Fix #4260 : Allow trailing arguments that accept void to be omitted

[Jack Williams (jack-williams)]

Fixes#4260

[Ryan Cavanaugh (RyanCavanaugh)]

TypeScript Bot (@typescript-bot) test this

[TypeScript Bot (typescript-bot)]

Heya Ryan Cavanaugh (@RyanCavanaugh), I've started to run the extended test suite on this PR at 2b44a1b. You can monitor the build here. It should now contribute to this PR's status checks.

[Ryan Cavanaugh (RyanCavanaugh)]

Jack Williams (@jack-williams) FYI I expect the test run from the bot to fail so don't get worried if it comes back red

[Jack Williams (jack-williams)]

No worries! Thanks for picking it up

[Jack Williams (jack-williams)]

This doesn't fix something like:

declarefunctionfoo<T=void>(x: T);foo();// T = void, expected 1 arg, 0 given

which I actually think is one of the more useful scenarios. I disabled this behavior because otherwise it means you have to do arity checking again after instantiation which messes with overloading. I'm wondering if we could put in a special case for 1 signature? If it's seems useful enough that is.

[Ryan Cavanaugh (RyanCavanaugh)]

Jack Williams (@jack-williams) I don't find that example super compelling given that it potentially requires multiple iterations of reasoning, e.g.

typeMaybeVoid=Textendsvoid ? void : object;declarefunctionfoo<T=void>(x: T,y: MaybeVoid<T>);foo();

[Jack Williams (jack-williams)]

Ryan Cavanaugh (@RyanCavanaugh) Ye I’m inclined to agree. Thanks for merging!

[Daniel Rosenwasser (DanielRosenwasser)]

Tags: void parameters void-typed parameters optional