I have to disagree here a little bit. Calling C functions from Rust is a very pleasant experience, but the other way around is not so nice. You usually have to manually create types that will unpack rust collections into C compatible structures (think decomposing `Vec` into ptr, len, capacity) & then ensure that memory passed between the two sides is free'd with the appropriate allocator. Even with `cbindgen` taking care of the mindless conversions for you, you still have to put a lot of thought into the API between the two languages.
I am currently working on a fairly involved C & Rust embedded systems project and getting the inter-language interface stable and memory-leak free took a good amount of effort. It probably didn't help that I don't have access to valgrind or gdb on this platform.
I feel this might come down to the scope one has in mind when thinking of the word "interop". I think one can reasonably simultaneously claim that the interop "mechanics" are excellent in that it's generally possible to create a Rust library that quacks like a C library and that basically any C library is usable by Rust code, but the interop "ergonomics" are suboptimal in that (as you say) actually writing the glue code can be a bit of an adventure.
I think that's a fair assessment. To your point `cbindgen` makes the mechanics of the whole thing painless & linking was trivial. That's worth a lot especially when compared to other languages.
I am currently working on a fairly involved C & Rust embedded systems project and getting the inter-language interface stable and memory-leak free took a good amount of effort. It probably didn't help that I don't have access to valgrind or gdb on this platform.