Clean up the semantics of package descriptions.

lib/src/source/cached.dart

 // Copyright (c) 2014, 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 pub.source.cached;
 
 import 'dart:async';
 
 import 'package:path/path.dart' as path;
 
@@ skipping 12 matching lines @@
 abstract class CachedSource extends Source {
   /// The root directory of this source's cache within the system cache.
   ///
   /// This shouldn't be overridden by subclasses.
   String get systemCacheRoot => path.join(systemCache.rootDir, name);
 
   /// If [id] is already in the system cache, just loads it from there.
   ///
   /// Otherwise, defers to the subclass.
   Future<Pubspec> doDescribe(PackageId id) async {
-    var packageDir = getDirectory(await resolveId(id));
+    var packageDir = getDirectory(id);
     if (fileExists(path.join(packageDir, "pubspec.yaml"))) {
       return new Pubspec.load(packageDir, systemCache.sources,
           expectedName: id.name);
     }
 
     return await describeUncached(id);
   }
 
   /// Loads the (possibly remote) pubspec for the package version identified by
   /// [id].
   ///
   /// This will only be called for packages that have not yet been installed in
   /// the system cache.
   Future<Pubspec> describeUncached(PackageId id);
 
   Future get(PackageId id, String symlink) {
     return downloadToSystemCache(id).then((pkg) {
       createPackageSymlink(id.name, pkg.dir, symlink);
     });
   }
 
-  /// Determines if the package with [id] is already downloaded to the system
-  /// cache.
-  ///
-  /// Depending on the source, this may throw an [ArgumentError] if [id] isn't
-  /// resolved using [resolveId].
+  /// Determines if the package identified by [id] is already downloaded to the
+  /// system cache.
   bool isInSystemCache(PackageId id) => dirExists(getDirectory(id));
 
   /// Downloads the package identified by [id] to the system cache.
   Future<Package> downloadToSystemCache(PackageId id);
 
   /// Returns the [Package]s that have been downloaded to the system cache.
   List<Package> getCachedPackages();
 
   /// Reinstalls all packages that have been previously installed into the
   /// system cache by this source.
   ///
   /// Returns a [Pair] whose first element is the packages that were
   /// successfully repaired and the second is the packages that failed to be
   /// repaired.
   Future<Pair<List<PackageId>, List<PackageId>>> repairCachedPackages();
 }