Immediately invoked async functions lead to non-working code

[fhammerschmidt]

Consider this example:

let wrapSomethingAsync: unit => unit = () => {
  let asyncFn = async () => {
    let test = await Js.Promise.resolve("Test")
    Js.log(test)
  }

  let _ = asyncFn()
}

this works and creates the following JS

function wrapSomethingAsync(param) {
  var asyncFn = async function (param) {
    var test = await Promise.resolve("Test");
    console.log(test);
  };
  asyncFn(undefined);
}

but when I immediately invoke the async function and make it anonymous

let wrapSomethingAsync: unit => unit = () => {
  let _ = (
    async () => {
      let test = await Js.Promise.resolve("Test")
      Js.log(test)
    }
  )()
}

it compiles to

function wrapSomethingAsync(param) {
  var test = await Promise.resolve("Test");
  console.log(test);
}

which misses the async keyword somewhere.

[cristianoc]

@fhammerschmidt here's a simpler instance:

let willBeInlined = async () => 3

let q = willBeInlined ()

gives

async function willBeInlined(param) {
  return 3;
}

var q = 3;

Would you say this should be avoided?

[fhammerschmidt]

I think your example is fine, as it still executes. But mine yields:

Uncaught SyntaxError: await is only valid in async functions and the top level bodies of modules

[cristianoc]

Both are actually problematic, as async behaviour is removed from what could be long-running computations.

#5755

[cristianoc]

Will be fixed in the next 10.1 release.