See rust-lang/rust-bindgen#109.

I would like to create a (temporary?) fork of bindgen that generates bindings targetting objc2. In particular, Encode and RefEncode impls, but the Message/MessageReceiver stuff has also changed.

In the end, what I really want is the ability to generate safe apis, but that's probably not gonna happen, it would at least require us to enrich every method with mutability information (NSData -length is immutable, while NSMutableData -setLength: is not), and we're never going to be able to generate a safe API for e.g. NSData -initWithBytesNoCopy:length:deallocator:.