anchor.diff:    final Map<Folder, List<Package>> folderToPackagesMap = {};
   
     /**
  -   * Mapping from [Uri]s to corresponding [_LinkNode]s.
  -   */
  -  final Map<Uri, _LinkNode> uriToNodeMap = {};
  +   * Mapping from [Uri]s to corresponding [Package]s.
  +   */
  +  final Map<Uri, Package> uriToPackageMap = {};
  +
  +  /**
  +   * Mapping from [Package]s to corresponding [_LinkNode]s.
  +   */
  +  final Map<Package, _LinkNode> packageToNodeMap = {};
   
     SummaryProvider(this.provider, this.getOutputFolder, AnalysisContext context)
         : context = context,
  
positive.code:    */
    @visibleForTesting
    Package getUnlinkedForUri(Uri uri) {
      Folder outputFolder = getOutputFolder(uri);
      if (outputFolder != null) {
        String uriStr = uri.toString();
        List<Package> packages = _getUnlinkedPackages(outputFolder);
        for (Package package in packages) {
          if (package._unitUris.contains(uriStr)) {
            return package;
          }
        }
      }
      return null;
    }
  
    /**
  
negative.code:    * bundle that contains [uri].
     */
    _LinkNode _getLinkNodeForUri(Uri uri) {
      Package package = getUnlinkedForUri(uri);
      return packageToNodeMap.putIfAbsent(package, () {
        if (package == null) {
          return null;
        }
  