Mixed bazel/soong build prototype for genrule

With this change, bazel_module is a specifiable property on
genrule module definitions. With bazel-enabled mode, soong_build will
defer to Bazel for information on these modules.

source build/soong/bazelenv.sh to enter bazel-enabled mode.

Test: Manually verified on bionic/libc genrules using aosp_cf_x86_phone-userdebug
Change-Id: I3619848186d50be7273a5eba31c79989b981d408

android/Android.bp

@@ -15,6 +15,7 @@ bootstrap_go_package {
         "apex.go",
         "api_levels.go",
         "arch.go",
+        "bazel_handler.go",
         "bazel_overlay.go",
         "config.go",
         "csuite_config.go",

android/bazel_handler.go

@@ -0,0 +1,239 @@
+// Copyright 2020 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 android
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"os"
+	"os/exec"
+	"runtime"
+	"strings"
+	"sync"
+)
+
+// Map key to describe bazel cquery requests.
+type cqueryKey struct {
+	label        string
+	starlarkExpr string
+}
+
+type BazelContext interface {
+	// The below methods involve queuing cquery requests to be later invoked
+	// by bazel. If any of these methods return (_, false), then the request
+	// has been queued to be run later.
+
+	// Returns result files built by building the given bazel target label.
+	GetAllFiles(label string) ([]string, bool)
+
+	// TODO(cparsons): Other cquery-related methods should be added here.
+	// ** End cquery methods
+
+	// Issues commands to Bazel to receive results for all cquery requests
+	// queued in the BazelContext.
+	InvokeBazel() error
+
+	// Returns true if bazel is enabled for the given configuration.
+	BazelEnabled() bool
+}
+
+// A context object which tracks queued requests that need to be made to Bazel,
+// and their results after the requests have been made.
+type bazelContext struct {
+	homeDir      string
+	bazelPath    string
+	outputBase   string
+	workspaceDir string
+
+	requests     map[cqueryKey]bool // cquery requests that have not yet been issued to Bazel
+	requestMutex sync.Mutex         // requests can be written in parallel
+
+	results map[cqueryKey]string // Results of cquery requests after Bazel invocations
+}
+
+var _ BazelContext = &bazelContext{}
+
+// A bazel context to use when Bazel is disabled.
+type noopBazelContext struct{}
+
+var _ BazelContext = noopBazelContext{}
+
+// A bazel context to use for tests.
+type MockBazelContext struct {
+	AllFiles map[string][]string
+}
+
+func (m MockBazelContext) GetAllFiles(label string) ([]string, bool) {
+	result, ok := m.AllFiles[label]
+	return result, ok
+}
+
+func (m MockBazelContext) InvokeBazel() error {
+	panic("unimplemented")
+}
+
+func (m MockBazelContext) BazelEnabled() bool {
+	return true
+}
+
+var _ BazelContext = MockBazelContext{}
+
+func (bazelCtx *bazelContext) GetAllFiles(label string) ([]string, bool) {
+	starlarkExpr := "', '.join([f.path for f in target.files.to_list()])"
+	result, ok := bazelCtx.cquery(label, starlarkExpr)
+	if ok {
+		bazelOutput := strings.TrimSpace(result)
+		return strings.Split(bazelOutput, ", "), true
+	} else {
+		return nil, false
+	}
+}
+
+func (n noopBazelContext) GetAllFiles(label string) ([]string, bool) {
+	panic("unimplemented")
+}
+
+func (n noopBazelContext) InvokeBazel() error {
+	panic("unimplemented")
+}
+
+func (n noopBazelContext) BazelEnabled() bool {
+	return false
+}
+
+func NewBazelContext(c *config) (BazelContext, error) {
+	if c.Getenv("USE_BAZEL") != "1" {
+		return noopBazelContext{}, nil
+	}
+
+	bazelCtx := bazelContext{requests: make(map[cqueryKey]bool)}
+	missingEnvVars := []string{}
+	if len(c.Getenv("BAZEL_HOME")) > 1 {
+		bazelCtx.homeDir = c.Getenv("BAZEL_HOME")
+	} else {
+		missingEnvVars = append(missingEnvVars, "BAZEL_HOME")
+	}
+	if len(c.Getenv("BAZEL_PATH")) > 1 {
+		bazelCtx.bazelPath = c.Getenv("BAZEL_PATH")
+	} else {
+		missingEnvVars = append(missingEnvVars, "BAZEL_PATH")
+	}
+	if len(c.Getenv("BAZEL_OUTPUT_BASE")) > 1 {
+		bazelCtx.outputBase = c.Getenv("BAZEL_OUTPUT_BASE")
+	} else {
+		missingEnvVars = append(missingEnvVars, "BAZEL_OUTPUT_BASE")
+	}
+	if len(c.Getenv("BAZEL_WORKSPACE")) > 1 {
+		bazelCtx.workspaceDir = c.Getenv("BAZEL_WORKSPACE")
+	} else {
+		missingEnvVars = append(missingEnvVars, "BAZEL_WORKSPACE")
+	}
+	if len(missingEnvVars) > 0 {
+		return nil, errors.New(fmt.Sprintf("missing required env vars to use bazel: %s", missingEnvVars))
+	} else {
+		return &bazelCtx, nil
+	}
+}
+
+func (context *bazelContext) BazelEnabled() bool {
+	return true
+}
+
+// Adds a cquery request to the Bazel request queue, to be later invoked, or
+// returns the result of the given request if the request was already made.
+// If the given request was already made (and the results are available), then
+// returns (result, true). If the request is queued but no results are available,
+// then returns ("", false).
+func (context *bazelContext) cquery(label string, starlarkExpr string) (string, bool) {
+	key := cqueryKey{label, starlarkExpr}
+	if result, ok := context.results[key]; ok {
+		return result, true
+	} else {
+		context.requestMutex.Lock()
+		defer context.requestMutex.Unlock()
+		context.requests[key] = true
+		return "", false
+	}
+}
+
+func pwdPrefix() string {
+	// Darwin doesn't have /proc
+	if runtime.GOOS != "darwin" {
+		return "PWD=/proc/self/cwd"
+	}
+	return ""
+}
+
+func (context *bazelContext) issueBazelCommand(command string, labels []string,
+	extraFlags ...string) (string, error) {
+
+	cmdFlags := []string{"--output_base=" + context.outputBase, command}
+	cmdFlags = append(cmdFlags, labels...)
+	cmdFlags = append(cmdFlags, extraFlags...)
+
+	bazelCmd := exec.Command(context.bazelPath, cmdFlags...)
+	bazelCmd.Dir = context.workspaceDir
+	bazelCmd.Env = append(os.Environ(), "HOME="+context.homeDir, pwdPrefix())
+
+	var stderr bytes.Buffer
+	bazelCmd.Stderr = &stderr
+
+	if output, err := bazelCmd.Output(); err != nil {
+		return "", fmt.Errorf("bazel command failed. command: [%s], error [%s]", bazelCmd, stderr)
+	} else {
+		return string(output), nil
+	}
+}
+
+// Issues commands to Bazel to receive results for all cquery requests
+// queued in the BazelContext.
+func (context *bazelContext) InvokeBazel() error {
+	context.results = make(map[cqueryKey]string)
+
+	var labels []string
+	var cqueryOutput string
+	var err error
+	for val, _ := range context.requests {
+		labels = append(labels, val.label)
+
+		// TODO(cparsons): Combine requests into a batch cquery request.
+		// TODO(cparsons): Use --query_file to avoid command line limits.
+		cqueryOutput, err = context.issueBazelCommand("cquery", []string{val.label},
+			"--output=starlark",
+			"--starlark:expr="+val.starlarkExpr)
+
+		if err != nil {
+			return err
+		} else {
+			context.results[val] = string(cqueryOutput)
+		}
+	}
+
+	// Issue a build command.
+	// TODO(cparsons): Invoking bazel execution during soong_build should be avoided;
+	// bazel actions should either be added to the Ninja file and executed later,
+	// or bazel should handle execution.
+	// TODO(cparsons): Use --target_pattern_file to avoid command line limits.
+	_, err = context.issueBazelCommand("build", labels)
+
+	if err != nil {
+		return err
+	}
+
+	// Clear requests.
+	context.requests = map[cqueryKey]bool{}
+	return nil
+}

android/config.go

@@ -85,6 +85,8 @@ type config struct {
 	// Only available on configs created by TestConfig
 	TestProductVariables *productVariables
 
+	BazelContext BazelContext
+
 	PrimaryBuilder           string
 	ConfigFileName           string
 	ProductVariablesFileName string
@@ -248,6 +250,8 @@ func TestConfig(buildDir string, env map[string]string, bp string, fs map[string
 		// Set testAllowNonExistentPaths so that test contexts don't need to specify every path
 		// passed to PathForSource or PathForModuleSrc.
 		testAllowNonExistentPaths: true,
+
+		BazelContext: noopBazelContext{},
 	}
 	config.deviceConfig = &deviceConfig{
 		config: config,
@@ -324,6 +328,20 @@ func TestArchConfig(buildDir string, env map[string]string, bp string, fs map[st
 	return testConfig
 }
 
+// Returns a config object which is "reset" for another bootstrap run.
+// Only per-run data is reset. Data which needs to persist across multiple
+// runs in the same program execution is carried over (such as Bazel context
+// or environment deps).
+func ConfigForAdditionalRun(c Config) (Config, error) {
+	newConfig, err := NewConfig(c.srcDir, c.buildDir, c.moduleListFile)
+	if err != nil {
+		return Config{}, err
+	}
+	newConfig.BazelContext = c.BazelContext
+	newConfig.envDeps = c.envDeps
+	return newConfig, nil
+}
+
 // New creates a new Config object.  The srcDir argument specifies the path to
 // the root source directory. It also loads the config file, if found.
 func NewConfig(srcDir, buildDir string, moduleListFile string) (Config, error) {
@@ -425,6 +443,10 @@ func NewConfig(srcDir, buildDir string, moduleListFile string) (Config, error) {
 		Bool(config.productVariables.GcovCoverage) ||
 			Bool(config.productVariables.ClangCoverage))
 
+	config.BazelContext, err = NewBazelContext(config)
+	if err != nil {
+		return Config{}, err
+	}
 	return Config{config}, nil
 }
 

android/makevars.go

@@ -128,7 +128,7 @@ var _ PathContext = MakeVarsContext(nil)
 type MakeVarsProvider func(ctx MakeVarsContext)
 
 func RegisterMakeVarsProvider(pctx PackageContext, provider MakeVarsProvider) {
-	makeVarsProviders = append(makeVarsProviders, makeVarsProvider{pctx, provider})
+	makeVarsInitProviders = append(makeVarsInitProviders, makeVarsProvider{pctx, provider})
 }
 
 // SingletonMakeVarsProvider is a Singleton with an extra method to provide extra values to be exported to Make.
@@ -142,7 +142,8 @@ type SingletonMakeVarsProvider interface {
 // registerSingletonMakeVarsProvider adds a singleton that implements SingletonMakeVarsProvider to the list of
 // MakeVarsProviders to run.
 func registerSingletonMakeVarsProvider(singleton SingletonMakeVarsProvider) {
-	makeVarsProviders = append(makeVarsProviders, makeVarsProvider{pctx, SingletonmakeVarsProviderAdapter(singleton)})
+	singletonMakeVarsProviders = append(singletonMakeVarsProviders,
+		makeVarsProvider{pctx, SingletonmakeVarsProviderAdapter(singleton)})
 }
 
 // SingletonmakeVarsProviderAdapter converts a SingletonMakeVarsProvider to a MakeVarsProvider.
@@ -171,7 +172,11 @@ type makeVarsProvider struct {
 	call MakeVarsProvider
 }
 
-var makeVarsProviders []makeVarsProvider
+// Collection of makevars providers that are registered in init() methods.
+var makeVarsInitProviders []makeVarsProvider
+
+// Collection of singleton makevars providers that are not registered as part of init() methods.
+var singletonMakeVarsProviders []makeVarsProvider
 
 type makeVarsContext struct {
 	SingletonContext
@@ -219,7 +224,7 @@ func (s *makeVarsSingleton) GenerateBuildActions(ctx SingletonContext) {
 	var vars []makeVarsVariable
 	var dists []dist
 	var phonies []phony
-	for _, provider := range makeVarsProviders {
+	for _, provider := range append(makeVarsInitProviders) {
 		mctx := &makeVarsContext{
 			SingletonContext: ctx,
 			pctx:             provider.pctx,
@@ -232,6 +237,25 @@ func (s *makeVarsSingleton) GenerateBuildActions(ctx SingletonContext) {
 		dists = append(dists, mctx.dists...)
 	}
 
+	for _, provider := range append(singletonMakeVarsProviders) {
+		mctx := &makeVarsContext{
+			SingletonContext: ctx,
+			pctx:             provider.pctx,
+		}
+
+		provider.call(mctx)
+
+		vars = append(vars, mctx.vars...)
+		phonies = append(phonies, mctx.phonies...)
+		dists = append(dists, mctx.dists...)
+	}
+
+	// Clear singleton makevars providers after use. Since these are in-memory
+	// singletons, this ensures state is reset if the build tree is processed
+	// multiple times.
+	// TODO(cparsons): Clean up makeVarsProviders to be part of the context.
+	singletonMakeVarsProviders = nil
+
 	ctx.VisitAllModules(func(m Module) {
 		if provider, ok := m.(ModuleMakeVarsProvider); ok && m.Enabled() {
 			mctx := &makeVarsContext{

bazel/bazelenv.sh

@@ -0,0 +1,74 @@
+#!/bin/bash
+
+# Copyright 2020 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.
+
+# Helper script for setting environment variables required for Bazel/Soong
+# mixed builds prototype. For development use only.
+#
+# Usage:
+#   export BAZEL_PATH=[some_bazel_path] && source bazelenv.sh
+#
+# If BAZEL_PATH is not set, `which bazel` will be used
+# to locate the appropriate bazel to use.
+
+
+# Function to find top of the source tree (if $TOP isn't set) by walking up the
+# tree.
+function gettop
+{
+    local TOPFILE=build/soong/root.bp
+    if [ -n "${TOP-}" -a -f "${TOP-}/${TOPFILE}" ] ; then
+        # The following circumlocution ensures we remove symlinks from TOP.
+        (cd $TOP; PWD= /bin/pwd)
+    else
+        if [ -f $TOPFILE ] ; then
+            # The following circumlocution (repeated below as well) ensures
+            # that we record the true directory name and not one that is
+            # faked up with symlink names.
+            PWD= /bin/pwd
+        else
+            local HERE=$PWD
+            T=
+            while [ \( ! \( -f $TOPFILE \) \) -a \( $PWD != "/" \) ]; do
+                \cd ..
+                T=`PWD= /bin/pwd -P`
+            done
+            \cd $HERE
+            if [ -f "$T/$TOPFILE" ]; then
+                echo $T
+            fi
+        fi
+    fi
+}
+
+BASE_DIR="$(mktemp -d)"
+
+if [ -z "$BAZEL_PATH" ] ; then
+    export BAZEL_PATH="$(which bazel)"
+fi
+
+export USE_BAZEL=1
+export BAZEL_HOME="$BASE_DIR/bazelhome"
+export BAZEL_OUTPUT_BASE="$BASE_DIR/output"
+export BAZEL_WORKSPACE="$(gettop)"
+
+echo "USE_BAZEL=${USE_BAZEL}"
+echo "BAZEL_PATH=${BAZEL_PATH}"
+echo "BAZEL_HOME=${BAZEL_HOME}"
+echo "BAZEL_OUTPUT_BASE=${BAZEL_OUTPUT_BASE}"
+echo "BAZEL_WORKSPACE=${BAZEL_WORKSPACE}"
+
+mkdir -p $BAZEL_HOME
+mkdir -p $BAZEL_OUTPUT_BASE

cmd/soong_build/main.go

@@ -51,30 +51,34 @@ func newNameResolver(config android.Config) *android.NameResolver {
 	return android.NewNameResolver(exportFilter)
 }
 
+func newContext(srcDir string, configuration android.Config) *android.Context {
+	ctx := android.NewContext()
+	ctx.Register()
+	if !shouldPrepareBuildActions() {
+		configuration.SetStopBefore(bootstrap.StopBeforePrepareBuildActions)
+	}
+	ctx.SetNameInterface(newNameResolver(configuration))
+	ctx.SetAllowMissingDependencies(configuration.AllowMissingDependencies())
+	return ctx
+}
+
+func newConfig(srcDir string) android.Config {
+	configuration, err := android.NewConfig(srcDir, bootstrap.BuildDir, bootstrap.ModuleListFile)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "%s", err)
+		os.Exit(1)
+	}
+	return configuration
+}
+
 func main() {
 	android.ReexecWithDelveMaybe()
 	flag.Parse()
 
 	// The top-level Blueprints file is passed as the first argument.
 	srcDir := filepath.Dir(flag.Arg(0))
-
-	ctx := android.NewContext()
-	ctx.Register()
-
-	configuration, err := android.NewConfig(srcDir, bootstrap.BuildDir, bootstrap.ModuleListFile)
-	if err != nil {
-		fmt.Fprintf(os.Stderr, "%s", err)
-		os.Exit(1)
-	}
-
-	if !shouldPrepareBuildActions() {
-		configuration.SetStopBefore(bootstrap.StopBeforePrepareBuildActions)
-	}
-
-	ctx.SetNameInterface(newNameResolver(configuration))
-
-	ctx.SetAllowMissingDependencies(configuration.AllowMissingDependencies())
-
+	var ctx *android.Context
+	configuration := newConfig(srcDir)
 	extraNinjaDeps := []string{configuration.ConfigFileName, configuration.ProductVariablesFileName}
 
 	// Read the SOONG_DELVE again through configuration so that there is a dependency on the environment variable
@@ -84,9 +88,31 @@ func main() {
 		// enabled even if it completed successfully.
 		extraNinjaDeps = append(extraNinjaDeps, filepath.Join(configuration.BuildDir(), "always_rerun_for_delve"))
 	}
-
+	if configuration.BazelContext.BazelEnabled() {
+		// Bazel-enabled mode. Soong runs in two passes.
+		// First pass: Analyze the build tree, but only store all bazel commands
+		// needed to correctly evaluate the tree in the second pass.
+		// TODO(cparsons): Don't output any ninja file, as the second pass will overwrite
+		// the incorrect results from the first pass, and file I/O is expensive.
+		firstCtx := newContext(srcDir, configuration)
+		bootstrap.Main(firstCtx.Context, configuration, extraNinjaDeps...)
+		// Invoke bazel commands and save results for second pass.
+		if err := configuration.BazelContext.InvokeBazel(); err != nil {
+			fmt.Fprintf(os.Stderr, "%s", err)
+			os.Exit(1)
+		}
+		// Second pass: Full analysis, using the bazel command results. Output ninja file.
+		secondPassConfig, err := android.ConfigForAdditionalRun(configuration)
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "%s", err)
+			os.Exit(1)
+		}
+		ctx = newContext(srcDir, secondPassConfig)
+		bootstrap.Main(ctx.Context, secondPassConfig, extraNinjaDeps...)
+	} else {
+		ctx = newContext(srcDir, configuration)
 		bootstrap.Main(ctx.Context, configuration, extraNinjaDeps...)
-
+	}
 	if bazelOverlayDir != "" {
 		if err := createBazelOverlay(ctx, bazelOverlayDir); err != nil {
 			fmt.Fprintf(os.Stderr, "%s", err)
@@ -105,7 +131,7 @@ func main() {
 	//  to affect the command line of the primary builder.
 	if shouldPrepareBuildActions() {
 		metricsFile := filepath.Join(bootstrap.BuildDir, "soong_build_metrics.pb")
-		err = android.WriteMetrics(configuration, metricsFile)
+		err := android.WriteMetrics(configuration, metricsFile)
 		if err != nil {
 			fmt.Fprintf(os.Stderr, "error writing soong_build metrics %s: %s", metricsFile, err)
 			os.Exit(1)

genrule/genrule.go

@@ -113,8 +113,10 @@ type generatorProperties struct {
 
 	// input files to exclude
 	Exclude_srcs []string `android:"path,arch_variant"`
-}
 
+	// in bazel-enabled mode, the bazel label to evaluate instead of this module
+	Bazel_module string
+}
 type Module struct {
 	android.ModuleBase
 	android.DefaultableModuleBase
@@ -186,6 +188,20 @@ func toolDepsMutator(ctx android.BottomUpMutatorContext) {
 	}
 }
 
+// Returns true if information was available from Bazel, false if bazel invocation still needs to occur.
+func (c *Module) generateBazelBuildActions(ctx android.ModuleContext, label string) bool {
+	bazelCtx := ctx.Config().BazelContext
+	filePaths, ok := bazelCtx.GetAllFiles(label)
+	if ok {
+		var bazelOutputFiles android.Paths
+		for _, bazelOutputFile := range filePaths {
+			bazelOutputFiles = append(bazelOutputFiles, android.PathForSource(ctx, bazelOutputFile))
+		}
+		c.outputFiles = bazelOutputFiles
+		c.outputDeps = bazelOutputFiles
+	}
+	return ok
+}
 func (g *Module) GenerateAndroidBuildActions(ctx android.ModuleContext) {
 	g.subName = ctx.ModuleSubDir()
 
@@ -456,6 +472,12 @@ func (g *Module) GenerateAndroidBuildActions(ctx android.ModuleContext) {
 
 	g.outputFiles = outputFiles.Paths()
 
+	bazelModuleLabel := g.properties.Bazel_module
+	bazelActionsUsed := false
+	if ctx.Config().BazelContext.BazelEnabled() && len(bazelModuleLabel) > 0 {
+		bazelActionsUsed = g.generateBazelBuildActions(ctx, bazelModuleLabel)
+	}
+	if !bazelActionsUsed {
 		// For <= 6 outputs, just embed those directly in the users. Right now, that covers >90% of
 		// the genrules on AOSP. That will make things simpler to look at the graph in the common
 		// case. For larger sets of outputs, inject a phony target in between to limit ninja file
@@ -464,18 +486,15 @@ func (g *Module) GenerateAndroidBuildActions(ctx android.ModuleContext) {
 			g.outputDeps = g.outputFiles
 		} else {
 			phonyFile := android.PathForModuleGen(ctx, "genrule-phony")
-
 			ctx.Build(pctx, android.BuildParams{
 				Rule:   blueprint.Phony,
 				Output: phonyFile,
 				Inputs: g.outputFiles,
 			})
-
 			g.outputDeps = android.Paths{phonyFile}
 		}
-
 	}
-
+}
 func hashSrcFiles(srcFiles android.Paths) string {
 	h := sha256.New()
 	for _, src := range srcFiles {

genrule/genrule_test.go

@@ -721,6 +721,39 @@ func TestGenruleDefaults(t *testing.T) {
 	}
 }
 
+func TestGenruleWithBazel(t *testing.T) {
+	bp := `
+		genrule {
+				name: "foo",
+				out: ["one.txt", "two.txt"],
+				bazel_module: "//foo/bar:bar",
+		}
+	`
+
+	config := testConfig(bp, nil)
+	config.BazelContext = android.MockBazelContext{
+		AllFiles: map[string][]string{
+			"//foo/bar:bar": []string{"bazelone.txt", "bazeltwo.txt"}}}
+
+	ctx := testContext(config)
+	_, errs := ctx.ParseFileList(".", []string{"Android.bp"})
+	if errs == nil {
+		_, errs = ctx.PrepareBuildActions(config)
+	}
+	if errs != nil {
+		t.Fatal(errs)
+	}
+	gen := ctx.ModuleForTests("foo", "").Module().(*Module)
+
+	expectedOutputFiles := []string{"bazelone.txt", "bazeltwo.txt"}
+	if !reflect.DeepEqual(gen.outputFiles.Strings(), expectedOutputFiles) {
+		t.Errorf("Expected output files: %q, actual: %q", expectedOutputFiles, gen.outputFiles)
+	}
+	if !reflect.DeepEqual(gen.outputDeps.Strings(), expectedOutputFiles) {
+		t.Errorf("Expected output deps: %q, actual: %q", expectedOutputFiles, gen.outputDeps)
+	}
+}
+
 type testTool struct {
 	android.ModuleBase
 	outputFile android.Path