Make Source.getDirectory synchronous.

lib/src/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 pub.source;
 
 import 'dart:async';
 
 import 'package:pub_semver/pub_semver.dart';
 
@@ skipping 89 matching lines @@
   /// This method is effectively protected: subclasses must implement it, but
   /// external code should not call this. Instead, call [describe].
   Future<Pubspec> doDescribe(PackageId id);
 
   /// Ensures [id] is available locally and creates a symlink at [symlink]
   /// pointing it.
   Future get(PackageId id, String symlink);
 
   /// Returns the directory where this package can (or could) be found locally.
   ///
-  /// If the source is cached, this will be a path in the system cache. In that
-  /// case, this will return a directory even if the package has not been
-  /// installed into the cache yet.
-  Future<String> getDirectory(PackageId id);
+  /// If the source is cached, this will be a path in the system cache.
+  /// Depending on the source, this may throw an [ArgumentError] if [id] isn't
+  /// resolved using [resolveId].
+  String getDirectory(PackageId id);
 
   /// Gives the source a chance to interpret and validate the description for
   /// a package coming from this source.
   ///
   /// When a [Pubspec] or [LockFile] 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, and
   /// to give the source a chance to canonicalize the description.
   ///
@@ skipping 51 matching lines @@
   /// package to determine information about the resolved id.
   ///
   /// The returned [PackageId] may have a description field that's invalid
   /// according to [parseDescription], although it must still be serializable
   /// to JSON and YAML. It must also be equal to [id] according to
   /// [descriptionsEqual].
   ///
   /// By default, this just returns [id].
   Future<PackageId> resolveId(PackageId id) => new Future.value(id);
 
+  /// Returns whether [id] is fully-resolved, according to [resolveId].
+  bool isResolved(PackageId id) => true;
+
   /// Returns the source's name.
   String toString() => name;
 }