Add flag for optimized resource shrinking with R8

If the flag is set we will:
 - pass --optimized-resource-shrinking to the r8 invocation
 - use non final fields for the generated R classes
 - not pass the aapt2 generated proguard rules, R8 will do the tracing of xml files

Bug: 325905703
Test: This is simply passing the flag through to R8, this is off by default
Change-Id: Ib2043f3201578c3bcd39c1de9a524fd78f6d795c

java/aar.go

@@ -351,6 +351,7 @@ type aaptBuildActionOptions struct {
 	classLoaderContexts            dexpreopt.ClassLoaderContextMap
 	excludedLibs                   []string
 	enforceDefaultTargetSdkVersion bool
+	forceNonFinalResourceIDs       bool
 	extraLinkFlags                 []string
 	aconfigTextFiles               android.Paths
 }
@@ -544,7 +545,8 @@ func (a *aapt) buildActions(ctx android.ModuleContext, opts aaptBuildActionOptio
 
 	if a.useResourceProcessorBusyBox(ctx) {
 		rJar := android.PathForModuleOut(ctx, "busybox/R.jar")
-		resourceProcessorBusyBoxGenerateBinaryR(ctx, rTxt, a.mergedManifestFile, rJar, staticDeps, a.isLibrary, a.aaptProperties.Aaptflags)
+		resourceProcessorBusyBoxGenerateBinaryR(ctx, rTxt, a.mergedManifestFile, rJar, staticDeps, a.isLibrary, a.aaptProperties.Aaptflags,
+			opts.forceNonFinalResourceIDs)
 		aapt2ExtractExtraPackages(ctx, extraPackages, rJar)
 		transitiveRJars = append(transitiveRJars, rJar)
 		a.rJar = rJar
@@ -608,7 +610,8 @@ var resourceProcessorBusyBox = pctx.AndroidStaticRule("resourceProcessorBusyBox"
 // using Bazel's ResourceProcessorBusyBox tool, which is faster than compiling the R.java files and
 // supports producing classes for static dependencies that only include resources from that dependency.
 func resourceProcessorBusyBoxGenerateBinaryR(ctx android.ModuleContext, rTxt, manifest android.Path,
-	rJar android.WritablePath, transitiveDeps transitiveAarDeps, isLibrary bool, aaptFlags []string) {
+	rJar android.WritablePath, transitiveDeps transitiveAarDeps, isLibrary bool, aaptFlags []string,
+	forceNonFinalIds bool) {
 
 	var args []string
 	var deps android.Paths
@@ -618,6 +621,9 @@ func resourceProcessorBusyBoxGenerateBinaryR(ctx android.ModuleContext, rTxt, ma
 		// to ResourceProcessorBusyBox so that it can regenerate R.class files with the final resource IDs for each
 		// package.
 		args, deps = transitiveDeps.resourceProcessorDeps()
+		if forceNonFinalIds {
+			args = append(args, "--finalFields=false")
+		}
 	} else {
 		// When compiling a library don't pass any dependencies as it only needs to generate an R.class file for this
 		// library.  Pass --finalFields=false so that the R.class file contains non-final fields so they don't get
@@ -1221,7 +1227,7 @@ func (a *AARImport) GenerateAndroidBuildActions(ctx android.ModuleContext) {
 		linkFlags, linkDeps, nil, overlayRes, transitiveAssets, nil, nil)
 
 	a.rJar = android.PathForModuleOut(ctx, "busybox/R.jar")
-	resourceProcessorBusyBoxGenerateBinaryR(ctx, a.rTxt, a.manifest, a.rJar, nil, true, nil)
+	resourceProcessorBusyBoxGenerateBinaryR(ctx, a.rTxt, a.manifest, a.rJar, nil, true, nil, false)
 
 	aapt2ExtractExtraPackages(ctx, a.extraAaptPackagesFile, a.rJar)
 

java/app.go

@@ -519,12 +519,15 @@ func (a *AndroidApp) aaptBuildActions(ctx android.ModuleContext) {
 		a.aapt.defaultManifestVersion = android.DefaultUpdatableModuleVersion
 	}
 
+	// Use non final ids if we are doing optimized shrinking and are using R8.
+	nonFinalIds := Bool(a.dexProperties.Optimize.Optimized_shrink_resources) && a.dexer.effectiveOptimizeEnabled()
 	a.aapt.buildActions(ctx,
 		aaptBuildActionOptions{
 			sdkContext:                     android.SdkContext(a),
 			classLoaderContexts:            a.classLoaderContexts,
 			excludedLibs:                   a.usesLibraryProperties.Exclude_uses_libs,
 			enforceDefaultTargetSdkVersion: a.enforceDefaultTargetSdkVersion(),
+			forceNonFinalResourceIDs:       nonFinalIds,
 			extraLinkFlags:                 aaptLinkFlags,
 			aconfigTextFiles:               getAconfigFilePaths(ctx),
 		},
@@ -547,7 +550,13 @@ func (a *AndroidApp) proguardBuildActions(ctx android.ModuleContext) {
 	staticLibProguardFlagFiles = android.FirstUniquePaths(staticLibProguardFlagFiles)
 
 	a.Module.extraProguardFlagsFiles = append(a.Module.extraProguardFlagsFiles, staticLibProguardFlagFiles...)
-	a.Module.extraProguardFlagsFiles = append(a.Module.extraProguardFlagsFiles, a.proguardOptionsFile)
+	if !Bool(a.dexProperties.Optimize.Optimized_shrink_resources) {
+		// When using the optimized shrinking the R8 enqueuer will traverse the xml files that become
+		// live for code references and (transitively) mark these as live.
+		// In this case we explicitly don't wan't the aapt2 generated keep files (which would keep the now
+		// dead code alive)
+		a.Module.extraProguardFlagsFiles = append(a.Module.extraProguardFlagsFiles, a.proguardOptionsFile)
+	}
 }
 
 func (a *AndroidApp) installPath(ctx android.ModuleContext) android.InstallPath {
@@ -580,7 +589,7 @@ func (a *AndroidApp) dexBuildActions(ctx android.ModuleContext) (android.Path, a
 	var packageResources = a.exportPackage
 
 	if ctx.ModuleName() != "framework-res" {
-		if Bool(a.dexProperties.Optimize.Shrink_resources) {
+		if a.dexProperties.resourceShrinkingEnabled() {
 			protoFile := android.PathForModuleOut(ctx, packageResources.Base()+".proto.apk")
 			aapt2Convert(ctx, protoFile, packageResources, "proto")
 			a.dexer.resourcesInput = android.OptionalPathForPath(protoFile)
@@ -603,7 +612,7 @@ func (a *AndroidApp) dexBuildActions(ctx android.ModuleContext) (android.Path, a
 		}
 
 		a.Module.compile(ctx, extraSrcJars, extraClasspathJars, extraCombinedJars)
-		if Bool(a.dexProperties.Optimize.Shrink_resources) {
+		if a.dexProperties.resourceShrinkingEnabled() {
 			binaryResources := android.PathForModuleOut(ctx, packageResources.Base()+".binary.out.apk")
 			aapt2Convert(ctx, binaryResources, a.dexer.resourcesOutput.Path(), "binary")
 			packageResources = binaryResources

java/dex.go

@@ -66,6 +66,12 @@ type DexProperties struct {
 		// If true, optimize for size by removing unused resources. Defaults to false.
 		Shrink_resources *bool
 
+		// If true, use optimized resource shrinking in R8, overriding the
+		// Shrink_resources setting. Defaults to false.
+		// Optimized shrinking means that R8 will trace and treeshake resources together with code
+		// and apply additional optimizations. This implies non final fields in the R classes.
+		Optimized_shrink_resources *bool
+
 		// Flags to pass to proguard.
 		Proguard_flags []string
 
@@ -105,6 +111,10 @@ func (d *dexer) effectiveOptimizeEnabled() bool {
 	return BoolDefault(d.dexProperties.Optimize.Enabled, d.dexProperties.Optimize.EnabledByDefault)
 }
 
+func (d *DexProperties) resourceShrinkingEnabled() bool {
+	return BoolDefault(d.Optimize.Optimized_shrink_resources, Bool(d.Optimize.Shrink_resources))
+}
+
 var d8, d8RE = pctx.MultiCommandRemoteStaticRules("d8",
 	blueprint.RuleParams{
 		Command: `rm -rf "$outDir" && mkdir -p "$outDir" && ` +
@@ -351,10 +361,14 @@ func (d *dexer) r8Flags(ctx android.ModuleContext, flags javaBuilderFlags) (r8Fl
 		r8Flags = append(r8Flags, "-ignorewarnings")
 	}
 
+	// resourcesInput is empty when we don't use resource shrinking, if on, pass these to R8
 	if d.resourcesInput.Valid() {
 		r8Flags = append(r8Flags, "--resource-input", d.resourcesInput.Path().String())
 		r8Deps = append(r8Deps, d.resourcesInput.Path())
 		r8Flags = append(r8Flags, "--resource-output", d.resourcesOutput.Path().String())
+		if Bool(opt.Optimized_shrink_resources) {
+			r8Flags = append(r8Flags, "--optimized-resource-shrinking")
+		}
 	}
 
 	return r8Flags, r8Deps