Unit type compiles to undeclare variable

[lukethenuke]

Description

Noticed a lot of runtime errors when upgrading fable from 3.2.6 to 4.4.1.
We do code splitting using FunctionComponent.Lazy and when using an empty prop type in the component it crashes on an undeclared variable, I have extracted and reproduced a minimal sample of the bug below.

Repro code

REPL

let inline Repro(f: 'T -> string): 'T -> string =
        let unused = f
        fun a -> $"{a}"

let bad = Repro (fun (props: unit) -> "s")
let ok = Repro (fun (props: string) -> "s")

export const bad = (() => {
    const unused = () => "s";
    return () => (`${a}`);
})();

export const ok = (() => {
    const unused = (props) => "s";
    return (a) => (`${a}`);
})();

notice in bad the string interpolation contains a reference to the undeclared variable a.

Expected and actual results

I'm unsure what to expect here, but the current results looks wrong.

Related information

I have tested different versions and this seems to be the behavior in version 3.7.10 and later.
Related issue? #1832