Propose a FIXIT when the return type is missing from the function definition

[dcci]

fn get_numbers(arr1 : String) {
  let num1 : Vec<i32> =
    arr1.split_whitespace().map(|s| s.parse().unwrap()).collect();
  return num1;
}


fn main() {
    let str = String::from("1 2 3 4");
    let num1 : Vec<i32> = get_numbers(str);
    println!("{}", num1[0]);
}

This obviously fails with:

triplets.rs:4:10: 4:14 error: mismatched types:
 expected `()`,
    found `collections::vec::Vec<i32>`
(expected (),
    found struct `collections::vec::Vec`) [E0308]
triplets.rs:4   return num1;
                       ^~~~
triplets.rs:4:10: 4:14 help: run `rustc --explain E0308` to see a detailed explanation

I think the compiler should try to propose a FIXIT, e.g.
maybe did you mean fn get_numbers(arr1 : String) -> Vec<i32>

Also, rustc --explain E0308 doesn't list the missing -> return_type case as "common mistake". Not sure if it's really worth listing it, but still, worth mentioning.

[Mark-Simulacrum]

Closing in favor of collective issue for this general problem: #41897.