anchor.diff:  import 'package:ddc/src/checker/dart_sdk.dart' show dartSdkDirectory, mockSdkSources;
   import 'package:ddc/src/checker/resolver.dart' show TypeResolver;
   
  -ArgResults parse(List argv) {
  -  var parser = new ArgParser()
  +final ArgParser argParser = new ArgParser()
       ..addFlag(
           'sdk-check', abbr: 's', help: 'Typecheck sdk libs', defaultsTo: false)
       ..addOption('log', abbr: 'l', help: 'Logging level', defaultsTo: 'severe')
  
positive.code: 
    if (args.rest.length == 0) {
      print('Expected filename.');
      exit(1);
    }
  
    String levelName = args['log'].toUpperCase();
  
negative.code: #!/usr/bin/env dart
  
  /// Command line tool to run the checker on a Dart program.
  library ddc.bin.checker;
  
  