x/build: add slowbots heuristics

[josharian]

Slowbots are awesome, but manual, and thus error-prone.

We could add some heuristics to automatically trigger appropriate slowbots. For example, any change that touches cmd/compile/internal/ssa/rewrite_ARCH.go should trigger slowbots for that arch (or set of arches). Similarly for any file named whatever_ARCH.s. Probably something similar for files named whatever_OS.go.

We could start small and improve heuristics over time. There'd be a few false positives, but probably few enough that it'd be worth it.

cc @bcmills @dmitshur

[mvdan]

Can I give ten thumbs up? :)

I think we could make this a bit smarter than just "did this file change at all?". For example, for Go files, we could ignore formatting and comment changes by comparing the before and after through go/format after dropping all comments. This isn't foolproof, because some relevantcomments like // +build, but this might help us with false positives.

[cagedmantis]

/cc @dmitris @toothrot

[dmitris]

fwd /cc @dmitshur

[dmitshur]

This sounds very reasonable to consider, thanks for the suggestion. There are 2 concerns to be mindful of.

Slowbots are currently very limited resources, and I want to ensure this doesn’t lead to them becoming exhausted. We can adjust things as you said, so it should be a manageable problem. Can also turn it into from automatically starting to just posting a comment with a suggestion.

Secondly, it’d be nice to prototype this first before committing to this feature. I’d like to see how much code and work it’ll take to make this happen.