Inline auto curried async functions produce invalid javascript

[lozlow]

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• Is it a bug? Usage questions should often be asked in the forum instead.
• Concise, focused, friendly issue title & description.
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• Is it already fixed in master? Instructions

see: rescript-lang/rescript-react#89

I noticed that when passing this async function:

let onSubmit = React.useCallback(async (_a, _b) => {
    await Promise.resolve()
})

it results in the following JS code which does not compile as the function is not async:

var onSubmit = React.useCallback(function (_a) {
      return function (_b) {
        return await Promise.resolve(undefined);
      };
    });

the issue can be avoided by assigning the callback to a variable:

let cb = async (_a, _b) => {
  await Promise.resolve()
}
let onSubmit = React.useCallback(cb)

compiles to:

async function cb(_a, _b) {
  return await Promise.resolve(undefined);
}

var onSubmit = React.useCallback(function (param) {
      return function (param$1) {
        return cb(param, param$1);
      };
    });

[cristianoc]

This seems to have to do with @uncurry bindings and inlined functions.
Self-contained repro:

type callback<'input, 'output> = 'input => 'output

@module("react")
external useCallback: (@uncurry ('input => 'output)) => callback<'input, 'output> = "useCallback"

let onSubmit = () =>
  useCallback(async (_a, b) => {
    await b
  })

[cristianoc]

@lozlow this should fix the issue of the generated code: #6010

[lozlow]

Thanks @cristianoc 🙌