anchor.diff:              formatOutput: formatOutput,
               generatedExtension: '.$partId.g.part',
               additionalOutputExtensions: additionalOutputExtensions,
  -            header: '',
  -            outputPartOf: false) {
  +            header: '') {
       if (!_partIdRegExp.hasMatch(partId)) {
         throw new ArgumentError.value(
             partId,
  
positive.code:   final String _generatedExtension;
  
    /// Whether to emit a standalone (non-`part`) file in this builder.
    final bool _isStandalone;
  
    /// Whether to include `part of` in the output.
    ///
    /// This allows the easy merging of outputs without multiple `part of`
    /// statements.
    final bool _outputPartOf;
  
    final String _header;
  
  
negative.code:       contentBuffer.writeln();
  
        String part;
        if (this is PartBuilder) {
          contentBuffer.writeln('part of $name;');
          part = computePartUrl(buildStep.inputId, outputId);
        } else {
          assert(this is SharedPartBuilder);
          var finalPartId = buildStep.inputId.changeExtension('.g.dart');
          part = computePartUrl(buildStep.inputId, finalPartId);
        }
  