Heads-up: UB due to misuse of mem::uninitialized will soon lead to panic

Here, this crate causes UB by "Producing an invalid value". Concretely, it produces a value of type Arc with mem::uninitialized(), which is not allowed because Arc must always guaranteed to be non-null. 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.

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.