Uncurrying breaks components with local type variables

[glennsl]

Repro, in v11 with uncurrying enabled:

module A = {
  @react.component
  let make = (type a, ~foo=?) => React.null
}

<A />

yields the error:

[E] Line 6, column 1:
This has type: A.props => (~foo: 'a=?) => React.element
  But this function argument is expecting:
    React.component<A.props> (defined as A.props => Jsx.element)
  
  The incompatible parts:
    (~foo: 'a=?) => React.element vs Jsx.element (defined as JsxU.element)

This works both in v10, and v11 with uncurrying disabled.

[glennsl]

The PPX produces this:

module A = {
  type props = {}
  let make = (type a, _: props) => (~foo=?) => React.null
  // and the usual bit...
}

[glennsl]

My guess is that because local type variables in uncurried functions seem to be compiled as curried function arguments, e.g. let f (type a) = ((Function$ (fun (x: a) -> x))[@res.arity 1]), somewhere they aren't being properly detected as uncurried and unwrapped, hence why the props are generated as empty. I haven't been able to find exactly where this happens though.

[zth]

@glennsl interesting! Maybe @cristianoc has a few pointers on where to look?

[glennsl]

Fixed by #6668