[diagnostic] warn on typeof undeclared variable

[vegerot]

Thanks for quick-lint! Big fan

While working on my first JS project in a while, I wrote this bug

function foo(obj1, obj2) {
  if (typeof obj !== typeof obj2) {…}
  …
}

and was disappointed quick-lint didn’t at least give me a warning

[strager]

typeof is often used to detect if a variable exists in the global scope. We can't know what the programmer intended for typeof in your example.

Can you think of a heuristic which will catch your example but not produce false positive warnings for things like typeof WebTransport?

[CoderMuffin]

@strager @vegerot maybe it should be a warning unless it is immediately compared to "undefined"?
maybe a config setting could be added to disable it if it is too aggressive