anchor.diff:  
   void main(List<String> argv) {
     var args = _parser.parse(argv);
  +  if (args['help'] as bool || argv.isEmpty) {
  +    print('Apply patch file to the SDK and report analysis errors from the '
  +        'resulting libraries.\n\n'
  +        'Usage: ${Platform.script.pathSegments.last} [options...]\n\n'
  +        '${_parser.usage}');
  +    return;
  +  }
     String baseDir = args['out'] as String;
     if (baseDir == null) {
       var tmp = Directory.systemTemp.createTempSync('check_sdk-');
  
positive.code:     'machine',
      '--sdk-warnings',
      '--no-hints',
      emptyProgramUri.toFilePath()
    ]);
  
  
negative.code:           'This name matches one of the possible targets in libraries.json '
            'and it is used to pick which patch files will be applied.',
        allowed: ['dartdevc', 'dart2js', 'dart2js_server', 'vm', 'flutter'],
        defaultsTo: 'dartdevc')
    ..addFlag('help', abbr: 'h', help: 'Display this message.');
  