Introduce a java_system_features_srcs wrapper for codegen

Use soong to aggregate all system feature-related build flags as input
to the existing system feature codegen tool. Use this instead of the
more clumsy raw genrule variant. This is an effective no-op in terms of
generated code or framework impact, but should improve maintainability.

Test: m --no-skip-soong-tests
Bug: 203143243
Change-Id: I67158dd6f0454556f8d75685cfc86a68b3e47089
diff --git a/systemfeatures/system_features.go b/systemfeatures/system_features.go
new file mode 100644
index 0000000..0c1a566
--- /dev/null
+++ b/systemfeatures/system_features.go
@@ -0,0 +1,102 @@
+// 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 systemfeatures
+
+import (
+	"fmt"
+	"sort"
+	"strings"
+
+	"android/soong/android"
+	"android/soong/genrule"
+)
+
+var (
+	pctx = android.NewPackageContext("android/soong/systemfeatures")
+)
+
+func init() {
+	registerSystemFeaturesComponents(android.InitRegistrationContext)
+}
+
+func registerSystemFeaturesComponents(ctx android.RegistrationContext) {
+	ctx.RegisterModuleType("java_system_features_srcs", JavaSystemFeaturesSrcsFactory)
+}
+
+type javaSystemFeaturesSrcs struct {
+	android.ModuleBase
+	properties struct {
+		// The fully qualified class name for the generated code, e.g., com.android.Foo
+		Full_class_name string
+	}
+	outputFiles android.WritablePaths
+}
+
+var _ genrule.SourceFileGenerator = (*javaSystemFeaturesSrcs)(nil)
+var _ android.SourceFileProducer = (*javaSystemFeaturesSrcs)(nil)
+
+func (m *javaSystemFeaturesSrcs) GenerateAndroidBuildActions(ctx android.ModuleContext) {
+	// Create a file name appropriate for the given fully qualified (w/ package) class name.
+	classNameParts := strings.Split(m.properties.Full_class_name, ".")
+	outputDir := android.PathForModuleGen(ctx)
+	outputFileName := classNameParts[len(classNameParts)-1] + ".java"
+	outputFile := android.PathForModuleGen(ctx, outputFileName).OutputPath
+
+	// Collect all RELEASE_SYSTEM_FEATURE_$K:$V build flags into a list of "$K:$V" pairs.
+	var features []string
+	for k, v := range ctx.Config().ProductVariables().BuildFlags {
+		if strings.HasPrefix(k, "RELEASE_SYSTEM_FEATURE_") {
+			shortFeatureName := strings.TrimPrefix(k, "RELEASE_SYSTEM_FEATURE_")
+			features = append(features, fmt.Sprintf("%s:%s", shortFeatureName, v))
+		}
+	}
+	// Ensure sorted outputs for consistency of flag ordering in ninja outputs.
+	sort.Strings(features)
+
+	rule := android.NewRuleBuilder(pctx, ctx)
+	rule.Command().Text("rm -rf").Text(outputDir.String())
+	rule.Command().Text("mkdir -p").Text(outputDir.String())
+	rule.Command().
+		BuiltTool("systemfeatures-gen-tool").
+		Flag(m.properties.Full_class_name).
+		FlagForEachArg("--feature=", features).
+		FlagWithArg("--readonly=", fmt.Sprint(ctx.Config().ReleaseUseSystemFeatureBuildFlags())).
+		FlagWithOutput(" > ", outputFile)
+	rule.Build(ctx.ModuleName(), "Generating systemfeatures srcs filegroup")
+
+	m.outputFiles = append(m.outputFiles, outputFile)
+}
+
+func (m *javaSystemFeaturesSrcs) Srcs() android.Paths {
+	return m.outputFiles.Paths()
+}
+
+func (m *javaSystemFeaturesSrcs) GeneratedSourceFiles() android.Paths {
+	return m.outputFiles.Paths()
+}
+
+func (m *javaSystemFeaturesSrcs) GeneratedDeps() android.Paths {
+	return m.outputFiles.Paths()
+}
+
+func (m *javaSystemFeaturesSrcs) GeneratedHeaderDirs() android.Paths {
+	return nil
+}
+
+func JavaSystemFeaturesSrcsFactory() android.Module {
+	module := &javaSystemFeaturesSrcs{}
+	module.AddProperties(&module.properties)
+	android.InitAndroidModule(module)
+	return module
+}