[Gradle MPP] Added duplicate source set name diagnostic

#KT-62601 Fixed

libraries/tools/kotlin-gradle-plugin/src/common/kotlin/org/jetbrains/kotlin/gradle/plugin/diagnostics/KotlinToolingDiagnostics.kt

@@ -665,6 +665,19 @@ object KotlinToolingDiagnostics {
             """.trimIndent()
         )
     }
+
+    object DuplicateSourceSetsError : ToolingDiagnosticFactory(FATAL) {
+        operator fun invoke(duplicatedSourceSets: Map<String, List<String>>): ToolingDiagnostic {
+            val duplicatesGroupsString = duplicatedSourceSets
+                .map { entry -> entry.value.joinToString(", ") }
+                .joinToString("], [", "[", "]")
+            return build(
+                "Duplicate Kotlin source sets have been detected: $duplicatesGroupsString." +
+                        " Keep in mind that source set names are case-insensitive," +
+                        " which means that `srcMain` and `sRcMain` are considered the same source set."
+            )
+        }
+    }
 }
 
 private fun String.indentLines(nSpaces: Int = 4, skipFirstLine: Boolean = true): String {

libraries/tools/kotlin-gradle-plugin/src/common/kotlin/org/jetbrains/kotlin/gradle/plugin/diagnostics/checkers/DuplicateSourceSetChecker.kt

@@ -0,0 +1,33 @@
+/*
+ * Copyright 2010-2023 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.diagnostics.checkers
+
+import org.jetbrains.kotlin.gradle.dsl.multiplatformExtensionOrNull
+import org.jetbrains.kotlin.gradle.plugin.diagnostics.*
+import org.jetbrains.kotlin.gradle.plugin.diagnostics.KotlinGradleProjectChecker
+import org.jetbrains.kotlin.gradle.plugin.diagnostics.KotlinGradleProjectCheckerContext
+import org.jetbrains.kotlin.gradle.plugin.diagnostics.KotlinToolingDiagnosticsCollector
+
+/**
+ * This checker is used to ensure that there are no duplicate source sets in MPP project.
+ *
+ * Examples of duplicated sourceSets: [jvmMain and jVmMain] or [macosMain and macOSMain]
+ *
+ */
+// TODO(Dmitrii Krasnov): Remove this checker once IDEA-317606 is resolved
+internal object DuplicateSourceSetChecker : KotlinGradleProjectChecker {
+    override suspend fun KotlinGradleProjectCheckerContext.runChecks(collector: KotlinToolingDiagnosticsCollector) {
+        val kotlin = project.multiplatformExtensionOrNull ?: return
+        val sourceSetNames = kotlin.awaitSourceSets().map { it.name }
+        val duplicateSourceSets = sourceSetNames
+            .groupBy { it.toLowerCase() }
+            .filter { (_, values) -> values.size > 1 }
+
+        if (duplicateSourceSets.isNotEmpty()) {
+            project.reportDiagnostic(KotlinToolingDiagnostics.DuplicateSourceSetsError(duplicateSourceSets))
+        }
+    }
+}

libraries/tools/kotlin-gradle-plugin/src/common/kotlin/org/jetbrains/kotlin/gradle/plugin/registerKotlinPluginExtensions.kt

@@ -26,6 +26,7 @@ import org.jetbrains.kotlin.gradle.plugin.diagnostics.checkers.CommonMainOrTestW
 import org.jetbrains.kotlin.gradle.plugin.diagnostics.checkers.DeprecatedKotlinNativeTargetsChecker
 import org.jetbrains.kotlin.gradle.plugin.diagnostics.checkers.DisabledCinteropCommonizationInHmppProjectChecker
 import org.jetbrains.kotlin.gradle.plugin.diagnostics.checkers.DisabledNativeTargetsChecker
+import org.jetbrains.kotlin.gradle.plugin.diagnostics.checkers.DuplicateSourceSetChecker
 import org.jetbrains.kotlin.gradle.plugin.diagnostics.checkers.ExperimentalK2UsageChecker
 import org.jetbrains.kotlin.gradle.plugin.diagnostics.checkers.InternalGradlePropertiesUsageChecker
 import org.jetbrains.kotlin.gradle.plugin.diagnostics.checkers.JsEnvironmentChecker
@@ -148,6 +149,7 @@ internal fun Project.registerKotlinPluginExtensions() {
         register(project, KotlinTargetAlreadyDeclaredChecker)
         register(project, InternalGradlePropertiesUsageChecker)
         register(project, WasmSourceSetsNotFoundChecker)
+        register(project, DuplicateSourceSetChecker)
 
         if (isMultiplatform) {
             register(project, KotlinMultiplatformAndroidGradlePluginCompatibilityChecker)

libraries/tools/kotlin-gradle-plugin/src/functionalTest/kotlin/org/jetbrains/kotlin/gradle/unitTests/diagnosticsTests/DuplicateSourceSetCheckerTest.kt

@@ -0,0 +1,47 @@
+/*
+ * Copyright 2010-2023 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.unitTests.diagnosticsTests
+
+import org.jetbrains.kotlin.gradle.dsl.multiplatformExtension
+import org.jetbrains.kotlin.gradle.util.assertNoDiagnostics
+import org.jetbrains.kotlin.gradle.util.buildProjectWithMPP
+import org.jetbrains.kotlin.gradle.util.checkDiagnostics
+import kotlin.test.Test
+import kotlin.test.assertFails
+
+class DuplicateSourceSetCheckerTest {
+
+    @Test
+    fun `target with custom name duplicates defualt name failes build`() {
+        val project = buildProjectWithMPP {
+            project.multiplatformExtension.applyDefaultHierarchyTemplate()
+            project.multiplatformExtension.linuxX64("linUX")
+        }
+        assertFails { project.evaluate() }
+        project.checkDiagnostics("DuplicateSourceSetChecker")
+    }
+
+    @Test
+    fun `target with custom name does not produce any diagnostics`() {
+        val project = buildProjectWithMPP {
+            project.multiplatformExtension.applyDefaultHierarchyTemplate()
+            project.multiplatformExtension.linuxX64("custom")
+        }
+        project.evaluate()
+        project.assertNoDiagnostics()
+    }
+
+    @Test
+    fun `several targets without custom name don't produce any diagnostics`() {
+        val project = buildProjectWithMPP {
+            project.multiplatformExtension.applyDefaultHierarchyTemplate()
+            project.multiplatformExtension.linuxX64()
+            project.multiplatformExtension.mingwX64()
+        }
+        project.evaluate()
+        project.assertNoDiagnostics()
+    }
+}

libraries/tools/kotlin-gradle-plugin/src/functionalTest/resources/expectedDiagnostics/DuplicateSourceSetChecker.txt

@@ -0,0 +1 @@
+[DuplicateSourceSetsError | FATAL] Duplicate Kotlin source sets have been detected: [linUXMain, linuxMain], [linUXTest, linuxTest]. Keep in mind that source set names are case-insensitive, which means that `srcMain` and `sRcMain` are considered the same source set.