Some CLs may refer to recently closed issues (e.g., fixups or followups). It'd be better if @gopherbot would post the usual "CL nnnn mentions this issue." comment in those situations.

Currently, the bot skips all closed issues when considering posting that message. This was done to avoid posting in really old, frozen issues (e.g., #1, #2, etc.) when they're accidentally referenced.

However, a better proxy is to check whether the issue has the FrozenDueToAge label, which the bot automatically applies to old issues that are closed (see here).

I ran into this in #21077 (comment).

I've discussed this change with @bradfitz at https://go-review.googlesource.com/c/39352/#message-8e361c0e3df415836dd3c4501d77fdf7beacc296.

CL incoming; this issue report is for posterity.