anchor.diff:  
     // This command is hidden as its currently experimental.
     FixCommand() : super(cmdName, 'Fix Dart source code.', hidden: true);
  +
  +  @override
  +  UsageEvent createUsageEvent(int exitCode) => FixUsageEvent(
  +        usagePath,
  +        exitCode: exitCode,
  +        args: argResults.arguments,
  +      );
   
     @override
     FutureOr<int> runImpl() async {
  
positive.code: import '../core.dart';
  import '../events.dart';
  import '../sdk.dart';
  import '../utils.dart';
  import 'analyze_impl.dart';
  
  class FixCommand extends DartdevCommand<int> {
  
negative.code:     if (edits.isEmpty) {
        log.stdout('Nothing to fix!');
      } else {
        progress = log.progress('Applying fixes');
        var fileCount = await _applyFixes(edits);
        progress.finish(showTiming: true);
        if (fileCount > 0) {
          log.stdout('Fixed $fileCount files.');
        }
      }
      return 0;
    }
  
    Future<int> _applyFixes(List<SourceFileEdit> edits) async {
      var files = <String>{};
      for (var edit in edits) {
        var fileName = edit.file;
        files.add(fileName);
        var file = File(fileName);
        var code = await file.exists() ? await file.readAsString() : '';
        code = SourceEdit.applySequence(code, edit.edits);
        await file.writeAsString(code);
      }
      return files.length;
    }
  }
  
  /// The [UsageEvent] for the fix command.
  