Update droidstubs build target

This allows to use Metalava to generate metadata files useful for
Android Studio as part of a droidstubs target.
Once those files have been created in a new metadata folder, they are
zipped to make it easier to transfer them into the
out/target/common/obj/PACKAGING folder where they can then be picked up
by the SDK build to be included there.

Bug: 142480924
Test: m sdk
Change-Id: I4be1c9e78369c65ee9cd94706c6d20ab0df6b797
diff --git a/java/droiddoc.go b/java/droiddoc.go
index 8a283cd..025beab 100644
--- a/java/droiddoc.go
+++ b/java/droiddoc.go
@@ -1193,6 +1193,9 @@
 
 	jdiffDocZip      android.WritablePath
 	jdiffStubsSrcJar android.WritablePath
+
+	metadataZip android.WritablePath
+	metadataDir android.WritablePath
 }
 
 // droidstubs passes sources files through Metalava to generate stub .java files that only contain the API to be
@@ -1304,7 +1307,8 @@
 	}
 
 	if Bool(d.properties.Write_sdk_values) {
-		cmd.FlagWithArg("--sdk-values ", android.PathForModuleOut(ctx, "out").String())
+		d.metadataDir = android.PathForModuleOut(ctx, "metadata")
+		cmd.FlagWithArg("--sdk-values ", d.metadataDir.String())
 	}
 
 	if Bool(d.properties.Create_doc_stubs) {
@@ -1511,6 +1515,18 @@
 		FlagWithOutput("-o ", d.Javadoc.stubsSrcJar).
 		FlagWithArg("-C ", stubsDir.String()).
 		FlagWithArg("-D ", stubsDir.String())
+
+	if Bool(d.properties.Write_sdk_values) {
+		d.metadataZip = android.PathForModuleOut(ctx, ctx.ModuleName()+"-metadata.zip")
+		rule.Command().
+			BuiltTool(ctx, "soong_zip").
+			Flag("-write_if_changed").
+			Flag("-d").
+			FlagWithOutput("-o ", d.metadataZip).
+			FlagWithArg("-C ", d.metadataDir.String()).
+			FlagWithArg("-D ", d.metadataDir.String())
+	}
+
 	rule.Restat()
 
 	zipSyncCleanupCmd(rule, srcJarDir)