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cmd/compile: nonsensical error message with recursive generic interfaces #47837

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4ad opened this issue Aug 20, 2021 · 3 comments
Closed

cmd/compile: nonsensical error message with recursive generic interfaces #47837

4ad opened this issue Aug 20, 2021 · 3 comments
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FrozenDueToAge NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one.
Milestone
Go1.18

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@4ad
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4ad commented Aug 20, 2021 •
edited

This is a follow-up to #47836, see that issue first.

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

Repro:

package p

type F[t F] interface {
	B() t
}

type Int0 int
type Int1 int

func (n Int0) B() Int1 { return Int1(n) }
func (n Int1) B() Int0 { return Int0(n) }

func id[t F[t]](v t) t { return v }

var _ = id(Int0(42))

Compiler rejects it with:

go build -gcflags=-G=3 j.go
# command-line-arguments
./j.go:15:11: Int0 does not satisfy F[t]: wrong method signature
	got  func (Int0).B() Int1
	want func (F[t ○string]).B() Int0
@4ad 4ad mentioned this issue Aug 20, 2021
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@mknyszek mknyszek added the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label Aug 20, 2021
@mknyszek mknyszek added this to the Go1.18 milestone Aug 20, 2021
@mknyszek
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CC @ianlancetaylor @griesemer

@griesemer griesemer self-assigned this Aug 22, 2021
@griesemer
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griesemer commented Aug 22, 2021 •
edited

This is a type checker (types2) failure.

@griesemer
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The compiler is now correctly reporting an error:

cannot use generic type F[t invalid type] without instantiation

This was fixed as part of other fixes. Closing.

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@mknyszek @4ad @griesemer @gopherbot