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go/types: specious "invalid recursive type" error? #60130

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mdempsky opened this issue May 11, 2023 · 3 comments
Open

go/types: specious "invalid recursive type" error? #60130

mdempsky opened this issue May 11, 2023 · 3 comments
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@griesemer
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NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one.
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Go1.23

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@mdempsky
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Given:

package p

type s struct { i i }
type i interface { s | any }

go/types currently reports:

/tmp/y.go:3:6: invalid recursive type s
/tmp/y.go:3:6: 	s refers to
/tmp/y.go:4:6: 	i refers to
/tmp/y.go:3:6: 	s

Notably, changing the field type from i to *i makes the error go away. I don't see any fundamental reason why that should make a difference though.

Synthetic test case, constructed while trying to write additional test cases for #60117.

/cc @adonovan @findleyr @griesemer @ianlancetaylor
@mdempsky mdempsky added the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label May 11, 2023
@adonovan
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Seems pretty clearly disallowed by the current spec wording:

https://go.dev/ref/spec#Interface_types:

An interface type T may not embed a type element that is, contains, or embeds T, directly or indirectly.

// illegal: Bad3 may not embed a union containing Bad3
type Bad3 interface {
~int | ~string | Bad3
}

But I don't see the technical reason why the restriction is necessary in this case, as s.i is an ordinary named field.

@griesemer
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The spec rule seems not sufficiently precisely spelled out. And there's probably a bug in the cycle check. Not urgent but added to my plate. Thanks for reporting.

@griesemer griesemer self-assigned this May 11, 2023
@griesemer griesemer added this to the Go1.21 milestone May 11, 2023
@griesemer griesemer modified the milestones: Go1.21, Go1.22 Jun 6, 2023
@griesemer
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Too late for 1.21.

@griesemer griesemer modified the milestones: Go1.22, Go1.23 Nov 30, 2023
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