Clean up the semantics of package descriptions.

lib/src/pubspec.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.pubspec;
 
 import 'package:path/path.dart' as path;
 import 'package:pub_semver/pub_semver.dart';
 import 'package:source_span/source_span.dart';
 import 'package:yaml/yaml.dart';
@@ skipping 478 matching lines @@
               specNode.nodes.keys.single.span);
         }
 
         descriptionNode = specNode.nodes[sourceName];
       } else {
         _error('A dependency specification must be a string or a mapping.',
             specNode.span);
       }
 
       // Let the source validate the description.
-      var description = _wrapFormatException('description',
-          descriptionNode.span, () {
+      var ref = _wrapFormatException('description', descriptionNode.span, () {
         var pubspecPath;
         if (_location != null && _isFileUri(_location)) {
           pubspecPath = path.fromUri(_location);
         }
 
-        return _sources[sourceName].parseDescription(
-            pubspecPath, descriptionNode.value, fromLockFile: false);
+        return _sources[sourceName].parseRef(name, descriptionNode.value,
+            containingPath: pubspecPath);
       });
 
-      dependencies.add(new PackageDep(
-          name, sourceName, versionConstraint, description));
+      dependencies.add(ref.withConstraint(versionConstraint));
     });
 
     return dependencies;
   }
 
   /// Parses [node] to a [VersionConstraint].
   VersionConstraint _parseVersionConstraint(YamlNode node) {
     if (node.value == null) return VersionConstraint.any;
     if (node.value is! String) {
       _error('A version constraint must be a string.', node.span);
@@ skipping 73 matching lines @@
     implements ApplicationException {
   PubspecException(String message, SourceSpan span)
       : super(message, span);
 }
 
 /// Returns whether [uri] is a file URI.
 ///
 /// This is slightly more complicated than just checking if the scheme is
 /// 'file', since relative URIs also refer to the filesystem on the VM.
 bool _isFileUri(Uri uri) => uri.scheme == 'file' || uri.scheme == '';