compare current revision against the parsed hash of the target revision

lib/bundler/source.rb

@@ -333,7 +333,7 @@ def to_s
     private
       def update
         if location.directory?
-          fetch if current_revision != @ref
+          fetch if current_revision != revision_for_ref
         else
           clone
         end
@@ -354,6 +354,10 @@ def current_revision
         Dir.chdir(location) { `git rev-parse HEAD`.strip }
       end
 
+      def revision_for_ref
+        Dir.chdir(location) { `git rev-parse #{@ref}`.strip }
+      end
+
       def checkout
         Dir.chdir(location) { `git checkout --quiet #{@ref}` }
       end