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

[jack-williams]

Fixes #4260

[RyanCavanaugh]

@typescript-bot test this

[typescript-bot]

Heya @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.

[RyanCavanaugh]

@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]

No worries! Thanks for picking it up

[jack-williams]

This doesn't fix something like:

declare function foo<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.

[RyanCavanaugh]

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

type MaybeVoid = T extends void ? void : object;
declare function foo<T = void>(x: T, y: MaybeVoid<T>);
foo();

[jack-williams]

@RyanCavanaugh Ye I’m inclined to agree. Thanks for merging!

[DanielRosenwasser]

Tags: void parameters void-typed parameters optional