Declaring extern "C" functions to be called from Rust

[DrTobe]

In chapter 9.1 "A little C with your Rust", the extern "C" function is declared with

pub extern "C" fn cool_function(
    i: cty::c_int,
    c: cty::c_char,
    cs: *mut CoolStruct
);

I was not able to successfully build my project with such a declaration, I always ended up having "free function without a body" errors. After having compared this approach with several other sources, it seems to me that the only correct way to declare this function would be

extern "C" {
    fn cool_function(
        i: cty::c_int,
        c: cty::c_char,
        cs: *mut CoolStruct
    );
}

The pub extern "C" fn ... syntax only seems to be valid to expose Rust's functions.

Please correct me if I'm wrong.

Furthermore, the #[link(name = "<library-name>")] could be prepended, possibly with a reference to further documentation.