A Mercurial changelog

I need to write this somewhere or I’ll forget how to do it.  I’ve recently started using branches in hg for my target environments instead of using separate repositories as is recommended by Kiln.  I got a request to produce a list of changes that would be going into the next production release and knew there must be a way of doing it in hg.  This is what I found,

hg log -r "ancestors(branch(test)) - ancestors(branch(prod))" 
                   -–style changelog > changes.txt

Seemed to do the trick.