Integrate better with bindgen

[eqrion]

Currently if you need to define an item in C/C++ and use it from Rust, you can use rust-bindgen and it will output the Rust definition for you.

This is problematic if that type needs to be used in a Rust FFI boundary, as cbindgen will try to output a second C/C++ definition for that type, which will cause errors.

I believe that if cbindgen is run before bindgen, we'll do the right thing and not output a definition for those items, but you will need to ensure you include the proper C/C++ files before the generated header.

I just added an annotation no-export which will prevent a type from being given a definition in the output header, which can help with this, but isn't optimal.

[eqrion]

I think an optimal solution could be:

# config.rs
[rust-bindgen]
mod = "generated"
header = "source.h"

We would then flag every item in mod generated as being from rust-bindgen and not give them definitions. We could then add an include to the output header for the header rust-bindgen generated from.

This depends on refactoring rustlib.rs to expose what mod items are from, which I've been meaning to do for a while.

[Gankra]

If cbindgen finds an undefined type, it will just ignore it, instead of failing?

[eqrion]

It will generate a warning in the console, but it won't fail to generate a header. In the future it might.

If you want to use this to not generate a definition for a type, you'll need some way of hiding it from cbindgen but not from rustc. Or maybe generating the definitition after cbindgen runs.

[eqrion]

I'm going to close this now as it's not clear what action is required here.