I believe there's a Rust RFC for a way to write mandatory tail calls with the become keyword. So then the code is actually defined to have a tail call, if it can't have a tail call it won't compile, if it can have one then that's what you get.

Some languages I was aware of are defined so that if what you wrote could be a tail call it is. However you might write code you thought was a tail call and you were wrong - in such languages it only blows up when it recurses too deep and runs out of stack. AIUI the Rust feature would reject this code.