x/tools/gopls: types.IsInterface "Named.check == nil but type is incomplete" panic in methodsets.EnsurePointer

[adonovan]

#!stacks
"runtime.gopanic" && "types.IsInterface" && "methodsets.EnsurePointer:+1"

Issue created by stacks.

The Named type passed to IsInterface has an Underlying type that is also a Named (indicating type checking is incomplete) yet the original Named (which may or may not be the same) has Named.check==nil (indicating type checking should be complete). This seems like a go/types bug.

This stack pY1Q7g was reported by telemetry:

• crash/crash
• runtime.gopanic:+69
• go/types.(*Named).under:+21
• go/types.under:+2
• go/types.IsInterface:=111
• golang.org/x/tools/gopls/internal/cache/methodsets.EnsurePointer:+1
• golang.org/x/tools/gopls/internal/cache/methodsets.methodSetInfo:+4
• golang.org/x/tools/gopls/internal/cache/methodsets.(*indexBuilder).build:+35
• golang.org/x/tools/gopls/internal/cache/methodsets.NewIndex:=82
• golang.org/x/tools/gopls/internal/cache.(*syntaxPackage).methodsets.func1:+1
• sync.(*Once).doSlow:+5
• sync.(*Once).Do:=67
• golang.org/x/tools/gopls/internal/cache.(*syntaxPackage).methodsets:+1
• golang.org/x/tools/gopls/internal/cache.storePackageResults:+3
• golang.org/x/tools/gopls/internal/cache.(*typeCheckBatch).handleSyntaxPackage.gowrap1:+0
• runtime.goexit:+0

golang.org/x/tools/gopls@v0.16.1 go1.23.0 linux/amd64 neovim (1)

[gabyhelp]

Related Issues and Documentation

• x/tools/gopls: panic in methodsets.NewIndex #60628 (closed)
• x/tools/gopls: types.Func.typ=nil panic in missingMethod with gopls@master built with go@master #59848 (closed)
• go.tools/go.types: goto _ crashes type checker #7537 (closed)
• go/types, types2: gopls crash in computeInterfaceTypeSet with "duplicate method" #51316 (closed)
• x/tools/gopls: interface conversion: types.Object is *types.Var, not *types.Func #67975 (closed)
• x/tools/gopls: respect go/analysis.Pass.RunDespiteErrors #33689 (closed)
• go/types, types2: gopls crash on method with type parameters #50427 (closed)
• x/tools/gopls: panic in OriginMethod #61196 (closed)
• go/types: interface.Complete panics for interfaces with duplicate methods #61737 (closed)
• x/tools/gopls: panic in analyzer due to type checker errors #32413 (closed)

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[adonovan]

cc: @griesemer @timothy-king