Require two type arguments for map literals (issue 4522).

utils/pub/lock_file.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('lock_file');
 
 #import('dart:json');
 #import('package.dart');
 #import('source_registry.dart');
 #import('utils.dart');
 #import('version.dart');
 #import('yaml/yaml.dart');
 
 /**
  * A parsed and validated `pubspec.lock` file.
  */
 class LockFile {
   /**
    * The packages this lockfile pins.
    */
   Map<String, PackageId> packages;
 
   LockFile._(this.packages);
 
   LockFile.empty()
-    : packages = <PackageId>{};
+    : packages = <String, PackageId>{};
 
   /**
    * Parses the lockfile whose text is [contents].
    */
   factory LockFile.parse(String contents, SourceRegistry sources) {
-    var packages = <PackageId>{};
+    var packages = <String, PackageId>{};
 
     if (contents.trim() == '') return new LockFile.empty();
 
     var parsed = loadYaml(contents);
 
     if (parsed.containsKey('packages')) {
       var packageEntries = parsed['packages'];
 
       packageEntries.forEach((name, spec) {
         // Parse the version.
@@ skipping 32 matching lines @@
       });
     }
 
     return new LockFile._(packages);
   }
 
   /**
    * Returns the serialized YAML text of the lock file.
    */
   String serialize() {
-    var packagesObj = <Map>{};
+    var packagesObj = <String, Map>{};
     packages.forEach((name, id) {
       packagesObj[name] = {
         'version': id.version.toString(),
         'source': id.source.name,
         'description': id.description
       };
     });
 
     // TODO(nweiz): Serialize using the YAML library once it supports
     // serialization. For now, we use JSON, since it's a subset of YAML anyway.
     return JSON.stringify({'packages': packagesObj});
   }
 }