C libraries often provide excellent ABI compatibility, and some C++ libraries do as well. However, many newer languages have no ABI compatibility at all.

Specifically, Haskell, OCaml, Rust, and (I believe) Go all require that if a module is recompiled, all of its transitive reverse dependencies must also be recompiled. In the case of Rust, there are at least two reasons for this:

1. Rust requires cross-crate inlining to get good performance. For example, slice indexing in Rust is implemented as a library call! If it cannot be inlined, performance will be terrible.
2. Rust uses monomorphization for generics. This allows for zero-cost abstractions, but means that generic code is compiled as part of the library user’s code, not as part of the library.

However, this leads to a problem. If a critical security fix needs to be made in a Rust library, all packages that depend on it must be recompiled. Koji should do this automatically.