First pass at version constraint solver.

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');
@@ skipping 44 matching lines @@
    */
   final Pubspec pubspec;
 
   /**
    * The ids of the packages that this package depends on. This is what is
    * specified in the pubspec when this package depends on another.
    */
   Collection<PackageRef> get dependencies() => pubspec.dependencies;
 
   /**
+   * 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()].
    */
   Package._(String dir, this.pubspec)
     : dir = dir,
       name = basename(dir);
 
   /**
    * Returns a debug string for the package.
    */
-  String toString() => '$name ($dir)';
+  String toString() => '$name $version ($dir)';
 }
 
 /**
  * An unambiguous resolved reference to a package. A package ID contains enough
  * information to correctly install the package.
  *
  * Note that it's possible for multiple distinct package IDs to point to
  * different directories that happen to contain identical packages. For example,
  * the same package may be available from multiple sources. As far as Pub is
  * concerned, those packages are different.
@@ skipping 66 matching lines @@
   final String name;
 
   /**
    * The [Source] used to look up the package.
    */
   final Source source;
 
   /**
    * The allowed package versions.
    */
-  final VersionConstraint version;
+  final VersionConstraint constraint;
 
   /**
    * 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);
+  PackageRef(this.name, this.source, this.constraint, this.description);
 
-  String toString() => "$name $version from $source ($description)";
+  String toString() => "$name $constraint from $source ($description)";
 }