go/types: interface.Complete panics for interfaces with duplicate methods

[istonegithub]

gopls version: v0.13.1 (go1.20.4)
gopls flags:
update flags: proxy
extension version: 0.39.1
go version: 1.20.4
environment: Visual Studio Code darwin
initialization error: undefined
issue timestamp: Thu, 03 Aug 2023 05:31:10 GMT
restart history:
Wed, 02 Aug 2023 07:06:29 GMT: activation (enabled: true)

ATTENTION: PLEASE PROVIDE THE DETAILS REQUESTED BELOW.

Describe what you observed.

panic: 41710: duplicate method GetByID

goroutine 9767 [running]:
go/types.computeInterfaceTypeSet.func2(0xa2ee, 0x14008235980, 0x1)
	  typeset.go:230  0x570
go/types.computeInterfaceTypeSet(0x0, 0x101123495%3F, 0x140081d3770)
	  typeset.go:257  0x21c
go/types.(*Interface).typeSet(...)
	  interface.go:29
go/types.(*Interface).Complete(...)
	  interface.go:143
golang.org/x/tools/gopls/internal/lsp/cache.typeCheckImpl({0x101576968, 0x140098a8810}, 0x10093fec0%3F, {{0x140015439c8, 0x15}, {0x140015439c8, 0x15}, {0x14001597000, 0x3}, {0x14008de5540, ...}, ...})
	  check.go:1481  0x6f8
golang.org/x/tools/gopls/internal/lsp/cache.(*typeCheckBatch).checkPackage(0x1400d6c6ec8%3F, {0x101576968, 0x140090556b0}, 0x140093dde60)
	  check.go:674  0x190
golang.org/x/tools/gopls/internal/lsp/cache.(*typeCheckBatch).handleSyntaxPackage(0x14007d21da0, {0x101576968, 0x140090556b0}, 0x14000995e00%3F, {0x140015439c8, 0x15})
	  check.go:532  0x3f4
golang.org/x/tools/gopls/internal/lsp/cache.(*snapshot).forEachPackageInternal.func2()
	  check.go:394  0x34
golang.org/x/sync/errgroup.(*Group).Go.func1()
	  errgroup.go:75  0x5c
created by golang.org/x/sync/errgroup.(*Group).Go
	  errgroup.go:72  0xa0
[Error - 12:35:43 PM] 

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[findleyr]

Hi @istonegithub, thanks for reporting. Is this crash reproducible for you?

[findleyr]

I have a reproducer:

package p

type I[P any] interface {
  m(P)
  m(P)
}

type X I[int]

Unlike var types, X will not be completed during type checking, so we encounter an incomplete interface that has duplicate methods, and therefore panic.

I'll note that we also panic when importing any package containing interfaces with duplicate methods, as the importer calls Complete(), but that panic is recovered.

CC @griesemer: I think it is incorrect for computeInterfaceTypeSet to panic here. Compare with the "cannot handle more than %d union terms..." error message in computeUnionTypeSet.

[gopherbot]

Change https://go.dev/cl/515555 mentions this issue: go/types, types2: don't panic during interface completion

[findleyr]

@gopherbot please backport to Go 1.21. This is a deterministic panic when correctly using the go/types API.

[gopherbot]

Backport issue(s) opened: #61743 (for 1.21), #61744 (for 1.20).

Remember to create the cherry-pick CL(s) as soon as the patch is submitted to master, according to https://go.dev/wiki/MinorReleases.

[gopherbot]

Change https://go.dev/cl/515636 mentions this issue: [release-branch.go1.21] go/types, types2: don't panic during interface completion

[findleyr]

@gopherbot please backport to Go 1.20. This is a deterministic panic when correctly using the go/types API.

[gopherbot]

Change https://go.dev/cl/515638 mentions this issue: [release-branch.go1.20] go/types, types2: don't panic during interface completion