As discovered in #1506, it is relatively easy to have a version mismatch between the cxx-bridge and the cxx crate in a complex project - i.e. cxx-bridge of one version generates the C++ code, and cxx crate of another version is built as part of Rust code. As anything else with Rust, I think this undefined behavior should be caught by the compiler if possible. FFI tends to be super error-prone, so reducing error surface would help.