Add `Box<T>` to the supported types, where `T: Sized`

[eliaslevy]

As of Rust 1.41.0:

Box<T>, where T: Sized is now ABI compatible with the C language's pointer (T*)
types. So if you have an extern "C" Rust function, called from C, your Rust function can
now use Box<T>, for some specific T, while using T* in C for the corresponding function.

(from Announcing Rust 1.41.0)

So that

#[no_mangle]
pub extern fn test() -> Box<i32> { Box::new(1i32) }

should generate

int32_t * test();

[emilio]

This makes sense. To be clear, you can already do this in C++ if you do:

template <typename T> using Box = T*;

For C, and maybe for function arguments, we probably want to do this automagically.

The reason why I think we shouldn't do it automatically for C++ members and such is that in C++ having Box<T> is actually useful (if you don't care about Box parameter-passing).

See also the discussion in #451

[mgeier]

For C, and maybe for function arguments, we probably want to do this automagically.

Are there any news on this?

It would be great to have this!

[emilio]

4ce324c fixed this.

[mgeier]

Thanks @emilio, this works great!