python: passing function reference introduces unnecessary closure

[joprice]

Description

When using the python backend and passing a function reference, it gets wrapped in an extra closure, with the outer function environment's arguments appended. This prevents passing a function to constructors like multiprocessing.Process, which require the function to be pickleable, failing with AttributeError: Can't pickle local object.

Repro code

[Please provide the F# code to reproduce the problem or a link to the REPL.
Ideally, it should be possible to easily turn this code into a unit test.](https://fable.io/repl/#?code=DYUwLgBA5hAUCUEC8d4Cg2kgJwK4DsIAzZYhDLCXABwBMBDMECAfXuxmTQh70KiA&html=Q&css=Q)

Expected and actual results

When passing a function as an argument

let g () = ()

let run f = f()

let update _arg  =
   run g

the function should be called directly as in the JS output:

export function g() {
}

export function run(f) {
    return f();
}

export function update(_arg) {
    run(() => {
        g();
    });
}

Instead, a local function _arrow1 is introduced with an extra _arg: Any=_arg param:

from collections.abc import Callable
from typing import (Any, TypeVar)

__A = TypeVar("__A")

def g(__unit: None=None) -> None:
    pass


def run(f: Callable[[], __A]) -> __A:
    return f(None)


def update(_arg: Any | None=None) -> None:
    def _arrow1(__unit: None=None, _arg: Any=_arg) -> None:
        g()

    run(_arrow1)

Related information

• Fable version: 4.19.3
• Operating system: OSX