anchor.diff:      return nodesOfFiles.putIfAbsent(file, () => new _LibraryNode(this, file));
     }
   
  -  void _appendDirectlyReference(
  +  void _appendDirectlyReferenced(
       LibraryCycle cycle,
       ApiSignature signature,
       List<FileState> directlyReferenced,
  
positive.code:     for (var user in _directUsers) {
        user.invalidate();
      }
    }
  
    @override
  
negative.code:     // Append direct referenced cycles.
      for (var node in scc) {
        var file = node.file;
        _appendDirectlyReferenced(cycle, signature, file.importedFiles);
        _appendDirectlyReferenced(cycle, signature, file.exportedFiles);
      }
  
      // Fill the cycle with libraries.
  