x/tools/gopls: stubmethods: nil deref of FuncType.Results in fromReturnStmt

[adonovan]

#!stacks
"runtime.sigpanic" && ("fromReturnStmt:+26" || "fromReturnStmt:+27")

Issue created by stacks.

Oops, the Results field is optional, and in any case NumFields is the correct measure:

	if len(funcType.Results.List) != len(ret.Results) {
		return nil, fmt.Errorf("%d-operand return statement in %d-result function",
			len(ret.Results),
			len(funcType.Results.List))
	}

This stack ArQqdg was reported by telemetry:

• crash/crash
• runtime.gopanic:+69
• runtime.panicmem:=262
• runtime.sigpanic:+19
• golang.org/x/tools/gopls/internal/golang/stubmethods.fromReturnStmt:+26
• golang.org/x/tools/gopls/internal/golang/stubmethods.GetIfaceStubInfo:+10
• golang.org/x/tools/gopls/internal/golang.quickFix:+44
• golang.org/x/tools/gopls/internal/golang.CodeActions:+65
• golang.org/x/tools/gopls/internal/server.(*server).CodeAction:+154
• golang.org/x/tools/gopls/internal/protocol.serverDispatch:+160
• golang.org/x/tools/gopls/internal/lsprpc.(*streamServer).ServeStream.ServerHandler.func3:+5
• golang.org/x/tools/gopls/internal/lsprpc.(*streamServer).ServeStream.handshaker.func4:+52
• golang.org/x/tools/gopls/internal/protocol.Handlers.MustReplyHandler.func1:+2
• golang.org/x/tools/gopls/internal/protocol.Handlers.AsyncHandler.func2.2:+3
• runtime.goexit:+0

golang.org/x/tools/[email protected] go1.23.3 darwin/arm64 other (5)

[gabyhelp]

Related Issues

• x/tools/gopls: nil Signature (?) deref in Completion #70634 (closed)
• x/tools/gopls: OOB index crash in completion.expectedReturnStmtType #70636 (closed)
• x/tools/gopls: bug report in GetIfaceStubInfo #70666
• x/tools/gopls: out-of-bounds index in "stub methods" code action #64087 (closed)
• x/tools/gopls: completion: failed type assertion in inferExpectedTypeArg #70889 (closed)
• x/tools/gopls: Hover: nil deref in parseDocLink #70635 (closed)
• x/tools/gopls: Completion: "ZeroString for unexpected type" panic #70744 (closed)
• x/tools/gopls: OOB index in stubmethods.fromValueSpec (reported by telemetry) #64545 (closed)
• x/tools/gopls: crash in Hover (telemetry) #69362
• x/tools/gopls: analysisinternal.ZeroValue crash on (presumably) unsafe.Pointer #70585 (closed)

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[adonovan]

I think this was fixed in passing by https://go.dev/cl/623156 which changed it to:

	rets := sig.Results()
	// The return operands and function results must match.
	// (Spread returns were rejected earlier.)
	if rets.Len() != len(ret.Results) {
		return nil, fmt.Errorf("%d-operand return statement in %d-result function",
			len(ret.Results),
			rets.Len())
	}