Fix update_homebrew script for releasing Dart on Mac using homebrew.

tools/apps/update_homebrew/bin/update_homebrew.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library update_homebrew;
 
 import 'dart:io';
 import 'dart:convert';
 import 'dart:async';
 import 'package:http/http.dart' as http;
@@ skipping 32 matching lines @@
   final moduleName = (channel == 'dev') ? 'DartDev' : 'DartStable';
   buffer.writeln('module $moduleName');
   final files = {'SDK64': 'sdk/dartsdk-macos-x64-release.zip',
                  'SDK32': 'sdk/dartsdk-macos-ia32-release.zip',
                  'DARTIUM': 'dartium/dartium-macos-ia32-release.zip'};
   return Future.forEach(files.keys, (key) {
     return getHash256(channel, revision, files[key]).then((hash) {
       final file = "channels/$channel/release/$revision/${files[key]}";
       buffer.writeln('  ${key}_FILE = "$file"');
       buffer.writeln('  ${key}_HASH = "$hash"');
-    })
+    });
   })
     .then((_) => getVersion(channel, revision))
     .then((version) {
       buffer.writeln('  VERSION = "$version"');
       buffer.writeln('end');
       return (new File('$repository/data/${channel}_info.rb').openWrite()
         ..write(buffer))
         .close();
     });
 }
 
 Future runGit(List<String> args) {
   print("git ${args.join(' ')}");
   return Process.run('git', args, workingDirectory: repository,
                      environment: gitEnvironment)
       .then((result) {
         print(result.stdout);
         print(result.stderr);
       });
 }
 
 main(args) {
   final parser = new ArgParser()
       ..addOption('revision', abbr: 'r')
       ..addOption('channel', abbr: 'c', allowed: ['dev', 'stable'])
       ..addOption('key', abbr: 'k');
   final options = parser.parse(args);
   final revision = options['revision'];
   final channel = options['channel'];
+  if ([revision, channel, options['key']].contains(null)) {
+    print("Usage: update_homebrew.dart -r revision -c channel -k ssh_key\n"
+          "  ssh_key should allow pushes to dart-lang/homebrew-dart on github");
+    return;
+  }
   final sshWrapper = Platform.script.resolve('ssh_with_key').toFilePath();
   gitEnvironment = {'GIT_SSH': sshWrapper,
                     'SSH_KEY_PATH': options['key']};
 
   Directory.systemTemp.createTemp('update_homebrew')
       .then((tempDir) {
         repository = tempDir.path;
       })
       .then((_) => runGit(
           ['clone', 'git@github.com:dart-lang/homebrew-dart.git', '.']))
       .then((_) => writeHomebrewInfo(channel, revision))
-      .then((_) => runGit(['add', '${channel}_info.rb']))

[Bill Hesse, 2014/10/01 14:18:43]

Now that the files are in the repository, the -a option to git commit adds
changes to them to the commit.

       .then((_) => runGit(['commit', '-a', '-m',
                            'Updated $channel branch to revision $revision']))
       .then((_) => runGit(['push']))
       .whenComplete(() => new Directory(repository).delete(recursive: true));
 }