There's nothing that guarantees that's constant-time. It's just written in a way that's likely to be constant-time, and observed to be constant-time with curren

There's nothing that guarantees that's constant-time. It's just written in a way that's likely to be constant-time, and observed to be constant-time with current compilers, but there's no reason why a specification-compliant compiler couldn't make it variable-time tomorrow. You can do exactly the same in Rust. Rust isn't any help there, but it doesn't obstruct you either.