cmd/compile: hash of unhashable type [4]int32

[wdvxdr1123]

Go version

gotip

Output of go env in your module/workspace:

GOARCH="arm64"
GOOS="darwin"

What did you do?

playground link: https://go.dev/play/p/WAX0OTneh60

What did you see happen?

panic: runtime error: hash of unhashable type [4]int32

goroutine 1 [running]:
main.main()
	/tmp/sandbox3460698193/prog.go:15 +0xc7

What did you expect to see?

no panic

[gopherbot]

Change https://go.dev/cl/567335 mentions this issue: cmd/compile: mark noalg for pointer to noalg type

[gopherbot]

Change https://go.dev/cl/567335 mentions this issue: cmd/compile: mark pointer to noalg type as noalg

[randall77]

Here's a simpler reproducer: https://go.dev/play/p/NGky0OURi8R

[wdvxdr1123]

I can reproduce with go1.21 and go1.22. Should we backport this fix?

[randall77]

I'm on the fence. We only backport serious issues with no workaround, which I'm not sure this qualifies. It has been a bug since 1.18 and this is the first anyone has reported it. I'm not sure what a workaround might be, though. Does introducing a use of the array type in both packages work as a workaround?

I'll open backports and we can discuss on those issues.

@gopherbot please open backport issues. This issue may warrant backporting. It causes program crashing in some very particular circumstances. (Use of reflect.ArrayOf, and just the right use / nonuse of the corresponding language type in particular packages.)

[gopherbot]

Backport issue(s) opened: #65982 (for 1.21), #65983 (for 1.22).

Remember to create the cherry-pick CL(s) as soon as the patch is submitted to master, according to https://go.dev/wiki/MinorReleases.