Initial support for converting jars to java9 system modules

Adds a java_system_modules module type that (when
EXPERIMENTAL_USE_OPENJDK9 is set to true) converts a list of
java library modules and prebuilt jars into system modules,
and plumbs the system modules through to the javac command
line.

Also exports the location of the system modules to make
variables, as well as the name of the default system module.

Test: TestClasspath in java_test.go, runs automatically as part of the build
Bug: 63986449
Change-Id: I27bd5d2010092422a27b69c91568e49010e02f40
diff --git a/Android.bp b/Android.bp
index ae31a60..1153aac 100644
--- a/Android.bp
+++ b/Android.bp
@@ -211,6 +211,7 @@
         "java/java.go",
         "java/proto.go",
         "java/resources.go",
+        "java/system_modules.go",
     ],
     testSrcs: [
         "java/java_test.go",
diff --git a/android/config.go b/android/config.go
index 5abda26..dca998f 100644
--- a/android/config.go
+++ b/android/config.go
@@ -88,6 +88,9 @@
 	captureBuild      bool // true for tests, saves build parameters for each module
 	ignoreEnvironment bool // true for tests, returns empty from all Getenv calls
 
+	useOpenJDK9    bool // Use OpenJDK9, but possibly target 1.8
+	targetOpenJDK9 bool // Use OpenJDK9 and target 1.9
+
 	OncePer
 }
 
@@ -183,6 +186,10 @@
 		config: config,
 	}
 
+	if err := config.fromEnv(); err != nil {
+		panic(err)
+	}
+
 	return Config{config}
 }
 
@@ -273,9 +280,31 @@
 	config.Targets = targets
 	config.BuildOsVariant = targets[Host][0].String()
 
+	if err := config.fromEnv(); err != nil {
+		return Config{}, err
+	}
+
 	return Config{config}, nil
 }
 
+func (c *config) fromEnv() error {
+	switch c.Getenv("EXPERIMENTAL_USE_OPENJDK9") {
+	case "":
+		// Use OpenJDK8
+	case "1.8":
+		// Use OpenJDK9, but target 1.8
+		c.useOpenJDK9 = true
+	case "true":
+		// Use OpenJDK9 and target 1.9
+		c.useOpenJDK9 = true
+		c.targetOpenJDK9 = true
+	default:
+		return fmt.Errorf(`Invalid value for EXPERIMENTAL_USE_OPENJDK9, should be "", "1.8", or "true"`)
+	}
+
+	return nil
+}
+
 func (c *config) RemoveAbandonedFiles() bool {
 	return false
 }
@@ -518,6 +547,16 @@
 	return Bool(c.ProductVariables.UseGoma)
 }
 
+// Returns true if OpenJDK9 prebuilts are being used
+func (c *config) UseOpenJDK9() bool {
+	return c.useOpenJDK9
+}
+
+// Returns true if -source 1.9 -target 1.9 is being passed to javac
+func (c *config) TargetOpenJDK9() bool {
+	return c.targetOpenJDK9
+}
+
 func (c *config) ClangTidy() bool {
 	return Bool(c.ProductVariables.ClangTidy)
 }
diff --git a/java/builder.go b/java/builder.go
index 118f239..8992f68 100644
--- a/java/builder.go
+++ b/java/builder.go
@@ -126,6 +126,7 @@
 	dxFlags       string
 	bootClasspath classpath
 	classpath     classpath
+	systemModules classpath
 	desugarFlags  string
 	aidlFlags     string
 	javaVersion   string
@@ -177,7 +178,16 @@
 	}
 
 	deps = append(deps, srcFileLists...)
-	deps = append(deps, flags.bootClasspath...)
+
+	var bootClasspath string
+	if flags.javaVersion == "1.9" {
+		deps = append(deps, flags.systemModules...)
+		bootClasspath = flags.systemModules.JavaSystemModules(ctx.Device())
+	} else {
+		deps = append(deps, flags.bootClasspath...)
+		bootClasspath = flags.bootClasspath.JavaBootClasspath(ctx.Device())
+	}
+
 	deps = append(deps, flags.classpath...)
 
 	ctx.ModuleBuild(pctx, android.ModuleBuildParams{
@@ -188,7 +198,7 @@
 		Implicits:   deps,
 		Args: map[string]string{
 			"javacFlags":    javacFlags,
-			"bootClasspath": flags.bootClasspath.JavaBootClasspath(ctx.Device()),
+			"bootClasspath": bootClasspath,
 			"classpath":     flags.classpath.JavaClasspath(),
 			"outDir":        android.PathForModuleOut(ctx, "classes"+suffix).String(),
 			"annoDir":       android.PathForModuleOut(ctx, "anno"+suffix).String(),
@@ -259,7 +269,7 @@
 	dumpDir := android.PathForModuleOut(ctx, "desugar_dumped_classes")
 
 	javaFlags := ""
-	if ctx.AConfig().Getenv("EXPERIMENTAL_USE_OPENJDK9") != "" {
+	if ctx.AConfig().UseOpenJDK9() {
 		javaFlags = "--add-opens java.base/java.lang.invoke=ALL-UNNAMED"
 	}
 
@@ -359,6 +369,21 @@
 	}
 }
 
+// Returns a --system argument in the form javac expects with -source 1.9.  If forceEmpty is true,
+// returns --system=none if the list is empty to ensure javac does not fall back to the default
+// system modules.
+func (x *classpath) JavaSystemModules(forceEmpty bool) string {
+	if len(*x) > 1 {
+		panic("more than one system module")
+	} else if len(*x) == 1 {
+		return "--system=" + strings.TrimSuffix((*x)[0].String(), "lib/modules")
+	} else if forceEmpty {
+		return "--system=none"
+	} else {
+		return ""
+	}
+}
+
 func (x *classpath) DesugarBootClasspath() []string {
 	if x == nil || *x == nil {
 		return nil
diff --git a/java/config/config.go b/java/config/config.go
index 70b8fe5..7d1fa29 100644
--- a/java/config/config.go
+++ b/java/config/config.go
@@ -27,6 +27,7 @@
 	pctx = android.NewPackageContext("android/soong/java/config")
 
 	DefaultBootclasspathLibraries = []string{"core-oj", "core-libart"}
+	DefaultSystemModules          = "core-system-modules"
 	DefaultLibraries              = []string{"ext", "framework", "okhttp"}
 )
 
@@ -47,9 +48,10 @@
 		// If a different javac is used the flag will be ignored and extra bridges will be inserted.
 		// The flag is implemented by https://android-review.googlesource.com/c/486427
 		`-XDskipDuplicateBridges=true`,
-	}, " "))
 
-	pctx.StaticVariable("DefaultJavaVersion", "1.8")
+		// b/65004097: prevent using java.lang.invoke.StringConcatFactory when using -target 1.9
+		`-XDstringConcat=inline`,
+	}, " "))
 
 	pctx.VariableConfigMethod("hostPrebuiltTag", android.Config.PrebuiltOS)
 
@@ -57,7 +59,7 @@
 		if override := config.(android.Config).Getenv("OVERRIDE_ANDROID_JAVA_HOME"); override != "" {
 			return override, nil
 		}
-		if jdk9 := config.(android.Config).Getenv("EXPERIMENTAL_USE_OPENJDK9"); jdk9 != "" {
+		if config.(android.Config).UseOpenJDK9() {
 			return "prebuilts/jdk/jdk9/${hostPrebuiltTag}", nil
 		}
 		return "prebuilts/jdk/jdk8/${hostPrebuiltTag}", nil
@@ -71,6 +73,7 @@
 	pctx.SourcePathVariable("JavadocCmd", "${JavaToolchain}/javadoc")
 	pctx.SourcePathVariable("JlinkCmd", "${JavaToolchain}/jlink")
 	pctx.SourcePathVariable("JmodCmd", "${JavaToolchain}/jmod")
+	pctx.SourcePathVariable("JrtFsJar", "${JavaHome}/lib/jrt-fs.jar")
 
 	pctx.SourcePathVariable("JarArgsCmd", "build/soong/scripts/jar-args.sh")
 	pctx.StaticVariable("SoongZipCmd", filepath.Join("${bootstrap.ToolDir}", "soong_zip"))
@@ -86,17 +89,3 @@
 		return "", nil
 	})
 }
-
-func StripJavac9Flags(flags []string) []string {
-	var ret []string
-	for _, f := range flags {
-		switch {
-		case strings.HasPrefix(f, "-J--add-modules="):
-			// drop
-		default:
-			ret = append(ret, f)
-		}
-	}
-
-	return ret
-}
diff --git a/java/config/makevars.go b/java/config/makevars.go
index 937d597..1453a07 100644
--- a/java/config/makevars.go
+++ b/java/config/makevars.go
@@ -27,8 +27,13 @@
 func makeVarsProvider(ctx android.MakeVarsContext) {
 	ctx.Strict("TARGET_DEFAULT_JAVA_LIBRARIES", strings.Join(DefaultLibraries, " "))
 	ctx.Strict("TARGET_DEFAULT_BOOTCLASSPATH_LIBRARIES", strings.Join(DefaultBootclasspathLibraries, " "))
+	ctx.Strict("DEFAULT_SYSTEM_MODULES", DefaultSystemModules)
 
-	ctx.Strict("DEFAULT_JAVA_LANGUAGE_VERSION", "${DefaultJavaVersion}")
+	if ctx.Config().TargetOpenJDK9() {
+		ctx.Strict("DEFAULT_JAVA_LANGUAGE_VERSION", "1.9")
+	} else {
+		ctx.Strict("DEFAULT_JAVA_LANGUAGE_VERSION", "1.8")
+	}
 
 	ctx.Strict("ANDROID_JAVA_HOME", "${JavaHome}")
 	ctx.Strict("ANDROID_JAVA_TOOLCHAIN", "${JavaToolchain}")
@@ -47,7 +52,7 @@
 		ctx.Strict("HOST_JAVAC", "${JavacCmd} ${CommonJdkFlags}")
 	}
 
-	if ctx.Config().IsEnvTrue("EXPERIMENTAL_USE_OPENJDK9") {
+	if ctx.Config().UseOpenJDK9() {
 		ctx.Strict("JLINK", "${JlinkCmd}")
 		ctx.Strict("JMOD", "${JmodCmd}")
 	}
diff --git a/java/java.go b/java/java.go
index 5393b06..c3b7557 100644
--- a/java/java.go
+++ b/java/java.go
@@ -116,6 +116,14 @@
 
 	// List of classes to pass to javac to use as annotation processors
 	Annotation_processor_classes []string
+
+	Openjdk9 struct {
+		// List of source files that should only be used when passing -source 1.9
+		Srcs []string
+
+		// List of javac flags that should only be used when passing -source 1.9
+		Javacflags []string
+	}
 }
 
 type CompilerDeviceProperties struct {
@@ -134,6 +142,9 @@
 
 	// If true, export a copy of the module as a -hostdex module for host testing.
 	Hostdex *bool
+
+	// When targeting 1.9, override the modules to use with --system
+	System_modules *string
 }
 
 // Module contains the properties and members used by all java module types
@@ -185,26 +196,39 @@
 	staticLibTag     = dependencyTag{name: "staticlib"}
 	libTag           = dependencyTag{name: "javalib"}
 	bootClasspathTag = dependencyTag{name: "bootclasspath"}
+	systemModulesTag = dependencyTag{name: "system modules"}
 	frameworkResTag  = dependencyTag{name: "framework-res"}
 )
 
 type sdkDep struct {
 	useModule, useFiles, useDefaultLibs, invalidVersion bool
 
-	module string
-	jar    android.Path
-	aidl   android.Path
+	module        string
+	systemModules string
+
+	jar  android.Path
+	aidl android.Path
+}
+
+func sdkStringToNumber(ctx android.BaseContext, v string) int {
+	switch v {
+	case "", "current", "system_current", "test_current":
+		return 10000
+	default:
+		if i, err := strconv.Atoi(v); err != nil {
+			ctx.PropertyErrorf("sdk_version", "invalid sdk version")
+			return -1
+		} else {
+			return i
+		}
+	}
 }
 
 func decodeSdkDep(ctx android.BaseContext, v string) sdkDep {
-	switch v {
-	case "", "current", "system_current", "test_current":
-		// OK
-	default:
-		if _, err := strconv.Atoi(v); err != nil {
-			ctx.PropertyErrorf("sdk_version", "invalid sdk version")
-			return sdkDep{}
-		}
+	i := sdkStringToNumber(ctx, v)
+	if i == -1 {
+		// Invalid sdk version, error handled by sdkStringToNumber.
+		return sdkDep{}
 	}
 
 	toFile := func(v string) sdkDep {
@@ -240,8 +264,9 @@
 
 	toModule := func(m string) sdkDep {
 		return sdkDep{
-			useModule: true,
-			module:    m,
+			useModule:     true,
+			module:        m,
+			systemModules: m + "_system_modules",
 		}
 	}
 
@@ -266,20 +291,31 @@
 }
 
 func (j *Module) deps(ctx android.BottomUpMutatorContext) {
-	if !proptools.Bool(j.properties.No_standard_libs) {
-		if ctx.Device() {
+	if ctx.Device() {
+		if !proptools.Bool(j.properties.No_standard_libs) {
 			sdkDep := decodeSdkDep(ctx, j.deviceProperties.Sdk_version)
 			if sdkDep.useDefaultLibs {
 				ctx.AddDependency(ctx.Module(), bootClasspathTag, config.DefaultBootclasspathLibraries...)
+				if ctx.AConfig().TargetOpenJDK9() {
+					ctx.AddDependency(ctx.Module(), systemModulesTag, config.DefaultSystemModules)
+				}
 				if !proptools.Bool(j.properties.No_framework_libs) {
 					ctx.AddDependency(ctx.Module(), libTag, config.DefaultLibraries...)
 				}
-			}
-			if sdkDep.useModule {
+			} else if sdkDep.useModule {
+				if ctx.AConfig().TargetOpenJDK9() {
+					ctx.AddDependency(ctx.Module(), systemModulesTag, sdkDep.systemModules)
+				}
 				ctx.AddDependency(ctx.Module(), bootClasspathTag, sdkDep.module)
 			}
+		} else if j.deviceProperties.System_modules == nil {
+			ctx.PropertyErrorf("no_standard_libs",
+				"system_modules is required to be set when no_standard_libs is true, did you mean no_framework_libs?")
+		} else if *j.deviceProperties.System_modules != "none" && ctx.AConfig().TargetOpenJDK9() {
+			ctx.AddDependency(ctx.Module(), systemModulesTag, *j.deviceProperties.System_modules)
 		}
 	}
+
 	ctx.AddDependency(ctx.Module(), libTag, j.properties.Libs...)
 	ctx.AddDependency(ctx.Module(), staticLibTag, j.properties.Static_libs...)
 	ctx.AddDependency(ctx.Module(), libTag, j.properties.Annotation_processors...)
@@ -335,6 +371,7 @@
 	staticJarResources android.Paths
 	aidlIncludeDirs    android.Paths
 	srcFileLists       android.Paths
+	systemModules      android.Path
 	aidlPreprocess     android.OptionalPath
 }
 
@@ -358,6 +395,15 @@
 			switch tag {
 			case android.DefaultsDepTag, android.SourceDepTag:
 				// Nothing to do
+			case systemModulesTag:
+				if deps.systemModules != nil {
+					panic("Found two system module dependencies")
+				}
+				sm := module.(*SystemModules)
+				if sm.outputFile == nil {
+					panic("Missing directory for system module dependency")
+				}
+				deps.systemModules = sm.outputFile
 			default:
 				ctx.ModuleErrorf("depends on non-java module %q", otherName)
 			}
@@ -397,19 +443,29 @@
 	var flags javaBuilderFlags
 
 	javacFlags := j.properties.Javacflags
-	if ctx.AConfig().Getenv("EXPERIMENTAL_USE_OPENJDK9") == "" {
-		javacFlags = config.StripJavac9Flags(javacFlags)
+	if ctx.AConfig().TargetOpenJDK9() {
+		javacFlags = append(javacFlags, j.properties.Openjdk9.Javacflags...)
+		j.properties.Srcs = append(j.properties.Srcs, j.properties.Openjdk9.Srcs...)
 	}
 
+	sdk := sdkStringToNumber(ctx, j.deviceProperties.Sdk_version)
 	if j.properties.Java_version != nil {
 		flags.javaVersion = *j.properties.Java_version
+	} else if ctx.Device() && sdk <= 23 {
+		flags.javaVersion = "1.7"
+	} else if ctx.Device() && sdk <= 26 || !ctx.AConfig().TargetOpenJDK9() {
+		flags.javaVersion = "1.8"
 	} else {
-		flags.javaVersion = "${config.DefaultJavaVersion}"
+		flags.javaVersion = "1.9"
 	}
 
 	flags.bootClasspath.AddPaths(deps.bootClasspath)
 	flags.classpath.AddPaths(deps.classpath)
 
+	if deps.systemModules != nil {
+		flags.systemModules = append(flags.systemModules, deps.systemModules)
+	}
+
 	if len(javacFlags) > 0 {
 		ctx.Variable(pctx, "javacFlags", strings.Join(javacFlags, " "))
 		flags.javacFlags = "$javacFlags"
diff --git a/java/java_test.go b/java/java_test.go
index a86973d..4729313 100644
--- a/java/java_test.go
+++ b/java/java_test.go
@@ -50,9 +50,12 @@
 
 	os.Exit(run())
 }
-
 func testJava(t *testing.T, bp string) *android.TestContext {
-	config := android.TestArchConfig(buildDir, nil)
+	return testJavaWithEnv(t, bp, nil)
+}
+
+func testJavaWithEnv(t *testing.T, bp string, env map[string]string) *android.TestContext {
+	config := android.TestArchConfig(buildDir, env)
 
 	ctx := android.NewTestArchContext()
 	ctx.RegisterModuleType("android_app", android.ModuleFactoryAdaptor(AndroidAppFactory))
@@ -60,6 +63,7 @@
 	ctx.RegisterModuleType("java_library_host", android.ModuleFactoryAdaptor(LibraryHostFactory))
 	ctx.RegisterModuleType("java_import", android.ModuleFactoryAdaptor(ImportFactory))
 	ctx.RegisterModuleType("java_defaults", android.ModuleFactoryAdaptor(defaultsFactory))
+	ctx.RegisterModuleType("java_system_modules", android.ModuleFactoryAdaptor(SystemModulesFactory))
 	ctx.RegisterModuleType("filegroup", android.ModuleFactoryAdaptor(genrule.FileGroupFactory))
 	ctx.RegisterModuleType("genrule", android.ModuleFactoryAdaptor(genrule.GenRuleFactory))
 	ctx.PreArchMutators(android.RegisterPrebuiltsPreArchMutators)
@@ -84,10 +88,28 @@
 				name: "%s",
 				srcs: ["a.java"],
 				no_standard_libs: true,
+				system_modules: "core-system-modules",
 			}
 		`, extra)
 	}
 
+	if config.TargetOpenJDK9() {
+		systemModules := []string{
+			"core-system-modules",
+			"android_stubs_current_system_modules",
+			"android_system_stubs_current_system_modules",
+			"android_test_stubs_current_system_modules",
+		}
+
+		for _, extra := range systemModules {
+			bp += fmt.Sprintf(`
+			java_system_modules {
+				name: "%s",
+			}
+		`, extra)
+		}
+	}
+
 	ctx.MockFileSystem(map[string][]byte{
 		"Android.bp": []byte(bp),
 		"a.java":     nil,
@@ -190,17 +212,20 @@
 	host          android.OsClass
 	properties    string
 	bootclasspath []string
+	system        string
 	classpath     []string
 }{
 	{
 		name:          "default",
 		bootclasspath: []string{"core-oj", "core-libart"},
+		system:        "core-system-modules",
 		classpath:     []string{"ext", "framework", "okhttp"},
 	},
 	{
 		name:          "blank sdk version",
 		properties:    `sdk_version: "",`,
 		bootclasspath: []string{"core-oj", "core-libart"},
+		system:        "core-system-modules",
 		classpath:     []string{"ext", "framework", "okhttp"},
 	},
 	{
@@ -208,6 +233,7 @@
 		name:          "sdk v14",
 		properties:    `sdk_version: "14",`,
 		bootclasspath: []string{`""`},
+		system:        "bootclasspath", // special value to tell 1.9 test to expect bootclasspath
 		classpath:     []string{"prebuilts/sdk/14/android.jar"},
 	},
 	{
@@ -215,6 +241,7 @@
 		name:          "current",
 		properties:    `sdk_version: "current",`,
 		bootclasspath: []string{"android_stubs_current"},
+		system:        "android_stubs_current_system_modules",
 		classpath:     []string{},
 	},
 	{
@@ -222,6 +249,7 @@
 		name:          "system_current",
 		properties:    `sdk_version: "system_current",`,
 		bootclasspath: []string{"android_system_stubs_current"},
+		system:        "android_system_stubs_current_system_modules",
 		classpath:     []string{},
 	},
 	{
@@ -229,12 +257,22 @@
 		name:          "test_current",
 		properties:    `sdk_version: "test_current",`,
 		bootclasspath: []string{"android_test_stubs_current"},
+		system:        "android_test_stubs_current_system_modules",
 		classpath:     []string{},
 	},
 	{
 
 		name:          "nostdlib",
-		properties:    `no_standard_libs: true`,
+		properties:    `no_standard_libs: true, system_modules: "none"`,
+		system:        "none",
+		bootclasspath: []string{`""`},
+		classpath:     []string{},
+	},
+	{
+
+		name:          "nostdlib system_modules",
+		properties:    `no_standard_libs: true, system_modules: "core-system-modules"`,
+		system:        "core-system-modules",
 		bootclasspath: []string{`""`},
 		classpath:     []string{},
 	},
@@ -263,7 +301,7 @@
 	{
 		name:       "host supported nostdlib",
 		host:       android.Host,
-		properties: `host_supported: true, no_standard_libs: true`,
+		properties: `host_supported: true, no_standard_libs: true, system_modules: "none"`,
 		classpath:  []string{},
 	},
 }
@@ -275,12 +313,17 @@
 			if testcase.moduleType != "" {
 				moduleType = testcase.moduleType
 			}
-			ctx := testJava(t, moduleType+` {
+
+			bp := moduleType + ` {
 				name: "foo",
 				srcs: ["a.java"],
-				`+testcase.properties+`
+				` + testcase.properties + `
+			}`
+
+			variant := "android_common"
+			if testcase.host == android.Host {
+				variant = android.BuildOs.String() + "_common"
 			}
-			`)
 
 			convertModulesToPaths := func(cp []string) []string {
 				ret := make([]string, len(cp))
@@ -293,33 +336,63 @@
 			bootclasspath := convertModulesToPaths(testcase.bootclasspath)
 			classpath := convertModulesToPaths(testcase.classpath)
 
-			variant := "android_common"
-			if testcase.host == android.Host {
-				variant = android.BuildOs.String() + "_common"
-			}
-			javac := ctx.ModuleForTests("foo", variant).Rule("javac")
-
-			got := strings.TrimPrefix(javac.Args["bootClasspath"], "-bootclasspath ")
 			bc := strings.Join(bootclasspath, ":")
-			if got != bc {
-				t.Errorf("bootclasspath expected %q != got %q", bc, got)
+			if bc != "" {
+				bc = "-bootclasspath " + bc
 			}
 
-			got = strings.TrimPrefix(javac.Args["classpath"], "-classpath ")
 			c := strings.Join(classpath, ":")
-			if got != c {
-				t.Errorf("classpath expected %q != got %q", c, got)
+			if c != "" {
+				c = "-classpath " + c
+			}
+			system := ""
+			if testcase.system == "none" {
+				system = "--system=none"
+			} else if testcase.system != "" {
+				system = "--system=" + filepath.Join(buildDir, ".intermediates", testcase.system, "android_common", "system") + "/"
 			}
 
-			var deps []string
-			if len(bootclasspath) > 0 && bootclasspath[0] != `""` {
-				deps = append(deps, bootclasspath...)
-			}
-			deps = append(deps, classpath...)
+			t.Run("1.8", func(t *testing.T) {
+				// Test default javac 1.8
+				ctx := testJava(t, bp)
 
-			if !reflect.DeepEqual(javac.Implicits.Strings(), deps) {
-				t.Errorf("implicits expected %q != got %q", deps, javac.Implicits.Strings())
-			}
+				javac := ctx.ModuleForTests("foo", variant).Rule("javac")
+
+				got := javac.Args["bootClasspath"]
+				if got != bc {
+					t.Errorf("bootclasspath expected %q != got %q", bc, got)
+				}
+
+				got = javac.Args["classpath"]
+				if got != c {
+					t.Errorf("classpath expected %q != got %q", c, got)
+				}
+
+				var deps []string
+				if len(bootclasspath) > 0 && bootclasspath[0] != `""` {
+					deps = append(deps, bootclasspath...)
+				}
+				deps = append(deps, classpath...)
+
+				if !reflect.DeepEqual(javac.Implicits.Strings(), deps) {
+					t.Errorf("implicits expected %q != got %q", deps, javac.Implicits.Strings())
+				}
+			})
+
+			// Test again with javac 1.9
+			t.Run("1.9", func(t *testing.T) {
+				ctx := testJavaWithEnv(t, bp, map[string]string{"EXPERIMENTAL_USE_OPENJDK9": "true"})
+
+				javac := ctx.ModuleForTests("foo", variant).Rule("javac")
+				got := javac.Args["bootClasspath"]
+				expected := system
+				if testcase.system == "bootclasspath" {
+					expected = bc
+				}
+				if got != expected {
+					t.Errorf("bootclasspath expected %q != got %q", expected, got)
+				}
+			})
 		})
 	}
 
diff --git a/java/system_modules.go b/java/system_modules.go
new file mode 100644
index 0000000..ddfc5cf
--- /dev/null
+++ b/java/system_modules.go
@@ -0,0 +1,144 @@
+// Copyright 2017 Google Inc. All rights reserved.
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package java
+
+import (
+	"fmt"
+	"io"
+	"strings"
+
+	"github.com/google/blueprint"
+
+	"android/soong/android"
+)
+
+// OpenJDK 9 introduces the concept of "system modules", which replace the bootclasspath.  This
+// file will produce the rules necessary to convert each unique set of bootclasspath jars into
+// system modules in a runtime image using the jmod and jlink tools.
+
+func init() {
+	android.RegisterModuleType("java_system_modules", SystemModulesFactory)
+
+	pctx.SourcePathVariable("moduleInfoJavaPath", "build/soong/scripts/jars-to-module-info-java.sh")
+}
+
+var (
+	jarsTosystemModules = pctx.AndroidStaticRule("jarsTosystemModules", blueprint.RuleParams{
+		Command: `rm -rf ${outDir} ${workDir} && mkdir -p ${workDir}/jmod && ` +
+			`${moduleInfoJavaPath} ${moduleName} $in > ${workDir}/module-info.java && ` +
+			`${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 ` +
+			`  --class-path ${workDir}/module.jar ${workDir}/jmod/${moduleName}.jmod && ` +
+			`${config.JlinkCmd} --module-path ${workDir}/jmod --add-modules ${moduleName} --output ${outDir} && ` +
+			`cp ${config.JrtFsJar} ${outDir}/lib/`,
+		CommandDeps: []string{
+			"${moduleInfoJavaPath}",
+			"${config.JavacCmd}",
+			"${config.SoongZipCmd}",
+			"${config.MergeZipsCmd}",
+			"${config.JmodCmd}",
+			"${config.JlinkCmd}",
+			"${config.JrtFsJar}",
+		},
+	},
+		"moduleName", "classpath", "outDir", "workDir")
+)
+
+func TransformJarsToSystemModules(ctx android.ModuleContext, moduleName string, jars android.Paths) android.WritablePath {
+	outDir := android.PathForModuleOut(ctx, "system")
+	workDir := android.PathForModuleOut(ctx, "modules")
+	outputFile := android.PathForModuleOut(ctx, "system/lib/modules")
+	outputs := android.WritablePaths{
+		outputFile,
+		android.PathForModuleOut(ctx, "system/lib/jrt-fs.jar"),
+		android.PathForModuleOut(ctx, "system/release"),
+	}
+
+	ctx.ModuleBuild(pctx, android.ModuleBuildParams{
+		Rule:        jarsTosystemModules,
+		Description: "system modules",
+		Outputs:     outputs,
+		Inputs:      jars,
+		Args: map[string]string{
+			"moduleName": moduleName,
+			"classpath":  strings.Join(jars.Strings(), ":"),
+			"workDir":    workDir.String(),
+			"outDir":     outDir.String(),
+		},
+	})
+
+	return outputFile
+}
+
+func SystemModulesFactory() android.Module {
+	module := &SystemModules{}
+	module.AddProperties(&module.properties)
+	android.InitAndroidArchModule(module, android.HostAndDeviceSupported, android.MultilibCommon)
+	return module
+}
+
+type SystemModules struct {
+	android.ModuleBase
+
+	properties SystemModulesProperties
+
+	outputFile android.Path
+}
+
+type SystemModulesProperties struct {
+	// List of java library modules that should be included in the system modules
+	Libs []string
+
+	// List of prebuilt jars that should be included in the system modules
+	Jars []string
+
+	// Sdk version that should be included in the system modules
+	Sdk_version *string
+}
+
+func (system *SystemModules) GenerateAndroidBuildActions(ctx android.ModuleContext) {
+	var jars android.Paths
+
+	ctx.VisitDirectDeps(func(module blueprint.Module) {
+		if ctx.OtherModuleDependencyTag(module) == libTag {
+			dep, _ := module.(Dependency)
+			jars = append(jars, dep.ClasspathFiles()...)
+		}
+	})
+
+	jars = append(jars, android.PathsForModuleSrc(ctx, system.properties.Jars)...)
+
+	if ctx.AConfig().TargetOpenJDK9() {
+		system.outputFile = TransformJarsToSystemModules(ctx, "java.base", jars)
+	}
+}
+
+func (system *SystemModules) DepsMutator(ctx android.BottomUpMutatorContext) {
+	ctx.AddDependency(ctx.Module(), libTag, system.properties.Libs...)
+}
+
+func (system *SystemModules) AndroidMk() android.AndroidMkData {
+	return android.AndroidMkData{
+		Custom: func(w io.Writer, name, prefix, moduleDir string, data android.AndroidMkData) {
+			if system.outputFile != nil {
+				makevar := "SOONG_SYSTEM_MODULES_" + name
+				fmt.Fprintln(w)
+				fmt.Fprintln(w, makevar, ":=", system.outputFile.String())
+				fmt.Fprintln(w, ".KATI_READONLY", ":=", makevar)
+			}
+		},
+	}
+}
diff --git a/scripts/jars-to-module-info-java.sh b/scripts/jars-to-module-info-java.sh
new file mode 100755
index 0000000..44be549
--- /dev/null
+++ b/scripts/jars-to-module-info-java.sh
@@ -0,0 +1,20 @@
+#!/bin/bash -e
+
+# Extracts the Java package names of all classes in the .jar files and writes a module-info.java
+# file to stdout that exports all of those packages.
+
+if [ -z "$1" ]; then
+  echo "usage: $0 <module name> <jar1> [<jar2> ...]" >&2
+  exit 1
+fi
+
+module_name=$1
+shift
+
+echo "module ${module_name} {"
+for j in "$@"; do zipinfo -1 $j ; done \
+  | grep -E '/[^/]*\.class$' \
+  | sed 's|\(.*\)/[^/]*\.class$|    exports \1;|g' \
+  | sed 's|/|.|g' \
+  | sort -u
+echo "}"