This extension is not distributed with Mercurial.
Author: Brendan Cully
When this extension is loaded, the diff command checks whether the first argument is a path to a repository. If so, a diff is performed against that repository. Pattern arguments work as usual, but revision lookup is slightly different: the first revision is looked up in the local repository, and the second in the remote.
Configure your .hgrc to enable the extension by adding following lines: