struct Foo;

fn test<'a>(a: &'a mut Foo) -> &'a mut Foo {
    loop {
        if foo(a).is_some() {
            return a;
        }
    }
}



fn foo<'a>(a: &'a mut Foo) -> Option<&'a mut Foo> {
    if rand::random::<bool>() { Some(a) } else { None }
}