rust/tests/ui/layout/null-pointer-optimization.rs

//! null pointer optimization with iota-reduction for enums.
//!
//! Iota-reduction is a rule from the Calculus of (Co-)Inductive Constructions:
//! "a destructor applied to an object built from a constructor behaves as expected".
//! See <https://coq.inria.fr/doc/language/core/conversion.html#iota-reduction>.
//!
//! This test verifies that null pointer optimization works correctly for both
//! Option<T> and custom enums, accounting for pointers and regions.

//@ run-pass

#![allow(unpredictable_function_pointer_comparisons)]

enum E<T> {
    Thing(isize, T),
    #[allow(dead_code)]
    Nothing((), ((), ()), [i8; 0]),
}

impl<T> E<T> {
    fn is_none(&self) -> bool {
        match *self {
            E::Thing(..) => false,
            E::Nothing(..) => true,
        }
    }

    fn get_ref(&self) -> (isize, &T) {
        match *self {
            E::Nothing(..) => panic!("E::get_ref(Nothing::<{}>)", stringify!(T)),
            E::Thing(x, ref y) => (x, y),
        }
    }
}

macro_rules! check_option {
    ($e:expr, $T:ty) => {{
        check_option!($e, $T, |ptr| assert_eq!(*ptr, $e));
    }};
    ($e:expr, $T:ty, |$v:ident| $chk:expr) => {{
        assert!(None::<$T>.is_none());
        let e = $e;
        let s_ = Some::<$T>(e);
        let $v = s_.as_ref().unwrap();
        $chk
    }};
}

macro_rules! check_fancy {
    ($e:expr, $T:ty) => {{
        check_fancy!($e, $T, |ptr| assert_eq!(*ptr, $e));
    }};
    ($e:expr, $T:ty, |$v:ident| $chk:expr) => {{
        assert!(E::Nothing::<$T>((), ((), ()), [23; 0]).is_none());
        let e = $e;
        let t_ = E::Thing::<$T>(23, e);
        match t_.get_ref() {
            (23, $v) => $chk,
            _ => panic!("Thing::<{}>(23, {}).get_ref() != (23, _)", stringify!($T), stringify!($e)),
        }
    }};
}

macro_rules! check_type {
    ($($a:tt)*) => {{
        check_option!($($a)*);
        check_fancy!($($a)*);
    }}
}

pub fn main() {
    check_type!(&17, &isize);
    check_type!(Box::new(18), Box<isize>);
    check_type!("foo".to_string(), String);
    check_type!(vec![20, 22], Vec<isize>);
    check_type!(main, fn(), |pthing| assert_eq!(main as fn(), *pthing as fn()));
}