anchor.diff:      log.onRecord.listen((LogRecord rec) {
         stderr.writeln(rec.message);
       });
  +  }
  +
  +  if (options.rest.length != 1) {
  +    return fail('Exactly one FILE should be given.');
     }
   
     var file = options.rest.single;
  
positive.code: import 'package:kernel/kernel.dart';
  import 'package:kernel/log.dart';
  
  ArgParser parser = new ArgParser()
    ..addOption('format',
        abbr: 'f',
        allowed: ['text', 'bin'],
  
negative.code:     return fail(getUsage());
    }
  
    try {
      options = parser.parse(args);
    } on FormatException catch (e) {
  