Give cached sources control over their cache directories.

utils/pub/source.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('source');
 
 #import('package.dart');
 
 /**
  * A source from which to install packages.
@@ skipping 17 matching lines @@
    * locally.
    */
   abstract bool get shouldCache();
 
   /**
    * Installs the package identified by [id] to [path]. Returns a [Future] that
    * completes when the installation was finished. The [Future] should resolve
    * to true if the package was found in the source and false if it wasn't. For
    * all other error conditions, it should complete with an exception.
    *
-   * If [shouldCache] is true, [path] will be a path to this source's
-   * subdirectory of the [PackageCache]'s cache directory. If [shouldCache] is
-   * false, [path] will be a path to the application's "packages" directory.
-   *
    * [path] is guaranteed not to exist, and its parent directory is guaranteed
    * to exist.
    */
   abstract Future<bool> install(PackageId id, String path);
 
   /**
+   * Returns the directory in the system cache that the package identified by
+   * [id] should be installed to. [parent] is this source's subdirectory in the
+   * system cache directory.
+   *
+   * This doesn't need to be implemented if [shouldCache] is false.
+   */
+  String systemCacheDirectory(PackageId id, String parent) =>
+    join(parent, packageName(id));
+
+  /**
    * When a [Pubspec] is parsed, it reads in the description for each
    * dependency. It is up to the dependency's [Source] to determine how that
    * should be interpreted. This will be called during parsing to validate that
    * the given [description] is well-formed according to this source. It should
    * return if the description is valid, or throw a [FormatException] if not.
    */
   void validateDescription(description) {}
 
   /**
    * Returns a human-friendly name for the package identified by [id]. This
    * method should be light-weight. It doesn't need to validate that the given
    * package exists.
    *
    * The package name should be lower-case and suitable for use in a filename.
    * It may contain forward slashes.
    */
   String packageName(PackageId id) => id.description;
 }