anchor.diff:  
   Future<void> main(List<String> args) async {
     ArgResults options;
  -
     try {
       options = _argParser.parse(args);
   
  
positive.code: final ArgParser _argParser = createCompilerArgParser()
    ..addFlag('train',
        help: 'Run through sample command line to produce snapshot',
        negatable: false)
    ..addOption('component-name', help: 'Name of the component')
    ..addOption('data-dir',
        help: 'Name of the subdirectory of //data for output files')
    ..addOption('manifest', help: 'Path to output Fuchsia package manifest');
  
  String _usage = '''
  Usage: compiler [options] input.dart
  
negative.code:     exitCode = compilerExitCode;
      return;
    }
  }
  