libc interop for opaque types

[jedbrown]

I'm using bindgen to process a header for a library that accepts arguments of type FILE*, which I've been handling using Builder::opaque_type. I'd like other parts of the code to be able to use libc::FILE in a way that matches the definition used by bindgen, but I can't find a way to do this. Is it possible (or a feature that makes sense to add) to tell bindgen that a given type is provided by the likes of libc::FILE?

As a concrete example, I'd like to be able to release a libc-memstream crate that provides a safe interface to libc::open_memstream to improve reliability when high-level bindings use it to extract strings from raw FFI interfaces that write information to a FILE* (like fputs and fprintf).

[pvdrz]

There's no feature that does exactly that, but you can do something like it by combining two features:

• First you need to call blocklist_type with FILE so there's no definition for FILE anywhere in your bindings. Given that blocklist methods are not recursive/transitive, all the uses of FILE in your bindings will still be present.

• Then you call raw_line with use libc::FILE;. Given that libc::FILE and FILE are the same type, they should be ABI compatible.

Let me know if this fixes your issue.

[jedbrown]

Thank you! This does what I need:

        .opaque_type("FILE") // don't chase the underlying types
        .blocklist_type("FILE") // and don't write a type in generated bindings
        .raw_line("use libc::FILE;") // write this instead

(If I leave out the first line, I get lots of warnings about the likes of _IO_read_ptr not using snake case.)

[pvdrz]

Oh yeah I didn't include it because you were already marking it as opaque 😅 but yeah, you also need that :)