anchor.diff:  
     /// Return `true` if there is an overlay associated with the file at the given
     /// [path].
  -  bool hasOverlay(String path) => _overlayContent.containsKey(path);
  +  bool hasOverlay(String path) => _overlays.containsKey(path);
   
     /// Remove any overlay of the file at the given [path]. The state of the file
     /// in the base resource provider will not be affected.
     bool removeOverlay(String path) {
  -    bool hadOverlay = _overlayContent.containsKey(path);
  -    _overlayContent.remove(path);
  -    _overlayModificationStamps.remove(path);
  -    return hadOverlay;
  +    return _overlays.remove(path) != null;
     }
   
     /// Overlay the content of the file at the given [path]. The file will appear
  
positive.code:   @override
    File renameSync(String newPath) {
      File newFile = _file.renameSync(newPath);
      if (provider.hasOverlay(path)) {
        provider.setOverlay(
          newPath,
          content: provider._getOverlayContent(path)!,
          modificationStamp: provider._getOverlayModificationStamp(path)!,
        );
        provider.removeOverlay(path);
      }
      return _OverlayFile(provider, newFile);
    }
  
  
negative.code:   /// modified in the base resource provider.
    void setOverlay(String path,
        {required String content, required int modificationStamp}) {
      _overlays[path] = _OverlayFileData(content, modificationStamp);
    }
  
    /// Copy any overlay for the file at the [oldPath] to be an overlay for the
    /// file with the [newPath].
    void _copyOverlay(String oldPath, String newPath) {
      var data = _overlays[oldPath];
      if (data != null) {
        _overlays[newPath] = data;
      }
    }
  
    /// Return the content of the overlay of the file at the given [path], or
    /// `null` if there is no overlay for the specified file.
    String? _getOverlayContent(String path) {
      return _overlays[path]?.content;
    }
  
    /// Return the modification stamp of the overlay of the file at the given
    /// [path], or `null` if there is no overlay for the specified file.
    int? _getOverlayModificationStamp(String path) {
      return _overlays[path]?.modificationStamp;
    }
  
    /// Return `true` if there is an overlay associated with at least one file
    /// contained inside the folder with the given [folderPath].
    bool _hasOverlayIn(String folderPath) => _overlays.keys
        .any((filePath) => pathContext.isWithin(folderPath, filePath));
  
    /// Move any overlay for the file at the [oldPath] to be an overlay for the
    /// file with the [newPath].
    void _moveOverlay(String oldPath, String newPath) {
      var data = _overlays.remove(oldPath);
      if (data != null) {
        _overlays[newPath] = data;
      }
    }
  
    /// Return the paths of all of the overlaid files that are children of the
    /// given [folder], either directly or indirectly.
    Iterable<String> _overlaysInFolder(String folderPath) => _overlays.keys
        .where((filePath) => pathContext.isWithin(folderPath, filePath));
  }
  
  