Added ResourceShrinker - strips unused resources from final APK.

--
MOS_MIGRATED_REVID=108039800

2 files changed, 1097 insertions, 0 deletions

diff --git a/src/tools/android/java/com/google/devtools/build/android/BUILD b/src/tools/android/java/com/google/devtools/build/android/BUILD
index 7d5d18991c..74c12552bf 100644
--- a/src/tools/android/java/com/google/devtools/build/android/BUILD
+++ b/src/tools/android/java/com/google/devtools/build/android/BUILD
@@ -39,6 +39,7 @@ java_library(
         "//src/main/java/com/google/devtools/common/options",
         "//third_party:android_common",
         "//third_party:apache_commons_compress",
+        "//third_party:asm",
         "//third_party:guava",
         "//third_party:jsr305",
     ],
diff --git a/src/tools/android/java/com/google/devtools/build/android/ResourceShrinker.java b/src/tools/android/java/com/google/devtools/build/android/ResourceShrinker.java
new file mode 100644
index 0000000000..08decb2f4d
--- /dev/null
+++ b/src/tools/android/java/com/google/devtools/build/android/ResourceShrinker.java
@@ -0,0 +1,1096 @@
+// Copyright 2015 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.android.SdkConstants.ANDROID_STYLE_RESOURCE_PREFIX;
+import static com.android.SdkConstants.ANDROID_URI;
+import static com.android.SdkConstants.ATTR_NAME;
+import static com.android.SdkConstants.ATTR_PARENT;
+import static com.android.SdkConstants.ATTR_TYPE;
+import static com.android.SdkConstants.DOT_CLASS;
+import static com.android.SdkConstants.DOT_GIF;
+import static com.android.SdkConstants.DOT_JPEG;
+import static com.android.SdkConstants.DOT_JPG;
+import static com.android.SdkConstants.DOT_PNG;
+import static com.android.SdkConstants.DOT_XML;
+import static com.android.SdkConstants.FD_RES_VALUES;
+import static com.android.SdkConstants.PREFIX_ANDROID;
+import static com.android.SdkConstants.STYLE_RESOURCE_PREFIX;
+import static com.android.SdkConstants.TAG_ITEM;
+import static com.android.SdkConstants.TAG_RESOURCES;
+import static com.android.SdkConstants.TAG_STYLE;
+import static com.android.utils.SdkUtils.endsWith;
+import static com.android.utils.SdkUtils.endsWithIgnoreCase;
+import static com.google.common.base.Charsets.UTF_8;
+
+import com.google.common.base.Charsets;
+import com.google.common.base.Joiner;
+import com.google.common.collect.Lists;
+import com.google.common.collect.Maps;
+import com.google.common.collect.Sets;
+import com.google.common.io.ByteStreams;
+import com.google.common.io.Closeables;
+import com.google.common.io.Files;
+
+import com.android.annotations.NonNull;
+import com.android.annotations.Nullable;
+import com.android.annotations.VisibleForTesting;
+import com.android.ide.common.resources.ResourceUrl;
+import com.android.ide.common.resources.configuration.DensityQualifier;
+import com.android.ide.common.resources.configuration.FolderConfiguration;
+import com.android.ide.common.resources.configuration.ResourceQualifier;
+import com.android.ide.common.xml.XmlPrettyPrinter;
+import com.android.resources.FolderTypeRelationship;
+import com.android.resources.ResourceFolderType;
+import com.android.resources.ResourceType;
+import com.android.utils.XmlUtils;
+
+import org.objectweb.asm.ClassReader;
+import org.objectweb.asm.ClassVisitor;
+import org.objectweb.asm.MethodVisitor;
+import org.objectweb.asm.Opcodes;
+import org.w3c.dom.Attr;
+import org.w3c.dom.Document;
+import org.w3c.dom.Element;
+import org.w3c.dom.NamedNodeMap;
+import org.w3c.dom.Node;
+import org.w3c.dom.NodeList;
+import org.xml.sax.SAXException;
+
+import java.io.BufferedReader;
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.IOException;
+import java.nio.charset.Charset;
+import java.nio.file.Path;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.IdentityHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.zip.ZipEntry;
+import java.util.zip.ZipInputStream;
+
+import javax.xml.parsers.ParserConfigurationException;
+
+/**
+ * Class responsible for searching through a Gradle built tree (after resource merging, compilation
+ * and ProGuarding has been completed, but before final .apk assembly), which figures out which
+ * resources if any are unused, and removes them. <p> It does this by examining <ul> <li>The merged
+ * manifest, to find root resource references (such as drawables used for activity icons)</li>
+ * <li>The merged R class (to find the actual integer constants assigned to resources)</li> <li>The
+ * ProGuard log files (to find the mapping from original symbol names to short names)</li>* <li>The
+ * merged resources (to find which resources reference other resources, e.g. drawable state lists
+ * including other drawables, or layouts including other layouts, or styles referencing other
+ * drawables, or menus items including action layouts, etc.)</li> <li>The ProGuard output classes
+ * (to find resource references in code that are actually reachable)</li> </ul> From all this, it
+ * builds up a reference graph, and based on the root references (e.g. from the manifest and from
+ * the remaining code) it computes which resources are actually reachable in the app, and anything
+ * that is not reachable is then marked for deletion. <p> A resource is referenced in code if either
+ * the field R.type.name is referenced (which is the case for non-final resource references, e.g. in
+ * libraries), or if the corresponding int value is referenced (for final resource values). We check
+ * this by looking at the ProGuard output classes with an ASM visitor. One complication is that code
+ * can also call {@code Resources#getIdentifier(String,String,String)} where they can pass in the
+ * names of resources to look up. To handle this scenario, we use the ClassVisitor to see if there
+ * are any calls to the specific {@code Resources#getIdentifier} method. If not, great, the usage
+ * analysis is completely accurate. If we <b>do</b> find one, we check <b>all</b> the string
+ * constants found anywhere in the app, and look to see if any look relevant. For example, if we
+ * find the string "string/foo" or "my.pkg:string/foo", we will then mark the string resource named
+ * foo (if any) as potentially used. Similarly, if we find just "foo" or "/foo", we will mark
+ * <b>all</b> resources named "foo" as potentially used. However, if the string is "bar/foo" or "
+ * foo " these strings are ignored. This means we can potentially miss resources usages where the
+ * resource name is completed computed (e.g. by concatenating individual characters or taking
+ * substrings of strings that do not look like resource names), but that seems extremely unlikely to
+ * be a real-world scenario. <p> For now, for reasons detailed in the code, this only applies to
+ * file-based resources like layouts, menus and drawables, not value-based resources like strings
+ * and dimensions.
+ */
+public class ResourceShrinker {
+
+  public static final int TYPICAL_RESOURCE_COUNT = 200;
+  private final Path rTxt;
+  private final Path proguardMapping;
+  private final Path classesJar;
+  private final Path mergedManifest;
+  private final Path mergedResourceDir;
+  private final String rPackagePath;
+
+  /**
+   * The computed set of unused resources
+   */
+  private List<Resource> unused;
+  /**
+   * List of all known resources (parsed from R.java)
+   */
+  private List<Resource> resources = Lists.newArrayListWithExpectedSize(TYPICAL_RESOURCE_COUNT);
+  /**
+   * Map from R field value to corresponding resource
+   */
+  private Map<Integer, Resource> valueToResource =
+      Maps.newHashMapWithExpectedSize(TYPICAL_RESOURCE_COUNT);
+  /**
+   * Map from resource type to map from resource name to resource object
+   */
+  private Map<ResourceType, Map<String, Resource>> typeToName =
+      Maps.newEnumMap(ResourceType.class);
+  /**
+   * Map from resource class owners (VM format class) to corresponding resource types. This will
+   * typically be the fully qualified names of the R classes, as well as any renamed versions of
+   * those discovered in the mapping.txt file from ProGuard
+   */
+  private Map<String, ResourceType> resourceClassOwners = Maps.newHashMapWithExpectedSize(20);
+
+  public ResourceShrinker(
+      @NonNull Path rTxt,
+      @NonNull Path classesJar,
+      @NonNull Path manifest,
+      @Nullable Path mapping,
+      @NonNull Path resources,
+      @NonNull String rPackageName) {
+    this.rTxt = rTxt;
+    proguardMapping = mapping;
+    this.classesJar = classesJar;
+    mergedManifest = manifest;
+    mergedResourceDir = resources;
+    this.rPackagePath = rPackageName.replace('.', '/');
+  }
+
+  public void shrink(Path destinationDir) throws IOException,
+      ParserConfigurationException, SAXException {
+    parseResourceTxtFile(rTxt);
+    recordMapping(proguardMapping);
+    recordUsages(classesJar);
+    recordManifestUsages(mergedManifest);
+    recordResources(mergedResourceDir);
+    keepPossiblyReferencedResources();
+    dumpReferences();
+    findUnused();
+    removeUnused(destinationDir);
+  }
+
+  /**
+   * Remove resources (already identified by {@link #shrink(Path)}).
+   *
+   * <p>This task will copy all remaining used resources over from the full resource directory to a
+   * new reduced resource directory. However, it can't just delete the resources, because it has no
+   * way to tell aapt to continue to use the same id's for the resources. When we re-run aapt on the
+   * stripped resource directory, it will assign new id's to some of the resources (to fill the
+   * gaps) which means the resource id's no longer match the constants compiled into the dex files,
+   * and as a result, the app crashes at runtime. <p> Therefore, it needs to preserve all id's by
+   * actually keeping all the resource names. It can still save a lot of space by making these
+   * resources tiny; e.g. all strings are set to empty, all styles, arrays and plurals are set to
+   * not contain any children, and most importantly, all file based resources like bitmaps and
+   * layouts are replaced by simple resource aliases which just point to @null.
+   *
+   * @param destination directory to copy resources into; if null, delete resources in place
+   */
+  private void removeUnused(Path destination) throws IOException,
+      ParserConfigurationException, SAXException {
+    assert unused != null; // should always call analyze() first
+    int resourceCount = unused.size() * 4; // *4: account for some resource folder repetition
+    Set<File> skip = Sets.newHashSetWithExpectedSize(resourceCount);
+    Set<File> rewrite = Sets.newHashSetWithExpectedSize(resourceCount);
+    for (Resource resource : unused) {
+      if (resource.declarations != null) {
+        for (File file : resource.declarations) {
+          String folder = file.getParentFile().getName();
+          ResourceFolderType folderType = ResourceFolderType.getFolderType(folder);
+          if (folderType != null && folderType != ResourceFolderType.VALUES) {
+            System.out.println("Deleted unused resource " + file);
+            assert skip != null;
+            skip.add(file);
+          } else {
+            // Can't delete values immediately; there can be many resources
+            // in this file, so we have to process them all
+            rewrite.add(file);
+          }
+        }
+      }
+    }
+    // Special case the base values.xml folder
+    File values = new File(mergedResourceDir.toFile(),
+        FD_RES_VALUES + File.separatorChar + "values.xml");
+    boolean valuesExists = values.exists();
+    if (valuesExists) {
+      rewrite.add(values);
+    }
+    Map<File, String> rewritten = Maps.newHashMapWithExpectedSize(rewrite.size());
+    // Delete value resources: Must rewrite the XML files
+    for (File file : rewrite) {
+      String xml = Files.toString(file, UTF_8);
+      Document document = XmlUtils.parseDocument(xml, true);
+      Element root = document.getDocumentElement();
+      if (root != null && TAG_RESOURCES.equals(root.getTagName())) {
+        List<String> removed = Lists.newArrayList();
+        stripUnused(root, removed);
+        System.out.println("Removed " + removed.size() + " unused resources from " + file + ":\n  "
+            + Joiner.on(", ").join(removed));
+        String formatted = XmlPrettyPrinter.prettyPrint(document, xml.endsWith("\n"));
+        rewritten.put(file, formatted);
+      }
+    }
+    if (valuesExists) {
+      String xml = rewritten.get(values);
+      if (xml == null) {
+        xml = Files.toString(values, UTF_8);
+      }
+      Document document = XmlUtils.parseDocument(xml, true);
+      Element root = document.getDocumentElement();
+      for (Resource resource : resources) {
+        if (resource.type == ResourceType.ID && !resource.hasDefault) {
+          Element item = document.createElement(TAG_ITEM);
+          item.setAttribute(ATTR_TYPE, resource.type.getName());
+          item.setAttribute(ATTR_NAME, resource.name);
+          root.appendChild(item);
+        } else if (!resource.reachable
+            && !resource.hasDefault
+            && resource.type != ResourceType.DECLARE_STYLEABLE
+            && resource.type != ResourceType.STYLE
+            && resource.type != ResourceType.PLURALS
+            && resource.type != ResourceType.ARRAY
+            && resource.isRelevantType()) {
+          Element item = document.createElement(TAG_ITEM);
+          item.setAttribute(ATTR_TYPE, resource.type.getName());
+          item.setAttribute(ATTR_NAME, resource.name);
+          root.appendChild(item);
+          String s = "@null";
+          item.appendChild(document.createTextNode(s));
+        }
+      }
+      String formatted = XmlPrettyPrinter.prettyPrint(document, xml.endsWith("\n"));
+      rewritten.put(values, formatted);
+    }
+    filteredCopy(mergedResourceDir.toFile(), destination, skip, rewritten);
+  }
+
+  /**
+   * Copies one resource directory tree into another; skipping some files, replacing the contents of
+   * some, and passing everything else through unmodified
+   */
+  private static void filteredCopy(File source, Path destination, Set<File> skip,
+      Map<File, String> replace) throws IOException {
+
+    File destinationFile = destination.toFile();
+    if (source.isDirectory()) {
+      File[] children = source.listFiles();
+      if (children != null) {
+        if (!destinationFile.exists()) {
+          boolean success = destinationFile.mkdirs();
+          if (!success) {
+            throw new IOException("Could not create " + destination);
+          }
+        }
+        for (File child : children) {
+          filteredCopy(child, destination.resolve(child.getName()), skip, replace);
+        }
+      }
+    } else if (!skip.contains(source) && source.isFile()) {
+      String contents = replace.get(source);
+      if (contents != null) {
+        Files.write(contents, destinationFile, Charsets.UTF_8);
+      } else {
+        Files.copy(source, destinationFile);
+      }
+    }
+  }
+
+  private void stripUnused(Element element, List<String> removed) {
+    ResourceType type = getResourceType(element);
+    if (type == ResourceType.ATTR) {
+      // Not yet properly handled
+      return;
+    }
+    Resource resource = getResource(element);
+    if (resource != null) {
+      if (resource.type == ResourceType.DECLARE_STYLEABLE
+          || resource.type == ResourceType.ATTR) {
+        // Don't strip children of declare-styleable; we're not correctly
+        // tracking field references of the R_styleable_attr fields yet
+        return;
+      }
+      if (!resource.reachable
+          && (resource.type == ResourceType.STYLE
+              || resource.type == ResourceType.PLURALS
+              || resource.type == ResourceType.ARRAY)) {
+        NodeList children = element.getChildNodes();
+        for (int i = children.getLength() - 1; i >= 0; i--) {
+          Node child = children.item(i);
+          element.removeChild(child);
+        }
+        return;
+      }
+    }
+    NodeList children = element.getChildNodes();
+    for (int i = children.getLength() - 1; i >= 0; i--) {
+      Node child = children.item(i);
+      if (child.getNodeType() == Node.ELEMENT_NODE) {
+        stripUnused((Element) child, removed);
+      }
+    }
+    if (resource != null && !resource.reachable) {
+      removed.add(resource.getUrl());
+      // for themes etc where .'s have been replaced by _'s
+      String name = element.getAttribute(ATTR_NAME);
+      if (name.isEmpty()) {
+        name = resource.name;
+      }
+      Node nextSibling = element.getNextSibling();
+      Node parent = element.getParentNode();
+      NodeList oldChildren = element.getChildNodes();
+      parent.removeChild(element);
+      Document document = element.getOwnerDocument();
+      element = document.createElement("item");
+      for (int i = 0; i < oldChildren.getLength(); i++) {
+        element.appendChild(oldChildren.item(i));
+      }
+      element.setAttribute(ATTR_NAME, name);
+      element.setAttribute(ATTR_TYPE, resource.type.getName());
+      String text = null;
+      switch (resource.type) {
+        case BOOL:
+          text = "true";
+          break;
+        case DIMEN:
+          text = "0dp";
+          break;
+        case INTEGER:
+          text = "0";
+          break;
+      }
+      element.setTextContent(text);
+      parent.insertBefore(element, nextSibling);
+    }
+  }
+
+  private static String getFieldName(Element element) {
+    return getFieldName(element.getAttribute(ATTR_NAME));
+  }
+
+  @Nullable
+  private Resource getResource(Element element) {
+    ResourceType type = getResourceType(element);
+    if (type != null) {
+      String name = getFieldName(element);
+      return getResource(type, name);
+    }
+    return null;
+  }
+
+  private static ResourceType getResourceType(Element element) {
+    String tagName = element.getTagName();
+    switch (tagName) {
+      case TAG_ITEM:
+        String typeName = element.getAttribute(ATTR_TYPE);
+        if (!typeName.isEmpty()) {
+          return ResourceType.getEnum(typeName);
+        }
+        break;
+      case "string-array":
+      case "integer-array":
+        return ResourceType.ARRAY;
+      default:
+        return ResourceType.getEnum(tagName);
+    }
+    return null;
+  }
+
+  private void findUnused() {
+    List<Resource> roots = Lists.newArrayList();
+    for (Resource resource : resources) {
+      if (resource.reachable && resource.type != ResourceType.ID
+          && resource.type != ResourceType.ATTR) {
+        roots.add(resource);
+      }
+    }
+    System.out.println("The root reachable resources are: " + Joiner.on(",\n   ").join(roots));
+    Map<Resource, Boolean> seen = new IdentityHashMap<>(resources.size());
+    for (Resource root : roots) {
+      visit(root, seen);
+    }
+    List<Resource> unused = Lists.newArrayListWithExpectedSize(resources.size());
+    for (Resource resource : resources) {
+      if (!resource.reachable && resource.isRelevantType()) {
+        unused.add(resource);
+      }
+    }
+    this.unused = unused;
+  }
+
+  private static void visit(Resource root, Map<Resource, Boolean> seen) {
+    if (seen.containsKey(root)) {
+      return;
+    }
+    seen.put(root, Boolean.TRUE);
+    root.reachable = true;
+    if (root.references != null) {
+      for (Resource referenced : root.references) {
+        visit(referenced, seen);
+      }
+    }
+  }
+
+  private void dumpReferences() {
+    for (Resource resource : resources) {
+      if (resource.references != null) {
+        System.out.println(resource + " => " + resource.references);
+      }
+    }
+  }
+
+  private void keepPossiblyReferencedResources() {
+    if (!mFoundGetIdentifier || mStrings == null) {
+      // No calls to android.content.res.Resources#getIdentifier; no need
+      // to worry about string references to resources
+      return;
+    }
+    List<String> strings = new ArrayList<String>(mStrings);
+    Collections.sort(strings);
+    System.out.println("android.content.res.Resources#getIdentifier present: "
+        + mFoundGetIdentifier);
+    System.out.println("Referenced Strings:");
+    for (String s : strings) {
+      s = s.trim().replace("\n", "\\n");
+      if (s.length() > 40) {
+        s = s.substring(0, 37) + "...";
+      } else if (s.isEmpty()) {
+        continue;
+      }
+      System.out.println("  " + s);
+    }
+    Set<String> names = Sets.newHashSetWithExpectedSize(50);
+    for (Map<String, Resource> map : typeToName.values()) {
+      names.addAll(map.keySet());
+    }
+    for (String string : mStrings) {
+      // Check whether the string looks relevant
+      // We consider three types of strings:
+      //  (1) simple resource names, e.g. "foo" from @layout/foo
+      //      These might be the parameter to a getIdentifier() call, or could
+      //      be composed into a fully qualified resource name for the getIdentifier()
+      //      method. We match these for *all* resource types.
+      //  (2) Relative source names, e.g. layout/foo, from @layout/foo
+      //      These might be composed into a fully qualified resource name for
+      //      getIdentifier().
+      //  (3) Fully qualified resource names of the form package:type/name.
+      int n = string.length();
+      boolean justName = true;
+      boolean haveSlash = false;
+      for (int i = 0; i < n; i++) {
+        char c = string.charAt(i);
+        if (c == '/') {
+          haveSlash = true;
+          justName = false;
+        } else if (c == '.' || c == ':') {
+          justName = false;
+        } else if (!Character.isJavaIdentifierPart(c)) {
+          // This shouldn't happen; we've filtered out these strings in
+          // the {@link #referencedString} method
+          assert false : string;
+          break;
+        }
+      }
+      String name;
+      if (justName) {
+        // Check name (below)
+        name = string;
+      } else if (!haveSlash) {
+        // If we have more than just a symbol name, we expect to also see a slash
+        //noinspection UnnecessaryContinue
+        continue;
+      } else {
+        // Try to pick out the resource name pieces; if we can find the
+        // resource type unambiguously; if not, just match on names
+        int slash = string.indexOf('/');
+        assert slash != -1; // checked with haveSlash above
+        name = string.substring(slash + 1);
+        if (name.isEmpty() || !names.contains(name)) {
+          continue;
+        }
+        // See if have a known specific resource type
+        if (slash > 0) {
+          int colon = string.indexOf(':');
+          String typeName = string.substring(colon != -1 ? colon + 1 : 0, slash);
+          ResourceType type = ResourceType.getEnum(typeName);
+          if (type == null) {
+            continue;
+          }
+          Resource resource = getResource(type, name);
+          if (resource != null) {
+            System.out.println("Marking " + resource + " used because it "
+                + "matches string pool constant " + string);
+          }
+          markReachable(resource);
+          continue;
+        }
+        // fall through and check the name
+      }
+      if (names.contains(name)) {
+        for (Map<String, Resource> map : typeToName.values()) {
+          Resource resource = map.get(string);
+          if (resource != null) {
+            System.out.println("Marking " + resource + " used because it "
+                + "matches string pool constant " + string);
+          }
+          markReachable(resource);
+        }
+      } else if (Character.isDigit(name.charAt(0))) {
+        // Just a number? There are cases where it calls getIdentifier by
+        // a String number; see for example SuggestionsAdapter in the support
+        // library which reports supporting a string like "2130837524" and
+        // "android.resource://com.android.alarmclock/2130837524".
+        try {
+          int id = Integer.parseInt(name);
+          if (id != 0) {
+            markReachable(valueToResource.get(id));
+          }
+        } catch (NumberFormatException e) {
+          // pass
+        }
+      }
+    }
+  }
+
+  private void recordResources(Path resDir)
+      throws IOException, SAXException, ParserConfigurationException {
+
+    File[] resourceFolders = resDir.toFile().listFiles();
+    if (resourceFolders != null) {
+      for (File folder : resourceFolders) {
+        ResourceFolderType folderType = ResourceFolderType.getFolderType(folder.getName());
+        if (folderType != null) {
+          recordResources(folderType, folder);
+        }
+      }
+    }
+  }
+
+  private void recordResources(@NonNull ResourceFolderType folderType, File folder)
+      throws ParserConfigurationException, SAXException, IOException {
+    File[] files = folder.listFiles();
+    FolderConfiguration config = FolderConfiguration.getConfigForFolder(folder.getName());
+    boolean isDefaultFolder = false;
+    if (config != null) {
+      isDefaultFolder = true;
+      for (int i = 0, n = FolderConfiguration.getQualifierCount(); i < n; i++) {
+        ResourceQualifier qualifier = config.getQualifier(i);
+        // Densities are special: even if they're present in just (say) drawable-hdpi
+        // we'll match it on any other density
+        if (qualifier != null && !(qualifier instanceof DensityQualifier)) {
+          isDefaultFolder = false;
+          break;
+        }
+      }
+    }
+    if (files != null) {
+      for (File file : files) {
+        String path = file.getPath();
+        boolean isXml = endsWithIgnoreCase(path, DOT_XML);
+        Resource from = null;
+        // Record resource for the whole file
+        if (folderType != ResourceFolderType.VALUES
+            && (isXml
+            || endsWith(path, DOT_PNG) //also true for endsWith(name, DOT_9PNG)
+            || endsWith(path, DOT_JPG)
+            || endsWith(path, DOT_GIF)
+            || endsWith(path, DOT_JPEG))) {
+          List<ResourceType> types = FolderTypeRelationship.getRelatedResourceTypes(
+              folderType);
+          ResourceType type = types.get(0);
+          assert type != ResourceType.ID : folderType;
+          String name = file.getName();
+          name = name.substring(0, name.indexOf('.'));
+          Resource resource = getResource(type, name);
+          if (resource != null) {
+            resource.addLocation(file);
+            if (isDefaultFolder) {
+              resource.hasDefault = true;
+            }
+            from = resource;
+          }
+        }
+        if (isXml) {
+          // For value files, and drawables and colors etc also pull in resource
+          // references inside the file
+          recordResourcesUsages(file, isDefaultFolder, from);
+        }
+      }
+    }
+  }
+
+  private void recordMapping(@Nullable Path mapping) throws IOException {
+    if (mapping == null || !mapping.toFile().exists()) {
+      return;
+    }
+    final String arrowIndicator = " -> ";
+    final String resourceIndicator = ".R$";
+    for (String line : Files.readLines(mapping.toFile(), UTF_8)) {
+      if (line.startsWith(" ") || line.startsWith("\t")) {
+        continue;
+      }
+      int index = line.indexOf(resourceIndicator);
+      if (index == -1) {
+        continue;
+      }
+      int arrow = line.indexOf(arrowIndicator, index + 3);
+      if (arrow == -1) {
+        continue;
+      }
+      String typeName = line.substring(index + resourceIndicator.length(), arrow);
+      ResourceType type = ResourceType.getEnum(typeName);
+      if (type == null) {
+        continue;
+      }
+      int end = line.indexOf(':', arrow + arrowIndicator.length());
+      if (end == -1) {
+        end = line.length();
+      }
+      String target = line.substring(arrow + arrowIndicator.length(), end).trim();
+      String ownerName = target.replace('.', '/');
+      resourceClassOwners.put(ownerName, type);
+    }
+  }
+
+  private void recordManifestUsages(Path manifest)
+      throws IOException, ParserConfigurationException, SAXException {
+    String xml = Files.toString(manifest.toFile(), UTF_8);
+    Document document = XmlUtils.parseDocument(xml, true);
+    recordManifestUsages(document.getDocumentElement());
+  }
+
+  private void recordResourcesUsages(@NonNull File file, boolean isDefaultFolder,
+      @Nullable Resource from)
+      throws IOException, ParserConfigurationException, SAXException {
+    String xml = Files.toString(file, UTF_8);
+    Document document = XmlUtils.parseDocument(xml, true);
+    recordResourceReferences(file, isDefaultFolder, document.getDocumentElement(), from);
+  }
+
+  @Nullable
+  private Resource getResource(@NonNull ResourceType type, @NonNull String name) {
+    Map<String, Resource> nameMap = typeToName.get(type);
+    if (nameMap != null) {
+      return nameMap.get(getFieldName(name));
+    }
+    return null;
+  }
+
+  @Nullable
+  private Resource getResource(@NonNull String possibleUrlReference) {
+    ResourceUrl url = ResourceUrl.parse(possibleUrlReference);
+    if (url != null && !url.framework) {
+      return getResource(url.type, url.name);
+    }
+    return null;
+  }
+
+  private void recordManifestUsages(Node node) {
+    short nodeType = node.getNodeType();
+    if (nodeType == Node.ELEMENT_NODE) {
+      Element element = (Element) node;
+      NamedNodeMap attributes = element.getAttributes();
+      for (int i = 0, n = attributes.getLength(); i < n; i++) {
+        Attr attr = (Attr) attributes.item(i);
+        markReachable(getResource(attr.getValue()));
+      }
+    } else if (nodeType == Node.TEXT_NODE) {
+      // Does this apply to any manifests??
+      String text = node.getNodeValue().trim();
+      markReachable(getResource(text));
+    }
+    NodeList children = node.getChildNodes();
+    for (int i = 0, n = children.getLength(); i < n; i++) {
+      Node child = children.item(i);
+      recordManifestUsages(child);
+    }
+  }
+
+  private void recordResourceReferences(@NonNull File file, boolean isDefaultFolder,
+      @NonNull Node node, @Nullable Resource from) {
+    short nodeType = node.getNodeType();
+    if (nodeType == Node.ELEMENT_NODE) {
+      Element element = (Element) node;
+      if (from != null) {
+        NamedNodeMap attributes = element.getAttributes();
+        for (int i = 0, n = attributes.getLength(); i < n; i++) {
+          Attr attr = (Attr) attributes.item(i);
+          Resource resource = getResource(attr.getValue());
+          if (resource != null) {
+            from.addReference(resource);
+          }
+        }
+        // Android Wear. We *could* limit ourselves to only doing this in files
+        // referenced from a manifest meta-data element, e.g.
+        // <meta-data android:name="com.google.android.wearable.beta.app"
+        //    android:resource="@xml/wearable_app_desc"/>
+        // but given that that property has "beta" in the name, it seems likely
+        // to change and therefore hardcoding it for that key risks breakage
+        // in the future.
+        if ("rawPathResId".equals(element.getTagName())) {
+          StringBuilder sb = new StringBuilder();
+          NodeList children = node.getChildNodes();
+          for (int i = 0, n = children.getLength(); i < n; i++) {
+            Node child = children.item(i);
+            if (child.getNodeType() == Element.TEXT_NODE
+                || child.getNodeType() == Element.CDATA_SECTION_NODE) {
+              sb.append(child.getNodeValue());
+            }
+          }
+          if (sb.length() > 0) {
+            Resource resource = getResource(ResourceType.RAW, sb.toString().trim());
+            from.addReference(resource);
+          }
+        }
+      }
+      Resource definition = getResource(element);
+      if (definition != null) {
+        from = definition;
+        definition.addLocation(file);
+        if (isDefaultFolder) {
+          definition.hasDefault = true;
+        }
+      }
+      String tagName = element.getTagName();
+      if (TAG_STYLE.equals(tagName)) {
+        if (element.hasAttribute(ATTR_PARENT)) {
+          String parent = element.getAttribute(ATTR_PARENT);
+          if (!parent.isEmpty() && !parent.startsWith(ANDROID_STYLE_RESOURCE_PREFIX)
+              && !parent.startsWith(PREFIX_ANDROID)) {
+            String parentStyle = parent;
+            if (!parentStyle.startsWith(STYLE_RESOURCE_PREFIX)) {
+              parentStyle = STYLE_RESOURCE_PREFIX + parentStyle;
+            }
+            Resource ps = getResource(getFieldName(parentStyle));
+            if (ps != null && definition != null) {
+              definition.addReference(ps);
+            }
+          }
+        } else {
+          // Implicit parent styles by name
+          String name = getFieldName(element);
+          while (true) {
+            int index = name.lastIndexOf('_');
+            if (index != -1) {
+              name = name.substring(0, index);
+              Resource ps = getResource(STYLE_RESOURCE_PREFIX + getFieldName(name));
+              if (ps != null && definition != null) {
+                definition.addReference(ps);
+              }
+            } else {
+              break;
+            }
+          }
+        }
+      }
+      if (TAG_ITEM.equals(tagName)) {
+        // In style? If so the name: attribute can be a reference
+        if (element.getParentNode() != null
+            && element.getParentNode().getNodeName().equals(TAG_STYLE)) {
+          String name = element.getAttributeNS(ANDROID_URI, ATTR_NAME);
+          if (!name.isEmpty() && !name.startsWith("android:")) {
+            Resource resource = getResource(ResourceType.ATTR, name);
+            if (definition == null) {
+              Element style = (Element) element.getParentNode();
+              definition = getResource(style);
+              if (definition != null) {
+                from = definition;
+                definition.addReference(resource);
+              }
+            }
+          }
+        }
+      }
+    } else if (nodeType == Node.TEXT_NODE || nodeType == Node.CDATA_SECTION_NODE) {
+      String text = node.getNodeValue().trim();
+      Resource textResource = getResource(getFieldName(text));
+      if (textResource != null && from != null) {
+        from.addReference(textResource);
+      }
+    }
+    NodeList children = node.getChildNodes();
+    for (int i = 0, n = children.getLength(); i < n; i++) {
+      Node child = children.item(i);
+      recordResourceReferences(file, isDefaultFolder, child, from);
+    }
+  }
+
+  public static String getFieldName(@NonNull String styleName) {
+    return styleName.replace('.', '_').replace('-', '_').replace(':', '_');
+  }
+
+  private static void markReachable(@Nullable Resource resource) {
+    if (resource != null) {
+      resource.reachable = true;
+    }
+  }
+
+  private Set<String> mStrings;
+  private boolean mFoundGetIdentifier;
+
+  private void referencedString(@NonNull String string) {
+    // See if the string is at all eligible; ignore strings that aren't
+    // identifiers (has java identifier chars and nothing but .:/), or are empty or too long
+    if (string.isEmpty() || string.length() > 80) {
+      return;
+    }
+    boolean haveIdentifierChar = false;
+    for (int i = 0, n = string.length(); i < n; i++) {
+      char c = string.charAt(i);
+      boolean identifierChar = Character.isJavaIdentifierPart(c);
+      if (!identifierChar && c != '.' && c != ':' && c != '/') {
+        // .:/ are for the fully qualified resuorce names
+        return;
+      } else if (identifierChar) {
+        haveIdentifierChar = true;
+      }
+    }
+    if (!haveIdentifierChar) {
+      return;
+    }
+    if (mStrings == null) {
+      mStrings = Sets.newHashSetWithExpectedSize(300);
+    }
+    mStrings.add(string);
+  }
+
+  private void recordUsages(Path jarFile) throws IOException {
+    if (!jarFile.toFile().exists()) {
+      return;
+    }
+    ZipInputStream zis = null;
+    try {
+      FileInputStream fis = new FileInputStream(jarFile.toFile());
+      try {
+        zis = new ZipInputStream(fis);
+        ZipEntry entry = zis.getNextEntry();
+        while (entry != null) {
+          String name = entry.getName();
+          if (name.endsWith(DOT_CLASS)) {
+            byte[] bytes = ByteStreams.toByteArray(zis);
+            if (bytes != null) {
+              ClassReader classReader = new ClassReader(bytes);
+              classReader.accept(new UsageVisitor(), 0);
+            }
+          }
+          entry = zis.getNextEntry();
+        }
+      } finally {
+        Closeables.close(fis, true);
+      }
+    } finally {
+      Closeables.close(zis, true);
+    }
+  }
+
+  private void parseResourceTxtFile(Path file) throws IOException {
+    BufferedReader reader = java.nio.file.Files.newBufferedReader(file, Charset.defaultCharset());
+    String line;
+    while ((line = reader.readLine()) != null) {
+      String[] tokens = line.split(" ");
+      ResourceType type = ResourceType.getEnum(tokens[1]);
+      resourceClassOwners.put(rPackagePath + "/R$" + type.getName(), type);
+      if (type == ResourceType.STYLEABLE) {
+        if (tokens[0].equals("int[]")) {
+          addResource(ResourceType.DECLARE_STYLEABLE, tokens[2], null);
+        } else {
+          // TODO(jongerrish): Implement stripping of styleables.
+        }
+      } else {
+        addResource(type, tokens[2], tokens[3]);
+      }
+    }
+  }
+
+  private void addResource(@NonNull ResourceType type, @NonNull String name,
+      @Nullable String value) {
+    int realValue = value != null ? Integer.decode(value) : -1;
+    Resource resource = getResource(type, name);
+    if (resource != null) {
+      //noinspection VariableNotUsedInsideIf
+      if (value != null) {
+        if (resource.value == -1) {
+          resource.value = realValue;
+        } else {
+          assert realValue == resource.value;
+        }
+      }
+      return;
+    }
+    resource = new Resource(type, name, realValue);
+    resources.add(resource);
+    if (realValue != -1) {
+      valueToResource.put(realValue, resource);
+    }
+    Map<String, Resource> nameMap = typeToName.get(type);
+    if (nameMap == null) {
+      nameMap = Maps.newHashMapWithExpectedSize(30);
+      typeToName.put(type, nameMap);
+    }
+    nameMap.put(name, resource);
+    // TODO: Assert that we don't set the same resource multiple times to different values.
+    // Could happen if you pass in stale data!
+  }
+
+  @VisibleForTesting
+  List<Resource> getAllResources() {
+    return resources;
+  }
+
+  /**
+   * Metadata about an Android resource
+   */
+  public static class Resource {
+
+    /**
+     * Type of resource
+     */
+    public ResourceType type;
+    /**
+     * Name of resource
+     */
+    public String name;
+    /**
+     * Integer id location
+     */
+    public int value;
+    /**
+     * Whether this resource can be reached from one of the roots (manifest, code)
+     */
+    public boolean reachable;
+    /**
+     * Whether this resource has a default definition (e.g. present in a resource folder with no
+     * qualifiers). For id references, an inline definition (@+id) does not count as a default
+     * definition.
+     */
+    public boolean hasDefault;
+    /**
+     * Resources this resource references. For example, a layout can reference another via an
+     * include; a style reference in a layout references that layout style, and so on.
+     */
+    public List<Resource> references;
+    public final List<File> declarations = Lists.newArrayList();
+
+    private Resource(ResourceType type, String name, int value) {
+      this.type = type;
+      this.name = name;
+      this.value = value;
+    }
+
+    @Override
+    public String toString() {
+      return type + ":" + name + ":" + value;
+    }
+
+    @SuppressWarnings("RedundantIfStatement") // Generated by IDE
+    @Override
+    public boolean equals(Object o) {
+      if (this == o) {
+        return true;
+      }
+      if (o == null || getClass() != o.getClass()) {
+        return false;
+      }
+      Resource resource = (Resource) o;
+      if (name != null ? !name.equals(resource.name) : resource.name != null) {
+        return false;
+      }
+      if (type != resource.type) {
+        return false;
+      }
+      return true;
+    }
+
+    @Override
+    public int hashCode() {
+      int result = type != null ? type.hashCode() : 0;
+      result = 31 * result + (name != null ? name.hashCode() : 0);
+      return result;
+    }
+
+    public void addLocation(@NonNull File file) {
+      declarations.add(file);
+    }
+
+    public void addReference(@Nullable Resource resource) {
+      if (resource != null) {
+        if (references == null) {
+          references = Lists.newArrayList();
+        } else if (references.contains(resource)) {
+          return;
+        }
+        references.add(resource);
+      }
+    }
+
+    public String getUrl() {
+      return '@' + type.getName() + '/' + name;
+    }
+
+    public boolean isRelevantType() {
+      return type != ResourceType.ID; // && getFolderType() != ResourceFolderType.VALUES;
+    }
+  }
+
+  private class UsageVisitor extends ClassVisitor {
+
+    public UsageVisitor() {
+      super(Opcodes.ASM4);
+    }
+
+    @Override
+    public MethodVisitor visitMethod(int access, final String name,
+        String desc, String signature, String[] exceptions) {
+      return new MethodVisitor(Opcodes.ASM4) {
+        @Override
+        public void visitLdcInsn(Object cst) {
+          if (cst instanceof Integer) {
+            Integer value = (Integer) cst;
+            markReachable(valueToResource.get(value));
+          } else if (cst instanceof String) {
+            String string = (String) cst;
+            referencedString(string);
+          }
+        }
+
+        @Override
+        public void visitFieldInsn(int opcode, String owner, String name, String desc) {
+          if (opcode == Opcodes.GETSTATIC) {
+            ResourceType type = resourceClassOwners.get(owner);
+            if (type != null) {
+              Resource resource = getResource(type, name);
+              if (resource != null) {
+                markReachable(resource);
+              }
+            }
+          }
+        }
+
+        @Override
+        public void visitMethodInsn(int opcode, String owner, String name, String desc) {
+          super.visitMethodInsn(opcode, owner, name, desc);
+          if (owner.equals("android/content/res/Resources")
+              && name.equals("getIdentifier")
+              && desc.equals(
+              "(Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;)I")) {
+            mFoundGetIdentifier = true;
+            // TODO: Check previous instruction and see if we can find a literal
+            // String; if so, we can more accurately dispatch the resource here
+            // rather than having to check the whole string pool!
+          }
+        }
+      };
+    }
+  }
+}