First stab at a dev server in pub using barback.

sdk/lib/_internal/pub/lib/src/source/path.dart

 // Copyright (c) 2013, 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.source.path;
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:path/path.dart' as path;
@@ skipping 34 matching lines @@
       } on FormatException catch(err) {
         return false;
       }
 
       createPackageSymlink(id.name, id.description["path"], destination,
           relative: id.description["relative"]);
       return true;
     });
   }
 
+  Future<String> getDirectory(PackageId id) {
+    return new Future(() {

[nweiz, 2013/07/25 22:58:58]

newFuture

[Bob Nystrom, 2013/07/26 20:20:11]

Done.

+      _validatePath(id.name, id.description);
+      return id.description["path"];
+    });
+  }
+
   /// Parses a path dependency. This takes in a path string and returns a map.
   /// The "path" key will be the original path but resolved relative to the
   /// containing path. The "relative" key will be `true` if the original path
   /// was relative.
   ///
   /// A path coming from a pubspec is a simple string. From a lock file, it's
   /// an expanded {"path": ..., "relative": ...} map.
   dynamic parseDescription(String containingPath, description,
                            {bool fromLockFile: false}) {
     if (fromLockFile) {
@@ skipping 44 matching lines @@
     if (dirExists(dir)) return;
 
     if (fileExists(dir)) {
       fail("Path dependency for package '$name' must refer to a "
            "directory, not a file. Was '$dir'.");
     }
 
     fail("Could not find package '$name' at '$dir'.");
   }
 }