gerrit: improve revert commit message template, if possible

[dmitshur]

When using Gerrit UI to create a revert of a CL, it populates the commit message with the following template:

Revert "{{.OriginalTitle}}"

This reverts commit {{.CommitHash}}.

Reason for revert: <INSERT REASONING HERE>

For example:

In most contexts of the Go project, we refer to changes by the CL number or a shortlink of the form golang.org/cl/nnn. This has some advantages compared to using the commit hash:

• shorter and less visual noise
• CL page contains code review discussion, in addition to the change; commit requires one extra click to get to discussion

If possible, we should consider changing the template to be:

Revert "{{.OriginalTitle}}"

This reverts https://golang.org/cl/{{.OriginalCL}}.

Reason for revert: <INSERT REASONING HERE>

Or perhaps the This reverts CL {{.OriginalCL}}. form.

Revert CLs are generally created in situations that involve more time pressure and stress compared to normal CLs, so it's less reliable for us to depend on people to remember to do this manually, or to reference documentation like at https://golang.org/wiki/CommitMessage. It's better to adjust the template.

Implementation

I'm not very familiar with the configurability of our Gerrit instance and whether this is possible. /cc @andybons @bradfitz From looking at its source at https://gerrit.googlesource.com/gerrit/+/v2.16.6/polygerrit-ui/app/elements/change/gr-confirm-revert-dialog/gr-confirm-revert-dialog.js#50, it may be the case that this is not a configurable Gerrit feature, and so this may be blocked on a feature request for Gerrit.

This issue is to investigate whether this is possible, and whether we agree it's a good idea. /cc @ianlancetaylor

[dmitshur]

As an idea to consider, if we can't easily control the template Gerrit UI uses, another approach could be to use our own infrastructure (maintner/gopherbot/gerritbot) to detect when a revert CL with that template is created, and have it automatically update the commit message to our preferred template.

However, this approach may involve significantly more work, and may not be reliable or have unintended side-effects.

---

Update in 2022: As a bonus, if we're using our infrastructure for this, we can also check that the revert was clean, and add a Code-Review+1 with a comment confirming that to make revert CLs easier for humans to review (and easier to spot a mistake if it happens).

In cases where a revert happens quickly, the git tree would be identical and can be used to short-circuit TryBots as well.

For example, patch set 3 of revert CL 378586 had the same tree as https://go.googlesource.com/go/+/1302f93c4e1eae0e625b372f9bb6bb48780af30f, and patch set 3 of revert CL 378587 had the same tree as https://go.googlesource.com/go/+/e4a6b84962cc2fb4f4b8bb532a84bab5bfd68d99. Computers can be better (and quicker) at spotting this than humans.

One clear risk of updating the commit message automatically is that requires it pushing a new patch set, that may race with the CL author doing the same. Just leaving code-review votes/comments won't run into that problem.

[mvdan]

I was about to file this exact same issue. I've created three revert CLs in the past week, and I'm getting tired of having to do this bit of extra work manually :)

[dmitshur]

I took a look at the latest Gerrit source to see if anything changed since 2019 to make this easier by now, and initially spotted a promising comment:

"// This is to give plugins a chance to update message" (source)

It turned out that an API event callback for "revert" was added in Gerrit CL 80750 back in 2016. I found a plugin that appears to make use of it for reference.

I'm not closely familiar with plugins, but from a quick look at https://gerrit-review.googlesource.com/Documentation/dev-plugins-lifecycle.html, the overhead in creating and maintaining a plugin may be too high to make this a good viable next step for resolving this Go issue specifically. (It might be a better fit for a general solution of making revert messages template-able or otherwise customizable for any Gerrit host to use.)