Fix false-positive on checking unused sourcesets in MPP+Android project

AGP could create 'AndroidSourceSet' that does not participate in any
compilation. For this 'AndroidSourceSet's plugin should mark
corresponding KotlinSourceSet as orphan and exclude from check.

Unfortunately filtering them on KotlinSourceSet does not work,
as AGP adds sourcesets into variants lazily. And MPP requires all
SourceSets to be created eagerly. This change excludes all
KotlinSourceSets created for Android compilation from such check.

^KT-48436 Fixed

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

@@ -29,7 +29,6 @@ import org.jetbrains.kotlin.konan.target.HostManager
 import org.jetbrains.kotlin.library.KLIB_PROPERTY_SHORT_NAME
 import org.jetbrains.kotlin.library.KLIB_PROPERTY_UNIQUE_NAME
 import org.junit.Assert
-import org.junit.Ignore
 import org.junit.Test
 import java.util.*
 import java.util.jar.JarFile
@@ -1624,6 +1623,25 @@ class NewMultiplatformIT : BaseGradleIT() {
         }
     }
 
+    // https://youtrack.jetbrains.com/issue/KT-48436
+    @Test
+    fun testUnusedSourceSetsReportAndroid() = with(Project("new-mpp-android", gradleVersion)) {
+        setupWorkingDir()
+
+        build(
+            "assembleDebug",
+            // https://issuetracker.google.com/issues/152187160
+            options = defaultBuildOptions().copy(androidGradlePluginVersion = AGPVersion.v4_2_0)
+        ) {
+            assertSuccessful()
+            assertNotContains(
+                UnusedSourceSetsChecker.WARNING_PREFIX_ONE,
+                UnusedSourceSetsChecker.WARNING_PREFIX_MANY,
+                UnusedSourceSetsChecker.WARNING_INTRO
+            )
+        }
+    }
+
     @Test
     fun testIncrementalCompilation() = with(Project("new-mpp-jvm-js-ic", gradleVersion)) {
         build("build") {

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

@@ -20,6 +20,7 @@ package org.jetbrains.kotlin.gradle.plugin
 
 import org.gradle.api.internal.HasConvention
 import org.gradle.api.plugins.ExtensionAware
+import org.gradle.api.plugins.ExtraPropertiesExtension
 
 @Deprecated("Conventions are deprecated in Gradle")
 internal inline fun <reified T : Any> Any.addConvention(name: String, plugin: T) {
@@ -42,3 +43,6 @@ internal inline fun <reified T : Any> Any.addExtension(name: String, extension:
 
 internal inline fun <reified T : Any> Any.getExtension(name: String): T? =
     (this as ExtensionAware).extensions.getByName(name) as T?
+
+inline val Any.extraProperties: ExtraPropertiesExtension
+    get() = (this as ExtensionAware).extensions.extraProperties

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

@@ -8,6 +8,8 @@ package org.jetbrains.kotlin.gradle.plugin.mpp
 import org.gradle.api.Project
 import org.jetbrains.kotlin.gradle.dsl.kotlinExtension
 import org.jetbrains.kotlin.gradle.plugin.KotlinSourceSet
+import org.jetbrains.kotlin.gradle.plugin.extraProperties
+import org.jetbrains.kotlin.gradle.plugin.whenEvaluated
 
 object UnusedSourceSetsChecker {
     const val WARNING_PREFIX_ONE =
@@ -35,11 +37,14 @@ object UnusedSourceSetsChecker {
     }
 
     fun checkSourceSets(project: Project) {
-        // TODO once Android compilations are configured eagerly, move this to afterEvaluate { ... } instead of taskGraph.whenReady { ... }
-        project.gradle.taskGraph.whenReady { _ ->
+        project.whenEvaluated {
             val compilationsBySourceSet = CompilationSourceSetUtil.compilationsBySourceSets(project)
             val unusedSourceSets = project.kotlinExtension.sourceSets.filter {
-                compilationsBySourceSet[it]?.isEmpty() ?: true
+                // Ignoring Android source sets
+                val isAndroidSourceSet = it.extraProperties.has(IS_ANDROID_SOURCE_SET) &&
+                        (it.extraProperties[IS_ANDROID_SOURCE_SET] as Boolean)
+
+                !isAndroidSourceSet && compilationsBySourceSet[it]?.isEmpty() ?: true
             }
             if (unusedSourceSets.isNotEmpty()) {
                 reportUnusedSourceSets(project, unusedSourceSets.toSet())

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

@@ -16,13 +16,22 @@ import org.jetbrains.kotlin.gradle.plugin.AbstractAndroidProjectHandler.Companio
 import org.jetbrains.kotlin.gradle.plugin.addConvention
 import org.jetbrains.kotlin.gradle.plugin.sources.KotlinSourceSetFactory.Companion.defaultSourceFolder
 
+internal const val IS_ANDROID_SOURCE_SET = "android-source-set"
+
 internal fun syncKotlinAndAndroidSourceSets(target: KotlinAndroidTarget) {
     val project = target.project
     val android = project.extensions.getByName("android") as BaseExtension
+    val kotlinExtension = project.kotlinExtension
 
+    val createdKotlinSourceSets = mutableSetOf<String>()
     android.sourceSets.all { androidSourceSet ->
         val kotlinSourceSetName = kotlinSourceSetNameForAndroidSourceSet(target, androidSourceSet.name)
-        val kotlinSourceSet = project.kotlinExtension.sourceSets.maybeCreate(kotlinSourceSetName)
+        createdKotlinSourceSets.add(kotlinSourceSetName)
+        val kotlinSourceSet = kotlinExtension.sourceSets.maybeCreate(kotlinSourceSetName)
+
+        // Marking KotlinSource set is created for Android compilation to ignore it in UnusedSourceSetChecker
+        kotlinSourceSet.extraProperties.set(IS_ANDROID_SOURCE_SET, true)
+
         androidSourceSet.addKotlinSources(kotlinSourceSet)
 
         createDefaultDependsOnEdges(target, kotlinSourceSet, androidSourceSet)