Initial kotlin support

Allow java libraries to specify .kt sources, precompile them with
kotlin, and then pass them in the classpath to javac.

Bug: 65219535
Test: java_test.go
Change-Id: Ife22b6ef82ced9ec26a9e5392b2dadacbb16546f
diff --git a/java/java.go b/java/java.go
index 770c9c1..3382cf2 100644
--- a/java/java.go
+++ b/java/java.go
@@ -198,6 +198,7 @@
 	bootClasspathTag = dependencyTag{name: "bootclasspath"}
 	systemModulesTag = dependencyTag{name: "system modules"}
 	frameworkResTag  = dependencyTag{name: "framework-res"}
+	kotlinStdlibTag  = dependencyTag{name: "kotlin-stdlib"}
 )
 
 type sdkDep struct {
@@ -326,6 +327,12 @@
 	if j.hasSrcExt(".proto") {
 		protoDeps(ctx, &j.protoProperties)
 	}
+
+	if j.hasSrcExt(".kt") {
+		// TODO(ccross): move this to a mutator pass that can tell if generated sources contain
+		// Kotlin files
+		ctx.AddDependency(ctx.Module(), kotlinStdlibTag, "kotlin-stdlib")
+	}
 }
 
 func hasSrcExt(srcs []string, ext string) bool {
@@ -373,6 +380,7 @@
 	srcJars            android.Paths
 	systemModules      android.Path
 	aidlPreprocess     android.OptionalPath
+	kotlinStdlib       android.Paths
 }
 
 func (j *Module) collectDeps(ctx android.ModuleContext) deps {
@@ -424,6 +432,8 @@
 				// generated by framework-res.apk
 				// TODO(ccross): aapt java files should go in a src jar
 			}
+		case kotlinStdlibTag:
+			deps.kotlinStdlib = dep.ClasspathFiles()
 		default:
 			panic(fmt.Errorf("unknown dependency %q for %q", otherName, ctx.ModuleName()))
 		}
@@ -492,7 +502,33 @@
 
 	var jars android.Paths
 
-	if len(srcFiles) > 0 {
+	if srcFiles.HasExt(".kt") {
+		// If there are kotlin files, compile them first but pass all the kotlin and java files
+		// kotlinc will use the java files to resolve types referenced by the kotlin files, but
+		// won't emit any classes for them.
+
+		flags.kotlincFlags = "-no-stdlib"
+		if ctx.Device() {
+			flags.kotlincFlags += " -no-jdk"
+		}
+
+		flags.kotlincClasspath = append(flags.kotlincClasspath, deps.kotlinStdlib...)
+		flags.kotlincClasspath = append(flags.kotlincClasspath, deps.classpath...)
+
+		kotlinJar := android.PathForModuleOut(ctx, "classes-kt.jar")
+		TransformKotlinToClasses(ctx, kotlinJar, srcFiles, srcJars, flags)
+		if ctx.Failed() {
+			return
+		}
+
+		// Make javac rule depend on the kotlinc rule
+		flags.classpath = append(flags.classpath, kotlinJar)
+		// Jar kotlin classes into the final jar after javac
+		jars = append(jars, kotlinJar)
+		jars = append(jars, deps.kotlinStdlib...)
+	}
+
+	if javaSrcFiles := srcFiles.FilterByExt(".java"); len(javaSrcFiles) > 0 {
 		var extraJarDeps android.Paths
 		if ctx.AConfig().IsEnvTrue("RUN_ERROR_PRONE") {
 			// If error-prone is enabled, add an additional rule to compile the java files into
@@ -501,13 +537,13 @@
 			// TODO(ccross): Once we always compile with javac9 we may be able to conditionally
 			//    enable error-prone without affecting the output class files.
 			errorprone := android.PathForModuleOut(ctx, "classes-errorprone.list")
-			RunErrorProne(ctx, errorprone, srcFiles, srcJars, flags)
+			RunErrorProne(ctx, errorprone, javaSrcFiles, srcJars, flags)
 			extraJarDeps = append(extraJarDeps, errorprone)
 		}
 
 		// Compile java sources into .class files
 		classes := android.PathForModuleOut(ctx, "classes-compiled.jar")
-		TransformJavaToClasses(ctx, classes, srcFiles, srcJars, flags, extraJarDeps)
+		TransformJavaToClasses(ctx, classes, javaSrcFiles, srcJars, flags, extraJarDeps)
 		if ctx.Failed() {
 			return
 		}