x/build: consider opting-in to longtest builders by default for cmd/go changes, if/when they're under 15 min

[dmitshur]

(I have a feeling @bcmills may have already filed an issue for this, but I couldn't find it. Maybe it was a comment instead.)

With the progress made on #37439 (comment) recently, it seems we can speed up longtest SlowBots to run in under 15 minutes or so. If that can be done, what is your preference on enabling longtest builders by default for changes that touch the go command? CC @bcmills, @jayconrod, @matloob.

In either case, we need to wait for #37439 to be completed first, and give it a little time to see if that on its own is sufficient. But I wanted to create a tracking issue to start gathering feedback eagerly.

I'm also looking for feedback on:

• If this is something we want to do, would you prefer that "cmd/go" changes are determined by the commit subject having the "cmd/go" path present (which is up to the author), or by looking whether any files in src/cmd/go directory are modified?

Also CC @golang/release.

[bcmills]

(I have a feeling @bcmills may have already filed an issue for this, but I couldn't find it. Maybe it was a comment instead.)

I think it was previously an implicit subtext of #37439. Thanks for filing it as a proper issue!

[bcmills]

If the longtest builders can be made to run at roughly the same latency as other TryBots, I think we would prefer to have them trigger by default (in much the same way that the x/tools 'bot triggers automatically).

I think we should use the same mechanism that we currently use to trigger x/tools, whatever that is. (I can't find it at the moment...)

[gopherbot]

Change https://golang.org/cl/279513 mentions this issue: dashboard: pick 4 TryBot helpers for -longtest SlowBots

[matloob]

This would be great! It would save me from accidentally submitting bugs in many cases...

[gopherbot]

Change https://golang.org/cl/334889 mentions this issue: cmd/go: update error messages in tests to match CL 332573

[bcmills]

We should also run longtest builders by default any time there are changes in src/vendor or src/cmd/vendor. We've had too many build breaks lately due to stray edits.