Add a Pub source that checks packages out from Git.

utils/pub/pub.dart

 // Copyright (c) 2012, 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.
 
 /**
  * The main entrypoint for the pub command line application.
  */
 #library('pub');
 
 #import('yaml/yaml.dart');
 
 #import('io.dart');
 #import('utils.dart');
 
 #source('system_cache.dart');
 #source('packages_dir.dart');
 #source('command_list.dart');
 #source('command_install.dart');
 #source('command_update.dart');
 #source('command_version.dart');
 #source('package.dart');
 #source('source.dart');
+#source('source_registry.dart');
 #source('sdk_source.dart');
+#source('git_source.dart');
 
 main() {
   final args = new Options().arguments;
 
   // TODO(rnystrom): In addition to explicit "help" and "version" commands,
   // should also add special-case support for --help and --version arguments to
   // be consistent with other Unix apps.
   final commands = {
     'list': new ListCommand(),
     'install': new InstallCommand(),
@@ skipping 29 matching lines @@
       printUsage(commands);
       return;
     }
 
     if (args[0] == '--version') {
       printVersion();
       return;
     }
   }
 
-  // TODO(rnystrom): Do we want this to be global?
   final cache = new SystemCache(cacheDir);
-
-  Source.defaultSource = new SdkSource(sdkDir);
+  cache.sources.register(new SdkSource(sdkDir));
+  cache.sources.register(new GitSource());
+  cache.sources.setDefault('sdk');
 
   // Select the command.
   final command = commands[args[0]];
   if (command == null) {
     print('Unknown command "${args[0]}".');
     print('Run "pub help" to see available commands.');
     exit(64); // See http://www.freebsd.org/cgi/man.cgi?query=sysexits.
     return;
   }
 
@@ skipping 43 matching lines @@
 
   void run(SystemCache cache_, List<String> args) {
     cache = cache_;
 
     // TODO(rnystrom): Each command should define the arguments it expects and
     // we can handle them generically here.
 
     // TODO(rnystrom): Will eventually need better logic to walk up
     // subdirectories until we hit one that looks package-like. For now, just
     // assume the cwd is it.
-    Package.load(workingDir).then((pkg) {
+    Package.load(workingDir, cache.sources).then((pkg) {
       packagesDir = new PackagesDir(pkg, cache);
       onRun();
     });
   }
 
   abstract void onRun();
 }