidentalOverrides/traitFunctionOverriddenByPropertyNoImpl.kt
+++ b/compiler/testData/diagnostics/tests/duplicateJvmSignature/accidentalOverrides/traitFunctionOverriddenByPropertyNoImpl.kt
@@ -1,4 +1,4 @@
-trait T {
+interface T {
     fun getX(): Int
 }
 
diff --git a/compiler/testData/diagnostics/tests/duplicateJvmSignature/accidentalOverrides/traitPropertyOverriddenByFunction.kt b/compiler/testData/diagnostics/tests/duplicateJvmSignature/accidentalOverrides/traitPropertyOverriddenByFunction.kt
index db45ec43175..c5be4f32551 100644
--- a/compiler/testData/diagnostics/tests/duplicateJvmSignature/accidentalOverrides/traitPropertyOverriddenByFunction.kt
+++ b/compiler/testData/diagnostics/tests/duplicateJvmSignature/accidentalOverrides/traitPropertyOverriddenByFunction.kt
@@ -1,4 +1,4 @@
-trait T {
+interface T {
     val x: Int
         get() = 1
 }
diff --git a/compiler/testData/diagnostics/tests/duplicateJvmSignature/accidentalOverrides/traitPropertyOverriddenByFunctionInTrait.kt b/compiler/testData/diagnostics/tests/duplicateJvmSignature/accidentalOverrides/traitPropertyOverriddenByFunctionInTrait.kt
index d969e1791a4..106aa378526 100644
--- a/compiler/testData/diagnostics/tests/duplicateJvmSignature/accidentalOverrides/traitPropertyOverriddenByFunctionInTrait.kt
+++ b/compiler/testData/diagnostics/tests/duplicateJvmSignature/accidentalOverrides/traitPropertyOverriddenByFunctionInTrait.kt
@@ -1,8 +1,8 @@
-trait T {
+interface T {
     val x: Int
         get() = 1
 }
 
-trait C : T {
+interface C : T {
     <!ACCIDENTAL_OVERRIDE!>fun getX()<!> = 1
 }
\ No newline at end of file
diff --git a/compiler/testData/diagnostics/tests/duplicateJvmSignature/accidentalOverrides/traitPropertyOverriddenByFunctionNoImpl.kt b/compiler/testData/diagnostics/tests/duplicateJvmSignature/accidentalOverrides/traitPropertyOverriddenByFunctionNoImpl.kt
index 40b17a13d66..de87b96c878 100644
--- a/compiler/testData/diagnostics/tests/duplicateJvmSignature/accidentalOverrides/traitPropertyOverriddenByFunctionNoImpl.kt
+++ b/compiler/testData/diagnostics/tests/duplicateJvmSignature/accidentalOverrides/traitPropertyOverriddenByFunctionNoImpl.kt
@@ -1,4 +1,4 @@
-trait T {
+interface T {
     val x: Int
 }
 
diff --git a/compiler/testData/diagnostics/tests/duplicateJvmSignature/bridges/fakeOverrideTrait.kt b/compiler/testData/diagnostics/tests/duplicateJvmSignature/bridges/fakeOverrideTrait.kt
index 9edaa67505c..8dfae66af87 100644
--- a/compiler/testData/diagnostics/tests/duplicateJvmSignature/bridges/fakeOverrideTrait.kt
+++ b/compiler/testData/diagnostics/tests/duplicateJvmSignature/bridges/fakeOverrideTrait.kt
@@ -1,6 +1,6 @@
 // !DIAGNOSTICS: -UNUSED_PARAMETER
 
-trait B<T> {
+interface B<T> {
     fun foo(t: T) {}
 }
 
diff --git a/compiler/testData/diagnostics/tests/duplicateJvmSignature/bridges/trait.kt b/compiler/testData/diagnostics/tests/duplicateJvmSignature/bridges/trait.kt
index 347a8b77304..d9f9b35cab0 100644
--- a/compiler/testData/diagnostics/tests/duplicateJvmSignature/bridges/trait.kt
+++ b/compiler/testData/diagnostics/tests/duplicateJvmSignature/bridges/trait.kt
@@ -1,6 +1,6 @@
 // !DIAGNOSTICS: -UNUSED_PARAMETER
 
-trait B<T> {
+interface B<T> {
     fun foo(t: T) {}
 }
 
diff --git a/compiler/testData/diagnostics/tests/duplicateJvmSignature/erasure/delegateToTwoTraits.kt b/compiler/testData/diagnostics/tests/duplicateJvmSignature/erasure/delegateToTwoTraits.kt
index 6bcfc98e761..aac2ee72029 100644
--- a/compiler/testData/diagnostics/tests/duplicateJvmSignature/erasure/delegateToTwoTraits.kt
+++ b/compiler/testData/diagnostics/tests/duplicateJvmSignature/erasure/delegateToTwoTraits.kt
@@ -1,10 +1,10 @@
 // !DIAGNOSTICS: -UNUSED_PARAMETER
 
-trait Foo<T> {
+interface Foo<T> {
     fun foo(l: List<T>)
 }
 
-trait Bar<T> {
+interface Bar<T> {
     fun foo(l: List<T>)
 }
 
diff --git a/compiler/testData/diagnostics/tests/duplicateJvmSignature/erasure/delegationAndOwnMethod.kt b/compiler/testData/diagnostics/tests/duplicateJvmSignature/erasure/delegationAndOwnMethod.kt
index 24bb8407236..6191d8ff095 100644
--- a/compiler/testData/diagnostics/tests/duplicateJvmSignature/erasure/delegationAndOwnMethod.kt
+++ b/compiler/testData/diagnostics/tests/duplicateJvmSignature/erasure/delegationAndOwnMethod.kt
@@ -1,6 +1,6 @@
 // !DIAGNOSTICS: -UNUSED_PARAMETER
 
-trait Foo<T> {
+interface Foo<T> {
     fun foo(l: List<T>)
 }
 
diff --git a/compiler/testData/diagnostics/tests/duplicateJvmSignature/erasure/delegationToTraitImplAndOwnMethod.kt b/compiler/testData/diagnostics/tests/duplicateJvmSignature/erasure/delegationToTraitImplAndOwnMethod.kt
index 7c4fb7ba4bb..7e6b4cec1b5 100644
--- a/compiler/testData/diagnostics/tests/duplicateJvmSignature/erasure/delegationToTraitImplAndOwnMethod.kt
+++ b/compiler/testData/diagnostics/tests/duplicateJvmSignature/erasure/delegationToTraitImplAndOwnMethod.kt
@@ -1,6 +1,6 @@
 // !DIAGNOSTICS: -UNUSED_PARAMETER
 
-trait Foo<T> {
+interface Foo<T> {
     fun foo(l: List<T>) {
 
     }
diff --git a/compiler/testData/diagnostics/tests/duplicateJvmSignature/erasure/inheritFromTwoTraits.kt b/compiler/testData/diagnostics/tests/duplicateJvmSignature/erasure/inheritFromTwoTraits.kt
index 8ea037951ba..a71a6f68d2e 100644
--- a/compiler/testData/diagnostics/tests/duplicateJvmSignature/erasure/inheritFromTwoTraits.kt
+++ b/compiler/testData/diagnostics/tests/duplicateJvmSignature/erasure/inheritFromTwoTraits.kt
@@ -1,10 +1,10 @@
 // !DIAGNOSTICS: -UNUSED_PARAMETER
 
-trait Foo<T> {
+interface Foo<T> {
     fun foo(l: List<T>) {}
 }
 
-trait Bar<T> {
+interface Bar<T> {
     fun foo(l: List<T>) {}
 }
 
diff --git a/compiler/testData/diagnostics/tests/duplicateJvmSignature/erasure/superTraitAndDelegationToTraitImpl.kt b/compiler/testData/diagnostics/tests/duplicateJvmSignature/erasure/superTraitAndDelegationToTraitImpl.kt
index 72745e0037a..32ababfffdd 100644
--- a/compiler/testData/diagnostics/tests/duplicateJvmSignature/erasure/superTraitAndDelegationToTraitImpl.kt
+++ b/compiler/testData/diagnostics/tests/duplicateJvmSignature/erasure/superTraitAndDelegationToTraitImpl.kt
@@ -1,10 +1,10 @@
 // !DIAGNOSTICS: -UNUSED_PARAMETER
 
-trait A<T> {
+interface A<T> {
     fun foo(l: List<T>)
 }
 
-trait B {
+interface B {
     fun foo(l: List<Int>) {}
 }
 
diff --git a/compiler/testData/diagnostics/tests/duplicateJvmSignature/erasure/twoTraitsAndOwnFunction.kt b/compiler/testData/diagnostics/tests/duplicateJvmSignature/erasure/twoTraitsAndOwnFunction.kt
index c684dce2dcb..9c29e9fc29a 100644
--- a/compiler/testData/diagnostics/tests/duplicateJvmSignature/erasure/twoTraitsAndOwnFunction.kt
+++ b/compiler/testData/diagnostics/tests/duplicateJvmSignature/erasure/twoTraitsAndOwnFunction.kt
@@ -1,10 +1,10 @@
 // !DIAGNOSTICS: -UNUSED_PARAMETER
 
-trait Foo<T> {
+interface Foo<T> {
     fun foo(l: List<T>) {}
 }
 
-trait Bar<T> {
+interface Bar<T> {
     fun foo(l: List<T>) {}
 }
 
diff --git a/compiler/testData/diagnostics/tests/duplicateJvmSignature/erasure/typeParameterWithBound.kt b/compiler/testData/diagnostics/tests/duplicateJvmSignature/erasure/typeParameterWithBound.kt
index d66ab7c93ba..ab5c6ef5fe2 100644
--- a/compiler/testData/diagnostics/tests/duplicateJvmSignature/erasure/typeParameterWithBound.kt
+++ b/compiler/testData/diagnostics/tests/duplicateJvmSignature/erasure/typeParameterWithBound.kt
@@ -1,6 +1,6 @@
 // !DIAGNOSTICS: -UNUSED_PARAMETER
 
-trait Foo
+interface Foo
 
 <!CONFLICTING_OVERLOADS!>fun <T: Foo> foo(x: T): T<!> {null!!}
 <!CONFLICTING_OVERLOADS!>fun foo(x: Foo): Foo<!> {null!!}
\ No newline at end of file
diff --git a/compiler/testData/diagnostics/tests/duplicateJvmSignature/erasure/typeParameterWithTwoBounds.kt b/compiler/testData/diagnostics/tests/duplicateJvmSignature/erasure/typeParameterWithTwoBounds.kt
index 3909c4424f9..ceadd5a3234 100644
--- a/compiler/testData/diagnostics/tests/duplicateJvmSignature/erasure/typeParameterWithTwoBounds.kt
+++ b/compiler/testData/diagnostics/tests/duplicateJvmSignature/erasure/typeParameterWithTwoBounds.kt
@@ -1,7 +1,7 @@
 // !DIAGNOSTICS: -UNUSED_PARAMETER
 
-trait Foo
-trait Bar
+interface Foo
+interface Bar
 
 <!CONFLICTING_JVM_DECLARATIONS!>fun <T: Foo> foo(x: T): T<!> where T: Bar {null!!}
 <!CONFLICTING_JVM_DECLARATIONS!>fun foo(x: Foo): Foo<!> {null!!}
diff --git a/compiler/testData/diagnostics/tests/duplicateJvmSignature/erasure/typeParameterWithTwoBoundsInWhere.kt b/compiler/testData/diagnostics/tests/duplicateJvmSignature/erasure/typeParameterWithTwoBoundsInWhere.kt
index e33242be422..426fa852797 100644
--- a/compiler/testData/diagnostics/tests/duplicateJvmSignature/erasure/typeParameterWithTwoBoundsInWhere.kt
+++ b/compiler/testData/diagnostics/tests/duplicateJvmSignature/erasure/typeParameterWithTwoBoundsInWhere.kt
@@ -1,7 +1,7 @@
 // !DIAGNOSTICS: -UNUSED_PARAMETER
 
-trait Foo
-trait Bar
+interface Foo
+interface Bar
 
 <!CONFLICTING_JVM_DECLARATIONS!>fun <T> foo(x: T): T<!> where T: Foo, T: Bar {null!!}
 <!CONFLICTING_JVM_DECLARATIONS!>fun foo(x: Foo): Foo<!> {null!!}
diff --git a/compiler/testData/diagnostics/tests/duplicateJvmSignature/functionAndProperty/trait.kt b/compiler/testData/diagnostics/tests/duplicateJvmSignature/functionAndProperty/trait.kt
index b121dc589a9..81fca7ab9c5 100644
--- a/compiler/testData/diagnostics/tests/duplicateJvmSignature/functionAndProperty/trait.kt
+++ b/compiler/testData/diagnostics/tests/duplicateJvmSignature/functionAndProperty/trait.kt
@@ -1,4 +1,4 @@
-trait T {
+interface T {
     val x: Int
         <!CONFLICTING_JVM_DECLARATIONS!>get()<!> = 1
     <!CONFLICTING_JVM_DECLARATIONS!>fun getX()<!> = 1
diff --git a/compiler/testData/diagnostics/tests/duplicateJvmSignature/functionAndProperty/withErrorTypes.kt b/compiler/testData/diagnostics/tests/duplicateJvmSignature/functionAndProperty/withErrorTypes.kt
index 4cda9be3e44..590b43d196c 100644
--- a/compiler/testData/diagnostics/tests/duplicateJvmSignature/functionAndProperty/withErrorTypes.kt
+++ b/compiler/testData/diagnostics/tests/duplicateJvmSignature/functionAndProperty/withErrorTypes.kt
@@ -1,4 +1,4 @@
-trait T {
+interface T {
     <!CONFLICTING_JVM_DECLARATIONS!>val x: <!UNRESOLVED_REFERENCE!>ErrorType<!><!>
     <!CONFLICTING_JVM_DECLARATIONS!>fun getX(): <!UNRESOLVED_REFERENCE!>ErrorType1<!><!>
 }
\ No newline at end of file
diff --git a/compiler/testData/diagnostics/tests/duplicateJvmSignature/missingNames.kt b/compiler/testData/diagnostics/tests/duplicateJvmSignature/missingNames.kt
index 1ecc779baaa..fb9c341bb22 100644
--- a/compiler/testData/diagnostics/tests/duplicateJvmSignature/missingNames.kt
+++ b/compiler/testData/diagnostics/tests/duplicateJvmSignature/missingNames.kt
@@ -16,7 +16,7 @@ object <!SYNTAX!><!>{
 
 }
 
-trait<!SYNTAX!><!> {
+interface<!SYNTAX!><!> {
 
 }
 
@@ -43,7 +43,7 @@ class Outer {
 
     }
 
-    <!REDECLARATION!>trait<!SYNTAX!><!> {
+    <!REDECLARATION!>interface<!SYNTAX!><!> {
 
     }<!>
 
diff --git a/compiler/testData/diagnostics/tests/duplicateJvmSignature/specialNames/delegationBy.kt b/compiler/testData/diagnostics/tests/duplicateJvmSignature/specialNames/delegationBy.kt
index 80ccd8f1618..5ea8a8690ad 100644
--- a/compiler/testData/diagnostics/tests/duplicateJvmSignature/specialNames/delegationBy.kt
+++ b/compiler/testData/diagnostics/tests/duplicateJvmSignature/specialNames/delegationBy.kt
@@ -1,4 +1,4 @@
-trait Foo
+interface Foo
 
 class <!CONFLICTING_JVM_DECLARATIONS!>Bar(f: Foo)<!> : Foo by f {
     <!CONFLICTING_JVM_DECLARATIONS!>val `$delegate_0`: Foo?<!> = null
diff --git a/compiler/testData/diagnostics/tests/duplicateJvmSignature/traitImpl/oneTrait.kt b/compiler/testData/diagnostics/tests/duplicateJvmSignature/traitImpl/oneTrait.kt
index e5d4ed3fa70..171fa6ce100 100644
--- a/compiler/testData/diagnostics/tests/duplicateJvmSignature/traitImpl/oneTrait.kt
+++ b/compiler/testData/diagnostics/tests/duplicateJvmSignature/traitImpl/oneTrait.kt
@@ -1,4 +1,4 @@
-trait T {
+interface T {
     fun getX() = 1
 }
 
diff --git a/compiler/testData/diagnostics/tests/duplicateJvmSignature/traitImpl/twoTraits.kt b/compiler/testData/diagnostics/tests/duplicateJvmSignature/traitImpl/twoTraits.kt
index 7f9179d9924..a1f17330267 100644
--- a/compiler/testData/diagnostics/tests/duplicateJvmSignature/traitImpl/twoTraits.kt
+++ b/compiler/testData/diagnostics/tests/duplicateJvmSignature/traitImpl/twoTraits.kt
@@ -1,8 +1,8 @@
-trait T1 {
+interface T1 {
     fun getX() = 1
 }
 
-trait T2 {
+interface T2 {
     val x: Int
         get() = 1
 }
diff --git a/compiler/testData/diagnostics/tests/dynamicTypes/delegationBy.kt b/compiler/testData/diagnostics/tests/dynamicTypes/delegationBy.kt
index 31f77fa7ee2..020a46b8a29 100644
--- a/compiler/testData/diagnostics/tests/dynamicTypes/delegationBy.kt
+++ b/compiler/testData/diagnostics/tests/dynamicTypes/delegationBy.kt
@@ -1,4 +1,4 @@
-trait Tr {
+interface Tr {
     fun foo()
 }
 
diff --git a/compiler/testData/diagnostics/tests/enum/AbstractOverrideInEnum.kt b/compiler/testData/diagnostics/tests/enum/AbstractOverrideInEnum.kt
index f37453fe03c..f053dfbf5a6 100644
--- a/compiler/testData/diagnostics/tests/enum/AbstractOverrideInEnum.kt
+++ b/compiler/testData/diagnostics/tests/enum/AbstractOverrideInEnum.kt
@@ -7,6 +7,6 @@ enum class E : T {
     abstract override fun f()
 }
 
-trait T {
+interface T {
     fun f()
 }
\ No newline at end of file
diff --git a/compiler/testData/diagnostics/tests/enum/enumImplementingTrait.kt b/compiler/testData/diagnostics/tests/enum/enumImplementingTrait.kt
index e0d0e769052..f26059f5e59 100644
--- a/compiler/testData/diagnostics/tests/enum/enumImplementingTrait.kt
+++ b/compiler/testData/diagnostics/tests/enum/enumImplementingTrait.kt
@@ -1,4 +1,4 @@
-trait T1 {
+interface T1 {
     fun foo()
 }
 
@@ -9,7 +9,7 @@ enum class EnumImplementingTraitWithFun: T1 {
     <!ABSTRACT_MEMBER_NOT_IMPLEMENTED!>E2<!>
 }
 
-trait T2 {
+interface T2 {
     val bar: Int
 }
 
diff --git a/compiler/testData/diagnostics/tests/enum/enumInheritance.kt b/compiler/testData/diagnostics/tests/enum/enumInheritance.kt
index 81fc0409dff..ff0f2a425fc 100644
--- a/compiler/testData/diagnostics/tests/enum/enumInheritance.kt
+++ b/compiler/testData/diagnostics/tests/enum/enumInheritance.kt
@@ -7,5 +7,5 @@ open class MyClass() {}
 
 enum class MyEnumBase() {}
 
-trait MyTrait {}
+interface MyTrait {}
 
diff --git a/compiler/testData/diagnostics/tests/enum/enumModifier.kt b/compiler/testData/diagnostics/tests/enum/enumModifier.kt
index 3f9a6e12e8d..15e6c87869d 100644
--- a/compiler/testData/diagnostics/tests/enum/enumModifier.kt
+++ b/compiler/testData/diagnostics/tests/enum/enumModifier.kt
@@ -6,7 +6,7 @@ class A {
 
 <!ILLEGAL_ENUM_ANNOTATION!>enum<!> object O {}
 
-<!ILLEGAL_ENUM_ANNOTATION!>enum<!> trait T {}
+<!ILLEGAL_ENUM_ANNOTATION!>enum<!> interface T {}
 
 <!ILLEGAL_ENUM_ANNOTATION!>enum<!> fun f() = 0
 
diff --git a/compiler/testData/diagnostics/tests/enum/inner/insideTrait.kt b/compiler/testData/diagnostics/tests/enum/inner/insideTrait.kt
index 4138b24d5c7..5d04181c73b 100644
--- a/compiler/testData/diagnostics/tests/enum/inner/insideTrait.kt
+++ b/compiler/testData/diagnostics/tests/enum/inner/insideTrait.kt
@@ -1,4 +1,4 @@
-trait A {
+interface A {
     enum class E {
         ENTRY
     }
diff --git a/compiler/testData/diagnostics/tests/extensions/ExtensionsCalledOnSuper.kt b/compiler/testData/diagnostics/tests/extensions/ExtensionsCalledOnSuper.kt
index 9f97b9eea92..16744a9ad03 100644
--- a/compiler/testData/diagnostics/tests/extensions/ExtensionsCalledOnSuper.kt
+++ b/compiler/testData/diagnostics/tests/extensions/ExtensionsCalledOnSuper.kt
@@ -1,4 +1,4 @@
-trait T {
+interface T {
     fun foo() {}
     fun buzz() {}
     fun buzz1(i : Int) {}
diff --git a/compiler/testData/diagnostics/tests/extensions/GenericIterator.kt b/compiler/testData/diagnostics/tests/extensions/GenericIterator.kt
index 5fbb228f3e8..a3f7c02519a 100644
--- a/compiler/testData/diagnostics/tests/extensions/GenericIterator.kt
+++ b/compiler/testData/diagnostics/tests/extensions/GenericIterator.kt
@@ -6,7 +6,7 @@ fun <T> java.util.Enumeration<T>.iterator() = object: Iterator<T> {
   override fun next() = nextElement()
 }
 
-trait MyIterator<T> {
+interface MyIterator<T> {
 
   fun hasNext() : Boolean
 
diff --git a/compiler/testData/diagnostics/tests/extensions/classObject.kt b/compiler/testData/diagnostics/tests/extensions/classObject.kt
index e392d98976b..e6d4e5aa45f 100644
--- a/compiler/testData/diagnostics/tests/extensions/classObject.kt
+++ b/compiler/testData/diagnostics/tests/extensions/classObject.kt
@@ -1,4 +1,4 @@
-trait Tr
+interface Tr
 
 class A { companion object }
 class B { companion object : Tr }
diff --git a/compiler/testData/diagnostics/tests/extensions/extensionMemberInClassObject.kt b/compiler/testData/diagnostics/tests/extensions/extensionMemberInClassObject.kt
index 8de61054bd3..6c7b9b17d6a 100644
--- a/compiler/testData/diagnostics/tests/extensions/extensionMemberInClassObject.kt
+++ b/compiler/testData/diagnostics/tests/extensions/extensionMemberInClassObject.kt
@@ -1,6 +1,6 @@
 // !DIAGNOSTICS: -UNUSED_PARAMETER
 
-trait JPAEntityClass<D> {
+interface JPAEntityClass<D> {
     fun <T> T.findByName(s: String): D {null!!}
 }
 
diff --git a/compiler/testData/diagnostics/tests/extensions/kt1875.kt b/compiler/testData/diagnostics/tests/extensions/kt1875.kt
index 3d2666e8e30..83654a9d1be 100644
--- a/compiler/testData/diagnostics/tests/extensions/kt1875.kt
+++ b/compiler/testData/diagnostics/tests/extensions/kt1875.kt
@@ -4,7 +4,7 @@ package kt1875
 
 fun f(a : Int?, b : Int.(Int)->Int) = a?.b(1) //unnecessary safe call warning
 
-trait T {
+interface T {
     val f : ((i: Int) -> Unit)?
 }
 
diff --git a/compiler/testData/diagnostics/tests/extensions/throwOutCandidatesByReceiver.kt b/compiler/testData/diagnostics/tests/extensions/throwOutCandidatesByReceiver.kt
index bd7b8379f5a..bbcef2b140c 100644
--- a/compiler/testData/diagnostics/tests/extensions/throwOutCandidatesByReceiver.kt
+++ b/compiler/testData/diagnostics/tests/extensions/throwOutCandidatesByReceiver.kt
@@ -23,7 +23,7 @@ fun test3(s: String?) {
     s.<!UNRESOLVED_REFERENCE_WRONG_RECEIVER!>foo<!>("a")
 }
 
-trait A
+interface A
 fun <T: A> T.c() {}
 
 fun test4() {
diff --git a/compiler/testData/diagnostics/tests/functionAsExpression/ScopeCheck.kt b/compiler/testData/diagnostics/tests/functionAsExpression/ScopeCheck.kt
index 108e658e5c3..b36419582fa 100644
--- a/compiler/testData/diagnostics/tests/functionAsExpression/ScopeCheck.kt
+++ b/compiler/testData/diagnostics/tests/functionAsExpression/ScopeCheck.kt
@@ -1,6 +1,6 @@
 // !DIAGNOSTICS: -UNUSED_VARIABLE
 
-trait B {
+interface B {
     fun b_fun() {}
 }
 
diff --git a/compiler/testData/diagnostics/tests/functionAsExpression/WithGenericParameters.kt b/compiler/testData/diagnostics/tests/functionAsExpression/WithGenericParameters.kt
index 9d1b25296f8..118af628948 100644
--- a/compiler/testData/diagnostics/tests/functionAsExpression/WithGenericParameters.kt
+++ b/compiler/testData/diagnostics/tests/functionAsExpression/WithGenericParameters.kt
@@ -1,6 +1,6 @@
 // !DIAGNOSTICS: -UNUSED_PARAMETER
 
-trait A
+interface A
 fun devNull(a: Any?){}
 
 val generic_fun = fun<!TYPE_PARAMETERS_NOT_ALLOWED!><T><!>(t: T): T = null!!
diff --git a/compiler/testData/diagnostics/tests/functionLiterals/ExpectedParameterTypeMismatchVariance.kt b/compiler/testData/diagnostics/tests/functionLiterals/ExpectedParameterTypeMismatchVariance.kt
index 08b3e7ba7eb..886f9079cc2 100644
--- a/compiler/testData/diagnostics/tests/functionLiterals/ExpectedParameterTypeMismatchVariance.kt
+++ b/compiler/testData/diagnostics/tests/functionLiterals/ExpectedParameterTypeMismatchVariance.kt
@@ -1,7 +1,7 @@
 package a
 
-trait Super
-trait Trait : Super
+interface Super
+interface Trait : Super
 class Sub : Trait
 
 fun foo(f: (Trait) -> Trait) = f
diff --git a/compiler/testData/diagnostics/tests/functionLiterals/LabeledFunctionLiterals.kt b/compiler/testData/diagnostics/tests/functionLiterals/LabeledFunctionLiterals.kt
index 17d3b8ddd79..ef9f257117a 100644
--- a/compiler/testData/diagnostics/tests/functionLiterals/LabeledFunctionLiterals.kt
+++ b/compiler/testData/diagnostics/tests/functionLiterals/LabeledFunctionLiterals.kt
@@ -1,9 +1,9 @@
 package h
 
 //traits to make ambiguity with function literal as an argument
-trait A
-trait B
-trait C: A, B
+interface A
+interface B
+interface C: A, B
 
 fun foo<T>(<!UNUSED_PARAMETER!>a<!>: A, f: () -> T): T = f()
 fun foo<T>(<!UNUSED_PARAMETER!>b<!>: B, f: () -> T): T = f()
diff --git a/compiler/testData/diagnostics/tests/functionLiterals/return/MixedReturnsFromLambda.kt b/compiler/testData/diagnostics/tests/functionLiterals/return/MixedReturnsFromLambda.kt
index 6db7f204afb..5d524cf4236 100644
--- a/compiler/testData/diagnostics/tests/functionLiterals/return/MixedReturnsFromLambda.kt
+++ b/compiler/testData/diagnostics/tests/functionLiterals/return/MixedReturnsFromLambda.kt
@@ -1,8 +1,8 @@
 // !CHECK_TYPE
 
-trait A
-trait B: A
-trait C: A
+interface A
+interface B: A
+interface C: A
 
 
 fun test(a: C, b: B) {
diff --git a/compiler/testData/diagnostics/tests/functionLiterals/returnNull.kt b/compiler/testData/diagnostics/tests/functionLiterals/returnNull.kt
index 8110dc40a3c..a8d7942f421 100644
--- a/compiler/testData/diagnostics/tests/functionLiterals/returnNull.kt
+++ b/compiler/testData/diagnostics/tests/functionLiterals/returnNull.kt
@@ -1,6 +1,6 @@
 package m
 
-trait Element
+interface Element
 
 fun test(handlers: Map<String, Element.()->Unit>) {
 
diff --git a/compiler/testData/diagnostics/tests/functionLiterals/returnNullWithReturn.kt b/compiler/testData/diagnostics/tests/functionLiterals/returnNullWithReturn.kt
index 23b8bcf37e6..bfb9427eff2 100644
--- a/compiler/testData/diagnostics/tests/functionLiterals/returnNullWithReturn.kt
+++ b/compiler/testData/diagnostics/tests/functionLiterals/returnNullWithReturn.kt
@@ -1,6 +1,6 @@
 package m
 
-trait Element
+interface Element
 
 fun test(handlers: Map<String, Element.()->Unit>) {
 
diff --git a/compiler/testData/diagnostics/tests/generics/argumentsForT.kt b/compiler/testData/diagnostics/tests/generics/argumentsForT.kt
index 62094b66761..603950448eb 100644
--- a/compiler/testData/diagnostics/tests/generics/argumentsForT.kt
+++ b/compiler/testData/diagnostics/tests/generics/argumentsForT.kt
@@ -2,6 +2,6 @@
 
 fun <T> foo(t: T<!WRONG_NUMBER_OF_TYPE_ARGUMENTS!><String, Int><!>) {}
 
-trait A
+interface A
 class B<T: A>
 fun <T> foo1(t: T<!WRONG_NUMBER_OF_TYPE_ARGUMENTS!><B<<!UPPER_BOUND_VIOLATED!>String<!>>><!>) {}
\ No newline at end of file
diff --git a/compiler/testData/diagnostics/tests/generics/recursive.kt b/compiler/testData/diagnostics/tests/generics/recursive.kt
index c2dc9fd7fd6..690c18b7f65 100644
--- a/compiler/testData/diagnostics/tests/generics/recursive.kt
+++ b/compiler/testData/diagnostics/tests/generics/recursive.kt
@@ -1,6 +1,6 @@
 // !DIAGNOSTICS: -ASSIGNED_BUT_NEVER_ACCESSED_VARIABLE -UNUSED_VALUE
 
-trait Rec<T>
+interface Rec<T>
 class A : Rec<A>
 class B : Rec<B>
 
diff --git a/compiler/testData/diagnostics/tests/generics/resolveGenericBoundsBeforeSupertypes.kt b/compiler/testData/diagnostics/tests/generics/resolveGenericBoundsBeforeSupertypes.kt
index bf658a20f36..543e3f9646b 100644
--- a/compiler/testData/diagnostics/tests/generics/resolveGenericBoundsBeforeSupertypes.kt
+++ b/compiler/testData/diagnostics/tests/generics/resolveGenericBoundsBeforeSupertypes.kt
@@ -2,6 +2,6 @@
 
 object O : Tr<V<*>>
 
-trait Tr<T>
+interface Tr<T>
 
 class V<out S>
diff --git a/compiler/testData/diagnostics/tests/generics/varProjection/setterNotProjectedOutAssign.kt b/compiler/testData/diagnostics/tests/generics/varProjection/setterNotProjectedOutAssign.kt
index ad1faefeef0..0483b755a92 100644
--- a/compiler/testData/diagnostics/tests/generics/varProjection/setterNotProjectedOutAssign.kt
+++ b/compiler/testData/diagnostics/tests/generics/varProjection/setterNotProjectedOutAssign.kt
@@ -1,5 +1,5 @@
 // !CHECK_TYPE
-trait Tr<T> {
+interface Tr<T> {
     var v: Tr<T>
 }
 
diff --git a/compiler/testData/diagnostics/tests/generics/varProjection/setterProjectedOutAssign.kt b/compiler/testData/diagnostics/tests/generics/varProjection/setterProjectedOutAssign.kt
index 781c69c09cc..2437a4ad028 100644
--- a/compiler/testData/diagnostics/tests/generics/varProjection/setterProjectedOutAssign.kt
+++ b/compiler/testData/diagnostics/tests/generics/varProjection/setterProjectedOutAssign.kt
@@ -1,7 +1,7 @@
 // !DIAGNOSTICS: -UNREACHABLE_CODE -UNUSED_PARAMETER
 // !CHECK_TYPE
 // t is unused due to KT-4233
-trait Tr<T> {
+interface Tr<T> {
     var v: T
 }
 
diff --git a/compiler/testData/diagnostics/tests/generics/varProjection/setterProjectedOutNoPlusAssign.kt b/compiler/testData/diagnostics/tests/generics/varProjection/setterProjectedOutNoPlusAssign.kt
index 8f92eb93981..bd8a66c4724 100644
--- a/compiler/testData/diagnostics/tests/generics/varProjection/setterProjectedOutNoPlusAssign.kt
+++ b/compiler/testData/diagnostics/tests/generics/varProjection/setterProjectedOutNoPlusAssign.kt
@@ -1,5 +1,5 @@
 // !DIAGNOSTICS: -UNREACHABLE_CODE
-trait Tr<T> {
+interface Tr<T> {
     var v: T
 }
 
diff --git a/compiler/testData/diagnostics/tests/generics/varProjection/setterProjectedOutPlusAssignDefined.kt b/compiler/testData/diagnostics/tests/generics/varProjection/setterProjectedOutPlusAssignDefined.kt
index a76e4ea4630..85a976ac8b7 100644
--- a/compiler/testData/diagnostics/tests/generics/varProjection/setterProjectedOutPlusAssignDefined.kt
+++ b/compiler/testData/diagnostics/tests/generics/varProjection/setterProjectedOutPlusAssignDefined.kt
@@ -1,5 +1,5 @@
 // !DIAGNOSTICS: -UNREACHABLE_CODE
-trait Tr<T> {
+interface Tr<T> {
     var v: T
 }
 
diff --git a/compiler/testData/diagnostics/tests/incompleteCode/checkNothingIsSubtype.kt b/compiler/testData/diagnostics/tests/incompleteCode/checkNothingIsSubtype.kt
index 07767db56ed..ad407c6bc68 100644
--- a/compiler/testData/diagnostics/tests/incompleteCode/checkNothingIsSubtype.kt
+++ b/compiler/testData/diagnostics/tests/incompleteCode/checkNothingIsSubtype.kt
@@ -1,7 +1,7 @@
 // !DIAGNOSTICS: -UNUSED_EXPRESSION
 package d
 
-trait A<T>
+interface A<T>
 
 fun infer<T>(<!UNUSED_PARAMETER!>a<!>: A<T>) : T {<!NO_RETURN_IN_FUNCTION_WITH_BLOCK_BODY!>}<!>
 
diff --git a/compiler/testData/diagnostics/tests/inference/constraints/equalityConstraintOnNullableType.kt b/compiler/testData/diagnostics/tests/inference/constraints/equalityConstraintOnNullableType.kt
index b85f61691c5..aae592088d5 100644
--- a/compiler/testData/diagnostics/tests/inference/constraints/equalityConstraintOnNullableType.kt
+++ b/compiler/testData/diagnostics/tests/inference/constraints/equalityConstraintOnNullableType.kt
@@ -1,6 +1,6 @@
 // !DIAGNOSTICS: -BASE_WITH_NULLABLE_UPPER_BOUND
 // !CHECK_TYPE
-trait A<T>
+interface A<T>
 
 fun <T> foo(a: A<T>, aN: A<T?>): T = throw Exception("$a $aN")
 
diff --git a/compiler/testData/diagnostics/tests/inference/constraints/kt7351ConstraintFromUnitExpectedType.kt b/compiler/testData/diagnostics/tests/inference/constraints/kt7351ConstraintFromUnitExpectedType.kt
index 4ab6d7d1a57..d49d4c3a0bc 100644
--- a/compiler/testData/diagnostics/tests/inference/constraints/kt7351ConstraintFromUnitExpectedType.kt
+++ b/compiler/testData/diagnostics/tests/inference/constraints/kt7351ConstraintFromUnitExpectedType.kt
@@ -2,9 +2,9 @@
 
 package kt7351
 
-trait Node
+interface Node
 
-trait Source<T> {
+interface Source<T> {
     fun f() : T
 }
 fun <T, S : Source<T>> S.woo() : T = this.f()
diff --git a/compiler/testData/diagnostics/tests/inference/constraints/notNullConstraintOnNullableType.kt b/compiler/testData/diagnostics/tests/inference/constraints/notNullConstraintOnNullableType.kt
index 901e59115a4..ebb32733fdf 100644
--- a/compiler/testData/diagnostics/tests/inference/constraints/notNullConstraintOnNullableType.kt
+++ b/compiler/testData/diagnostics/tests/inference/constraints/notNullConstraintOnNullableType.kt
@@ -1,9 +1,9 @@
 // !CHECK_TYPE
-trait A<T>
+interface A<T>
 
-trait In<in T>
+interface In<in T>
 
-trait Out<out T>
+interface Out<out T>
 
 fun <T: Any> doT(t: T?): T = throw Exception("$t")
 fun <T: Any> doOut(o: Out<T?>): T { throw Exception("$o") }
diff --git a/compiler/testData/diagnostics/tests/inference/constraints/subtypeConstraintOnNullableType.kt b/compiler/testData/diagnostics/tests/inference/constraints/subtypeConstraintOnNullableType.kt
index 20e5c1b5d74..c9466330f55 100644
--- a/compiler/testData/diagnostics/tests/inference/constraints/subtypeConstraintOnNullableType.kt
+++ b/compiler/testData/diagnostics/tests/inference/constraints/subtypeConstraintOnNullableType.kt
@@ -1,8 +1,8 @@
 // !DIAGNOSTICS: -BASE_WITH_NULLABLE_UPPER_BOUND
 // !CHECK_TYPE
-trait A<T>
+interface A<T>
 
-trait Out<out T>
+interface Out<out T>
 
 fun <T> foo(a: A<T>, o: Out<T?>): T = throw Exception("$a $o")
 
diff --git a/compiler/testData/diagnostics/tests/inference/constraints/supertypeConstraintOnNullableType.kt b/compiler/testData/diagnostics/tests/inference/constraints/supertypeConstraintOnNullableType.kt
index f7c98c3d87f..7eb272e4d00 100644
--- a/compiler/testData/diagnostics/tests/inference/constraints/supertypeConstraintOnNullableType.kt
+++ b/compiler/testData/diagnostics/tests/inference/constraints/supertypeConstraintOnNullableType.kt
@@ -1,8 +1,8 @@
 // !DIAGNOSTICS: -BASE_WITH_NULLABLE_UPPER_BOUND
 // !CHECK_TYPE
-trait A<T>
+interface A<T>
 
-trait In<in T>
+interface In<in T>
 
 fun <T> foo(a: A<T>, i: In<T>): T = throw Exception("$a $i")
 
diff --git a/compiler/testData/diagnostics/tests/inference/nestedCalls/binaryExpressions.kt b/compiler/testData/diagnostics/tests/inference/nestedCalls/binaryExpressions.kt
index 0fb771d5223..44e791a7adb 100644
--- a/compiler/testData/diagnostics/tests/inference/nestedCalls/binaryExpressions.kt
+++ b/compiler/testData/diagnostics/tests/inference/nestedCalls/binaryExpressions.kt
@@ -1,10 +1,10 @@
 package h
 
-trait A<T> {}
+interface A<T> {}
 
 fun <T> newA(): A<T> = throw Exception()
 
-trait Z
+interface Z
 
 fun <T> id(t: T): T = t
 
diff --git a/compiler/testData/diagnostics/tests/inference/nestedCalls/completeNestedForVariableAsFunctionCall.kt b/compiler/testData/diagnostics/tests/inference/nestedCalls/completeNestedForVariableAsFunctionCall.kt
index 9525f5ec59f..ee388bc2f2e 100644
--- a/compiler/testData/diagnostics/tests/inference/nestedCalls/completeNestedForVariableAsFunctionCall.kt
+++ b/compiler/testData/diagnostics/tests/inference/nestedCalls/completeNestedForVariableAsFunctionCall.kt
@@ -1,6 +1,6 @@
 package j
 
-trait MyFunc<T> {}
+interface MyFunc<T> {}
 
 class A(val b: B) {
 }
diff --git a/compiler/testData/diagnostics/tests/inference/nestedCalls/makeNullableIfSafeCall.kt b/compiler/testData/diagnostics/tests/inference/nestedCalls/makeNullableIfSafeCall.kt
index fe6ed6b92fc..247b064a19a 100644
--- a/compiler/testData/diagnostics/tests/inference/nestedCalls/makeNullableIfSafeCall.kt
+++ b/compiler/testData/diagnostics/tests/inference/nestedCalls/makeNullableIfSafeCall.kt
@@ -1,11 +1,11 @@
 package a
 
-trait A {
+interface A {
     val b: B
     val nb: B?
 }
 
-trait B {
+interface B {
     fun foo(): Int
 }
 
diff --git a/compiler/testData/diagnostics/tests/inference/opposite.kt b/compiler/testData/diagnostics/tests/inference/opposite.kt
index 8d9a02237b4..842dfeb34d4 100644
--- a/compiler/testData/diagnostics/tests/inference/opposite.kt
+++ b/compiler/testData/diagnostics/tests/inference/opposite.kt
@@ -1,7 +1,7 @@
 package a
 
-trait Persistent
-trait PersistentFactory<T>
+interface Persistent
+interface PersistentFactory<T>
 
 class Relation<Source: Persistent, Target: Persistent>(
         val sources: PersistentFactory<Source>,
diff --git a/compiler/testData/diagnostics/tests/inference/regressions/kt2283.kt b/compiler/testData/diagnostics/tests/inference/regressions/kt2283.kt
index edf1d078551..885332963fc 100644
--- a/compiler/testData/diagnostics/tests/inference/regressions/kt2283.kt
+++ b/compiler/testData/diagnostics/tests/inference/regressions/kt2283.kt
@@ -2,7 +2,7 @@
 package a
 
 
-trait Foo<A>
+interface Foo<A>
 
 fun <A, B> Foo<A>.map(<!UNUSED_PARAMETER!>f<!>: (A) -> B): Foo<B> = object : Foo<B> {}
 
diff --git a/compiler/testData/diagnostics/tests/inference/regressions/kt2320.kt b/compiler/testData/diagnostics/tests/inference/regressions/kt2320.kt
index d4f539a6032..58fd4574321 100644
--- a/compiler/testData/diagnostics/tests/inference/regressions/kt2320.kt
+++ b/compiler/testData/diagnostics/tests/inference/regressions/kt2320.kt
@@ -1,9 +1,9 @@
 //KT-2320 failure of complex case of type inference
 package i
 
-trait NotMap<B>
+interface NotMap<B>
 
-trait Entry<B> {
+interface Entry<B> {
     fun getValue(): B
 }
 
diff --git a/compiler/testData/diagnostics/tests/inference/regressions/kt2505.kt b/compiler/testData/diagnostics/tests/inference/regressions/kt2505.kt
index c29cc4de561..1cf5f033ff8 100644
--- a/compiler/testData/diagnostics/tests/inference/regressions/kt2505.kt
+++ b/compiler/testData/diagnostics/tests/inference/regressions/kt2505.kt
@@ -4,7 +4,7 @@
 
 package a
 
-trait MyType {}
+interface MyType {}
 class MyClass<T> : MyType {}
 
 public open class HttpResponse() {
diff --git a/compiler/testData/diagnostics/tests/inference/regressions/kt2841.kt b/compiler/testData/diagnostics/tests/inference/regressions/kt2841.kt
index a132cc388d9..fc9a779053e 100644
--- a/compiler/testData/diagnostics/tests/inference/regressions/kt2841.kt
+++ b/compiler/testData/diagnostics/tests/inference/regressions/kt2841.kt
@@ -1,6 +1,6 @@
 package a
 
-trait Closeable {}
+interface Closeable {}
 class C : Closeable {}
 
 public inline fun <T: Closeable, R> T.use1(block: (T)-> R) : R {
diff --git a/compiler/testData/diagnostics/tests/inference/regressions/kt2841_it.kt b/compiler/testData/diagnostics/tests/inference/regressions/kt2841_it.kt
index aa0fbcbe7bd..71a2754783b 100644
--- a/compiler/testData/diagnostics/tests/inference/regressions/kt2841_it.kt
+++ b/compiler/testData/diagnostics/tests/inference/regressions/kt2841_it.kt
@@ -1,6 +1,6 @@
 package a
 
-trait Closeable {
+interface Closeable {
     fun close() {}
 }
 
diff --git a/compiler/testData/diagnostics/tests/inference/regressions/kt2841_it_this.kt b/compiler/testData/diagnostics/tests/inference/regressions/kt2841_it_this.kt
index 988a80d322a..0ddd3367e39 100644
--- a/compiler/testData/diagnostics/tests/inference/regressions/kt2841_it_this.kt
+++ b/compiler/testData/diagnostics/tests/inference/regressions/kt2841_it_this.kt
@@ -1,6 +1,6 @@
 package a
 
-trait Closeable {
+interface Closeable {
     fun close() {}
 }
 
diff --git a/compiler/testData/diagnostics/tests/inference/regressions/kt2841_this.kt b/compiler/testData/diagnostics/tests/inference/regressions/kt2841_this.kt
index 1eb4c5f5808..ad85125cb40 100644
--- a/compiler/testData/diagnostics/tests/inference/regressions/kt2841_this.kt
+++ b/compiler/testData/diagnostics/tests/inference/regressions/kt2841_this.kt
@@ -1,6 +1,6 @@
 package a
 
-trait Closeable {
+interface Closeable {
     fun close() {}
 }
 
diff --git a/compiler/testData/diagnostics/tests/inference/regressions/kt2842.kt b/compiler/testData/diagnostics/tests/inference/regressions/kt2842.kt
index 14aea41848c..cfaf66d57b6 100644
--- a/compiler/testData/diagnostics/tests/inference/regressions/kt2842.kt
+++ b/compiler/testData/diagnostics/tests/inference/regressions/kt2842.kt
@@ -1,6 +1,6 @@
 package c
 
-trait A<T>
+interface A<T>
 
 fun test(a: A<Int>?) {
     a<!UNSAFE_CALL!>.<!>foo() //no error
diff --git a/compiler/testData/diagnostics/tests/inference/regressions/kt3301.kt b/compiler/testData/diagnostics/tests/inference/regressions/kt3301.kt
index 32fcb64bfb3..7352d758547 100644
--- a/compiler/testData/diagnostics/tests/inference/regressions/kt3301.kt
+++ b/compiler/testData/diagnostics/tests/inference/regressions/kt3301.kt
@@ -2,8 +2,8 @@
 
 package arrays
 
-trait A
-trait B
+interface A
+interface B
 
 object CAB : A, B
 object DAB : A, B
diff --git a/compiler/testData/diagnostics/tests/inference/reportingImprovements/NoAmbiguityForDifferentFunctionTypes.kt b/compiler/testData/diagnostics/tests/inference/reportingImprovements/NoAmbiguityForDifferentFunctionTypes.kt
index 235b80dd691..7d177138b51 100644
--- a/compiler/testData/diagnostics/tests/inference/reportingImprovements/NoAmbiguityForDifferentFunctionTypes.kt
+++ b/compiler/testData/diagnostics/tests/inference/reportingImprovements/NoAmbiguityForDifferentFunctionTypes.kt
@@ -1,6 +1,6 @@
 package a
 
-trait Closeable {}
+interface Closeable {}
 class C : Closeable {}
 
 fun <T: Closeable, R> T.foo(block: (T)-> R) = block
diff --git a/compiler/testData/diagnostics/tests/inference/typeInferenceExpectedTypeMismatch.kt b/compiler/testData/diagnostics/tests/inference/typeInferenceExpectedTypeMismatch.kt
index 9ce13d9435a..d6962f5007d 100644
--- a/compiler/testData/diagnostics/tests/inference/typeInferenceExpectedTypeMismatch.kt
+++ b/compiler/testData/diagnostics/tests/inference/typeInferenceExpectedTypeMismatch.kt
@@ -11,14 +11,14 @@ fun newList<S>() : ArrayList<S> {
     return ArrayList<S>()
 }
 
-trait Out<out T>
-trait In<in T>
+interface Out<out T>
+interface In<in T>
 
-trait Two<T, R>
+interface Two<T, R>
 
-trait A
-trait B: A
-trait C: A
+interface A
+interface B: A
+interface C: A
 
 fun <T, R> foo(o: Out<T>, i: In<R>): Two<T, R> = throw Exception("$o $i")
 
diff --git a/compiler/testData/diagnostics/tests/inference/upperBounds/doNotInferFromBoundsOnly.kt b/compiler/testData/diagnostics/tests/inference/upperBounds/doNotInferFromBoundsOnly.kt
index a663002f8d0..1e5cd3be0e3 100644
--- a/compiler/testData/diagnostics/tests/inference/upperBounds/doNotInferFromBoundsOnly.kt
+++ b/compiler/testData/diagnostics/tests/inference/upperBounds/doNotInferFromBoundsOnly.kt
@@ -1,6 +1,6 @@
 package a
 
-trait A
+interface A
 
 fun <T> emptyList(): List<T> = throw Exception()
 
diff --git a/compiler/testData/diagnostics/tests/inference/upperBounds/intersectUpperBounds.kt b/compiler/testData/diagnostics/tests/inference/upperBounds/intersectUpperBounds.kt
index 7a340945d98..1d727a2feb2 100644
--- a/compiler/testData/diagnostics/tests/inference/upperBounds/intersectUpperBounds.kt
+++ b/compiler/testData/diagnostics/tests/inference/upperBounds/intersectUpperBounds.kt
@@ -2,11 +2,11 @@
 
 package s
 
-trait In<in T>
+interface In<in T>
 
-trait A
-trait B
-trait C: A, B
+interface A
+interface B
+interface C: A, B
 
 fun <T> foo(in1: In<T>, in2: In<T>): T = throw Exception("$in1 $in2")
 
diff --git a/compiler/testData/diagnostics/tests/inference/upperBounds/nonNullUpperBound.kt b/compiler/testData/diagnostics/tests/inference/upperBounds/nonNullUpperBound.kt
index 92dcd5508bf..21379475c41 100644
--- a/compiler/testData/diagnostics/tests/inference/upperBounds/nonNullUpperBound.kt
+++ b/compiler/testData/diagnostics/tests/inference/upperBounds/nonNullUpperBound.kt
@@ -4,7 +4,7 @@ fun <T: Any> foo(v: Any): T? = unescape(v)
 
 //--------------
 
-trait A
+interface A
 
 fun <R : A> unescapeA(value: Any): R? = throw Exception("$value")
 
diff --git a/compiler/testData/diagnostics/tests/inline/nonVirtualMembersWithInline.kt b/compiler/testData/diagnostics/tests/inline/nonVirtualMembersWithInline.kt
index 4a2765e39a7..c3a09923a59 100644
--- a/compiler/testData/diagnostics/tests/inline/nonVirtualMembersWithInline.kt
+++ b/compiler/testData/diagnostics/tests/inline/nonVirtualMembersWithInline.kt
@@ -27,7 +27,7 @@ abstract class A {
 }
 
 
-trait B {
+interface B {
 
     inline private fun good1() {}
     inline public final fun good2() {}
diff --git a/compiler/testData/diagnostics/tests/inner/deepInnerClass.kt b/compiler/testData/diagnostics/tests/inner/deepInnerClass.kt
index 715960984f0..0ca1ab2dad2 100644
--- a/compiler/testData/diagnostics/tests/inner/deepInnerClass.kt
+++ b/compiler/testData/diagnostics/tests/inner/deepInnerClass.kt
@@ -1,4 +1,4 @@
-trait P<U, Y>
+interface P<U, Y>
 
 class A<T> {
     class B {
diff --git a/compiler/testData/diagnostics/tests/inner/extensionLambdaInsideNestedClass.kt b/compiler/testData/diagnostics/tests/inner/extensionLambdaInsideNestedClass.kt
index da5f275fa8e..556cf1985ee 100644
--- a/compiler/testData/diagnostics/tests/inner/extensionLambdaInsideNestedClass.kt
+++ b/compiler/testData/diagnostics/tests/inner/extensionLambdaInsideNestedClass.kt
@@ -22,6 +22,6 @@ class B {
 
 open class Request(private val handler: ActionContext.() -> Unit) {}
 
-trait ActionContext {
+interface ActionContext {
     val session : Map<String, String>
 }
\ No newline at end of file
diff --git a/compiler/testData/diagnostics/tests/inner/illegalModifier.kt b/compiler/testData/diagnostics/tests/inner/illegalModifier.kt
index dc22042df29..340d6175aa8 100644
--- a/compiler/testData/diagnostics/tests/inner/illegalModifier.kt
+++ b/compiler/testData/diagnostics/tests/inner/illegalModifier.kt
@@ -2,12 +2,12 @@
 <!ILLEGAL_MODIFIER!>inner<!> val prop = 42
 
 <!ILLEGAL_MODIFIER!>inner<!> class A
-<!ILLEGAL_MODIFIER!>inner<!> trait B
+<!ILLEGAL_MODIFIER!>inner<!> interface B
 <!ILLEGAL_MODIFIER!>inner<!> object C
 
 class D {
     inner class E
-    <!ILLEGAL_MODIFIER!>inner<!> trait F
+    <!ILLEGAL_MODIFIER!>inner<!> interface F
     <!ILLEGAL_MODIFIER!>inner<!> object G
     <!ILLEGAL_MODIFIER!>inner<!> enum class R
     <!ILLEGAL_MODIFIER!>inner<!> annotation class S
@@ -22,7 +22,7 @@ enum class H {
     inner class J
 }
 
-trait K {
+interface K {
     <!INNER_CLASS_IN_TRAIT!>inner<!> class L
 }
 
diff --git a/compiler/testData/diagnostics/tests/inner/innerThisSuper.kt b/compiler/testData/diagnostics/tests/inner/innerThisSuper.kt
index d281a90a3bc..93fec418bc3 100644
--- a/compiler/testData/diagnostics/tests/inner/innerThisSuper.kt
+++ b/compiler/testData/diagnostics/tests/inner/innerThisSuper.kt
@@ -1,4 +1,4 @@
-trait Trait {
+interface Trait {
     fun bar() = 42
 }
 
diff --git a/compiler/testData/diagnostics/tests/inner/localThisSuper.kt b/compiler/testData/diagnostics/tests/inner/localThisSuper.kt
index a2c87bc61e5..ecc13ab9fa8 100644
--- a/compiler/testData/diagnostics/tests/inner/localThisSuper.kt
+++ b/compiler/testData/diagnostics/tests/inner/localThisSuper.kt
@@ -1,4 +1,4 @@
-trait Trait {
+interface Trait {
     fun bar() = 42
 }
 
diff --git a/compiler/testData/diagnostics/tests/inner/nestedClassAccessedViaInstanceReference.kt b/compiler/testData/diagnostics/tests/inner/nestedClassAccessedViaInstanceReference.kt
index 95b3b9e8619..1bf30bf8e15 100644
--- a/compiler/testData/diagnostics/tests/inner/nestedClassAccessedViaInstanceReference.kt
+++ b/compiler/testData/diagnostics/tests/inner/nestedClassAccessedViaInstanceReference.kt
@@ -1,4 +1,4 @@
-trait N { fun foo() = 1 }
+interface N { fun foo() = 1 }
 
 class WithClassObject {
     companion object {}
diff --git a/compiler/testData/diagnostics/tests/inner/outerProtectedMember.kt b/compiler/testData/diagnostics/tests/inner/outerProtectedMember.kt
index f296afce973..5f0064e9227 100644
--- a/compiler/testData/diagnostics/tests/inner/outerProtectedMember.kt
+++ b/compiler/testData/diagnostics/tests/inner/outerProtectedMember.kt
@@ -1,6 +1,6 @@
 // KT-2100
 
-trait I {
+interface I {
     val x : String
 }
 
diff --git a/compiler/testData/diagnostics/tests/inner/traits.kt b/compiler/testData/diagnostics/tests/inner/traits.kt
index 22ae17ed3c0..7135bf91889 100644
--- a/compiler/testData/diagnostics/tests/inner/traits.kt
+++ b/compiler/testData/diagnostics/tests/inner/traits.kt
@@ -1,11 +1,11 @@
 // KT-1188
 
-trait Foo {
+interface Foo {
     val b : Bar
     val b1 : Foo.Bar
-    trait Bar {}
+    interface Bar {}
 }
 
-trait Foo2 : Foo {
+interface Foo2 : Foo {
     val bb1 : Foo.Bar
 }
diff --git a/compiler/testData/diagnostics/tests/j+k/GenericsInSupertypes.kt b/compiler/testData/diagnostics/tests/j+k/GenericsInSupertypes.kt
index be3e53a03ab..4c9969aaa63 100644
--- a/compiler/testData/diagnostics/tests/j+k/GenericsInSupertypes.kt
+++ b/compiler/testData/diagnostics/tests/j+k/GenericsInSupertypes.kt
@@ -9,7 +9,7 @@ public interface G<TG> {
 
 package p;
 
-public trait A<TA> {
+public interface A<TA> {
     fun foo(p: A<TA>)
 }
 
diff --git a/compiler/testData/diagnostics/tests/j+k/InnerClassFromJava.kt b/compiler/testData/diagnostics/tests/j+k/InnerClassFromJava.kt
index 674063ec398..cb9f85d3466 100644
--- a/compiler/testData/diagnostics/tests/j+k/InnerClassFromJava.kt
+++ b/compiler/testData/diagnostics/tests/j+k/InnerClassFromJava.kt
@@ -5,12 +5,12 @@ public interface I extends Boo {
 }
 
 // FILE: Baz.kt
-public trait Foo {
+public interface Foo {
     companion object {
         public val EMPTY: Foo = object : Foo{}
     }
 }
 
-trait Boo
+interface Boo
 
 public class Baz : Bar.I
\ No newline at end of file
diff --git a/compiler/testData/diagnostics/tests/j+k/kt6720_abstractProperty.kt b/compiler/testData/diagnostics/tests/j+k/kt6720_abstractProperty.kt
index b406a3a6ffc..f092b608f92 100644
--- a/compiler/testData/diagnostics/tests/j+k/kt6720_abstractProperty.kt
+++ b/compiler/testData/diagnostics/tests/j+k/kt6720_abstractProperty.kt
@@ -1,6 +1,6 @@
 // FILE: AC.kt
 
-trait A {
+interface A {
     val a: Int
 }
 
diff --git a/compiler/testData/diagnostics/tests/j+k/traitDefaultCall.kt b/compiler/testData/diagnostics/tests/j+k/traitDefaultCall.kt
index 3ea6f225197..3ee1de5aa45 100644
--- a/compiler/testData/diagnostics/tests/j+k/traitDefaultCall.kt
+++ b/compiler/testData/diagnostics/tests/j+k/traitDefaultCall.kt
@@ -6,7 +6,7 @@ public interface Test {
 }
 
 // FILE: test.kt
-trait KTrait : Test {
+interface KTrait : Test {
     fun ktest() {
         <!TRAIT_CANT_CALL_DEFAULT_METHOD_VIA_SUPER!>super.test()<!>
 
diff --git a/compiler/testData/diagnostics/tests/labels/labelReferencesInsideObjectExpressions.kt b/compiler/testData/diagnostics/tests/labels/labelReferencesInsideObjectExpressions.kt
index 1ed711d3d89..a1c0881c106 100644
--- a/compiler/testData/diagnostics/tests/labels/labelReferencesInsideObjectExpressions.kt
+++ b/compiler/testData/diagnostics/tests/labels/labelReferencesInsideObjectExpressions.kt
@@ -1,8 +1,8 @@
-trait A {
+interface A {
     fun foo()
 }
 
-trait B {
+interface B {
     fun bar()
 }
 
diff --git a/compiler/testData/diagnostics/tests/modifiers/IllegalModifiers.kt b/compiler/testData/diagnostics/tests/modifiers/IllegalModifiers.kt
index 5d4790d90d0..2b7bdc8e2d9 100644
--- a/compiler/testData/diagnostics/tests/modifiers/IllegalModifiers.kt
+++ b/compiler/testData/diagnostics/tests/modifiers/IllegalModifiers.kt
@@ -10,7 +10,7 @@ abstract class A() {
     <!ILLEGAL_MODIFIER!>abstract<!> protected set
 }
 
-<!TRAIT_CAN_NOT_BE_FINAL!>final<!> trait T {}
+<!TRAIT_CAN_NOT_BE_FINAL!>final<!> interface T {}
 
 class FinalClass() {
     <!NON_FINAL_MEMBER_IN_FINAL_CLASS!>open<!> fun foo() {}
diff --git a/compiler/testData/diagnostics/tests/modifiers/defaultModifier.kt b/compiler/testData/diagnostics/tests/modifiers/defaultModifier.kt
index 29a2a6e2848..0b2d020f1f6 100644
--- a/compiler/testData/diagnostics/tests/modifiers/defaultModifier.kt
+++ b/compiler/testData/diagnostics/tests/modifiers/defaultModifier.kt
@@ -27,7 +27,7 @@ class D {
     <!COMPANION_OBJECT_NOT_ALLOWED!>companion<!> object
 }
 
-<!ILLEGAL_MODIFIER!>companion<!> trait H {
+<!ILLEGAL_MODIFIER!>companion<!> interface H {
     companion object
 }
 
diff --git a/compiler/testData/diagnostics/tests/modifiers/incompatibleVarianceModifiers.kt b/compiler/testData/diagnostics/tests/modifiers/incompatibleVarianceModifiers.kt
index 65a6b0a5938..7902c43d96f 100644
--- a/compiler/testData/diagnostics/tests/modifiers/incompatibleVarianceModifiers.kt
+++ b/compiler/testData/diagnostics/tests/modifiers/incompatibleVarianceModifiers.kt
@@ -1,8 +1,8 @@
 // !DIAGNOSTICS: -UNUSED_VARIABLE
 
-trait Foo<T>
-trait Foo1<<!INCOMPATIBLE_MODIFIERS!>in<!> <!INCOMPATIBLE_MODIFIERS!>out<!> T>
-trait Foo2<<!REPEATED_MODIFIER!>in<!> <!REPEATED_MODIFIER!>in<!> T>
+interface Foo<T>
+interface Foo1<<!INCOMPATIBLE_MODIFIERS!>in<!> <!INCOMPATIBLE_MODIFIERS!>out<!> T>
+interface Foo2<<!REPEATED_MODIFIER!>in<!> <!REPEATED_MODIFIER!>in<!> T>
 
 fun test1(foo: Foo<<!INCOMPATIBLE_MODIFIERS!>in<!> <!INCOMPATIBLE_MODIFIERS!>out<!> Int>) = foo
 fun test2(): Foo<<!REPEATED_MODIFIER!>in<!> <!REPEATED_MODIFIER!>in<!> Int> = throw Exception()
diff --git a/compiler/testData/diagnostics/tests/multimodule/duplicateClass/duplicateSuperClass.kt b/compiler/testData/diagnostics/tests/multimodule/duplicateClass/duplicateSuperClass.kt
index 1c7c0c25f5f..73f4f212412 100644
--- a/compiler/testData/diagnostics/tests/multimodule/duplicateClass/duplicateSuperClass.kt
+++ b/compiler/testData/diagnostics/tests/multimodule/duplicateClass/duplicateSuperClass.kt
@@ -4,7 +4,7 @@
 
 package p
 
-public trait A
+public interface A
 public class B : A
 public class M1 {
     public val b: B = B()
@@ -15,7 +15,7 @@ public class M1 {
 
 package p
 
-public trait A
+public interface A
 
 public fun foo(a: A) {
 }
diff --git a/compiler/testData/diagnostics/tests/multimodule/duplicateClass/genericSuperClass.kt b/compiler/testData/diagnostics/tests/multimodule/duplicateClass/genericSuperClass.kt
index f314f262fbb..69e03860965 100644
--- a/compiler/testData/diagnostics/tests/multimodule/duplicateClass/genericSuperClass.kt
+++ b/compiler/testData/diagnostics/tests/multimodule/duplicateClass/genericSuperClass.kt
@@ -4,9 +4,9 @@
 
 package p
 
-public trait A<T>
-public trait C
-public trait D<T>
+public interface A<T>
+public interface C
+public interface D<T>
 public class B : A<Int>, C, D<Int>
 public class M1 {
     public val b: B = B()
@@ -17,9 +17,9 @@ public class M1 {
 
 package p
 
-public trait A
-public trait C<T>
-public trait D<T>
+public interface A
+public interface C<T>
+public interface D<T>
 
 public fun a(a: A) {
 }
diff --git a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/classGenericsInParams.kt b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/classGenericsInParams.kt
index f655228dd2e..0e18c8328c5 100644
--- a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/classGenericsInParams.kt
+++ b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/classGenericsInParams.kt
@@ -4,7 +4,7 @@
 // FILE: a.kt
 package p
 
-public trait B<T> {
+public interface B<T> {
     public fun foo(a: T)
 }
 
@@ -12,7 +12,7 @@ public trait B<T> {
 // FILE: b.kt
 package p
 
-public trait C<X> : B<X> {
+public interface C<X> : B<X> {
     override fun foo(a: X)
 
 }
@@ -21,7 +21,7 @@ public trait C<X> : B<X> {
 // FILE: b.kt
 package p
 
-public trait B<T> {
+public interface B<T> {
     public fun foo(a: T)
 }
 
diff --git a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/classGenericsInParamsBoundMismatch.kt b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/classGenericsInParamsBoundMismatch.kt
index 64a88dd85f3..c5517ab355e 100644
--- a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/classGenericsInParamsBoundMismatch.kt
+++ b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/classGenericsInParamsBoundMismatch.kt
@@ -4,7 +4,7 @@
 // FILE: a.kt
 package p
 
-public trait B<T> {
+public interface B<T> {
     public fun foo(a: T?)
 }
 
@@ -12,7 +12,7 @@ public trait B<T> {
 // FILE: b.kt
 package p
 
-public trait C<X> : B<X> {
+public interface C<X> : B<X> {
     override fun foo(a: X?)
 
 }
@@ -21,9 +21,9 @@ public trait C<X> : B<X> {
 // FILE: b.kt
 package p
 
-public trait Tr
+public interface Tr
 
-public trait B<T: Tr?> {
+public interface B<T: Tr?> {
     public fun foo(a: T?)
 }
 
diff --git a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/classGenericsInParamsIndexMismatch.kt b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/classGenericsInParamsIndexMismatch.kt
index bd30e5bc977..4616eec5f97 100644
--- a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/classGenericsInParamsIndexMismatch.kt
+++ b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/classGenericsInParamsIndexMismatch.kt
@@ -4,7 +4,7 @@
 // FILE: a.kt
 package p
 
-public trait B<T, _> {
+public interface B<T, _> {
     public fun foo(a: T?)
 }
 
@@ -12,7 +12,7 @@ public trait B<T, _> {
 // FILE: b.kt
 package p
 
-public trait C<X, _> : B<X, _> {
+public interface C<X, _> : B<X, _> {
     override fun foo(a: X?)
 
 }
@@ -21,7 +21,7 @@ public trait C<X, _> : B<X, _> {
 // FILE: b.kt
 package p
 
-public trait B<_, T> {
+public interface B<_, T> {
     public fun foo(a: T?)
 }
 
diff --git a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/classGenericsInParamsNameMismatch.kt b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/classGenericsInParamsNameMismatch.kt
index 09ea2e65ce8..29319ea33d2 100644
--- a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/classGenericsInParamsNameMismatch.kt
+++ b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/classGenericsInParamsNameMismatch.kt
@@ -4,7 +4,7 @@
 // FILE: a.kt
 package p
 
-public trait B<T> {
+public interface B<T> {
     public fun foo(a: T)
 }
 
@@ -12,7 +12,7 @@ public trait B<T> {
 // FILE: b.kt
 package p
 
-public trait C<X> : B<X> {
+public interface C<X> : B<X> {
     override fun foo(a: X)
 
 }
@@ -21,7 +21,7 @@ public trait C<X> : B<X> {
 // FILE: b.kt
 package p
 
-public trait B<T1> {
+public interface B<T1> {
     public fun foo(a: T1)
 }
 
diff --git a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/classGenericsInReturnType.kt b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/classGenericsInReturnType.kt
index 5ed12f3a289..c34bad8053e 100644
--- a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/classGenericsInReturnType.kt
+++ b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/classGenericsInReturnType.kt
@@ -4,7 +4,7 @@
 // FILE: a.kt
 package p
 
-public trait B<T> {
+public interface B<T> {
     public fun foo(): T
 }
 
@@ -12,7 +12,7 @@ public trait B<T> {
 // FILE: b.kt
 package p
 
-public trait C<X> : B<X> {
+public interface C<X> : B<X> {
     override fun foo(): X
 
 }
@@ -21,7 +21,7 @@ public trait C<X> : B<X> {
 // FILE: b.kt
 package p
 
-public trait B<T> {
+public interface B<T> {
     public fun foo(): T
 }
 
diff --git a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/classVsFunctionGenericsInParamsMismatch.kt b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/classVsFunctionGenericsInParamsMismatch.kt
index 46478cdea13..10e5ac41d46 100644
--- a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/classVsFunctionGenericsInParamsMismatch.kt
+++ b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/classVsFunctionGenericsInParamsMismatch.kt
@@ -2,7 +2,7 @@
 // FILE: a.kt
 package p
 
-public trait B<T> {
+public interface B<T> {
     public fun <R> foo(a: T, b : R)
 }
 
@@ -10,7 +10,7 @@ public trait B<T> {
 // FILE: b.kt
 package p
 
-public trait C : B<Any?> {
+public interface C : B<Any?> {
     override fun <R> foo(a: Any?, b : R)
 
 }
@@ -19,7 +19,7 @@ public trait C : B<Any?> {
 // FILE: b.kt
 package p
 
-public trait B {
+public interface B {
     public fun <T, R> foo(a: T, b: R)
 }
 
diff --git a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/covariantReturnTypes.kt b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/covariantReturnTypes.kt
index 4ae00f94b8c..526164bc3fb 100644
--- a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/covariantReturnTypes.kt
+++ b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/covariantReturnTypes.kt
@@ -4,7 +4,7 @@
 // FILE: a.kt
 package p
 
-public trait B {
+public interface B {
     public fun getParent(): B?
 }
 
@@ -12,7 +12,7 @@ public trait B {
 // FILE: b.kt
 package p
 
-public trait C : B {
+public interface C : B {
     override fun getParent(): B?
 
 }
@@ -21,7 +21,7 @@ public trait C : B {
 // FILE: b.kt
 package p
 
-public trait B {
+public interface B {
     public fun getParent(): Any?
 }
 
diff --git a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/differenceInParamNames.kt b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/differenceInParamNames.kt
index 2c886b60d7f..8216b3b3826 100644
--- a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/differenceInParamNames.kt
+++ b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/differenceInParamNames.kt
@@ -4,7 +4,7 @@
 // FILE: a.kt
 package p
 
-public trait B {
+public interface B {
     public fun foo(a: Int, b: String): B?
 }
 
@@ -12,7 +12,7 @@ public trait B {
 // FILE: b.kt
 package p
 
-public trait C : B {
+public interface C : B {
     override fun foo(a: Int, b: String): B?
 
 }
@@ -21,7 +21,7 @@ public trait C : B {
 // FILE: b.kt
 package p
 
-public trait B {
+public interface B {
     public fun foo(a1: Int, b1: String): B?
 }
 
diff --git a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/differentGenericsInParams.kt b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/differentGenericsInParams.kt
index dd765ec7db5..de288240c3e 100644
--- a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/differentGenericsInParams.kt
+++ b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/differentGenericsInParams.kt
@@ -4,14 +4,14 @@
 // FILE: a.kt
 package p
 
-public trait G1<T>
-public trait G2<A, B>
+public interface G1<T>
+public interface G2<A, B>
 
 // MODULE: m1(m0)
 // FILE: a.kt
 package p
 
-public trait B {
+public interface B {
     public fun foo(a: G1<Int>?, b: G2<B, String>?)
 }
 
@@ -19,7 +19,7 @@ public trait B {
 // FILE: b.kt
 package p
 
-public trait C : B {
+public interface C : B {
     override fun foo(a: G1<Int>?, b: G2<B, String>?)
 
 }
@@ -28,7 +28,7 @@ public trait C : B {
 // FILE: b.kt
 package p
 
-public trait B {
+public interface B {
     public fun foo(a: G1<out Any?>?, b: G2<Int, out Any?>?)
 }
 
diff --git a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/differentNumberOfParams.kt b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/differentNumberOfParams.kt
index 6384bf6263c..10ed61a7b4a 100644
--- a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/differentNumberOfParams.kt
+++ b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/differentNumberOfParams.kt
@@ -2,7 +2,7 @@
 // FILE: a.kt
 package p
 
-public trait B {
+public interface B {
     public fun foo(a: Int, b: String): B?
 }
 
@@ -10,7 +10,7 @@ public trait B {
 // FILE: b.kt
 package p
 
-public trait C : B {
+public interface C : B {
     override fun foo(a: Int, b: String): B?
 
 }
@@ -19,7 +19,7 @@ public trait C : B {
 // FILE: b.kt
 package p
 
-public trait B {
+public interface B {
     public fun foo(a: Int, b: String, c: Int = 0): B?
 }
 
diff --git a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/differentReturnTypes.kt b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/differentReturnTypes.kt
index 2d8d73cafb0..c5a2ae6e589 100644
--- a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/differentReturnTypes.kt
+++ b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/differentReturnTypes.kt
@@ -4,7 +4,7 @@
 // FILE: a.kt
 package p
 
-public trait B {
+public interface B {
     public fun getParent(): B?
 }
 
@@ -12,7 +12,7 @@ public trait B {
 // FILE: b.kt
 package p
 
-public trait C : B {
+public interface C : B {
     override fun getParent(): B?
 
 }
@@ -21,7 +21,7 @@ public trait C : B {
 // FILE: b.kt
 package p
 
-public trait B {
+public interface B {
     public fun getParent(): Int
 }
 
diff --git a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/extensionMatch.kt b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/extensionMatch.kt
index 1aa5dc3c464..ca4e7ae7fc1 100644
--- a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/extensionMatch.kt
+++ b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/extensionMatch.kt
@@ -4,7 +4,7 @@
 // FILE: a.kt
 package p
 
-public trait B {
+public interface B {
     public fun String.getParent(): B?
 }
 
@@ -21,7 +21,7 @@ public class C : B {
 // FILE: b.kt
 package p
 
-public trait B {
+public interface B {
     public fun String.getParent(): B?
 }
 
diff --git a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/functionGenericsInParams.kt b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/functionGenericsInParams.kt
index b54c491a2c3..5a77fca6ea8 100644
--- a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/functionGenericsInParams.kt
+++ b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/functionGenericsInParams.kt
@@ -4,7 +4,7 @@
 // FILE: a.kt
 package p
 
-public trait B {
+public interface B {
     public fun <T> foo(a: T): B?
 }
 
@@ -12,7 +12,7 @@ public trait B {
 // FILE: b.kt
 package p
 
-public trait C : B {
+public interface C : B {
     override fun <T> foo(a: T): B?
 
 }
@@ -21,7 +21,7 @@ public trait C : B {
 // FILE: b.kt
 package p
 
-public trait B {
+public interface B {
     public fun <T> foo(a: T): B?
 }
 
diff --git a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/functionGenericsInParamsBoundsMismatch.kt b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/functionGenericsInParamsBoundsMismatch.kt
index 11e29337334..cba582efada 100644
--- a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/functionGenericsInParamsBoundsMismatch.kt
+++ b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/functionGenericsInParamsBoundsMismatch.kt
@@ -4,7 +4,7 @@
 // FILE: a.kt
 package p
 
-public trait B {
+public interface B {
     public fun <T> foo(a: T): B?
 }
 
@@ -12,7 +12,7 @@ public trait B {
 // FILE: b.kt
 package p
 
-public trait C : B {
+public interface C : B {
     override fun <T> foo(a: T): B?
 
 }
@@ -21,9 +21,9 @@ public trait C : B {
 // FILE: b.kt
 package p
 
-public trait Tr
+public interface Tr
 
-public trait B {
+public interface B {
     public fun <T: Tr?> foo(a: T): B?
 }
 
diff --git a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/functionGenericsInParamsEqNull.kt b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/functionGenericsInParamsEqNull.kt
index fd4333fa1f0..664571d7d31 100644
--- a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/functionGenericsInParamsEqNull.kt
+++ b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/functionGenericsInParamsEqNull.kt
@@ -4,7 +4,7 @@
 // FILE: a.kt
 package p
 
-public trait B {
+public interface B {
     public fun <T> foo(a: T): B?
 }
 
@@ -12,7 +12,7 @@ public trait B {
 // FILE: b.kt
 package p
 
-public trait C : B {
+public interface C : B {
     override fun <T> foo(a: T): B?
 
 }
@@ -21,7 +21,7 @@ public trait C : B {
 // FILE: b.kt
 package p
 
-public trait B {
+public interface B {
     public fun <T> foo(a: T): B?
 }
 
diff --git a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/functionGenericsInParamsNotIs.kt b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/functionGenericsInParamsNotIs.kt
index dfe50080dbb..fbee8deeebb 100644
--- a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/functionGenericsInParamsNotIs.kt
+++ b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/functionGenericsInParamsNotIs.kt
@@ -4,7 +4,7 @@
 // FILE: a.kt
 package p
 
-public trait B {
+public interface B {
     public fun <T> foo(a: T): B?
 }
 
@@ -12,7 +12,7 @@ public trait B {
 // FILE: b.kt
 package p
 
-public trait C : B {
+public interface C : B {
     override fun <T> foo(a: T): B?
 
 }
@@ -21,7 +21,7 @@ public trait C : B {
 // FILE: b.kt
 package p
 
-public trait B {
+public interface B {
     public fun <T> foo(a: T): B?
 }
 
diff --git a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/functionGenericsInParamsReturnFooT.kt b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/functionGenericsInParamsReturnFooT.kt
index b2bb4cf53f0..eedb07f2980 100644
--- a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/functionGenericsInParamsReturnFooT.kt
+++ b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/functionGenericsInParamsReturnFooT.kt
@@ -4,9 +4,9 @@
 // FILE: a.kt
 package p
 
-public trait Foo<T>
+public interface Foo<T>
 
-public trait B {
+public interface B {
     public fun <T> foo(a: T): Foo<T>
 }
 
@@ -14,7 +14,7 @@ public trait B {
 // FILE: b.kt
 package p
 
-public trait C : B {
+public interface C : B {
     override fun <T> foo(a: T): Foo<T>
 
 }
@@ -23,9 +23,9 @@ public trait C : B {
 // FILE: b.kt
 package p
 
-public trait Foo<T>
+public interface Foo<T>
 
-public trait B {
+public interface B {
     public fun <T> foo(a: T): Foo<T>
 }
 
diff --git a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/functionGenericsInParamsReturnT.kt b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/functionGenericsInParamsReturnT.kt
index 0dc4ae48a59..41dc5643fc5 100644
--- a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/functionGenericsInParamsReturnT.kt
+++ b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/functionGenericsInParamsReturnT.kt
@@ -4,7 +4,7 @@
 // FILE: a.kt
 package p
 
-public trait B {
+public interface B {
     public fun <T> foo(a: T): T
 }
 
@@ -12,7 +12,7 @@ public trait B {
 // FILE: b.kt
 package p
 
-public trait C : B {
+public interface C : B {
     override fun <T> foo(a: T): T
 
 }
@@ -21,7 +21,7 @@ public trait C : B {
 // FILE: b.kt
 package p
 
-public trait B {
+public interface B {
     public fun <T> foo(a: T): T
 }
 
diff --git a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/noGenericsInParams.kt b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/noGenericsInParams.kt
index 51e6d8c4210..84cbfb3e873 100644
--- a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/noGenericsInParams.kt
+++ b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/noGenericsInParams.kt
@@ -3,7 +3,7 @@
 // FILE: a.kt
 package p
 
-public trait B {
+public interface B {
     public fun foo(a: Int, b: String): B?
 }
 
@@ -11,7 +11,7 @@ public trait B {
 // FILE: b.kt
 package p
 
-public trait C : B {
+public interface C : B {
     override fun foo(a: Int, b: String): B?
 
 }
@@ -20,7 +20,7 @@ public trait C : B {
 // FILE: b.kt
 package p
 
-public trait B {
+public interface B {
     public fun foo(a: Int, b: String): B?
 }
 
diff --git a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/noParams.kt b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/noParams.kt
index b89799a8c1e..93d62b46463 100644
--- a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/noParams.kt
+++ b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/noParams.kt
@@ -4,7 +4,7 @@
 // FILE: a.kt
 package p
 
-public trait B {
+public interface B {
     public fun getParent(): B?
 }
 
@@ -21,7 +21,7 @@ public class C : B {
 // FILE: b.kt
 package p
 
-public trait B {
+public interface B {
     public fun getParent(): B?
 }
 
diff --git a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/sameGenericsInParams.kt b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/sameGenericsInParams.kt
index 2d51f1c54ac..5b09a2c6188 100644
--- a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/sameGenericsInParams.kt
+++ b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/sameGenericsInParams.kt
@@ -4,14 +4,14 @@
 // FILE: a.kt
 package p
 
-public trait G1<T>
-public trait G2<A, B>
+public interface G1<T>
+public interface G2<A, B>
 
 // MODULE: m1(m0)
 // FILE: a.kt
 package p
 
-public trait B {
+public interface B {
     public fun foo(a: G1<Int>, b: G2<B, String>): B?
 }
 
@@ -19,7 +19,7 @@ public trait B {
 // FILE: b.kt
 package p
 
-public trait C : B {
+public interface C : B {
     override fun foo(a: G1<Int>, b: G2<B, String>): B?
 
 }
@@ -28,7 +28,7 @@ public trait C : B {
 // FILE: b.kt
 package p
 
-public trait B {
+public interface B {
     public fun foo(a: G1<Int>, b: G2<B, String>): B?
 }
 
diff --git a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/simpleWithInheritance.kt b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/simpleWithInheritance.kt
index 3b744395658..e91afea2b00 100644
--- a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/simpleWithInheritance.kt
+++ b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/simpleWithInheritance.kt
@@ -2,7 +2,7 @@
 // FILE: a.kt
 package p
 
-public trait B {
+public interface B {
     public fun getParent(): B?
 }
 
@@ -10,7 +10,7 @@ public trait B {
 // FILE: b.kt
 package p
 
-public trait C : B {
+public interface C : B {
     override fun getParent(): B?
 
 }
@@ -19,11 +19,11 @@ public trait C : B {
 // FILE: b.kt
 package p
 
-public trait B {
+public interface B {
     public fun getParent(): B?
 }
 
-public trait D : B {
+public interface D : B {
     override fun getParent(): B?
 }
 
diff --git a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/substitutedGenericInParams.kt b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/substitutedGenericInParams.kt
index 1e1f7af281f..99c243becf6 100644
--- a/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/substitutedGenericInParams.kt
+++ b/compiler/testData/diagnostics/tests/multimodule/duplicateMethod/substitutedGenericInParams.kt
@@ -2,7 +2,7 @@
 // FILE: a.kt
 package p
 
-public trait B<T> {
+public interface B<T> {
     public fun foo(a: T)
 }
 
@@ -10,7 +10,7 @@ public trait B<T> {
 // FILE: b.kt
 package p
 
-public trait C : B<String> {
+public interface C : B<String> {
     override fun foo(a: String)
 
 }
@@ -19,7 +19,7 @@ public trait C : B<String> {
 // FILE: b.kt
 package p
 
-public trait B {
+public interface B {
     public fun foo(a: String)
 }
 
diff --git a/compiler/testData/diagnostics/tests/multimodule/duplicateSuper/differentSuperTraits.kt b/compiler/testData/diagnostics/tests/multimodule/duplicateSuper/differentSuperTraits.kt
index e464dd3e5af..99450485c7a 100644
--- a/compiler/testData/diagnostics/tests/multimodule/duplicateSuper/differentSuperTraits.kt
+++ b/compiler/testData/diagnostics/tests/multimodule/duplicateSuper/differentSuperTraits.kt
@@ -2,26 +2,26 @@
 // FILE: x.kt
 package p
 
-public trait Base {
+public interface Base {
     public fun foo() {}
 }
 
-public trait A : Base {
+public interface A : Base {
     override fun foo() {}
 }
 
-public trait C : A
+public interface C : A
 
 
 // MODULE: m2
 // FILE: x.kt
 package p
 
-public trait Base {
+public interface Base {
     public fun foo() {}
 }
 
-public trait B : Base
+public interface B : Base
 
 // MODULE: m3(m1, m2)
 // FILE: x.kt
diff --git a/compiler/testData/diagnostics/tests/multimodule/duplicateSuper/sameSuperTrait.kt b/compiler/testData/diagnostics/tests/multimodule/duplicateSuper/sameSuperTrait.kt
index beec4542a11..b6d5d833f04 100644
--- a/compiler/testData/diagnostics/tests/multimodule/duplicateSuper/sameSuperTrait.kt
+++ b/compiler/testData/diagnostics/tests/multimodule/duplicateSuper/sameSuperTrait.kt
@@ -2,21 +2,21 @@
 // FILE: x.kt
 package p
 
-public trait Base {
+public interface Base {
     public fun foo() {}
 }
 
-public trait A : Base
+public interface A : Base
 
 // MODULE: m2
 // FILE: x.kt
 package p
 
-public trait Base {
+public interface Base {
     public fun foo() {}
 }
 
-public trait B : Base
+public interface B : Base
 
 // MODULE: m3(m1, m2)
 // FILE: x.kt
diff --git a/compiler/testData/diagnostics/tests/multimodule/duplicateSuper/sameSuperTraitDifferentBounds.kt b/compiler/testData/diagnostics/tests/multimodule/duplicateSuper/sameSuperTraitDifferentBounds.kt
index fe614275034..4c1e52747a4 100644
--- a/compiler/testData/diagnostics/tests/multimodule/duplicateSuper/sameSuperTraitDifferentBounds.kt
+++ b/compiler/testData/diagnostics/tests/multimodule/duplicateSuper/sameSuperTraitDifferentBounds.kt
@@ -2,21 +2,21 @@
 // FILE: x.kt
 package p
 
-public trait Base {
+public interface Base {
     public fun <T> foo(t: Array<T>) {}
 }
 
-public trait A : Base
+public interface A : Base
 
 // MODULE: m2
 // FILE: x.kt
 package p
 
-public trait Base {
+public interface Base {
     public fun <T: Base> foo(t: Array<T>) {}
 }
 
-public trait B : Base
+public interface B : Base
 
 // MODULE: m3(m1, m2)
 // FILE: x.kt
diff --git a/compiler/testData/diagnostics/tests/multimodule/duplicateSuper/sameSuperTraitGenerics.kt b/compiler/testData/diagnostics/tests/multimodule/duplicateSuper/sameSuperTraitGenerics.kt
index ce74602efd8..6fceaf1f9e1 100644
--- a/compiler/testData/diagnostics/tests/multimodule/duplicateSuper/sameSuperTraitGenerics.kt
+++ b/compiler/testData/diagnostics/tests/multimodule/duplicateSuper/sameSuperTraitGenerics.kt
@@ -2,21 +2,21 @@
 // FILE: x.kt
 package p
 
-public trait Base<T> {
+public interface Base<T> {
     public fun foo(t: T) {}
 }
 
-public trait A<T> : Base<T>
+public interface A<T> : Base<T>
 
 // MODULE: m2
 // FILE: x.kt
 package p
 
-public trait Base<T> {
+public interface Base<T> {
     public fun foo(t: T) {}
 }
 
-public trait B : Base<String>
+public interface B : Base<String>
 
 // MODULE: m3(m1, m2)
 // FILE: x.kt
diff --git a/compiler/testData/diagnostics/tests/nullableTypes/redundantNullableInSupertype.kt b/compiler/testData/diagnostics/tests/nullableTypes/redundantNullableInSupertype.kt
index f0958284d4f..5c0780f4e90 100644
--- a/compiler/testData/diagnostics/tests/nullableTypes/redundantNullableInSupertype.kt
+++ b/compiler/testData/diagnostics/tests/nullableTypes/redundantNullableInSupertype.kt
@@ -1,5 +1,5 @@
-trait A
-trait X: A<!NULLABLE_SUPERTYPE!>?<!><!REDUNDANT_NULLABLE!>?<!> {
+interface A
+interface X: A<!NULLABLE_SUPERTYPE!>?<!><!REDUNDANT_NULLABLE!>?<!> {
 
 }
 
diff --git a/compiler/testData/diagnostics/tests/numbers/numbersInSimpleConstraints.kt b/compiler/testData/diagnostics/tests/numbers/numbersInSimpleConstraints.kt
index 181a152ecb4..a80068ed652 100644
--- a/compiler/testData/diagnostics/tests/numbers/numbersInSimpleConstraints.kt
+++ b/compiler/testData/diagnostics/tests/numbers/numbersInSimpleConstraints.kt
@@ -38,7 +38,7 @@ fun test() {
 
 fun use(vararg a: Any?) = a
 
-trait Inv<T>
+interface Inv<T>
 
 fun <T> exactBound(t: T, l: Inv<T>): T = throw Exception("$t $l")
 
@@ -50,7 +50,7 @@ fun testExactBound(invS: Inv<String>, invI: Inv<Int>, invB: Inv<Byte>) {
     b checkType { _<Byte>() }
 }
 
-trait Cov<out T>
+interface Cov<out T>
 
 fun <T> lowerBound(t: T, l : Cov<T>): T = throw Exception("$t $l")
 
@@ -62,7 +62,7 @@ fun testLowerBound(cov: Cov<String>, covN: Cov<Number>) {
     n checkType { _<Number>() }
 }
 
-trait Contr<in T>
+interface Contr<in T>
 
 fun <T> upperBound(t: T, l: Contr<T>): T = throw Exception("$t $l")
 
diff --git a/compiler/testData/diagnostics/tests/objects/objectLiteralExpressionTypeMismatch.kt b/compiler/testData/diagnostics/tests/objects/objectLiteralExpressionTypeMismatch.kt
index 324f54a836c..c33e4d8c577 100644
--- a/compiler/testData/diagnostics/tests/objects/objectLiteralExpressionTypeMismatch.kt
+++ b/compiler/testData/diagnostics/tests/objects/objectLiteralExpressionTypeMismatch.kt
@@ -1,6 +1,6 @@
-trait A
+interface A
 
-trait B
+interface B
 
 fun test1(): B = <!TYPE_MISMATCH!>object : A<!> {
 }
diff --git a/compiler/testData/diagnostics/tests/objects/upperBoundViolated.kt b/compiler/testData/diagnostics/tests/objects/upperBoundViolated.kt
index 20162fc1ec9..7482dad5350 100644
--- a/compiler/testData/diagnostics/tests/objects/upperBoundViolated.kt
+++ b/compiler/testData/diagnostics/tests/objects/upperBoundViolated.kt
@@ -1,4 +1,4 @@
-trait Trait<N : Number>
+interface Trait<N : Number>
 
 object O1 : Trait<Int>
 
diff --git a/compiler/testData/diagnostics/tests/operatorsOverloading/IteratorAmbiguity.kt b/compiler/testData/diagnostics/tests/operatorsOverloading/IteratorAmbiguity.kt
index 43802e11053..82e00331c6d 100644
--- a/compiler/testData/diagnostics/tests/operatorsOverloading/IteratorAmbiguity.kt
+++ b/compiler/testData/diagnostics/tests/operatorsOverloading/IteratorAmbiguity.kt
@@ -1,9 +1,9 @@
 //KT-1821 Write test for ITERATOR_AMBIGUITY diagnostic
 
-trait MyCollectionInterface {
+interface MyCollectionInterface {
 }
 
-trait MyAnotherCollectionInterface {
+interface MyAnotherCollectionInterface {
 }
 
 class MyCollection : MyCollectionInterface, MyAnotherCollectionInterface {
diff --git a/compiler/testData/diagnostics/tests/overload/kt2493.kt b/compiler/testData/diagnostics/tests/overload/kt2493.kt
index 2d8bcf47b24..d3c35d046d3 100644
--- a/compiler/testData/diagnostics/tests/overload/kt2493.kt
+++ b/compiler/testData/diagnostics/tests/overload/kt2493.kt
@@ -1,5 +1,5 @@
-trait A
-trait B
+interface A
+interface B
 
 fun <R: A> R.f() {
 }
diff --git a/compiler/testData/diagnostics/tests/override/AllPrivateFromSuperTypes.kt b/compiler/testData/diagnostics/tests/override/AllPrivateFromSuperTypes.kt
index a2c9376c61b..e92b440e116 100644
--- a/compiler/testData/diagnostics/tests/override/AllPrivateFromSuperTypes.kt
+++ b/compiler/testData/diagnostics/tests/override/AllPrivateFromSuperTypes.kt
@@ -1,6 +1,6 @@
 package test
 
-trait A {
+interface A {
     private val a: String
       get() = "AAAA!"
 }
diff --git a/compiler/testData/diagnostics/tests/override/AllProtectedFromSupertypes.kt b/compiler/testData/diagnostics/tests/override/AllProtectedFromSupertypes.kt
index 9e3a75bf896..7660abbd08e 100644
--- a/compiler/testData/diagnostics/tests/override/AllProtectedFromSupertypes.kt
+++ b/compiler/testData/diagnostics/tests/override/AllProtectedFromSupertypes.kt
@@ -1,6 +1,6 @@
 package test
 
-trait A {
+interface A {
     protected val a: String
 }
 
diff --git a/compiler/testData/diagnostics/tests/override/CannotInferVisibilityForProperty.kt b/compiler/testData/diagnostics/tests/override/CannotInferVisibilityForProperty.kt
index bc5ade515cc..864d1ec4901 100644
--- a/compiler/testData/diagnostics/tests/override/CannotInferVisibilityForProperty.kt
+++ b/compiler/testData/diagnostics/tests/override/CannotInferVisibilityForProperty.kt
@@ -1,13 +1,13 @@
-trait T {
+interface T {
     internal var foo: Long
 }
 
-trait U {
+interface U {
     protected var foo: Long
 }
 
-trait V : T, U {
+interface V : T, U {
     <!CANNOT_INFER_VISIBILITY!>override var foo: Long<!>
 }
 
-trait <!CANNOT_INFER_VISIBILITY!>W<!> : T, U
+interface <!CANNOT_INFER_VISIBILITY!>W<!> : T, U
diff --git a/compiler/testData/diagnostics/tests/override/CannotInferVisibilityForPropertySetter.kt b/compiler/testData/diagnostics/tests/override/CannotInferVisibilityForPropertySetter.kt
index b65e0979cd5..041675041c8 100644
--- a/compiler/testData/diagnostics/tests/override/CannotInferVisibilityForPropertySetter.kt
+++ b/compiler/testData/diagnostics/tests/override/CannotInferVisibilityForPropertySetter.kt
@@ -1,13 +1,13 @@
-trait T {
+interface T {
     public var foo: Short
         internal set
 }
 
-trait U {
+interface U {
     public var foo: Short
         protected set
 }
 
-trait V : T, U {
+interface V : T, U {
     <!CANNOT_INFER_VISIBILITY!>override var foo: Short<!>
 }
diff --git a/compiler/testData/diagnostics/tests/override/DefaultParameterValues-NoErrorsWhenInheritingFromOneTypeTwice.kt b/compiler/testData/diagnostics/tests/override/DefaultParameterValues-NoErrorsWhenInheritingFromOneTypeTwice.kt
index 0c640b509c1..a27d78224ca 100644
--- a/compiler/testData/diagnostics/tests/override/DefaultParameterValues-NoErrorsWhenInheritingFromOneTypeTwice.kt
+++ b/compiler/testData/diagnostics/tests/override/DefaultParameterValues-NoErrorsWhenInheritingFromOneTypeTwice.kt
@@ -1,8 +1,8 @@
-trait Y {
+interface Y {
     fun foo(a : Int = 1)
 }
 
-trait YSub : Y {
+interface YSub : Y {
 
 }
 
diff --git a/compiler/testData/diagnostics/tests/override/Delegation.kt b/compiler/testData/diagnostics/tests/override/Delegation.kt
index c3bbd70a80c..14558ca7464 100644
--- a/compiler/testData/diagnostics/tests/override/Delegation.kt
+++ b/compiler/testData/diagnostics/tests/override/Delegation.kt
@@ -1,18 +1,18 @@
 package test
 
-trait X {
+interface X {
     fun foo(): String? {
         return null
     }
 }
 
-trait Y {
+interface Y {
     fun foo(): String {
         return "foo"
     }
 }
 
-trait Incompatible {
+interface Incompatible {
     fun foo(): Int {
         return 3
     }
diff --git a/compiler/testData/diagnostics/tests/override/DelegationFun.kt b/compiler/testData/diagnostics/tests/override/DelegationFun.kt
index e2236b35b97..b7ff2c55ef7 100644
--- a/compiler/testData/diagnostics/tests/override/DelegationFun.kt
+++ b/compiler/testData/diagnostics/tests/override/DelegationFun.kt
@@ -1,6 +1,6 @@
 package delegation
 
-trait Aaa {
+interface Aaa {
     fun foo()
 }
 
diff --git a/compiler/testData/diagnostics/tests/override/DelegationVal.kt b/compiler/testData/diagnostics/tests/override/DelegationVal.kt
index 076e5775265..7f7a506b5b5 100644
--- a/compiler/testData/diagnostics/tests/override/DelegationVal.kt
+++ b/compiler/testData/diagnostics/tests/override/DelegationVal.kt
@@ -1,6 +1,6 @@
 package delegation
 
-trait Aaa {
+interface Aaa {
     val i: Int
 }
 
diff --git a/compiler/testData/diagnostics/tests/override/DelegationVar.kt b/compiler/testData/diagnostics/tests/override/DelegationVar.kt
index 5b8b34d62be..4c9a70763c1 100644
--- a/compiler/testData/diagnostics/tests/override/DelegationVar.kt
+++ b/compiler/testData/diagnostics/tests/override/DelegationVar.kt
@@ -1,6 +1,6 @@
 package delegation
 
-trait Aaa {
+interface Aaa {
     var i: Int
 }
 
diff --git a/compiler/testData/diagnostics/tests/override/DuplicateMethod.kt b/compiler/testData/diagnostics/tests/override/DuplicateMethod.kt
index aefa4f1673f..15a21f53ec4 100644
--- a/compiler/testData/diagnostics/tests/override/DuplicateMethod.kt
+++ b/compiler/testData/diagnostics/tests/override/DuplicateMethod.kt
@@ -1,4 +1,4 @@
-trait Some {
+interface Some {
     fun test()
 }
 
diff --git a/compiler/testData/diagnostics/tests/override/EqualityOfIntersectionTypes.kt b/compiler/testData/diagnostics/tests/override/EqualityOfIntersectionTypes.kt
index 7f312dd056f..fc35e955bac 100644
--- a/compiler/testData/diagnostics/tests/override/EqualityOfIntersectionTypes.kt
+++ b/compiler/testData/diagnostics/tests/override/EqualityOfIntersectionTypes.kt
@@ -1,7 +1,7 @@
-trait Foo
-trait Bar
+interface Foo
+interface Bar
 
-trait A {
+interface A {
     fun <T> foo()
     where T : Foo, T : Bar
     = Unit
diff --git a/compiler/testData/diagnostics/tests/override/FakeOverrideAbstractAndNonAbstractFun.kt b/compiler/testData/diagnostics/tests/override/FakeOverrideAbstractAndNonAbstractFun.kt
index 4ba1095f8fb..7c8c385152a 100644
--- a/compiler/testData/diagnostics/tests/override/FakeOverrideAbstractAndNonAbstractFun.kt
+++ b/compiler/testData/diagnostics/tests/override/FakeOverrideAbstractAndNonAbstractFun.kt
@@ -2,7 +2,7 @@ open class Ccc() {
     fun foo() = 1
 }
 
-trait Ttt {
+interface Ttt {
     fun foo(): Int
 }
 
diff --git a/compiler/testData/diagnostics/tests/override/FakeOverrideDifferentDeclarationSignatures.kt b/compiler/testData/diagnostics/tests/override/FakeOverrideDifferentDeclarationSignatures.kt
index 39c650a1da5..aba4ace8df5 100644
--- a/compiler/testData/diagnostics/tests/override/FakeOverrideDifferentDeclarationSignatures.kt
+++ b/compiler/testData/diagnostics/tests/override/FakeOverrideDifferentDeclarationSignatures.kt
@@ -1,4 +1,4 @@
-trait A {
+interface A {
     fun f(): String = "string"
 }
 
diff --git a/compiler/testData/diagnostics/tests/override/Generics.kt b/compiler/testData/diagnostics/tests/override/Generics.kt
index f63317b147e..6813df144a0 100644
--- a/compiler/testData/diagnostics/tests/override/Generics.kt
+++ b/compiler/testData/diagnostics/tests/override/Generics.kt
@@ -1,6 +1,6 @@
 package override.generics
 
-trait MyTrait<T> {
+interface MyTrait<T> {
     fun foo(t: T) : T
 }
 
@@ -9,7 +9,7 @@ abstract class MyAbstractClass<T> {
     abstract val pr : T
 }
 
-trait MyProps<T> {
+interface MyProps<T> {
     val p : T
 }
 
diff --git a/compiler/testData/diagnostics/tests/override/MultipleDefaultParametersInSupertypes.kt b/compiler/testData/diagnostics/tests/override/MultipleDefaultParametersInSupertypes.kt
index aad916d41ef..f6aa6986f7c 100644
--- a/compiler/testData/diagnostics/tests/override/MultipleDefaultParametersInSupertypes.kt
+++ b/compiler/testData/diagnostics/tests/override/MultipleDefaultParametersInSupertypes.kt
@@ -1,8 +1,8 @@
-trait X {
+interface X {
     fun foo(a : Int = 1)
 }
 
-trait Y {
+interface Y {
     fun foo(a : Int = 1)
 }
 
diff --git a/compiler/testData/diagnostics/tests/override/MultipleDefaultParametersInSupertypesNoOverride.kt b/compiler/testData/diagnostics/tests/override/MultipleDefaultParametersInSupertypesNoOverride.kt
index c3cc0415c30..71f542a7d31 100644
--- a/compiler/testData/diagnostics/tests/override/MultipleDefaultParametersInSupertypesNoOverride.kt
+++ b/compiler/testData/diagnostics/tests/override/MultipleDefaultParametersInSupertypesNoOverride.kt
@@ -1,8 +1,8 @@
-trait X {
+interface X {
     fun foo(a : Int = 1)
 }
 
-trait Y {
+interface Y {
     fun foo(a : Int = 1)
 }
 
diff --git a/compiler/testData/diagnostics/tests/override/MultipleDefaultsAndNamesInSupertypes.kt b/compiler/testData/diagnostics/tests/override/MultipleDefaultsAndNamesInSupertypes.kt
index 8f1c3bd0105..72d41113c68 100644
--- a/compiler/testData/diagnostics/tests/override/MultipleDefaultsAndNamesInSupertypes.kt
+++ b/compiler/testData/diagnostics/tests/override/MultipleDefaultsAndNamesInSupertypes.kt
@@ -1,4 +1,4 @@
-trait A {
+interface A {
     fun foo(x: Int = 42): Int
 }
 
@@ -6,7 +6,7 @@ open class B {
     fun foo(x: Int = 239) = x
 }
 
-trait C {
+interface C {
     fun foo(y: Int)
 }
 
diff --git a/compiler/testData/diagnostics/tests/override/MultipleDefaultsInSupertypesNoExplicitOverride.kt b/compiler/testData/diagnostics/tests/override/MultipleDefaultsInSupertypesNoExplicitOverride.kt
index 1acf36d6750..cf5ffb10eeb 100644
--- a/compiler/testData/diagnostics/tests/override/MultipleDefaultsInSupertypesNoExplicitOverride.kt
+++ b/compiler/testData/diagnostics/tests/override/MultipleDefaultsInSupertypesNoExplicitOverride.kt
@@ -1,8 +1,8 @@
-trait X {
+interface X {
     fun foo(a : Int = 1)
 }
 
-trait Y {
+interface Y {
     fun foo(a : Int = 1)
 }
 
diff --git a/compiler/testData/diagnostics/tests/override/NonGenerics.kt b/compiler/testData/diagnostics/tests/override/NonGenerics.kt
index 6b36752da73..30a3688a219 100644
--- a/compiler/testData/diagnostics/tests/override/NonGenerics.kt
+++ b/compiler/testData/diagnostics/tests/override/NonGenerics.kt
@@ -1,6 +1,6 @@
 package override.normal
 
-trait MyTrait {
+interface MyTrait {
     fun foo()
     val pr : Unit
 }
diff --git a/compiler/testData/diagnostics/tests/override/ObjectDelegationManyImpl.kt b/compiler/testData/diagnostics/tests/override/ObjectDelegationManyImpl.kt
index d40355f0a7e..88b245e5a67 100644
--- a/compiler/testData/diagnostics/tests/override/ObjectDelegationManyImpl.kt
+++ b/compiler/testData/diagnostics/tests/override/ObjectDelegationManyImpl.kt
@@ -1,8 +1,8 @@
-trait D {
+interface D {
     fun foo()
 }
 
-trait E {
+interface E {
     fun foo() {}
 }
 
diff --git a/compiler/testData/diagnostics/tests/override/ParameterDefaultValues-DefaultValueFromOnlyOneSupertype.kt b/compiler/testData/diagnostics/tests/override/ParameterDefaultValues-DefaultValueFromOnlyOneSupertype.kt
index 9624f096d3c..158db681970 100644
--- a/compiler/testData/diagnostics/tests/override/ParameterDefaultValues-DefaultValueFromOnlyOneSupertype.kt
+++ b/compiler/testData/diagnostics/tests/override/ParameterDefaultValues-DefaultValueFromOnlyOneSupertype.kt
@@ -1,8 +1,8 @@
-trait X {
+interface X {
     fun foo(a : Int = 1)
 }
 
-trait Y {
+interface Y {
     fun foo(a : Int)
 }
 
diff --git a/compiler/testData/diagnostics/tests/override/ParentInheritsManyImplementations.kt b/compiler/testData/diagnostics/tests/override/ParentInheritsManyImplementations.kt
index 3af5d5d2385..1d53f7b54bb 100644
--- a/compiler/testData/diagnostics/tests/override/ParentInheritsManyImplementations.kt
+++ b/compiler/testData/diagnostics/tests/override/ParentInheritsManyImplementations.kt
@@ -1,16 +1,16 @@
 package d
 
-trait A {
+interface A {
     fun foo() = 1
 }
 
-trait B {
+interface B {
     fun foo() = 2
 }
 
 open <!MANY_IMPL_MEMBER_NOT_IMPLEMENTED!>class C<!> : A, B {}
 
-trait E {
+interface E {
     fun foo(): Int
 }
 
diff --git a/compiler/testData/diagnostics/tests/override/ProtectedAndPrivateFromSupertypes.kt b/compiler/testData/diagnostics/tests/override/ProtectedAndPrivateFromSupertypes.kt
index b686ba515ec..e1c459df79d 100644
--- a/compiler/testData/diagnostics/tests/override/ProtectedAndPrivateFromSupertypes.kt
+++ b/compiler/testData/diagnostics/tests/override/ProtectedAndPrivateFromSupertypes.kt
@@ -1,10 +1,10 @@
 package test
 
-trait A {
+interface A {
     protected val a: String
 }
 
-trait B {
+interface B {
     protected val a: String
 }
 
diff --git a/compiler/testData/diagnostics/tests/override/SuspiciousCase1.kt b/compiler/testData/diagnostics/tests/override/SuspiciousCase1.kt
index 4d70df96987..e80e4732343 100644
--- a/compiler/testData/diagnostics/tests/override/SuspiciousCase1.kt
+++ b/compiler/testData/diagnostics/tests/override/SuspiciousCase1.kt
@@ -1,11 +1,11 @@
 // NamedFunctionDescriptor.substitute substitutes "overrides"
 // this test checks it does it properly
 
-trait Foo<P> {
+interface Foo<P> {
     fun quux(p: P, q: Int = 17) : Int = 18
 }
 
-trait Bar<Q> : Foo<Q>
+interface Bar<Q> : Foo<Q>
 
 abstract class Baz() : Bar<String>
 
diff --git a/compiler/testData/diagnostics/tests/override/ToAbstractMembersFromSuper-kt1996.kt b/compiler/testData/diagnostics/tests/override/ToAbstractMembersFromSuper-kt1996.kt
index 562b38d826a..2c1da2c5766 100644
--- a/compiler/testData/diagnostics/tests/override/ToAbstractMembersFromSuper-kt1996.kt
+++ b/compiler/testData/diagnostics/tests/override/ToAbstractMembersFromSuper-kt1996.kt
@@ -1,10 +1,10 @@
 // http://youtrack.jetbrains.com/issue/KT-1996
 
-trait Foo {
+interface Foo {
     fun foo(): Unit
 }
 
-trait Bar {
+interface Bar {
     fun foo(): Unit
 }
 
diff --git a/compiler/testData/diagnostics/tests/override/kt1862.kt b/compiler/testData/diagnostics/tests/override/kt1862.kt
index bd70fba2f22..88d385ce68e 100644
--- a/compiler/testData/diagnostics/tests/override/kt1862.kt
+++ b/compiler/testData/diagnostics/tests/override/kt1862.kt
@@ -6,6 +6,6 @@ open class Bbb() : Aaa() {
     override fun foo() = 2
 }
 
-trait Ccc : <!TRAIT_WITH_SUPERCLASS!>Aaa<!>
+interface Ccc : <!TRAIT_WITH_SUPERCLASS!>Aaa<!>
 
 class Ddd() : Bbb(), Ccc
\ No newline at end of file
diff --git a/compiler/testData/diagnostics/tests/override/kt2052.kt b/compiler/testData/diagnostics/tests/override/kt2052.kt
index 5c772f6ce8d..4bd747ddc11 100644
--- a/compiler/testData/diagnostics/tests/override/kt2052.kt
+++ b/compiler/testData/diagnostics/tests/override/kt2052.kt
@@ -1,4 +1,4 @@
-trait Runnable {
+interface Runnable {
     fun run()
 }
 
diff --git a/compiler/testData/diagnostics/tests/override/kt2491.kt b/compiler/testData/diagnostics/tests/override/kt2491.kt
index 02f0b8b74b9..6a924bc1985 100644
--- a/compiler/testData/diagnostics/tests/override/kt2491.kt
+++ b/compiler/testData/diagnostics/tests/override/kt2491.kt
@@ -1,4 +1,4 @@
-trait T {
+interface T {
     public fun foo()
 }
 
diff --git a/compiler/testData/diagnostics/tests/override/kt4763.kt b/compiler/testData/diagnostics/tests/override/kt4763.kt
index cf9e4e67730..1cecb093fb9 100644
--- a/compiler/testData/diagnostics/tests/override/kt4763.kt
+++ b/compiler/testData/diagnostics/tests/override/kt4763.kt
@@ -1,4 +1,4 @@
-trait A {
+interface A {
     fun f(): String
 }
 
diff --git a/compiler/testData/diagnostics/tests/override/kt4763property.kt b/compiler/testData/diagnostics/tests/override/kt4763property.kt
index ccd9a1fe0a4..68689497fd3 100644
--- a/compiler/testData/diagnostics/tests/override/kt4763property.kt
+++ b/compiler/testData/diagnostics/tests/override/kt4763property.kt
@@ -1,4 +1,4 @@
-trait P {
+interface P {
     var f: Number
 }
 
diff --git a/compiler/testData/diagnostics/tests/override/kt4785.kt b/compiler/testData/diagnostics/tests/override/kt4785.kt
index a7c6036c4f7..a248fd77428 100644
--- a/compiler/testData/diagnostics/tests/override/kt4785.kt
+++ b/compiler/testData/diagnostics/tests/override/kt4785.kt
@@ -1,4 +1,4 @@
-trait T {
+interface T {
     internal fun foo()
 }
 
diff --git a/compiler/testData/diagnostics/tests/override/kt4785classObject.kt b/compiler/testData/diagnostics/tests/override/kt4785classObject.kt
index f74c61f073a..9f62206d000 100644
--- a/compiler/testData/diagnostics/tests/override/kt4785classObject.kt
+++ b/compiler/testData/diagnostics/tests/override/kt4785classObject.kt
@@ -1,8 +1,8 @@
-trait A {
+interface A {
     internal fun foo()
 }
 
-trait B {
+interface B {
     protected fun foo() {}
 }
 
diff --git a/compiler/testData/diagnostics/tests/override/kt4785delegation.kt b/compiler/testData/diagnostics/tests/override/kt4785delegation.kt
index 77e944c980e..8a4d927d59e 100644
--- a/compiler/testData/diagnostics/tests/override/kt4785delegation.kt
+++ b/compiler/testData/diagnostics/tests/override/kt4785delegation.kt
@@ -1,8 +1,8 @@
-trait A {
+interface A {
     internal fun foo()
 }
 
-trait B {
+interface B {
     protected fun foo()
 }
 
diff --git a/compiler/testData/diagnostics/tests/override/kt880.kt b/compiler/testData/diagnostics/tests/override/kt880.kt
index a8dad78b8d4..814e808b9fe 100644
--- a/compiler/testData/diagnostics/tests/override/kt880.kt
+++ b/compiler/testData/diagnostics/tests/override/kt880.kt
@@ -1,6 +1,6 @@
 // KT-880 Overload resolution ambiguity
 
-public trait I {
+public interface I {
     open fun test() : Unit
 }
 
diff --git a/compiler/testData/diagnostics/tests/override/parameterNames/changeOnOverrideDiagnostic.kt b/compiler/testData/diagnostics/tests/override/parameterNames/changeOnOverrideDiagnostic.kt
index 99580fc2937..50667f7f418 100644
--- a/compiler/testData/diagnostics/tests/override/parameterNames/changeOnOverrideDiagnostic.kt
+++ b/compiler/testData/diagnostics/tests/override/parameterNames/changeOnOverrideDiagnostic.kt
@@ -1,8 +1,8 @@
-trait A {
+interface A {
     fun b(a : Int)
 }
 
-trait B : A {}
+interface B : A {}
 
 class C1 : A {
     override fun b(<!PARAMETER_NAME_CHANGED_ON_OVERRIDE!>b<!> : Int) {}
diff --git a/compiler/testData/diagnostics/tests/override/parameterNames/differentNamesInSupertypesDiagnostic.kt b/compiler/testData/diagnostics/tests/override/parameterNames/differentNamesInSupertypesDiagnostic.kt
index 55eb4b013ca..1c30aadf745 100644
--- a/compiler/testData/diagnostics/tests/override/parameterNames/differentNamesInSupertypesDiagnostic.kt
+++ b/compiler/testData/diagnostics/tests/override/parameterNames/differentNamesInSupertypesDiagnostic.kt
@@ -1,14 +1,14 @@
-trait C {
+interface C {
     fun foo(a : Int)
 }
 
-trait D {
+interface D {
     fun foo(b : Int)
 }
 
-<!DIFFERENT_NAMES_FOR_THE_SAME_PARAMETER_IN_SUPERTYPES!>trait E<!> : C, D
+<!DIFFERENT_NAMES_FOR_THE_SAME_PARAMETER_IN_SUPERTYPES!>interface E<!> : C, D
 
-trait F : C, D {
+interface F : C, D {
     override fun foo(<!PARAMETER_NAME_CHANGED_ON_OVERRIDE!>a<!> : Int) {
         throw UnsupportedOperationException()
     }
diff --git a/compiler/testData/diagnostics/tests/override/parameterNames/kjkHierarchy.kt b/compiler/testData/diagnostics/tests/override/parameterNames/kjkHierarchy.kt
index 3819cf581f9..f59a7ce622b 100644
--- a/compiler/testData/diagnostics/tests/override/parameterNames/kjkHierarchy.kt
+++ b/compiler/testData/diagnostics/tests/override/parameterNames/kjkHierarchy.kt
@@ -1,6 +1,6 @@
 // FILE: Super.kt
 
-trait Super {
+interface Super {
     fun foo(superName: Int)
 }
 
diff --git a/compiler/testData/diagnostics/tests/override/parameterNames/kjkWithSeveralSupers.kt b/compiler/testData/diagnostics/tests/override/parameterNames/kjkWithSeveralSupers.kt
index ca04ebc0162..f37808091db 100644
--- a/compiler/testData/diagnostics/tests/override/parameterNames/kjkWithSeveralSupers.kt
+++ b/compiler/testData/diagnostics/tests/override/parameterNames/kjkWithSeveralSupers.kt
@@ -1,6 +1,6 @@
 // FILE: KSuper.kt
 
-trait KSuper {
+interface KSuper {
     fun foo(ksuperName: Int)
 }
 
diff --git a/compiler/testData/diagnostics/tests/override/parameterNames/kotlinInheritsBothJavaAndKotlin.kt b/compiler/testData/diagnostics/tests/override/parameterNames/kotlinInheritsBothJavaAndKotlin.kt
index e1d8929395c..4ce9afec0c8 100644
--- a/compiler/testData/diagnostics/tests/override/parameterNames/kotlinInheritsBothJavaAndKotlin.kt
+++ b/compiler/testData/diagnostics/tests/override/parameterNames/kotlinInheritsBothJavaAndKotlin.kt
@@ -6,7 +6,7 @@ interface JavaInterface {
 
 // FILE: kotlin.kt
 
-trait KotlinTrait {
+interface KotlinTrait {
     public fun foo(someOtherName: Int) {}
 }
 
diff --git a/compiler/testData/diagnostics/tests/override/parameterNames/kotlinInheritsJava.kt b/compiler/testData/diagnostics/tests/override/parameterNames/kotlinInheritsJava.kt
index 947dc2dbe86..46b4e945af2 100644
--- a/compiler/testData/diagnostics/tests/override/parameterNames/kotlinInheritsJava.kt
+++ b/compiler/testData/diagnostics/tests/override/parameterNames/kotlinInheritsJava.kt
@@ -11,7 +11,7 @@ class SimpleSubclass : JavaInterface {
 }
 
 
-trait SubtraitWithFakeOverride : JavaInterface
+interface SubtraitWithFakeOverride : JavaInterface
 
 class Subclass : SubtraitWithFakeOverride {
     override fun foo(otherKotlinName: Int) {}
diff --git a/compiler/testData/diagnostics/tests/platformTypes/commonSupertype/withNothing.kt b/compiler/testData/diagnostics/tests/platformTypes/commonSupertype/withNothing.kt
index 3e6f24548a3..0da7d01003c 100644
--- a/compiler/testData/diagnostics/tests/platformTypes/commonSupertype/withNothing.kt
+++ b/compiler/testData/diagnostics/tests/platformTypes/commonSupertype/withNothing.kt
@@ -12,7 +12,7 @@ public class J {
 
 import p.*
 
-trait Out<out T1>
+interface Out<out T1>
 
 fun <T> f(a: Out<T>, b: Out<T>, c: Out<T>): T = null!!
 fun <T> out(t: T): Out<MutableList<T>> = null!!
diff --git a/compiler/testData/diagnostics/tests/platformTypes/methodCall/multipleExactBounds.kt b/compiler/testData/diagnostics/tests/platformTypes/methodCall/multipleExactBounds.kt
index 171a9d6308d..5c998b4ecce 100644
--- a/compiler/testData/diagnostics/tests/platformTypes/methodCall/multipleExactBounds.kt
+++ b/compiler/testData/diagnostics/tests/platformTypes/methodCall/multipleExactBounds.kt
@@ -1,9 +1,9 @@
 import java.util.HashMap
 
-trait ModuleDescriptorImpl
-trait ModuleInfo
-trait ResolverForModule
-trait ResolverForProject<M1, R1>
+interface ModuleDescriptorImpl
+interface ModuleInfo
+interface ResolverForModule
+interface ResolverForProject<M1, R1>
 
 class ResolverForProjectImpl<M : ModuleInfo, R : ResolverForModule>(
         <!UNUSED_PARAMETER!>descriptorByModule<!>: Map<M, ModuleDescriptorImpl>,
diff --git a/compiler/testData/diagnostics/tests/platformTypes/methodCall/multipleExactBoundsNullable.kt b/compiler/testData/diagnostics/tests/platformTypes/methodCall/multipleExactBoundsNullable.kt
index 400f0c159e5..72cd6adfb41 100644
--- a/compiler/testData/diagnostics/tests/platformTypes/methodCall/multipleExactBoundsNullable.kt
+++ b/compiler/testData/diagnostics/tests/platformTypes/methodCall/multipleExactBoundsNullable.kt
@@ -1,6 +1,6 @@
 import java.util.HashMap
 
-trait ResolverForProject<M1> {
+interface ResolverForProject<M1> {
     val exposeM: M1 get() = null!!
 }
 
@@ -9,7 +9,7 @@ class ResolverForProjectImpl<M>(
         <!UNUSED_PARAMETER!>delegateResolver<!>: ResolverForProject<M>
 ) : ResolverForProject<M>
 
-trait WithFoo {
+interface WithFoo {
     fun foo()
 }
 
diff --git a/compiler/testData/diagnostics/tests/platformTypes/methodCall/singleton.kt b/compiler/testData/diagnostics/tests/platformTypes/methodCall/singleton.kt
index 0d1be396e8d..6505d5bf312 100644
--- a/compiler/testData/diagnostics/tests/platformTypes/methodCall/singleton.kt
+++ b/compiler/testData/diagnostics/tests/platformTypes/methodCall/singleton.kt
@@ -1,6 +1,6 @@
 // !DIAGNOSTICS: -UNUSED_PARAMETER -UNUSED_VARIABLE
 
-trait Foo
+interface Foo
 
 fun test() {
     var nullable: Foo? = null
diff --git a/compiler/testData/diagnostics/tests/platformTypes/supertypeArgumentsExplicit.kt b/compiler/testData/diagnostics/tests/platformTypes/supertypeArgumentsExplicit.kt
index b269d1b4a96..51d087d07ff 100644
--- a/compiler/testData/diagnostics/tests/platformTypes/supertypeArgumentsExplicit.kt
+++ b/compiler/testData/diagnostics/tests/platformTypes/supertypeArgumentsExplicit.kt
@@ -1,14 +1,14 @@
 // !EXPLICIT_FLEXIBLE_TYPES
 // !DIAGNOSTICS: -BASE_WITH_NULLABLE_UPPER_BOUND
 
-trait A<T>
-trait B<T>: A<ft<T, T?>>
+interface A<T>
+interface B<T>: A<ft<T, T?>>
 
-trait C: A<String>, B<String>
-trait D: B<String>, A<String>
-trait E: A<String?>, B<String?>
-trait F: A<String?>, B<String>
+interface C: A<String>, B<String>
+interface D: B<String>, A<String>
+interface E: A<String?>, B<String?>
+interface F: A<String?>, B<String>
 
-trait G: <!INCONSISTENT_TYPE_PARAMETER_VALUES!>A<String>, B<String?><!>
-trait H: <!INCONSISTENT_TYPE_PARAMETER_VALUES!>A<Int>, B<String><!>
-trait I: <!INCONSISTENT_TYPE_PARAMETER_VALUES!>B<Int>, A<String><!>
\ No newline at end of file
+interface G: <!INCONSISTENT_TYPE_PARAMETER_VALUES!>A<String>, B<String?><!>
+interface H: <!INCONSISTENT_TYPE_PARAMETER_VALUES!>A<Int>, B<String><!>
+interface I: <!INCONSISTENT_TYPE_PARAMETER_VALUES!>B<Int>, A<String><!>
\ No newline at end of file
diff --git a/compiler/testData/diagnostics/tests/platformTypes/supertypeTypeArguments.kt b/compiler/testData/diagnostics/tests/platformTypes/supertypeTypeArguments.kt
index 48c821f00b4..6554d91e6e0 100644
--- a/compiler/testData/diagnostics/tests/platformTypes/supertypeTypeArguments.kt
+++ b/compiler/testData/diagnostics/tests/platformTypes/supertypeTypeArguments.kt
@@ -1,2 +1,2 @@
-trait ExtMap<K, V> : Map<K, V>
+interface ExtMap<K, V> : Map<K, V>
 class HashMapEx<K, V> : java.util.HashMap<K, V>(), ExtMap<K, V>
\ No newline at end of file
diff --git a/compiler/testData/diagnostics/tests/recovery/namelessToplevelDeclarations.kt b/compiler/testData/diagnostics/tests/recovery/namelessToplevelDeclarations.kt
index 067f80d0a19..8736f3d1155 100644
--- a/compiler/testData/diagnostics/tests/recovery/namelessToplevelDeclarations.kt
+++ b/compiler/testData/diagnostics/tests/recovery/namelessToplevelDeclarations.kt
@@ -13,7 +13,7 @@ class<!SYNTAX!><!> {
 
 }
 
-trait<!SYNTAX!><!> {
+interface<!SYNTAX!><!> {
 
 }
 
diff --git a/compiler/testData/diagnostics/tests/regressions/UnavaliableQualifiedThis.kt b/compiler/testData/diagnostics/tests/regressions/UnavaliableQualifiedThis.kt
index 0f80fe99ccf..db6a738d76d 100644
--- a/compiler/testData/diagnostics/tests/regressions/UnavaliableQualifiedThis.kt
+++ b/compiler/testData/diagnostics/tests/regressions/UnavaliableQualifiedThis.kt
@@ -1,4 +1,4 @@
-trait Iterator<out T> {
+interface Iterator<out T> {
  fun next() : T
  val hasNext : Boolean
 
diff --git a/compiler/testData/diagnostics/tests/regressions/kt1489_1728.kt b/compiler/testData/diagnostics/tests/regressions/kt1489_1728.kt
index 11acf7d5ad3..633fe0e5cd0 100644
--- a/compiler/testData/diagnostics/tests/regressions/kt1489_1728.kt
+++ b/compiler/testData/diagnostics/tests/regressions/kt1489_1728.kt
@@ -1,7 +1,7 @@
 package kt606_dependents
 
 //KT-1489 Code analyzer fails with assertion
-trait AutoCloseable{
+interface AutoCloseable{
     fun close()
 }
 
diff --git a/compiler/testData/diagnostics/tests/regressions/kt174.kt b/compiler/testData/diagnostics/tests/regressions/kt174.kt
index 660cb39f78e..89a926afc6b 100644
--- a/compiler/testData/diagnostics/tests/regressions/kt174.kt
+++ b/compiler/testData/diagnostics/tests/regressions/kt174.kt
@@ -1,5 +1,5 @@
 // KT-174 Nullability info for extension function receivers
-trait Tree {}
+interface Tree {}
 
 fun Any?.TreeValue() : Tree {
   if (this is Tree) return <!DEBUG_INFO_SMARTCAST!>this<!>
diff --git a/compiler/testData/diagnostics/tests/regressions/kt302.kt b/compiler/testData/diagnostics/tests/regressions/kt302.kt
index 3f5dba1ebe0..7905dcb3ef8 100644
--- a/compiler/testData/diagnostics/tests/regressions/kt302.kt
+++ b/compiler/testData/diagnostics/tests/regressions/kt302.kt
@@ -2,11 +2,11 @@
 
 package kt302
 
-trait A {
+interface A {
     open fun foo() {}
 }
 
-trait B {
+interface B {
     open fun foo() {}
 }
 
diff --git a/compiler/testData/diagnostics/tests/regressions/kt307.kt b/compiler/testData/diagnostics/tests/regressions/kt307.kt
index 3cbb585a647..4d9355d9d9f 100644
--- a/compiler/testData/diagnostics/tests/regressions/kt307.kt
+++ b/compiler/testData/diagnostics/tests/regressions/kt307.kt
@@ -4,7 +4,7 @@ open class AL {
     fun get(i : Int) : Any? = i
 }
 
-trait ALE<T> : <!TRAIT_WITH_SUPERCLASS!>AL<!> {
+interface ALE<T> : <!TRAIT_WITH_SUPERCLASS!>AL<!> {
 fun getOrNull(index: Int, value: T) : T {
 return <!UNCHECKED_CAST!>get(index) as? T<!> ?: value
 }
diff --git a/compiler/testData/diagnostics/tests/regressions/kt316.kt b/compiler/testData/diagnostics/tests/regressions/kt316.kt
index db9253f127b..4816e9763f5 100644
--- a/compiler/testData/diagnostics/tests/regressions/kt316.kt
+++ b/compiler/testData/diagnostics/tests/regressions/kt316.kt
@@ -1,6 +1,6 @@
 // KT-316 Members of traits must be open by default
 
-trait B {
+interface B {
     fun bar() {}
     fun foo() {}
 }
diff --git a/compiler/testData/diagnostics/tests/regressions/kt353.kt b/compiler/testData/diagnostics/tests/regressions/kt353.kt
index a6633c930fa..2ca5f2a2e29 100644
--- a/compiler/testData/diagnostics/tests/regressions/kt353.kt
+++ b/compiler/testData/diagnostics/tests/regressions/kt353.kt
@@ -1,6 +1,6 @@
 // KT-353 Generic type argument inference sometimes doesn't work
 
-trait A {
+interface A {
     fun <T> gen() : T
 }
 
diff --git a/compiler/testData/diagnostics/tests/regressions/kt4827.kt b/compiler/testData/diagnostics/tests/regressions/kt4827.kt
index e39d7a40565..17c922a7038 100644
--- a/compiler/testData/diagnostics/tests/regressions/kt4827.kt
+++ b/compiler/testData/diagnostics/tests/regressions/kt4827.kt
@@ -1,7 +1,7 @@
 // KT-4827 UOE at PackageType.throwException()
 // EA-53605
 
-public trait TestInterface {
+public interface TestInterface {
 }
 
 class C {
diff --git a/compiler/testData/diagnostics/tests/regressions/kt604.kt b/compiler/testData/diagnostics/tests/regressions/kt604.kt
index de0926b0208..3d2d8f8f2cd 100644
--- a/compiler/testData/diagnostics/tests/regressions/kt604.kt
+++ b/compiler/testData/diagnostics/tests/regressions/kt604.kt
@@ -1,13 +1,13 @@
 // KT-604 Internal frontend error
 
-trait ChannelPipeline {
+interface ChannelPipeline {
 
 }
 
 class DefaultChannelPipeline() : ChannelPipeline {
 }
 
-trait ChannelPipelineFactory{
+interface ChannelPipelineFactory{
     fun getPipeline() : ChannelPipeline
 }
 
diff --git a/compiler/testData/diagnostics/tests/resolve/invoke/invokeAsExtension.kt b/compiler/testData/diagnostics/tests/resolve/invoke/invokeAsExtension.kt
index 229e713d50e..34e25109c11 100644
--- a/compiler/testData/diagnostics/tests/resolve/invoke/invokeAsExtension.kt
+++ b/compiler/testData/diagnostics/tests/resolve/invoke/invokeAsExtension.kt
@@ -8,7 +8,7 @@ fun test(foo: Foo) {
 }
 
 //variable as member
-trait A {
+interface A {
     val foo: Foo
 }
 
@@ -22,7 +22,7 @@ fun test(a: A) {
 }
 
 //variable as extension
-trait B {
+interface B {
 }
 val B.foo: Foo
     get() = Foo()
@@ -36,9 +36,9 @@ fun test(b: B) {
 }
 
 //variable as member extension
-trait C
+interface C
 
-trait D {
+interface D {
     val C.foo: Foo
 
     fun test(c: C) {
diff --git a/compiler/testData/diagnostics/tests/resolve/invoke/invokeAsMember.kt b/compiler/testData/diagnostics/tests/resolve/invoke/invokeAsMember.kt
index c3f09111379..82451afac38 100644
--- a/compiler/testData/diagnostics/tests/resolve/invoke/invokeAsMember.kt
+++ b/compiler/testData/diagnostics/tests/resolve/invoke/invokeAsMember.kt
@@ -8,7 +8,7 @@ fun test(foo: Foo) {
 }
 
 //variable as member
-trait A {
+interface A {
     val foo: Foo
 }
 
@@ -21,7 +21,7 @@ fun test(a: A) {
 }
 
 //variable as extension
-trait B {}
+interface B {}
 val B.foo: Foo
     get() = Foo()
 
@@ -35,9 +35,9 @@ fun test(b: B) {
 }
 
 //variable as member extension
-trait C
+interface C
 
-trait D {
+interface D {
     val C.foo: Foo
 
     fun test(c: C) {
diff --git a/compiler/testData/diagnostics/tests/resolve/invoke/invokeAsMemberExtension.kt b/compiler/testData/diagnostics/tests/resolve/invoke/invokeAsMemberExtension.kt
index 06425369b39..ea3d5fb4220 100644
--- a/compiler/testData/diagnostics/tests/resolve/invoke/invokeAsMemberExtension.kt
+++ b/compiler/testData/diagnostics/tests/resolve/invoke/invokeAsMemberExtension.kt
@@ -1,7 +1,7 @@
 class Foo
 
 //no variable
-trait A {
+interface A {
     fun Foo.invoke() {}
 
     fun test(foo: Foo) {
@@ -10,7 +10,7 @@ trait A {
 }
 
 //variable as member
-trait B {
+interface B {
     val foo: Foo
 }
 
@@ -38,7 +38,7 @@ fun test(c: C, b: B) {
 
 
 //variable as extension,
-trait D {
+interface D {
 }
 val D.foo: Foo
     get() = Foo()
@@ -66,9 +66,9 @@ fun test(e: E, d: D) {
 }
 
 //variable as member extension
-trait F
+interface F
 
-trait G {
+interface G {
     val F.foo: Foo
     fun Foo.invoke()
 
@@ -92,13 +92,13 @@ fun test(g: G, f: F) {
 }
 
 //variable as member extension (2)
-trait X
+interface X
 
-trait U {
+interface U {
     val X.foo: Foo
 }
 
-trait V {
+interface V {
     fun Foo.invoke() {}
 
     fun U.test(x: X) {
diff --git a/compiler/testData/diagnostics/tests/resolve/invoke/invokeAsMemberExtensionToExplicitReceiver.kt b/compiler/testData/diagnostics/tests/resolve/invoke/invokeAsMemberExtensionToExplicitReceiver.kt
index 1d75d9a9f40..6957b44b076 100644
--- a/compiler/testData/diagnostics/tests/resolve/invoke/invokeAsMemberExtensionToExplicitReceiver.kt
+++ b/compiler/testData/diagnostics/tests/resolve/invoke/invokeAsMemberExtensionToExplicitReceiver.kt
@@ -1,5 +1,5 @@
-trait A
-trait Foo {
+interface A
+interface Foo {
     fun A.invoke()
 }
 
diff --git a/compiler/testData/diagnostics/tests/resolve/invoke/kt4321InvokeOnEnum.kt b/compiler/testData/diagnostics/tests/resolve/invoke/kt4321InvokeOnEnum.kt
index 3c0d7ae7326..5895e7121b7 100644
--- a/compiler/testData/diagnostics/tests/resolve/invoke/kt4321InvokeOnEnum.kt
+++ b/compiler/testData/diagnostics/tests/resolve/invoke/kt4321InvokeOnEnum.kt
@@ -11,7 +11,7 @@ enum class DOMElementTestClasses {
 
 
 // use case 2
-trait EnumStyleClass {
+interface EnumStyleClass {
     fun invoke() {}
 }
 enum class TestClasses : EnumStyleClass {
diff --git a/compiler/testData/diagnostics/tests/resolve/invoke/valNamedInvoke.kt b/compiler/testData/diagnostics/tests/resolve/invoke/valNamedInvoke.kt
index 548dba784c6..6ac2e1c5cbc 100644
--- a/compiler/testData/diagnostics/tests/resolve/invoke/valNamedInvoke.kt
+++ b/compiler/testData/diagnostics/tests/resolve/invoke/valNamedInvoke.kt
@@ -1,4 +1,4 @@
-trait A
+interface A
 
 fun foo(invoke: A.()->Unit, a: A) {
     a.invoke()
diff --git a/compiler/testData/diagnostics/tests/resolve/nestedCalls/argumentsInParentheses.kt b/compiler/testData/diagnostics/tests/resolve/nestedCalls/argumentsInParentheses.kt
index 10e8c6099fc..334cae7f974 100644
--- a/compiler/testData/diagnostics/tests/resolve/nestedCalls/argumentsInParentheses.kt
+++ b/compiler/testData/diagnostics/tests/resolve/nestedCalls/argumentsInParentheses.kt
@@ -1,4 +1,4 @@
-trait Foo<T>
+interface Foo<T>
 
 class Bar {
     fun <T> invoke(): Foo<T> = throw Exception()
diff --git a/compiler/testData/diagnostics/tests/resolve/nestedCalls/kt7597.kt b/compiler/testData/diagnostics/tests/resolve/nestedCalls/kt7597.kt
index de99dbeab71..9d8aac8a083 100644
--- a/compiler/testData/diagnostics/tests/resolve/nestedCalls/kt7597.kt
+++ b/compiler/testData/diagnostics/tests/resolve/nestedCalls/kt7597.kt
@@ -1,6 +1,6 @@
 // !CHECK_TYPE
 
-trait Inv<I>
+interface Inv<I>
 
 fun <S, T: S> Inv<T>.reduce2(): S = null!!
 
diff --git a/compiler/testData/diagnostics/tests/resolve/specialConstructions/elvisAsCall.kt b/compiler/testData/diagnostics/tests/resolve/specialConstructions/elvisAsCall.kt
index 61629d19dcf..c087d7ac479 100644
--- a/compiler/testData/diagnostics/tests/resolve/specialConstructions/elvisAsCall.kt
+++ b/compiler/testData/diagnostics/tests/resolve/specialConstructions/elvisAsCall.kt
@@ -1,6 +1,6 @@
 package a
 
-trait A
+interface A
 fun doList(l: List<Int>) = l
 fun doInt(i: Int) = i
 fun getList(): List<Int>? = null
diff --git a/compiler/testData/diagnostics/tests/resolve/specialConstructions/exclExclAsCall.kt b/compiler/testData/diagnostics/tests/resolve/specialConstructions/exclExclAsCall.kt
index 9e3669006e8..148cdc00581 100644
--- a/compiler/testData/diagnostics/tests/resolve/specialConstructions/exclExclAsCall.kt
+++ b/compiler/testData/diagnostics/tests/resolve/specialConstructions/exclExclAsCall.kt
@@ -1,6 +1,6 @@
 package a
 
-trait A
+interface A
 
 fun <T>id(t: T): T = t
 fun doList(l: List<Int>) = l
diff --git a/compiler/testData/diagnostics/tests/resolve/specialConstructions/multipleSuperClasses.kt b/compiler/testData/diagnostics/tests/resolve/specialConstructions/multipleSuperClasses.kt
index 10772f81a8c..1764d1da8d0 100644
--- a/compiler/testData/diagnostics/tests/resolve/specialConstructions/multipleSuperClasses.kt
+++ b/compiler/testData/diagnostics/tests/resolve/specialConstructions/multipleSuperClasses.kt
@@ -1,11 +1,11 @@
 // !DIAGNOSTICS: -UNUSED_VARIABLE
 
-trait A
-trait B
+interface A
+interface B
 
-trait C: A, B
-trait D: A, B
-trait E: A, B
+interface C: A, B
+interface D: A, B
+interface E: A, B
 
 fun foo(c: C?, d: D?, e: E?) {
     val a: A? = <!TYPE_MISMATCH!>c ?: d<!> ?: e
diff --git a/compiler/testData/diagnostics/tests/scopes/VisibilityInheritModifier.kt b/compiler/testData/diagnostics/tests/scopes/VisibilityInheritModifier.kt
index 82d83383986..b7c6fc5a2c3 100644
--- a/compiler/testData/diagnostics/tests/scopes/VisibilityInheritModifier.kt
+++ b/compiler/testData/diagnostics/tests/scopes/VisibilityInheritModifier.kt
@@ -56,7 +56,7 @@ class K : H() {
 }
 
 //-------------
-trait T {
+interface T {
     public fun foo() {}
 }
 
@@ -68,15 +68,15 @@ class M : L() {
     <!CANNOT_WEAKEN_ACCESS_PRIVILEGE!>internal<!> override fun foo() {}
 }
 //---------------
-trait R {
+interface R {
     <!INCOMPATIBLE_MODIFIERS!>internal<!> <!INCOMPATIBLE_MODIFIERS!>protected<!> fun foo() {}
 }
 
-trait P : R {
+interface P : R {
     <!CANNOT_CHANGE_ACCESS_PRIVILEGE!>internal<!> override fun foo() {}
 }
 
-trait Q : R {
+interface Q : R {
     protected override fun foo() {}
 }
 
diff --git a/compiler/testData/diagnostics/tests/scopes/kt1248.kt b/compiler/testData/diagnostics/tests/scopes/kt1248.kt
index fd0a7bfd2ae..d7d37268638 100644
--- a/compiler/testData/diagnostics/tests/scopes/kt1248.kt
+++ b/compiler/testData/diagnostics/tests/scopes/kt1248.kt
@@ -1,7 +1,7 @@
 //KT-1248 Control visibility of overrides needed
 package kt1248
 
-trait ParseResult<out T> {
+interface ParseResult<out T> {
     public val success : Boolean
     public val value : T
 }
diff --git a/compiler/testData/diagnostics/tests/scopes/kt151.kt b/compiler/testData/diagnostics/tests/scopes/kt151.kt
index e50bbf6526d..182c835bf31 100644
--- a/compiler/testData/diagnostics/tests/scopes/kt151.kt
+++ b/compiler/testData/diagnostics/tests/scopes/kt151.kt
@@ -19,7 +19,7 @@ open class C {
     internal open fun foo() {}
 }
 
-trait T {
+interface T {
     protected fun foo() {}
 }
 
diff --git a/compiler/testData/diagnostics/tests/scopes/kt1579.kt b/compiler/testData/diagnostics/tests/scopes/kt1579.kt
index bea21ba1abd..6c1ef8f6c63 100644
--- a/compiler/testData/diagnostics/tests/scopes/kt1579.kt
+++ b/compiler/testData/diagnostics/tests/scopes/kt1579.kt
@@ -1,8 +1,8 @@
 //FILE:a.kt
-//KT-1579 Can't import nested class/trait
+//KT-1579 Can't import nested class/interface
 package lib
-trait WithInner {
-    trait Inner {
+interface WithInner {
+    interface Inner {
     }
 }
 //FILE:b.kt
diff --git a/compiler/testData/diagnostics/tests/scopes/kt1580.kt b/compiler/testData/diagnostics/tests/scopes/kt1580.kt
index f28d9e83456..a0775c494fb 100644
--- a/compiler/testData/diagnostics/tests/scopes/kt1580.kt
+++ b/compiler/testData/diagnostics/tests/scopes/kt1580.kt
@@ -1,8 +1,8 @@
 //FILE:a.kt
-//KT-1580 Can't access nested class/trait from other package
+//KT-1580 Can't access nested class/interface from other package
 package lib
-trait WithInner {
-    trait Inner {
+interface WithInner {
+    interface Inner {
     }
 }
 
diff --git a/compiler/testData/diagnostics/tests/scopes/kt1822.kt b/compiler/testData/diagnostics/tests/scopes/kt1822.kt
index 75282544459..85a07b95ec1 100644
--- a/compiler/testData/diagnostics/tests/scopes/kt1822.kt
+++ b/compiler/testData/diagnostics/tests/scopes/kt1822.kt
@@ -5,7 +5,7 @@ open class C {
     internal open fun foo() {}
 }
 
-trait T {
+interface T {
     protected fun foo() {}
 }
 
@@ -17,11 +17,11 @@ open class A {
     internal open fun foo() {}
 }
 
-trait B {
+interface B {
     protected fun foo() {}
 }
 
-trait D {
+interface D {
     public fun foo() {}
 }
 
diff --git a/compiler/testData/diagnostics/tests/scopes/stopResolutionOnAmbiguity.kt b/compiler/testData/diagnostics/tests/scopes/stopResolutionOnAmbiguity.kt
index 0af67217928..28db2c26a69 100644
--- a/compiler/testData/diagnostics/tests/scopes/stopResolutionOnAmbiguity.kt
+++ b/compiler/testData/diagnostics/tests/scopes/stopResolutionOnAmbiguity.kt
@@ -1,6 +1,6 @@
 package c
 
-trait B {
+interface B {
     fun bar() {}
 }
 
diff --git a/compiler/testData/diagnostics/tests/scopes/visibility.kt b/compiler/testData/diagnostics/tests/scopes/visibility.kt
index e7069c4be8d..b20b2763ad6 100644
--- a/compiler/testData/diagnostics/tests/scopes/visibility.kt
+++ b/compiler/testData/diagnostics/tests/scopes/visibility.kt
@@ -2,7 +2,7 @@
 package test_visibility
 
 <!PACKAGE_MEMBER_CANNOT_BE_PROTECTED!>protected<!> class ProtectedClass
-<!PACKAGE_MEMBER_CANNOT_BE_PROTECTED!>protected<!> trait ProtectedTrait
+<!PACKAGE_MEMBER_CANNOT_BE_PROTECTED!>protected<!> interface ProtectedTrait
 
 <!PACKAGE_MEMBER_CANNOT_BE_PROTECTED!>protected<!> val protected_val : Int = 4
 <!PACKAGE_MEMBER_CANNOT_BE_PROTECTED!>protected<!> fun protected_fun() {}
@@ -42,7 +42,7 @@ fun test3(a: A) {
     a.<!INVISIBLE_MEMBER!>f<!>(0, <!TOO_MANY_ARGUMENTS!>1<!>) //todo .bMethod()
 }
 
-trait T
+interface T
 
 open class C : T {
     protected var i : Int = 34
diff --git a/compiler/testData/diagnostics/tests/secondaryConstructors/constructorInTrait.kt b/compiler/testData/diagnostics/tests/secondaryConstructors/constructorInTrait.kt
index d7825e8687f..aa6be73d7e4 100644
--- a/compiler/testData/diagnostics/tests/secondaryConstructors/constructorInTrait.kt
+++ b/compiler/testData/diagnostics/tests/secondaryConstructors/constructorInTrait.kt
@@ -1,3 +1,3 @@
-trait A {
+interface A {
     <!CONSTRUCTOR_IN_TRAIT!>constructor()
 <!>}
\ No newline at end of file
diff --git a/compiler/testData/diagnostics/tests/secondaryConstructors/delegationByWithoutPrimary.kt b/compiler/testData/diagnostics/tests/secondaryConstructors/delegationByWithoutPrimary.kt
index 8163abc6ef4..7e25869a417 100644
--- a/compiler/testData/diagnostics/tests/secondaryConstructors/delegationByWithoutPrimary.kt
+++ b/compiler/testData/diagnostics/tests/secondaryConstructors/delegationByWithoutPrimary.kt
@@ -1,4 +1,4 @@
-trait A
+interface A
 class AImpl : A
 
 class B : <!UNSUPPORTED!>A by AImpl()<!> {
diff --git a/compiler/testData/diagnostics/tests/secondaryConstructors/noSupertypeInitWithSecondaryConstructors.kt b/compiler/testData/diagnostics/tests/secondaryConstructors/noSupertypeInitWithSecondaryConstructors.kt
index 83d0dd91591..7b5fe15c5e8 100644
--- a/compiler/testData/diagnostics/tests/secondaryConstructors/noSupertypeInitWithSecondaryConstructors.kt
+++ b/compiler/testData/diagnostics/tests/secondaryConstructors/noSupertypeInitWithSecondaryConstructors.kt
@@ -1,6 +1,6 @@
 open class B
-trait C
-trait D
+interface C
+interface D
 class A : C, B, D {
     constructor()
 }
diff --git a/compiler/testData/diagnostics/tests/secondaryConstructors/superSecondaryNonExisting.kt b/compiler/testData/diagnostics/tests/secondaryConstructors/superSecondaryNonExisting.kt
index f8c63832afd..3609fa8a6d4 100644
--- a/compiler/testData/diagnostics/tests/secondaryConstructors/superSecondaryNonExisting.kt
+++ b/compiler/testData/diagnostics/tests/secondaryConstructors/superSecondaryNonExisting.kt
@@ -3,7 +3,7 @@ open class B(x: Double) {
     constructor(x: Int): this(1.0)
     constructor(x: String): this(1.0)
 }
-trait C
+interface C
 class A : B, C {
     constructor(): <!NONE_APPLICABLE!>super<!>(' ')
     <!EXPLICIT_DELEGATION_CALL_REQUIRED!>constructor(x: Int)<!>
diff --git a/compiler/testData/diagnostics/tests/smartCasts/combineWithNoSelectorInfo.kt b/compiler/testData/diagnostics/tests/smartCasts/combineWithNoSelectorInfo.kt
index fdb1e785cb5..94778fe7ac0 100644
--- a/compiler/testData/diagnostics/tests/smartCasts/combineWithNoSelectorInfo.kt
+++ b/compiler/testData/diagnostics/tests/smartCasts/combineWithNoSelectorInfo.kt
@@ -7,7 +7,7 @@ fun dispatch(request: Request) {
     }
 }
 
-trait Request {
+interface Request {
     fun getRequestURI(): String?
     fun getMethod(): String?
 }
diff --git a/compiler/testData/diagnostics/tests/smartCasts/inference/intersectionTypes.kt b/compiler/testData/diagnostics/tests/smartCasts/inference/intersectionTypes.kt
index f7a08cacea8..d8ee70a052b 100644
--- a/compiler/testData/diagnostics/tests/smartCasts/inference/intersectionTypes.kt
+++ b/compiler/testData/diagnostics/tests/smartCasts/inference/intersectionTypes.kt
@@ -8,9 +8,9 @@ fun <T> two(u: T, <!UNUSED_PARAMETER!>v<!>: T): T = u
 
 fun <T> three(<!UNUSED_PARAMETER!>a<!>: T, <!UNUSED_PARAMETER!>b<!>: T, c: T): T = c
 
-trait A
-trait B: A
-trait C: A
+interface A
+interface B: A
+interface C: A
 
 fun test(a: A, b: B, c: C) {
     if (a is B && a is C) {
diff --git a/compiler/testData/diagnostics/tests/smartCasts/inference/kt4009.kt b/compiler/testData/diagnostics/tests/smartCasts/inference/kt4009.kt
index 98f3a0c5c9a..0be198177d7 100644
--- a/compiler/testData/diagnostics/tests/smartCasts/inference/kt4009.kt
+++ b/compiler/testData/diagnostics/tests/smartCasts/inference/kt4009.kt
@@ -1,9 +1,9 @@
-trait PsiElement {
+interface PsiElement {
     fun getText(): String
     fun getParent(): PsiElement
 }
 
-trait JetExpression : PsiElement
+interface JetExpression : PsiElement
 
 fun foo1(e: PsiElement) {
     var current: PsiElement? = e
diff --git a/compiler/testData/diagnostics/tests/smartCasts/inference/kt4403.kt b/compiler/testData/diagnostics/tests/smartCasts/inference/kt4403.kt
index cd8185a85d6..71f2c591f58 100644
--- a/compiler/testData/diagnostics/tests/smartCasts/inference/kt4403.kt
+++ b/compiler/testData/diagnostics/tests/smartCasts/inference/kt4403.kt
@@ -1,7 +1,7 @@
 //KT-4403 Wrong "type mismatch" on smart cast with inference
 
-trait A
-trait B : A
+interface A
+interface B : A
 
 fun <T> T.f(): T = this
 
diff --git a/compiler/testData/diagnostics/tests/smartCasts/inference/kt4415.kt b/compiler/testData/diagnostics/tests/smartCasts/inference/kt4415.kt
index 7335640eb12..cced68127f8 100644
--- a/compiler/testData/diagnostics/tests/smartCasts/inference/kt4415.kt
+++ b/compiler/testData/diagnostics/tests/smartCasts/inference/kt4415.kt
@@ -1,6 +1,6 @@
 //KT-4415 Class Auto-Cast Bug
 
-trait SelfJson
+interface SelfJson
 
 object A {
     fun find(<!UNUSED_PARAMETER!>clz<!>:Class<*>){  }
diff --git a/compiler/testData/diagnostics/tests/smartCasts/inference/smartCastOnReceiver.kt b/compiler/testData/diagnostics/tests/smartCasts/inference/smartCastOnReceiver.kt
index c91ed164bc8..99427844d31 100644
--- a/compiler/testData/diagnostics/tests/smartCasts/inference/smartCastOnReceiver.kt
+++ b/compiler/testData/diagnostics/tests/smartCasts/inference/smartCastOnReceiver.kt
@@ -1,5 +1,5 @@
-trait A
-trait B
+interface A
+interface B
 
 class Test {
     fun test(a: A?, b: B, list: MutableList<Pair<A, B>>) {
diff --git a/compiler/testData/diagnostics/tests/smartCasts/kt3572.kt b/compiler/testData/diagnostics/tests/smartCasts/kt3572.kt
index bbc0f322f75..fc792d1ca81 100644
--- a/compiler/testData/diagnostics/tests/smartCasts/kt3572.kt
+++ b/compiler/testData/diagnostics/tests/smartCasts/kt3572.kt
@@ -1,4 +1,4 @@
-trait Printer {
+interface Printer {
     fun print()
 }
 
diff --git a/compiler/testData/diagnostics/tests/smartCasts/publicVals/kt4409.kt b/compiler/testData/diagnostics/tests/smartCasts/publicVals/kt4409.kt
index 0379d2af41c..e561417654d 100644
--- a/compiler/testData/diagnostics/tests/smartCasts/publicVals/kt4409.kt
+++ b/compiler/testData/diagnostics/tests/smartCasts/publicVals/kt4409.kt
@@ -1,4 +1,4 @@
-public trait A {
+public interface A {
     public val x: Any
 }
 
diff --git a/compiler/testData/diagnostics/tests/smartCasts/variables/kt7599.kt b/compiler/testData/diagnostics/tests/smartCasts/variables/kt7599.kt
index 429a34e22c4..84dbc6bce2e 100644
--- a/compiler/testData/diagnostics/tests/smartCasts/variables/kt7599.kt
+++ b/compiler/testData/diagnostics/tests/smartCasts/variables/kt7599.kt
@@ -1,4 +1,4 @@
-trait A {
+interface A {
     fun ok(): Boolean
 }
 
diff --git a/compiler/testData/diagnostics/tests/substitutions/starProjections.kt b/compiler/testData/diagnostics/tests/substitutions/starProjections.kt
index dc7de4f934f..05ac2b406ef 100644
--- a/compiler/testData/diagnostics/tests/substitutions/starProjections.kt
+++ b/compiler/testData/diagnostics/tests/substitutions/starProjections.kt
@@ -1,6 +1,6 @@
 // !CHECK_TYPE
 
-trait A<R, T: A<R, T>> {
+interface A<R, T: A<R, T>> {
     fun r(): R
     fun t(): T
 }
@@ -10,7 +10,7 @@ fun testA(a: A<*, *>) {
     a.t().checkType { _<A<*, *>>() }
 }
 
-trait B<R, T: B<List<R>, <!UPPER_BOUND_VIOLATED!>T<!>>> {
+interface B<R, T: B<List<R>, <!UPPER_BOUND_VIOLATED!>T<!>>> {
     fun r(): R
     fun t(): T
 }
diff --git a/compiler/testData/diagnostics/tests/subtyping/kt2069.kt b/compiler/testData/diagnostics/tests/subtyping/kt2069.kt
index 80fb566a259..c2c70d7bcb8 100644
--- a/compiler/testData/diagnostics/tests/subtyping/kt2069.kt
+++ b/compiler/testData/diagnostics/tests/subtyping/kt2069.kt
@@ -1,7 +1,7 @@
 //KT-2069 Cannot call super method when superclass has type parameters
 package kt2069
 
-trait T1 {
+interface T1 {
     fun foo() {}
 }
 
diff --git a/compiler/testData/diagnostics/tests/subtyping/kt3159.kt b/compiler/testData/diagnostics/tests/subtyping/kt3159.kt
index a72f45f25e1..6f85c700263 100644
--- a/compiler/testData/diagnostics/tests/subtyping/kt3159.kt
+++ b/compiler/testData/diagnostics/tests/subtyping/kt3159.kt
@@ -1,4 +1,4 @@
-trait Super {
+interface Super {
     var v: CharSequence
     val v2: CharSequence
 }
diff --git a/compiler/testData/diagnostics/tests/thisAndSuper/Super.kt b/compiler/testData/diagnostics/tests/thisAndSuper/Super.kt
index b35d6be9238..db35d1b96c8 100644
--- a/compiler/testData/diagnostics/tests/thisAndSuper/Super.kt
+++ b/compiler/testData/diagnostics/tests/thisAndSuper/Super.kt
@@ -1,6 +1,6 @@
 package example
 
-trait T {
+interface T {
     fun foo() {}
 }
 open class C() {
@@ -42,7 +42,7 @@ class A<E>() : C(), T {
     }
 }
 
-trait G<T> {
+interface G<T> {
     fun foo() {}
 }
 
diff --git a/compiler/testData/diagnostics/tests/thisAndSuper/notAccessibleSuperInTrait.kt b/compiler/testData/diagnostics/tests/thisAndSuper/notAccessibleSuperInTrait.kt
index 52dcd4e77da..c9565beb36d 100644
--- a/compiler/testData/diagnostics/tests/thisAndSuper/notAccessibleSuperInTrait.kt
+++ b/compiler/testData/diagnostics/tests/thisAndSuper/notAccessibleSuperInTrait.kt
@@ -2,7 +2,7 @@ open class A {
     open fun foo() {}
 }
 
-trait ATrait : <!TRAIT_WITH_SUPERCLASS!>A<!> {
+interface ATrait : <!TRAIT_WITH_SUPERCLASS!>A<!> {
 
     override fun foo() {
         <!SUPERCLASS_NOT_ACCESSIBLE_FROM_TRAIT!>super<A><!>.foo()
diff --git a/compiler/testData/diagnostics/tests/thisAndSuper/thisInPropertyInitializer.kt b/compiler/testData/diagnostics/tests/thisAndSuper/thisInPropertyInitializer.kt
index 8876f572337..c89681277bf 100644
--- a/compiler/testData/diagnostics/tests/thisAndSuper/thisInPropertyInitializer.kt
+++ b/compiler/testData/diagnostics/tests/thisAndSuper/thisInPropertyInitializer.kt
@@ -1,4 +1,4 @@
-trait Base {
+interface Base {
     fun foo()
 }
 val String.test: Base = <!EXTENSION_PROPERTY_WITH_BACKING_FIELD!>object: Base<!> {
diff --git a/compiler/testData/diagnostics/tests/thisAndSuper/traitSuperCall.kt b/compiler/testData/diagnostics/tests/thisAndSuper/traitSuperCall.kt
index 297cb817b14..11485e6d46e 100644
--- a/compiler/testData/diagnostics/tests/thisAndSuper/traitSuperCall.kt
+++ b/compiler/testData/diagnostics/tests/thisAndSuper/traitSuperCall.kt
@@ -1,12 +1,12 @@
 // FILE: test.kt
 
-public trait Test {
+public interface Test {
     fun test(): String {
         return "123";
     }
 }
 
-trait KTrait : Test {
+interface KTrait : Test {
     fun ktest() {
         super.test()
 
diff --git a/compiler/testData/diagnostics/tests/traitWithRequired/abstractClass.kt b/compiler/testData/diagnostics/tests/traitWithRequired/abstractClass.kt
index 9d692f9770a..1b1c68bf368 100644
--- a/compiler/testData/diagnostics/tests/traitWithRequired/abstractClass.kt
+++ b/compiler/testData/diagnostics/tests/traitWithRequired/abstractClass.kt
@@ -1,6 +1,6 @@
 open class Required
 
-trait Trait : <!TRAIT_WITH_SUPERCLASS!>Required<!>
+interface Trait : <!TRAIT_WITH_SUPERCLASS!>Required<!>
 
 abstract <!UNMET_TRAIT_REQUIREMENT!>class Abstract<!> : Trait
 
diff --git a/compiler/testData/diagnostics/tests/traitWithRequired/anonymousObjectExtendsTraitWithRequired.kt b/compiler/testData/diagnostics/tests/traitWithRequired/anonymousObjectExtendsTraitWithRequired.kt
index 526735148e5..2be1de89415 100644
--- a/compiler/testData/diagnostics/tests/traitWithRequired/anonymousObjectExtendsTraitWithRequired.kt
+++ b/compiler/testData/diagnostics/tests/traitWithRequired/anonymousObjectExtendsTraitWithRequired.kt
@@ -1,6 +1,6 @@
 open class Required
 
-trait A : <!TRAIT_WITH_SUPERCLASS!>Required<!>
+interface A : <!TRAIT_WITH_SUPERCLASS!>Required<!>
 
 val a = <!UNMET_TRAIT_REQUIREMENT!>object<!> : A {}
 val b: A = object : A, Required() {}
diff --git a/compiler/testData/diagnostics/tests/traitWithRequired/differentGenericArguments.kt b/compiler/testData/diagnostics/tests/traitWithRequired/differentGenericArguments.kt
index 07219c7e9e0..ab90db2cd01 100644
--- a/compiler/testData/diagnostics/tests/traitWithRequired/differentGenericArguments.kt
+++ b/compiler/testData/diagnostics/tests/traitWithRequired/differentGenericArguments.kt
@@ -1,8 +1,8 @@
 open class Generic<T>
 
-trait A : <!TRAIT_WITH_SUPERCLASS!>Generic<Int><!>
+interface A : <!TRAIT_WITH_SUPERCLASS!>Generic<Int><!>
 
-trait B : <!TRAIT_WITH_SUPERCLASS!>Generic<String><!>
+interface B : <!TRAIT_WITH_SUPERCLASS!>Generic<String><!>
 
 <!UNMET_TRAIT_REQUIREMENT, UNMET_TRAIT_REQUIREMENT!>class Y<!> : <!INCONSISTENT_TYPE_PARAMETER_VALUES!>A, B<!>
 class Z : <!INCONSISTENT_TYPE_PARAMETER_VALUES!>A, B, Generic<Int>()<!>
diff --git a/compiler/testData/diagnostics/tests/traitWithRequired/kt3006.kt b/compiler/testData/diagnostics/tests/traitWithRequired/kt3006.kt
index af94dbd8859..426c86fda20 100644
--- a/compiler/testData/diagnostics/tests/traitWithRequired/kt3006.kt
+++ b/compiler/testData/diagnostics/tests/traitWithRequired/kt3006.kt
@@ -1,7 +1,7 @@
 open class Base {
 }
 
-trait Derived: <!TRAIT_WITH_SUPERCLASS!>Base<!> {
+interface Derived: <!TRAIT_WITH_SUPERCLASS!>Base<!> {
     fun foo() {
         f1(this@Derived)
     }
diff --git a/compiler/testData/diagnostics/tests/traitWithRequired/manyRequirementsDisallowed.kt b/compiler/testData/diagnostics/tests/traitWithRequired/manyRequirementsDisallowed.kt
index 9b665610693..7c8060832e7 100644
--- a/compiler/testData/diagnostics/tests/traitWithRequired/manyRequirementsDisallowed.kt
+++ b/compiler/testData/diagnostics/tests/traitWithRequired/manyRequirementsDisallowed.kt
@@ -1,4 +1,4 @@
 open class A
 open class B
 
-trait C : <!TRAIT_WITH_SUPERCLASS!>A<!>, <!MANY_CLASSES_IN_SUPERTYPE_LIST!>B<!>
\ No newline at end of file
+interface C : <!TRAIT_WITH_SUPERCLASS!>A<!>, <!MANY_CLASSES_IN_SUPERTYPE_LIST!>B<!>
\ No newline at end of file
diff --git a/compiler/testData/diagnostics/tests/traitWithRequired/manyTraitsRequireSameClass.kt b/compiler/testData/diagnostics/tests/traitWithRequired/manyTraitsRequireSameClass.kt
index 31275536e00..693178cab97 100644
--- a/compiler/testData/diagnostics/tests/traitWithRequired/manyTraitsRequireSameClass.kt
+++ b/compiler/testData/diagnostics/tests/traitWithRequired/manyTraitsRequireSameClass.kt
@@ -1,12 +1,12 @@
 open class Required
 
-trait A : <!TRAIT_WITH_SUPERCLASS!>Required<!>
+interface A : <!TRAIT_WITH_SUPERCLASS!>Required<!>
 
-trait B : A, <!TRAIT_WITH_SUPERCLASS!>Required<!>
+interface B : A, <!TRAIT_WITH_SUPERCLASS!>Required<!>
 
-trait C : <!TRAIT_WITH_SUPERCLASS!>Required<!>
+interface C : <!TRAIT_WITH_SUPERCLASS!>Required<!>
 
-trait D : B, <!TRAIT_WITH_SUPERCLASS!>Required<!>
+interface D : B, <!TRAIT_WITH_SUPERCLASS!>Required<!>
 
 <!UNMET_TRAIT_REQUIREMENT, UNMET_TRAIT_REQUIREMENT, UNMET_TRAIT_REQUIREMENT!>class W<!> : D
 class X : D, Required()
diff --git a/compiler/testData/diagnostics/tests/traitWithRequired/requirementFulfilledBySubclass.kt b/compiler/testData/diagnostics/tests/traitWithRequired/requirementFulfilledBySubclass.kt
index 0199b50f515..99cea06bcfc 100644
--- a/compiler/testData/diagnostics/tests/traitWithRequired/requirementFulfilledBySubclass.kt
+++ b/compiler/testData/diagnostics/tests/traitWithRequired/requirementFulfilledBySubclass.kt
@@ -1,6 +1,6 @@
 open class RequiredBase
 
-trait Trait : <!TRAIT_WITH_SUPERCLASS!>RequiredBase<!>
+interface Trait : <!TRAIT_WITH_SUPERCLASS!>RequiredBase<!>
 
 open class RequiredDerived : RequiredBase()
 
diff --git a/compiler/testData/diagnostics/tests/traitWithRequired/traitExtendsTraitWithRequired.kt b/compiler/testData/diagnostics/tests/traitWithRequired/traitExtendsTraitWithRequired.kt
index 500ac2773c7..b771f2d842b 100644
--- a/compiler/testData/diagnostics/tests/traitWithRequired/traitExtendsTraitWithRequired.kt
+++ b/compiler/testData/diagnostics/tests/traitWithRequired/traitExtendsTraitWithRequired.kt
@@ -1,8 +1,8 @@
 open class Required(val value: String)
 
-trait First : <!TRAIT_WITH_SUPERCLASS!>Required<!>
+interface First : <!TRAIT_WITH_SUPERCLASS!>Required<!>
 
-trait Second : First
+interface Second : First
 
 <!UNMET_TRAIT_REQUIREMENT!>class Y<!> : Second
 class Z : Second, Required(":o)")
diff --git a/compiler/testData/diagnostics/tests/traitWithRequired/traitRequiresAny.kt b/compiler/testData/diagnostics/tests/traitWithRequired/traitRequiresAny.kt
index 530eeb6df11..8f65d3eddf9 100644
--- a/compiler/testData/diagnostics/tests/traitWithRequired/traitRequiresAny.kt
+++ b/compiler/testData/diagnostics/tests/traitWithRequired/traitRequiresAny.kt
@@ -1,4 +1,4 @@
-trait AnyTrait : <!TRAIT_WITH_SUPERCLASS!>Any<!>
+interface AnyTrait : <!TRAIT_WITH_SUPERCLASS!>Any<!>
 
 class Foo : AnyTrait
 
diff --git a/compiler/testData/diagnostics/tests/traitWithRequired/traitSupertypeList.kt b/compiler/testData/diagnostics/tests/traitWithRequired/traitSupertypeList.kt
index 78e8dd956e9..219d5b6ff57 100644
--- a/compiler/testData/diagnostics/tests/traitWithRequired/traitSupertypeList.kt
+++ b/compiler/testData/diagnostics/tests/traitWithRequired/traitSupertypeList.kt
@@ -1,9 +1,9 @@
 open class bar()
 
-trait Foo<!CONSTRUCTOR_IN_TRAIT!>()<!> : <!TRAIT_WITH_SUPERCLASS!>bar<!><!SUPERTYPE_INITIALIZED_IN_TRAIT!>()<!>, <!MANY_CLASSES_IN_SUPERTYPE_LIST, SUPERTYPE_APPEARS_TWICE!>bar<!>, <!MANY_CLASSES_IN_SUPERTYPE_LIST, SUPERTYPE_APPEARS_TWICE!>bar<!> {
+interface Foo<!CONSTRUCTOR_IN_TRAIT!>()<!> : <!TRAIT_WITH_SUPERCLASS!>bar<!><!SUPERTYPE_INITIALIZED_IN_TRAIT!>()<!>, <!MANY_CLASSES_IN_SUPERTYPE_LIST, SUPERTYPE_APPEARS_TWICE!>bar<!>, <!MANY_CLASSES_IN_SUPERTYPE_LIST, SUPERTYPE_APPEARS_TWICE!>bar<!> {
 }
 
-trait Foo2 : <!TRAIT_WITH_SUPERCLASS!>bar<!>, Foo {
+interface Foo2 : <!TRAIT_WITH_SUPERCLASS!>bar<!>, Foo {
 }
 
 open class Foo1() : bar(), <!SUPERTYPE_NOT_INITIALIZED, MANY_CLASSES_IN_SUPERTYPE_LIST, SUPERTYPE_APPEARS_TWICE!>bar<!>, Foo, <!SUPERTYPE_APPEARS_TWICE!>Foo<!><!NO_CONSTRUCTOR!>()<!> {}
diff --git a/compiler/testData/diagnostics/tests/traitWithRequired/uninheritableTraitDifferentGenericArguments.kt b/compiler/testData/diagnostics/tests/traitWithRequired/uninheritableTraitDifferentGenericArguments.kt
index 3d6e92afd39..d9788d49103 100644
--- a/compiler/testData/diagnostics/tests/traitWithRequired/uninheritableTraitDifferentGenericArguments.kt
+++ b/compiler/testData/diagnostics/tests/traitWithRequired/uninheritableTraitDifferentGenericArguments.kt
@@ -1,7 +1,7 @@
 open class Generic<T>
 
-trait A : <!TRAIT_WITH_SUPERCLASS!>Generic<String><!>
+interface A : <!TRAIT_WITH_SUPERCLASS!>Generic<String><!>
 
-trait B : <!TRAIT_WITH_SUPERCLASS!>Generic<Int><!>
+interface B : <!TRAIT_WITH_SUPERCLASS!>Generic<Int><!>
 
-trait C : <!INCONSISTENT_TYPE_PARAMETER_VALUES!>A, B<!>
+interface C : <!INCONSISTENT_TYPE_PARAMETER_VALUES!>A, B<!>
diff --git a/compiler/testData/diagnostics/tests/variance/Class.kt b/compiler/testData/diagnostics/tests/variance/Class.kt
index 0f1ed851ea8..5bd90ac9c06 100644
--- a/compiler/testData/diagnostics/tests/variance/Class.kt
+++ b/compiler/testData/diagnostics/tests/variance/Class.kt
@@ -1,18 +1,18 @@
-trait In<in T>
-trait Out<out T>
-trait Inv<T>
+interface In<in T>
+interface Out<out T>
+interface Inv<T>
 
-trait TypeBounds1<in I, out O, P, X : <!TYPE_VARIANCE_CONFLICT(I; in; out; I)!>I<!>>
-trait TypeBounds2<in I, out O, P, X : O>
-trait TypeBounds3<in I, out O, P, X : P>
-trait TypeBounds4<in I, out O, P, X : In<I>>
-trait TypeBounds5<in I, out O, P, X : In<<!TYPE_VARIANCE_CONFLICT(O; out; in; In<O>)!>O<!>>>
+interface TypeBounds1<in I, out O, P, X : <!TYPE_VARIANCE_CONFLICT(I; in; out; I)!>I<!>>
+interface TypeBounds2<in I, out O, P, X : O>
+interface TypeBounds3<in I, out O, P, X : P>
+interface TypeBounds4<in I, out O, P, X : In<I>>
+interface TypeBounds5<in I, out O, P, X : In<<!TYPE_VARIANCE_CONFLICT(O; out; in; In<O>)!>O<!>>>
 
-trait WhereTypeBounds1<in I, out O, P, X> where X : <!TYPE_VARIANCE_CONFLICT(I; in; out; I)!>I<!>
-trait WhereTypeBounds2<in I, out O, P, X> where X : O
-trait WhereTypeBounds3<in I, out O, P, X> where X : P
-trait WhereTypeBounds4<in I, out O, P, X> where X : In<I>
-trait WhereTypeBounds5<in I, out O, P, X> where X : In<<!TYPE_VARIANCE_CONFLICT(O; out; in; In<O>)!>O<!>>
+interface WhereTypeBounds1<in I, out O, P, X> where X : <!TYPE_VARIANCE_CONFLICT(I; in; out; I)!>I<!>
+interface WhereTypeBounds2<in I, out O, P, X> where X : O
+interface WhereTypeBounds3<in I, out O, P, X> where X : P
+interface WhereTypeBounds4<in I, out O, P, X> where X : In<I>
+interface WhereTypeBounds5<in I, out O, P, X> where X : In<<!TYPE_VARIANCE_CONFLICT(O; out; in; In<O>)!>O<!>>
 
 class SubClass1<in I, out O, P> : Out<<!TYPE_VARIANCE_CONFLICT(I; in; out; Out<I>)!>I<!>>
 class SubClass2<in I, out O, P> : Out<O>
diff --git a/compiler/testData/diagnostics/tests/variance/Function.kt b/compiler/testData/diagnostics/tests/variance/Function.kt
index 6759027da40..9d008952063 100644
--- a/compiler/testData/diagnostics/tests/variance/Function.kt
+++ b/compiler/testData/diagnostics/tests/variance/Function.kt
@@ -1,9 +1,9 @@
-trait In<in T>
-trait Out<out T>
-trait Inv<T>
+interface In<in T>
+interface Out<out T>
+interface Inv<T>
 fun <T> getT(): T = null!!
 
-trait Test<in I, out O, P> {
+interface Test<in I, out O, P> {
     fun parameters1(i: I, o: <!TYPE_VARIANCE_CONFLICT(O; out; in; O)!>O<!>, p: P)
     fun parameters2(i: In<<!TYPE_VARIANCE_CONFLICT(I; in; out; In<I>)!>I<!>>)
     fun parameters3(i: In<O>)
diff --git a/compiler/testData/diagnostics/tests/variance/FunctionTypes.kt b/compiler/testData/diagnostics/tests/variance/FunctionTypes.kt
index e36928a1330..87418e61ed0 100644
--- a/compiler/testData/diagnostics/tests/variance/FunctionTypes.kt
+++ b/compiler/testData/diagnostics/tests/variance/FunctionTypes.kt
@@ -1,7 +1,7 @@
-trait In<in T>
+interface In<in T>
 fun <T> getT(): T = null!!
 
-trait Test<in I, out O, P> {
+interface Test<in I, out O, P> {
     fun ok1(i: (O) -> I) : (I) -> O
     fun ok2(i: (P) -> P) : (P) -> P
     fun ok3(i: (In<I>) -> In<O>) = getT<(In<O>) -> In<I>>()
diff --git a/compiler/testData/diagnostics/tests/variance/InPosition.kt b/compiler/testData/diagnostics/tests/variance/InPosition.kt
index 403ee306bb0..550b0f0fc1b 100644
--- a/compiler/testData/diagnostics/tests/variance/InPosition.kt
+++ b/compiler/testData/diagnostics/tests/variance/InPosition.kt
@@ -1,9 +1,9 @@
-trait In<in T>
-trait Out<out T>
-trait Inv<T>
-trait Pair<out X, out Y>
+interface In<in T>
+interface Out<out T>
+interface Inv<T>
+interface Pair<out X, out Y>
 
-trait Test<in I, out O, P> {
+interface Test<in I, out O, P> {
     fun ok1(i: I)
     fun ok2(i: In<O>)
     fun ok3(i: In<In<I>>)
diff --git a/compiler/testData/diagnostics/tests/variance/InvariantPosition.kt b/compiler/testData/diagnostics/tests/variance/InvariantPosition.kt
index 96dd46da951..96c60aea28f 100644
--- a/compiler/testData/diagnostics/tests/variance/InvariantPosition.kt
+++ b/compiler/testData/diagnostics/tests/variance/InvariantPosition.kt
@@ -1,9 +1,9 @@
-trait In<in T>
-trait Out<out T>
-trait Inv<T>
-trait Pair<out X, out Y>
+interface In<in T>
+interface Out<out T>
+interface Inv<T>
+interface Pair<out X, out Y>
 
-trait Test<in I, out O, P> {
+interface Test<in I, out O, P> {
     var ok1: Inv<P>
     var ok2: P
     var ok3: Out<In<P>>
diff --git a/compiler/testData/diagnostics/tests/variance/NullableTypes.kt b/compiler/testData/diagnostics/tests/variance/NullableTypes.kt
index 1321ba9926c..2f0df3a258b 100644
--- a/compiler/testData/diagnostics/tests/variance/NullableTypes.kt
+++ b/compiler/testData/diagnostics/tests/variance/NullableTypes.kt
@@ -1,10 +1,10 @@
-trait In<in I>
-trait Out<out O>
-trait Inv<P>
+interface In<in I>
+interface Out<out O>
+interface Inv<P>
 fun <T> getT(): T = null!!
 
 
-trait Test<in I : Any, out O : Any, P : Any> {
+interface Test<in I : Any, out O : Any, P : Any> {
     fun ok1(i: I?) : O?
     fun ok2(i: In<O?>?) : Out<O?>?
     fun ok3(i: Inv<in O?>) = getT<Inv<in I?>>()
diff --git a/compiler/testData/diagnostics/tests/variance/OutPosition.kt b/compiler/testData/diagnostics/tests/variance/OutPosition.kt
index e07933736fe..000dbc57291 100644
--- a/compiler/testData/diagnostics/tests/variance/OutPosition.kt
+++ b/compiler/testData/diagnostics/tests/variance/OutPosition.kt
@@ -1,9 +1,9 @@
-trait In<in T>
-trait Out<out T>
-trait Inv<T>
-trait Pair<out X, out Y>
+interface In<in T>
+interface Out<out T>
+interface Inv<T>
+interface Pair<out X, out Y>
 
-trait Test<in I, out O, P> {
+interface Test<in I, out O, P> {
     fun ok1(): O
     fun ok2(): In<I>
     fun ok3(): In<In<O>>
diff --git a/compiler/testData/diagnostics/tests/variance/PrimaryConstructor.kt b/compiler/testData/diagnostics/tests/variance/PrimaryConstructor.kt
index 32192a50558..a601fb7987b 100644
--- a/compiler/testData/diagnostics/tests/variance/PrimaryConstructor.kt
+++ b/compiler/testData/diagnostics/tests/variance/PrimaryConstructor.kt
@@ -1,6 +1,6 @@
-trait In<in T>
-trait Out<out T>
-trait Inv<T>
+interface In<in T>
+interface Out<out T>
+interface Inv<T>
 
 fun <T> getT(): T = null!!
 
diff --git a/compiler/testData/diagnostics/tests/variance/ValProperty.kt b/compiler/testData/diagnostics/tests/variance/ValProperty.kt
index 2699705866a..206c78f1220 100644
--- a/compiler/testData/diagnostics/tests/variance/ValProperty.kt
+++ b/compiler/testData/diagnostics/tests/variance/ValProperty.kt
@@ -1,6 +1,6 @@
-trait In<in T>
-trait Out<out T>
-trait Inv<T>
+interface In<in T>
+interface Out<out T>
+interface Inv<T>
 
 class Delegate<T> {
     fun get(t: Any, p: PropertyMetadata): T = null!!
diff --git a/compiler/testData/diagnostics/tests/variance/VarProperty.kt b/compiler/testData/diagnostics/tests/variance/VarProperty.kt
index 5e8812c2c0b..dedb3307d46 100644
--- a/compiler/testData/diagnostics/tests/variance/VarProperty.kt
+++ b/compiler/testData/diagnostics/tests/variance/VarProperty.kt
@@ -1,6 +1,6 @@
-trait In<in T>
-trait Out<out T>
-trait Inv<T>
+interface In<in T>
+interface Out<out T>
+interface Inv<T>
 
 class Delegate<T> {
     fun get(t: Any, p: PropertyMetadata): T = null!!
diff --git a/compiler/testData/diagnostics/tests/variance/Visibility.kt b/compiler/testData/diagnostics/tests/variance/Visibility.kt
index cee2c4a1b72..55d8c56afe0 100644
--- a/compiler/testData/diagnostics/tests/variance/Visibility.kt
+++ b/compiler/testData/diagnostics/tests/variance/Visibility.kt
@@ -1,4 +1,4 @@
-trait Test<in I, out O> {
+interface Test<in I, out O> {
     val internal_val: <!TYPE_VARIANCE_CONFLICT!>I<!>
     public val public_val: <!TYPE_VARIANCE_CONFLICT!>I<!>
     protected val protected_val: <!TYPE_VARIANCE_CONFLICT!>I<!>
diff --git a/compiler/testData/diagnostics/tests/variance/privateToThis/Trait.kt b/compiler/testData/diagnostics/tests/variance/privateToThis/Trait.kt
index cc19666ccdb..3e72d50861e 100644
--- a/compiler/testData/diagnostics/tests/variance/privateToThis/Trait.kt
+++ b/compiler/testData/diagnostics/tests/variance/privateToThis/Trait.kt
@@ -1,4 +1,4 @@
-internal trait Test</*0*/ in I> {
+internal interface Test</*0*/ in I> {
     private/*private to this*/ final fun foo(): I {
         throw Exception()
     }
diff --git a/compiler/testData/diagnostics/testsWithJsStdLib/dynamicTypes/delegationBy.kt b/compiler/testData/diagnostics/testsWithJsStdLib/dynamicTypes/delegationBy.kt
index bf23d780a78..b21ee696104 100644
--- a/compiler/testData/diagnostics/testsWithJsStdLib/dynamicTypes/delegationBy.kt
+++ b/compiler/testData/diagnostics/testsWithJsStdLib/dynamicTypes/delegationBy.kt
@@ -1,4 +1,4 @@
-trait Tr {
+interface Tr {
     fun foo()
 }
 
diff --git a/compiler/testData/diagnostics/testsWithJsStdLib/dynamicTypes/inference.kt b/compiler/testData/diagnostics/testsWithJsStdLib/dynamicTypes/inference.kt
index 894e20bb58b..195c6108764 100644
--- a/compiler/testData/diagnostics/testsWithJsStdLib/dynamicTypes/inference.kt
+++ b/compiler/testData/diagnostics/testsWithJsStdLib/dynamicTypes/inference.kt
@@ -3,7 +3,7 @@
 
 fun <T> foo(t1: T, t2: T): T = t1
 
-trait Tr
+interface Tr
 class C: Tr
 fun <T: Tr> foo1(t1: T, t2: T): T = t1
 
diff --git a/compiler/testData/diagnostics/testsWithJsStdLib/dynamicTypes/overrides.kt b/compiler/testData/diagnostics/testsWithJsStdLib/dynamicTypes/overrides.kt
index d372b4a2b58..53a745600b0 100644
--- a/compiler/testData/diagnostics/testsWithJsStdLib/dynamicTypes/overrides.kt
+++ b/compiler/testData/diagnostics/testsWithJsStdLib/dynamicTypes/overrides.kt
@@ -1,18 +1,18 @@
-trait P
-trait R
+interface P
+interface R
 
-trait A {
+interface A {
     fun foo(p: P): R
     fun dynamic(p: dynamic): dynamic
 }
 
-trait B : A {
+interface B : A {
     override fun foo(p: dynamic): dynamic
     override fun dynamic(p: P): R
 }
 
-trait A1 {
+interface A1 {
     fun foo(p: dynamic): dynamic
 }
 
-trait C : A, A1
\ No newline at end of file
+interface C : A, A1
\ No newline at end of file
diff --git a/compiler/testData/diagnostics/testsWithJsStdLib/dynamicTypes/supertypesAndBounds.kt b/compiler/testData/diagnostics/testsWithJsStdLib/dynamicTypes/supertypesAndBounds.kt
index 267e111d84e..5153971a2bd 100644
--- a/compiler/testData/diagnostics/testsWithJsStdLib/dynamicTypes/supertypesAndBounds.kt
+++ b/compiler/testData/diagnostics/testsWithJsStdLib/dynamicTypes/supertypesAndBounds.kt
@@ -1,4 +1,4 @@
-trait Tr : <!DYNAMIC_SUPERTYPE!>dynamic<!>
+interface Tr : <!DYNAMIC_SUPERTYPE!>dynamic<!>
 
 fun <T: <!DYNAMIC_UPPER_BOUND!>dynamic<!>> foo() {}
 
diff --git a/compiler/testData/diagnostics/testsWithJsStdLib/native/optionlBody/native.kt b/compiler/testData/diagnostics/testsWithJsStdLib/native/optionlBody/native.kt
index 5aaac4d22ca..2d56b6fc0ae 100644
--- a/compiler/testData/diagnostics/testsWithJsStdLib/native/optionlBody/native.kt
+++ b/compiler/testData/diagnostics/testsWithJsStdLib/native/optionlBody/native.kt
@@ -17,7 +17,7 @@ native
 fun String.bar(): Int = noImpl
 
 native
-trait T {
+interface T {
     val baz: Int
 
     fun foo()
diff --git a/compiler/testData/diagnostics/testsWithJsStdLib/native/optionlBody/nativeGetter.kt b/compiler/testData/diagnostics/testsWithJsStdLib/native/optionlBody/nativeGetter.kt
index 013d2ca2bdd..a24f4ef62a9 100644
--- a/compiler/testData/diagnostics/testsWithJsStdLib/native/optionlBody/nativeGetter.kt
+++ b/compiler/testData/diagnostics/testsWithJsStdLib/native/optionlBody/nativeGetter.kt
@@ -5,7 +5,7 @@ fun String.bar(n: Int): Int? = noImpl
 
 
 native
-trait T {
+interface T {
     nativeGetter
     fun foo(d: Double): String?
     nativeGetter
diff --git a/compiler/testData/diagnostics/testsWithJsStdLib/unsupportedFeatures/localClassifier.kt b/compiler/testData/diagnostics/testsWithJsStdLib/unsupportedFeatures/localClassifier.kt
index 4b421b320df..caafd08d4de 100644
--- a/compiler/testData/diagnostics/testsWithJsStdLib/unsupportedFeatures/localClassifier.kt
+++ b/compiler/testData/diagnostics/testsWithJsStdLib/unsupportedFeatures/localClassifier.kt
@@ -3,10 +3,10 @@
 fun foo() {
     <!NON_TOPLEVEL_CLASS_DECLARATION!>class A<!> {
         inner <!NON_TOPLEVEL_CLASS_DECLARATION!>class E<!> {
-            <!NESTED_CLASS_NOT_ALLOWED, NON_TOPLEVEL_CLASS_DECLARATION!>trait T<!>
+            <!NESTED_CLASS_NOT_ALLOWED, NON_TOPLEVEL_CLASS_DECLARATION!>interface T<!>
         }
     }
 
-    <!NON_TOPLEVEL_CLASS_DECLARATION!>trait T<!> {
+    <!NON_TOPLEVEL_CLASS_DECLARATION!>interface T<!> {
     }
 }
diff --git a/compiler/testData/diagnostics/testsWithJsStdLib/unsupportedFeatures/nestedInnerClassifier.kt b/compiler/testData/diagnostics/testsWithJsStdLib/unsupportedFeatures/nestedInnerClassifier.kt
index a4e17120965..95715883076 100644
--- a/compiler/testData/diagnostics/testsWithJsStdLib/unsupportedFeatures/nestedInnerClassifier.kt
+++ b/compiler/testData/diagnostics/testsWithJsStdLib/unsupportedFeatures/nestedInnerClassifier.kt
@@ -4,8 +4,8 @@ class A {
 
         inner <!NON_TOPLEVEL_CLASS_DECLARATION!>class D<!>
 
-        <!NON_TOPLEVEL_CLASS_DECLARATION!>trait T<!> {
-            <!NON_TOPLEVEL_CLASS_DECLARATION!>trait A<!>
+        <!NON_TOPLEVEL_CLASS_DECLARATION!>interface T<!> {
+            <!NON_TOPLEVEL_CLASS_DECLARATION!>interface A<!>
             <!NON_TOPLEVEL_CLASS_DECLARATION!>class B<!>
         }
 
@@ -14,8 +14,8 @@ class A {
 
     inner <!NON_TOPLEVEL_CLASS_DECLARATION!>class I<!>
 
-    <!NON_TOPLEVEL_CLASS_DECLARATION!>trait T<!> {
-        <!NON_TOPLEVEL_CLASS_DECLARATION!>trait A<!>
+    <!NON_TOPLEVEL_CLASS_DECLARATION!>interface T<!> {
+        <!NON_TOPLEVEL_CLASS_DECLARATION!>interface A<!>
         <!NON_TOPLEVEL_CLASS_DECLARATION!>class B<!>
 
         companion object {}
@@ -30,22 +30,22 @@ class A {
     companion object {}
 }
 
-trait T {
+interface T {
     <!NON_TOPLEVEL_CLASS_DECLARATION!>class B<!> {
         <!NON_TOPLEVEL_CLASS_DECLARATION!>class C<!>
 
         inner <!NON_TOPLEVEL_CLASS_DECLARATION!>class D<!>
 
-        <!NON_TOPLEVEL_CLASS_DECLARATION!>trait T<!> {
-            <!NON_TOPLEVEL_CLASS_DECLARATION!>trait A<!>
+        <!NON_TOPLEVEL_CLASS_DECLARATION!>interface T<!> {
+            <!NON_TOPLEVEL_CLASS_DECLARATION!>interface A<!>
             <!NON_TOPLEVEL_CLASS_DECLARATION!>class B<!>
         }
 
         companion object {}
     }
 
-    <!NON_TOPLEVEL_CLASS_DECLARATION!>trait T<!> {
-        <!NON_TOPLEVEL_CLASS_DECLARATION!>trait A<!>
+    <!NON_TOPLEVEL_CLASS_DECLARATION!>interface T<!> {
+        <!NON_TOPLEVEL_CLASS_DECLARATION!>interface A<!>
         <!NON_TOPLEVEL_CLASS_DECLARATION!>class B<!>
 
         companion object {}
@@ -68,8 +68,8 @@ enum class E {
 
         inner <!NON_TOPLEVEL_CLASS_DECLARATION!>class D<!>
 
-        <!NON_TOPLEVEL_CLASS_DECLARATION!>trait T<!> {
-            <!NON_TOPLEVEL_CLASS_DECLARATION!>trait A<!>
+        <!NON_TOPLEVEL_CLASS_DECLARATION!>interface T<!> {
+            <!NON_TOPLEVEL_CLASS_DECLARATION!>interface A<!>
             <!NON_TOPLEVEL_CLASS_DECLARATION!>class B<!>
         }
 
@@ -78,8 +78,8 @@ enum class E {
 
     inner <!NON_TOPLEVEL_CLASS_DECLARATION!>class I<!>
 
-    <!NON_TOPLEVEL_CLASS_DECLARATION!>trait T<!> {
-        <!NON_TOPLEVEL_CLASS_DECLARATION!>trait A<!>
+    <!NON_TOPLEVEL_CLASS_DECLARATION!>interface T<!> {
+        <!NON_TOPLEVEL_CLASS_DECLARATION!>interface A<!>
         <!NON_TOPLEVEL_CLASS_DECLARATION!>class B<!>
 
         companion object {}
diff --git a/compiler/testData/diagnostics/testsWithStdLib/annotations/jvmOverloads/jvmOverloadsOnAbstractMethods.kt b/compiler/testData/diagnostics/testsWithStdLib/annotations/jvmOverloads/jvmOverloadsOnAbstractMethods.kt
index 2d72d8da6ad..47403afbd7e 100644
--- a/compiler/testData/diagnostics/testsWithStdLib/annotations/jvmOverloads/jvmOverloadsOnAbstractMethods.kt
+++ b/compiler/testData/diagnostics/testsWithStdLib/annotations/jvmOverloads/jvmOverloadsOnAbstractMethods.kt
@@ -1,4 +1,4 @@
-trait T {
+interface T {
     <!OVERLOADS_ABSTRACT!>@kotlin.jvm.overloads fun foo(s: String = "OK")<!>
 }
 
diff --git a/compiler/testData/diagnostics/testsWithStdLib/annotations/platformStatic/functions.kt b/compiler/testData/diagnostics/testsWithStdLib/annotations/platformStatic/functions.kt
index f5dfa1a51dd..432e89e7508 100644
--- a/compiler/testData/diagnostics/testsWithStdLib/annotations/platformStatic/functions.kt
+++ b/compiler/testData/diagnostics/testsWithStdLib/annotations/platformStatic/functions.kt
@@ -27,7 +27,7 @@ class A {
     }
 }
 
-trait B {
+interface B {
     companion object {
         <!PLATFORM_STATIC_NOT_IN_OBJECT!>platformStatic fun a1()<!> {
 
diff --git a/compiler/testData/diagnostics/testsWithStdLib/callableReference/function/abstractClassConstructors.kt b/compiler/testData/diagnostics/testsWithStdLib/callableReference/function/abstractClassConstructors.kt
index d64483c26b0..9afebc524cc 100644
--- a/compiler/testData/diagnostics/testsWithStdLib/callableReference/function/abstractClassConstructors.kt
+++ b/compiler/testData/diagnostics/testsWithStdLib/callableReference/function/abstractClassConstructors.kt
@@ -1,5 +1,5 @@
 // !DIAGNOSTICS: -UNUSED_EXPRESSION
-trait A
+interface A
 abstract class B
 annotation class C
 enum class D
diff --git a/compiler/testData/diagnostics/testsWithStdLib/callableReference/property/abstractPropertyViaSubclasses.kt b/compiler/testData/diagnostics/testsWithStdLib/callableReference/property/abstractPropertyViaSubclasses.kt
index 1c7924844a1..0f5adfb8e4b 100644
--- a/compiler/testData/diagnostics/testsWithStdLib/callableReference/property/abstractPropertyViaSubclasses.kt
+++ b/compiler/testData/diagnostics/testsWithStdLib/callableReference/property/abstractPropertyViaSubclasses.kt
@@ -2,7 +2,7 @@
 
 import kotlin.reflect.KMemberProperty
 
-trait Base {
+interface Base {
     val x: Any
 }
 
diff --git a/compiler/testData/diagnostics/testsWithStdLib/native/override.kt b/compiler/testData/diagnostics/testsWithStdLib/native/override.kt
index 262ed68555a..57ab03f7b76 100644
--- a/compiler/testData/diagnostics/testsWithStdLib/native/override.kt
+++ b/compiler/testData/diagnostics/testsWithStdLib/native/override.kt
@@ -1,6 +1,6 @@
 import kotlin.jvm.*
 
-trait Base {
+interface Base {
     fun foo()
 }
 
diff --git a/compiler/testData/diagnostics/testsWithStdLib/native/trait.kt b/compiler/testData/diagnostics/testsWithStdLib/native/trait.kt
index e312f88ad3c..c318b5b2350 100644
--- a/compiler/testData/diagnostics/testsWithStdLib/native/trait.kt
+++ b/compiler/testData/diagnostics/testsWithStdLib/native/trait.kt
@@ -1,6 +1,6 @@
 import kotlin.jvm.*
 
-trait Tr {
+interface Tr {
     <!NATIVE_DECLARATION_IN_TRAIT!>native fun foo()<!>
     <!NATIVE_DECLARATION_IN_TRAIT, NATIVE_DECLARATION_CANNOT_HAVE_BODY!>native fun bar()<!> {}
 
diff --git a/compiler/testData/evaluate/constant/classObjectProperty.kt b/compiler/testData/evaluate/constant/classObjectProperty.kt
index b44b2fa3450..f541f11805f 100644
--- a/compiler/testData/evaluate/constant/classObjectProperty.kt
+++ b/compiler/testData/evaluate/constant/classObjectProperty.kt
@@ -44,6 +44,6 @@ fun foo() {
     }
 }
 
-trait Foo {
+interface Foo {
     fun f()
 }
\ No newline at end of file
diff --git a/compiler/testData/evaluate/constant/finalProperty.kt b/compiler/testData/evaluate/constant/finalProperty.kt
index 74c23ffa565..fb1c28c70f3 100644
--- a/compiler/testData/evaluate/constant/finalProperty.kt
+++ b/compiler/testData/evaluate/constant/finalProperty.kt
@@ -50,6 +50,6 @@ fun foo() {
     val prop8 = A().a + 1
 }
 
-trait Foo {
+interface Foo {
     fun f()
 }
\ No newline at end of file
diff --git a/compiler/testData/evaluate/constant/localVal.kt b/compiler/testData/evaluate/constant/localVal.kt
index fb86944ab89..9c5cbf1febf 100644
--- a/compiler/testData/evaluate/constant/localVal.kt
+++ b/compiler/testData/evaluate/constant/localVal.kt
@@ -48,6 +48,6 @@ fun foo() {
     val prop8 = a + 1
 }
 
-trait Foo {
+interface Foo {
     fun f()
 }
\ No newline at end of file
diff --git a/compiler/testData/evaluate/constant/localVar.kt b/compiler/testData/evaluate/constant/localVar.kt
index a607b8a6172..5b8a2688f99 100644
--- a/compiler/testData/evaluate/constant/localVar.kt
+++ b/compiler/testData/evaluate/constant/localVar.kt
@@ -48,6 +48,6 @@ fun foo() {
     val prop8 = a + 1
 }
 
-trait Foo {
+interface Foo {
     fun f()
 }
\ No newline at end of file
diff --git a/compiler/testData/evaluate/constant/nonFinalProperty.kt b/compiler/testData/evaluate/constant/nonFinalProperty.kt
index 41f11e20855..78035a28a04 100644
--- a/compiler/testData/evaluate/constant/nonFinalProperty.kt
+++ b/compiler/testData/evaluate/constant/nonFinalProperty.kt
@@ -51,6 +51,6 @@ fun foo() {
     val prop8 = A().a + 1
 }
 
-trait Foo {
+interface Foo {
     fun f()
 }
\ No newline at end of file
diff --git a/compiler/testData/evaluate/constant/objectProperty.kt b/compiler/testData/evaluate/constant/objectProperty.kt
index 83e55f2c15d..6132aecda7c 100644
--- a/compiler/testData/evaluate/constant/objectProperty.kt
+++ b/compiler/testData/evaluate/constant/objectProperty.kt
@@ -43,6 +43,6 @@ fun foo() {
     }
 }
 
-trait Foo {
+interface Foo {
     fun f()
 }
\ No newline at end of file
diff --git a/compiler/testData/evaluate/constant/topLevelVal.kt b/compiler/testData/evaluate/constant/topLevelVal.kt
index 602dcbdfa88..29a0a0105f5 100644
--- a/compiler/testData/evaluate/constant/topLevelVal.kt
+++ b/compiler/testData/evaluate/constant/topLevelVal.kt
@@ -42,6 +42,6 @@ fun foo() {
     val prop6 = a + 1
 }
 
-trait Foo {
+interface Foo {
     fun f()
 }
\ No newline at end of file
diff --git a/compiler/testData/evaluate/constant/topLevelVar.kt b/compiler/testData/evaluate/constant/topLevelVar.kt
index 28390177672..717d8087726 100644
--- a/compiler/testData/evaluate/constant/topLevelVar.kt
+++ b/compiler/testData/evaluate/constant/topLevelVar.kt
@@ -42,6 +42,6 @@ fun foo() {
     val prop6 = a + 1
 }
 
-trait Foo {
+interface Foo {
     fun f()
 }
\ No newline at end of file
diff --git a/compiler/testData/integration/ant/js/suppressWarnings/root1/foo.kt b/compiler/testData/integration/ant/js/suppressWarnings/root1/foo.kt
index b97b1e74260..46efcd61cca 100644
--- a/compiler/testData/integration/ant/js/suppressWarnings/root1/foo.kt
+++ b/compiler/testData/integration/ant/js/suppressWarnings/root1/foo.kt
@@ -7,7 +7,7 @@ fun foo(p: Int??) {
 
 }
 
-trait T {
+interface T {
     abstract fun foo()
 }
 
diff --git a/compiler/testData/integration/ant/jvm/suppressWarnings/hello.kt b/compiler/testData/integration/ant/jvm/suppressWarnings/hello.kt
index 17ad0702849..3aa467c4ea8 100644
--- a/compiler/testData/integration/ant/jvm/suppressWarnings/hello.kt
+++ b/compiler/testData/integration/ant/jvm/suppressWarnings/hello.kt
@@ -4,7 +4,7 @@ fun foo(p: Int??) {
 
 }
 
-trait T {
+interface T {
     abstract fun foo()
 }
 
diff --git a/compiler/testData/lineNumber/trait.kt b/compiler/testData/lineNumber/trait.kt
index 935f56ab7ed..f0a8880d08c 100644
--- a/compiler/testData/lineNumber/trait.kt
+++ b/compiler/testData/lineNumber/trait.kt
@@ -1,4 +1,4 @@
-trait A {
+interface A {
     fun foo() = test.lineNumber()
     
     fun bar(): Int {
diff --git a/compiler/testData/loadJava/compiledKotlin/annotations/MultiDimensionalArrayMethod.kt b/compiler/testData/loadJava/compiledKotlin/annotations/MultiDimensionalArrayMethod.kt
index c2f78f22e6f..5d51003f956 100644
--- a/compiler/testData/loadJava/compiledKotlin/annotations/MultiDimensionalArrayMethod.kt
+++ b/compiler/testData/loadJava/compiledKotlin/annotations/MultiDimensionalArrayMethod.kt
@@ -3,7 +3,7 @@ package test
 
 annotation class Anno(val s: String)
 
-trait T {
+interface T {
     Anno("foo")
     fun foo(): Array<Array<Array<T>>>
 
diff --git a/compiler/testData/loadJava/compiledKotlin/annotations/parameters/FunctionInTrait.kt b/compiler/testData/loadJava/compiledKotlin/annotations/parameters/FunctionInTrait.kt
index a4ffcb65b13..53410070168 100644
--- a/compiler/testData/loadJava/compiledKotlin/annotations/parameters/FunctionInTrait.kt
+++ b/compiler/testData/loadJava/compiledKotlin/annotations/parameters/FunctionInTrait.kt
@@ -3,6 +3,6 @@ package test
 
 annotation class Anno
 
-trait Trait {
+interface Trait {
     fun foo([Anno] x: String) = 42
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/annotations/propertiesWithoutBackingFields/NestedTrait.kt b/compiler/testData/loadJava/compiledKotlin/annotations/propertiesWithoutBackingFields/NestedTrait.kt
index 4b3be4fdcc7..f0b91434720 100644
--- a/compiler/testData/loadJava/compiledKotlin/annotations/propertiesWithoutBackingFields/NestedTrait.kt
+++ b/compiler/testData/loadJava/compiledKotlin/annotations/propertiesWithoutBackingFields/NestedTrait.kt
@@ -3,7 +3,7 @@ package test
 annotation class Anno
 
 class Class {
-    trait Trait {
+    interface Trait {
         [Anno] val property: Int
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/annotations/propertiesWithoutBackingFields/Trait.kt b/compiler/testData/loadJava/compiledKotlin/annotations/propertiesWithoutBackingFields/Trait.kt
index 0454006a9cd..5d238dffc50 100644
--- a/compiler/testData/loadJava/compiledKotlin/annotations/propertiesWithoutBackingFields/Trait.kt
+++ b/compiler/testData/loadJava/compiledKotlin/annotations/propertiesWithoutBackingFields/Trait.kt
@@ -2,6 +2,6 @@ package test
 
 annotation class Anno
 
-trait Trait {
+interface Trait {
     [Anno] val property: Int
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/annotations/propertiesWithoutBackingFields/TraitClassObject.kt b/compiler/testData/loadJava/compiledKotlin/annotations/propertiesWithoutBackingFields/TraitClassObject.kt
index 2d2b2025b92..2a4491fcca5 100644
--- a/compiler/testData/loadJava/compiledKotlin/annotations/propertiesWithoutBackingFields/TraitClassObject.kt
+++ b/compiler/testData/loadJava/compiledKotlin/annotations/propertiesWithoutBackingFields/TraitClassObject.kt
@@ -2,7 +2,7 @@ package test
 
 annotation class Anno
 
-trait Trait {
+interface Trait {
     companion object {
         [Anno] val property: Int
             get() = 42
diff --git a/compiler/testData/loadJava/compiledKotlin/class/ClassMemberConflict.kt b/compiler/testData/loadJava/compiledKotlin/class/ClassMemberConflict.kt
index c45d2c81be0..3ae0a3d9b3b 100644
--- a/compiler/testData/loadJava/compiledKotlin/class/ClassMemberConflict.kt
+++ b/compiler/testData/loadJava/compiledKotlin/class/ClassMemberConflict.kt
@@ -3,7 +3,7 @@ package test
 
 class ConstructorTypeParamClassObjectTypeConflict<test> {
     companion object {
-        trait test
+        interface test
     }
 
     val some: test? = throw Exception()
diff --git a/compiler/testData/loadJava/compiledKotlin/class/ClassParamReferencesSelf.kt b/compiler/testData/loadJava/compiledKotlin/class/ClassParamReferencesSelf.kt
index e28efeedca1..9f333a018b0 100644
--- a/compiler/testData/loadJava/compiledKotlin/class/ClassParamReferencesSelf.kt
+++ b/compiler/testData/loadJava/compiledKotlin/class/ClassParamReferencesSelf.kt
@@ -1,5 +1,5 @@
 package test
 
-trait TraitWithP<P>
+interface TraitWithP<P>
 
 class ClassParamReferencesSelf<A : TraitWithP<A>>
diff --git a/compiler/testData/loadJava/compiledKotlin/class/InheritSubstitutedMethod.kt b/compiler/testData/loadJava/compiledKotlin/class/InheritSubstitutedMethod.kt
index b5a3fe15d2f..517e8f1236d 100644
--- a/compiler/testData/loadJava/compiledKotlin/class/InheritSubstitutedMethod.kt
+++ b/compiler/testData/loadJava/compiledKotlin/class/InheritSubstitutedMethod.kt
@@ -1,7 +1,7 @@
 //ALLOW_AST_ACCESS
 package test
 
-public trait A<T> {
+public interface A<T> {
     fun bar(): T
     fun foo(): T = bar()
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/class/InheritTraitWithFunctionParam.kt b/compiler/testData/loadJava/compiledKotlin/class/InheritTraitWithFunctionParam.kt
index 1fcc3c569f1..57153118418 100644
--- a/compiler/testData/loadJava/compiledKotlin/class/InheritTraitWithFunctionParam.kt
+++ b/compiler/testData/loadJava/compiledKotlin/class/InheritTraitWithFunctionParam.kt
@@ -1,6 +1,6 @@
 package test
 
-trait Trait {
+interface Trait {
     open fun f(a: String) {
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/class/InheritTraitWithParam.kt b/compiler/testData/loadJava/compiledKotlin/class/InheritTraitWithParam.kt
index 027afdd15e8..25ee354d44c 100644
--- a/compiler/testData/loadJava/compiledKotlin/class/InheritTraitWithParam.kt
+++ b/compiler/testData/loadJava/compiledKotlin/class/InheritTraitWithParam.kt
@@ -1,5 +1,5 @@
 package test
 
-trait Aaa<P>
+interface Aaa<P>
 
 class Bbb() : Aaa<java.util.Random>
diff --git a/compiler/testData/loadJava/compiledKotlin/class/RecursiveGeneric.kt b/compiler/testData/loadJava/compiledKotlin/class/RecursiveGeneric.kt
index 9dedca787dc..35f21b2c562 100644
--- a/compiler/testData/loadJava/compiledKotlin/class/RecursiveGeneric.kt
+++ b/compiler/testData/loadJava/compiledKotlin/class/RecursiveGeneric.kt
@@ -1,10 +1,10 @@
 //ALLOW_AST_ACCESS
 package test
 
-trait Rec<R, out T: Rec<R, T>> {
+interface Rec<R, out T: Rec<R, T>> {
     fun t(): T
 }
 
-trait Super {
+interface Super {
     fun foo(p: Rec<*, *>) = p.t()
 }
\ No newline at end of file
diff --git a/compiler/testData/loadJava/compiledKotlin/class/SingleAbstractMethod.kt b/compiler/testData/loadJava/compiledKotlin/class/SingleAbstractMethod.kt
index 71f52f15c73..aa3e2b5e6b7 100644
--- a/compiler/testData/loadJava/compiledKotlin/class/SingleAbstractMethod.kt
+++ b/compiler/testData/loadJava/compiledKotlin/class/SingleAbstractMethod.kt
@@ -1,5 +1,5 @@
 package test
 
-public trait SingleAbstractMethod {
+public interface SingleAbstractMethod {
     fun foo()
 }
\ No newline at end of file
diff --git a/compiler/testData/loadJava/compiledKotlin/class/Trait.kt b/compiler/testData/loadJava/compiledKotlin/class/Trait.kt
index 100e972734f..f3bfbf4e89f 100644
--- a/compiler/testData/loadJava/compiledKotlin/class/Trait.kt
+++ b/compiler/testData/loadJava/compiledKotlin/class/Trait.kt
@@ -1,3 +1,3 @@
 package test
 
-trait Trtrtr
+interface Trtrtr
diff --git a/compiler/testData/loadJava/compiledKotlin/class/javaBean/JavaBeanAbstractGetter.kt b/compiler/testData/loadJava/compiledKotlin/class/javaBean/JavaBeanAbstractGetter.kt
index c973107933b..46bf946b2f0 100644
--- a/compiler/testData/loadJava/compiledKotlin/class/javaBean/JavaBeanAbstractGetter.kt
+++ b/compiler/testData/loadJava/compiledKotlin/class/javaBean/JavaBeanAbstractGetter.kt
@@ -1,6 +1,6 @@
 package test
 
-public trait JavaBeanAbstractGetter {
+public interface JavaBeanAbstractGetter {
     //final val red: Int
     public abstract fun getRed(): Int
     //final val blue: Int
diff --git a/compiler/testData/loadJava/compiledKotlin/classFun/FunDelegationToTraitImpl.kt b/compiler/testData/loadJava/compiledKotlin/classFun/FunDelegationToTraitImpl.kt
index 4b0dcb7b986..2eab00c8bb5 100644
--- a/compiler/testData/loadJava/compiledKotlin/classFun/FunDelegationToTraitImpl.kt
+++ b/compiler/testData/loadJava/compiledKotlin/classFun/FunDelegationToTraitImpl.kt
@@ -2,7 +2,7 @@ package test
 
 // test composed from KT-2193
 
-trait A {
+interface A {
     open fun f(): String = "test"
 }
 
diff --git a/compiler/testData/loadJava/compiledKotlin/classFun/TraitFinalFun.kt b/compiler/testData/loadJava/compiledKotlin/classFun/TraitFinalFun.kt
index d906faa3f09..da2fd30a122 100644
--- a/compiler/testData/loadJava/compiledKotlin/classFun/TraitFinalFun.kt
+++ b/compiler/testData/loadJava/compiledKotlin/classFun/TraitFinalFun.kt
@@ -2,6 +2,6 @@
 
 package test
 
-trait A {
+interface A {
     final fun f(): String = "test"
 }
\ No newline at end of file
diff --git a/compiler/testData/loadJava/compiledKotlin/classFun/TraitOpenFun.kt b/compiler/testData/loadJava/compiledKotlin/classFun/TraitOpenFun.kt
index 719deb93964..42325b99188 100644
--- a/compiler/testData/loadJava/compiledKotlin/classFun/TraitOpenFun.kt
+++ b/compiler/testData/loadJava/compiledKotlin/classFun/TraitOpenFun.kt
@@ -2,6 +2,6 @@
 
 package test
 
-trait A {
+interface A {
     fun f(): String = "test"
 }
\ No newline at end of file
diff --git a/compiler/testData/loadJava/compiledKotlin/classObject/ClassObjectExtendsTrait.kt b/compiler/testData/loadJava/compiledKotlin/classObject/ClassObjectExtendsTrait.kt
index 29271b710be..a88eb812216 100644
--- a/compiler/testData/loadJava/compiledKotlin/classObject/ClassObjectExtendsTrait.kt
+++ b/compiler/testData/loadJava/compiledKotlin/classObject/ClassObjectExtendsTrait.kt
@@ -1,6 +1,6 @@
 package test
 
-trait Bbb
+interface Bbb
 
 class ClassObjectextendsTrait {
     companion object : Bbb {
diff --git a/compiler/testData/loadJava/compiledKotlin/classObject/ClassObjectExtendsTraitWithTP.kt b/compiler/testData/loadJava/compiledKotlin/classObject/ClassObjectExtendsTraitWithTP.kt
index b1c7808e9d3..142134b0c38 100644
--- a/compiler/testData/loadJava/compiledKotlin/classObject/ClassObjectExtendsTraitWithTP.kt
+++ b/compiler/testData/loadJava/compiledKotlin/classObject/ClassObjectExtendsTraitWithTP.kt
@@ -1,6 +1,6 @@
 package test
 
-trait Bbb<P>
+interface Bbb<P>
 
 class ClassObjectExtendsTraitWithTP {
     companion object : Bbb<String> {
diff --git a/compiler/testData/loadJava/compiledKotlin/classObject/Delegation.kt b/compiler/testData/loadJava/compiledKotlin/classObject/Delegation.kt
index 0e5081cf714..7602c61fcb8 100644
--- a/compiler/testData/loadJava/compiledKotlin/classObject/Delegation.kt
+++ b/compiler/testData/loadJava/compiledKotlin/classObject/Delegation.kt
@@ -1,6 +1,6 @@
 package test
 
-trait T {
+interface T {
     fun foo(): Int
 }
 
diff --git a/compiler/testData/loadJava/compiledKotlin/classObject/classObjectInTraitStaticFields.kt b/compiler/testData/loadJava/compiledKotlin/classObject/classObjectInTraitStaticFields.kt
index 8c3c948b699..72e1cef42a9 100644
--- a/compiler/testData/loadJava/compiledKotlin/classObject/classObjectInTraitStaticFields.kt
+++ b/compiler/testData/loadJava/compiledKotlin/classObject/classObjectInTraitStaticFields.kt
@@ -1,7 +1,7 @@
 //ALLOW_AST_ACCESS
 package test
 
-trait Test {
+interface Test {
 
     companion object {
 
diff --git a/compiler/testData/loadJava/compiledKotlin/enum/enumWithInnerClasses.kt b/compiler/testData/loadJava/compiledKotlin/enum/enumWithInnerClasses.kt
index 6d89bdebdbf..baf01776b15 100644
--- a/compiler/testData/loadJava/compiledKotlin/enum/enumWithInnerClasses.kt
+++ b/compiler/testData/loadJava/compiledKotlin/enum/enumWithInnerClasses.kt
@@ -8,7 +8,7 @@ enum class Enum {
 
     class Nested
 
-    trait Trait
+    interface Trait
 
     val c: Int = 1
 
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/ClassObject.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/ClassObject.kt
index 6ea9f30d9f7..3b0cada48c0 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/ClassObject.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/ClassObject.kt
@@ -1,6 +1,6 @@
 package test
 
-trait TheTrait {
+interface TheTrait {
   companion object {
   }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/InheritMethodsDifferentReturnTypes.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/InheritMethodsDifferentReturnTypes.kt
index 83aa1ea2273..06bcfde5895 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/InheritMethodsDifferentReturnTypes.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/InheritMethodsDifferentReturnTypes.kt
@@ -1,16 +1,16 @@
 package test
 
 public class InheritMethodsDifferentReturnTypes {
-    public trait Super1 {
+    public interface Super1 {
         public fun foo(): CharSequence?
         public fun bar(): String?
     }
 
-    public trait Super2 {
+    public interface Super2 {
         public fun foo(): String?
         public fun bar(): CharSequence?
     }
 
-    public trait Sub: Super1, Super2 {
+    public interface Sub: Super1, Super2 {
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/InheritMethodsDifferentReturnTypesGeneric.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/InheritMethodsDifferentReturnTypesGeneric.kt
index 47c847a1c67..a198dff07f7 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/InheritMethodsDifferentReturnTypesGeneric.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/InheritMethodsDifferentReturnTypesGeneric.kt
@@ -1,16 +1,16 @@
 package test
 
 public class InheritMethodsDifferentReturnTypesGeneric {
-    public trait Super1<F, B> {
+    public interface Super1<F, B> {
         public fun foo(): F?
         public fun bar(): B?
     }
 
-    public trait Super2<FF, BB> {
+    public interface Super2<FF, BB> {
         public fun foo(): FF?
         public fun bar(): BB?
     }
 
-    public trait Sub: Super1<String, CharSequence>, Super2<CharSequence, String> {
+    public interface Sub: Super1<String, CharSequence>, Super2<CharSequence, String> {
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/RemoveRedundantProjectionKind.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/RemoveRedundantProjectionKind.kt
index a30fb2d2fd4..1ecc51a10ea 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/RemoveRedundantProjectionKind.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/RemoveRedundantProjectionKind.kt
@@ -1,6 +1,6 @@
 package test
 
-public trait RemoveRedundantProjectionKind {
+public interface RemoveRedundantProjectionKind {
     public fun f(p0: Collection<CharSequence?>?)
     public fun f(p0: Comparable<CharSequence?>?)
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/UnboundWildcard.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/UnboundWildcard.kt
index 8aa3de94956..bdd20ed84c1 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/UnboundWildcard.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/UnboundWildcard.kt
@@ -3,5 +3,5 @@ package test
 public final class UnboundWildcard {
     public final fun foo(): MyClass<*>? = throw UnsupportedOperationException()
 
-    public trait MyClass<T: CharSequence?>
+    public interface MyClass<T: CharSequence?>
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/StarProjection.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/StarProjection.kt
index 3277572e158..aafc90b87f7 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/StarProjection.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/StarProjection.kt
@@ -3,5 +3,5 @@ package test
 public final class StarProjection {
     public final fun foo(): MyClass<*> = throw UnsupportedOperationException()
 
-    public trait MyClass<T: CharSequence?>
+    public interface MyClass<T: CharSequence?>
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/PropagateTypeArgumentNullable.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/PropagateTypeArgumentNullable.kt
index 71c791ad155..033131bbbc0 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/PropagateTypeArgumentNullable.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/PropagateTypeArgumentNullable.kt
@@ -1,8 +1,8 @@
 package test
 
-public trait PropagateTypeArgumentNullable {
+public interface PropagateTypeArgumentNullable {
 
-    public trait Super {
+    public interface Super {
         public fun outS(p: List<String?>)
 
         public fun invOutS(p : MutableList<List<String?>>)
@@ -15,7 +15,7 @@ public trait PropagateTypeArgumentNullable {
 
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun outS(p: List<String?>)
 
         override fun invOutS(p : MutableList<List<String?>>)
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/ChangeProjectionKind1.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/ChangeProjectionKind1.kt
index ee8a934352e..5759ec597fe 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/ChangeProjectionKind1.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/ChangeProjectionKind1.kt
@@ -1,15 +1,15 @@
 //ALLOW_AST_ACCESS
 package test
 
-public trait ChangeProjectionKind1 {
+public interface ChangeProjectionKind1 {
 
-    public trait Super {
+    public interface Super {
         public fun foo(p: MutableList<in String>)
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun foo(p: MutableList<in String>)
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/ChangeProjectionKind2.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/ChangeProjectionKind2.kt
index 405b1c1b0ae..83b0097586b 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/ChangeProjectionKind2.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/ChangeProjectionKind2.kt
@@ -1,14 +1,14 @@
 package test
 
-public trait ChangeProjectionKind2 {
+public interface ChangeProjectionKind2 {
 
-    public trait Super {
+    public interface Super {
         public fun foo(p: MutableList<String>)
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun foo(p: MutableList<String>)
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/DeeplySubstitutedClassParameter.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/DeeplySubstitutedClassParameter.kt
index 94ca7fb568d..3e3f9c38378 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/DeeplySubstitutedClassParameter.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/DeeplySubstitutedClassParameter.kt
@@ -1,18 +1,18 @@
 package test
 
-public trait DeeplySubstitutedClassParameter {
+public interface DeeplySubstitutedClassParameter {
 
-    public trait Super<T> {
+    public interface Super<T> {
         public fun foo(t: T)
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Middle<E>: Super<E> {
+    public interface Middle<E>: Super<E> {
         override fun foo(t: E)
     }
 
-    public trait Sub: Middle<String> {
+    public interface Sub: Middle<String> {
         override fun foo(t: String)
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/DeeplySubstitutedClassParameter2.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/DeeplySubstitutedClassParameter2.kt
index f69f9d9b7ff..ecd4466cde8 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/DeeplySubstitutedClassParameter2.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/DeeplySubstitutedClassParameter2.kt
@@ -1,17 +1,17 @@
 package test
 
-public trait DeeplySubstitutedClassParameter2 {
+public interface DeeplySubstitutedClassParameter2 {
 
-    public trait Super<T> {
+    public interface Super<T> {
         public fun foo(t: T)
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Middle<E>: Super<E> {
+    public interface Middle<E>: Super<E> {
     }
 
-    public trait Sub: Middle<String> {
+    public interface Sub: Middle<String> {
         override fun foo(t: String)
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritMutability.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritMutability.kt
index b0217380f47..813702267c4 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritMutability.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritMutability.kt
@@ -1,14 +1,14 @@
 package test
 
-public trait InheritMutability {
+public interface InheritMutability {
 
-    public trait Super {
+    public interface Super {
         public fun foo(p: MutableList<String>)
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun foo(p: MutableList<String>)
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritNotVararg.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritNotVararg.kt
index d4f6fd41c22..ddd3eb4fbb6 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritNotVararg.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritNotVararg.kt
@@ -1,15 +1,15 @@
 //ALLOW_AST_ACCESS
 package test
 
-public trait InheritNotVararg {
+public interface InheritNotVararg {
 
-    public trait Super {
+    public interface Super {
         public fun foo(p0: Array<out String>?)
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun foo(p0: Array<out String>?)
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritNotVarargInteger.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritNotVarargInteger.kt
index aa7c450a6c4..0bc806430eb 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritNotVarargInteger.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritNotVarargInteger.kt
@@ -1,15 +1,15 @@
 //ALLOW_AST_ACCESS
 package test
 
-public trait InheritNotVarargInteger {
+public interface InheritNotVarargInteger {
 
-    public trait Super {
+    public interface Super {
         public fun foo(p0: Array<out Int>?)
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun foo(p0: Array<out Int>?)
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritNotVarargNotNull.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritNotVarargNotNull.kt
index 8a35ed77855..79fa84c7728 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritNotVarargNotNull.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritNotVarargNotNull.kt
@@ -1,15 +1,15 @@
 //ALLOW_AST_ACCESS
 package test
 
-public trait InheritNotVarargNotNull {
+public interface InheritNotVarargNotNull {
 
-    public trait Super {
+    public interface Super {
         public fun foo(p: Array<out String>)
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun foo(p: Array<out String>)
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritNotVarargPrimitive.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritNotVarargPrimitive.kt
index 57b55f25b9a..de903f64e8c 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritNotVarargPrimitive.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritNotVarargPrimitive.kt
@@ -1,14 +1,14 @@
 package test
 
-public trait InheritNotVarargPrimitive {
+public interface InheritNotVarargPrimitive {
 
-    public trait Super {
+    public interface Super {
         public fun foo(p0: IntArray?)
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun foo(p0: IntArray?)
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritNullability.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritNullability.kt
index 58f2b7dc065..d281e63e6d6 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritNullability.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritNullability.kt
@@ -1,14 +1,14 @@
 package test
 
-public trait InheritNullability {
+public interface InheritNullability {
 
-    public trait Super {
+    public interface Super {
         public fun foo(p0: String)
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun foo(p0: String)
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritProjectionKind.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritProjectionKind.kt
index d5ecfe05d02..073523ed6c0 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritProjectionKind.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritProjectionKind.kt
@@ -1,15 +1,15 @@
 //ALLOW_AST_ACCESS
 package test
 
-public trait InheritProjectionKind {
+public interface InheritProjectionKind {
 
-    public trait Super {
+    public interface Super {
         public fun foo(p: MutableList<in String>)
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun foo(p: MutableList<in String>)
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritReadOnliness.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritReadOnliness.kt
index 7b01458aae0..e2b11bc646c 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritReadOnliness.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritReadOnliness.kt
@@ -1,14 +1,14 @@
 package test
 
-public trait InheritReadOnliness {
+public interface InheritReadOnliness {
 
-    public trait Super {
+    public interface Super {
         public fun foo(p: List<String>)
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun foo(p: List<String>)
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritVararg.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritVararg.kt
index ad89aecd444..e1c7374661a 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritVararg.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritVararg.kt
@@ -1,14 +1,14 @@
 package test
 
-public trait InheritVararg {
+public interface InheritVararg {
 
-    public trait Super {
+    public interface Super {
         public fun foo(vararg p0: String?)
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun foo(vararg p0: String?)
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritVarargInteger.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritVarargInteger.kt
index 36eb9b3ed47..a8bb4d6fc81 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritVarargInteger.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritVarargInteger.kt
@@ -1,14 +1,14 @@
 package test
 
-public trait InheritVarargInteger {
+public interface InheritVarargInteger {
 
-    public trait Super {
+    public interface Super {
         public fun foo(vararg p0: Int?)
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun foo(vararg p0: Int?)
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritVarargNotNull.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritVarargNotNull.kt
index 0e364802675..6d00d885a2a 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritVarargNotNull.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritVarargNotNull.kt
@@ -1,15 +1,15 @@
 //ALLOW_AST_ACCESS
 package test
 
-public trait InheritVarargNotNull {
+public interface InheritVarargNotNull {
 
-    public trait Super {
+    public interface Super {
         public fun foo(vararg p: String)
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun foo(vararg p: String)
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritVarargPrimitive.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritVarargPrimitive.kt
index b2f627c8586..520a9eb2775 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritVarargPrimitive.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/InheritVarargPrimitive.kt
@@ -1,14 +1,14 @@
 package test
 
-public trait InheritVarargPrimitive {
+public interface InheritVarargPrimitive {
 
-    public trait Super {
+    public interface Super {
         public fun foo(vararg p0: Int)
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun foo(vararg p0: Int)
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/Kt3302.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/Kt3302.kt
index 0d2f87aa30d..ea6378921f2 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/Kt3302.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/Kt3302.kt
@@ -1,20 +1,20 @@
 package test
 
 // See SubclassFromGenericAndNot, as well
-public trait Kt3302 {
-    public trait BSONObject  {
+public interface Kt3302 {
+    public interface BSONObject  {
         public fun put(p0: String, p1: Any): Any?
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait LinkedHashMap<K, V>  {
+    public interface LinkedHashMap<K, V>  {
         public fun put(key: K, value: V): V?
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait BasicBSONObject : LinkedHashMap<String, Any>, BSONObject {
+    public interface BasicBSONObject : LinkedHashMap<String, Any>, BSONObject {
         override fun put(key: String, value: Any): Any?
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/MutableToReadOnly.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/MutableToReadOnly.kt
index ac5d13e7a1c..41f5e55735e 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/MutableToReadOnly.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/MutableToReadOnly.kt
@@ -1,14 +1,14 @@
 package test
 
-public trait MutableToReadOnly {
+public interface MutableToReadOnly {
 
-    public trait Super {
+    public interface Super {
         public fun foo(p: MutableList<String>)
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun foo(p: MutableList<String>)
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/NotNullToNullable.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/NotNullToNullable.kt
index 0c7f45ed64d..53e423decc1 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/NotNullToNullable.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/NotNullToNullable.kt
@@ -1,14 +1,14 @@
 package test
 
-public trait NotNullToNullable {
+public interface NotNullToNullable {
 
-    public trait Super {
+    public interface Super {
         public fun foo(p0: String)
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun foo(p0: String)
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/NullableToNotNull.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/NullableToNotNull.kt
index 924682611f0..b49a39243f8 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/NullableToNotNull.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/NullableToNotNull.kt
@@ -1,14 +1,14 @@
 package test
 
-public trait NullableToNotNull {
+public interface NullableToNotNull {
 
-    public trait Super {
+    public interface Super {
         public fun foo(p0: String?)
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun foo(p0: String?)
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/NullableToNotNullKotlinSignature.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/NullableToNotNullKotlinSignature.kt
index cf11f06dedf..7fc8c9823c8 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/NullableToNotNullKotlinSignature.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/NullableToNotNullKotlinSignature.kt
@@ -1,14 +1,14 @@
 package test
 
-public trait NullableToNotNullKotlinSignature {
+public interface NullableToNotNullKotlinSignature {
 
-    public trait Super {
+    public interface Super {
         public fun foo(p: String?)
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun foo(p: String?)
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/OverrideWithErasedParameter.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/OverrideWithErasedParameter.kt
index 3e74342628f..627f4df7991 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/OverrideWithErasedParameter.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/OverrideWithErasedParameter.kt
@@ -1,14 +1,14 @@
 package test
 
-public trait OverrideWithErasedParameter {
+public interface OverrideWithErasedParameter {
 
-    public trait Super<T> {
+    public interface Super<T> {
         public fun foo(p0: T?)
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub<T>: Super<T> {
+    public interface Sub<T>: Super<T> {
         override fun foo(p0: T?)
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/ReadOnlyToMutable.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/ReadOnlyToMutable.kt
index 1f6e29bc233..e142671e6b7 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/ReadOnlyToMutable.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/ReadOnlyToMutable.kt
@@ -1,14 +1,14 @@
 package test
 
-public trait ReadOnlyToMutable {
+public interface ReadOnlyToMutable {
 
-    public trait Super {
+    public interface Super {
         public fun foo(p: List<String>)
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun foo(p: List<String>)
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/SubclassFromGenericAndNot.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/SubclassFromGenericAndNot.kt
index ff273173e02..8a5cdb1db32 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/SubclassFromGenericAndNot.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/SubclassFromGenericAndNot.kt
@@ -1,21 +1,21 @@
 package test
 
 // Extracted from KT-3302, see Kt3302 test, as well
-public trait SubclassFromGenericAndNot {
+public interface SubclassFromGenericAndNot {
 
-    public trait NonGeneric  {
+    public interface NonGeneric  {
         public fun foo(p0: String)
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Generic<T>  {
+    public interface Generic<T>  {
         public fun foo(key: T)
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub : NonGeneric, Generic<String> {
+    public interface Sub : NonGeneric, Generic<String> {
         override fun foo(key: String)
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/SubstitutedClassParameter.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/SubstitutedClassParameter.kt
index cd9732d60e0..79ef8cc0e35 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/SubstitutedClassParameter.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/SubstitutedClassParameter.kt
@@ -1,14 +1,14 @@
 package test
 
-public trait SubstitutedClassParameter {
+public interface SubstitutedClassParameter {
 
-    public trait Super<T> {
+    public interface Super<T> {
         public fun foo(t: T)
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super<String> {
+    public interface Sub: Super<String> {
         override fun foo(t: String)
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/SubstitutedClassParameters.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/SubstitutedClassParameters.kt
index 6a1d0abe309..85321bba64e 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/SubstitutedClassParameters.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/parameter/SubstitutedClassParameters.kt
@@ -1,20 +1,20 @@
 package test
 
-public trait SubstitutedClassParameters {
+public interface SubstitutedClassParameters {
 
-    public trait Super1<T> {
+    public interface Super1<T> {
         public fun foo(t: T)
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Super2<E> {
+    public interface Super2<E> {
         public fun foo(t: E)
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super1<String>, Super2<String> {
+    public interface Sub: Super1<String>, Super2<String> {
         override fun foo(t: String)
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/AddNotNullJavaSubtype.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/AddNotNullJavaSubtype.kt
index 3788f264811..b75f2459d36 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/AddNotNullJavaSubtype.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/AddNotNullJavaSubtype.kt
@@ -1,14 +1,14 @@
 package test
 
-public trait AddNotNullJavaSubtype  {
+public interface AddNotNullJavaSubtype  {
 
-    public trait Super {
+    public interface Super {
         public fun foo(): CharSequence?
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun foo(): String
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/AddNotNullSameJavaType.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/AddNotNullSameJavaType.kt
index 216c9d16883..7a9d4d310e4 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/AddNotNullSameJavaType.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/AddNotNullSameJavaType.kt
@@ -1,14 +1,14 @@
 package test
 
-public trait AddNotNullSameJavaType {
+public interface AddNotNullSameJavaType {
 
-    public trait Super {
+    public interface Super {
         public fun foo(): CharSequence?
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun foo(): CharSequence
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/AddNullabilityJavaSubtype.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/AddNullabilityJavaSubtype.kt
index ad181b72234..845e69f7db0 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/AddNullabilityJavaSubtype.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/AddNullabilityJavaSubtype.kt
@@ -1,14 +1,14 @@
 package test
 
-public trait AddNullabilityJavaSubtype {
+public interface AddNullabilityJavaSubtype {
 
-    public trait Super {
+    public interface Super {
         public fun foo(): CharSequence
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun foo(): String
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/AddNullabilitySameGenericType1.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/AddNullabilitySameGenericType1.kt
index 31d3673d134..be0ba649599 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/AddNullabilitySameGenericType1.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/AddNullabilitySameGenericType1.kt
@@ -1,14 +1,14 @@
 package test
 
-public trait AddNullabilitySameGenericType1 {
+public interface AddNullabilitySameGenericType1 {
 
-    public trait Super {
+    public interface Super {
         public fun foo(): MutableList<String>
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun foo(): MutableList<String>
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/AddNullabilitySameGenericType2.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/AddNullabilitySameGenericType2.kt
index eafbf6d76e6..2503019c921 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/AddNullabilitySameGenericType2.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/AddNullabilitySameGenericType2.kt
@@ -1,14 +1,14 @@
 package test
 
-public trait AddNullabilitySameGenericType2 {
+public interface AddNullabilitySameGenericType2 {
 
-    public trait Super {
+    public interface Super {
         public fun foo(): MutableList<String>
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun foo(): MutableList<String>
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/AddNullabilitySameJavaType.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/AddNullabilitySameJavaType.kt
index 34716b6de79..846a400fff8 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/AddNullabilitySameJavaType.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/AddNullabilitySameJavaType.kt
@@ -1,14 +1,14 @@
 package test
 
-public trait AddNullabilitySameJavaType {
+public interface AddNullabilitySameJavaType {
 
-    public trait Super {
+    public interface Super {
         public fun foo(): CharSequence
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun foo(): CharSequence
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/CantMakeImmutableInSubclass.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/CantMakeImmutableInSubclass.kt
index 3c4b1e6e788..5749bf66543 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/CantMakeImmutableInSubclass.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/CantMakeImmutableInSubclass.kt
@@ -1,14 +1,14 @@
 package test
 
-public trait CantMakeImmutableInSubclass {
+public interface CantMakeImmutableInSubclass {
 
-    public trait Super {
+    public interface Super {
         public fun foo(): MutableCollection<String>
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun foo(): MutableList<String>
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/DeeplySubstitutedClassParameter.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/DeeplySubstitutedClassParameter.kt
index 38985e9013c..4e3cedd56ed 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/DeeplySubstitutedClassParameter.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/DeeplySubstitutedClassParameter.kt
@@ -1,18 +1,18 @@
 package test
 
-public trait DeeplySubstitutedClassParameter {
+public interface DeeplySubstitutedClassParameter {
 
-    public trait Super<T> {
+    public interface Super<T> {
         public fun foo(): T
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Middle<E>: Super<E> {
+    public interface Middle<E>: Super<E> {
         override fun foo(): E
     }
 
-    public trait Sub: Middle<String> {
+    public interface Sub: Middle<String> {
         override fun foo(): String
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/DeeplySubstitutedClassParameter2.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/DeeplySubstitutedClassParameter2.kt
index a1ec7f4b73f..d3203fefb8e 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/DeeplySubstitutedClassParameter2.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/DeeplySubstitutedClassParameter2.kt
@@ -1,17 +1,17 @@
 package test
 
-public trait DeeplySubstitutedClassParameter2 {
+public interface DeeplySubstitutedClassParameter2 {
 
-    public trait Super<T> {
+    public interface Super<T> {
         public fun foo(): T
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Middle<E>: Super<E> {
+    public interface Middle<E>: Super<E> {
     }
 
-    public trait Sub: Middle<String> {
+    public interface Sub: Middle<String> {
         override fun foo(): String
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/HalfSubstitutedTypeParameters.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/HalfSubstitutedTypeParameters.kt
index 4e9c0968e64..833add25e23 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/HalfSubstitutedTypeParameters.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/HalfSubstitutedTypeParameters.kt
@@ -1,16 +1,16 @@
 package test
 
-public trait HalfSubstitutedTypeParameters {
+public interface HalfSubstitutedTypeParameters {
 
-    public trait TrickyList<X, E>: MutableList<E> {}
+    public interface TrickyList<X, E>: MutableList<E> {}
 
-    public trait Super {
+    public interface Super {
         public fun foo(): MutableList<String?>
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun foo(): TrickyList<Int, String?>
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/InheritNullabilityGenericSubclassSimple.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/InheritNullabilityGenericSubclassSimple.kt
index a0ef6f5b9be..47ceaf41ea1 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/InheritNullabilityGenericSubclassSimple.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/InheritNullabilityGenericSubclassSimple.kt
@@ -1,14 +1,14 @@
 package test
 
-public trait InheritNullabilityGenericSubclassSimple {
+public interface InheritNullabilityGenericSubclassSimple {
 
-    public trait Super {
+    public interface Super {
         public fun foo(): MutableCollection<String>
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun foo(): MutableList<String>
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/InheritNullabilityJavaSubtype.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/InheritNullabilityJavaSubtype.kt
index 502952f0788..94669946df5 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/InheritNullabilityJavaSubtype.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/InheritNullabilityJavaSubtype.kt
@@ -1,14 +1,14 @@
 package test
 
-public trait InheritNullabilityJavaSubtype {
+public interface InheritNullabilityJavaSubtype {
 
-    public trait Super {
+    public interface Super {
         public fun foo(): CharSequence
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun foo(): String
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/InheritNullabilitySameGenericType.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/InheritNullabilitySameGenericType.kt
index 172b9e626df..52e229cdca1 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/InheritNullabilitySameGenericType.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/InheritNullabilitySameGenericType.kt
@@ -1,14 +1,14 @@
 package test
 
-public trait InheritNullabilitySameGenericType {
+public interface InheritNullabilitySameGenericType {
 
-    public trait Super {
+    public interface Super {
         public fun foo(): MutableList<String>
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun foo(): MutableList<String>
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/InheritNullabilitySameJavaType.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/InheritNullabilitySameJavaType.kt
index de5f4f4a73d..5039ec73cf9 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/InheritNullabilitySameJavaType.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/InheritNullabilitySameJavaType.kt
@@ -1,14 +1,14 @@
 package test
 
-public trait InheritNullabilitySameJavaType {
+public interface InheritNullabilitySameJavaType {
 
-    public trait Super {
+    public interface Super {
         public fun foo(): CharSequence
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun foo(): CharSequence
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/InheritProjectionKind.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/InheritProjectionKind.kt
index cc1cce6d917..98b09b7b7ae 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/InheritProjectionKind.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/InheritProjectionKind.kt
@@ -1,15 +1,15 @@
 //ALLOW_AST_ACCESS
 package test
 
-public trait InheritProjectionKind {
+public interface InheritProjectionKind {
 
-    public trait Super {
+    public interface Super {
         public fun foo(): MutableCollection<out Number>
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun foo(): MutableList<out Number>
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/InheritReadOnlinessOfArgument.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/InheritReadOnlinessOfArgument.kt
index 22c40fff363..1668ade67f7 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/InheritReadOnlinessOfArgument.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/InheritReadOnlinessOfArgument.kt
@@ -1,14 +1,14 @@
 package test
 
-public trait InheritReadOnlinessOfArgument {
+public interface InheritReadOnlinessOfArgument {
 
-    public trait Super {
+    public interface Super {
         public fun foo(): List<List<String>>
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun foo(): List<List<String>>
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/InheritReadOnlinessSameClass.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/InheritReadOnlinessSameClass.kt
index a2aa64cb5ea..1dcdbf6ef8f 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/InheritReadOnlinessSameClass.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/InheritReadOnlinessSameClass.kt
@@ -1,14 +1,14 @@
 package test
 
-public trait InheritReadOnlinessSameClass {
+public interface InheritReadOnlinessSameClass {
 
-    public trait Super {
+    public interface Super {
         public fun foo(): List<String>
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun foo(): List<String>
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/InheritReadOnlinessSubclass.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/InheritReadOnlinessSubclass.kt
index ff1baea0afa..4431b54d18a 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/InheritReadOnlinessSubclass.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/InheritReadOnlinessSubclass.kt
@@ -1,14 +1,14 @@
 package test
 
-public trait InheritReadOnlinessSubclass {
+public interface InheritReadOnlinessSubclass {
 
-    public trait Super {
+    public interface Super {
         public fun foo(): Collection<String>
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun foo(): List<String>
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/SameProjectionKind.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/SameProjectionKind.kt
index ab2adb2f3e3..6be64670886 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/SameProjectionKind.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/SameProjectionKind.kt
@@ -1,15 +1,15 @@
 //ALLOW_AST_ACCESS
 package test
 
-public trait SameProjectionKind {
+public interface SameProjectionKind {
 
-    public trait Super {
+    public interface Super {
         public fun foo(): MutableCollection<out Number?>?
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun foo(): MutableCollection<out Number?>?
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/SubclassFromGenericAndNot.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/SubclassFromGenericAndNot.kt
index afa037d4568..051a5121c22 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/SubclassFromGenericAndNot.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/SubclassFromGenericAndNot.kt
@@ -1,20 +1,20 @@
 package test
 
-public trait SubclassFromGenericAndNot {
+public interface SubclassFromGenericAndNot {
 
-    public trait NonGeneric  {
+    public interface NonGeneric  {
         public fun foo(): String?
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Generic<T>  {
+    public interface Generic<T>  {
         public fun foo(): T
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub : NonGeneric, Generic<String> {
+    public interface Sub : NonGeneric, Generic<String> {
         override fun foo(): String
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/SubclassOfCollection.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/SubclassOfCollection.kt
index d4159b0dd5d..891dfb4eb00 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/SubclassOfCollection.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/SubclassOfCollection.kt
@@ -1,5 +1,5 @@
 package test
 
-public trait SubclassOfCollection<E>: MutableCollection<E> {
+public interface SubclassOfCollection<E>: MutableCollection<E> {
     override fun iterator() : MutableIterator<E>
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/SubclassOfMapEntry.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/SubclassOfMapEntry.kt
index 10c7c39f0e2..25bf767dac3 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/SubclassOfMapEntry.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/SubclassOfMapEntry.kt
@@ -1,5 +1,5 @@
 package test
 
-public trait SubclassOfMapEntry<K, V>: MutableMap.MutableEntry<K, V> {
+public interface SubclassOfMapEntry<K, V>: MutableMap.MutableEntry<K, V> {
     override fun setValue(value: V) : V
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/SubstitutedClassParameter.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/SubstitutedClassParameter.kt
index 02adf379735..e9ba9cea0d3 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/SubstitutedClassParameter.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/SubstitutedClassParameter.kt
@@ -1,14 +1,14 @@
 package test
 
-public trait SubstitutedClassParameter {
+public interface SubstitutedClassParameter {
 
-    public trait Super<T> {
+    public interface Super<T> {
         public fun foo(): T
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super<String> {
+    public interface Sub: Super<String> {
         override fun foo(): String
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/SubstitutedClassParameters.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/SubstitutedClassParameters.kt
index 3cb8c75ab78..f0345f50486 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/SubstitutedClassParameters.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/SubstitutedClassParameters.kt
@@ -1,20 +1,20 @@
 package test
 
-public trait SubstitutedClassParameters {
+public interface SubstitutedClassParameters {
 
-    public trait Super1<T> {
+    public interface Super1<T> {
         public fun foo(): T
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Super2<E> {
+    public interface Super2<E> {
         public fun foo(): E
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super1<String>, Super2<String> {
+    public interface Sub: Super1<String>, Super2<String> {
         override fun foo(): String
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/TwoSuperclassesConflictingProjectionKinds.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/TwoSuperclassesConflictingProjectionKinds.kt
index b13eec046aa..9323ba57a08 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/TwoSuperclassesConflictingProjectionKinds.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/TwoSuperclassesConflictingProjectionKinds.kt
@@ -1,21 +1,21 @@
 //ALLOW_AST_ACCESS
 package test
 
-public trait TwoSuperclassesConflictingProjectionKinds {
+public interface TwoSuperclassesConflictingProjectionKinds {
 
-    public trait Super1 {
+    public interface Super1 {
         public fun foo(): MutableCollection<CharSequence>
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Super2 {
+    public interface Super2 {
         public fun foo(): MutableCollection<out CharSequence>
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super1, Super2 {
+    public interface Sub: Super1, Super2 {
         override fun foo(): MutableCollection<CharSequence>
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/TwoSuperclassesInvariantAndCovariantInferMutability.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/TwoSuperclassesInvariantAndCovariantInferMutability.kt
index fc100276007..7a2d21e1787 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/TwoSuperclassesInvariantAndCovariantInferMutability.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/TwoSuperclassesInvariantAndCovariantInferMutability.kt
@@ -1,20 +1,20 @@
 package test
 
-public trait TwoSuperclassesInvariantAndCovariantInferMutability {
+public interface TwoSuperclassesInvariantAndCovariantInferMutability {
 
-    public trait Super1 {
+    public interface Super1 {
         public fun foo(): List<List<String>>
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Super2 {
+    public interface Super2 {
         public fun foo(): MutableList<MutableList<String>>
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super1, Super2 {
+    public interface Sub: Super1, Super2 {
         override fun foo(): MutableList<MutableList<String>>
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/TwoSuperclassesInvariantAndCovariantInferNullability.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/TwoSuperclassesInvariantAndCovariantInferNullability.kt
index 619d3384d30..378c2efaffe 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/TwoSuperclassesInvariantAndCovariantInferNullability.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/TwoSuperclassesInvariantAndCovariantInferNullability.kt
@@ -1,20 +1,20 @@
 package test
 
-public trait TwoSuperclassesInvariantAndCovariantInferNullability {
+public interface TwoSuperclassesInvariantAndCovariantInferNullability {
 
-    public trait Super1 {
+    public interface Super1 {
         public fun foo(): List<String?>
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Super2 {
+    public interface Super2 {
         public fun foo(): MutableList<String>
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super1, Super2 {
+    public interface Sub: Super1, Super2 {
         override fun foo(): MutableList<String>
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/TwoSuperclassesMutableAndNot.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/TwoSuperclassesMutableAndNot.kt
index 6f735c2b6a5..54e2687c1b3 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/TwoSuperclassesMutableAndNot.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/TwoSuperclassesMutableAndNot.kt
@@ -1,20 +1,20 @@
 package test
 
-public trait TwoSuperclassesMutableAndNot {
+public interface TwoSuperclassesMutableAndNot {
 
-    public trait Super1 {
+    public interface Super1 {
         public fun foo(): MutableCollection<String>
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Super2 {
+    public interface Super2 {
         public fun foo(): List<String>
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super1, Super2 {
+    public interface Sub: Super1, Super2 {
         override fun foo(): MutableList<String>
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/TwoSuperclassesReturnJavaSubtype.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/TwoSuperclassesReturnJavaSubtype.kt
index d6ec4d471e1..72dd34122e3 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/TwoSuperclassesReturnJavaSubtype.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/TwoSuperclassesReturnJavaSubtype.kt
@@ -1,20 +1,20 @@
 package test
 
-public trait TwoSuperclassesReturnJavaSubtype {
+public interface TwoSuperclassesReturnJavaSubtype {
 
-    public trait Super1 {
+    public interface Super1 {
         public fun foo(): CharSequence?
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Super2 {
+    public interface Super2 {
         public fun foo(): CharSequence
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super1, Super2 {
+    public interface Sub: Super1, Super2 {
         override fun foo(): String
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/TwoSuperclassesReturnSameJavaType.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/TwoSuperclassesReturnSameJavaType.kt
index 49a9a598501..992bb022971 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/TwoSuperclassesReturnSameJavaType.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/TwoSuperclassesReturnSameJavaType.kt
@@ -1,20 +1,20 @@
 package test
 
-public trait TwoSuperclassesReturnSameJavaType {
+public interface TwoSuperclassesReturnSameJavaType {
 
-    public trait Super1 {
+    public interface Super1 {
         public fun foo(): CharSequence?
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Super2 {
+    public interface Super2 {
         public fun foo(): CharSequence
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super1, Super2 {
+    public interface Sub: Super1, Super2 {
         override fun foo(): CharSequence
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/TwoSuperclassesSupplementNotNull.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/TwoSuperclassesSupplementNotNull.kt
index 50f4406acb2..166aaa8192a 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/TwoSuperclassesSupplementNotNull.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/TwoSuperclassesSupplementNotNull.kt
@@ -1,20 +1,20 @@
 package test
 
-public trait TwoSuperclassesSupplementNotNull {
+public interface TwoSuperclassesSupplementNotNull {
 
-    public trait Super1 {
+    public interface Super1 {
         public fun foo(): List<String?>
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Super2 {
+    public interface Super2 {
         public fun foo(): List<String>?
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super1, Super2 {
+    public interface Sub: Super1, Super2 {
         override fun foo(): List<String>
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/TypeParamOfClass.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/TypeParamOfClass.kt
index 081631672a7..4df690d47b7 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/TypeParamOfClass.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/TypeParamOfClass.kt
@@ -1,14 +1,14 @@
 package test
 
-public trait TypeParamOfClass {
+public interface TypeParamOfClass {
 
-    public trait Super<T> {
+    public interface Super<T> {
         public fun foo(): T
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub<T>: Super<T> {
+    public interface Sub<T>: Super<T> {
         override fun foo(): T
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/TypeParamOfClassSubstituted.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/TypeParamOfClassSubstituted.kt
index 813a4d3196a..f2d7e717073 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/TypeParamOfClassSubstituted.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/TypeParamOfClassSubstituted.kt
@@ -1,14 +1,14 @@
 package test
 
-public trait TypeParamOfClassSubstituted {
+public interface TypeParamOfClassSubstituted {
 
-    public trait Super<T> {
+    public interface Super<T> {
         public fun foo(): T
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super<String> {
+    public interface Sub: Super<String> {
         override fun foo(): String
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/TypeParamOfFun.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/TypeParamOfFun.kt
index 90bc7764f29..17efec439f8 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/TypeParamOfFun.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/return/TypeParamOfFun.kt
@@ -1,14 +1,14 @@
 package test
 
-public trait TypeParamOfFun {
+public interface TypeParamOfFun {
 
-    public trait Super {
+    public interface Super {
         public fun <T> foo(): T
 
         public fun dummy() // to avoid loading as SAM interface
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun <E> foo(): E
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/typeParameter/InheritMutability.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/typeParameter/InheritMutability.kt
index 453fd1756f2..5f828660626 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/typeParameter/InheritMutability.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/typeParameter/InheritMutability.kt
@@ -1,12 +1,12 @@
 package test
 
-public trait InheritMutability {
+public interface InheritMutability {
 
-    public trait Super {
+    public interface Super {
         public fun <A: MutableList<String>> foo(a: A)
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun <B: MutableList<String>> foo(a: B)
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/typeParameter/InheritNullability.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/typeParameter/InheritNullability.kt
index 5753c4d2fac..ece069e6bc5 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/typeParameter/InheritNullability.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/typeParameter/InheritNullability.kt
@@ -1,12 +1,12 @@
 package test
 
-public trait InheritNullability {
+public interface InheritNullability {
 
-    public trait Super {
+    public interface Super {
         public fun <A: CharSequence> foo(a: A)
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun <B: CharSequence> foo(a: B)
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/typeParameter/InheritReadOnliness.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/typeParameter/InheritReadOnliness.kt
index 81a1e0f0b07..7122b05089a 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/typeParameter/InheritReadOnliness.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/typeParameter/InheritReadOnliness.kt
@@ -1,12 +1,12 @@
 package test
 
-public trait InheritReadOnliness {
+public interface InheritReadOnliness {
 
-    public trait Super {
+    public interface Super {
         public fun <A: List<String>> foo(a: A)
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun <B: List<String>> foo(a: B)
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/typeParameter/TwoBounds.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/typeParameter/TwoBounds.kt
index dacf5136a8c..dbfd33bbfac 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/typeParameter/TwoBounds.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/typeParameter/TwoBounds.kt
@@ -1,12 +1,12 @@
 package test
 
-public trait TwoBounds {
+public interface TwoBounds {
 
-    public trait Super {
+    public interface Super {
         public fun <A: CharSequence> foo(a: A) where A: Cloneable
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun <B: CharSequence> foo(a: B) where B: Cloneable
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/typeParameter/TwoSuperclasses.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/typeParameter/TwoSuperclasses.kt
index 83a477b579e..f558260b68a 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/typeParameter/TwoSuperclasses.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/typeParameter/TwoSuperclasses.kt
@@ -1,16 +1,16 @@
 package test
 
-public trait TwoSuperclasses {
+public interface TwoSuperclasses {
 
-    public trait Super1 {
+    public interface Super1 {
         public fun <A: CharSequence> foo(a: A)
     }
 
-    public trait Super2 {
+    public interface Super2 {
         public fun <B: CharSequence> foo(a: B)
     }
 
-    public trait Sub: Super1, Super2 {
+    public interface Sub: Super1, Super2 {
         override fun <C: CharSequence> foo(a: C)
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/typeParameter/TwoTypeParameters.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/typeParameter/TwoTypeParameters.kt
index 84777759049..3a40e0fe4e9 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/typeParameter/TwoTypeParameters.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/typeParameter/TwoTypeParameters.kt
@@ -1,12 +1,12 @@
 package test
 
-public trait TwoTypeParameters {
+public interface TwoTypeParameters {
 
-    public trait Super {
+    public interface Super {
         public fun <A: CharSequence, B: Cloneable> foo(a: A, b: B)
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun <B: CharSequence, A: Cloneable> foo(a: B, b: A)
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/typeParameter/UseParameterAsUpperBound.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/typeParameter/UseParameterAsUpperBound.kt
index 8f2a4121b68..dec2c25d0d6 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/typeParameter/UseParameterAsUpperBound.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/typeParameter/UseParameterAsUpperBound.kt
@@ -1,12 +1,12 @@
 package test
 
-public trait UseParameterAsUpperBound {
+public interface UseParameterAsUpperBound {
 
-    public trait Super {
+    public interface Super {
         public fun <A, B: A> foo(a: A, b: B)
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun <B, A: B> foo(a: B, b: A)
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/typeParameter/UseParameterInUpperBound.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/typeParameter/UseParameterInUpperBound.kt
index b3782f7cd65..bcd168bda16 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/typeParameter/UseParameterInUpperBound.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/typeParameter/UseParameterInUpperBound.kt
@@ -1,12 +1,12 @@
 package test
 
-public trait UseParameterInUpperBound {
+public interface UseParameterInUpperBound {
 
-    public trait Super {
+    public interface Super {
         public fun <A, B: List<A>> foo(a: A, b: B)
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun <B, A: List<B>> foo(a: B, b: A)
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/typeParameter/UseParameterInUpperBoundWithKotlinSignature.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/typeParameter/UseParameterInUpperBoundWithKotlinSignature.kt
index 78bec2f2bb0..e23dfc29ef3 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/typeParameter/UseParameterInUpperBoundWithKotlinSignature.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/kotlinSignature/propagation/typeParameter/UseParameterInUpperBoundWithKotlinSignature.kt
@@ -1,12 +1,12 @@
 package test
 
-public trait UseParameterInUpperBoundWithKotlinSignature {
+public interface UseParameterInUpperBoundWithKotlinSignature {
 
-    public trait Super {
+    public interface Super {
         public fun <A, B: List<A>> foo(a: A, b: B)
     }
 
-    public trait Sub: Super {
+    public interface Sub: Super {
         override fun <B, A: List<B>> foo(b: B, a: A)
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/library/LoadIterable.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/library/LoadIterable.kt
index 1c511ceba6a..5919d38f437 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/library/LoadIterable.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/library/LoadIterable.kt
@@ -1,6 +1,6 @@
 package test
 
-public trait LoadIterable<T> {
+public interface LoadIterable<T> {
     public fun getIterable(): MutableIterable<T>?
     public fun setIterable(p0: Iterable<T>?)
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/library/LoadIterator.kt b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/library/LoadIterator.kt
index 6961dcf5c7a..2507f007d66 100644
--- a/compiler/testData/loadJava/compiledKotlin/fromLoadJava/library/LoadIterator.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fromLoadJava/library/LoadIterator.kt
@@ -1,6 +1,6 @@
 package test
 
-public trait LoadIterator<T> {
+public interface LoadIterator<T> {
     public fun getIterator(): MutableIterator<T>?
     public fun setIterator(p0: Iterator<T>?)
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fun/DeclaredMemberOverridesDelegated.kt b/compiler/testData/loadJava/compiledKotlin/fun/DeclaredMemberOverridesDelegated.kt
index e1905be2a94..4d051165ef9 100644
--- a/compiler/testData/loadJava/compiledKotlin/fun/DeclaredMemberOverridesDelegated.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fun/DeclaredMemberOverridesDelegated.kt
@@ -1,10 +1,10 @@
 package test
 
-trait X {
+interface X {
     fun foo()
 }
 
-trait Y : X {
+interface Y : X {
 }
 
 class B(val a: X) : X by a, Y {
diff --git a/compiler/testData/loadJava/compiledKotlin/fun/InheritMethodsDifferentReturnTypesAndVisibilities.kt b/compiler/testData/loadJava/compiledKotlin/fun/InheritMethodsDifferentReturnTypesAndVisibilities.kt
index 22f48cf32c6..56b6a97f8d0 100644
--- a/compiler/testData/loadJava/compiledKotlin/fun/InheritMethodsDifferentReturnTypesAndVisibilities.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fun/InheritMethodsDifferentReturnTypesAndVisibilities.kt
@@ -1,14 +1,14 @@
 package test
 
-public trait Super1 {
+public interface Super1 {
     public fun foo(): CharSequence
     private fun bar(): String
 }
 
-public trait Super2 {
+public interface Super2 {
     private fun foo(): String
     public fun bar(): CharSequence
 }
 
-public trait Sub: Super1, Super2 {
+public interface Sub: Super1, Super2 {
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fun/InheritValAndVar.kt b/compiler/testData/loadJava/compiledKotlin/fun/InheritValAndVar.kt
index da7b91104bb..b18f4353c81 100644
--- a/compiler/testData/loadJava/compiledKotlin/fun/InheritValAndVar.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fun/InheritValAndVar.kt
@@ -1,14 +1,14 @@
 package test
 
-public trait Super1 {
+public interface Super1 {
     val x: String
     var y: String
 }
 
-public trait Super2 {
+public interface Super2 {
     var x: String
     val y: String
 }
 
-public trait Sub: Super1, Super2 {
+public interface Sub: Super1, Super2 {
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fun/InheritValsDifferentTypes.kt b/compiler/testData/loadJava/compiledKotlin/fun/InheritValsDifferentTypes.kt
index 63759c05d2e..2df0330ac8d 100644
--- a/compiler/testData/loadJava/compiledKotlin/fun/InheritValsDifferentTypes.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fun/InheritValsDifferentTypes.kt
@@ -1,14 +1,14 @@
 package test
 
-public trait Super1 {
+public interface Super1 {
     val x: String
     val y: CharSequence
 }
 
-public trait Super2 {
+public interface Super2 {
     val x: CharSequence
     val y: String
 }
 
-public trait Sub: Super1, Super2 {
+public interface Sub: Super1, Super2 {
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fun/NoDelegationForFunctionInheritedFromTraitSuperClass.kt b/compiler/testData/loadJava/compiledKotlin/fun/NoDelegationForFunctionInheritedFromTraitSuperClass.kt
index 1bc312bf1ed..0814ecc70ac 100644
--- a/compiler/testData/loadJava/compiledKotlin/fun/NoDelegationForFunctionInheritedFromTraitSuperClass.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fun/NoDelegationForFunctionInheritedFromTraitSuperClass.kt
@@ -4,7 +4,7 @@ abstract class A {
     abstract fun foo()
 }
 
-trait X : A {
+interface X : A {
     fun bar() {
     }
 }
diff --git a/compiler/testData/loadJava/compiledKotlin/fun/NoSamAdapter.kt b/compiler/testData/loadJava/compiledKotlin/fun/NoSamAdapter.kt
index 56722ba6d48..86e6ec5b0dc 100644
--- a/compiler/testData/loadJava/compiledKotlin/fun/NoSamAdapter.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fun/NoSamAdapter.kt
@@ -1,6 +1,6 @@
 package test
 
-public trait TaskObject {
+public interface TaskObject {
     fun foo(r: Runnable)
 }
 
diff --git a/compiler/testData/loadJava/compiledKotlin/fun/NoSamConstructor.kt b/compiler/testData/loadJava/compiledKotlin/fun/NoSamConstructor.kt
index 91cd7ae7e6d..8ff364512fd 100644
--- a/compiler/testData/loadJava/compiledKotlin/fun/NoSamConstructor.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fun/NoSamConstructor.kt
@@ -1,5 +1,5 @@
 package test
 
-public trait Runnable {
+public interface Runnable {
     fun run()
 }
\ No newline at end of file
diff --git a/compiler/testData/loadJava/compiledKotlin/fun/PropagateDeepSubclass.kt b/compiler/testData/loadJava/compiledKotlin/fun/PropagateDeepSubclass.kt
index 69cbb457ac8..278978992c1 100644
--- a/compiler/testData/loadJava/compiledKotlin/fun/PropagateDeepSubclass.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fun/PropagateDeepSubclass.kt
@@ -1,6 +1,6 @@
 package test
 
-trait A {
+interface A {
   fun foo() {}
 
   fun bar() {}
diff --git a/compiler/testData/loadJava/compiledKotlin/fun/genericWithTypeVariables/FunParamTwoUpperBounds.kt b/compiler/testData/loadJava/compiledKotlin/fun/genericWithTypeVariables/FunParamTwoUpperBounds.kt
index 3941dd674d9..b5445808ac2 100644
--- a/compiler/testData/loadJava/compiledKotlin/fun/genericWithTypeVariables/FunParamTwoUpperBounds.kt
+++ b/compiler/testData/loadJava/compiledKotlin/fun/genericWithTypeVariables/FunParamTwoUpperBounds.kt
@@ -1,7 +1,7 @@
 package test
 
-trait Foo
-trait Bar
+interface Foo
+interface Bar
 
 fun <T> foo(): Unit
         where T : Foo, T : Bar
diff --git a/compiler/testData/loadJava/compiledKotlin/memberOrder/innerClasses.kt b/compiler/testData/loadJava/compiledKotlin/memberOrder/innerClasses.kt
index 2503e31b83b..16ed1ff1e3f 100644
--- a/compiler/testData/loadJava/compiledKotlin/memberOrder/innerClasses.kt
+++ b/compiler/testData/loadJava/compiledKotlin/memberOrder/innerClasses.kt
@@ -5,6 +5,6 @@ class O {
     inner class A2
     class B1
     inner class B2
-    trait C1
-    trait C2
+    interface C1
+    interface C2
 }
\ No newline at end of file
diff --git a/compiler/testData/loadJava/compiledKotlin/prop/OverrideTraitVal.kt b/compiler/testData/loadJava/compiledKotlin/prop/OverrideTraitVal.kt
index af98fd5137a..5ee880f0164 100644
--- a/compiler/testData/loadJava/compiledKotlin/prop/OverrideTraitVal.kt
+++ b/compiler/testData/loadJava/compiledKotlin/prop/OverrideTraitVal.kt
@@ -1,7 +1,7 @@
 //ALLOW_AST_ACCESS
 package test
 
-trait Trait {
+interface Trait {
     val shape: String
 }
 
diff --git a/compiler/testData/loadJava/compiledKotlin/prop/TraitFinalVar.kt b/compiler/testData/loadJava/compiledKotlin/prop/TraitFinalVar.kt
index 82b6fac1f6e..211ad5593f7 100644
--- a/compiler/testData/loadJava/compiledKotlin/prop/TraitFinalVar.kt
+++ b/compiler/testData/loadJava/compiledKotlin/prop/TraitFinalVar.kt
@@ -2,7 +2,7 @@
 
 package test
 
-trait A {
+interface A {
     var v: String
         get() = "test"
         set(value) {
diff --git a/compiler/testData/loadJava/compiledKotlin/prop/TraitOpenVal.kt b/compiler/testData/loadJava/compiledKotlin/prop/TraitOpenVal.kt
index ec6bf93ad2e..8ce94123cf1 100644
--- a/compiler/testData/loadJava/compiledKotlin/prop/TraitOpenVal.kt
+++ b/compiler/testData/loadJava/compiledKotlin/prop/TraitOpenVal.kt
@@ -2,7 +2,7 @@
 
 package test
 
-trait A {
+interface A {
     val v: String
         get() = "test"
 }
\ No newline at end of file
diff --git a/compiler/testData/loadJava/compiledKotlin/prop/VarDelegationToTraitImpl.kt b/compiler/testData/loadJava/compiledKotlin/prop/VarDelegationToTraitImpl.kt
index 819754f5272..68cb487a80f 100644
--- a/compiler/testData/loadJava/compiledKotlin/prop/VarDelegationToTraitImpl.kt
+++ b/compiler/testData/loadJava/compiledKotlin/prop/VarDelegationToTraitImpl.kt
@@ -2,7 +2,7 @@ package test
 
 // test composed from KT-2193
 
-trait A {
+interface A {
     open var v: String
         get() = "test"
         set(value) {
diff --git a/compiler/testData/loadJava/compiledKotlin/visibility/InternalAbstractTraitMembersOverridden.kt b/compiler/testData/loadJava/compiledKotlin/visibility/InternalAbstractTraitMembersOverridden.kt
index 2b022f3abf9..fb1e41fbbdb 100644
--- a/compiler/testData/loadJava/compiledKotlin/visibility/InternalAbstractTraitMembersOverridden.kt
+++ b/compiler/testData/loadJava/compiledKotlin/visibility/InternalAbstractTraitMembersOverridden.kt
@@ -1,7 +1,7 @@
 //ALLOW_AST_ACCESS
 package test
 
-trait A {
+interface A {
     internal fun f() : Int
     internal val v : Int
     public var p : Int
diff --git a/compiler/testData/loadJava/compiledKotlin/visibility/InternalTraitMembers.kt b/compiler/testData/loadJava/compiledKotlin/visibility/InternalTraitMembers.kt
index 3b6baffd352..79f342af7df 100644
--- a/compiler/testData/loadJava/compiledKotlin/visibility/InternalTraitMembers.kt
+++ b/compiler/testData/loadJava/compiledKotlin/visibility/InternalTraitMembers.kt
@@ -1,6 +1,6 @@
 package test
 
-trait A {
+interface A {
     internal fun f() : Int
     internal val v : Int
     public var p : Int
diff --git a/compiler/testData/loadJava/compiledKotlin/visibility/InternalTraitMembersInherited.kt b/compiler/testData/loadJava/compiledKotlin/visibility/InternalTraitMembersInherited.kt
index e5b18701b67..6ebb066ee81 100644
--- a/compiler/testData/loadJava/compiledKotlin/visibility/InternalTraitMembersInherited.kt
+++ b/compiler/testData/loadJava/compiledKotlin/visibility/InternalTraitMembersInherited.kt
@@ -1,6 +1,6 @@
 package test
 
-trait A {
+interface A {
     internal open fun f() : Int = 0
     internal open val v : Int
         get() = 0
diff --git a/compiler/testData/loadJava/compiledKotlinWithStdlib/mutability/LoadIterable.kt b/compiler/testData/loadJava/compiledKotlinWithStdlib/mutability/LoadIterable.kt
index d37c9e22694..5f4be2a404d 100644
--- a/compiler/testData/loadJava/compiledKotlinWithStdlib/mutability/LoadIterable.kt
+++ b/compiler/testData/loadJava/compiledKotlinWithStdlib/mutability/LoadIterable.kt
@@ -2,7 +2,7 @@ package test
 
 import org.jetbrains.annotations.*
 
-public trait LoadIterable<T> {
+public interface LoadIterable<T> {
     Mutable
     public fun getIterable(): MutableIterable<T>?
     public fun setIterable([Mutable] p0: MutableIterable<T>?)
diff --git a/compiler/testData/loadJava/compiledKotlinWithStdlib/mutability/LoadIterableWithConflict.kt b/compiler/testData/loadJava/compiledKotlinWithStdlib/mutability/LoadIterableWithConflict.kt
index 1ca3be99181..692c6979b8d 100644
--- a/compiler/testData/loadJava/compiledKotlinWithStdlib/mutability/LoadIterableWithConflict.kt
+++ b/compiler/testData/loadJava/compiledKotlinWithStdlib/mutability/LoadIterableWithConflict.kt
@@ -2,7 +2,7 @@ package test
 
 import org.jetbrains.annotations.*
 
-public trait LoadIterableWithConflict<T> {
+public interface LoadIterableWithConflict<T> {
     [ReadOnly] [Mutable]
     public fun getIterable(): MutableIterable<T>?
     public fun setIterable([ReadOnly] [Mutable] p0: MutableIterable<T>?)
diff --git a/compiler/testData/loadJava/compiledKotlinWithStdlib/mutability/LoadIterableWithNullability.kt b/compiler/testData/loadJava/compiledKotlinWithStdlib/mutability/LoadIterableWithNullability.kt
index a12cab694f6..2a8f4828924 100644
--- a/compiler/testData/loadJava/compiledKotlinWithStdlib/mutability/LoadIterableWithNullability.kt
+++ b/compiler/testData/loadJava/compiledKotlinWithStdlib/mutability/LoadIterableWithNullability.kt
@@ -2,7 +2,7 @@ package test
 
 import org.jetbrains.annotations.*
 
-public trait LoadIterableWithNullability<T> {
+public interface LoadIterableWithNullability<T> {
     Mutable
     public fun getIterable(): MutableIterable<T>
     public fun setIterable([Mutable] p0: MutableIterable<T>)
diff --git a/compiler/testData/loadJava/compiledKotlinWithStdlib/mutability/LoadIterableWithPropagation.kt b/compiler/testData/loadJava/compiledKotlinWithStdlib/mutability/LoadIterableWithPropagation.kt
index 12bc5b12de1..48ec8e1d2ce 100644
--- a/compiler/testData/loadJava/compiledKotlinWithStdlib/mutability/LoadIterableWithPropagation.kt
+++ b/compiler/testData/loadJava/compiledKotlinWithStdlib/mutability/LoadIterableWithPropagation.kt
@@ -3,8 +3,8 @@ package test
 import java.util.ArrayList
 import org.jetbrains.annotations.*
 
-public trait LoadIterableWithPropagation {
-    public trait LoadIterable<T> {
+public interface LoadIterableWithPropagation {
+    public interface LoadIterable<T> {
         Mutable
         public fun getIterable(): MutableIterable<T>?
         public fun setIterable([Mutable] p0: MutableIterable<T>?)
diff --git a/compiler/testData/loadJava/javaAgainstKotlin/signaturePropagation/InheritExtensionAndNot/supers.kt b/compiler/testData/loadJava/javaAgainstKotlin/signaturePropagation/InheritExtensionAndNot/supers.kt
index 8395f7c57a9..e62b22c23d1 100644
--- a/compiler/testData/loadJava/javaAgainstKotlin/signaturePropagation/InheritExtensionAndNot/supers.kt
+++ b/compiler/testData/loadJava/javaAgainstKotlin/signaturePropagation/InheritExtensionAndNot/supers.kt
@@ -1,11 +1,11 @@
 package test
 
-public trait Super1 {
+public interface Super1 {
     public fun String.foo()
     public fun Array<String>.bar()
 }
 
-public trait Super2 {
+public interface Super2 {
     public fun foo(p: String)
     public fun bar(vararg p: String)
 }
diff --git a/compiler/testData/loadJava/javaAgainstKotlin/signaturePropagation/SubclassFromTraitImplementation/TraitAndImpl.kt b/compiler/testData/loadJava/javaAgainstKotlin/signaturePropagation/SubclassFromTraitImplementation/TraitAndImpl.kt
index 8c22ca36e2e..831d7e8e23f 100644
--- a/compiler/testData/loadJava/javaAgainstKotlin/signaturePropagation/SubclassFromTraitImplementation/TraitAndImpl.kt
+++ b/compiler/testData/loadJava/javaAgainstKotlin/signaturePropagation/SubclassFromTraitImplementation/TraitAndImpl.kt
@@ -1,6 +1,6 @@
 package test
 
-trait Trait {
+interface Trait {
   fun foo(): String = "foo"
 
   fun bar(): String = "bar"
diff --git a/compiler/testData/loadJava/kotlinAgainstCompiledJavaWithKotlin/InheritParameterName.kt b/compiler/testData/loadJava/kotlinAgainstCompiledJavaWithKotlin/InheritParameterName.kt
index 37d46535777..1947a46a0aa 100644
--- a/compiler/testData/loadJava/kotlinAgainstCompiledJavaWithKotlin/InheritParameterName.kt
+++ b/compiler/testData/loadJava/kotlinAgainstCompiledJavaWithKotlin/InheritParameterName.kt
@@ -1,6 +1,6 @@
 package test
 
-trait B {
+interface B {
     fun foo(kotlinName: Int)
 }
 
diff --git a/compiler/testData/loadJava/kotlinAgainstCompiledJavaWithKotlin/javaRefersToKotlin.kt b/compiler/testData/loadJava/kotlinAgainstCompiledJavaWithKotlin/javaRefersToKotlin.kt
index b8ebf98b8fc..d246def9408 100644
--- a/compiler/testData/loadJava/kotlinAgainstCompiledJavaWithKotlin/javaRefersToKotlin.kt
+++ b/compiler/testData/loadJava/kotlinAgainstCompiledJavaWithKotlin/javaRefersToKotlin.kt
@@ -1,5 +1,5 @@
 package test
 
-trait K1 : J {
+interface K1 : J {
     override fun foo(k: K?)
 }
\ No newline at end of file
diff --git a/compiler/testData/loadJava/kotlinAgainstCompiledJavaWithKotlin/javaRefersToKotlin/K.kt b/compiler/testData/loadJava/kotlinAgainstCompiledJavaWithKotlin/javaRefersToKotlin/K.kt
index 38a3d12f5fa..b9421ff1014 100644
--- a/compiler/testData/loadJava/kotlinAgainstCompiledJavaWithKotlin/javaRefersToKotlin/K.kt
+++ b/compiler/testData/loadJava/kotlinAgainstCompiledJavaWithKotlin/javaRefersToKotlin/K.kt
@@ -1,3 +1,3 @@
 package test
 
-trait K
\ No newline at end of file
+interface K
\ No newline at end of file
diff --git a/compiler/testData/loadJava/kotlinAgainstCompiledJavaWithKotlin/propagationAgainstDeserializedSuperclass/K.kt b/compiler/testData/loadJava/kotlinAgainstCompiledJavaWithKotlin/propagationAgainstDeserializedSuperclass/K.kt
index 8f1eb163a72..9e966981ce5 100644
--- a/compiler/testData/loadJava/kotlinAgainstCompiledJavaWithKotlin/propagationAgainstDeserializedSuperclass/K.kt
+++ b/compiler/testData/loadJava/kotlinAgainstCompiledJavaWithKotlin/propagationAgainstDeserializedSuperclass/K.kt
@@ -1,5 +1,5 @@
 package test
 
-trait K {
+interface K {
     public fun foo(l: MutableList<String>): String
 }
\ No newline at end of file
diff --git a/compiler/testData/psi/DefaultKeyword.kt b/compiler/testData/psi/DefaultKeyword.kt
index b9408a7b2ec..a4417076ad8 100644
--- a/compiler/testData/psi/DefaultKeyword.kt
+++ b/compiler/testData/psi/DefaultKeyword.kt
@@ -33,7 +33,7 @@ object A {
     companion object
 }
 
-trait A {
+interface A {
     companion object
 
     class C {
diff --git a/compiler/testData/psi/DefaultKeyword.txt b/compiler/testData/psi/DefaultKeyword.txt
index eb230ed3e19..098e5cdc5f6 100644
--- a/compiler/testData/psi/DefaultKeyword.txt
+++ b/compiler/testData/psi/DefaultKeyword.txt
@@ -158,7 +158,7 @@ JetFile: DefaultKeyword.kt
       PsiElement(RBRACE)('}')
   PsiWhiteSpace('\n\n')
   CLASS
-    PsiElement(trait)('trait')
+    PsiElement(interface)('interface')
     PsiWhiteSpace(' ')
     PsiElement(IDENTIFIER)('A')
     PsiWhiteSpace(' ')
diff --git a/compiler/testData/psi/TraitConstructor.kt b/compiler/testData/psi/TraitConstructor.kt
index 31fe90fd1ab..f8f4d16f12a 100644
--- a/compiler/testData/psi/TraitConstructor.kt
+++ b/compiler/testData/psi/TraitConstructor.kt
@@ -1,2 +1,2 @@
-trait TestTrait(val a: Int, var b: String, c: Double)
-trait TestTrait()
\ No newline at end of file
+interface TestTrait(val a: Int, var b: String, c: Double)
+interface TestTrait()
\ No newline at end of file
diff --git a/compiler/testData/psi/TraitConstructor.txt b/compiler/testData/psi/TraitConstructor.txt
index de7b7ae4b39..f1f0d6e384c 100644
--- a/compiler/testData/psi/TraitConstructor.txt
+++ b/compiler/testData/psi/TraitConstructor.txt
@@ -2,7 +2,7 @@ JetFile: TraitConstructor.kt
   PACKAGE_DIRECTIVE
     <empty list>
   CLASS
-    PsiElement(trait)('trait')
+    PsiElement(interface)('interface')
     PsiWhiteSpace(' ')
     PsiElement(IDENTIFIER)('TestTrait')
     PRIMARY_CONSTRUCTOR
@@ -43,7 +43,7 @@ JetFile: TraitConstructor.kt
         PsiElement(RPAR)(')')
   PsiWhiteSpace('\n')
   CLASS
-    PsiElement(trait)('trait')
+    PsiElement(interface)('interface')
     PsiWhiteSpace(' ')
     PsiElement(IDENTIFIER)('TestTrait')
     PRIMARY_CONSTRUCTOR
diff --git a/compiler/testData/psi/annotation/onFile/fileAnnotationInWrongPlace.kt b/compiler/testData/psi/annotation/onFile/fileAnnotationInWrongPlace.kt
index 33134b6e936..06e3f41875f 100644
--- a/compiler/testData/psi/annotation/onFile/fileAnnotationInWrongPlace.kt
+++ b/compiler/testData/psi/annotation/onFile/fileAnnotationInWrongPlace.kt
@@ -10,4 +10,4 @@ fun func() {}
 class C
 
 [file:]
-trait T
+interface T
diff --git a/compiler/testData/psi/annotation/onFile/fileAnnotationInWrongPlace.txt b/compiler/testData/psi/annotation/onFile/fileAnnotationInWrongPlace.txt
index 1ad029663f2..54f5875da84 100644
--- a/compiler/testData/psi/annotation/onFile/fileAnnotationInWrongPlace.txt
+++ b/compiler/testData/psi/annotation/onFile/fileAnnotationInWrongPlace.txt
@@ -88,6 +88,6 @@ JetFile: fileAnnotationInWrongPlace.kt
           <empty list>
         PsiElement(RBRACKET)(']')
     PsiWhiteSpace('\n')
-    PsiElement(trait)('trait')
+    PsiElement(interface)('interface')
     PsiWhiteSpace(' ')
     PsiElement(IDENTIFIER)('T')
\ No newline at end of file
diff --git a/compiler/testData/recursiveProcessor/declarations.kt b/compiler/testData/recursiveProcessor/declarations.kt
index 221a1776ee4..780d73fbb4c 100644
--- a/compiler/testData/recursiveProcessor/declarations.kt
+++ b/compiler/testData/recursiveProcessor/declarations.kt
@@ -4,7 +4,7 @@ fun <T1> T1.func(a: T1): T1 = a
 val <T2> T2.prop: T2? = null
 var propVar: Any? = null
 
-trait Trait<T3> {
+interface Trait<T3> {
     fun traitFunc(): Unit {}
     val traitProp: Any?
 }
@@ -24,8 +24,8 @@ object Object {
     val objProp: Any? = null
 }
 
-trait Outer {
-    trait NestedTrait {
+interface Outer {
+    interface NestedTrait {
         fun nestedTraitFun() {}
     }
 
diff --git a/compiler/testData/renderer/Classes.kt b/compiler/testData/renderer/Classes.kt
index 253f20f5042..88025ee9481 100644
--- a/compiler/testData/renderer/Classes.kt
+++ b/compiler/testData/renderer/Classes.kt
@@ -22,7 +22,7 @@ public open class TheClass<out T : Int, X> [AnotherAnnotation] () {
 internal class InternalClass {
 }
 
-trait TheTrait {
+interface TheTrait {
   fun abstractFun()
 
   companion object : TheClass<Int, Int> {
@@ -32,7 +32,7 @@ trait TheTrait {
 
 public class WithReified<reified A, reified out B>
 
-public trait TwoUpperBounds<T> where T : Number, T : Any
+public interface TwoUpperBounds<T> where T : Number, T : Any
 
 //package rendererTest
 //internal final annotation class TheAnnotation : kotlin.Annotation defined in rendererTest
diff --git a/compiler/testData/renderer/GlobalFunctions.kt b/compiler/testData/renderer/GlobalFunctions.kt
index 88261778537..eb68cc0a21b 100644
--- a/compiler/testData/renderer/GlobalFunctions.kt
+++ b/compiler/testData/renderer/GlobalFunctions.kt
@@ -12,8 +12,8 @@ public fun Int.ext(): Int {}
 
 public fun <out T> withTypeParam(a: Array<T>): Int {}
 
-trait Foo
-trait Bar
+interface Foo
+interface Bar
 
 fun <P> funTypeParameterWithTwoUpperBounds() where P : Foo, P : Bar = 17
 
diff --git a/compiler/testData/renderer/InheritedMembersVisibility.kt b/compiler/testData/renderer/InheritedMembersVisibility.kt
index 391a7607021..d89e893e4c0 100644
--- a/compiler/testData/renderer/InheritedMembersVisibility.kt
+++ b/compiler/testData/renderer/InheritedMembersVisibility.kt
@@ -1,4 +1,4 @@
-trait A {
+interface A {
     val v: Int
     public var int: Int
         private set
diff --git a/compiler/testData/renderer/KeywordsInNames.kt b/compiler/testData/renderer/KeywordsInNames.kt
index 21e40e46ce4..1c92b06d8f7 100644
--- a/compiler/testData/renderer/KeywordsInNames.kt
+++ b/compiler/testData/renderer/KeywordsInNames.kt
@@ -2,16 +2,16 @@ annotation class `true`
 
 val `val` = 5
 
-`true` trait `trait`
+`true` interface `interface`
 
 class `class`<`in`>(p: `in`?) {
    inner class `class`
 }
 
-val `is` = `class`<`trait`>(null).`class`()
-val `in` = `class`<`trait`>(null)
+val `is` = `class`<`interface`>(null).`class`()
+val `in` = `class`<`interface`>(null)
 
-fun <`in` : `trait`> `trait`.`fun`(`false`: `trait`): `trait` where `in` : Number
+fun <`in` : `interface`> `interface`.`fun`(`false`: `interface`): `interface` where `in` : Number
 
 val AS_SAFE = 1
 val NOT_IN = 2
@@ -20,7 +20,7 @@ val NOT_IS = 3
 //internal final annotation class `true` : kotlin.Annotation defined in root package
 //public constructor `true`() defined in `true`
 //internal val `val`: kotlin.Int defined in root package
-//`true` internal interface `trait` defined in root package
+//`true` internal interface `interface` defined in root package
 //internal final class `class`<`in`> defined in root package
 //<`in`> defined in `class`
 //public constructor `class`<`in`>(p: `in`?) defined in `class`
@@ -28,10 +28,10 @@ val NOT_IS = 3
 //internal final inner class `class` defined in `class`
 //public constructor `class`() defined in `class`.`class`
 //internal val `is`: `class`.`class` defined in root package
-//internal val `in`: `class`<`trait`> defined in root package
-//internal fun <`in` : `trait`> `trait`.`fun`(`false`: `trait`): `trait` where `in` : kotlin.Number defined in root package
-//<`in` : `trait` & kotlin.Number> defined in `fun`
-//value-parameter val `false`: `trait` defined in `fun`
+//internal val `in`: `class`<`interface`> defined in root package
+//internal fun <`in` : `interface`> `interface`.`fun`(`false`: `interface`): `interface` where `in` : kotlin.Number defined in root package
+//<`in` : `interface` & kotlin.Number> defined in `fun`
+//value-parameter val `false`: `interface` defined in `fun`
 //internal val AS_SAFE: kotlin.Int defined in root package
 //internal val NOT_IN: kotlin.Int defined in root package
 //internal val NOT_IS: kotlin.Int defined in root package
diff --git a/compiler/testData/repl/classes/simpleTrait.repl b/compiler/testData/repl/classes/simpleTrait.repl
index e976e55c927..160c0565415 100644
--- a/compiler/testData/repl/classes/simpleTrait.repl
+++ b/compiler/testData/repl/classes/simpleTrait.repl
@@ -1,5 +1,5 @@
->>> trait A
->>> trait B : A {
+>>> interface A
+>>> interface B : A {
 ...    fun foo() = 45
 ... }
 >>> javaClass<A>().isAssignableFrom(javaClass<B>())
diff --git a/compiler/testData/resolve/PropertyAndFunctionNameClash.resolve b/compiler/testData/resolve/PropertyAndFunctionNameClash.resolve
index 9dee49d1649..68535f62030 100644
--- a/compiler/testData/resolve/PropertyAndFunctionNameClash.resolve
+++ b/compiler/testData/resolve/PropertyAndFunctionNameClash.resolve
@@ -1,6 +1,6 @@
 open class HtmlTag
 
-trait NavigationBuilder {
+interface NavigationBuilder {
     public var text: ((String) -> String)?
     ~in_NB~var inNavigationBuilder: Int
 }
@@ -10,7 +10,7 @@ fun HtmlTag.navigation(body: NavigationBuilder.() -> Unit) {
 fun HtmlTag.a(contents: A.() -> Unit) {
 }
 
-trait A : HtmlTag {
+interface A : HtmlTag {
     ~text_in_A~var text: String
     ~in_A~var inA: Int
 }
diff --git a/compiler/testData/resolve/Super.resolve b/compiler/testData/resolve/Super.resolve
index 75e54307ee8..9a7a3397370 100644
--- a/compiler/testData/resolve/Super.resolve
+++ b/compiler/testData/resolve/Super.resolve
@@ -1,4 +1,4 @@
-~T~trait T {
+~T~interface T {
     fun foo() {}
 }
 ~C~open class C() {
@@ -25,7 +25,7 @@
     }
 }
 
-~G~trait G<T> {
+~G~interface G<T> {
     fun foo() {}
 }
 
diff --git a/compiler/testData/resolve/imports/ImportConflictBetweenImportedAndRootPackage.resolve b/compiler/testData/resolve/imports/ImportConflictBetweenImportedAndRootPackage.resolve
index ecc00e7bfa6..65e5dd8818c 100644
--- a/compiler/testData/resolve/imports/ImportConflictBetweenImportedAndRootPackage.resolve
+++ b/compiler/testData/resolve/imports/ImportConflictBetweenImportedAndRootPackage.resolve
@@ -8,10 +8,10 @@ val a1: `fromOtherPackage`TestClass? = null
 
 //FILE:fromRoot.kt
 //----------------------------------------------------------------------------------
-trait ~fromRoot~TestClass
+interface ~fromRoot~TestClass
 
 //FILE:fromOtherPackage.kt
 //----------------------------------------------------------------------------------
 package testing
 
-trait ~fromOtherPackage~TestClass
\ No newline at end of file
+interface ~fromOtherPackage~TestClass
\ No newline at end of file
diff --git a/compiler/testData/resolve/imports/ImportConflictBetweenImportedAndSamePackage.resolve b/compiler/testData/resolve/imports/ImportConflictBetweenImportedAndSamePackage.resolve
index 2fb61f8cac5..4f19cf5fc71 100644
--- a/compiler/testData/resolve/imports/ImportConflictBetweenImportedAndSamePackage.resolve
+++ b/compiler/testData/resolve/imports/ImportConflictBetweenImportedAndSamePackage.resolve
@@ -10,7 +10,7 @@ val a1: `fromSamePackage`TestClass? = null
 //----------------------------------------------------------------------------------
 package otherPackage
 
-trait ~fromOtherPackage~TestClass
+interface ~fromOtherPackage~TestClass
 
 
 //FILE:fromSamePackage.kt
diff --git a/compiler/testData/resolve/imports/ImportNonBlockingAnalysis.resolve b/compiler/testData/resolve/imports/ImportNonBlockingAnalysis.resolve
index 94a35f57eac..7fe7b8c5bdf 100644
--- a/compiler/testData/resolve/imports/ImportNonBlockingAnalysis.resolve
+++ b/compiler/testData/resolve/imports/ImportNonBlockingAnalysis.resolve
@@ -5,8 +5,8 @@ package test
 import testing.InTesting2
 import testing.InTesting1
 
-trait ~InTest1~InTest1 : `InTesting1`InTesting1
-trait ~InTest2~InTest2 : `InTesting2`InTesting2
+interface ~InTest1~InTest1 : `InTesting1`InTesting1
+interface ~InTest2~InTest2 : `InTesting2`InTesting2
 
 //FILE:testing.kt
 //----------------------------------------------------------------------------------
@@ -14,5 +14,5 @@ package testing
 
 import test.InTest2
 
-trait ~InTesting1~InTesting1 : `InTest2`InTest2
-trait ~InTesting2~InTesting2
+interface ~InTesting1~InTesting1 : `InTest2`InTest2
+interface ~InTesting2~InTesting2
diff --git a/compiler/testData/resolve/imports/ImportResolveOrderStable.resolve b/compiler/testData/resolve/imports/ImportResolveOrderStable.resolve
index 680e85831cc..647a892a56f 100644
--- a/compiler/testData/resolve/imports/ImportResolveOrderStable.resolve
+++ b/compiler/testData/resolve/imports/ImportResolveOrderStable.resolve
@@ -8,7 +8,7 @@ import testing.allUnder.*
 
 // The goal is to activate lazy resolve in order Second, Other
 class FirstOrder: `other`Other, FirstInternal
-trait FirstInternal: `exact`Second
+interface FirstInternal: `exact`Second
 
 
 
@@ -22,7 +22,7 @@ import testing.allUnder.*
 
 // The goal is to activate lazy resolve in order Other, Second
 class FirstOrder: FirstInternal, `other`Other
-trait FirstInternal: `exact`Second
+interface FirstInternal: `exact`Second
 
 
 
@@ -30,16 +30,16 @@ trait FirstInternal: `exact`Second
 //----------------------------------------------------------------------------------
 package testing.allUnder
 
-trait ~allUnder~Second
+interface ~allUnder~Second
 
 //FILE:secondForExactImport.kt
 //----------------------------------------------------------------------------------
 package testing.exact
 
-trait ~exact~Second
+interface ~exact~Second
 
 //FILE:someOther.kt
 //----------------------------------------------------------------------------------
 package testing.other
 
-trait ~other~Other
\ No newline at end of file
+interface ~other~Other
\ No newline at end of file
diff --git a/compiler/testData/resolve/labels/labelForPropertyInGetter.resolve b/compiler/testData/resolve/labels/labelForPropertyInGetter.resolve
index 3dcae60460c..d76aa0a685d 100644
--- a/compiler/testData/resolve/labels/labelForPropertyInGetter.resolve
+++ b/compiler/testData/resolve/labels/labelForPropertyInGetter.resolve
@@ -1,4 +1,4 @@
-trait Base {
+interface Base {
     fun foo()
 }
 
diff --git a/compiler/testData/resolve/labels/labelForPropertyInSetter.resolve b/compiler/testData/resolve/labels/labelForPropertyInSetter.resolve
index c9d22a39e8a..b53b527f8ee 100644
--- a/compiler/testData/resolve/labels/labelForPropertyInSetter.resolve
+++ b/compiler/testData/resolve/labels/labelForPropertyInSetter.resolve
@@ -1,4 +1,4 @@
-trait Base {
+interface Base {
     fun foo()
 }
 
diff --git a/compiler/testData/resolveConstructorDelegationCalls/superPrimary.kt b/compiler/testData/resolveConstructorDelegationCalls/superPrimary.kt
index 73106ef7960..b1a2bc749b6 100644
--- a/compiler/testData/resolveConstructorDelegationCalls/superPrimary.kt
+++ b/compiler/testData/resolveConstructorDelegationCalls/superPrimary.kt
@@ -1,5 +1,5 @@
 open class B(x: Int)
-trait C
+interface C
 class A : B, C {
     <caret>constructor(): super(1) { }
 }
diff --git a/compiler/testData/resolveConstructorDelegationCalls/superPrimary.txt b/compiler/testData/resolveConstructorDelegationCalls/superPrimary.txt
index 41fbde535fa..1ffdf1c42c5 100644
--- a/compiler/testData/resolveConstructorDelegationCalls/superPrimary.txt
+++ b/compiler/testData/resolveConstructorDelegationCalls/superPrimary.txt
@@ -1,5 +1,5 @@
 open class B(x: Int)
-trait C
+interface C
 class A : B, C {
     <caret>constructor(): super(1) { }
 }
diff --git a/compiler/testData/resolveConstructorDelegationCalls/superPrimaryEmpty.kt b/compiler/testData/resolveConstructorDelegationCalls/superPrimaryEmpty.kt
index 6271104ef4c..dbf60bc57b9 100644
--- a/compiler/testData/resolveConstructorDelegationCalls/superPrimaryEmpty.kt
+++ b/compiler/testData/resolveConstructorDelegationCalls/superPrimaryEmpty.kt
@@ -1,5 +1,5 @@
 open class B
-trait C
+interface C
 class A : B, C {
     <caret>constructor(): super() { }
 }
diff --git a/compiler/testData/resolveConstructorDelegationCalls/superPrimaryEmpty.txt b/compiler/testData/resolveConstructorDelegationCalls/superPrimaryEmpty.txt
index 9fa46de7ad2..388b9244457 100644
--- a/compiler/testData/resolveConstructorDelegationCalls/superPrimaryEmpty.txt
+++ b/compiler/testData/resolveConstructorDelegationCalls/superPrimaryEmpty.txt
@@ -1,5 +1,5 @@
 open class B
-trait C
+interface C
 class A : B, C {
     <caret>constructor(): super() { }
 }
diff --git a/compiler/testData/resolveConstructorDelegationCalls/superPrimaryImplicit.kt b/compiler/testData/resolveConstructorDelegationCalls/superPrimaryImplicit.kt
index 20d6cd5b876..d5592972dcf 100644
--- a/compiler/testData/resolveConstructorDelegationCalls/superPrimaryImplicit.kt
+++ b/compiler/testData/resolveConstructorDelegationCalls/superPrimaryImplicit.kt
@@ -1,5 +1,5 @@
 open class B
-trait C
+interface C
 class A : B, C {
     <caret>constructor() { }
 }
diff --git a/compiler/testData/resolveConstructorDelegationCalls/superPrimaryImplicit.txt b/compiler/testData/resolveConstructorDelegationCalls/superPrimaryImplicit.txt
index 4e557d66a65..cbda5bb38ad 100644
--- a/compiler/testData/resolveConstructorDelegationCalls/superPrimaryImplicit.txt
+++ b/compiler/testData/resolveConstructorDelegationCalls/superPrimaryImplicit.txt
@@ -1,5 +1,5 @@
 open class B
-trait C
+interface C
 class A : B, C {
     <caret>constructor() { }
 }
diff --git a/compiler/testData/resolveConstructorDelegationCalls/superSecondary.kt b/compiler/testData/resolveConstructorDelegationCalls/superSecondary.kt
index 111832c5d55..8ca7fc13f10 100644
--- a/compiler/testData/resolveConstructorDelegationCalls/superSecondary.kt
+++ b/compiler/testData/resolveConstructorDelegationCalls/superSecondary.kt
@@ -1,7 +1,7 @@
 open class B {
     constructor(x: Int) {}
 }
-trait C
+interface C
 class A : B, C {
     <caret>constructor(): super(1) { }
 }
diff --git a/compiler/testData/resolveConstructorDelegationCalls/superSecondary.txt b/compiler/testData/resolveConstructorDelegationCalls/superSecondary.txt
index 7ddfad21676..1aeba0d9b4c 100644
--- a/compiler/testData/resolveConstructorDelegationCalls/superSecondary.txt
+++ b/compiler/testData/resolveConstructorDelegationCalls/superSecondary.txt
@@ -1,7 +1,7 @@
 open class B {
     constructor(x: Int) {}
 }
-trait C
+interface C
 class A : B, C {
     <caret>constructor(): super(1) { }
 }
diff --git a/compiler/testData/resolveConstructorDelegationCalls/superSecondaryImplicit.kt b/compiler/testData/resolveConstructorDelegationCalls/superSecondaryImplicit.kt
index be3bff3c20e..c8116ea7c32 100644
--- a/compiler/testData/resolveConstructorDelegationCalls/superSecondaryImplicit.kt
+++ b/compiler/testData/resolveConstructorDelegationCalls/superSecondaryImplicit.kt
@@ -1,7 +1,7 @@
 open class B {
     constructor() {}
 }
-trait C
+interface C
 class A : B, C {
     <caret>constructor() { }
 }
diff --git a/compiler/testData/resolveConstructorDelegationCalls/superSecondaryImplicit.txt b/compiler/testData/resolveConstructorDelegationCalls/superSecondaryImplicit.txt
index 3fb3bd10b32..5b0fd6f3236 100644
--- a/compiler/testData/resolveConstructorDelegationCalls/superSecondaryImplicit.txt
+++ b/compiler/testData/resolveConstructorDelegationCalls/superSecondaryImplicit.txt
@@ -1,7 +1,7 @@
 open class B {
     constructor() {}
 }
-trait C
+interface C
 class A : B, C {
     <caret>constructor() { }
 }
diff --git a/compiler/testData/resolveConstructorDelegationCalls/superSecondaryOverload.kt b/compiler/testData/resolveConstructorDelegationCalls/superSecondaryOverload.kt
index 509cf4f1c0c..40df040e867 100644
--- a/compiler/testData/resolveConstructorDelegationCalls/superSecondaryOverload.kt
+++ b/compiler/testData/resolveConstructorDelegationCalls/superSecondaryOverload.kt
@@ -2,7 +2,7 @@ open class B(x: Double) {
     constructor(x: Int) {}
     constructor(x: String) {}
 }
-trait C
+interface C
 class A : B, C {
     <caret>constructor(): super("abc") { }
 }
diff --git a/compiler/testData/resolveConstructorDelegationCalls/superSecondaryOverload.txt b/compiler/testData/resolveConstructorDelegationCalls/superSecondaryOverload.txt
index f1e377840f0..0bea777662f 100644
--- a/compiler/testData/resolveConstructorDelegationCalls/superSecondaryOverload.txt
+++ b/compiler/testData/resolveConstructorDelegationCalls/superSecondaryOverload.txt
@@ -2,7 +2,7 @@ open class B(x: Double) {
     constructor(x: Int) {}
     constructor(x: String) {}
 }
-trait C
+interface C
 class A : B, C {
     <caret>constructor(): super("abc") { }
 }
diff --git a/compiler/testData/resolvedCalls/functionTypes/valOfExtensionFunctionType.kt b/compiler/testData/resolvedCalls/functionTypes/valOfExtensionFunctionType.kt
index 52c77b2e2b7..1db2e15b8a8 100644
--- a/compiler/testData/resolvedCalls/functionTypes/valOfExtensionFunctionType.kt
+++ b/compiler/testData/resolvedCalls/functionTypes/valOfExtensionFunctionType.kt
@@ -1,4 +1,4 @@
-trait A {
+interface A {
     val foo: Int.()->Unit
 
     fun test() {
diff --git a/compiler/testData/resolvedCalls/functionTypes/valOfExtensionFunctionType.txt b/compiler/testData/resolvedCalls/functionTypes/valOfExtensionFunctionType.txt
index 1b52dd128e9..596c3e9269d 100644
--- a/compiler/testData/resolvedCalls/functionTypes/valOfExtensionFunctionType.txt
+++ b/compiler/testData/resolvedCalls/functionTypes/valOfExtensionFunctionType.txt
@@ -1,4 +1,4 @@
-trait A {
+interface A {
     val foo: Int.()->Unit
 
     fun test() {
diff --git a/compiler/testData/resolvedCalls/functionTypes/valOfExtensionFunctionTypeInvoke.kt b/compiler/testData/resolvedCalls/functionTypes/valOfExtensionFunctionTypeInvoke.kt
index 0ddcfad66f8..0d36a46d1ba 100644
--- a/compiler/testData/resolvedCalls/functionTypes/valOfExtensionFunctionTypeInvoke.kt
+++ b/compiler/testData/resolvedCalls/functionTypes/valOfExtensionFunctionTypeInvoke.kt
@@ -1,4 +1,4 @@
-trait A {
+interface A {
     val foo: Int.()->Unit
 
     fun test() {
diff --git a/compiler/testData/resolvedCalls/functionTypes/valOfExtensionFunctionTypeInvoke.txt b/compiler/testData/resolvedCalls/functionTypes/valOfExtensionFunctionTypeInvoke.txt
index 4375c4cddd7..8ed821533f3 100644
--- a/compiler/testData/resolvedCalls/functionTypes/valOfExtensionFunctionTypeInvoke.txt
+++ b/compiler/testData/resolvedCalls/functionTypes/valOfExtensionFunctionTypeInvoke.txt
@@ -1,4 +1,4 @@
-trait A {
+interface A {
     val foo: Int.()->Unit
 
     fun test() {
diff --git a/compiler/testData/resolvedCalls/functionTypes/valOfFunctionType.kt b/compiler/testData/resolvedCalls/functionTypes/valOfFunctionType.kt
index bc7c508eecb..950b612da58 100644
--- a/compiler/testData/resolvedCalls/functionTypes/valOfFunctionType.kt
+++ b/compiler/testData/resolvedCalls/functionTypes/valOfFunctionType.kt
@@ -1,4 +1,4 @@
-trait A {
+interface A {
     val foo: (Int)->Int
 }
 
diff --git a/compiler/testData/resolvedCalls/functionTypes/valOfFunctionType.txt b/compiler/testData/resolvedCalls/functionTypes/valOfFunctionType.txt
index 1c52afe2a0b..6386144288d 100644
--- a/compiler/testData/resolvedCalls/functionTypes/valOfFunctionType.txt
+++ b/compiler/testData/resolvedCalls/functionTypes/valOfFunctionType.txt
@@ -1,4 +1,4 @@
-trait A {
+interface A {
     val foo: (Int)->Int
 }
 
diff --git a/compiler/testData/resolvedCalls/functionTypes/valOfFunctionTypeInvoke.kt b/compiler/testData/resolvedCalls/functionTypes/valOfFunctionTypeInvoke.kt
index ce3c9349213..c15d29afe04 100644
--- a/compiler/testData/resolvedCalls/functionTypes/valOfFunctionTypeInvoke.kt
+++ b/compiler/testData/resolvedCalls/functionTypes/valOfFunctionTypeInvoke.kt
@@ -1,4 +1,4 @@
-trait A {
+interface A {
     val foo: (Int)->Int
 }
 
diff --git a/compiler/testData/resolvedCalls/functionTypes/valOfFunctionTypeInvoke.txt b/compiler/testData/resolvedCalls/functionTypes/valOfFunctionTypeInvoke.txt
index 614de01fa99..79e91aef144 100644
--- a/compiler/testData/resolvedCalls/functionTypes/valOfFunctionTypeInvoke.txt
+++ b/compiler/testData/resolvedCalls/functionTypes/valOfFunctionTypeInvoke.txt
@@ -1,4 +1,4 @@
-trait A {
+interface A {
     val foo: (Int)->Int
 }
 
diff --git a/compiler/testData/resolvedCalls/hasBothDispatchAndExtensionReceivers.kt b/compiler/testData/resolvedCalls/hasBothDispatchAndExtensionReceivers.kt
index 65af828148a..5e244b71f06 100644
--- a/compiler/testData/resolvedCalls/hasBothDispatchAndExtensionReceivers.kt
+++ b/compiler/testData/resolvedCalls/hasBothDispatchAndExtensionReceivers.kt
@@ -2,7 +2,7 @@ class A {
     fun B.foo() {}
 }
 
-trait B
+interface B
 
 fun bar(a: A, b: B) {
     with (a) {
diff --git a/compiler/testData/resolvedCalls/hasBothDispatchAndExtensionReceivers.txt b/compiler/testData/resolvedCalls/hasBothDispatchAndExtensionReceivers.txt
index cb2e2a42770..7284936dd93 100644
--- a/compiler/testData/resolvedCalls/hasBothDispatchAndExtensionReceivers.txt
+++ b/compiler/testData/resolvedCalls/hasBothDispatchAndExtensionReceivers.txt
@@ -2,7 +2,7 @@ class A {
     fun B.foo() {}
 }
 
-trait B
+interface B
 
 fun bar(a: A, b: B) {
     with (a) {
diff --git a/compiler/testData/resolvedCalls/hasBothDispatchAndExtensionReceiversWithoutExplicitReceiver.kt b/compiler/testData/resolvedCalls/hasBothDispatchAndExtensionReceiversWithoutExplicitReceiver.kt
index 7c5e2390443..5ed43b236d4 100644
--- a/compiler/testData/resolvedCalls/hasBothDispatchAndExtensionReceiversWithoutExplicitReceiver.kt
+++ b/compiler/testData/resolvedCalls/hasBothDispatchAndExtensionReceiversWithoutExplicitReceiver.kt
@@ -2,7 +2,7 @@ class A {
     fun B.foo() {}
 }
 
-trait B
+interface B
 
 fun bar(a: A, b: B) {
     with (a) {
diff --git a/compiler/testData/resolvedCalls/hasBothDispatchAndExtensionReceiversWithoutExplicitReceiver.txt b/compiler/testData/resolvedCalls/hasBothDispatchAndExtensionReceiversWithoutExplicitReceiver.txt
index 9394bc1338d..120feb28091 100644
--- a/compiler/testData/resolvedCalls/hasBothDispatchAndExtensionReceiversWithoutExplicitReceiver.txt
+++ b/compiler/testData/resolvedCalls/hasBothDispatchAndExtensionReceiversWithoutExplicitReceiver.txt
@@ -2,7 +2,7 @@ class A {
     fun B.foo() {}
 }
 
-trait B
+interface B
 
 fun bar(a: A, b: B) {
     with (a) {
diff --git a/compiler/testData/resolvedCalls/realExamples/stringPlusInBuilders.kt b/compiler/testData/resolvedCalls/realExamples/stringPlusInBuilders.kt
index e8799a68b01..e2d8f9f38ed 100644
--- a/compiler/testData/resolvedCalls/realExamples/stringPlusInBuilders.kt
+++ b/compiler/testData/resolvedCalls/realExamples/stringPlusInBuilders.kt
@@ -1,4 +1,4 @@
-trait Element {
+interface Element {
     fun render(builder: StringBuilder, indent: String)
 }
 
diff --git a/compiler/testData/resolvedCalls/realExamples/stringPlusInBuilders.txt b/compiler/testData/resolvedCalls/realExamples/stringPlusInBuilders.txt
index c4dadd1f22c..e72bd4bf941 100644
--- a/compiler/testData/resolvedCalls/realExamples/stringPlusInBuilders.txt
+++ b/compiler/testData/resolvedCalls/realExamples/stringPlusInBuilders.txt
@@ -1,4 +1,4 @@
-trait Element {
+interface Element {
     fun render(builder: StringBuilder, indent: String)
 }
 
diff --git a/compiler/testData/type-checker-test.kt b/compiler/testData/type-checker-test.kt
index 516a8b4433d..fbe82903fc1 100644
--- a/compiler/testData/type-checker-test.kt
+++ b/compiler/testData/type-checker-test.kt
@@ -38,14 +38,14 @@ fun f(a : Int) : Int {a}
 fun f(a : Float, b : Int) : Float {a}
 fun f<T>(a : Float) : T {a}
 
-trait Parent
-trait A: Parent
-trait B: Parent
+interface Parent
+interface A: Parent
+interface B: Parent
 
-trait Rec<T>
+interface Rec<T>
 class ARec : Rec<ARec>
 class BRec : Rec<BRec>
-trait SubRec<T>: Rec<T>
+interface SubRec<T>: Rec<T>
 
-trait Star<T : Star<T>>
-trait SubStar<T : SubStar<T>> : Star<T>
\ No newline at end of file
+interface Star<T : Star<T>>
+interface SubStar<T : SubStar<T>> : Star<T>
\ No newline at end of file
diff --git a/compiler/testData/type/binding/explicit/inProjection.kt b/compiler/testData/type/binding/explicit/inProjection.kt
index 57479213acb..8081347081b 100644
--- a/compiler/testData/type/binding/explicit/inProjection.kt
+++ b/compiler/testData/type/binding/explicit/inProjection.kt
@@ -1,6 +1,6 @@
-trait Inv<T>
-trait In<in I>
-trait Out<out O>
+interface Inv<T>
+interface In<in I>
+interface Out<out O>
 
 
 val foo: Inv<in In<in Out<in Int>>> = null!!
diff --git a/compiler/testData/type/binding/explicit/outProjection.kt b/compiler/testData/type/binding/explicit/outProjection.kt
index ca9daf9b89b..2bc4c868c8d 100644
--- a/compiler/testData/type/binding/explicit/outProjection.kt
+++ b/compiler/testData/type/binding/explicit/outProjection.kt
@@ -1,6 +1,6 @@
-trait Inv<T>
-trait In<in I>
-trait Out<out O>
+interface Inv<T>
+interface In<in I>
+interface Out<out O>
 
 
 val foo: Inv<out In<out Out<out Int>>> = null!!
diff --git a/compiler/testData/type/binding/explicit/typeWithBracket.kt b/compiler/testData/type/binding/explicit/typeWithBracket.kt
index ad36e6d6ae6..c0860f6a563 100644
--- a/compiler/testData/type/binding/explicit/typeWithBracket.kt
+++ b/compiler/testData/type/binding/explicit/typeWithBracket.kt
@@ -1,4 +1,4 @@
-trait Inv<I>
+interface Inv<I>
 
 val foo: Inv<out ((Inv<Int>)?)> = null!!
 /*
diff --git a/compiler/testData/type/binding/implicit/inProjection.kt b/compiler/testData/type/binding/implicit/inProjection.kt
index 0a0df0499aa..229b5c2176c 100644
--- a/compiler/testData/type/binding/implicit/inProjection.kt
+++ b/compiler/testData/type/binding/implicit/inProjection.kt
@@ -1,6 +1,6 @@
-trait Inv<T>
-trait In<in I>
-trait Out<out O>
+interface Inv<T>
+interface In<in I>
+interface Out<out O>
 
 
 fun <T> getT(): T = null!!
diff --git a/compiler/testData/type/binding/implicit/outProjection.kt b/compiler/testData/type/binding/implicit/outProjection.kt
index 52c5398eea7..18150126dc5 100644
--- a/compiler/testData/type/binding/implicit/outProjection.kt
+++ b/compiler/testData/type/binding/implicit/outProjection.kt
@@ -1,6 +1,6 @@
-trait Inv<T>
-trait In<in I>
-trait Out<out O>
+interface Inv<T>
+interface In<in I>
+interface Out<out O>
 
 
 fun <T> getT(): T = null!!
diff --git a/compiler/testData/type/binding/implicit/typeWithBracket.kt b/compiler/testData/type/binding/implicit/typeWithBracket.kt
index ed633a9e502..aaaad1db39f 100644
--- a/compiler/testData/type/binding/implicit/typeWithBracket.kt
+++ b/compiler/testData/type/binding/implicit/typeWithBracket.kt
@@ -1,4 +1,4 @@
-trait Inv<I>
+interface Inv<I>
 
 fun <T> getT(): T = null!!
 
diff --git a/compiler/testData/writeFlags/class/accessFlags/publicInnerInterface.kt b/compiler/testData/writeFlags/class/accessFlags/publicInnerInterface.kt
index 0ed166d19e3..b6d6bbee1c1 100644
--- a/compiler/testData/writeFlags/class/accessFlags/publicInnerInterface.kt
+++ b/compiler/testData/writeFlags/class/accessFlags/publicInnerInterface.kt
@@ -1,5 +1,5 @@
 public class Foo() {
-   public trait MyTrait {
+   public interface MyTrait {
    }
 }
 
diff --git a/compiler/testData/writeFlags/class/accessFlags/publicInterface.kt b/compiler/testData/writeFlags/class/accessFlags/publicInterface.kt
index 928c0aa3b23..5dc36e13db7 100644
--- a/compiler/testData/writeFlags/class/accessFlags/publicInterface.kt
+++ b/compiler/testData/writeFlags/class/accessFlags/publicInterface.kt
@@ -1,4 +1,4 @@
-public trait MyTrait {
+public interface MyTrait {
 }
 
 // TESTED_OBJECT_KIND: class
diff --git a/compiler/testData/writeFlags/class/deprecatedFlag/trait.kt b/compiler/testData/writeFlags/class/deprecatedFlag/trait.kt
index 10fb0bae3c3..56e2a960a11 100644
--- a/compiler/testData/writeFlags/class/deprecatedFlag/trait.kt
+++ b/compiler/testData/writeFlags/class/deprecatedFlag/trait.kt
@@ -1,4 +1,4 @@
-deprecated("") public trait MyTrait {
+deprecated("") public interface MyTrait {
 }
 
 // TESTED_OBJECT_KIND: class
diff --git a/compiler/testData/writeFlags/class/visibility/internal/innerTrait.kt b/compiler/testData/writeFlags/class/visibility/internal/innerTrait.kt
index 2eb3546370c..c729ec91e81 100644
--- a/compiler/testData/writeFlags/class/visibility/internal/innerTrait.kt
+++ b/compiler/testData/writeFlags/class/visibility/internal/innerTrait.kt
@@ -1,5 +1,5 @@
 class Foo {
-  trait MyClass {
+  interface MyClass {
   }
 }
 
diff --git a/compiler/testData/writeFlags/class/visibility/internal/trait.kt b/compiler/testData/writeFlags/class/visibility/internal/trait.kt
index decaf46b670..0159ceab694 100644
--- a/compiler/testData/writeFlags/class/visibility/internal/trait.kt
+++ b/compiler/testData/writeFlags/class/visibility/internal/trait.kt
@@ -1,4 +1,4 @@
-trait MyClass {
+interface MyClass {
 }
 
 // TESTED_OBJECT_KIND: class
diff --git a/compiler/testData/writeFlags/class/visibility/private/innerTrait.kt b/compiler/testData/writeFlags/class/visibility/private/innerTrait.kt
index a98d1288027..71511c5434a 100644
--- a/compiler/testData/writeFlags/class/visibility/private/innerTrait.kt
+++ b/compiler/testData/writeFlags/class/visibility/private/innerTrait.kt
@@ -1,5 +1,5 @@
 class Foo {
-  private trait MyClass {
+  private interface MyClass {
   }
 }
 
diff --git a/compiler/testData/writeFlags/class/visibility/private/trait.kt b/compiler/testData/writeFlags/class/visibility/private/trait.kt
index 73519fafceb..ae929a2a14a 100644
--- a/compiler/testData/writeFlags/class/visibility/private/trait.kt
+++ b/compiler/testData/writeFlags/class/visibility/private/trait.kt
@@ -1,4 +1,4 @@
-private trait MyClass {
+private interface MyClass {
 }
 
 // TESTED_OBJECT_KIND: class
diff --git a/compiler/testData/writeFlags/class/visibility/public/innerTrait.kt b/compiler/testData/writeFlags/class/visibility/public/innerTrait.kt
index 14230c2ad16..992e923cd8f 100644
--- a/compiler/testData/writeFlags/class/visibility/public/innerTrait.kt
+++ b/compiler/testData/writeFlags/class/visibility/public/innerTrait.kt
@@ -1,5 +1,5 @@
 class Foo {
-  public trait MyClass {
+  public interface MyClass {
   }
 }
 
diff --git a/compiler/testData/writeFlags/class/visibility/public/trait.kt b/compiler/testData/writeFlags/class/visibility/public/trait.kt
index 6474e8547ff..1127f93e63a 100644
--- a/compiler/testData/writeFlags/class/visibility/public/trait.kt
+++ b/compiler/testData/writeFlags/class/visibility/public/trait.kt
@@ -1,4 +1,4 @@
-public trait MyClass {
+public interface MyClass {
 }
 
 // TESTED_OBJECT_KIND: class
diff --git a/compiler/testData/writeFlags/property/classObject/trait/delegatedProtectedVar.kt b/compiler/testData/writeFlags/property/classObject/trait/delegatedProtectedVar.kt
index f6f8a7bd43d..9327e128689 100644
--- a/compiler/testData/writeFlags/property/classObject/trait/delegatedProtectedVar.kt
+++ b/compiler/testData/writeFlags/property/classObject/trait/delegatedProtectedVar.kt
@@ -8,7 +8,7 @@ class TestDelegate() {
     }
 }
 
-trait Test {
+interface Test {
   companion object {
     protected var prop: Int by TestDelegate()
   }
diff --git a/compiler/testData/writeFlags/property/classObject/trait/delegatedPublicVal.kt b/compiler/testData/writeFlags/property/classObject/trait/delegatedPublicVal.kt
index a5e20461659..8f2b1f37946 100644
--- a/compiler/testData/writeFlags/property/classObject/trait/delegatedPublicVal.kt
+++ b/compiler/testData/writeFlags/property/classObject/trait/delegatedPublicVal.kt
@@ -4,7 +4,7 @@ class TestDelegate() {
     }
 }
 
-trait Test {
+interface Test {
   companion object {
     public val prop: Int by TestDelegate()
   }
diff --git a/compiler/testData/writeFlags/property/classObject/trait/internalVal.kt b/compiler/testData/writeFlags/property/classObject/trait/internalVal.kt
index 5e683811d47..8efb6af7605 100644
--- a/compiler/testData/writeFlags/property/classObject/trait/internalVal.kt
+++ b/compiler/testData/writeFlags/property/classObject/trait/internalVal.kt
@@ -1,4 +1,4 @@
-trait Test {
+interface Test {
   companion object {
     val prop: Int = 0;
   }
diff --git a/compiler/testData/writeFlags/property/classObject/trait/internalVar.kt b/compiler/testData/writeFlags/property/classObject/trait/internalVar.kt
index e702feafe76..c0fab7bcef3 100644
--- a/compiler/testData/writeFlags/property/classObject/trait/internalVar.kt
+++ b/compiler/testData/writeFlags/property/classObject/trait/internalVar.kt
@@ -1,4 +1,4 @@
-trait Test {
+interface Test {
   companion object {
     var prop: Int = 0;
   }
diff --git a/compiler/testData/writeFlags/property/classObject/trait/internalVarPrivateSet.kt b/compiler/testData/writeFlags/property/classObject/trait/internalVarPrivateSet.kt
index 1e44a6f72c4..83c76732140 100644
--- a/compiler/testData/writeFlags/property/classObject/trait/internalVarPrivateSet.kt
+++ b/compiler/testData/writeFlags/property/classObject/trait/internalVarPrivateSet.kt
@@ -1,4 +1,4 @@
-trait Test {
+interface Test {
   companion object {
     var prop: Int = 0
       private set
diff --git a/compiler/testData/writeFlags/property/classObject/trait/noBackingField.kt b/compiler/testData/writeFlags/property/classObject/trait/noBackingField.kt
index 134974165db..e7f6a804a29 100644
--- a/compiler/testData/writeFlags/property/classObject/trait/noBackingField.kt
+++ b/compiler/testData/writeFlags/property/classObject/trait/noBackingField.kt
@@ -1,4 +1,4 @@
-trait Test {
+interface Test {
   companion object {
     var prop: Int
       get() {
diff --git a/compiler/testData/writeFlags/property/classObject/trait/privateVal.kt b/compiler/testData/writeFlags/property/classObject/trait/privateVal.kt
index a50ec0ef3ec..6d4377cf9a5 100644
--- a/compiler/testData/writeFlags/property/classObject/trait/privateVal.kt
+++ b/compiler/testData/writeFlags/property/classObject/trait/privateVal.kt
@@ -1,4 +1,4 @@
-trait Test {
+interface Test {
   companion object {
     private val prop = 0;
   }
diff --git a/compiler/testData/writeFlags/property/classObject/trait/privateVar.kt b/compiler/testData/writeFlags/property/classObject/trait/privateVar.kt
index 42cc3f626dc..920ecceabbd 100644
--- a/compiler/testData/writeFlags/property/classObject/trait/privateVar.kt
+++ b/compiler/testData/writeFlags/property/classObject/trait/privateVar.kt
@@ -1,4 +1,4 @@
-trait Test {
+interface Test {
   companion object {
     private var prop = 0;
   }
diff --git a/compiler/testData/writeFlags/property/classObject/trait/protectedVal.kt b/compiler/testData/writeFlags/property/classObject/trait/protectedVal.kt
index be22ea7a9ee..1fa7908a250 100644
--- a/compiler/testData/writeFlags/property/classObject/trait/protectedVal.kt
+++ b/compiler/testData/writeFlags/property/classObject/trait/protectedVal.kt
@@ -1,4 +1,4 @@
-trait Test {
+interface Test {
   companion object {
     protected val prop: Int = 0
   }
diff --git a/compiler/testData/writeFlags/property/classObject/trait/protectedVarPrivateSet.kt b/compiler/testData/writeFlags/property/classObject/trait/protectedVarPrivateSet.kt
index 01e3ebdb493..351d3c38462 100644
--- a/compiler/testData/writeFlags/property/classObject/trait/protectedVarPrivateSet.kt
+++ b/compiler/testData/writeFlags/property/classObject/trait/protectedVarPrivateSet.kt
@@ -1,4 +1,4 @@
-trait Test {
+interface Test {
   companion object {
     protected var prop: Int = 0
       private set
diff --git a/compiler/testData/writeFlags/property/classObject/trait/publicVal.kt b/compiler/testData/writeFlags/property/classObject/trait/publicVal.kt
index 8baaed18a9d..2a7f7a435c9 100644
--- a/compiler/testData/writeFlags/property/classObject/trait/publicVal.kt
+++ b/compiler/testData/writeFlags/property/classObject/trait/publicVal.kt
@@ -1,4 +1,4 @@
-trait Test {
+interface Test {
   companion object {
     public val prop: Int = 0;
   }
diff --git a/compiler/testData/writeFlags/property/classObject/trait/publicValNonDefault.kt b/compiler/testData/writeFlags/property/classObject/trait/publicValNonDefault.kt
index 96426d70215..bc69fec307b 100644
--- a/compiler/testData/writeFlags/property/classObject/trait/publicValNonDefault.kt
+++ b/compiler/testData/writeFlags/property/classObject/trait/publicValNonDefault.kt
@@ -1,4 +1,4 @@
-trait Test {
+interface Test {
   companion object {
     public val prop: Int = 0
       get() {
diff --git a/compiler/testData/writeFlags/property/classObject/trait/publicVar.kt b/compiler/testData/writeFlags/property/classObject/trait/publicVar.kt
index c7b4c80f4aa..0592a51be66 100644
--- a/compiler/testData/writeFlags/property/classObject/trait/publicVar.kt
+++ b/compiler/testData/writeFlags/property/classObject/trait/publicVar.kt
@@ -1,4 +1,4 @@
-trait Test {
+interface Test {
   companion object {
     public var prop: Int = 0
   }
diff --git a/compiler/testData/writeFlags/property/classObject/trait/publicVarNonDefault.kt b/compiler/testData/writeFlags/property/classObject/trait/publicVarNonDefault.kt
index c906b7d8602..64a46513fec 100644
--- a/compiler/testData/writeFlags/property/classObject/trait/publicVarNonDefault.kt
+++ b/compiler/testData/writeFlags/property/classObject/trait/publicVarNonDefault.kt
@@ -1,4 +1,4 @@
-trait Test {
+interface Test {
   companion object {
     public var prop: Int = 0
       set(i : Int) {
diff --git a/compiler/testData/writeFlags/property/classObject/trait/publicVarPrivateSet.kt b/compiler/testData/writeFlags/property/classObject/trait/publicVarPrivateSet.kt
index c92e0eb90f2..6582aa047a3 100644
--- a/compiler/testData/writeFlags/property/classObject/trait/publicVarPrivateSet.kt
+++ b/compiler/testData/writeFlags/property/classObject/trait/publicVarPrivateSet.kt
@@ -1,4 +1,4 @@
-trait Test {
+interface Test {
   companion object {
     public var prop: Int = 0
       private set
diff --git a/compiler/testData/writeFlags/property/classObject/trait/publicVarProtectedSet.kt b/compiler/testData/writeFlags/property/classObject/trait/publicVarProtectedSet.kt
index fd9db353663..dae77bd9504 100644
--- a/compiler/testData/writeFlags/property/classObject/trait/publicVarProtectedSet.kt
+++ b/compiler/testData/writeFlags/property/classObject/trait/publicVarProtectedSet.kt
@@ -1,4 +1,4 @@
-trait Test {
+interface Test {
   companion object {
     public var prop: Int = 0
       protected set
diff --git a/compiler/testData/writeFlags/property/classObject/trait/publicVarPublicSet.kt b/compiler/testData/writeFlags/property/classObject/trait/publicVarPublicSet.kt
index b9b73820007..1280dc23708 100644
--- a/compiler/testData/writeFlags/property/classObject/trait/publicVarPublicSet.kt
+++ b/compiler/testData/writeFlags/property/classObject/trait/publicVarPublicSet.kt
@@ -1,4 +1,4 @@
-trait Test {
+interface Test {
   companion object {
     public var prop: Int = 0
       public set
diff --git a/compiler/testData/writeSignature/declarationSiteVariance/MappedSupertypeWithVariance.kt b/compiler/testData/writeSignature/declarationSiteVariance/MappedSupertypeWithVariance.kt
index 9441498ed92..0b99bc77992 100644
--- a/compiler/testData/writeSignature/declarationSiteVariance/MappedSupertypeWithVariance.kt
+++ b/compiler/testData/writeSignature/declarationSiteVariance/MappedSupertypeWithVariance.kt
@@ -1,5 +1,5 @@
 
-trait Derived<A>: List<A>
+interface Derived<A>: List<A>
 
 // class: Derived
 // jvm signature:     Derived
diff --git a/compiler/testData/writeSignature/declarationSiteVariance/SuperTraitWithVariance.kt b/compiler/testData/writeSignature/declarationSiteVariance/SuperTraitWithVariance.kt
index b2dc85c7503..4b9fea8083f 100644
--- a/compiler/testData/writeSignature/declarationSiteVariance/SuperTraitWithVariance.kt
+++ b/compiler/testData/writeSignature/declarationSiteVariance/SuperTraitWithVariance.kt
@@ -1,5 +1,5 @@
 
-trait Base<A, in B, out C>
+interface Base<A, in B, out C>
 class Derived<A, B, C>: Base<A, B, C>
 
 // class: Derived
diff --git a/compiler/testData/writeSignature/declarationSiteVariance/SuperTypeWithVarianceInArguments.kt b/compiler/testData/writeSignature/declarationSiteVariance/SuperTypeWithVarianceInArguments.kt
index 7e8ac77788c..b89a1092ecc 100644
--- a/compiler/testData/writeSignature/declarationSiteVariance/SuperTypeWithVarianceInArguments.kt
+++ b/compiler/testData/writeSignature/declarationSiteVariance/SuperTypeWithVarianceInArguments.kt
@@ -1,6 +1,6 @@
 
-trait Base<A, in B, out C>
-trait Intermediate<A>
+interface Base<A, in B, out C>
+interface Intermediate<A>
 class Derived<A, B, C>: Intermediate<Base<A, B, C>>
 
 // class: Derived