[ES6] Inline argument type for arrow function requires parentheses

[calebegg]

Inline (/** Foo */-style) type annotations are ignored for single-argument arrow functions unless the (normally optional) parentheses are included around the argument.

See demo

[concavelenz]

@Dominator008

[Dominator008]

This is a bit ambiguous. I can interpret the example

let foo = /** number */ x => x * 2;

as trying to cast the variable foo = (x => x * 2) to the type number, although "inline casting" isn't supported and one needs to parenthesize x => x * 2 as (x => x * 2).

The /** number */ JSDocInfo is currently attached to the FUNCTION node, which one can argue is correct.

[MatrixFrog]

I agree, I think the way it is now is fine (and is well documented internally though admittedly not externally).

[calebegg]

That's fair. I do wish there was some sort of "this inline annotation has no effect here" warning. I've made this mistake several times, and I've corrected it several times in code reviews.