Given a value of a Drop type that is conditionally moved on one branch, how does rustc ensure the destructor runs exactly once across both paths at the end of the function?

struct Res(String); impl Drop for Res { fn drop(&mut self) { println!("drop"); } } fn consume(r: Res) {} fn maybe(flag: bool) { let r = Res(String::from("x")); if flag { consume(r); } }