cmd/compile: compiler panic for generic alias type

[griesemer]

From #46477 (comment):

The following code snippet causes the Go compiler to panic (https://go.dev/play/p/PBvqgMjEs4S?v=gotip)

package main

type Seq[V any] = func(yield func(V) bool)

func f[E any](seq Seq[E]) {
	return
}

func main() {
	f(Seq[int](nil))
}

Marking for 1.23 in case it's a trivial oversight that we can easily address. But not a release blocker.

cc: @mdempsky for visibility. This looks like a noder issue.

[gabyhelp]

Similar Issues

• cmd/compile: generics + constant cycle causes panic in type checker #52748
• cmd/compile: panic for cyclic generic interfaces #56045

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[Carrotman42]

Possibly related to this minimal repro I was just devising:

package main

type OVal[O any] struct {}

type TVal[T any] = OVal[T]

var x TVal[bool]

func main() {}

The panic is the same index out of range [0] with length 0 message.

(sorry for the noise if not - I can file a new issue if desired)

[gopherbot]

Change https://go.dev/cl/593715 mentions this issue: cmd/compile: support generic alias type

[gopherbot]

Change https://go.dev/cl/593797 mentions this issue: [release-branch.go1.23] cmd/compile: support generic alias type