Add Kotlin sources output as a separate output directory for kapt.

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/internal/Kapt3KotlinGradleSubplugin.kt

@@ -293,6 +293,7 @@ class Kapt3KotlinGradleSubplugin : KotlinGradleSubplugin<KotlinCompile> {
 
         kaptTask.stubsDir = getKaptStubsDir()
         kaptTask.destinationDir = sourcesOutputDir
+        kaptTask.kotlinSourcesDestinationDir = kotlinSourcesOutputDir
         kaptTask.classesDir = classesOutputDir
 
         javaSourceSet?.output?.apply {

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/internal/KaptTask.kt

@@ -39,6 +39,9 @@ open class KaptTask : ConventionTask(), CompilerArgumentAware<K2JVMCompilerArgum
     @get:OutputDirectory
     lateinit var destinationDir: File
 
+    @get:OutputDirectory
+    lateinit var kotlinSourcesDestinationDir: File
+
     override fun createCompilerArgs(): K2JVMCompilerArguments = K2JVMCompilerArguments()
 
     override fun setupCompilerArgs(args: K2JVMCompilerArguments, defaultsOnly: Boolean) {
@@ -75,6 +78,7 @@ open class KaptTask : ConventionTask(), CompilerArgumentAware<K2JVMCompilerArgum
          * (annotation processing is not incremental) */
         destinationDir.clearDirectory()
         classesDir.clearDirectory()
+        kotlinSourcesDestinationDir.clearDirectory()
 
         val sourceRootsFromKotlin = kotlinCompileTask.sourceRootsContainer.sourceRoots
         val rawSourceRoots = FilteringSourceRootsContainer(sourceRootsFromKotlin, { !isInsideDestinationDirs(it) })