anchor.diff:     * bundle that contains [uri].
      */
     _LinkNode _getLinkNodeForUri(Uri uri) {
  -    return uriToNodeMap.putIfAbsent(uri, () {
  -      Package package = getUnlinkedForUri(uri);
  +    Package package = getUnlinkedForUri(uri);
  +    return packageToNodeMap.putIfAbsent(package, () {
         if (package == null) {
           return null;
         }
  
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:   final Map<Folder, List<Package>> folderToPackagesMap = {};
  
    /**
     * 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,
  