cmd/soong_build/bazel_overlay.go - android_build_soong - Gitiles

 // 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 main

 import (
 	"android/soong/android"
 	"fmt"
 	"io/ioutil"
 	"os"
 	"path/filepath"
 	"reflect"
 	"strings"

 	"github.com/google/blueprint"
 	"github.com/google/blueprint/proptools"
 )

 const (
 	soongModuleLoad = `package(default_visibility = ["//visibility:public"])
 load("//:soong_module.bzl", "soong_module")

 `

 	// A BUILD file target snippet representing a Soong module
 	soongModuleTarget = `soong_module(
     name = "%s",
     module_name = "%s",
     module_type = "%s",
     module_variant = "%s",
     deps = %s,
 %s)`

 	// The soong_module rule implementation in a .bzl file
 	soongModuleBzl = `SoongModuleInfo = provider(
     fields = {
         "name": "Name of module",
         "type": "Type of module",
         "variant": "Variant of module",
     },
 )

 def _merge_dicts(*dicts):
     """Adds a list of dictionaries into a single dictionary."""

     # If keys are repeated in multiple dictionaries, the latter one "wins".
     result = {}
     for d in dicts:
         result.update(d)

     return result

 def _generic_soong_module_impl(ctx):
     return [
         SoongModuleInfo(
             name = ctx.attr.module_name,
             type = ctx.attr.module_type,
             variant = ctx.attr.module_variant,
         ),
     ]

 _COMMON_ATTRS = {
     "module_name": attr.string(mandatory = True),
     "module_type": attr.string(mandatory = True),
     "module_variant": attr.string(),
     "deps": attr.label_list(providers = [SoongModuleInfo]),
 }


 generic_soong_module = rule(
     implementation = _generic_soong_module_impl,
     attrs = _COMMON_ATTRS,
 )

 # TODO(jingwen): auto generate Soong module shims
 def _soong_filegroup_impl(ctx):
     return [SoongModuleInfo(),]

 soong_filegroup = rule(
     implementation = _soong_filegroup_impl,
     # Matches https://cs.android.com/android/platform/superproject/+/master:build/soong/android/filegroup.go;l=25-40;drc=6a6478d49e78703ba22a432c41d819c8df79ef6c
     attrs = _merge_dicts(_COMMON_ATTRS, {
         "srcs": attr.string_list(doc = "srcs lists files that will be included in this filegroup"),
         "exclude_srcs": attr.string_list(),
         "path": attr.string(doc = "The base path to the files. May be used by other modules to determine which portion of the path to use. For example, when a filegroup is used as data in a cc_test rule, the base path is stripped off the path and the remaining path is used as the installation directory."),
         "export_to_make_var": attr.string(doc = "Create a make variable with the specified name that contains the list of files in the filegroup, relative to the root of the source tree."),
     })
 )

 soong_module_rule_map = {
     "filegroup": soong_filegroup,
 }

 # soong_module is a macro that supports arbitrary kwargs, and uses module_type to
 # expand to the right underlying shim.
 def soong_module(name, module_type, **kwargs):
     soong_module_rule = soong_module_rule_map.get(module_type)

     if soong_module_rule == None:
         # This module type does not have an existing rule to map to, so use the
         # generic_soong_module rule instead.
         generic_soong_module(
             name = name,
             module_type = module_type,
             module_name = kwargs.pop("module_name", ""),
             module_variant = kwargs.pop("module_variant", ""),
             deps = kwargs.pop("deps", []),
         )
     else:
         soong_module_rule(
             name = name,
             module_type = module_type,
             **kwargs,
         )
 `
 )

 func targetNameWithVariant(c *blueprint.Context, logicModule blueprint.Module) string {
 	name := ""
 	if c.ModuleSubDir(logicModule) != "" {
 		// TODO(b/162720883): Figure out a way to drop the "--" variant suffixes.
 		name = c.ModuleName(logicModule) + "--" + c.ModuleSubDir(logicModule)
 	} else {
 		name = c.ModuleName(logicModule)
 	}

 	return strings.Replace(name, "//", "", 1)
 }

 func qualifiedTargetLabel(c *blueprint.Context, logicModule blueprint.Module) string {
 	return "//" +
 		packagePath(c, logicModule) +
 		":" +
 		targetNameWithVariant(c, logicModule)
 }

 func packagePath(c *blueprint.Context, logicModule blueprint.Module) string {
 	return filepath.Dir(c.BlueprintFile(logicModule))
 }

 func escapeString(s string) string {
 	s = strings.ReplaceAll(s, "\\", "\\\\")
 	return strings.ReplaceAll(s, "\"", "\\\"")
 }

 func makeIndent(indent int) string {
 	if indent < 0 {
 		panic(fmt.Errorf("indent column cannot be less than 0, but got %d", indent))
 	}
 	return strings.Repeat("    ", indent)
 }

 // prettyPrint a property value into the equivalent Starlark representation
 // recursively.
 func prettyPrint(propertyValue reflect.Value, indent int) (string, error) {
 	if isZero(propertyValue) {
 		// A property value being set or unset actually matters -- Soong does set default
 		// values for unset properties, like system_shared_libs = ["libc", "libm", "libdl"] at
 		// https://cs.android.com/android/platform/superproject/+/master:build/soong/cc/linker.go;l=281-287;drc=f70926eef0b9b57faf04c17a1062ce50d209e480
 		//
 		// In Bazel-parlance, we would use "attr.<type>(default = <default value>)" to set the default
 		// value of unset attributes.
 		return "", nil
 	}

 	var ret string
 	switch propertyValue.Kind() {
 	case reflect.String:
 		ret = fmt.Sprintf("\"%v\"", escapeString(propertyValue.String()))
 	case reflect.Bool:
 		ret = strings.Title(fmt.Sprintf("%v", propertyValue.Interface()))
 	case reflect.Int, reflect.Uint, reflect.Int64:
 		ret = fmt.Sprintf("%v", propertyValue.Interface())
 	case reflect.Ptr:
 		return prettyPrint(propertyValue.Elem(), indent)
 	case reflect.Slice:
 		ret = "[\n"
 		for i := 0; i < propertyValue.Len(); i++ {
 			indexedValue, err := prettyPrint(propertyValue.Index(i), indent+1)
 			if err != nil {
 				return "", err
 			}

 			if indexedValue != "" {
 				ret += makeIndent(indent + 1)
 				ret += indexedValue
 				ret += ",\n"
 			}
 		}
 		ret += makeIndent(indent)
 		ret += "]"
 	case reflect.Struct:
 		ret = "{\n"
 		// Sort and print the struct props by the key.
 		structProps := extractStructProperties(propertyValue, indent)
 		for _, k := range android.SortedStringKeys(structProps) {
 			ret += makeIndent(indent + 1)
 			ret += "\"" + k + "\": "
 			ret += structProps[k]
 			ret += ",\n"
 		}
 		ret += makeIndent(indent)
 		ret += "}"
 	case reflect.Interface:
 		// TODO(b/164227191): implement pretty print for interfaces.
 		// Interfaces are used for for arch, multilib and target properties.
 		return "", nil
 	default:
 		return "", fmt.Errorf(
 			"unexpected kind for property struct field: %s", propertyValue.Kind())
 	}
 	return ret, nil
 }

 func extractStructProperties(structValue reflect.Value, indent int) map[string]string {
 	if structValue.Kind() != reflect.Struct {
 		panic(fmt.Errorf("Expected a reflect.Struct type, but got %s", structValue.Kind()))
 	}

 	ret := map[string]string{}
 	structType := structValue.Type()
 	for i := 0; i < structValue.NumField(); i++ {
 		field := structType.Field(i)
 		if field.PkgPath != "" {
 			// Skip unexported fields. Some properties are
 			// internal to Soong only, and these fields do not have PkgPath.
 			continue
 		}
 		if proptools.HasTag(field, "blueprint", "mutated") {
 			continue
 		}

 		fieldValue := structValue.Field(i)
 		if isZero(fieldValue) {
 			// Ignore zero-valued fields
 			continue
 		}

 		propertyName := proptools.PropertyNameForField(field.Name)
 		prettyPrintedValue, err := prettyPrint(fieldValue, indent+1)
 		if err != nil {
 			panic(
 				fmt.Errorf(
 					"Error while parsing property: %q. %s",
 					propertyName,
 					err))
 		}
 		if prettyPrintedValue != "" {
 			ret[propertyName] = prettyPrintedValue
 		}
 	}

 	return ret
 }

 func isStructPtr(t reflect.Type) bool {
 	return t.Kind() == reflect.Ptr && t.Elem().Kind() == reflect.Struct
 }

 // Generically extract module properties and types into a map, keyed by the module property name.
 func extractModuleProperties(aModule android.Module) map[string]string {
 	ret := map[string]string{}

 	// Iterate over this android.Module's property structs.
 	for _, properties := range aModule.GetProperties() {
 		propertiesValue := reflect.ValueOf(properties)
 		// Check that propertiesValue is a pointer to the Properties struct, like
 		// *cc.BaseLinkerProperties or *java.CompilerProperties.
 		//
 		// propertiesValue can also be type-asserted to the structs to
 		// manipulate internal props, if needed.
 		if isStructPtr(propertiesValue.Type()) {
 			structValue := propertiesValue.Elem()
 			for k, v := range extractStructProperties(structValue, 0) {
 				ret[k] = v
 			}
 		} else {
 			panic(fmt.Errorf(
 				"properties must be a pointer to a struct, got %T",
 				propertiesValue.Interface()))
 		}

 	}

 	return ret
 }

 func createBazelOverlay(ctx *android.Context, bazelOverlayDir string) error {
 	blueprintCtx := ctx.Context
 	blueprintCtx.VisitAllModules(func(module blueprint.Module) {
 		buildFile, err := buildFileForModule(blueprintCtx, module)
 		if err != nil {
 			panic(err)
 		}

 		buildFile.Write([]byte(generateSoongModuleTarget(blueprintCtx, module) + "\n\n"))
 		buildFile.Close()
 	})

 	if err := writeReadOnlyFile(bazelOverlayDir, "WORKSPACE", ""); err != nil {
 		return err
 	}

 	if err := writeReadOnlyFile(bazelOverlayDir, "BUILD", ""); err != nil {
 		return err
 	}

 	return writeReadOnlyFile(bazelOverlayDir, "soong_module.bzl", soongModuleBzl)
 }

 var ignoredProps map[string]bool = map[string]bool{
 	"name":       true, // redundant, since this is explicitly generated for every target
 	"from":       true, // reserved keyword
 	"in":         true, // reserved keyword
 	"arch":       true, // interface prop type is not supported yet.
 	"multilib":   true, // interface prop type is not supported yet.
 	"target":     true, // interface prop type is not supported yet.
 	"visibility": true, // Bazel has native visibility semantics. Handle later.
 }

 func shouldGenerateAttribute(prop string) bool {
 	return !ignoredProps[prop]
 }

 // props is an unsorted map. This function ensures that
 // the generated attributes are sorted to ensure determinism.
 func propsToAttributes(props map[string]string) string {
 	var attributes string
 	for _, propName := range android.SortedStringKeys(props) {
 		if shouldGenerateAttribute(propName) {
 			attributes += fmt.Sprintf("    %s = %s,\n", propName, props[propName])
 		}
 	}
 	return attributes
 }

 // Convert a module and its deps and props into a Bazel macro/rule
 // representation in the BUILD file.
 func generateSoongModuleTarget(
 	blueprintCtx *blueprint.Context,
 	module blueprint.Module) string {

 	var props map[string]string
 	if aModule, ok := module.(android.Module); ok {
 		props = extractModuleProperties(aModule)
 	}
 	attributes := propsToAttributes(props)

 	// TODO(b/163018919): DirectDeps can have duplicate (module, variant)
 	// items, if the modules are added using different DependencyTag. Figure
 	// out the implications of that.
 	depLabels := map[string]bool{}
 	blueprintCtx.VisitDirectDeps(module, func(depModule blueprint.Module) {
 		depLabels[qualifiedTargetLabel(blueprintCtx, depModule)] = true
 	})

 	depLabelList := "[\n"
 	for depLabel, _ := range depLabels {
 		depLabelList += "        \""
 		depLabelList += depLabel
 		depLabelList += "\",\n"
 	}
 	depLabelList += "    ]"

 	return fmt.Sprintf(
 		soongModuleTarget,
 		targetNameWithVariant(blueprintCtx, module),
 		blueprintCtx.ModuleName(module),
 		blueprintCtx.ModuleType(module),
 		blueprintCtx.ModuleSubDir(module),
 		depLabelList,
 		attributes)
 }

 func buildFileForModule(ctx *blueprint.Context, module blueprint.Module) (*os.File, error) {
 	// Create nested directories for the BUILD file
 	dirPath := filepath.Join(bazelOverlayDir, packagePath(ctx, module))
 	if _, err := os.Stat(dirPath); os.IsNotExist(err) {
 		os.MkdirAll(dirPath, os.ModePerm)
 	}
 	// Open the file for appending, and create it if it doesn't exist
 	f, err := os.OpenFile(
 		filepath.Join(dirPath, "BUILD.bazel"),
 		os.O_APPEND|os.O_CREATE|os.O_WRONLY,
 		0644)
 	if err != nil {
 		return nil, err
 	}

 	// If the file is empty, add the load statement for the `soong_module` rule
 	fi, err := f.Stat()
 	if err != nil {
 		return nil, err
 	}
 	if fi.Size() == 0 {
 		f.Write([]byte(soongModuleLoad + "\n"))
 	}

 	return f, nil
 }

 // The overlay directory should be read-only, sufficient for bazel query.
 func writeReadOnlyFile(dir string, baseName string, content string) error {
 	workspaceFile := filepath.Join(bazelOverlayDir, baseName)
 	// 0444 is read-only
 	return ioutil.WriteFile(workspaceFile, []byte(content), 0444)
 }

 func isZero(value reflect.Value) bool {
 	switch value.Kind() {
 	case reflect.Func, reflect.Map, reflect.Slice:
 		return value.IsNil()
 	case reflect.Array:
 		valueIsZero := true
 		for i := 0; i < value.Len(); i++ {
 			valueIsZero = valueIsZero && isZero(value.Index(i))
 		}
 		return valueIsZero
 	case reflect.Struct:
 		valueIsZero := true
 		for i := 0; i < value.NumField(); i++ {
 			if value.Field(i).CanSet() {
 				valueIsZero = valueIsZero && isZero(value.Field(i))
 			}
 		}
 		return valueIsZero
 	case reflect.Ptr:
 		if !value.IsNil() {
 			return isZero(reflect.Indirect(value))
 		} else {
 			return true
 		}
 	default:
 		zeroValue := reflect.Zero(value.Type())
 		result := value.Interface() == zeroValue.Interface()
 		return result
 	}
 }
	// 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 main

	import (
	"android/soong/android"
	"fmt"
	"io/ioutil"
	"os"
	"path/filepath"
	"reflect"
	"strings"

	"github.com/google/blueprint"
	"github.com/google/blueprint/proptools"
	)

	const (
	soongModuleLoad = `package(default_visibility = ["//visibility:public"])
	load("//:soong_module.bzl", "soong_module")

	`

	// A BUILD file target snippet representing a Soong module
	soongModuleTarget = `soong_module(
	name = "%s",
	module_name = "%s",
	module_type = "%s",
	module_variant = "%s",
	deps = %s,
	%s)`

	// The soong_module rule implementation in a .bzl file
	soongModuleBzl = `SoongModuleInfo = provider(
	fields = {
	"name": "Name of module",
	"type": "Type of module",
	"variant": "Variant of module",
	},
	)

	def _merge_dicts(*dicts):
	"""Adds a list of dictionaries into a single dictionary."""

	# If keys are repeated in multiple dictionaries, the latter one "wins".
	result = {}
	for d in dicts:
	result.update(d)

	return result

	def _generic_soong_module_impl(ctx):
	return [
	SoongModuleInfo(
	name = ctx.attr.module_name,
	type = ctx.attr.module_type,
	variant = ctx.attr.module_variant,
	),
	]

	_COMMON_ATTRS = {
	"module_name": attr.string(mandatory = True),
	"module_type": attr.string(mandatory = True),
	"module_variant": attr.string(),
	"deps": attr.label_list(providers = [SoongModuleInfo]),
	}


	generic_soong_module = rule(
	implementation = _generic_soong_module_impl,
	attrs = _COMMON_ATTRS,
	)

	# TODO(jingwen): auto generate Soong module shims
	def _soong_filegroup_impl(ctx):
	return [SoongModuleInfo(),]

	soong_filegroup = rule(
	implementation = _soong_filegroup_impl,
	# Matches https://cs.android.com/android/platform/superproject/+/master:build/soong/android/filegroup.go;l=25-40;drc=6a6478d49e78703ba22a432c41d819c8df79ef6c
	attrs = _merge_dicts(_COMMON_ATTRS, {
	"srcs": attr.string_list(doc = "srcs lists files that will be included in this filegroup"),
	"exclude_srcs": attr.string_list(),
	"path": attr.string(doc = "The base path to the files. May be used by other modules to determine which portion of the path to use. For example, when a filegroup is used as data in a cc_test rule, the base path is stripped off the path and the remaining path is used as the installation directory."),
	"export_to_make_var": attr.string(doc = "Create a make variable with the specified name that contains the list of files in the filegroup, relative to the root of the source tree."),
	})
	)

	soong_module_rule_map = {
	"filegroup": soong_filegroup,
	}

	# soong_module is a macro that supports arbitrary kwargs, and uses module_type to
	# expand to the right underlying shim.
	def soong_module(name, module_type, **kwargs):
	soong_module_rule = soong_module_rule_map.get(module_type)

	if soong_module_rule == None:
	# This module type does not have an existing rule to map to, so use the
	# generic_soong_module rule instead.
	generic_soong_module(
	name = name,
	module_type = module_type,
	module_name = kwargs.pop("module_name", ""),
	module_variant = kwargs.pop("module_variant", ""),
	deps = kwargs.pop("deps", []),
	)
	else:
	soong_module_rule(
	name = name,
	module_type = module_type,
	**kwargs,
	)
	`
	)

	func targetNameWithVariant(c *blueprint.Context, logicModule blueprint.Module) string {
	name := ""
	if c.ModuleSubDir(logicModule) != "" {
	// TODO(b/162720883): Figure out a way to drop the "--" variant suffixes.
	name = c.ModuleName(logicModule) + "--" + c.ModuleSubDir(logicModule)
	} else {
	name = c.ModuleName(logicModule)
	}

	return strings.Replace(name, "//", "", 1)
	}

	func qualifiedTargetLabel(c *blueprint.Context, logicModule blueprint.Module) string {
	return "//" +
	packagePath(c, logicModule) +
	":" +
	targetNameWithVariant(c, logicModule)
	}

	func packagePath(c *blueprint.Context, logicModule blueprint.Module) string {
	return filepath.Dir(c.BlueprintFile(logicModule))
	}

	func escapeString(s string) string {
	s = strings.ReplaceAll(s, "\\", "\\\\")
	return strings.ReplaceAll(s, "\"", "\\\"")
	}

	func makeIndent(indent int) string {
	if indent < 0 {
	panic(fmt.Errorf("indent column cannot be less than 0, but got %d", indent))
	}
	return strings.Repeat(" ", indent)
	}

	// prettyPrint a property value into the equivalent Starlark representation
	// recursively.
	func prettyPrint(propertyValue reflect.Value, indent int) (string, error) {
	if isZero(propertyValue) {
	// A property value being set or unset actually matters -- Soong does set default
	// values for unset properties, like system_shared_libs = ["libc", "libm", "libdl"] at
	// https://cs.android.com/android/platform/superproject/+/master:build/soong/cc/linker.go;l=281-287;drc=f70926eef0b9b57faf04c17a1062ce50d209e480
	//
	// In Bazel-parlance, we would use "attr.<type>(default = <default value>)" to set the default
	// value of unset attributes.
	return "", nil
	}

	var ret string
	switch propertyValue.Kind() {
	case reflect.String:
	ret = fmt.Sprintf("\"%v\"", escapeString(propertyValue.String()))
	case reflect.Bool:
	ret = strings.Title(fmt.Sprintf("%v", propertyValue.Interface()))
	case reflect.Int, reflect.Uint, reflect.Int64:
	ret = fmt.Sprintf("%v", propertyValue.Interface())
	case reflect.Ptr:
	return prettyPrint(propertyValue.Elem(), indent)
	case reflect.Slice:
	ret = "[\n"
	for i := 0; i < propertyValue.Len(); i++ {
	indexedValue, err := prettyPrint(propertyValue.Index(i), indent+1)
	if err != nil {
	return "", err
	}

	if indexedValue != "" {
	ret += makeIndent(indent + 1)
	ret += indexedValue
	ret += ",\n"
	}
	}
	ret += makeIndent(indent)
	ret += "]"
	case reflect.Struct:
	ret = "{\n"
	// Sort and print the struct props by the key.
	structProps := extractStructProperties(propertyValue, indent)
	for _, k := range android.SortedStringKeys(structProps) {
	ret += makeIndent(indent + 1)
	ret += "\"" + k + "\": "
	ret += structProps[k]
	ret += ",\n"
	}
	ret += makeIndent(indent)
	ret += "}"
	case reflect.Interface:
	// TODO(b/164227191): implement pretty print for interfaces.
	// Interfaces are used for for arch, multilib and target properties.
	return "", nil
	default:
	return "", fmt.Errorf(
	"unexpected kind for property struct field: %s", propertyValue.Kind())
	}
	return ret, nil
	}

	func extractStructProperties(structValue reflect.Value, indent int) map[string]string {
	if structValue.Kind() != reflect.Struct {
	panic(fmt.Errorf("Expected a reflect.Struct type, but got %s", structValue.Kind()))
	}

	ret := map[string]string{}
	structType := structValue.Type()
	for i := 0; i < structValue.NumField(); i++ {
	field := structType.Field(i)
	if field.PkgPath != "" {
	// Skip unexported fields. Some properties are
	// internal to Soong only, and these fields do not have PkgPath.
	continue
	}
	if proptools.HasTag(field, "blueprint", "mutated") {
	continue
	}

	fieldValue := structValue.Field(i)
	if isZero(fieldValue) {
	// Ignore zero-valued fields
	continue
	}

	propertyName := proptools.PropertyNameForField(field.Name)
	prettyPrintedValue, err := prettyPrint(fieldValue, indent+1)
	if err != nil {
	panic(
	fmt.Errorf(
	"Error while parsing property: %q. %s",
	propertyName,
	err))
	}
	if prettyPrintedValue != "" {
	ret[propertyName] = prettyPrintedValue
	}
	}

	return ret
	}

	func isStructPtr(t reflect.Type) bool {
	return t.Kind() == reflect.Ptr && t.Elem().Kind() == reflect.Struct
	}

	// Generically extract module properties and types into a map, keyed by the module property name.
	func extractModuleProperties(aModule android.Module) map[string]string {
	ret := map[string]string{}

	// Iterate over this android.Module's property structs.
	for _, properties := range aModule.GetProperties() {
	propertiesValue := reflect.ValueOf(properties)
	// Check that propertiesValue is a pointer to the Properties struct, like
	// cc.BaseLinkerProperties or java.CompilerProperties.
	//
	// propertiesValue can also be type-asserted to the structs to
	// manipulate internal props, if needed.
	if isStructPtr(propertiesValue.Type()) {
	structValue := propertiesValue.Elem()
	for k, v := range extractStructProperties(structValue, 0) {
	ret[k] = v
	}
	} else {
	panic(fmt.Errorf(
	"properties must be a pointer to a struct, got %T",
	propertiesValue.Interface()))
	}

	}

	return ret
	}

	func createBazelOverlay(ctx *android.Context, bazelOverlayDir string) error {
	blueprintCtx := ctx.Context
	blueprintCtx.VisitAllModules(func(module blueprint.Module) {
	buildFile, err := buildFileForModule(blueprintCtx, module)
	if err != nil {
	panic(err)
	}

	buildFile.Write([]byte(generateSoongModuleTarget(blueprintCtx, module) + "\n\n"))
	buildFile.Close()
	})

	if err := writeReadOnlyFile(bazelOverlayDir, "WORKSPACE", ""); err != nil {
	return err
	}

	if err := writeReadOnlyFile(bazelOverlayDir, "BUILD", ""); err != nil {
	return err
	}

	return writeReadOnlyFile(bazelOverlayDir, "soong_module.bzl", soongModuleBzl)
	}

	var ignoredProps map[string]bool = map[string]bool{
	"name": true, // redundant, since this is explicitly generated for every target
	"from": true, // reserved keyword
	"in": true, // reserved keyword
	"arch": true, // interface prop type is not supported yet.
	"multilib": true, // interface prop type is not supported yet.
	"target": true, // interface prop type is not supported yet.
	"visibility": true, // Bazel has native visibility semantics. Handle later.
	}

	func shouldGenerateAttribute(prop string) bool {
	return !ignoredProps[prop]
	}

	// props is an unsorted map. This function ensures that
	// the generated attributes are sorted to ensure determinism.
	func propsToAttributes(props map[string]string) string {
	var attributes string
	for _, propName := range android.SortedStringKeys(props) {
	if shouldGenerateAttribute(propName) {
	attributes += fmt.Sprintf(" %s = %s,\n", propName, props[propName])
	}
	}
	return attributes
	}

	// Convert a module and its deps and props into a Bazel macro/rule
	// representation in the BUILD file.
	func generateSoongModuleTarget(
	blueprintCtx *blueprint.Context,
	module blueprint.Module) string {

	var props map[string]string
	if aModule, ok := module.(android.Module); ok {
	props = extractModuleProperties(aModule)
	}
	attributes := propsToAttributes(props)

	// TODO(b/163018919): DirectDeps can have duplicate (module, variant)
	// items, if the modules are added using different DependencyTag. Figure
	// out the implications of that.
	depLabels := map[string]bool{}
	blueprintCtx.VisitDirectDeps(module, func(depModule blueprint.Module) {
	depLabels[qualifiedTargetLabel(blueprintCtx, depModule)] = true
	})

	depLabelList := "[\n"
	for depLabel, _ := range depLabels {
	depLabelList += " \""
	depLabelList += depLabel
	depLabelList += "\",\n"
	}
	depLabelList += " ]"

	return fmt.Sprintf(
	soongModuleTarget,
	targetNameWithVariant(blueprintCtx, module),
	blueprintCtx.ModuleName(module),
	blueprintCtx.ModuleType(module),
	blueprintCtx.ModuleSubDir(module),
	depLabelList,
	attributes)
	}

	func buildFileForModule(ctx blueprint.Context, module blueprint.Module) (os.File, error) {
	// Create nested directories for the BUILD file
	dirPath := filepath.Join(bazelOverlayDir, packagePath(ctx, module))
	if _, err := os.Stat(dirPath); os.IsNotExist(err) {
	os.MkdirAll(dirPath, os.ModePerm)
	}
	// Open the file for appending, and create it if it doesn't exist
	f, err := os.OpenFile(
	filepath.Join(dirPath, "BUILD.bazel"),
	os.O_APPEND\|os.O_CREATE\|os.O_WRONLY,
	0644)
	if err != nil {
	return nil, err
	}

	// If the file is empty, add the load statement for the `soong_module` rule
	fi, err := f.Stat()
	if err != nil {
	return nil, err
	}
	if fi.Size() == 0 {
	f.Write([]byte(soongModuleLoad + "\n"))
	}

	return f, nil
	}

	// The overlay directory should be read-only, sufficient for bazel query.
	func writeReadOnlyFile(dir string, baseName string, content string) error {
	workspaceFile := filepath.Join(bazelOverlayDir, baseName)
	// 0444 is read-only
	return ioutil.WriteFile(workspaceFile, []byte(content), 0444)
	}

	func isZero(value reflect.Value) bool {
	switch value.Kind() {
	case reflect.Func, reflect.Map, reflect.Slice:
	return value.IsNil()
	case reflect.Array:
	valueIsZero := true
	for i := 0; i < value.Len(); i++ {
	valueIsZero = valueIsZero && isZero(value.Index(i))
	}
	return valueIsZero
	case reflect.Struct:
	valueIsZero := true
	for i := 0; i < value.NumField(); i++ {
	if value.Field(i).CanSet() {
	valueIsZero = valueIsZero && isZero(value.Field(i))
	}
	}
	return valueIsZero
	case reflect.Ptr:
	if !value.IsNil() {
	return isZero(reflect.Indirect(value))
	} else {
	return true
	}
	default:
	zeroValue := reflect.Zero(value.Type())
	result := value.Interface() == zeroValue.Interface()
	return result
	}
	}