Async functions define unused parameter

[CarlOlson]

Given:

let x = async () => ()

Actual:

async function x(param) {}

Expected:

async function x() {}

I'd consider this a bug. While it shouldn't matter, some libraries try to be too clever and cause issues. Jest is one example I found:

  ● Simple_Test › async props

    thrown: "Exceeded timeout of 5000 ms for a test while waiting for `done()` to be called.
    Add a timeout value to this test to increase the timeout, if this is a long-running test. See https://jestjs.io/docs/api#testname-fn-timeout."

    > 11 |         test("async props", (async function (param) {

I don't use it, but I think Angular would be another example. They check function parameters for dependency injection.

---

Found the source:

https://github.com/rescript-lang/rescript-compiler/blob/654fa489f9b02c922cc4393ae076cda6dcdc49f0/jscomp/ml/typecore.ml#L2932-L2938

Changing param will change the output parameter name.

[fhammerschmidt]

This is fixed in ReScript 11 with uncurried mode.

I don't think it will ever be "fixed" in curried mode. But you can always uncurry explicitly:

let x = async (. ()) => ()

gives you the expected result.

[CarlOlson]

The explicit uncurried version does work on master, but doesn't work on 10.1.4.

I don't think it will ever be "fixed" in curried mode.

Can you elaborate why?

[fhammerschmidt]

Oh, I did not realize that I tested it with 10.1.2 which is the latest stable version on the playground. Sorry!

Yes, apparently 10.1.3 has introduced this regression.

I cannot recall exactly what it was, maybe I am mistaken. But it seemed to be not trivial to remove the "param" in curried mode. I don't know the intricacies. Maybe @cristianoc does.

In V11 this was fixed here: #6131