Issues with outcome printer and arity0

[cristianoc]

See

• Issues with outcome printer and arity0 #512
• arity0 hovering issues rescript-vscode#440

One case resolved, this case still outstanding:

// hovering on inferred type: (. unit, unit) => int
let arity0c = (. (), ()) => 3

// hovering on inferred type: (. unit) => int
let arity0d = (. ()) => {
  let f = () => 3
  f
}

[cristianoc]

The desired type for arity0d is (. unit) => (unit) => int, except this type is currently equivalent to (. unit, unit) => int.
So the type with the intended semantics is currently not expressible.

[stale]

The rescript-lang/syntax repo is obsolete and will be archived soon. If this issue is still relevant, please reopen in the compiler repo (https://github.com/rescript-lang/rescript-compiler) or comment here to ask for it to be moved. Thank you for your contributions.