First pass at version constraint solver.

utils/pub/package.dart

Index: utils/pub/package.dart
diff --git a/utils/pub/package.dart b/utils/pub/package.dart
index 7bb50dfa653420c36e12a8b79f5ab9bc471dc0e5..cb96493686f8664828f3db747927660c3331cfee 100644
--- a/utils/pub/package.dart
+++ b/utils/pub/package.dart
@@ -61,6 +61,15 @@ class Package {
    */
   Collection<PackageRef> get dependencies() => pubspec.dependencies;
 
+  // TODO(rnystrom): This is so far only used for mock packages in tests. Is
+  // it worth keeping this around?

[nweiz, 2012/06/18 18:29:19]

Seems fine to me.

[Bob Nystrom, 2012/06/20 01:40:04]

Done.

+  /**
+   * Constructs a package with the given name and pubspec. The package will
+   * no directory associated with it.
+   */
+  Package.inMemory(this.name, this.pubspec)
+    : dir = null;
+
   /**
    * Constructs a package. This should not be called directly. Instead, acquire
    * packages from [load()].
@@ -72,7 +81,7 @@ class Package {
   /**
    * Returns a debug string for the package.
    */
-  String toString() => '$name ($dir)';
+  String toString() => '$name $version ($dir)';
 }
 
 /**