x/tools/gopls: impossible nil panic in reflect.ValueOf

[adonovan]

#!stacks
"runtime.sigpanic" && "abi.(*Type).Kind" && "reflect.unpackEface" && "reflect.ValueOf"

Issue created by stacks.

More memory corruption:

// unpackEface converts the empty interface i to a Value.
func unpackEface(i any) Value {
	e := (*abi.EmptyInterface)(unsafe.Pointer(&i))
	// NOTE: don't read e.word until we know whether it is really a pointer or not.
	t := e.Type
	if t == nil {
		return Value{}
	}
	f := flag(t.Kind()) <-- panics because t is nil
	if t.IfaceIndir() {
		f |= flagIndir
	}
	return Value{t, e.Data, f}
}

This stack H6zSwQ was reported by telemetry:

• crash/crash
• runtime.throw:+9
• runtime.sigpanic:+16
• internal/abi.(*Type).Kind:=197
• reflect.unpackEface:=164
• reflect.ValueOf:=2980
• encoding/json.(*decodeState).unmarshal:+1
• encoding/json.Unmarshal:+11
• golang.org/x/tools/internal/jsonrpc2.wireVersionTag.UnmarshalJSON:+2
• golang.org/x/tools/internal/jsonrpc2.(*wireVersionTag).UnmarshalJSON:+0
• encoding/json.(*decodeState).literalStore:+10
• encoding/json.(*decodeState).value:+31
• encoding/json.(*decodeState).object:+163
• encoding/json.(*decodeState).value:+17
• encoding/json.(*decodeState).unmarshal:+10
• encoding/json.Unmarshal:+11
• golang.org/x/tools/internal/jsonrpc2.DecodeMessage:+2
• golang.org/x/tools/internal/jsonrpc2.(*headerStream).Read:+44
• golang.org/x/tools/internal/jsonrpc2.(*conn).run:+4
• golang.org/x/tools/internal/jsonrpc2.(*conn).Go.gowrap1:+0

golang.org/x/tools/gopls@v0.18.1 go1.24.3 darwin/arm64 vscode (1)

[gabyhelp]

Related Issues

• x/tools/gopls: Package.Path called on nil Package in AddTestForFunc #73687 (closed)
• x/tools/gopls: Hover: invalid nil entry in types.Defs map #69362 (closed)
• x/tools/gopls: analysisinternal.ZeroValue crash on (presumably) unsafe.Pointer #70585 (closed)
• x/tools/gopls: Completion: "ZeroString for unexpected type" panic #70744 (closed)
• x/tools/gopls: nil *types.Package panic in testKind #73096 (closed)
• x/tools/gopls: Completion: nil deref in expectedCompositeLiteralType #72136 (closed)
• x/tools/gopls: Hover: nil deref in golang.StdSymbolOf #70969 (closed)
• x/tools/gopls: fillstruct with anonymous structs panics #40980 (closed)
• x/tools/gopls: nil Signature (?) deref in Completion #70634 (closed)
• x/tools/gopls: stubmethods: nil deref of FuncType.Results in fromReturnStmt #70967 (closed)

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