x/build/cmd/coordinator: some CLs exp subrepo left strange active trybots running

[dmitshur]

A few CLs (147877, 147797, 146197) in the exp subrepo started trybots.

They each ended with a trybot run that started, but never finished. E.g.:

TryBots beginning. Status page: https://farmer.golang.org/try?commit=0d16b4a3

As a result, farmer shows 3 active trybot runs now, with -2 remaining builds each:

/cc @bradfitz

Reporting this for our reference, since I'm about to redeploy coordinator and we might lose this information.

[dmitshur]

The "Builds Remaining" number calculation is clearly wrong. I've noticed it's sometimes wrong even elsewhere, for trybots that succeed properly. E.g., from this trybot run:

[bradfitz]

Fallout from #17626. Specifically from https://go-review.googlesource.com/c/build/+/143538/ ... before that CL the number of builders in a tryset was always equal to the number of try builders. Apparently I missed that we had made that assumption.

Easy enough fix.

[dmitshur]

Thanks for diagnosing the issue.

[gopherbot]

Change https://golang.org/cl/149437 mentions this issue: cmd/coordinator: fix trybot remaining builds count for subrepos