Make VersionSolver source- and description-aware.

utils/pub/package.dart

Index: utils/pub/package.dart
diff --git a/utils/pub/package.dart b/utils/pub/package.dart
index 1449b9e8921e944d656f312b075e28c3a1ac33aa..46345ed92891f1efd5b2a84e1c3d8e3bb1b52eef 100644
--- a/utils/pub/package.dart
+++ b/utils/pub/package.dart
@@ -116,7 +116,7 @@ class PackageId implements Comparable, Hashable {
    * The name of the package being identified. This will be the human-friendly
    * name like "uilib".
    */
-  String get name() => source.packageName(this);
+  String get name() => source.packageName(description);
 
   int hashCode() => name.hashCode() ^
                     source.name.hashCode() ^
@@ -145,6 +145,11 @@ class PackageId implements Comparable, Hashable {
 
     return version.compareTo(other.version);
   }
+
+  /**
+   * Returns the pubspec for this package.
+   */
+  Future<Pubspec> describe() => source.describe(this);
 }
 
 /**
@@ -154,11 +159,6 @@ class PackageId implements Comparable, Hashable {
  */
 class PackageRef {
   /**
-   * The name of the package being referenced.
-   */
-  final String name;
-
-  /**
    * The [Source] used to look up the package.
    */
   final Source source;
@@ -174,7 +174,19 @@ class PackageRef {
    */
   final description;
 
-  PackageRef(this.name, this.source, this.constraint, this.description);
+  /**
+   * The name of the package being referenced.
+   */
+  String get name() => source.packageName(description);
+
+  PackageRef(this.source, this.constraint, this.description);
 
   String toString() => "$name $constraint from $source ($description)";
+
+  /**
+   * Returns a [PackageId] generated from this [PackageRef] with the given
+   * concrete version.
+   */
+  PackageId atVersion(Version version) =>
+    new PackageId(source, version, description);
 }