[easy] make VerboseCLIOutput forward compatible with future HSL IO ch…

[fredemmott]

…ange

HSL IO is changing writeAsync() to return Awaitable<int>, but the function here is Awaitable<void> - return await is no longer compatible.

Tangentially, I'm a little surprised that explicit return values are OK in Awaitable functions :/

[Wilfred]

@fredemmott what were you expecting? The following works:

async function foo(): Awaitable<int> {
  return 1;
}

This code seems equivalent AFAICS.

[fredemmott]

https://travis-ci.org/github/hhvm/hsl-experimental/jobs/680389022

The function here returns Awaitable<void>, not int. Posted in feedback group about explicit returns being OK for Awaitable<void> which feels like a bug

[fredemmott]

This is closer to:

async function foo(): Awaitable<void> {
  return 1; // int, not void
}

[Wilfred]

but return; is appropriate in an Awaitable<void>, and writeFailureDetailsAsync is awaitable void. Your foo is rejected by the type checker, as I'd expect. I think I've misunderstood something.

[jjergus]

@Wilfred This is an example that passes typechecker but perhaps shouldn't:

async function void1(): Awaitable<void> {
}

async function void2(): Awaitable<void> {
  return await void1();
}

[Wilfred]

Oh, I was being dumb! I was looking at the new version of the code, and totally missed the old version.

Yeah, that's fine as far as inference is concerned. We have some additional typechecker checks to make sure that you don't write return; in a non-void function or return ...; in a void function, but looks like it misses Awaitable<void>.

void handling could use some refactoring to better handle cases like this.