Add MaxChainedCallsOnSameLine style rule (#4985)

Add a new rule MaxChainedCallsOnSameLine to limit the number of chained calls on placed on a single line. This works well alongside CascadingCallWrapping in #4979 to make long call chains more readable by wrapping them on new lines.

detekt-core/src/main/resources/default-detekt-config.yml

@@ -582,6 +582,9 @@ style:
     active: false
   MandatoryBracesLoops:
     active: false
+  MaxChainedCallsOnSameLine:
+    active: false
+    maxChainedCalls: 5
   MaxLineLength:
     active: true
     maxLineLength: 120

detekt-rules-style/src/main/kotlin/io/gitlab/arturbosch/detekt/rules/style/MaxChainedCallsOnSameLine.kt

@@ -0,0 +1,79 @@
+package io.gitlab.arturbosch.detekt.rules.style
+
+import io.gitlab.arturbosch.detekt.api.CodeSmell
+import io.gitlab.arturbosch.detekt.api.Config
+import io.gitlab.arturbosch.detekt.api.Debt
+import io.gitlab.arturbosch.detekt.api.Entity
+import io.gitlab.arturbosch.detekt.api.Issue
+import io.gitlab.arturbosch.detekt.api.Rule
+import io.gitlab.arturbosch.detekt.api.Severity
+import io.gitlab.arturbosch.detekt.api.config
+import io.gitlab.arturbosch.detekt.api.internal.Configuration
+import org.jetbrains.kotlin.psi.KtExpression
+import org.jetbrains.kotlin.psi.KtQualifiedExpression
+import org.jetbrains.kotlin.psi.KtUnaryExpression
+
+/**
+ * Limits the number of chained calls which can be placed on a single line.
+ *
+ * <noncompliant>
+ * a().b().c().d().e().f()
+ * </noncompliant>
+ *
+ * <compliant>
+ * a().b().c()
+ *   .d().e().f()
+ * </compliant>
+ */
+class MaxChainedCallsOnSameLine(config: Config = Config.empty) : Rule(config) {
+    override val issue = Issue(
+        id = javaClass.simpleName,
+        severity = Severity.Style,
+        description = "Chained calls beyond the maximum should be wrapped to a new line.",
+        debt = Debt.FIVE_MINS,
+    )
+
+    @Configuration("maximum chained calls allowed on a single line")
+    private val maxChainedCalls: Int by config(defaultValue = 5)
+
+    override fun visitQualifiedExpression(expression: KtQualifiedExpression) {
+        super.visitQualifiedExpression(expression)
+
+        // skip if the parent is also a call on the same line to avoid duplicated warnings
+        val parent = expression.parent
+        if (parent is KtQualifiedExpression && !parent.callOnNewLine()) return
+
+        val chainedCalls = expression.countChainedCalls() + 1
+        if (chainedCalls > maxChainedCalls) {
+            report(
+                CodeSmell(
+                    issue = issue,
+                    entity = Entity.from(expression),
+                    message = "$chainedCalls chained calls on a single line; more than $maxChainedCalls calls should " +
+                        "be wrapped to a new line."
+                )
+            )
+        }
+    }
+
+    private fun KtExpression.countChainedCalls(): Int {
+        return when (this) {
+            is KtQualifiedExpression ->
+                if (callOnNewLine()) 0 else receiverExpression.countChainedCalls() + 1
+            is KtUnaryExpression -> baseExpression?.countChainedCalls() ?: 0
+            else -> 0
+        }
+    }
+
+    private fun KtQualifiedExpression.callOnNewLine(): Boolean {
+        val receiver = receiverExpression
+        val selector = selectorExpression ?: return false
+
+        val receiverEnd = receiver.startOffsetInParent + receiver.textLength
+        val selectorStart = selector.startOffsetInParent
+
+        return text
+            .subSequence(startIndex = receiverEnd, endIndex = selectorStart)
+            .contains('\n')
+    }
+}

detekt-rules-style/src/main/kotlin/io/gitlab/arturbosch/detekt/rules/style/StyleGuideProvider.kt

@@ -99,6 +99,7 @@ class StyleGuideProvider : DefaultRuleSetProvider {
             UseOrEmpty(config),
             UseAnyOrNoneInsteadOfFind(config),
             UnnecessaryBackticks(config),
+            MaxChainedCallsOnSameLine(config),
         )
     )
 }

detekt-rules-style/src/test/kotlin/io/gitlab/arturbosch/detekt/rules/style/MaxChainedCallsOnSameLineSpec.kt

@@ -0,0 +1,107 @@
+package io.gitlab.arturbosch.detekt.rules.style
+
+import io.gitlab.arturbosch.detekt.test.TestConfig
+import io.gitlab.arturbosch.detekt.test.assertThat
+import io.gitlab.arturbosch.detekt.test.compileAndLint
+import org.junit.jupiter.api.Test
+
+class MaxChainedCallsOnSameLineSpec {
+    @Test
+    fun `does not report 2 calls on a single line with a max of 3`() {
+        val rule = MaxChainedCallsOnSameLine(TestConfig(mapOf("maxChainedCalls" to 3)))
+        val code = "val a = 0.plus(0)"
+
+        assertThat(rule.compileAndLint(code)).isEmpty()
+    }
+
+    @Test
+    fun `does not report 3 calls on a single line with a max of 3`() {
+        val rule = MaxChainedCallsOnSameLine(TestConfig(mapOf("maxChainedCalls" to 3)))
+        val code = "val a = 0.plus(0).plus(0)"
+
+        assertThat(rule.compileAndLint(code)).isEmpty()
+    }
+
+    @Test
+    fun `reports 4 calls on a single line with a max of 3`() {
+        val rule = MaxChainedCallsOnSameLine(TestConfig(mapOf("maxChainedCalls" to 3)))
+        val code = "val a = 0.plus(0).plus(0).plus(0)"
+
+        assertThat(rule.compileAndLint(code)).hasSize(1)
+    }
+
+    @Test
+    fun `reports 4 safe qualified calls on a single line with a max of 3`() {
+        val rule = MaxChainedCallsOnSameLine(TestConfig(mapOf("maxChainedCalls" to 3)))
+        val code = "val a = 0?.plus(0)?.plus(0)?.plus(0)"
+
+        assertThat(rule.compileAndLint(code)).hasSize(1)
+    }
+
+    @Test
+    fun `reports 4 non-null asserted calls on a single line with a max of 3`() {
+        val rule = MaxChainedCallsOnSameLine(TestConfig(mapOf("maxChainedCalls" to 3)))
+        val code = "val a = 0!!.plus(0)!!.plus(0)!!.plus(0)"
+
+        assertThat(rule.compileAndLint(code)).hasSize(1)
+    }
+
+    @Test
+    fun `reports once for 7 calls on a single line with a max of 3`() {
+        val rule = MaxChainedCallsOnSameLine(TestConfig(mapOf("maxChainedCalls" to 3)))
+        val code = "val a = 0.plus(0).plus(0).plus(0).plus(0).plus(0).plus(0)"
+
+        assertThat(rule.compileAndLint(code)).hasSize(1)
+    }
+
+    @Test
+    fun `does not report 5 calls on separate lines with a max of 3`() {
+        val rule = MaxChainedCallsOnSameLine(TestConfig(mapOf("maxChainedCalls" to 3)))
+        val code = """
+            val a = 0
+                .plus(0)
+                .plus(0)
+                .plus(0)
+                .plus(0)
+        """
+
+        assertThat(rule.compileAndLint(code)).isEmpty()
+    }
+
+    @Test
+    fun `does not report 3 calls on same line with wrapped calls with a max of 3`() {
+        val rule = MaxChainedCallsOnSameLine(TestConfig(mapOf("maxChainedCalls" to 3)))
+        val code = """
+            val a = 0.plus(0).plus(0)
+                .plus(0).plus(0).plus(0)
+                .plus(0).plus(0).plus(0)
+        """
+
+        assertThat(rule.compileAndLint(code)).isEmpty()
+    }
+
+    @Test
+    fun `reports 4 calls on same line with wrapped calls with a max of 3`() {
+        val rule = MaxChainedCallsOnSameLine(TestConfig(mapOf("maxChainedCalls" to 3)))
+        val code = """
+            val a = 0.plus(0).plus(0).plus(0)
+                .plus(0)
+                .plus(0)
+        """
+
+        assertThat(rule.compileAndLint(code)).hasSize(1)
+    }
+
+    @Test
+    fun `reports 4 calls on wrapped line with with a max of 3`() {
+        val rule = MaxChainedCallsOnSameLine(TestConfig(mapOf("maxChainedCalls" to 3)))
+        val code = """
+            val a = 0
+                .plus(0)
+                .plus(0).plus(0).plus(0).plus(0)
+                .plus(0)
+        """
+
+        assertThat(rule.compileAndLint(code)).hasSize(1)
+    }
+}