As I wrote in IM, it should already work, but CQ will schedule builds on the same builders as master branch.

Also, I've just checked and CQ sets revision='HEAD' property regardless of the branch the CL is from, hence recipe running your build/test will default to checking out master. So, the work items are:

1. on CQ side:  setting branch="xxx" property
2. bot_update: recognize branch if not yet recognized. Note, possibly refs/heads/xxx can be passed a revision property and already recognized by bot_update.
3. make sure your recipes don't hardcode master anywhere. I guess chromium ones already like that, at least they respect revision=deadbeef propery.

Actually, I think even better would be to not touch CQ at all, but instead let bot_update examine CL using Gerrit API and realize which branch the CL is against. This is where we want to move anyway and it simplifies logic.

The actionable items in comment 2 are all related to CQ and bot_update and recipes, so removing from Gerrit triage list.

tl;dr It's already possible. Back you, Jamie :)

+machenbach@ has already taught bot_update to under Gerrit CL branches and fetch appropriate code. Next - ensure your recipes don't override that autodetection and perhaps also fix assumption throughout recipes that they run on master branch.

Very cool Andrii. I'll experiment with a tryjob on a branch really quick and just see what happens. No idea if the recipe can support this.

I think this "just works". See https://chromium-review.googlesource.com/c/angle/angle/+/663418

The bots will use ToT Chromium, with a branch of ANGLE. Seems like a pretty good test case for a branch of ANGLE.

This will all 'just work' if your branches are in heads.

It doesn't yet work for branches in branch-heads. That requires more involved changes of bot_update.py. Started on it here https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/571823 - but gave up after realizing that it gets more complicated than I had time...