JSXv4: Locally abstract types do not seem to be in scope in the component body

[glennsl]

Based on the following two scenarios causing errors:

Repro 1

module type T = {
  type t
}

@react.component
let make = (type a, ~foo: module(T with type t = a)) => {
  module T = unpack(foo)
  <div />
}

yields the error:

[E] Line 7, column 13:
The type of this packed module contains variables:
module(T with type t = 'type-a0)

Repro 2

module type T = {
  type t
}

@react.component
let make = (type a, ~foo) => {
  module T = unpack(foo: T with type t = a)
  <div />
}

yields the error:

[E] Line 7, column 41:
This type constructor, `a`, can't be found.
  If you wanted to write a recursive type, don't forget the `rec` in `type rec`

[mununki]

The current output:

@react.component
let make = (type a, ~a: a) => a

// transformed to

type props<'a> = {a: 'a}
let make = ({a, _}: props<'\"type-a">) => a

I couldn't remember the reason why it generates the type variable '\"type-a" for type a in the transformation. No reason not to use just type a.

The expected output would be this:

let make = (type a, {a, _}: props<a>) => a

[glennsl]

I couldn't remember the reason why it generates the type variable '"type-a" for type a in the transformation. No reason not to use just type a.

I remember. It was discussed here: rescript-lang/syntax#490 (comment)