I noted that #548 and have a similar issue.

Create a library crate firstly:

cargo new --lib example

Then, add them in lib.rs:

#[repr(C)]
pub struct Example {
    pub f: extern "C" fn(usize, usize) -> !,
}

#[no_mangle]
pub extern "C" fn add_itr(f: *const Example, a: usize, b: usize) -> ! {
    unsafe {
        ((*f).f)(a, b)
    }
}

#[no_mangle]
pub extern "C" fn add() -> ! {
    loop{}
}

And run this command in your terminal:

cbindgen --crate example --output example.h

Now, please see example.h, the output is that:

#include  ...

// notes here!!
struct Example;

extern "C" {

void add_itr(const Example *f, uintptr_t a, uintptr_t b);

void add();

} // extern "C"

The function which has ! return type was be ignored, but the other one add was emited successfully.

I think that we can add similar behavior to the structure, like emitting to void(*f)(size_t, size_t). And for the Nerver type, may be believe that C functions void(*)( ... some params ...) will never return is a good idea.

For more cases, about a C function pointer with Never return type, I noted that the following code can not be emited to C header:

// lib.rs
#[no_mangle]
pub extern "C" fn add(f: extern "C" fn() -> !) -> ! {
    f()
}

I think it's the key of this issue.

Could we possibly solve it?