x/tools/internal/refactor/inline: panic in needsParens

[adonovan]

#!stacks
"gopanic" && "inline.needsParens:+4"

Issue created by stacks.

	res, err := st.inlineCall()
...
	// Replace the call (or some node that encloses it) by new syntax.
	assert(res.old != nil, "old is nil")
	assert(res.new != nil, "new is nil")
...
	if needsParens(caller.path, res.old, res.new) {
...
func needsParens(callPath []ast.Node, old, new ast.Node) bool {
	// Find enclosing old node and its parent.
	i := slices.Index(callPath, old)
	if i == -1 {
		panic("not found") <--- here
	}

This stack 0imOzQ was reported by telemetry:

• crash/crash
• runtime.gopanic:+69
• golang.org/x/tools/internal/refactor/inline.needsParens:+4
• golang.org/x/tools/internal/refactor/inline.(*state).inline:+47
• golang.org/x/tools/internal/refactor/inline.Inline:+13
• golang.org/x/tools/gopls/internal/golang.inlineCall:+59
• golang.org/x/tools/gopls/internal/golang.ApplyFix:+41
• golang.org/x/tools/gopls/internal/server.(*commandHandler).ApplyFix.func1:+1
• golang.org/x/tools/gopls/internal/server.(*commandHandler).run.func2:+3
• golang.org/x/tools/gopls/internal/server.(*commandHandler).run:+77
• golang.org/x/tools/gopls/internal/server.(*commandHandler).ApplyFix:+2
• golang.org/x/tools/gopls/internal/protocol/command.Dispatch:+31
• golang.org/x/tools/gopls/internal/server.(*server).ResolveCodeAction:+21
• golang.org/x/tools/gopls/internal/protocol.serverDispatch:+46
• 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/[email protected] go1.23.3 darwin/arm64 vscode (1)

[adonovan]

Another strange one: it appears to be a simple case of inlineCall returning a res.old node that is not an element of caller.path, but auditing all assignments to res.old, they all look like legitimate ancestors of the call node. Also, we have test coverage of at least all the strategies, so if any strategy were to return a non-ancestral node, it would be caught deterministically by the tests.