Refactor Source to take the system cache as a parameter.

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.
 
 #library('system_cache');
 
 #import('io.dart');
 #import('package.dart');
+#import('source.dart');
 #import('source_registry.dart');
 #import('utils.dart');
 
 /**
  * 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.
  */
 class SystemCache {
@@ skipping 14 matching lines @@
 
   /**
    * Creates a new package cache which is backed by the given directory on the
    * user's file system.
    */
   SystemCache(this.rootDir)
   : _pendingInstalls = new Map<PackageId, Future<Package>>(),
     sources = new SourceRegistry();
 
   /**
+   * Registers a new source. This source may not have the same name as a source

[Bob Nystrom, 2012/07/10 16:12:36]

"may" -> "must"

[nweiz, 2012/07/10 18:13:01]

Done.

+   * that's already been registered.
+   */
+  void register(Source source) {
+    source.bind(this);
+    sources.register(source);
+  }
+
+  /**
    * 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) =>
@@ skipping 12 matching lines @@
    * == false` to the system cache.
    */
   Future<Package> install(PackageId id) {
     if (!id.source.shouldCache) {
       throw new IllegalArgumentException("Package $id is not cacheable.");
     }
 
     var pending = _pendingInstalls[id];
     if (pending != null) return pending;
 
-    var sourceDir = join(rootDir, id.source.name);
-    var path = id.source.systemCacheDirectory(id, sourceDir);
+    var path = id.source.systemCacheDirectory(id);
     var future = exists(path).chain((exists) {
       // TODO(nweiz): better error handling
       if (exists) throw 'Package $id is already installed.';
       return ensureDir(dirname(path));
     }).chain((_) {
       return id.source.install(id, path);
     }).chain((found) {
       if (!found) throw 'Package $id not found.';
       return Package.load(path, sources);
     });
 
     always(future, () => _pendingInstalls.remove(id));
     _pendingInstalls[id] = future;
     return future;
   }
 }