Add exported_java_aconfig_library

Add a rule to generate a JAR file containing code for all aconfig flags
in all packages. This is intended for apps compiled outside the
platform.

Also add a rule to include the new JAR file among the SDK artifacts.

Note: a future CL will refine the aconfig command line options used, or
filter the aconfig output: right now the JAR really contains *all*
flags; we want it to include only *exported* flags.

Bug: 311151343
Test: m sdk dist # manually verify that this generates $(gettop)/out/dist/android-flags.jar
Change-Id: I73481a9f723a0e5487cfcd2ee697873ecc4e8275
diff --git a/aconfig/exported_java_aconfig_library.go b/aconfig/exported_java_aconfig_library.go
new file mode 100644
index 0000000..45c5e39
--- /dev/null
+++ b/aconfig/exported_java_aconfig_library.go
@@ -0,0 +1,56 @@
+// Copyright 2023 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 aconfig
+
+import (
+	"android/soong/android"
+)
+
+func ExportedJavaDeclarationsLibraryFactory() android.Singleton {
+	return &exportedJavaDeclarationsLibrarySingleton{}
+}
+
+type exportedJavaDeclarationsLibrarySingleton struct {
+	intermediatePath android.OutputPath
+}
+
+func (this *exportedJavaDeclarationsLibrarySingleton) GenerateBuildActions(ctx android.SingletonContext) {
+	// Find all of the aconfig_declarations modules
+	var cacheFiles android.Paths
+	ctx.VisitAllModules(func(module android.Module) {
+		if !ctx.ModuleHasProvider(module, DeclarationsProviderKey) {
+			return
+		}
+		decl := ctx.ModuleProvider(module, DeclarationsProviderKey).(DeclarationsProviderData)
+		cacheFiles = append(cacheFiles, decl.IntermediateCacheOutputPath)
+	})
+
+	// Generate build action for aconfig
+	this.intermediatePath = android.PathForIntermediates(ctx, "exported_java_aconfig_library.jar")
+	ctx.Build(pctx, android.BuildParams{
+		Rule:        exportedJavaRule,
+		Inputs:      cacheFiles,
+		Output:      this.intermediatePath,
+		Description: "exported_java_aconfig_library",
+		Args: map[string]string{
+			"cache_files": android.JoinPathsWithPrefix(cacheFiles, " "),
+		},
+	})
+	ctx.Phony("exported_java_aconfig_library", this.intermediatePath)
+}
+
+func (this *exportedJavaDeclarationsLibrarySingleton) MakeVars(ctx android.MakeVarsContext) {
+	ctx.DistForGoalWithFilename("sdk", this.intermediatePath, "android-flags.jar")
+}