Some code in this crate causes UB by "Producing an invalid value". In the near future the call to mem::uninitialized() will panic to avoid UB, and our crater run determined that this crate will be affected.

There are macros involved, so I could not entirely determined where the bad call is happening, but uninitialized is called by code generated in this crate so I suppose this repo maks most sense. You can check the crater log for a backtrace.

mem::uninitialized() is deprecated since Rust 1.39. The intended replacement is MaybeUninit, which tracks the possibility of uninitialized values at the type level to make sure the compiler does not make any false assumptions.