anchor.diff:    /// Function that determines how the generated code is formatted.
     final OutputFormatter formatOutput;
   
  -  /// What underlying generators are wrapped to form this [Builder].
  -  final List<Generator> generators;
  -
  -  /// For a given `.dart` file what extension is used to generate code.
  -  ///
  -  /// Defaults to `.g.dart`.
  -  final String generatedExtension;
  +  /// The generators run for each targeted library.
  +  final List<Generator> _generators;
  +
  +  /// The [buildExtensions] configuration for `.dart`
  +  final String _generatedExtension;
   
     /// Whether to emit a standalone (non-`part`) file in this builder.
  -  final bool isStandalone;
  +  final bool _isStandalone;
   
     final bool _requireLibraryDirective;
   
  -  /// Wrap [generators] to form a [Builder]-compatible API.
  -  ///
  -  /// 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'
  -  /// ```
  -  _Builder(this.generators,
  +  /// Wrap [_generators] to form a [Builder]-compatible API.
  +  _Builder(this._generators,
         {OutputFormatter formatOutput,
  -      this.generatedExtension: '.g.dart',
  -      this.isStandalone: false,
  +      String generatedExtension: '.g.dart',
  +      bool isStandalone: false,
         bool requireLibraryDirective: true})
  -      : formatOutput = formatOutput ?? _formatter.format,
  +      : _generatedExtension = generatedExtension,
  +        _isStandalone = isStandalone,
  +        formatOutput = formatOutput ?? _formatter.format,
           _requireLibraryDirective = requireLibraryDirective {
  -    if (generatedExtension == null) {
  +    if (_generatedExtension == null) {
         throw new ArgumentError.notNull('generatedExtension');
       }
  -    if (generatedExtension.isEmpty || !generatedExtension.startsWith('.')) {
  -      throw new ArgumentError.value(generatedExtension, 'generatedExtension',
  +    if (_generatedExtension.isEmpty || !_generatedExtension.startsWith('.')) {
  +      throw new ArgumentError.value(_generatedExtension, 'generatedExtension',
             'Extension must be in the format of .*');
       }
  -    if (this.isStandalone && this.generators.length > 1) {
  +    if (this._isStandalone && this._generators.length > 1) {
         throw new ArgumentError(
             'A standalone file can only be generated from a single Generator.');
       }
  
positive.code:   }
  }
  
  class PartBuilder extends _Builder {
    PartBuilder(List<Generator> generators,
        {OutputFormatter formatOutput,
        String generatedExtension: '.g.dart',
  
negative.code:     final outputId = _generatedFile(buildStep.inputId);
  
      var contentBuffer = new StringBuffer();
      if (!_isStandalone) {
        var asset = buildStep.inputId;
        var name = nameOfPartial(
          library,
  