[no-invalid-void-type] Should accept void | Promise<void>

[garyking]

I've got a function that accepts a function, that should return void. But it can sometimes be async, so it would return Promise<void>. The rule should accept a union of both.

So that the following is acceptable:

async function foo(bar: () => void | Promise<void>) {
  await bar();
}

The other option would be to, of course, only accept Promise<void>, but then I'd have to put async on even funcs that don't use await, and then I'd get lint errors because of that. I think the solution proposed here is easier, and should still be in line with the spirit of the rule.

[bradzacher]

seems reasonable - happy to accept a PR

[Raynos]

👍 ; ran into this issue today as well.