Note, when I tried this, it did output a number, but not the number I expected.

Specifically, I tried this on a branch associated with https://chromium-review.googlesource.com/c/707535/ and got the output "1", but I expected "15".

I dug a bit deeper. Seems like when Gerrit is used as the codereview, we only set patchset number when using the `git cl patch` command. Quinten, did you happen to create your local branch from an existing CL that way?

As for uploading a patch, here is where we set the issue number:
https://cs.chromium.org/chromium/tools/depot_tools/git_cl.py?type=cs&q=PatchsetConfigKey&sq=package:chromium&l=3111

The issue number is parsed from the output of `git push`, in particular this line:
  remote:   https://chromium-review.googlesource.com/#/c/chromium/src/+/812117 Check in google-api-client and its dependencies to webkitpy [WIP]
Unfortunately, the URL does not have patch number. So we might have to get it from somewhere else.

Yeah, I just finished the same line of research.

I think the only option here is to make an http call when the user asks for the patchset, and cache it in gerritpatchset then. I'm not going to do that in "git cl upload" since it's already slow enough as it is.

https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/815137

#2: Yep, you're right, I had created that branch via git cl patch.

#3, 4: Thanks Aaron!

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/tools/depot_tools/+/e8856eea42cf284071511107e818ce9980b30636

commit e8856eea42cf284071511107e818ce9980b30636
Author: Aaron Gable <agable@chromium.org>
Date: Thu Dec 07 23:38:59 2017

git-cl: fix 'status --field=patch' for Gerrit

We don't set the branch.<name>.gerritpatchset git config value
during "git cl upload" because it isn't returned from the
server either during push or during any of our subsequent RPCs,
and adding another RPC just for that metadata would be slower
that we would like.

But calling "git cl status" already makes an RPC per branch, so
take advantage of that to cache the gerritpatchset value during
that operation.

R=robertma

Bug:  792611 
Change-Id: I37b09f3c4cfced86668b457eff82f2424012b14b
Reviewed-on: https://chromium-review.googlesource.com/815137
Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>
Commit-Queue: Aaron Gable <agable@chromium.org>

[modify] https://crrev.com/e8856eea42cf284071511107e818ce9980b30636/git_cl.py