anchor.diff:          help:
               'Whether to generate a stand-alone executable or an AOT snapshot.')
       ..addOption('packages',
  -        valueHelp: 'path', help: 'Where to find a package spec file.');
  +        valueHelp: 'path', help: 'Where to find a package spec file.')
  +    ..addFlag('verbose',
  +        abbr: 'v', negatable: false, help: 'Enables more verbose output.');
   
  -  final ArgResults parsedArgs = parser.parse(args);
  +  ArgResults parsedArgs;
  +  try {
  +    parsedArgs = parser.parse(args);
  +  } on FormatException catch (e) {
  +    stderr.writeln('Error: ${e.message}');
  +    await stderr.flush();
  +    printUsage(parser);
  +    exit(1);
  +  }
   
     if (parsedArgs['help']) {
       printUsage(parser);
  
positive.code:     }
  
      if (kind == Kind.exe) {
        print('Generating executable.');
        await writeAppendedExecutable(dartaotruntime, snapshotFile, outputFile);
  
        if (Platform.isLinux || Platform.isMacOS) {
          print('Marking binary executable.');
          await markExecutable(outputFile);
        }
      }
  
negative.code:   }
  
    try {
      await generateNative(
          kind,
          sourcePath,
          outputPath,
          parsedArgs['packages'],
          parsedArgs['define'],
          parsedArgs['enable-asserts'],
          parsedArgs['verbose']);
    } catch (e) {
      stderr.writeln('Failed to generate native files:');
      stderr.writeln(e);
  