types2, go/types: type-checking expands type forever

[griesemer]

This is from a comment in #48951, reported by @jkmpariab. Reproducer:

package p

type Fooer interface {
	Foo()
}

type Fooable[F Fooer] struct {
	ptr F
}

func (f *Fooable[F]) Adapter() *Fooable[*FooerImpl[F]] {
	return &Fooable[*FooerImpl[F]]{&FooerImpl[F]{}}
}

//
// By removing the 'F Fooer' type param, program compiles sucessfully
//            |||||||||
//            vvvvvvvvv
type FooerImpl[F Fooer] struct {
}

func (fi *FooerImpl[F]) Foo() {}

cc: @findleyr

[findleyr]

Hmm, why exactly is this package invalid? Looks ok to me, and a fix I'm working on for another recursive case makes this type-check without error.

[griesemer]

Premature conclusion. I've adjusted the title.

[gopherbot]

Change https://golang.org/cl/356490 mentions this issue: go/types: ensure named types are expanded after type-checking

[gopherbot]

Change https://golang.org/cl/356515 mentions this issue: cmd/compile/internal/types2: ensure named types are expanded after type-checking

[jkmpariab]

@griesemer The issue is not fixed yet. i'm testing on

go version devel go1.18-bde0463da3 Tue Oct 19 11:52:34 2021 +0000 linux/amd64

please reopen the issue

[findleyr]

The issue was closed when the change went in to go/types. It will be fixed in the compiler with the CL above.

[griesemer]

This is now fixed in the type-checkers, but the compiler still has an issue. Filed separate #49068 for that.