Discussion in the UCG raised an interesting unwind-related concern: right now, it is legitimate (or at least, not unreasonable) for code to assume that every (Rust) function either returns or panics. Which means with
catch_unwind, it'll definitely panic.
take_mut crucially rely on this and become unsound once there is a way for Rust code to unwind that is not caught by
catch_unwind. I believe even
rayon scoped threads would become unsound.
oh nvm I see @Amanieu already raised that here oops