cmd/compile: incorrect runtime panic on switch statement involving generic slice/map/func type

[mdempsky]

https://go.dev/play/p/4Wa1-HERtli?v=gotip

This program should run silently and exit with success.

With Go 1.18 and tip, it silently miscompiles as a program that raises a runtime panic instead.

Normally, I'm of the opinion that silent miscompilations are severe issues that merit a backport and fix. But I think this case is very unlikely in practice. If anyone disagrees or thinks there's an easy way to fix the 1.18 frontend to handle this correctly (or at least ICE instead), feel free to speak up.

/cc @randall77 @dr2chase @cuonglm

[cuonglm]

Could we just simply suppress the conversion to interface{} if type is not comparable?

[gopherbot]

Change https://go.dev/cl/415634 mentions this issue: cmd/compile: don't convert to interface{} for un-comparable types in generic switch

[mdempsky]

Could we just simply suppress the conversion to interface{} if type is not comparable?

Nice idea. I think that should work, yeah.

[cuonglm]

@gopherbot please backport this to go1.18

[gopherbot]

Backport issue(s) opened: #53752 (for 1.18).

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