Make VersionSolver source- and description-aware.

utils/pub/utils.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.
 
 /**
  * Generic utility functions. Stuff that should possibly be in core.
  */
 #library('utils');
 
 /** Thrown by methods that parse text when the text isn't a valid. */
 class FormatException implements Exception {
   final String message;
 
   FormatException(this.message);
 
   String toString() => message;
 }
 
 /** A pair of values. */
 class Pair<E, F> {
   E first;
   F last;
 
   Pair(this.first, this.last);
 
   String toString() => '($first, $last)';
+
+  bool operator==(other) {
+    if (other is! Pair) return false;
+    return other.first == first && other.last == last;
+  }
 }
 
 // TODO(rnystrom): Move into String?
 /** Pads [source] to [length] by adding spaces at the end. */
 String padRight(String source, int length) {
   final result = new StringBuffer();
   result.add(source);
 
   while (result.length < length) {
     result.add(' ');
@@ skipping 51 matching lines @@
   var buffer = new StringBuffer();
   var start = 0;
   for (var match in matcher.allMatches(source)) {
     buffer.add(source.substring(start, match.start()));
     start = match.end();
     buffer.add(fn(match));
   }
   buffer.add(source.substring(start));
   return buffer.toString();
 }