go/types: inconsistent type checking results with recursive aliases on 1.22 and 1.23

[timothy-king]

Opening a new issue for #50729 (comment) .

go/types is giving inconsistent errors with recursive aliases on this example https://go.dev/play/p/CO_3yd7yyrV :

type A = E[any]

type X interface {
	G(c A)
}

type E[T any] interface {
	L(A)
}

On the 1.22 playground this fails with the error:

./prog.go:12:4: invalid use of type alias A in recursive type (see go.dev/issue/50729)

Go build failed.

On the 1.23 playground, this fails with the error:

# [play]
vet: ./prog.go:12:4: invalid use of type alias A in recursive type (see go.dev/issue/50729)

Go vet failed.

Program exited.

gotip succeeds and outputs:

Program exited.

On 1.22 and 1.23, commenting out G(c A) makes the vet warning go away. As does moving the declaration of X below E.

cc @griesemer

[gabyhelp]

Related Issues and Documentation

• cmd/compile: handle alias types in recursive types more consistently #50729
• go/types: avoid certain problems with recursive alias type declarations
• go/types, types2: report an error when using a broken alias
• [release-branch.go1.11] go/types: avoid certain problems with recursive alias type declarations
• gccgo: spurious "invalid recursive alias" error on anonymous, recursive interfaces #56065
• gccgo: internal compiler error for (invalid) program using interface aliases #25302 (closed)
• go/types: erroneously accepts recursive type aliases #25141 (closed)
• go/types: specious "invalid recursive type" error? #60130
• cmd/compile: valid type using type aliases reported as invalid #18640 (closed)
• go/types: var declaration changes representation of its type (alias related) #66704 (closed)

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[cherrymui]

If I understand the post correctly, it looks like the behavior on tip is correct, whereas 1.22 and 1.23 are wrong? So you're suggesting a backport? Thanks.

[griesemer]

We may not be able to easily backport a fix because we don't have the same infrastructure (Alias type nodes) enabled in 1.22/23. But this needs to be investigated first.

[cherrymui]

Thanks. If this only affects recursive aliases like this, we probably don't need to backport.

We need to decide whether tip if correct.

[griesemer]

@timothy-king Is there anything left to do here?

[timothy-king]

Tip is correct. If we are not going to backport for 1.23 (#70230 (comment)), then there is nothing to do here.