Support subcommands in pub and pub help.

sdk/lib/_internal/pub/lib/src/command/cache_list.dart

Index: sdk/lib/_internal/pub/lib/src/command/cache_list.dart
diff --git a/sdk/lib/_internal/pub/lib/src/command/cache.dart b/sdk/lib/_internal/pub/lib/src/command/cache_list.dart
similarity index 51%
copy from sdk/lib/_internal/pub/lib/src/command/cache.dart
copy to sdk/lib/_internal/pub/lib/src/command/cache_list.dart
index 97e5dbe7614ec99e4d209b792aab7b9eed431b82..d774a6ba7c249e5f716b6fcc9c1468b366077046 100644
--- a/sdk/lib/_internal/pub/lib/src/command/cache.dart
+++ b/sdk/lib/_internal/pub/lib/src/command/cache_list.dart
@@ -2,50 +2,32 @@
 // 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 pub.command.cache;
+library pub.command.cache_list;
 
 import 'dart:async';
 import 'dart:convert';
 
 import '../command.dart';
-import '../exit_codes.dart' as exit_codes;
-import '../io.dart';
 import '../log.dart' as log;
 
-/// Handles the `cache` pub command.
-class CacheCommand extends PubCommand {
-  String get description => "Inspect the system cache.";
+/// Handles the `cache list` pub command.
+class CacheListCommand extends PubCommand {
+  String get description => "List packages in the system cache.";
   String get usage => "pub cache list";
   bool get hidden => true;
   bool get requiresEntrypoint => false;
-  bool get takesArguments => true;
 
   Future onRun() {
-    // TODO(rnystrom): Use subcommand for "list".
-    if (commandOptions.rest.length != 1) {
-      log.error('The cache command expects one argument.');
-      this.printUsage();
-      return flushThenExit(exit_codes.USAGE);
-    }
-
-    if ((commandOptions.rest[0] != 'list')) {
-      log.error('Unknown cache command "${commandOptions.rest[0]}".');
-      this.printUsage();
-      return flushThenExit(exit_codes.USAGE);
-    }
-
-    // TODO(keertip): Add flag to list packages from non default sources
+    // TODO(keertip): Add flag to list packages from non default sources.
     var packagesObj = <String, Map>{};
 
     for (var package in cache.sources.defaultSource.getCachedPackages()) {
-
       var packageInfo = packagesObj.putIfAbsent(package.name, () => {});
       packageInfo[package.version.toString()] = {'location': package.dir};
     }
 
-    // TODO(keertip): Add support for non-JSON format
-    // and check for --format flag
+    // TODO(keertip): Add support for non-JSON format and check for --format
+    // flag.
     log.message(JSON.encode({'packages': packagesObj}));
   }
 }
-