x/build/cmd/gopherbot: comment on bad subrepo issue references

[prattmic]

Most subrepos track issues on golang/go, and thus require issue references in commit messages in the form golang/go#nnn, otherwise the reference will not work properly.

Gopherbot could detect raw #nnn issue references on subrepos and leave a comment suggesting changing them.

e.g., on https://golang.org/cl/375754, I put the wrong issue reference and didn't notice until after I submitted the CL.

[cherrymui]

If you use the git-codereview tool, it automatically rewrites #nnn references on subrepos to golang/go#nnn.

[bcmills]

That's true, but it is surprisingly easy to forget to install the git-codereview commit hooks when cloning the subrepos.

[prattmic]

I'll put forth the (potentially controversial) opinion that any git-codereview hook fix/error should have a corresponding presubmit check on Gerrit.

There is no guarantee that everyone will use git-codereview, so enforcement on Gerrit is more consistent. Using git-codereview will then simply mean that these issues will be caught earlier, or fixed automatically for you.

[cherrymui]

(I'm not saying we should not add the check, but just mentioning a "workaround" (otherwise I'd never remember to add "golang/go"))

forget to install the git-codereview commit hooks when cloning the subrepos.

Without the hooks it doesn't add the Change-ID. That's how I remembered to install the hooks.

[cagedmantis]

/cc @golang/release

[dmitshur]

forth the (potentially controversial) opinion that any git-codereview hook fix/error should have a corresponding presubmit check on Gerrit.

First bullet point of issue #18548 is related. (It also serves to show this isn't a controversial opinion—having such a check at the server level would be very nice, it just hasn't been implemented yet.)