Confusing error on mismatched argument count of function parameters

[phil-opp]

Example:

fn main() {
    bar(1, foo);
}

fn foo(a: u16) {}

fn bar<F>(a: u16, mut f: F) where F: FnMut(u16, u8) {
    f(a, 0);
}

The problem is the second argument in the bar call (foo) takes only one argument instead of the expected 2 arguments. However, the error looks like there is something wrong with the argument count of the bar call:

Error on nightly & beta:

error[E0593]: function takes 1 argument but 2 arguments are required
 --> <anon>:2:5
  |
2 |     bar(1, foo);
  |     ^^^ expected function that takes 2 arguments
  |
  = note: required by `bar`

Error on stable:

error[E0281]: type mismatch: the type `fn(u16) {foo}` implements the trait `std::ops::FnMut<(u16,)>`, but the trait `std::ops::FnMut<(u16, u8)>` is required (expected a tuple with 2 elements, found one with 1 elements)
 --> <anon>:2:5
  |
2 |     bar(1, foo);
  |     ^^^
  |
  = note: required by `bar`

Instead, the ^^^ should point to the faulty argument:

error[E0593]: function takes 1 argument but 2 arguments are required
 --> <anon>:2:5
  |
2 |     bar(1, foo);
  |            ^^^ expected function that takes 2 arguments
  |
  = note: required by `bar`

cc @oli-obk

[estebank]

Current output:

error[E0593]: function is expected to take 2 arguments, but it takes 1 argument
 --> src/main.rs:2:5
  |
2 |     bar(1, foo);
  |     ^^^ expected function that takes 2 arguments
...
5 | fn foo(a: u16) {}
  | -------------- takes 1 argument
  |
note: required by `bar`
 --> src/main.rs:7:1
  |
7 | fn bar<F>(a: u16, mut f: F) where F: FnMut(u16, u8) {
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Ideally it should also point at the foo being passed as an argument and at the F: FnMut(u16, u8) restriction.