> Only if you primarily work with `cargo` and want to interact with C from Rust.

In what way(s) does Rust's C interop depend on cargo?

> The other way around has far less support and `rustc` does not standardize the object generation.

I believe in this context the understanding is that you're going to be using `extern "C"` and/or `#[repr(C)]` in your Rust code, which gives you a plain C interface. I think attempting to use "raw" Rust code from other languages is a rare phenomenon, if it's even attempted at all.

> This is actively preventing projects like `systemd` to adopt Rust into their project as an example.

Could you point out specific instances from that thread? From a quick glance I didn't see any obvious instances of someone saying that using Rust from C is problematic.

> In what way(s) does Rust's C interop depend on cargo?

Do rust and cargo allow for multiple interpretations of the same C header file across different objects in the same program? That's how C libraries are often implemented in practice due to preprocessor tricks, though I wish it wasn't normal to do this sort of thing.

Rust and Cargo do not build C programs, so, the answer to that is "no", strictly speaking.

However, some people use cargo's build scripts to build c programs, which then you can link into your Rust program. Support would then depend on whatever the person wrote with the script, which in my experience usually delegates to whatever build system that project uses. So it should work fine.

I would expect so. Rust and Cargo don't consume C header files directly at all. They consume bindings generated by bindgen (or hand written if you prefer). So you could probably generate mulitple bindings if you needed multiple interpretations of a C header.

If the header files are consumed by C code that is then consumed by Rust then you'll have full support for what C supports because it will be compiled by a C compiler.

https://github.com/rust-lang/rust/issues/73632 needs to be addressed and then integrated into meson before systemd could consider adopting rust.

Thanks for the example!

I guess looking at that pedantically that's "just" a tooling issue, rather than an issue with the Rust language itself. That's not really a useful distinction from an end user's perspective, though; it's friction either way, and worth addressing.