x/build/cmd/gerritbot: posts duplicate messages whenever Gerrit message IDs change

[ianlancetaylor]

Starting at about 08 Nov 2021 02:47:26 -0800 GerritBot sent a large number of duplicate comments. These were comments made in Gerrit on CLs imported into GitHub. Those comments has already been echoed back to the original GitHub pull requests. They were then duplicated on November 8. This affected more than 50 pull requests.

Some Sample GitHub pull requests showing the duplicate comments:

golang/debug#7 (the first one I found)
golang/sys#114
#44998
#29726
#44535 (the last one I found)

CC @golang/osp-team

[dmitshur]

From taking a brief look, a part of the cause seems to be originating from Gerrit: some change there caused message IDs on existing comments to become different, and that led to messages that gerritbot posted to be slightly different, and defeating it's de-duplication logic.

For example, these two GitHub comments:

1. cmd/racebuild: add linux/s390x support build#37 (comment)
2. cmd/racebuild: add linux/s390x support build#37 (comment)

Are both referring to Heschi's only comment in Gerrit on that CL, but the former's URL includes:

Visit [golang.org/cl/336511](https://go-review.googlesource.com/c/build/+/336511#message-212851e6ca26bb1c864f1e79ada86a8f8f5211c0).

While this morning's one has a different message ID:

Visit [golang.org/cl/336511](https://go-review.googlesource.com/c/build/+/336511#message-c61585b95b9aa13f9d1b62707afb294cee7a2119).

gerritbot's de-duplication algorithm can be improved, but this also means unless Gerrit IDs change again (hopefully not something that happens often) this type of issue shouldn't keep happening.