Bump KtLint to 0.43.2 and add TrailingComma rule

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

@@ -403,6 +403,11 @@ formatting:
   StringTemplate:
     active: true
     autoCorrect: true
+  TrailingComma:
+    active: false
+    autoCorrect: true
+    allowTrailingComma: false
+    allowTrailingCommaOnCallSite: false
 
 naming:
   active: true

detekt-formatting/src/main/kotlin/io/gitlab/arturbosch/detekt/formatting/KtLintMultiRule.kt

@@ -47,6 +47,7 @@ import io.gitlab.arturbosch.detekt.formatting.wrappers.SpacingAroundUnaryOperato
 import io.gitlab.arturbosch.detekt.formatting.wrappers.SpacingBetweenDeclarationsWithAnnotations
 import io.gitlab.arturbosch.detekt.formatting.wrappers.SpacingBetweenDeclarationsWithComments
 import io.gitlab.arturbosch.detekt.formatting.wrappers.StringTemplate
+import io.gitlab.arturbosch.detekt.formatting.wrappers.TrailingComma
 import org.jetbrains.kotlin.com.intellij.lang.ASTNode
 import org.jetbrains.kotlin.com.intellij.psi.impl.source.JavaDummyElement
 import org.jetbrains.kotlin.com.intellij.psi.impl.source.JavaDummyHolder
@@ -103,6 +104,7 @@ class KtLintMultiRule(config: Config = Config.empty) : MultiRule() {
         SpacingAroundUnaryOperator(config),
         SpacingBetweenDeclarationsWithAnnotations(config),
         SpacingBetweenDeclarationsWithComments(config),
+        TrailingComma(config),
     )
 
     override fun visit(root: KtFile) {

detekt-formatting/src/main/kotlin/io/gitlab/arturbosch/detekt/formatting/wrappers/TrailingComma.kt

@@ -0,0 +1,33 @@
+package io.gitlab.arturbosch.detekt.formatting.wrappers
+
+import com.pinterest.ktlint.core.api.FeatureInAlphaState
+import com.pinterest.ktlint.core.api.UsesEditorConfigProperties
+import com.pinterest.ktlint.ruleset.experimental.trailingcomma.TrailingCommaRule
+import io.gitlab.arturbosch.detekt.api.Config
+import io.gitlab.arturbosch.detekt.api.config
+import io.gitlab.arturbosch.detekt.api.internal.AutoCorrectable
+import io.gitlab.arturbosch.detekt.api.internal.Configuration
+import io.gitlab.arturbosch.detekt.formatting.FormattingRule
+
+/**
+ * See <a href="https://ktlint.github.io/#rule-spacing">ktlint-website</a> for documentation.
+ */
+@OptIn(FeatureInAlphaState::class)
+@AutoCorrectable(since = "1.19.0")
+class TrailingComma(config: Config) : FormattingRule(config) {
+
+    override val wrapping = TrailingCommaRule()
+    override val issue = issueFor("Rule to mandate/forbid trailing commas")
+
+    @Configuration("Defines whether a trailing comma (or no trailing comma) should be enforced on the defining side")
+    private val allowTrailingComma by config(false)
+
+    @Configuration("Defines whether a trailing comma (or no trailing comma) should be enforced on the calling side")
+    private val allowTrailingCommaOnCallSite by config(false)
+
+    override fun overrideEditorConfigProperties(): Map<UsesEditorConfigProperties.EditorConfigProperty<*>, String> =
+        mapOf(
+            TrailingCommaRule.allowTrailingCommaProperty to allowTrailingComma.toString(),
+            TrailingCommaRule.allowTrailingCommaOnCallSiteProperty to allowTrailingCommaOnCallSite.toString(),
+        )
+}

detekt-formatting/src/test/kotlin/io/gitlab/arturbosch/detekt/formatting/TestFiles.kt

@@ -5,11 +5,12 @@ import io.github.detekt.test.utils.compileContentForTest
 import io.github.detekt.test.utils.compileForTest
 import io.github.detekt.test.utils.resource
 import io.gitlab.arturbosch.detekt.api.Finding
+import org.intellij.lang.annotations.Language
 import org.jetbrains.kotlin.com.intellij.openapi.util.text.StringUtilRt
 import java.io.File
 import java.nio.file.Paths
 
-fun FormattingRule.lint(content: String, fileName: String = "Test.kt"): List<Finding> {
+fun FormattingRule.lint(@Language("kotlin") content: String, fileName: String = "Test.kt"): List<Finding> {
     val root = compileContentForTest(content, fileName)
     this.visit(root)
     root.node.visit { node -> this.apply(node) }

detekt-formatting/src/test/kotlin/io/gitlab/arturbosch/detekt/formatting/TrailingCommaSpec.kt

@@ -0,0 +1,109 @@
+package io.gitlab.arturbosch.detekt.formatting
+
+import io.gitlab.arturbosch.detekt.formatting.wrappers.TrailingComma
+import io.gitlab.arturbosch.detekt.test.TestConfig
+import io.gitlab.arturbosch.detekt.test.assertThat
+import org.spekframework.spek2.Spek
+import org.spekframework.spek2.style.specification.describe
+
+private const val ALLOW_TRAILING_COMMA = "allowTrailingComma"
+private const val ALLOW_TRAILING_COMMA_ON_CALL_SITE = "allowTrailingCommaOnCallSite"
+
+/**
+ * Some test cases were used directly from KtLint to verify the wrapper rule:
+ *
+ * https://github.com/pinterest/ktlint/blob/master/ktlint-ruleset-experimental/src/test/kotlin/com/pinterest/ktlint/ruleset/experimental/TrailingCommaRuleTest.kt
+ */
+class TrailingCommaSpec : Spek({
+
+    describe("unnecessary comma") {
+
+        it("reports unnecessary comma on function call") {
+            val code =
+                """
+                val foo1 = listOf("a", "b",)
+                """.trimIndent()
+            val findings = TrailingComma(TestConfig(mapOf(ALLOW_TRAILING_COMMA to false))).lint(code)
+            assertThat(findings).hasSize(1)
+        }
+
+        it("reports unnecessary comma on constructor call") {
+            val code =
+                """
+                val foo2 = Pair(1, 2,)
+                """.trimIndent()
+            val findings = TrailingComma(TestConfig(mapOf(ALLOW_TRAILING_COMMA to false))).lint(code)
+            assertThat(findings).hasSize(1)
+        }
+
+        it("reports unnecessary comma on generic type definition") {
+            val code =
+                """
+                val foo3: List<String,> = emptyList()
+                """.trimIndent()
+            val findings = TrailingComma(TestConfig(mapOf(ALLOW_TRAILING_COMMA to false))).lint(code)
+            assertThat(findings).hasSize(1)
+        }
+
+        it("reports unnecessary comma on array get") {
+            val code =
+                """
+                val foo4 = Array(2) { 42 }
+                val bar4 = foo4[1,]
+                """.trimIndent()
+            val findings = TrailingComma(TestConfig(mapOf(ALLOW_TRAILING_COMMA to false))).lint(code)
+            assertThat(findings).hasSize(1)
+        }
+
+        it("reports unnecessary comma on annotation") {
+            val code =
+                """
+                @Foo5([1, 2,])
+                val foo5: Int = 0
+                """.trimIndent()
+            val findings = TrailingComma(TestConfig(mapOf(ALLOW_TRAILING_COMMA to false))).lint(code)
+            assertThat(findings).hasSize(1)
+        }
+    }
+
+    describe("missing comma") {
+
+        it("reports missing comma on function call") {
+            val code =
+                """
+                data class Foo1(val bar: Int)
+                data class Foo2(
+                   val bar: Int
+                )
+                """.trimIndent()
+            val findings = TrailingComma(TestConfig(mapOf(ALLOW_TRAILING_COMMA to true))).lint(code)
+            assertThat(findings).hasSize(1)
+        }
+
+        it("reports missing comma on function call") {
+            val code =
+                """
+                val foo1 = listOf("a", "b")
+                val foo2 = listOf(
+                    "a", 
+                    "b"
+                )
+                """.trimIndent()
+            val findings = TrailingComma(TestConfig(mapOf(ALLOW_TRAILING_COMMA_ON_CALL_SITE to true))).lint(code)
+            assertThat(findings).hasSize(1)
+        }
+
+        it("reports missing comma on constructor call") {
+            val code =
+                """
+                val foo2 = Pair(1, 2)
+                val foo2 = Pair(
+                    1, 
+                    2
+                )
+                """.trimIndent()
+            val findings = TrailingComma(TestConfig(mapOf(ALLOW_TRAILING_COMMA_ON_CALL_SITE to true))).lint(code)
+            assertThat(findings).hasSize(1)
+        }
+    }
+})

gradle/libs.versions.toml

@@ -2,7 +2,7 @@
 dokka = "1.5.30"
 jacoco = "0.8.7"
 kotlin = "1.5.31"
-ktlint = "0.42.1"
+ktlint = "0.43.0"
 spek = "2.0.17"
 
 [libraries]