Add experimental option to use OpenJDK 11 toolchain.

With this change, setting the environment variable
EXPERIMENTAL_USE_OPENJDK11_TOOLCHAIN=true switches from the OpenJDK 9
toolchain to the OpenJDK 11 one (prebuilts/jdk/jdk11).

Since the version of the java.base module has to match the version of
the jlink tool which consumes it, the --module-version argument to the
jmod create call is also switched.

Test: make
Test: EXPERIMENTAL_USE_OPENJDK11_TOOLCHAIN make
Bug: 131683177
Change-Id: I606d22538165f309fe5537bd67a26390b1dd5771

java/config/config.go

@@ -86,6 +86,14 @@ func init() {
 		// This is set up and guaranteed by soong_ui
 		return ctx.Config().Getenv("ANDROID_JAVA_HOME")
 	})
+	pctx.VariableFunc("JlinkVersion", func(ctx android.PackageVarContext) string {
+		switch ctx.Config().Getenv("EXPERIMENTAL_USE_OPENJDK11_TOOLCHAIN") {
+		case "true":
+			return "11"
+		default:
+			return "9"
+		}
+	})
 
 	pctx.SourcePathVariable("JavaToolchain", "${JavaHome}/bin")
 	pctx.SourcePathVariableWithEnvOverride("JavacCmd",

java/config/makevars.go

@@ -38,6 +38,7 @@ func makeVarsProvider(ctx android.MakeVarsContext) {
 	ctx.Strict("ANDROID_JAVA_HOME", "${JavaHome}")
 	ctx.Strict("ANDROID_JAVA8_HOME", "prebuilts/jdk/jdk8/${hostPrebuiltTag}")
 	ctx.Strict("ANDROID_JAVA9_HOME", "prebuilts/jdk/jdk9/${hostPrebuiltTag}")
+	ctx.Strict("ANDROID_JAVA11_HOME", "prebuilts/jdk/jdk11/${hostPrebuiltTag}")
 	ctx.Strict("ANDROID_JAVA_TOOLCHAIN", "${JavaToolchain}")
 	ctx.Strict("JAVA", "${JavaCmd} ${JavaVmFlags}")
 	ctx.Strict("JAVAC", "${JavacCmd} ${JavacVmFlags}")

java/system_modules.go

@@ -40,7 +40,9 @@ var (
 			`${config.JavacCmd} --system=none --patch-module=java.base=${classpath} ${workDir}/module-info.java && ` +
 			`${config.SoongZipCmd} -jar -o ${workDir}/classes.jar -C ${workDir} -f ${workDir}/module-info.class && ` +
 			`${config.MergeZipsCmd} -j ${workDir}/module.jar ${workDir}/classes.jar $in && ` +
-			`${config.JmodCmd} create --module-version 9 --target-platform android ` +
+			// Note: The version of the java.base module created must match the version
+			// of the jlink tool which consumes it.
+			`${config.JmodCmd} create --module-version ${config.JlinkVersion} --target-platform android ` +
 			`  --class-path ${workDir}/module.jar ${workDir}/jmod/java.base.jmod && ` +
 			`${config.JlinkCmd} --module-path ${workDir}/jmod --add-modules java.base --output ${outDir} ` +
 			// Note: The system-modules jlink plugin is disabled because (a) it is not