Right now we're only supporting rietveld in the recipe tryjob; eventually we will support gerrit, but recipes are only in repos which use rietveld at the moment.

Would it be bad to just call something like `git cl description` once we download the patch? Or should we maybe hit the rietveld API? I was planning on making a recipe module that allows you to look at tags for a CL somewhere, since I figure other recipes would want to do this.

I'd prefer you call "git cl description -d[isplay]", as I've implemented it for Gerrit as well.

However, bot_update typically doesn't set issue property on a branch, it usually doesn't even have branch checked-out, and even worse, the patch is applied, but not committed to local index (e.g., dirty tree).

Easiest way around would be extending git cl description to work with arbitrary issue and codereview server, say

git cl descr --display --issue XXXX [--gerrit | --rietveld] --server yyy.zzz

We aren't going to do this approach; it was deemed too complicated.