What were you expecting to find? A function which returns an empty type will always diverge - ie there is no return of control, because that return would have a value that we've said never exists. In a systems language like Rust there are functions like this for example std::process::exit is a function which... well, hopefully it's obvious why that doesn't return. You could imagine that likewise if one day the Linux kernel's reboot routine was Rust, that too would never return.