Get codebase ready for actually supporting versioning.

utils/pub/system_cache.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 system-wide cache of installed packages.
  *
  * This cache contains all packages that are downloaded from the internet.
  * Packages that are available locally (e.g. from the SDK) don't use this cache.
  */
@@ skipping 22 matching lines @@
     sources = new SourceRegistry();
 
   /**
    * Loads all of the package ids in the cache and returns them.
    */
   Future<List<PackageId>> listAll() {
     return listDir(rootDir).chain((paths) {
       final sources = paths.map((path) {
         final source = sources[basename(path)];
         return listDir(path).transform((subpaths) {
+          // TODO(rnystrom): Once there are cached packages and this path is
+          // being used, figure out how version numbers should be acquired.
           return subpaths.map((subpath) =>
-            new PackageId(basename(subpath), source));
+            new PackageId(basename(subpath), source, Version.none));
         });
       });
       return Futures.wait(sources).transform(flatten);
     });
   }
 
   /**
    * Ensures that the package identified by [id] is installed to the cache,
    * loads it, and returns it.
    *
@@ skipping 20 matching lines @@
         throw 'Package ${id.fullName} not found in source "${id.source.name}".';
       }
       return Package.load(path, sources);
     });
 
     always(future, () => _pendingInstalls.remove(id));
     _pendingInstalls[id] = future;
     return future;
   }
 }