Provide an opt-out flag for separate classes dirs with Gradle 4.0+

Issue #KT-19774 Fixed

(cherry picked from commit 2aa6f5a)

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/dsl/KotlinProjectExtension.kt

@@ -18,9 +18,10 @@ package org.jetbrains.kotlin.gradle.dsl
 
 import org.gradle.api.Project
 import org.gradle.api.internal.plugins.DslObject
+import kotlin.reflect.KClass
 
-internal fun Project.createKotlinExtension() {
-    val kotlinExt = extensions.create("kotlin", KotlinProjectExtension::class.java)
+internal fun Project.createKotlinExtension(extensionClass: KClass<out KotlinProjectExtension>) {
+    val kotlinExt = extensions.create("kotlin", extensionClass.java)
     DslObject(kotlinExt).extensions.create("experimental", ExperimentalExtension::class.java)
 }
 
@@ -29,6 +30,14 @@ open class KotlinProjectExtension {
             get() = DslObject(this).extensions.getByType(ExperimentalExtension::class.java)!!
 }
 
+open class KotlinJvmProjectExtension : KotlinProjectExtension() {
+    /**
+     * With Gradle 4.0+, disables the separate output directory for Kotlin, falling back to sharing the deprecated
+     * single classes directory per source set. With Gradle < 4.0, has no effect.
+     * */
+    var copyClassesToJavaOutput = false
+}
+
 open class ExperimentalExtension {
     var coroutines: Coroutines? = null
 }

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

@@ -0,0 +1,50 @@
+package org.jetbrains.kotlin.gradle.plugin
+
+import org.gradle.api.Project
+import org.gradle.api.Task
+import org.gradle.api.specs.Spec
+import org.gradle.api.tasks.compile.JavaCompile
+import org.jetbrains.kotlin.gradle.dsl.KotlinJvmProjectExtension
+import org.jetbrains.kotlin.gradle.utils.ParsedGradleVersion
+import java.util.*
+
+object CopyClassesToJavaOutputStatus {
+    fun isEnabled(project: Project): Boolean {
+        val kotlinJvmExt = project.kotlinJvmExt ?: return false
+        if (kotlinJvmExt.copyClassesToJavaOutput) {
+            if (isGradleVersionTooLow(project) && warningReportedForProject.add(project)) {
+                project.logger.kotlinWarn(gradleVersionTooLowWarningMessage)
+            }
+            addCacheWarningToJavaTasks(project)
+            return true
+        }
+        return false
+    }
+
+    private val warningReportedForProject = Collections.newSetFromMap<Project>(WeakHashMap())
+
+    private fun isGradleVersionTooLow(project: Project): Boolean {
+        return (ParsedGradleVersion.parse(project.gradle.gradleVersion) ?: return false) < ParsedGradleVersion(4, 0)
+    }
+
+    private fun addCacheWarningToJavaTasks(project: Project) {
+        project.tasks.withType(JavaCompile::class.java).all {
+            val warningCacheIfSpec = Spec<Task> {
+                if (warningReportedForProject.add(project)) {
+                    project.logger.kotlinWarn(buildCacheWarningMessage)
+                }
+                return@Spec true
+            }
+            it.outputs.javaClass.getMethod("cacheIf", Spec::class.java).invoke(it.outputs, warningCacheIfSpec)
+        }
+    }
+
+    const val buildCacheWarningMessage = "The 'kotlin.copyClassesToJavaOutput' option should not be used with Gradle " +
+            "build cache"
+
+    const val gradleVersionTooLowWarningMessage = "The 'kotlin.copyClassesToJavaOutput' option has no effect when " +
+            "used with Gradle < 4.0"
+
+    private val Project.kotlinJvmExt: KotlinJvmProjectExtension?
+        get() = extensions.findByType(KotlinJvmProjectExtension::class.java)
+}

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

@@ -55,8 +55,10 @@ internal abstract class KotlinSourceSetProcessor<T : AbstractKotlinCompile<*>>(
     abstract protected fun doTargetSpecificProcessing()
     protected val logger = Logging.getLogger(this.javaClass)!!
 
-    protected val isSeparateClassesDirSupported: Boolean =
-            sourceSet.output.javaClass.methods.any { it.name == "getClassesDirs" }
+    protected val isSeparateClassesDirSupported: Boolean by lazy {
+        !CopyClassesToJavaOutputStatus.isEnabled(project) &&
+                sourceSet.output.javaClass.methods.any { it.name == "getClassesDirs" }
+    }
 
     protected val sourceSetName: String = sourceSet.name
     protected val sourceRootDir: String = "src/$sourceSetName/kotlin"

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

@@ -19,17 +19,20 @@ package org.jetbrains.kotlin.gradle.plugin
 import org.gradle.api.Plugin
 import org.gradle.api.Project
 import org.gradle.api.internal.file.FileResolver
-import org.gradle.api.internal.plugins.DslObject
 import org.gradle.api.logging.Logger
 import org.gradle.api.logging.Logging
-import org.jetbrains.kotlin.gradle.dsl.ExperimentalExtension
+import org.jetbrains.kotlin.gradle.dsl.KotlinJvmProjectExtension
 import org.jetbrains.kotlin.gradle.dsl.KotlinProjectExtension
 import org.jetbrains.kotlin.gradle.dsl.createKotlinExtension
 import org.jetbrains.kotlin.gradle.internal.KotlinSourceSetProviderImpl
-import org.jetbrains.kotlin.gradle.tasks.*
+import org.jetbrains.kotlin.gradle.tasks.AndroidTasksProvider
+import org.jetbrains.kotlin.gradle.tasks.Kotlin2JsTasksProvider
+import org.jetbrains.kotlin.gradle.tasks.KotlinCommonTasksProvider
+import org.jetbrains.kotlin.gradle.tasks.KotlinTasksProvider
 import java.io.FileNotFoundException
 import java.util.*
 import javax.inject.Inject
+import kotlin.reflect.KClass
 
 abstract class KotlinBasePluginWrapper(protected val fileResolver: FileResolver): Plugin<Project> {
     private val log = Logging.getLogger(this.javaClass)
@@ -40,18 +43,23 @@ abstract class KotlinBasePluginWrapper(protected val fileResolver: FileResolver)
         System.setProperty(org.jetbrains.kotlin.cli.common.KOTLIN_COMPILER_ENVIRONMENT_KEEPALIVE_PROPERTY, "true")
         val kotlinGradleBuildServices = KotlinGradleBuildServices.getInstance(project.gradle)
 
-        project.createKotlinExtension()
+        project.createKotlinExtension(projectExtensionClass)
 
         val plugin = getPlugin(kotlinGradleBuildServices)
         plugin.apply(project)
     }
 
     internal abstract fun getPlugin(kotlinGradleBuildServices: KotlinGradleBuildServices): Plugin<Project>
+
+    open val projectExtensionClass: KClass<out KotlinProjectExtension> get() = KotlinProjectExtension::class
 }
 
 open class KotlinPluginWrapper @Inject constructor(fileResolver: FileResolver): KotlinBasePluginWrapper(fileResolver) {
     override fun getPlugin(kotlinGradleBuildServices: KotlinGradleBuildServices) =
             KotlinPlugin(KotlinTasksProvider(), KotlinSourceSetProviderImpl(fileResolver), kotlinPluginVersion, kotlinGradleBuildServices)
+
+    override val projectExtensionClass: KClass<out KotlinJvmProjectExtension>
+        get() = KotlinJvmProjectExtension::class
 }
 
 open class KotlinCommonPluginWrapper @Inject constructor(fileResolver: FileResolver): KotlinBasePluginWrapper(fileResolver) {