Overloaded call notation doesn't work with trait bounds

[nikomatsakis]

I expect this example to compile:

lunch-box. emacs -nw
#![feature(overloaded_calls)]

use std::ops::FnMut;

fn call_it_mut<F:FnMut(int)->int>(f: &mut F, x: int) -> int {
    f(x)
}

fn main() { }

but in fact it yields:

/home/nmatsakis/tmp/foo.rs:6:5: 6:17 error: the trait `core::ops::Fn<<generic #9>,<generic #10>>` is
 not implemented for the type `&&mut F`
/home/nmatsakis/tmp/foo.rs:6     (&mut *f)(x)
                                 ^~~~~~~~~~~~
/home/nmatsakis/tmp/foo.rs:6:5: 6:17 error: the type of this value must be known in this context
/home/nmatsakis/tmp/foo.rs:6     (&mut *f)(x)
                                 ^~~~~~~~~~~~
/home/nmatsakis/tmp/foo.rs:6:5: 6:17 error: cannot use call notation; the first type parameter for t
he function trait is neither a tuple nor unit [E0059]
/home/nmatsakis/tmp/foo.rs:6     (&mut *f)(x)
                                 ^~~~~~~~~~~~
error: aborting due to 3 previous errors

I was not able to get it to compile without resorting to f.call_mut((x,))

[japaric]

This is compiling now, but f(x) must be changed to (*f)(x). But that's #18742 I think.

[alexcrichton]

Closing in favor of #18742