add cache list command to pub

utils/pub/command_cache.dart

Index: utils/pub/command_cache.dart
===================================================================
--- utils/pub/command_cache.dart	(revision 0)
+++ utils/pub/command_cache.dart	(revision 0)
@@ -0,0 +1,50 @@
+// Copyright (c) 2013, 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 command_cache;
+
+import 'dart:async';
+import 'dart:io';
+import 'dart:json' as json;
+
+import 'exit_codes.dart' as exit_codes;
+import 'log.dart' as log;
+import 'pub.dart';
+
+
+/// Handles the `cache` pub command.
+class CacheCommand extends PubCommand { 
+  String get description => "Inspect the system cache.";
+  String get usage => 'pub cache list';
+  bool get requiresEntrypoint => false;
+  
+  Future onRun() {
+    if (commandOptions.rest.length != 1) {
+      log.error('The cache command expects one argument.');
+      this.printUsage();
+      exit(exit_codes.USAGE);
+    }
+    
+    if ((commandOptions.rest[0] != 'list')) {
+      log.error('Unknown cache command "${commandOptions.rest[0]}".');
+      this.printUsage();
+      exit(exit_codes.USAGE);
+    }
+    
+    // TODO(keertip): Add flag to list packages from non default sources
+    return cache.sources.defaultSource.getCachedPackages().then((packages){
+      var packagesObj = <String, Map>{};
+      for (var package in packages){
+        packagesObj[package.name] = {
+          'version': package.version.toString(),
+          'location': package.dir
+        };
+      }
+      // TODO(keertip): Add support for non-JSON format 
+      // and check for --format flag
+      log.message( json.stringify({'packages': packagesObj}));
+    });
+  }  
+}
+