Another case of inlining breaking async

[cknitt]

Broken.resi:

let broken: unit => promise<unit>

Broken.res:

@module("SomeModule")
external someExternal: unit => promise<unit> = "someExternal"

let doSomethingAsync = async () => {
  await someExternal()
}

let broken = () => doSomethingAsync()

JS output does not compile because function has no async:

function broken(param) {
  return await SomeModule.someExternal();
}

/cc @cristianoc

[cknitt]

External is not needed. Even easier repro:

Broken.resi:

let broken: (unit => promise<'a>) => promise<'a>

Broken.resi:

let doSomethingAsync = async someAsyncFunction => {
  await someAsyncFunction()
}

let broken = someAsyncFunction => doSomethingAsync(someAsyncFunction)

[cristianoc]

Not sure I understand either of the two examples. Why are there interface files. And if there are how many files are needed to repro.

[cknitt]

There is an interface file because otherwise both functions will be exported and the inlining does not happen.
The whole thing is extracted from real-world code and very very much simplified.

Actually a single file is enough to reproduce if we use %%private:

%%private(
  let doSomethingAsync = async someAsyncFunction => {
    await someAsyncFunction()
  }
)

let broken = someAsyncFunction => doSomethingAsync(someAsyncFunction)

results in

function broken(someAsyncFunction) {
  return await Curry._1(someAsyncFunction, undefined);
}

[cristianoc]

OK without using private, one can just do the same with a module, or shadowing:

module M: {
  let broken: (unit => promise<'a>) => promise<'a>
} = {
  let doSomethingAsync = async (someAsyncFunction) => {
    await someAsyncFunction()
  }

  let broken = someAsyncFunction => doSomethingAsync(someAsyncFunction)
}

let broken = async (someAsyncFunction) => {
  await someAsyncFunction()
}

let broken = someAsyncFunction => broken(someAsyncFunction)

[cristianoc]

I'll go with the latter, and notice that this prevents inlining:

let broken = async (someAsyncFunction) => {
  await someAsyncFunction()
}

let _ = Js.log(broken)

let broken = someAsyncFunction => broken(someAsyncFunction)

[cristianoc]

@cknitt can you try if this #5790 resolved the issue?

[cknitt]

@cristianoc Yes! It works! 🎉

Let's merge and do an rc.5.

[cristianoc]

I'll merge and apply to master too.