Remove KotlinMetadataTarget's KotlinTargetComponent in favour of KotlinSoftwareComponent.kt

^KT-44322 fixed

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/kotlin/org/jetbrains/kotlin/gradle/NewMultiplatformIT.kt

@@ -714,16 +714,18 @@ class NewMultiplatformIT : BaseGradleIT() {
             }
         }
 
-        gradleBuildScript().appendText("\n" + """
+        gradleBuildScript().appendText(
+            "\n" + """
             kotlin.sourceSets.all {
                 it.languageSettings {
                     languageVersion = '1.3'
                     apiVersion = '1.3' 
                 }
             }
-        """.trimIndent())
+        """.trimIndent()
+        )
 
-        listOf( "compileKotlinMetadata", "compileKotlinJvm6", "compileKotlinNodeJs").forEach {
+        listOf("compileKotlinMetadata", "compileKotlinJvm6", "compileKotlinNodeJs").forEach {
             build(it) {
                 assertSuccessful()
                 assertTasksExecuted(":$it")
@@ -1015,15 +1017,20 @@ class NewMultiplatformIT : BaseGradleIT() {
             assertSuccessful()
 
             val groupDir = projectDir.resolve("repo/com/example/")
-            val targetArtifactIdAppendices = listOf("metadata", "jvm6", "nodejs", "linux64")
+            val targetArtifactIdAppendices = listOf(null, "jvm6", "nodejs", "linux64")
 
-            val sourceJarSourceRoots = targetArtifactIdAppendices.associate { artifact ->
-                val sourcesJar = JarFile(groupDir.resolve("sample-lib-$artifact/1.0/sample-lib-$artifact-1.0-sources.jar"))
+            val sourceJarSourceRoots = targetArtifactIdAppendices.associateWith { artifact ->
+                val sourcesJarPath = if (artifact != null) "sample-lib-$artifact/1.0/sample-lib-$artifact-1.0-sources.jar"
+                else "sample-lib/1.0/sample-lib-1.0-sources.jar"
+                val sourcesJar = JarFile(groupDir.resolve(sourcesJarPath))
                 val sourcesDirs = sourcesJar.entries().asSequence().map { it.name.substringBefore("/") }.toSet() - "META-INF"
-                artifact to sourcesDirs
+                sourcesDirs
             }
 
-            assertEquals(setOf("commonMain"), sourceJarSourceRoots["metadata"])
+            assertEquals(
+                setOf("commonMain", "jvm6Main", "linux64Main", "macos64Main", "mingw64Main", "mingw86Main", "nodeJsMain"),
+                sourceJarSourceRoots[null]
+            )
             assertEquals(setOf("commonMain", "jvm6Main"), sourceJarSourceRoots["jvm6"])
             assertEquals(setOf("commonMain", "nodeJsMain"), sourceJarSourceRoots["nodejs"])
             assertEquals(setOf("commonMain", "linux64Main"), sourceJarSourceRoots["linux64"])
@@ -1361,26 +1368,29 @@ class NewMultiplatformIT : BaseGradleIT() {
     fun testDependenciesDsl() = with(transformProjectWithPluginsDsl("newMppDependenciesDsl")) {
         val originalBuildscriptContent = gradleBuildScript("app").readText()
 
-        fun testDependencies() = testResolveAllConfigurations("app", options = defaultBuildOptions().copy(warningMode = WarningMode.Summary)) {
-            assertContains(">> :app:testNonTransitiveStringNotationApiDependenciesMetadata --> junit-4.12.jar")
-            assertEquals(
-                1,
-                (Regex.escape(">> :app:testNonTransitiveStringNotationApiDependenciesMetadata") + " .*").toRegex().findAll(output).count()
-            )
+        fun testDependencies() =
+            testResolveAllConfigurations("app", options = defaultBuildOptions().copy(warningMode = WarningMode.Summary)) {
+                assertContains(">> :app:testNonTransitiveStringNotationApiDependenciesMetadata --> junit-4.12.jar")
+                assertEquals(
+                    1,
+                    (Regex.escape(">> :app:testNonTransitiveStringNotationApiDependenciesMetadata") + " .*").toRegex().findAll(output)
+                        .count()
+                )
 
-            assertContains(">> :app:testNonTransitiveDependencyNotationApiDependenciesMetadata --> kotlin-reflect-${defaultBuildOptions().kotlinVersion}.jar")
-            assertEquals(
-                1,
-                (Regex.escape(">> :app:testNonTransitiveStringNotationApiDependenciesMetadata") + " .*").toRegex().findAll(output).count()
-            )
+                assertContains(">> :app:testNonTransitiveDependencyNotationApiDependenciesMetadata --> kotlin-reflect-${defaultBuildOptions().kotlinVersion}.jar")
+                assertEquals(
+                    1,
+                    (Regex.escape(">> :app:testNonTransitiveStringNotationApiDependenciesMetadata") + " .*").toRegex().findAll(output)
+                        .count()
+                )
 
-            assertContains(">> :app:testExplicitKotlinVersionApiDependenciesMetadata --> kotlin-reflect-1.3.0.jar")
-            assertContains(">> :app:testExplicitKotlinVersionImplementationDependenciesMetadata --> kotlin-reflect-1.2.71.jar")
-            assertContains(">> :app:testExplicitKotlinVersionCompileOnlyDependenciesMetadata --> kotlin-reflect-1.2.70.jar")
-            assertContains(">> :app:testExplicitKotlinVersionRuntimeOnlyDependenciesMetadata --> kotlin-reflect-1.2.60.jar")
+                assertContains(">> :app:testExplicitKotlinVersionApiDependenciesMetadata --> kotlin-reflect-1.3.0.jar")
+                assertContains(">> :app:testExplicitKotlinVersionImplementationDependenciesMetadata --> kotlin-reflect-1.2.71.jar")
+                assertContains(">> :app:testExplicitKotlinVersionCompileOnlyDependenciesMetadata --> kotlin-reflect-1.2.70.jar")
+                assertContains(">> :app:testExplicitKotlinVersionRuntimeOnlyDependenciesMetadata --> kotlin-reflect-1.2.60.jar")
 
-            assertContains(">> :app:testProjectWithConfigurationApiDependenciesMetadata --> output.txt")
-        }
+                assertContains(">> :app:testProjectWithConfigurationApiDependenciesMetadata --> output.txt")
+            }
 
         testDependencies()
 

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/dsl/KotlinMultiplatformExtension.kt

@@ -8,12 +8,13 @@ package org.jetbrains.kotlin.gradle.dsl
 import groovy.lang.Closure
 import org.gradle.api.InvalidUserCodeException
 import org.gradle.api.NamedDomainObjectCollection
+import org.gradle.api.Project
 import org.gradle.util.ConfigureUtil
 import org.jetbrains.kotlin.gradle.plugin.*
 import org.jetbrains.kotlin.gradle.plugin.mpp.*
 
-open class KotlinMultiplatformExtension :
-    KotlinProjectExtension(),
+open class KotlinMultiplatformExtension(project: Project) :
+    KotlinProjectExtension(project),
     KotlinTargetContainerWithPresetFunctions,
     KotlinTargetContainerWithJsPresetFunctions,
     KotlinTargetContainerWithNativeShortcuts {
@@ -50,7 +51,7 @@ open class KotlinMultiplatformExtension :
     fun targetFromPreset(preset: KotlinTargetPreset<*>, configure: Closure<*>) = targetFromPreset(preset, preset.name, configure)
 
     internal val rootSoftwareComponent: KotlinSoftwareComponent by lazy {
-        KotlinSoftwareComponentWithCoordinatesAndPublication("kotlin", targets)
+        KotlinSoftwareComponentWithCoordinatesAndPublication(project, "kotlin", targets)
     }
 }
 

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/dsl/KotlinProjectExtension.kt

@@ -26,7 +26,7 @@ import kotlin.reflect.KClass
 private const val KOTLIN_PROJECT_EXTENSION_NAME = "kotlin"
 
 internal fun Project.createKotlinExtension(extensionClass: KClass<out KotlinProjectExtension>): KotlinProjectExtension {
-    val kotlinExt = extensions.create(KOTLIN_PROJECT_EXTENSION_NAME, extensionClass.java)
+    val kotlinExt = extensions.create(KOTLIN_PROJECT_EXTENSION_NAME, extensionClass.java, this)
     DslObject(kotlinExt).extensions.create("experimental", ExperimentalExtension::class.java)
     return kotlinExtension
 }
@@ -43,7 +43,7 @@ internal val Project.multiplatformExtensionOrNull: KotlinMultiplatformExtension?
 internal val Project.multiplatformExtension: KotlinMultiplatformExtension
     get() = extensions.getByName(KOTLIN_PROJECT_EXTENSION_NAME) as KotlinMultiplatformExtension
 
-open class KotlinProjectExtension : KotlinSourceSetContainer {
+open class KotlinProjectExtension(internal val project: Project) : KotlinSourceSetContainer {
     val experimental: ExperimentalExtension
         get() = DslObject(this).extensions.getByType(ExperimentalExtension::class.java)
 
@@ -67,32 +67,32 @@ open class KotlinProjectExtension : KotlinSourceSetContainer {
         }
 }
 
-abstract class KotlinSingleTargetExtension : KotlinProjectExtension() {
+abstract class KotlinSingleTargetExtension(project: Project) : KotlinProjectExtension(project) {
     abstract val target: KotlinTarget
 
     open fun target(body: Closure<out KotlinTarget>) = ConfigureUtil.configure(body, target)
 }
 
-abstract class KotlinSingleJavaTargetExtension : KotlinSingleTargetExtension() {
+abstract class KotlinSingleJavaTargetExtension(project: Project) : KotlinSingleTargetExtension(project) {
     abstract override val target: KotlinWithJavaTarget<*>
 }
 
-open class KotlinJvmProjectExtension : KotlinSingleJavaTargetExtension() {
+open class KotlinJvmProjectExtension(project: Project) : KotlinSingleJavaTargetExtension(project) {
     override lateinit var target: KotlinWithJavaTarget<KotlinJvmOptions>
         internal set
 
     open fun target(body: KotlinWithJavaTarget<KotlinJvmOptions>.() -> Unit) = target.run(body)
 }
 
-open class Kotlin2JsProjectExtension : KotlinSingleJavaTargetExtension() {
+open class Kotlin2JsProjectExtension(project: Project) : KotlinSingleJavaTargetExtension(project) {
     override lateinit var target: KotlinWithJavaTarget<KotlinJsOptions>
         internal set
 
     open fun target(body: KotlinWithJavaTarget<KotlinJsOptions>.() -> Unit) = target.run(body)
 }
 
-open class KotlinJsProjectExtension :
-    KotlinSingleTargetExtension(),
+open class KotlinJsProjectExtension(project: Project) :
+    KotlinSingleTargetExtension(project),
     KotlinJsCompilerTypeHolder {
     lateinit var irPreset: KotlinJsIrSingleTargetPreset
 
@@ -224,14 +224,14 @@ open class KotlinJsProjectExtension :
         }
 }
 
-open class KotlinCommonProjectExtension : KotlinSingleJavaTargetExtension() {
+open class KotlinCommonProjectExtension(project: Project) : KotlinSingleJavaTargetExtension(project) {
     override lateinit var target: KotlinWithJavaTarget<KotlinMultiplatformCommonOptions>
         internal set
 
     open fun target(body: KotlinWithJavaTarget<KotlinMultiplatformCommonOptions>.() -> Unit) = target.run(body)
 }
 
-open class KotlinAndroidProjectExtension : KotlinSingleTargetExtension() {
+open class KotlinAndroidProjectExtension(project: Project) : KotlinSingleTargetExtension(project) {
     override lateinit var target: KotlinAndroidTarget
         internal set
 

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/mpp/KotlinMetadataTarget.kt

@@ -15,8 +15,6 @@ import org.jetbrains.kotlin.gradle.targets.metadata.isCompatibilityMetadataVaria
 import org.jetbrains.kotlin.gradle.targets.metadata.isKotlinGranularMetadataEnabled
 import javax.inject.Inject
 
-internal const val COMMON_MAIN_ELEMENTS_CONFIGURATION_NAME = "commonMainMetadataElements"
-
 open class KotlinMetadataTarget @Inject constructor(project: Project) :
     KotlinOnlyTarget<AbstractKotlinCompilation<*>>(project, KotlinPlatformType.common) {
 
@@ -29,57 +27,11 @@ open class KotlinMetadataTarget @Inject constructor(project: Project) :
         get() = super.artifactsTaskName
 
     override val kotlinComponents: Set<KotlinTargetComponent> by lazy {
-        if (!project.isKotlinGranularMetadataEnabled)
-            super.kotlinComponents
-        else {
-            val usageContexts = mutableSetOf<DefaultKotlinUsageContext>()
-
-            // This usage value is only needed for Maven scope mapping. Don't replace it with a custom Kotlin Usage value
-            val javaApiUsage = project.usageByName("java-api-jars")
-
-            usageContexts += run {
-                val allMetadataJar = project.tasks.named(KotlinMetadataTargetConfigurator.ALL_METADATA_JAR_NAME)
-                val allMetadataArtifact = project.artifacts.add(Dependency.ARCHIVES_CONFIGURATION, allMetadataJar) {
-                    it.classifier = if (project.isCompatibilityMetadataVariantEnabled) "all" else ""
-                }
-
-                DefaultKotlinUsageContext(
-                    compilations.getByName(KotlinCompilation.MAIN_COMPILATION_NAME),
-                    javaApiUsage,
-                    apiElementsConfigurationName,
-                    overrideConfigurationArtifacts = setOf(allMetadataArtifact)
-                )
-            }
-
-            if (PropertiesProvider(project).enableCompatibilityMetadataVariant == true) {
-                // Ensure that consumers who expect Kotlin 1.2.x metadata package can still get one:
-                // publish the old metadata artifact:
-                usageContexts += run {
-                    DefaultKotlinUsageContext(
-                        compilations.getByName(KotlinCompilation.MAIN_COMPILATION_NAME),
-                        javaApiUsage,
-                        /** this configuration is created by [KotlinMetadataTargetConfigurator.createCommonMainElementsConfiguration] */
-                        COMMON_MAIN_ELEMENTS_CONFIGURATION_NAME
-                    )
-                }
-            }
-
-            val component =
-                createKotlinVariant(targetName, compilations.getByName(KotlinCompilation.MAIN_COMPILATION_NAME), usageContexts).apply {
-                    publishable = false // this component is not published on its own, its variants are included in the 'root' module
-                }
-
-            val sourcesJarTask =
-                sourcesJarTask(project, lazy { project.kotlinExtension.sourceSets.toSet() }, null, targetName.toLowerCase())
-
-            component.sourcesArtifacts = setOf(
-                project.artifacts.add(Dependency.ARCHIVES_CONFIGURATION, sourcesJarTask).apply {
-                    this as ConfigurablePublishArtifact
-                    classifier = "sources"
-                }
-            )
-
-            setOf(component)
-        }
+        /*
+        Metadata Target does not have a KotlinTargetComponent on it's own.
+        Responsibility is shifted to the root KotlinSoftwareComponent
+        */
+        emptySet<KotlinTargetComponent>()
     }
-}
+}
+

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/mpp/KotlinMultiplatformPlugin.kt

@@ -200,116 +200,6 @@ class KotlinMultiplatformPlugin(
         }
     }
 
-    private fun configurePublishingWithMavenPublish(project: Project) = project.pluginManager.withPlugin("maven-publish") { _ ->
-
-        val targets = project.multiplatformExtension.targets
-        val metadataTarget = project.multiplatformExtension.metadata()
-        val kotlinSoftwareComponent = project.multiplatformExtension.rootSoftwareComponent
-
-        project.extensions.configure(PublishingExtension::class.java) { publishing ->
-
-            // The root publication that references the platform specific publications as its variants:
-            publishing.publications.create("kotlinMultiplatform", MavenPublication::class.java).apply {
-                from(kotlinSoftwareComponent)
-                (this as MavenPublicationInternal).publishWithOriginalFileName()
-                kotlinSoftwareComponent.publicationDelegate = this@apply
-
-                metadataTarget.kotlinComponents.filterIsInstance<KotlinTargetComponentWithPublication>()
-                    .single().publicationDelegate = this@apply
-
-                project.whenEvaluated {
-                    if (!metadataTarget.publishable) return@whenEvaluated
-                    metadataTarget.kotlinComponents
-                        .flatMap { component -> component.sourcesArtifacts }
-                        .forEach { sourcesArtifact -> artifact(sourcesArtifact) }
-                }
-            }
-
-            // Enforce the order of creating the publications, since the metadata publication is used in the other publications:
-            metadataTarget.createMavenPublications(publishing.publications)
-            targets
-                .withType(AbstractKotlinTarget::class.java).matching { it.publishable && it.name != METADATA_TARGET_NAME }
-                .all {
-                    if (it is KotlinAndroidTarget || it is KotlinMetadataTarget)
-                    // Android targets have their variants created in afterEvaluate; TODO handle this better?
-                    // Kotlin Metadata targets rely on complete source sets hierearchy and cannot be inspected for publication earlier
-                        project.whenEvaluated { it.createMavenPublications(publishing.publications) }
-                    else
-                        it.createMavenPublications(publishing.publications)
-                }
-        }
-
-        project.components.add(kotlinSoftwareComponent)
-    }
-
-    private fun rewritePom(
-        pom: MavenPom,
-        pomRewriter: PomDependenciesRewriter,
-        shouldRewritePomDependencies: Provider<Boolean>,
-        includeOnlySpecifiedDependencies: Provider<Set<ModuleCoordinates>>?
-    ) {
-        pom.withXml { xml ->
-            if (shouldRewritePomDependencies.get())
-                pomRewriter.rewritePomMppDependenciesToActualTargetModules(xml, includeOnlySpecifiedDependencies)
-        }
-    }
-
-    private fun AbstractKotlinTarget.createMavenPublications(publications: PublicationContainer) {
-        components
-            .map { gradleComponent -> gradleComponent to kotlinComponents.single { it.name == gradleComponent.name } }
-            .filter { (_, kotlinComponent) -> kotlinComponent.publishable }
-            .forEach { (gradleComponent, kotlinComponent) ->
-                val componentPublication = publications.create(kotlinComponent.name, MavenPublication::class.java).apply {
-                    // do this in whenEvaluated since older Gradle versions seem to check the files in the variant eagerly:
-                    project.whenEvaluated {
-                        from(gradleComponent)
-                        kotlinComponent.sourcesArtifacts.forEach { sourceArtifact ->
-                            artifact(sourceArtifact)
-                        }
-                    }
-                    (this as MavenPublicationInternal).publishWithOriginalFileName()
-                    artifactId = kotlinComponent.defaultArtifactId
-
-                    val pomRewriter = PomDependenciesRewriter(project, kotlinComponent)
-                    val shouldRewritePomDependencies =
-                        project.provider { PropertiesProvider(project).keepMppDependenciesIntactInPoms != true }
-
-                    rewritePom(
-                        pom,
-                        pomRewriter,
-                        shouldRewritePomDependencies,
-                        dependenciesForPomRewriting(this@createMavenPublications)
-                    )
-                }
-
-                (kotlinComponent as? KotlinTargetComponentWithPublication)?.publicationDelegate = componentPublication
-                publicationConfigureActions.all { it.execute(componentPublication) }
-            }
-    }
-
-    /**
-     * The metadata targets need their POMs to only include the dependencies from the commonMain API configuration.
-     * The actual apiElements configurations of metadata targets now contain dependencies from all source sets, but, as the consumers who
-     * can't read Gradle module metadata won't resolve a dependency on an MPP to the granular metadata variant and won't then choose the
-     * right dependencies for each source set, we put only the dependencies of the legacy common variant into the POM, i.e. commonMain API.
-     */
-    private fun dependenciesForPomRewriting(target: AbstractKotlinTarget): Provider<Set<ModuleCoordinates>>? =
-        if (target !is KotlinMetadataTarget || !target.project.isKotlinGranularMetadataEnabled)
-            null
-        else {
-            val commonMain = target.project.kotlinExtension.sourceSets.findByName(KotlinSourceSet.COMMON_MAIN_SOURCE_SET_NAME)
-            if (commonMain == null)
-                null
-            else
-                target.project.provider {
-                    val project = target.project
-
-                    // Only the commonMain API dependencies can be published for consumers who can't read Gradle project metadata
-                    val commonMainApi = project.sourceSetDependencyConfigurationByScope(commonMain, KotlinDependencyScope.API_SCOPE)
-                    val commonMainDependencies = commonMainApi.allDependencies
-                    commonMainDependencies.map { ModuleCoordinates(it.group, it.name, it.version) }.toSet()
-                }
-        }
 
     private fun configureSourceSets(project: Project) = with(project.multiplatformExtension) {
         val production = sourceSets.create(KotlinSourceSet.COMMON_MAIN_SOURCE_SET_NAME)

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/mpp/KotlinSoftwareComponent.kt

@@ -17,44 +17,95 @@ import org.gradle.api.component.SoftwareComponent
 import org.gradle.api.internal.component.SoftwareComponentInternal
 import org.gradle.api.internal.component.UsageContext
 import org.gradle.api.publish.maven.MavenPublication
-import org.jetbrains.kotlin.gradle.plugin.KotlinCompilation
-import org.jetbrains.kotlin.gradle.plugin.KotlinTarget
-import org.jetbrains.kotlin.gradle.plugin.ProjectLocalConfigurations
+import org.jetbrains.kotlin.gradle.dsl.kotlinExtension
+import org.jetbrains.kotlin.gradle.dsl.multiplatformExtension
+import org.jetbrains.kotlin.gradle.plugin.*
+import org.jetbrains.kotlin.gradle.plugin.KotlinCompilation.Companion.MAIN_COMPILATION_NAME
+import org.jetbrains.kotlin.gradle.plugin.PropertiesProvider
+import org.jetbrains.kotlin.gradle.plugin.usageByName
+import org.jetbrains.kotlin.gradle.targets.metadata.COMMON_MAIN_ELEMENTS_CONFIGURATION_NAME
+import org.jetbrains.kotlin.gradle.targets.metadata.KotlinMetadataTargetConfigurator
+import org.jetbrains.kotlin.gradle.targets.metadata.isCompatibilityMetadataVariantEnabled
+import org.jetbrains.kotlin.gradle.targets.metadata.isKotlinGranularMetadataEnabled
 
 abstract class KotlinSoftwareComponent(
+    private val project: Project,
     private val name: String,
     protected val kotlinTargets: Iterable<KotlinTarget>
 ) : SoftwareComponentInternal, ComponentWithVariants {
 
-    private val metadataTarget: KotlinMetadataTarget
-        get() = kotlinTargets.filterIsInstance<KotlinMetadataTarget>().single()
-
-    override fun getUsages(): Set<UsageContext> = (metadataTarget.components.single() as SoftwareComponentInternal).usages
-
-    override fun getVariants(): Set<SoftwareComponent> =
-        kotlinTargets.minus(metadataTarget).flatMap { it.components }.toSet()
-
     override fun getName(): String = name
 
+    override fun getVariants(): Set<SoftwareComponent> = kotlinTargets
+        .filter { target -> target !is KotlinMetadataTarget }
+        .flatMap { it.components }.toSet()
+
+    private val _usages: Set<UsageContext> by lazy {
+        val metadataTarget = project.multiplatformExtension.metadata()
+
+        if (!project.isKotlinGranularMetadataEnabled) {
+            val metadataCompilation = metadataTarget.compilations.getByName(MAIN_COMPILATION_NAME)
+            return@lazy metadataTarget.createUsageContexts(metadataCompilation)
+        }
+
+        mutableSetOf<UsageContext>().apply {
+            // This usage value is only needed for Maven scope mapping. Don't replace it with a custom Kotlin Usage value
+            val javaApiUsage = project.usageByName("java-api-jars")
+
+            val allMetadataJar = project.tasks.named(KotlinMetadataTargetConfigurator.ALL_METADATA_JAR_NAME)
+            val allMetadataArtifact = project.artifacts.add(Dependency.ARCHIVES_CONFIGURATION, allMetadataJar) { allMetadataArtifact ->
+                allMetadataArtifact.classifier = if (project.isCompatibilityMetadataVariantEnabled) "all" else ""
+            }
+
+            this += DefaultKotlinUsageContext(
+                compilation = metadataTarget.compilations.getByName(MAIN_COMPILATION_NAME),
+                usage = javaApiUsage,
+                dependencyConfigurationName = metadataTarget.apiElementsConfigurationName,
+                overrideConfigurationArtifacts = setOf(allMetadataArtifact)
+            )
+
+
+            if (project.isCompatibilityMetadataVariantEnabled) {
+                // Ensure that consumers who expect Kotlin 1.2.x metadata package can still get one:
+                // publish the old metadata artifact:
+                this += run {
+                    DefaultKotlinUsageContext(
+                        metadataTarget.compilations.getByName(MAIN_COMPILATION_NAME),
+                        javaApiUsage,
+                        /** this configuration is created by [KotlinMetadataTargetConfigurator.createCommonMainElementsConfiguration] */
+                        COMMON_MAIN_ELEMENTS_CONFIGURATION_NAME
+                    )
+                }
+            }
+        }
+    }
+
+    override fun getUsages(): Set<UsageContext> {
+        return _usages
+    }
+
+
+    val sourcesArtifacts: Set<PublishArtifact> by lazy {
+        val sourcesJarTask = sourcesJarTask(project, lazy { project.kotlinExtension.sourceSets.toSet() }, null, name.toLowerCase())
+        val sourcesJarArtifact = project.artifacts.add(Dependency.ARCHIVES_CONFIGURATION, sourcesJarTask) { sourcesJarArtifact ->
+            sourcesJarArtifact.classifier = "sources"
+        }
+        setOf(sourcesJarArtifact)
+    }
+
     // This property is declared in the parent type to allow the usages to reference it without forcing the subtypes to load,
     // which is needed for compatibility with older Gradle versions
     var publicationDelegate: MavenPublication? = null
 }
 
-class KotlinSoftwareComponentWithCoordinatesAndPublication(name: String, kotlinTargets: Iterable<KotlinTarget>) :
-    KotlinSoftwareComponent(name, kotlinTargets), ComponentWithCoordinates {
+class KotlinSoftwareComponentWithCoordinatesAndPublication(project: Project, name: String, kotlinTargets: Iterable<KotlinTarget>) :
+    KotlinSoftwareComponent(project, name, kotlinTargets), ComponentWithCoordinates {
 
     override fun getCoordinates(): ModuleVersionIdentifier = getCoordinatesFromPublicationDelegateAndProject(
         publicationDelegate, kotlinTargets.first().project, null
     )
 }
 
-// At the moment all KN artifacts have JAVA_API usage.
-// TODO: Replace it with a specific usage
-object NativeUsage {
-    const val KOTLIN_KLIB = "kotlin-klib"
-}
-
 interface KotlinUsageContext : UsageContext {
     val compilation: KotlinCompilation<*>
     val dependencyConfigurationName: String
@@ -117,4 +168,4 @@ class DefaultKotlinUsageContext(
     override fun getCapabilities(): Set<Capability> = emptySet()
 
     override fun getGlobalExcludes(): Set<ExcludeRule> = emptySet()
-}
+}

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/mpp/Publishing.kt

@@ -0,0 +1,131 @@
+/*
+ * Copyright 2010-2021 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.gradle.plugin.mpp
+
+import org.gradle.api.Project
+import org.gradle.api.provider.Provider
+import org.gradle.api.publish.PublicationContainer
+import org.gradle.api.publish.PublishingExtension
+import org.gradle.api.publish.maven.MavenPom
+import org.gradle.api.publish.maven.MavenPublication
+import org.gradle.api.publish.maven.internal.publication.MavenPublicationInternal
+import org.jetbrains.kotlin.gradle.dsl.kotlinExtension
+import org.jetbrains.kotlin.gradle.dsl.multiplatformExtension
+import org.jetbrains.kotlin.gradle.plugin.KotlinSourceSet
+import org.jetbrains.kotlin.gradle.plugin.PropertiesProvider
+import org.jetbrains.kotlin.gradle.plugin.sources.KotlinDependencyScope
+import org.jetbrains.kotlin.gradle.plugin.sources.sourceSetDependencyConfigurationByScope
+import org.jetbrains.kotlin.gradle.plugin.whenEvaluated
+import org.jetbrains.kotlin.gradle.targets.metadata.isKotlinGranularMetadataEnabled
+
+internal fun configurePublishingWithMavenPublish(project: Project) = project.pluginManager.withPlugin("maven-publish") {
+    project.extensions.configure(PublishingExtension::class.java) { publishing ->
+        createRootPublication(project, publishing)
+        createTargetPublications(project, publishing)
+    }
+
+    project.components.add(project.multiplatformExtension.rootSoftwareComponent)
+}
+
+/**
+ * The root publication that references the platform specific publications as its variants
+ */
+private fun createRootPublication(project: Project, publishing: PublishingExtension) {
+    val kotlinSoftwareComponent = project.multiplatformExtension.rootSoftwareComponent
+
+    publishing.publications.create("kotlinMultiplatform", MavenPublication::class.java).apply {
+        from(kotlinSoftwareComponent)
+        (this as MavenPublicationInternal).publishWithOriginalFileName()
+        kotlinSoftwareComponent.publicationDelegate = this@apply
+        kotlinSoftwareComponent.sourcesArtifacts.forEach { sourceArtifact ->
+            artifact(sourceArtifact)
+        }
+    }
+}
+
+private fun createTargetPublications(project: Project, publishing: PublishingExtension) {
+    val kotlin = project.multiplatformExtension
+    // Enforce the order of creating the publications, since the metadata publication is used in the other publications:
+    kotlin.targets
+        .withType(AbstractKotlinTarget::class.java)
+        .matching { it.publishable }
+        .all { kotlinTarget ->
+            if (kotlinTarget is KotlinAndroidTarget)
+            // Android targets have their variants created in afterEvaluate; TODO handle this better?
+                project.whenEvaluated { kotlinTarget.createMavenPublications(publishing.publications) }
+            else
+                kotlinTarget.createMavenPublications(publishing.publications)
+        }
+}
+
+private fun AbstractKotlinTarget.createMavenPublications(publications: PublicationContainer) {
+    components
+        .map { gradleComponent -> gradleComponent to kotlinComponents.single { it.name == gradleComponent.name } }
+        .filter { (_, kotlinComponent) -> kotlinComponent.publishable }
+        .forEach { (gradleComponent, kotlinComponent) ->
+            val componentPublication = publications.create(kotlinComponent.name, MavenPublication::class.java).apply {
+                // do this in whenEvaluated since older Gradle versions seem to check the files in the variant eagerly:
+                project.whenEvaluated {
+                    from(gradleComponent)
+                    kotlinComponent.sourcesArtifacts.forEach { sourceArtifact ->
+                        artifact(sourceArtifact)
+                    }
+                }
+                (this as MavenPublicationInternal).publishWithOriginalFileName()
+                artifactId = kotlinComponent.defaultArtifactId
+
+                val pomRewriter = PomDependenciesRewriter(project, kotlinComponent)
+                val shouldRewritePomDependencies =
+                    project.provider { PropertiesProvider(project).keepMppDependenciesIntactInPoms != true }
+
+                rewritePom(
+                    pom,
+                    pomRewriter,
+                    shouldRewritePomDependencies,
+                    dependenciesForPomRewriting(this@createMavenPublications)
+                )
+            }
+
+            (kotlinComponent as? KotlinTargetComponentWithPublication)?.publicationDelegate = componentPublication
+            publicationConfigureActions.all { it.execute(componentPublication) }
+        }
+}
+
+private fun rewritePom(
+    pom: MavenPom,
+    pomRewriter: PomDependenciesRewriter,
+    shouldRewritePomDependencies: Provider<Boolean>,
+    includeOnlySpecifiedDependencies: Provider<Set<ModuleCoordinates>>?
+) {
+    pom.withXml { xml ->
+        if (shouldRewritePomDependencies.get())
+            pomRewriter.rewritePomMppDependenciesToActualTargetModules(xml, includeOnlySpecifiedDependencies)
+    }
+}
+
+/**
+ * The metadata targets need their POMs to only include the dependencies from the commonMain API configuration.
+ * The actual apiElements configurations of metadata targets now contain dependencies from all source sets, but, as the consumers who
+ * can't read Gradle module metadata won't resolve a dependency on an MPP to the granular metadata variant and won't then choose the
+ * right dependencies for each source set, we put only the dependencies of the legacy common variant into the POM, i.e. commonMain API.
+ */
+private fun dependenciesForPomRewriting(target: AbstractKotlinTarget): Provider<Set<ModuleCoordinates>>? =
+    if (target !is KotlinMetadataTarget || !target.project.isKotlinGranularMetadataEnabled)
+        null
+    else {
+        val commonMain = target.project.kotlinExtension.sourceSets.findByName(KotlinSourceSet.COMMON_MAIN_SOURCE_SET_NAME)
+        if (commonMain == null)
+            null
+        else
+            target.project.provider {
+                val project = target.project
+
+                // Only the commonMain API dependencies can be published for consumers who can't read Gradle project metadata
+                val commonMainApi = project.sourceSetDependencyConfigurationByScope(commonMain, KotlinDependencyScope.API_SCOPE)
+                val commonMainDependencies = commonMainApi.allDependencies
+                commonMainDependencies.map { ModuleCoordinates(it.group, it.name, it.version) }.toSet()
+            }
+    }

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/metadata/KotlinMetadataTargetConfigurator.kt

@@ -31,6 +31,7 @@ import org.jetbrains.kotlin.gradle.utils.addExtendsFromRelation
 import org.jetbrains.kotlin.gradle.utils.lowerCamelCaseName
 import org.jetbrains.kotlin.statistics.metrics.BooleanMetrics
 
+internal const val COMMON_MAIN_ELEMENTS_CONFIGURATION_NAME = "commonMainMetadataElements"
 internal const val ALL_COMPILE_METADATA_CONFIGURATION_NAME = "allSourceSetsCompileDependenciesMetadata"
 internal const val ALL_RUNTIME_METADATA_CONFIGURATION_NAME = "allSourceSetsRuntimeDependenciesMetadata"