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
diff --git a/android/Android.bp b/android/Android.bp
index a1b5159..7aa228e 100644
--- a/android/Android.bp
+++ b/android/Android.bp
@@ -15,6 +15,7 @@
         "apex.go",
         "api_levels.go",
         "arch.go",
+        "bazel_handler.go",
         "bazel_overlay.go",
         "config.go",
         "csuite_config.go",
diff --git a/android/bazel_handler.go b/android/bazel_handler.go
new file mode 100644
index 0000000..d4f6e4c
--- /dev/null
+++ b/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
+}
diff --git a/android/config.go b/android/config.go
index 8df65f7..345f26e 100644
--- a/android/config.go
+++ b/android/config.go
@@ -85,6 +85,8 @@
 	// Only available on configs created by TestConfig
 	TestProductVariables *productVariables
 
+	BazelContext BazelContext
+
 	PrimaryBuilder           string
 	ConfigFileName           string
 	ProductVariablesFileName string
@@ -248,6 +250,8 @@
 		// 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 @@
 	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 @@
 		Bool(config.productVariables.GcovCoverage) ||
 			Bool(config.productVariables.ClangCoverage))
 
+	config.BazelContext, err = NewBazelContext(config)
+	if err != nil {
+		return Config{}, err
+	}
 	return Config{config}, nil
 }
 
diff --git a/android/makevars.go b/android/makevars.go
index 374986e..3ca7792 100644
--- a/android/makevars.go
+++ b/android/makevars.go
@@ -128,7 +128,7 @@
 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 @@
 // 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 @@
 	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 @@
 	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 @@
 		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{