JSX: error with fragment after fixing children type

[cknitt]

rescript-lang/rescript-react#94 fixes the children type for <>, React.Fragment, React.StrictMode and React.Suspense by making it React.element instead of 'children.

This causes an issue with <>:

<>
  <A />
  <B />
</>

now gives the following error without location:

This has type: array<'a>
  Somewhere wanted: React.element (defined as JsxU.element)

The components React.Fragment, React.StrictMode and React.Suspense still work fine though, so it seems there is some special handling for <> in the PPX that needs to be adapted.

[mununki]

I'll look into it later tonight! Thanks!

[mununki]

Have a quick look, and found there is a different transformation process for <> </> from other react components. I think there is no need to be special for that fragment expression against <React.Fragment> </React.Fragment>.
Unifying it would be a fix for this issue.

[mununki]

a bit weirder.

module A = {
  @react.component
  let make = () => {
    <>
      <div />
    </>
  }
}

This has type:
    React.component<React.fragmentProps> (defined as
      React.fragmentProps => Jsx.element)
  Somewhere wanted: string

[cknitt]

That's in JSX 4 classic mode, right? I was using automatic mode.

[mununki]

That's in JSX 4 classic mode, right? I was using automatic mode.

Yes. JSX 4 classic and automatic has different build error each. I'll write down the summary.

[mununki]

Here are the summarized issues regarding the shorthand syntax <> </>:

1. JSX4 automatic: As per the AST after JSX4 transformation, React.array is missing. Having a single child is fine.

<> <div /> <div /> </>

2. JSX4 classic with a single child: It doesn't match the React.createElement signature. It should have Pexp_record [ "children", ...] instead of Pexp_array []

<> <div /> </>

3. JSX4 classic with a multiple children: It doesn't match the React.createElement signature. It needs to use React.createElementVariadic as others.

<> <div /> <div /> </>

4. JSX4 classic: transformed to ReactDOM.createElement* instead of React.createElement* That is why the error message complains about expecting string.

[mununki]

I don't feel the need to change the type definition of the fragment for JSX3 or modify the ppx yet, as long as working fine.