anchor.diff:      final outputId = _generatedFile(buildStep.inputId);
   
       var contentBuffer = new StringBuffer();
  -    if (!isStandalone) {
  +    if (!_isStandalone) {
         var asset = buildStep.inputId;
         var name = nameOfPartial(
           library,
  
positive.code: 
    @override
    Map<String, List<String>> get buildExtensions => {
          '.dart': [generatedExtension]
        };
  
    AssetId _generatedFile(AssetId input) =>
        input.changeExtension(generatedExtension);
  
    Future _generateForLibrary(
        LibraryElement library, BuildStep buildStep) async {
      log.fine('Running $generators for ${buildStep.inputId}');
      var generatedOutputs =
          await _generate(library, generators, buildStep).toList();
  
      // Don't output useless files.
      //
  
negative.code:   }
  }
  
  /// A [Builder] which generateds `part of` files.
  class PartBuilder extends _Builder {
    /// Wrap [generators] as a [Builder] that generates `part of` files.
    ///
    /// [generatedExtension] indicates what files will be created for each `.dart`
    /// input. Defaults to `.g.dart`.
    ///
    /// [formatOutput] is called to format the generated code. Defaults to
    /// [DartFormatter.format].
    ///
    /// May set [requireLibraryDirective] to `false` in order to opt-in to
    /// supporting a `1.25.0` feature of `part of` being usable without an
    /// explicit `library` directive. Developers should restrict their `pubspec`
    /// accordingly:
    /// ```yaml
    /// sdk: '>=1.25.0 <2.0.0'
    /// ```
    PartBuilder(List<Generator> generators,
        {OutputFormatter formatOutput,
        String generatedExtension: '.g.dart',
  