Build build_flags.json in soong

Define release_flags_json module type to install build_flags.json in
'etc'. release_flags_json reads the json files generated from the
soong release-config command.

Bug: 324996303
Test: build and see if the files are installed
Change-Id: I8cdcb7c61dd75cc54e4912d2ed7d1687f424151c

aconfig/build_flags/Android.bp

@@ -14,6 +14,7 @@ bootstrap_go_package {
     ],
     srcs: [
         "all_build_flag_declarations.go",
+        "build_flags.go",
         "declarations.go",
         "init.go",
     ],

aconfig/build_flags/build_flags.go

@@ -0,0 +1,71 @@
+// Copyright 2024 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 build_flags
+
+import (
+	"fmt"
+
+	"android/soong/android"
+)
+
+const (
+	outJsonFileName = "build_flags.json"
+)
+
+func init() {
+	registerBuildFlagsModuleType(android.InitRegistrationContext)
+}
+
+func registerBuildFlagsModuleType(ctx android.RegistrationContext) {
+	ctx.RegisterModuleType("build_flags_json", buildFlagsFactory)
+}
+
+type buildFlags struct {
+	android.ModuleBase
+
+	outputPath android.OutputPath
+}
+
+func buildFlagsFactory() android.Module {
+	module := &buildFlags{}
+	android.InitAndroidArchModule(module, android.DeviceSupported, android.MultilibCommon)
+	return module
+}
+
+func (m *buildFlags) GenerateAndroidBuildActions(ctx android.ModuleContext) {
+	// Read the build_flags_<partition>.json file generated by soong
+	// 'release-config' command.
+	srcPath := android.PathForOutput(ctx, "release-config", fmt.Sprintf("build_flags_%s.json", m.PartitionTag(ctx.DeviceConfig())))
+	m.outputPath = android.PathForModuleOut(ctx, outJsonFileName).OutputPath
+
+	// The 'release-config' command is called for every build, and generates the
+	// build_flags_<partition>.json file.
+	// Update the output file only if the source file is changed.
+	ctx.Build(pctx, android.BuildParams{
+		Rule:   android.CpIfChanged,
+		Input:  srcPath,
+		Output: m.outputPath,
+	})
+
+	installPath := android.PathForModuleInstall(ctx, "etc")
+	ctx.InstallFile(installPath, outJsonFileName, m.outputPath)
+}
+
+func (m *buildFlags) AndroidMkEntries() []android.AndroidMkEntries {
+	return []android.AndroidMkEntries{android.AndroidMkEntries{
+		Class:      "ETC",
+		OutputFile: android.OptionalPathForPath(m.outputPath),
+	}}
+}

aconfig/build_flags/init.go

@@ -69,6 +69,7 @@ var (
 
 func init() {
 	RegisterBuildComponents(android.InitRegistrationContext)
+	pctx.Import("android/soong/android")
 	pctx.HostBinToolVariable("buildFlagDeclarations", "build-flag-declarations")
 }
 

cmd/release_config/release_config/main.go

@@ -120,7 +120,7 @@ func main() {
 			panic(err)
 		}
 	}
-	if err = config.WritePartitionBuildFlags(outputDir, product, targetRelease); err != nil {
+	if err = config.WritePartitionBuildFlags(outputDir); err != nil {
 		panic(err)
 	}
 

cmd/release_config/release_config_lib/release_config.go

@@ -284,13 +284,15 @@ func (config *ReleaseConfig) GenerateReleaseConfig(configs *ReleaseConfigs) erro
 	return nil
 }
 
-func (config *ReleaseConfig) WritePartitionBuildFlags(outDir, product, targetRelease string) error {
+func (config *ReleaseConfig) WritePartitionBuildFlags(outDir string) error {
 	var err error
 	for partition, flags := range config.PartitionBuildFlags {
 		slices.SortFunc(flags.FlagArtifacts, func(a, b *rc_proto.FlagArtifact) int {
 			return cmp.Compare(*a.FlagDeclaration.Name, *b.FlagDeclaration.Name)
 		})
-		if err = WriteMessage(filepath.Join(outDir, fmt.Sprintf("build_flags_%s-%s-%s.json", partition, config.Name, product)), flags); err != nil {
+		// The json file name must not be modified as this is read from
+		// build_flags_json module
+		if err = WriteMessage(filepath.Join(outDir, fmt.Sprintf("build_flags_%s.json", partition)), flags); err != nil {
 			return err
 		}
 	}