Action for resource shrinking with aapt2

Introduces the ResourcesZip class to more easily handle processing merged resources.

RELNOTES: None
PiperOrigin-RevId: 169622715

15 files changed, 493 insertions, 109 deletions

diff --git a/src/tools/android/java/com/google/devtools/build/android/Aapt2ResourcePackagingAction.java b/src/tools/android/java/com/google/devtools/build/android/Aapt2ResourcePackagingAction.java
index 4b53f88423..2ddcdc9acc 100644
--- a/src/tools/android/java/com/google/devtools/build/android/Aapt2ResourcePackagingAction.java
+++ b/src/tools/android/java/com/google/devtools/build/android/Aapt2ResourcePackagingAction.java
@@ -23,6 +23,7 @@ import com.google.devtools.build.android.AndroidResourceMerger.MergingException;
 import com.google.devtools.build.android.AndroidResourceProcessingAction.Options;
 import com.google.devtools.build.android.aapt2.Aapt2ConfigOptions;
 import com.google.devtools.build.android.aapt2.CompiledResources;
+import com.google.devtools.build.android.aapt2.PackagedResources;
 import com.google.devtools.build.android.aapt2.ResourceCompiler;
 import com.google.devtools.build.android.aapt2.ResourceLinker;
 import com.google.devtools.build.android.aapt2.StaticLibrary;
@@ -84,13 +85,9 @@ public class Aapt2ResourcePackagingAction {
       final Path densityManifest = tmp.resolve("manifest-filtered/AndroidManifest.xml");
 
       final Path processedManifest = tmp.resolve("manifest-processed/AndroidManifest.xml");
-      final Path dummyManifest = tmp.resolve("manifest-aapt-dummy/AndroidManifest.xml");
       final Path databindingResourcesRoot =
           Files.createDirectories(tmp.resolve("android_data_binding_resources"));
-      final Path databindingMetaData =
-          Files.createDirectories(tmp.resolve("android_data_binding_metadata"));
       final Path compiledResources = Files.createDirectories(tmp.resolve("compiled"));
-      final Path staticLinkedOut = Files.createDirectories(tmp.resolve("static-linked"));
       final Path linkedOut = Files.createDirectories(tmp.resolve("linked"));
 
       profiler.recordEndOf("setup").startTask("merging");
@@ -157,30 +154,31 @@ public class Aapt2ResourcePackagingAction {
                 .map(DependencyAndroidData::getStaticLibrary)
                 .collect(toList());
 
-        ResourceLinker.create(aaptConfigOptions.aapt2, linkedOut)
-            .profileUsing(profiler)
-            .dependencies(ImmutableList.of(StaticLibrary.from(aaptConfigOptions.androidJar)))
-            .include(dependencies)
-            .buildVersion(aaptConfigOptions.buildToolsVersion)
-            .filterToDensity(densitiesToFilter)
-            .link(compiled)
-            .copyPackageTo(options.packagePath)
-            .copyProguardTo(options.proguardOutput)
-            .copyMainDexProguardTo(options.mainDexProguardOutput)
-            .createSourceJar(options.srcJarOutput)
-            .copyRTxtTo(options.rOutput);
+        final PackagedResources packagedResources =
+            ResourceLinker.create(aaptConfigOptions.aapt2, linkedOut)
+                .profileUsing(profiler)
+                .dependencies(ImmutableList.of(StaticLibrary.from(aaptConfigOptions.androidJar)))
+                .include(dependencies)
+                .buildVersion(aaptConfigOptions.buildToolsVersion)
+                .filterToDensity(densitiesToFilter)
+                .link(compiled)
+                .copyPackageTo(options.packagePath)
+                .copyProguardTo(options.proguardOutput)
+                .copyMainDexProguardTo(options.mainDexProguardOutput)
+                .createSourceJar(options.srcJarOutput)
+                .copyRTxtTo(options.rOutput);
         profiler.recordEndOf("link");
-      }
-      if (options.resourcesOutput != null) {
-        profiler.startTask("package");
-        // The compiled resources and the merged resources should be the same.
-        // TODO(corysmith): Decompile or otherwise provide the exact resources in the apk.
-        AndroidResourceOutputs.createResourcesZip(
-            mergedAndroidData.getResourceDir(),
-            mergedAndroidData.getAssetDir(),
-            options.resourcesOutput,
-            false /* compress */);
-        profiler.recordEndOf("package");
+        if (options.resourcesOutput != null) {
+          profiler.startTask("package");
+          // The compiled resources and the merged resources should be the same.
+          // TODO(corysmith): Decompile or otherwise provide the exact resources in the apk.
+          ResourcesZip.from(
+                  mergedAndroidData.getResourceDir(),
+                  mergedAndroidData.getAssetDir(),
+                  packagedResources.resourceIds())
+              .writeTo(options.resourcesOutput, false /* compress */);
+          profiler.recordEndOf("package");
+        }
       }
     } catch (MergingException e) {
       logger.severe("Merging exception: " + e.getMessage());
diff --git a/src/tools/android/java/com/google/devtools/build/android/Aapt2ResourceShrinkingAction.java b/src/tools/android/java/com/google/devtools/build/android/Aapt2ResourceShrinkingAction.java
new file mode 100644
index 0000000000..2fbae70f40
--- /dev/null
+++ b/src/tools/android/java/com/google/devtools/build/android/Aapt2ResourceShrinkingAction.java
@@ -0,0 +1,128 @@
+// Copyright 2017 The Bazel Authors. 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 com.google.devtools.build.android;
+
+import static java.util.stream.Collectors.toSet;
+
+import com.android.builder.core.VariantConfiguration;
+import com.google.common.collect.ImmutableList;
+import com.google.common.util.concurrent.ListenableFuture;
+import com.google.common.util.concurrent.ListeningExecutorService;
+import com.google.devtools.build.android.ResourceShrinkerAction.Options;
+import com.google.devtools.build.android.aapt2.Aapt2ConfigOptions;
+import com.google.devtools.build.android.aapt2.CompiledResources;
+import com.google.devtools.build.android.aapt2.ResourceCompiler;
+import com.google.devtools.build.android.aapt2.ResourceLinker;
+import com.google.devtools.build.android.aapt2.StaticLibrary;
+import com.google.devtools.common.options.OptionsParser;
+import java.io.Closeable;
+import java.io.File;
+import java.nio.file.Path;
+import java.util.concurrent.ExecutionException;
+import java.util.function.Function;
+
+/**
+ * An action to perform resource shrinking using the Gradle resource shrinker.
+ *
+ * <pre>
+ * Example Usage:
+ *   java/com/google/build/android/ResourceShrinkerAction
+ *       --aapt2 path to sdk/aapt2
+ *       --annotationJar path to sdk/annotationJar
+ *       --androidJar path to sdk/androidJar
+ *       --shrunkJar path to proguard dead code removal jar
+ *       --resources path to processed resources zip
+ *       --rTxt path to processed resources R.txt
+ *       --primaryManifest path to processed resources AndroidManifest.xml
+ *       --dependencyManifest path to dependency library manifest (repeated flag)
+ *       --shrunkResourceApk path to write shrunk ap_
+ *       --shrunkResources path to write shrunk resources zip
+ * </pre>
+ */
+public class Aapt2ResourceShrinkingAction {
+
+  public static void main(String[] args) throws Exception {
+    final Profiler profiler = LoggingProfiler.createAndStart("shrink").startTask("flags");
+    // Parse arguments.
+    OptionsParser optionsParser =
+        OptionsParser.newOptionsParser(Options.class, Aapt2ConfigOptions.class);
+    optionsParser.parseAndExitUponError(args);
+    Aapt2ConfigOptions aapt2ConfigOptions = optionsParser.getOptions(Aapt2ConfigOptions.class);
+    Options options = optionsParser.getOptions(Options.class);
+    options.dependencyManifests =
+        Converters.concatLists(options.dependencyManifests, options.deprecatedDependencyManifests);
+    profiler.recordEndOf("flags").startTask("setup");
+
+    final ListeningExecutorService executorService = ExecutorServiceCloser.createDefaultService();
+    try (ScopedTemporaryDirectory scopedTmp =
+            new ScopedTemporaryDirectory("android_resources_tmp");
+        Closeable closer = ExecutorServiceCloser.createWith(executorService)) {
+
+      Path workingResourcesDirectory = scopedTmp.subDirectoryOf("resources");
+      final ResourceCompiler resourceCompiler =
+          ResourceCompiler.create(
+              executorService,
+              workingResourcesDirectory,
+              aapt2ConfigOptions.aapt2,
+              aapt2ConfigOptions.buildToolsVersion);
+      profiler.recordEndOf("setup").startTask("compile");
+
+      final ResourcesZip resourcesZip =
+          ResourcesZip.createFrom(
+              options.resourcesZip, scopedTmp.subDirectoryOf("merged-resources"));
+      final CompiledResources compiled =
+          resourcesZip
+              .shrink(
+                  options
+                      .dependencyManifests
+                      .stream()
+                      .map(Path::toFile)
+                      .map(manifestToPackageUsing(executorService))
+                      .map(futureToString())
+                      .collect(toSet()),
+                  options.rTxt,
+                  options.shrunkJar,
+                  options.primaryManifest,
+                  options.proguardMapping,
+                  options.log,
+                  scopedTmp.subDirectoryOf("shrunk-resources"))
+              .writeArchiveTo(options.shrunkResources, false)
+              .compile(resourceCompiler, workingResourcesDirectory);
+      profiler.recordEndOf("compile");
+
+      ResourceLinker.create(aapt2ConfigOptions.aapt2, scopedTmp.subDirectoryOf("linking"))
+          .profileUsing(profiler)
+          .dependencies(ImmutableList.of(StaticLibrary.from(aapt2ConfigOptions.androidJar)))
+          .link(compiled)
+          .copyPackageTo(options.shrunkApk)
+          .copyRTxtTo(options.rTxtOutput);
+      profiler.recordEndOf("shrink");
+    }
+  }
+
+  static Function<File, ListenableFuture<String>> manifestToPackageUsing(
+      ListeningExecutorService executor) {
+    return f -> executor.submit(() -> VariantConfiguration.getManifestPackage(f));
+  }
+
+  static Function<ListenableFuture<String>, String> futureToString() {
+    return f -> {
+      try {
+        return f.get();
+      } catch (InterruptedException | ExecutionException e) {
+        throw new RuntimeException(e);
+      }
+    };
+  }
+}
diff --git a/src/tools/android/java/com/google/devtools/build/android/AaptCommandBuilder.java b/src/tools/android/java/com/google/devtools/build/android/AaptCommandBuilder.java
index ad645a6fdd..f4b70fc930 100644
--- a/src/tools/android/java/com/google/devtools/build/android/AaptCommandBuilder.java
+++ b/src/tools/android/java/com/google/devtools/build/android/AaptCommandBuilder.java
@@ -27,6 +27,7 @@ import java.nio.file.Files;
 import java.nio.file.Path;
 import java.util.Collection;
 import java.util.List;
+import java.util.Optional;
 import java.util.stream.Collectors;
 import javax.annotation.Nullable;
 
@@ -164,6 +165,13 @@ public class AaptCommandBuilder {
     return flags.build();
   }
 
+  public AaptCommandBuilder add(String flag, Optional<Path> optionalPath) {
+    Preconditions.checkNotNull(flag);
+    Preconditions.checkNotNull(optionalPath);
+    optionalPath.map(p -> add(flag, p));
+    return this;
+  }
+
   /** Wrapper for potentially adding flags to an AaptCommandBuilder based on a conditional. */
   public interface ConditionalAaptCommandBuilder {
     /**
@@ -190,6 +198,14 @@ public class AaptCommandBuilder {
     AaptCommandBuilder thenAdd(String flag, @Nullable Path value);
 
     /**
+     * Adds a single flag and associated path value to the builder if the value is non-null and the
+     * condition was true.
+     *
+     * @see AaptCommandBuilder#add(String,Optional)
+     */
+    AaptCommandBuilder thenAdd(String flag, Optional<Path> value);
+
+    /**
      * Adds the values in the collection to the builder, each preceded by the given flag, if the
      * collection was non-empty and the condition was true.
      *
@@ -224,6 +240,11 @@ public class AaptCommandBuilder {
     }
 
     @Override
+    public AaptCommandBuilder thenAdd(String flag, @Nullable Optional<Path> value) {
+      return originalCommandBuilder.add(flag, value);
+    }
+
+    @Override
     public AaptCommandBuilder thenAddRepeated(String flag, Collection<String> values) {
       return originalCommandBuilder.addRepeated(flag, values);
     }
@@ -256,6 +277,13 @@ public class AaptCommandBuilder {
     }
 
     @Override
+    public AaptCommandBuilder thenAdd(String flag, Optional<Path> value) {
+      Preconditions.checkNotNull(flag);
+      Preconditions.checkNotNull(value);
+      return originalCommandBuilder;
+    }
+
+    @Override
     public AaptCommandBuilder thenAddRepeated(String flag, Collection<String> values) {
       Preconditions.checkNotNull(flag);
       Preconditions.checkNotNull(values);
diff --git a/src/tools/android/java/com/google/devtools/build/android/AndroidResourceMergingAction.java b/src/tools/android/java/com/google/devtools/build/android/AndroidResourceMergingAction.java
index 7beac4760a..78393dcc3b 100644
--- a/src/tools/android/java/com/google/devtools/build/android/AndroidResourceMergingAction.java
+++ b/src/tools/android/java/com/google/devtools/build/android/AndroidResourceMergingAction.java
@@ -280,8 +280,8 @@ public class AndroidResourceMergingAction {
 
         // For now, try compressing the library resources that we pass to the validator. This takes
         // extra CPU resources to pack and unpack (~2x), but can reduce the zip size (~4x).
-        AndroidResourceOutputs.createResourcesZip(
-            resourcesDir, mergedData.getAssetDir(), options.resourcesOutput, true /* compress */);
+        ResourcesZip.from(resourcesDir, mergedData.getAssetDir())
+            .writeTo(options.resourcesOutput, true /* compress */);
         logger.fine(
             String.format(
                 "Create resources.zip finished at %sms", timer.elapsed(TimeUnit.MILLISECONDS)));
diff --git a/src/tools/android/java/com/google/devtools/build/android/AndroidResourceOutputs.java b/src/tools/android/java/com/google/devtools/build/android/AndroidResourceOutputs.java
index 97c261610e..d6558ed437 100644
--- a/src/tools/android/java/com/google/devtools/build/android/AndroidResourceOutputs.java
+++ b/src/tools/android/java/com/google/devtools/build/android/AndroidResourceOutputs.java
@@ -338,33 +338,6 @@ public class AndroidResourceOutputs {
     }
   }
 
-  /**
-   * Creates a zip file containing the provided android resources and assets.
-   *
-   * @param resourcesRoot The root containing android resources to be written.
-   * @param assetsRoot The root containing android assets to be written.
-   * @param output The path to write the zip file
-   * @param compress Whether or not to compress the content
-   * @throws IOException
-   */
-  public static void createResourcesZip(
-      Path resourcesRoot, Path assetsRoot, Path output, boolean compress) throws IOException {
-    try (final ZipBuilder zip = ZipBuilder.createFor(output)) {
-      if (Files.exists(resourcesRoot)) {
-        ZipBuilderVisitor visitor = new ZipBuilderVisitor(zip, resourcesRoot, "res");
-        visitor.setCompress(compress);
-        Files.walkFileTree(resourcesRoot, visitor);
-        visitor.writeEntries();
-      }
-      if (Files.exists(assetsRoot)) {
-        ZipBuilderVisitor visitor = new ZipBuilderVisitor(zip, assetsRoot, "assets");
-        visitor.setCompress(compress);
-        Files.walkFileTree(assetsRoot, visitor);
-        visitor.writeEntries();
-      }
-    }
-  }
-
   /** Creates a zip archive from all found R.java files. */
   public static void createSrcJar(Path generatedSourcesRoot, Path srcJar, boolean staticIds) {
     try {
diff --git a/src/tools/android/java/com/google/devtools/build/android/AndroidResourceProcessingAction.java b/src/tools/android/java/com/google/devtools/build/android/AndroidResourceProcessingAction.java
index 4380a0b69b..4ec9ebcf92 100644
--- a/src/tools/android/java/com/google/devtools/build/android/AndroidResourceProcessingAction.java
+++ b/src/tools/android/java/com/google/devtools/build/android/AndroidResourceProcessingAction.java
@@ -437,7 +437,7 @@ public class AndroidResourceProcessingAction {
       }
 
       if (options.packageType == VariantType.LIBRARY) {
-        resourceProcessor.writeDummyManifestForAapt(dummyManifest, options.packageForR);
+        AndroidResourceProcessor.writeDummyManifestForAapt(dummyManifest, options.packageForR);
         processedData =
             new MergedAndroidData(
                 processedData.getResourceDir(), processedData.getAssetDir(), dummyManifest);
@@ -488,11 +488,8 @@ public class AndroidResourceProcessingAction {
             generatedSources, options.rOutput, VariantType.LIBRARY == options.packageType);
       }
       if (options.resourcesOutput != null) {
-        AndroidResourceOutputs.createResourcesZip(
-            processedData.getResourceDir(),
-            processedData.getAssetDir(),
-            options.resourcesOutput,
-            false /* compress */);
+        ResourcesZip.from(processedData.getResourceDir(), processedData.getAssetDir())
+            .writeTo(options.resourcesOutput, false /* compress */);
       }
       logger.fine(
           String.format("Packaging finished at %sms", timer.elapsed(TimeUnit.MILLISECONDS)));
diff --git a/src/tools/android/java/com/google/devtools/build/android/ResourceProcessorBusyBox.java b/src/tools/android/java/com/google/devtools/build/android/ResourceProcessorBusyBox.java
index a5f9271696..317599989f 100644
--- a/src/tools/android/java/com/google/devtools/build/android/ResourceProcessorBusyBox.java
+++ b/src/tools/android/java/com/google/devtools/build/android/ResourceProcessorBusyBox.java
@@ -126,6 +126,12 @@ public class ResourceProcessorBusyBox {
       void call(String[] args) throws Exception {
         Aapt2ResourcePackagingAction.main(args);
       }
+    },
+    SHRINK_AAPT2() {
+      @Override
+      void call(String[] args) throws Exception {
+        Aapt2ResourceShrinkingAction.main(args);
+      }
     };
 
     abstract void call(String[] args) throws Exception;
@@ -152,7 +158,7 @@ public class ResourceProcessorBusyBox {
           "The processing tool to execute. "
               + "Valid tools: PACKAGE, VALIDATE, GENERATE_BINARY_R, GENERATE_LIBRARY_R, PARSE, "
               + "MERGE, GENERATE_AAR, SHRINK, MERGE_MANIFEST, COMPILE_LIBRARY_RESOURCES, "
-              + "LINK_STATIC_LIBRARY, AAPT2_PACKAGE."
+              + "LINK_STATIC_LIBRARY, AAPT2_PACKAGE, SHRINK_AAPT2."
     )
     public Tool tool;
   }
diff --git a/src/tools/android/java/com/google/devtools/build/android/ResourceShrinkerAction.java b/src/tools/android/java/com/google/devtools/build/android/ResourceShrinkerAction.java
index f8cd48722e..8e0a5995d3 100644
--- a/src/tools/android/java/com/google/devtools/build/android/ResourceShrinkerAction.java
+++ b/src/tools/android/java/com/google/devtools/build/android/ResourceShrinkerAction.java
@@ -327,11 +327,8 @@ public class ResourceShrinkerAction {
           null /* publicResourcesOut */,
           null /* dataBindingInfoOut */);
       if (options.shrunkResources != null) {
-        AndroidResourceOutputs.createResourcesZip(
-            shrunkResources,
-            resourceFiles.resolve("assets"),
-            options.shrunkResources,
-            false /* compress */);
+        ResourcesZip.from(shrunkResources, resourceFiles.resolve("assets"))
+            .writeTo(options.shrunkResources, false /* compress */);
       }
       if (options.rTxtOutput != null) {
         AndroidResourceOutputs.copyRToOutput(
diff --git a/src/tools/android/java/com/google/devtools/build/android/ResourcesZip.java b/src/tools/android/java/com/google/devtools/build/android/ResourcesZip.java
new file mode 100644
index 0000000000..e5436ad388
--- /dev/null
+++ b/src/tools/android/java/com/google/devtools/build/android/ResourcesZip.java
@@ -0,0 +1,184 @@
+// Copyright 2017 The Bazel Authors. 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 com.google.devtools.build.android;
+
+import static com.google.common.base.Predicates.not;
+
+import com.android.build.gradle.tasks.ResourceUsageAnalyzer;
+import com.google.common.collect.ImmutableList;
+import com.google.common.io.ByteStreams;
+import com.google.devtools.build.android.AndroidResourceOutputs.ZipBuilder;
+import com.google.devtools.build.android.AndroidResourceOutputs.ZipBuilderVisitor;
+import com.google.devtools.build.android.aapt2.CompiledResources;
+import com.google.devtools.build.android.aapt2.ResourceCompiler;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.Optional;
+import java.util.Set;
+import java.util.concurrent.ExecutionException;
+import java.util.zip.ZipEntry;
+import java.util.zip.ZipFile;
+import javax.annotation.Nullable;
+import javax.xml.parsers.ParserConfigurationException;
+import org.xml.sax.SAXException;
+
+/** Represents a collection of raw, merged resources with an optional id list. */
+public class ResourcesZip {
+
+  private final Path resourcesRoot;
+  private final Path assetsRoot;
+  private final Optional<Path> ids;
+
+  private ResourcesZip(Path resourcesRoot, Path assetsRoot, Optional<Path> ids) {
+    this.resourcesRoot = resourcesRoot;
+    this.assetsRoot = assetsRoot;
+    this.ids = ids;
+  }
+
+  /**
+   * @param resourcesRoot The root of the raw resources.
+   * @param assetsRoot The root of the raw assets.
+   */
+  public static ResourcesZip from(Path resourcesRoot, Path assetsRoot) {
+    return new ResourcesZip(resourcesRoot, assetsRoot, Optional.empty());
+  }
+
+  /**
+   * @param resourcesRoot The root of the raw resources.
+   * @param assetsRoot The root of the raw assets.
+   * @param resourceIds Optional path to a file containing the resource ids.
+   */
+  public static ResourcesZip from(Path resourcesRoot, Path assetsRoot, Path resourceIds) {
+    return new ResourcesZip(
+        resourcesRoot, assetsRoot, Optional.of(resourceIds).filter(Files::exists));
+  }
+
+  /** Creates a ResourcesZip from an archive by expanding into the workingDirectory. */
+  public static ResourcesZip createFrom(Path resourcesZip, Path workingDirectory)
+      throws IOException {
+    // Expand resource files zip into working directory.
+    final ZipFile zipFile = new ZipFile(resourcesZip.toFile());
+
+    zipFile
+        .stream()
+        .filter(not(ZipEntry::isDirectory))
+        .forEach(
+            entry -> {
+              Path output = workingDirectory.resolve(entry.getName());
+              try {
+                Files.createDirectories(output.getParent());
+                try (FileOutputStream fos = new FileOutputStream(output.toFile())) {
+                  ByteStreams.copy(zipFile.getInputStream(entry), fos);
+                }
+              } catch (IOException e) {
+                throw new RuntimeException(e);
+              }
+            });
+    return from(
+        Files.createDirectories(workingDirectory.resolve("res")),
+        Files.createDirectories(workingDirectory.resolve("assets")),
+        workingDirectory.resolve("ids.txt"));
+  }
+
+  /**
+   * Creates a zip file containing the provided android resources and assets.
+   *
+   * @param output The path to write the zip file
+   * @param compress Whether or not to compress the content
+   * @throws IOException
+   */
+  public void writeTo(Path output, boolean compress) throws IOException {
+    try (final ZipBuilder zip = ZipBuilder.createFor(output)) {
+      if (Files.exists(resourcesRoot)) {
+        ZipBuilderVisitor visitor = new ZipBuilderVisitor(zip, resourcesRoot, "res");
+        visitor.setCompress(compress);
+        Files.walkFileTree(resourcesRoot, visitor);
+        if (!Files.exists(resourcesRoot.resolve("values/public.xml"))) {
+          // add an empty public xml, if one doesn't exist. The ResourceUsageAnalyzer expects one.
+          visitor.addEntry(
+              resourcesRoot.resolve("values").resolve("public.xml"),
+              "<resources></resources>".getBytes(StandardCharsets.UTF_8));
+        }
+        visitor.writeEntries();
+      }
+      if (Files.exists(assetsRoot)) {
+        ZipBuilderVisitor visitor = new ZipBuilderVisitor(zip, assetsRoot, "assets");
+        visitor.setCompress(compress);
+        Files.walkFileTree(assetsRoot, visitor);
+        visitor.writeEntries();
+      }
+
+      ids.ifPresent(
+          p -> {
+            try {
+              zip.addEntry("ids.txt", Files.readAllBytes(p), ZipEntry.STORED);
+            } catch (IOException e) {
+              throw new RuntimeException(e);
+            }
+          });
+    }
+  }
+
+  /** Removes unused resources from the archived resources. */
+  public ShrunkResources shrink(
+      Set<String> packages,
+      Path rTxt,
+      Path classJar,
+      Path manifest,
+      @Nullable Path proguardMapping,
+      Path logFile,
+      Path workingDirectory)
+      throws ParserConfigurationException, IOException, SAXException {
+
+    new ResourceUsageAnalyzer(
+            packages, rTxt, classJar, manifest, proguardMapping, resourcesRoot, logFile)
+        .shrink(workingDirectory);
+    return ShrunkResources.of(
+        new ResourcesZip(workingDirectory, assetsRoot, ids),
+        new UnvalidatedAndroidData(
+            ImmutableList.of(workingDirectory), ImmutableList.of(assetsRoot), manifest));
+  }
+
+  static class ShrunkResources {
+
+    private ResourcesZip resourcesZip;
+    private UnvalidatedAndroidData unvalidatedAndroidData;
+
+    private ShrunkResources(
+        ResourcesZip resourcesZip, UnvalidatedAndroidData unvalidatedAndroidData) {
+      this.resourcesZip = resourcesZip;
+      this.unvalidatedAndroidData = unvalidatedAndroidData;
+    }
+
+    public static ShrunkResources of(
+        ResourcesZip resourcesZip, UnvalidatedAndroidData unvalidatedAndroidData) {
+      return new ShrunkResources(resourcesZip, unvalidatedAndroidData);
+    }
+
+    public ShrunkResources writeArchiveTo(Path archivePath, boolean compress) throws IOException {
+      resourcesZip.writeTo(archivePath, compress);
+      return this;
+    }
+
+    public CompiledResources compile(ResourceCompiler compiler, Path workingDirectory)
+        throws InterruptedException, ExecutionException, IOException {
+      return unvalidatedAndroidData
+          .compile(compiler, workingDirectory)
+          .addStableIds(resourcesZip.ids);
+    }
+  }
+}
diff --git a/src/tools/android/java/com/google/devtools/build/android/ScopedTemporaryDirectory.java b/src/tools/android/java/com/google/devtools/build/android/ScopedTemporaryDirectory.java
index f7bcc88dfb..e9c1ca6a48 100644
--- a/src/tools/android/java/com/google/devtools/build/android/ScopedTemporaryDirectory.java
+++ b/src/tools/android/java/com/google/devtools/build/android/ScopedTemporaryDirectory.java
@@ -47,6 +47,14 @@ final class ScopedTemporaryDirectory extends SimpleFileVisitor<Path> implements
     return this.path;
   }
 
+  public Path subDirectoryOf(String... directories) throws IOException {
+    Path sub = this.path;
+    for (String directory : directories) {
+      sub = sub.resolve(directory);
+    }
+    return Files.createDirectories(sub);
+  }
+
   private void makeWritable(Path file) throws IOException {
     FileStore fileStore = Files.getFileStore(file);
     if (IS_WINDOWS && fileStore.supportsFileAttributeView(DosFileAttributeView.class)) {
diff --git a/src/tools/android/java/com/google/devtools/build/android/aapt2/CompiledResources.java b/src/tools/android/java/com/google/devtools/build/android/aapt2/CompiledResources.java
index aa13dc35ce..21eb59dd15 100644
--- a/src/tools/android/java/com/google/devtools/build/android/aapt2/CompiledResources.java
+++ b/src/tools/android/java/com/google/devtools/build/android/aapt2/CompiledResources.java
@@ -13,6 +13,7 @@
 // limitations under the License.
 package com.google.devtools.build.android.aapt2;
 
+import com.google.common.base.Preconditions;
 import com.google.common.collect.ImmutableList;
 import com.google.devtools.build.android.ManifestContainer;
 import java.io.IOException;
@@ -34,21 +35,24 @@ public class CompiledResources implements ManifestContainer {
   private final Path resources;
   private final Path manifest;
   private final List<Path> assetsDirs;
+  private final Optional<Path> stableIds;
 
-  private CompiledResources(Path resources, Path manifest, List<Path> assetsDirs) {
+  private CompiledResources(
+      Path resources, Path manifest, List<Path> assetsDirs, Optional<Path> stableIds) {
     this.resources = resources;
     this.manifest = manifest;
     this.assetsDirs = assetsDirs;
+    this.stableIds = stableIds;
   }
 
   public static CompiledResources from(Path resources, Path manifest) {
-    return from(resources, manifest, null);
+    return from(resources, manifest, ImmutableList.of());
   }
 
   public static CompiledResources from(
       Path resources, Path manifest, @Nullable List<Path> assetDirs) {
     return new CompiledResources(
-        resources, manifest, Optional.ofNullable(assetDirs).orElseGet(ImmutableList::of));
+        resources, manifest, assetDirs != null ? assetDirs : ImmutableList.of(), Optional.empty());
   }
 
   public Path getZip() {
@@ -57,22 +61,37 @@ public class CompiledResources implements ManifestContainer {
 
   /** Copies resources archive to a path and returns the new {@link CompiledResources} */
   public CompiledResources copyResourcesZipTo(Path destination) throws IOException {
-    return new CompiledResources(Files.copy(resources, destination), manifest, assetsDirs);
+    return new CompiledResources(
+        Files.copy(resources, destination), manifest, assetsDirs, stableIds);
   }
 
   @Override
   public Path getManifest() {
+    Preconditions.checkState(Files.exists(manifest));
     return manifest;
   }
 
   public List<String> getAssetsStrings() {
     return assetsDirs
         .stream()
+        .map(
+            p -> {
+              Preconditions.checkArgument(Files.exists(p), "does not exist %s", p);
+              return p;
+            })
         .map(Path::toString)
         .collect(Collectors.toList());
   }
 
   public CompiledResources processManifest(Function<Path, Path> processManifest) {
-    return new CompiledResources(resources, processManifest.apply(manifest), assetsDirs);
+    return new CompiledResources(resources, processManifest.apply(manifest), assetsDirs, stableIds);
+  }
+
+  public CompiledResources addStableIds(Optional<Path> stableIds) {
+    return new CompiledResources(resources, manifest, assetsDirs, stableIds);
+  }
+
+  public Optional<Path> getStableIds() {
+    return stableIds;
   }
 }
diff --git a/src/tools/android/java/com/google/devtools/build/android/aapt2/PackagedResources.java b/src/tools/android/java/com/google/devtools/build/android/aapt2/PackagedResources.java
index 77c9c66cc6..6f77b5966e 100644
--- a/src/tools/android/java/com/google/devtools/build/android/aapt2/PackagedResources.java
+++ b/src/tools/android/java/com/google/devtools/build/android/aapt2/PackagedResources.java
@@ -17,6 +17,7 @@ import com.google.devtools.build.android.AndroidResourceOutputs;
 import java.io.IOException;
 import java.nio.file.Files;
 import java.nio.file.Path;
+import javax.annotation.Nullable;
 
 /** Represents the packaged, flattened resources. */
 public class PackagedResources {
@@ -26,19 +27,43 @@ public class PackagedResources {
   private final Path proguardConfig;
   private final Path mainDexProguard;
   private final Path javaSourceDirectory;
+  private final Path resourceIds;
 
   private PackagedResources(
-      Path apk, Path rTxt, Path proguardConfig, Path mainDexProguard, Path javaSourceDirectory) {
+      Path apk,
+      Path rTxt,
+      Path proguardConfig,
+      Path mainDexProguard,
+      Path javaSourceDirectory,
+      Path resourceIds) {
     this.apk = apk;
     this.rTxt = rTxt;
     this.proguardConfig = proguardConfig;
     this.mainDexProguard = mainDexProguard;
     this.javaSourceDirectory = javaSourceDirectory;
+    this.resourceIds = resourceIds;
   }
 
-  public PackagedResources copyPackageTo(Path packagePath) throws IOException {
+  public static PackagedResources of(
+      Path outPath,
+      Path rTxt,
+      Path proguardConfig,
+      Path mainDexProguard,
+      Path javaSourceDirectory,
+      Path resourceIds)
+      throws IOException {
     return new PackagedResources(
-        copy(apk, packagePath), rTxt, proguardConfig, mainDexProguard, javaSourceDirectory);
+        outPath, rTxt, proguardConfig, mainDexProguard, javaSourceDirectory, resourceIds);
+  }
+
+  public PackagedResources copyPackageTo(Path packagePath) throws IOException {
+    return of(
+        copy(apk, packagePath),
+        rTxt,
+        proguardConfig,
+        mainDexProguard,
+        javaSourceDirectory,
+        resourceIds);
   }
 
   public PackagedResources copyRTxtTo(Path rOutput) throws IOException {
@@ -46,7 +71,12 @@ public class PackagedResources {
       return this;
     }
     return new PackagedResources(
-        apk, copy(rTxt, rOutput), proguardConfig, mainDexProguard, javaSourceDirectory);
+        apk,
+        copy(rTxt, rOutput),
+        proguardConfig,
+        mainDexProguard,
+        javaSourceDirectory,
+        resourceIds);
   }
 
   private Path copy(Path from, Path out) throws IOException {
@@ -59,8 +89,13 @@ public class PackagedResources {
     if (proguardOut == null) {
       return this;
     }
-    return new PackagedResources(
-        apk, rTxt, copy(proguardConfig, proguardOut), mainDexProguard, javaSourceDirectory);
+    return of(
+        apk,
+        rTxt,
+        copy(proguardConfig, proguardOut),
+        mainDexProguard,
+        javaSourceDirectory,
+        resourceIds);
   }
 
   public PackagedResources copyMainDexProguardTo(Path mainDexProguardOut) throws IOException {
@@ -68,21 +103,23 @@ public class PackagedResources {
       return this;
     }
     return of(
-        apk, rTxt, proguardConfig, copy(mainDexProguard, mainDexProguardOut), javaSourceDirectory);
+        apk,
+        rTxt,
+        proguardConfig,
+        copy(mainDexProguard, mainDexProguardOut),
+        javaSourceDirectory,
+        resourceIds);
   }
 
-  public PackagedResources createSourceJar(Path sourceJarPath) throws IOException {
+  public PackagedResources createSourceJar(@Nullable Path sourceJarPath) throws IOException {
     if (sourceJarPath == null) {
       return this;
     }
     AndroidResourceOutputs.createSrcJar(javaSourceDirectory, sourceJarPath, false);
-    return of(apk, rTxt, proguardConfig, mainDexProguard, sourceJarPath);
+    return of(apk, rTxt, proguardConfig, mainDexProguard, sourceJarPath, resourceIds);
   }
 
-  public static PackagedResources of(
-      Path outPath, Path rTxt, Path proguardConfig, Path mainDexProguard, Path javaSourceDirectory)
-      throws IOException {
-    return new PackagedResources(
-        outPath, rTxt, proguardConfig, mainDexProguard, javaSourceDirectory);
+  public Path resourceIds() {
+    return resourceIds;
   }
 }
diff --git a/src/tools/android/java/com/google/devtools/build/android/aapt2/ResourceCompiler.java b/src/tools/android/java/com/google/devtools/build/android/aapt2/ResourceCompiler.java
index 6084f6710f..5f8b842859 100644
--- a/src/tools/android/java/com/google/devtools/build/android/aapt2/ResourceCompiler.java
+++ b/src/tools/android/java/com/google/devtools/build/android/aapt2/ResourceCompiler.java
@@ -46,7 +46,7 @@ public class ResourceCompiler {
     private final Path aapt2;
     private final Revision buildToolsVersion;
 
-    public CompileTask(
+    private CompileTask(
         Path file, Path compiledResourcesOut, Path aapt2, Revision buildToolsVersion) {
       this.file = file;
       this.compiledResourcesOut = compiledResourcesOut;
@@ -56,17 +56,16 @@ public class ResourceCompiler {
 
     @Override
     public Path call() throws Exception {
-        logger.fine(
-            new AaptCommandBuilder(aapt2)
-                .forBuildToolsVersion(buildToolsVersion)
-                .forVariantType(VariantType.LIBRARY)
-                .add("compile")
-                .add("-v")
-                .add("--legacy")
-                .add("-o", compiledResourcesOut.toString())
-                .add(file.toString())
-                .execute("Compiling " + file));
-
+      logger.fine(
+          new AaptCommandBuilder(aapt2)
+              .forBuildToolsVersion(buildToolsVersion)
+              .forVariantType(VariantType.LIBRARY)
+              .add("compile")
+              .add("-v")
+              .add("--legacy")
+              .add("-o", compiledResourcesOut.toString())
+              .add(file.toString())
+              .execute("Compiling " + file));
 
       String type = file.getParent().getFileName().toString();
       String filename = file.getFileName().toString();
diff --git a/src/tools/android/java/com/google/devtools/build/android/aapt2/ResourceLinker.java b/src/tools/android/java/com/google/devtools/build/android/aapt2/ResourceLinker.java
index 8c26b5b8b8..e15ee6670f 100644
--- a/src/tools/android/java/com/google/devtools/build/android/aapt2/ResourceLinker.java
+++ b/src/tools/android/java/com/google/devtools/build/android/aapt2/ResourceLinker.java
@@ -17,6 +17,7 @@ import com.android.builder.core.VariantType;
 import com.android.repository.Revision;
 import com.google.common.base.Joiner;
 import com.google.common.base.MoreObjects;
+import com.google.common.base.Preconditions;
 import com.google.common.collect.ImmutableList;
 import com.google.common.io.ByteStreams;
 import com.google.devtools.build.android.AaptCommandBuilder;
@@ -50,14 +51,15 @@ public class ResourceLinker {
   private final Path workingDirectory;
 
   private List<StaticLibrary> linkAgainst = ImmutableList.of();
+
   private Revision buildToolsVersion;
-  private List<String> densities;
+  private List<String> densities = ImmutableList.of();
   private Path androidJar;
   private Profiler profiler = Profiler.empty();
   private List<String> uncompressedExtensions = ImmutableList.of();
   private List<String> resourceConfigs = ImmutableList.of();
   private Path baseApk;
-  private List<StaticLibrary> include;
+  private List<StaticLibrary> include = ImmutableList.of();
 
   private ResourceLinker(Path aapt2, Path workingDirectory) {
     this.aapt2 = aapt2;
@@ -65,6 +67,7 @@ public class ResourceLinker {
   }
 
   public static ResourceLinker create(Path aapt2, Path workingDirectory) {
+    Preconditions.checkArgument(Files.exists(workingDirectory));
     return new ResourceLinker(aapt2, workingDirectory);
   }
 
@@ -142,13 +145,14 @@ public class ResourceLinker {
   }
 
   public PackagedResources link(CompiledResources compiled) {
-    final Path outPath = workingDirectory.resolve("bin.apk");
-    Path rTxt = workingDirectory.resolve("R.txt");
-    Path proguardConfig = workingDirectory.resolve("proguard.cfg");
-    Path mainDexProguard = workingDirectory.resolve("proguard.maindex.cfg");
-    Path javaSourceDirectory = workingDirectory.resolve("java");
-
     try {
+      final Path outPath = workingDirectory.resolve("bin.apk");
+      Path rTxt = workingDirectory.resolve("R.txt");
+      Path proguardConfig = workingDirectory.resolve("proguard.cfg");
+      Path mainDexProguard = workingDirectory.resolve("proguard.maindex.cfg");
+      Path javaSourceDirectory = Files.createDirectories(workingDirectory.resolve("java"));
+      Path resourceIds = workingDirectory.resolve("ids.txt");
+
       profiler.startTask("fulllink");
       logger.finer(
           new AaptCommandBuilder(aapt2)
@@ -157,13 +161,16 @@ public class ResourceLinker {
               .add("link")
               .whenVersionIsAtLeast(new Revision(23))
               .thenAdd("--no-version-vectors")
+              // Turn off namespaced resources
               .add("--no-static-lib-packages")
               .when(Objects.equals(logger.getLevel(), Level.FINE))
               .thenAdd("-v")
               .add("--manifest", compiled.getManifest())
+              // Enables resource redefinition and merging
               .add("--auto-add-overlay")
               .when(densities.size() == 1)
               .thenAddRepeated("--preferred-density", densities)
+              .add("--stable-ids", compiled.getStableIds())
               .addRepeated("-A", compiled.getAssetsStrings())
               .addRepeated("-I", StaticLibrary.toPathStrings(linkAgainst))
               .addRepeated("-R", StaticLibrary.toPathStrings(include))
@@ -178,6 +185,7 @@ public class ResourceLinker {
               .when(!resourceConfigs.isEmpty())
               .thenAdd("-c", Joiner.on(',').join(resourceConfigs))
               .add("--output-text-symbols", rTxt)
+              .add("--emit-ids", resourceIds)
               .add("--java", javaSourceDirectory)
               .add("--proguard", proguardConfig)
               .add("--proguard-main-dex", mainDexProguard)
@@ -187,7 +195,7 @@ public class ResourceLinker {
       profiler.startTask("optimize");
       if (densities.size() < 2) {
         return PackagedResources.of(
-            outPath, rTxt, proguardConfig, mainDexProguard, javaSourceDirectory);
+            outPath, rTxt, proguardConfig, mainDexProguard, javaSourceDirectory, resourceIds);
       }
       final Path optimized = workingDirectory.resolve("optimized.apk");
       logger.finer(
@@ -201,7 +209,7 @@ public class ResourceLinker {
               .execute(String.format("Optimizing %s", compiled.getManifest())));
       profiler.recordEndOf("optimize");
       return PackagedResources.of(
-          optimized, rTxt, proguardConfig, mainDexProguard, javaSourceDirectory);
+          optimized, rTxt, proguardConfig, mainDexProguard, javaSourceDirectory, resourceIds);
     } catch (IOException e) {
       throw new LinkError(e);
     }
diff --git a/src/tools/android/java/com/google/devtools/build/android/aapt2/StaticLibrary.java b/src/tools/android/java/com/google/devtools/build/android/aapt2/StaticLibrary.java
index 54ba743224..142d7fefb1 100644
--- a/src/tools/android/java/com/google/devtools/build/android/aapt2/StaticLibrary.java
+++ b/src/tools/android/java/com/google/devtools/build/android/aapt2/StaticLibrary.java
@@ -16,6 +16,7 @@ package com.google.devtools.build.android.aapt2;
 import static com.google.common.collect.ImmutableList.toImmutableList;
 
 import com.google.common.annotations.VisibleForTesting;
+import com.google.common.base.Predicates;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.Lists;
 import java.io.IOException;
@@ -134,6 +135,7 @@ public class StaticLibrary {
     return libraries
         .stream()
         .map(StaticLibrary::asAssetPathStrings)
+        .filter(Predicates.isNull())
         .flatMap(List::stream)
         .map(Object::toString)
         .collect(toImmutableList());