What does HackerNews think of uniffi-rs?
a multi-language bindings generator for rust
https://github.com/mozilla/uniffi-rs
While this works, the bigger pain (at least on iOS) is that the Rust-Compiler LLVM and Xcode LLVM are not always in sync leading to strange bugs. Also, packaging Rust libraries into a nice XCFramework (or even SPM Module) works, but usually involves hacky shell scripts.
The reason why you'd still want to do this is if there's a Rust library that has no equivalent on the Kotlin or Swift side. There're a lot of good crates / libraries for Rust would require an expensive re-implementation in Swift or Kotlin. Also, because Rust doesn't have a garbage collector, it is easier to embed in garbage collected languages like Kotlin without running into situations where the two garbage collectors don't agree.