Do you mean Rust code compiled to a shared library and imported into RustPython at runtime, or Rust code added into the binary at compile-time? The latter we have, and it's how much of our standard library is implemented. The former is a WIP, as it requires a stable Rust ABI for Rust->Rust FFI, which is not currently one of the Rust project's goals, and the current solutions are fairly verbose and clunky to work with.

Is there documentation to assist with pursuing the latter in Rust projects?
Can you instantiate, pass around, and manipulate Rust structs/types from Python?

I think what he’s asking is whether it is possible to use regular rust crates from RustPython. If I got it wrong please correct me. Also, I have the same doubt.

Sorry for not responding earlier, it is certainly possible to store Rust structs in PyObjects and we do that quite a bit in the codebase; you can look in the vm/src/stdlib subdirectory for some examples, specifically socket for a module that's centered almost completely around a built-in class.