x/tools/gopls: panic in methodsets.NewIndex

[buth]

gopls version: v0.12.2 (go1.20.4)
gopls flags:
update flags: proxy
extension version: 0.38.0
go version: 1.20.4
environment: Visual Studio Code darwin
initialization error: undefined
issue timestamp: Tue, 06 Jun 2023 01:34:11 GMT
restart history:
Tue, 06 Jun 2023 01:29:42 GMT: manual (enabled: true)
Tue, 06 Jun 2023 01:30:36 GMT: manual (enabled: true)
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Tue, 06 Jun 2023 01:34:09 GMT: manual (enabled: true)

ATTENTION: PLEASE PROVIDE THE DETAILS REQUESTED BELOW.

Describe what you observed.

The following code immediately caused a crash.

package crash

type a[K any] *[]K

func (*a[K]) a() {}

panic: interface conversion: types.Object is nil, not *types.Func

goroutine 181 [running]:
golang.org/x/tools/internal/typeparams.OriginMethod(0x14000758660)
	  common.go:108  0x14c
golang.org/x/tools/gopls/internal/lsp/source/methodsets.(*indexBuilder).build.func2(0x140000491c0, 0x14000758660)
	  methodsets.go:248  0x1c4
golang.org/x/tools/gopls/internal/lsp/source/methodsets.methodSetInfo({0x10383ecf0, 0x1400015cc40}, 0x14000775718)
	  methodsets.go:309  0x1f0
golang.org/x/tools/gopls/internal/lsp/source/methodsets.(*indexBuilder).build(0x14000775a68, 0x14000048a00, 0x1400009c6e0)
	  methodsets.go:261  0x4f0
golang.org/x/tools/gopls/internal/lsp/source/methodsets.NewIndex(...)
	  methodsets.go:98
golang.org/x/tools/gopls/internal/lsp/cache.typeCheckImpl({0x1038427c8, 0x1400074bf50}, 0x102c206f0%3F, {{0x14000122dc8, 0x18}, {0x14000122dc8, 0x18}, {0x140002825d0, 0x5}, {0x14000226510, ...}, ...})
	  check.go:1269  0x1b4
golang.org/x/tools/gopls/internal/lsp/cache.(*typeCheckBatch).checkPackage(0x1400042fec8%3F, {0x1038427c8, 0x1400074b380}, 0x14000744360)
	  check.go:634  0x190
golang.org/x/tools/gopls/internal/lsp/cache.(*typeCheckBatch).handleSyntaxPackage(0x1400009c690, {0x1038427c8, 0x1400074b380}, 0x0%3F, {0x14000122dc8, 0x18})
	  check.go:518  0x3d0
golang.org/x/tools/gopls/internal/lsp/cache.(*snapshot).forEachPackageInternal.func2()
	  check.go:401  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 - 9:34:09 PM] 

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[findleyr]

Thank you for the report (especially the repro!). We will fix this gopls crash.

Moving to the Go issue tracker, since it is a gopls issue.

[findleyr]

CC @adonovan

[adonovan]

Let me echo Rob's thanks for providing a minimal reproducible test case--this was a tremendous help and time-saver.

The root cause is a bug in OriginMethod for ill-typed methods where the receiver is *C[T] and the underlying type of C is itself a pointer. Obviously it's a type error to declare such a method, but OriginMethod shouldn't fail.

[adonovan]

On further digging, the problem is an inconsistency between NewMethodSet (which enumerates the methods, including the ill-typed one) and LookupFieldOrMethod (which disavows the ill-typed method). See #60634

[gopherbot]

Change https://go.dev/cl/501197 mentions this issue: internal/typeparams: work around LookupFieldOrMethod inconsistency