> Rust's signed arithmetic is fully specified to wrap around.

Well, kind of. It's currently documented to wrap in release mode by default, but it's just that - a default. You're free to enable overflow checks in release mode (or disable them in debug if you really like oddball configurations), and either way overflow is considered a logic error that devs shouldn't rely on (and basically can't rely on when not in control of the end binary since it's the end user who controls overflow checks).

The Rust devs are theoretically open to making signed overflow panic by default, but consider such a change unlikely unless "something materially changes" [0].

[0]: https://github.com/rust-lang/rust/issues/47739#issuecomment-...

No. If you want wrapping, ask for it with Wrapping<T> or the specific Wrapping types, or the wrapping arithmetic APIs

It's true that since it's safe and faster, release builds default to wrapping rather than panic, but it's still wrong if you overflow any of Rust's default integer types, it's just that in a safe language it won't be Undefined Behaviour.

"I can't be bothered to do it correctly" speaks to the quality of the rest of the product, it's a Brown M&M [read about the Van Halen test if you don't know what a Brown M&M means]