cmd/compile: "F is not a generic type" when F is a recursive generic interface

[4ad]

On tip (e9e0d1e) with -gcflags=-G=3

Repro:

package p

type F[t F[t]] interface {}

Compiler rejects it with:

go build -gcflags=-G=3 j.go
# command-line-arguments
./j.go:3:10: F is not a generic type

However, it accepts this:

package p

type F[t F] interface {}

But that has other problems, see #47837.

[mknyszek]

CC @ianlancetaylor @griesemer

[tdakkota]

Seems like duplicate of #47796

[4ad]

Yep, seems like a dupe. In fact, I was trying to write that exact Eq when I found this.

[mknyszek]

Closing as duplicate of #47796.