Flow: Generic type parameters not supported on arrow functions

[clark-pan]

I'm using version v1.1.0-alpha.2

Generic types for arrow functions don't seem to be working.

[Thom1729]

Thanks for the find.

I'll take a more detailed look at this, but this may be a case where we'll have to use an unreliable heuristic. It looks like you're using JSX as well, and <T> looks like a JSX tag. It is absolutely impossible for a sublime syntax to tell the difference in the general case. In fact, I'm not sure how this isn't a genuine grammatical ambiguity.

See this TypeScript issue, which is closed as a “Design Limitation”.

In the mean time, I'd suggest using function<> as a workaround.

[clark-pan]

Thanks for looking into it. I'm not 100% familiar with how sublime syntax stuff works, but is there no way to capture the opening tag of jsx and only consider it jsx if theres a closing matching tag?

So a just on its own is considered flow type, but is actually what makes it JSX (or as well i guess)

[clark-pan]

I've also worked around it by separating the definition of the type and the implementation:

type Foo<T: Object> = (a: T) => T
const foo:Foo<*> = (a) => {
  //...
}

[neutraali]

Don't know whether this is related to generic types, class properties or just angle bracket type definitions in particular, but:

export default class ExampleComponent extends React.Component<Props> {
	_iframe: React.Ref<typeof HTMLIFrameElement>
	// Syntax highlighting broken beyond this point

This happens with most angle-bracket stuff, for example Array<string>.

[Thom1729]

@neutraali I've just fixed this in 1.0.19. The problem was that typeof expected an expression, and so it parsed the > as a greater-than operator. I have modified the Flow extension so that typeof will expect a LeftExpression. Please let me know if that problem recurs.

[neutraali]

Thanks @Thom1729 👍 - Will do just as soon as you upload that to Package Control 😸