anchor.diff:  
     /// The list of files this library file references as parts.
     List<FileState?> get partedFiles {
  -    if (_partedFiles == null) {
  -      _partedFiles = <FileState?>[];
  -      for (var uri in _unlinked2!.parts) {
  -        _fileForRelativeUri(uri).map(
  -          (file) {
  -            _partedFiles!.add(file);
  -            if (file != null) {
  -              _fsState._partToLibraries
  -                  .putIfAbsent(file, () => <FileState>[])
  -                  .add(this);
  -            }
  -          },
  -          (_) {},
  -        );
  -      }
  -    }
  -    return _partedFiles!;
  +    return _partedFiles ??= _unlinked2!.parts.map((uri) {
  +      return _fileForRelativeUri(uri).map(
  +        (file) {
  +          if (file != null) {
  +            _fsState._partToLibraries
  +                .putIfAbsent(file, () => <FileState>[])
  +                .add(this);
  +          }
  +          return file;
  +        },
  +        (_) => null,
  +      );
  +    }).toList();
     }
   
     /// The external names referenced by the file.
  
positive.code: 
    /// The list of files this file imports.
    List<FileState?> get importedFiles {
      if (_importedFiles == null) {
        _importedFiles = <FileState?>[];
        for (var directive in _unlinked2!.imports) {
          var uri = _selectRelativeUri(directive);
          _fileForRelativeUri(uri).map(
            (file) {
              _importedFiles!.add(file);
            },
            (_) {},
          );
        }
      }
      return _importedFiles!;
    }
  
    LibraryCycle? get internal_libraryCycle => _libraryCycle;
  
negative.code: 
    /// The list of files this file exports.
    List<FileState?> get exportedFiles {
      return _exportedFiles ??= _unlinked2!.exports.map((directive) {
        var uri = _selectRelativeUri(directive);
        return _fileForRelativeUri(uri).map(
          (file) => file,
          (_) => null,
        );
      }).toList();
    }
  
    @override
  