// tries to narrow `'static` to `'a`
struct Narrowing<'a> {
    covariant: &'a (),
}

impl<'a> Foo<'a> {
    fn smaller(v: &mut &'a i32) {}

    fn bigger(v: &mut &'static i32) {
        Self::smaller(v)
    }
}

// tries to widen `'a` to `'static`
struct Widening<'a> {
    covariant: &'a (),
}

impl<'a> Widening<'a> {
    fn smaller(v: &mut &'a i32) {
        Self::bigger(v)
    }

    fn bigger(v: &mut &'static i32) {}
}