Git cherry-pick, merge and revert (including the Gerrit button) do not include Change-Id in commit message

[Mark McLoughlin]

I used the gerrit revert button for this: https://review.openstack.org/#/c/36605/

You see in Patch Set 1, gerrit didn't include a Change-Id in the commit message

So, when I had to rebase (which was odd, there was no conflicts) I needed to manually add the Change-Id

[Jeremy Stanley (fungi)]

I hadn't noticed that button existed, but the obvious workaround here (for those stumbling across this bug) is merely to revert locally and then propose that change for review, since the commit hook should add a Change Id header for you.

Chances are this is an upstream bug, and likely fixed since the 2.4 release we're running. If someone gets a chance to see whether there's a patch we can easily backport for this it would be appreciated!

[Clark Boylan (cboylan)]

It is worth noting that the Change Id hook that git review installs will not add a Change Id to revert commits. Instead what you can git is `git revert` then `git commit --amend` which will cause the hook to run and add a Change Id.

[Jeremy Stanley (fungi)]

After some thorough research, I see why this is the way it is. Not all git subcommands which create or update the commit message go through the same code paths and most (aside from git commit) cannot safely trigger this hook.

http://git.661346.n2.nabble.com/git-revert-doesn-t-run-commit-msg-hook-td7559622.html

http://git.661346.n2.nabble.com/cherry-pick-pre-commit-hook-td5815961.html

There are other hooks which could be used for some of these, but only by for example embedding the change-id into the commit message template and requiring the user to uncomment it by explicitly amending that commit. I found nothing which was any easier or less confusing than the current workarounds.