This bug has nothing to do with memory safety or borrowing. It's just an old fashion logic bug, and the panic prevents any memory unsafety from happening. This

This bug has nothing to do with memory safety or borrowing. It's just an old fashion logic bug, and the panic prevents any memory unsafety from happening. This bug was in the regex-syntax crate, which doesn't use any unsafe. The regex crate itself does have two uses of unsafe however (one for eliding bounds checks in the inner DFA loop and another for eliding bounds checks in Teddy).