cmd/compile: remove assert in internal/noder

[rsc]

There's a func assert in cmd/compile/internal/noder with a TODO to remove.
(It would be a bad experience for users to hit the panic instead of a good error message.)
It's only reachable in the generics implementation, so it doesn't need to be
removed until Go 1.18. Filing this issue to make sure we remember.

[toothrot]

The Go 1.18 tree is now open, so it may make sense to address this issue now.

[toothrot]

@griesemer @findleyr

[griesemer]

@mdempsky @danscales I've looked at the noder code but I'm not sure what there is to do here. This can't be about removing all asserts, and I didn't see an obvious TODO related to a specific assert in a quick search.

[danscales]

I think Russ is saying we should remove the Assert function and all its uses eventually (possibly replacing many of them with a panic with an error message). Maybe we can check with him again on this. In any case, I think we can wait on this until near the end of the release cycle.

[mdempsky]

There's base.Assertf now, so we can more easily include more details in the panic message. But in general, the asserts in noder are being used like the asserts in types2: as extra consistency checks that should never fail; or if they do, then the error message isn't going to be actionable by end users anyway.

[toothrot]

Checking in again, as this issue is labeled a release blocker.

[heschi]

Ping again from the release team: what information is this issue waiting on?

[griesemer]

I believe this can be closed, but I'll leave to @mdempsky do decide.

[mdempsky]

I don't think there's any action to take here. The asserts are just internal consistency checks. They're not expected to fire on user code.