Kapt3: Always write Kotlin stubs to .java files, and make javac always parse them from source files, not from JCTree (in order to support incremental compilation).

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

@@ -180,10 +180,10 @@ class Kapt3KotlinGradleSubplugin : KotlinGradleSubplugin<KotlinCompile> {
         }
 
         pluginOptions += SubpluginOption("useLightAnalysis", "${kaptExtension.useLightAnalysis}")
+        pluginOptions += SubpluginOption("stubs", getKaptStubsDir(project, sourceSetName).canonicalPath)
 
         if (project.hasProperty(VERBOSE_OPTION_NAME) && project.property(VERBOSE_OPTION_NAME) == "true") {
             pluginOptions += SubpluginOption("verbose", "true")
-            pluginOptions += SubpluginOption("stubs", getKaptStubsDir(project, sourceSetName).canonicalPath)
         }
     }
 

plugins/kapt3/src/org/jetbrains/kotlin/kapt3/Kapt3Extension.kt

@@ -18,7 +18,6 @@ package org.jetbrains.kotlin.kapt3
 
 import com.intellij.openapi.project.Project
 import com.sun.tools.javac.tree.JCTree
-import com.sun.tools.javac.tree.JCTree.JCCompilationUnit
 import org.jetbrains.kotlin.analyzer.AnalysisResult
 import org.jetbrains.kotlin.cli.common.messages.CompilerMessageLocation
 import org.jetbrains.kotlin.cli.common.messages.CompilerMessageSeverity
@@ -49,7 +48,7 @@ class ClasspathBasedKapt3Extension(
         javaSourceRoots: List<File>,
         sourcesOutputDir: File,
         classFilesOutputDir: File,
-        stubsOutputDir: File?,
+        stubsOutputDir: File,
         incrementalDataOutputDir: File?,
         options: Map<String, String>,
         aptOnly: Boolean,
@@ -98,7 +97,7 @@ abstract class AbstractKapt3Extension(
         val javaSourceRoots: List<File>,
         val sourcesOutputDir: File,
         val classFilesOutputDir: File,
-        val stubsOutputDir: File?,
+        val stubsOutputDir: File,
         val incrementalDataOutputDir: File?,
         val options: Map<String, String>,
         val aptOnly: Boolean,
@@ -141,13 +140,13 @@ abstract class AbstractKapt3Extension(
         val (kaptContext, generationState) = compileStubs(project, module, bindingTrace.bindingContext, files.toList())
 
         try {
+            generateKotlinSourceStubs(kaptContext, generationState)
             val javaSourceFiles = collectJavaSourceFiles()
-            val kotlinSourceStubs = generateKotlinSourceStubs(kaptContext, generationState)
 
             val (annotationProcessingTime) = measureTimeMillis {
                 kaptContext.doAnnotationProcessing(
                         javaSourceFiles, processors, compileClasspath, annotationProcessingClasspath,
-                        sourcesOutputDir, classFilesOutputDir, kotlinSourceStubs)
+                        sourcesOutputDir, classFilesOutputDir)
             }
 
             logger.info { "Annotation processing took $annotationProcessingTime ms" }
@@ -202,7 +201,7 @@ abstract class AbstractKapt3Extension(
         return Pair(KaptContext(logger, compiledClasses, origins, options), generationState)
     }
 
-    private fun generateKotlinSourceStubs(kaptContext: KaptContext, generationState: GenerationState): JavacList<JCCompilationUnit> {
+    private fun generateKotlinSourceStubs(kaptContext: KaptContext, generationState: GenerationState) {
         val converter = ClassFileToSourceStubConverter(kaptContext, generationState.typeMapper, generateNonExistentClass = true)
 
         val (stubGenerationTime, kotlinSourceStubs) = measureTimeMillis {
@@ -214,11 +213,10 @@ abstract class AbstractKapt3Extension(
 
         saveStubs(kotlinSourceStubs)
         saveIncrementalData(generationState, logger.messageCollector, converter)
-        return kotlinSourceStubs
     }
 
     private fun collectJavaSourceFiles(): List<File> {
-        val javaFilesFromJavaSourceRoots = javaSourceRoots.flatMap {
+        val javaFilesFromJavaSourceRoots = (javaSourceRoots + stubsOutputDir).flatMap {
             root -> root.walk().filter { it.isFile && it.extension == "java" }.toList()
         }
         logger.info { "Java source files: " + javaFilesFromJavaSourceRoots.joinToString { it.canonicalPath } }
@@ -227,12 +225,11 @@ abstract class AbstractKapt3Extension(
     }
 
     protected open fun saveStubs(stubs: JavacList<JCTree.JCCompilationUnit>) {
-        val outputDir = stubsOutputDir ?: return
         for (stub in stubs) {
             val className = (stub.defs.first { it is JCTree.JCClassDecl } as JCTree.JCClassDecl).simpleName.toString()
 
             val packageName = stub.packageName?.toString() ?: ""
-            val packageDir = if (packageName.isEmpty()) outputDir else File(outputDir, packageName.replace('.', '/'))
+            val packageDir = if (packageName.isEmpty()) stubsOutputDir else File(stubsOutputDir, packageName.replace('.', '/'))
             packageDir.mkdirs()
             File(packageDir, className + ".java").writeText(stub.toString())
         }
@@ -246,7 +243,7 @@ abstract class AbstractKapt3Extension(
 
         generationState.factory.writeAll(incrementalDataOutputDir) { file, sources, output ->
             val stubFileObject = converter.bindings[file.relativePath.substringBeforeLast(".class", missingDelimiterValue = "")]
-            if (stubFileObject != null && stubsOutputDir != null) {
+            if (stubFileObject != null) {
                 val stubFile = File(stubsOutputDir, stubFileObject.name)
                 if (stubFile.exists()) {
                     messageCollector.report(CompilerMessageSeverity.OUTPUT,

plugins/kapt3/src/org/jetbrains/kotlin/kapt3/Kapt3Plugin.kt

@@ -153,10 +153,16 @@ class Kapt3ComponentRegistrar : ComponentRegistrar {
 
         val apClasspath = configuration.get(ANNOTATION_PROCESSOR_CLASSPATH)?.map(::File)
 
-        if (sourcesOutputDir == null || classFilesOutputDir == null || apClasspath == null) {
+        if (sourcesOutputDir == null || classFilesOutputDir == null || apClasspath == null || stubsOutputDir == null) {
             if (isAptOnly) {
-                val subject = if (apClasspath == null) "Annotation processing classpath" else "Generated files output directories"
+                val nonExistentOptionName = when {
-                logger.warn("$subject is not specified, skipping annotation processing")
+                    sourcesOutputDir == null -> "Sources output directory"
+                    classFilesOutputDir == null -> "Classes output directory"
+                    apClasspath == null -> "Annotation processing classpath"
+                    stubsOutputDir == null -> "Stubs output directory"
+                    else -> throw IllegalStateException()
+                }
+                logger.warn("$nonExistentOptionName is not specified, skipping annotation processing")
                 AnalysisHandlerExtension.registerExtension(project, AbortAnalysisHandlerExtension())
             }
             return

plugins/kapt3/test/org/jetbrains/kotlin/kapt3/test/KotlinKapt3IntegrationTests.kt

@@ -71,7 +71,7 @@ class KotlinKapt3IntegrationTests : AbstractKotlinKapt3IntegrationTest() {
 
             val bindings = kaptExtension.savedBindings!!
 
-            test(stubsOutputDir!!, incrementalDataOutputDir!!, bindings)
+            test(stubsOutputDir, incrementalDataOutputDir!!, bindings)
         }
     }