"pubspec" -> "pubspec.yaml".

utils/pub/package.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('package');
 
 #import('io.dart');
 #import('pubspec.dart');
 #import('source.dart');
 #import('source_registry.dart');
 #import('version.dart');
 
 /**
  * A named, versioned, unit of code and resource reuse.
  */
 class Package {
   /**
    * Loads the package whose root directory is [packageDir].
    */
   static Future<Package> load(String packageDir, SourceRegistry sources) {
-    var pubspecPath = join(packageDir, 'pubspec');
+    var pubspecPath = join(packageDir, 'pubspec.yaml');
 
     return fileExists(pubspecPath).chain((exists) {
       if (exists) {
         return readTextFile(pubspecPath).transform((contents) {
           return new Pubspec.parse(contents, sources);
         });
       } else {
         // If there is no pubspec, we implicitly treat that as a package with
         // no dependencies.
         return new Future.immediate(new Pubspec.empty());
@@ skipping 132 matching lines @@
   /**
    * The metadata used to identify the package being referenced. The
    * interpretation of this will vary based on the [source].
    */
   final description;
 
   PackageRef(this.name, this.source, this.version, this.description);
 
   String toString() => "$name $version from $source ($description)";
 }