trait Closure<'t> {}
impl<'t, F: Fn(&'t ())> Closure<'t> for F {}

fn restrict_fn(_: impl Fn(&'static ())) {}
fn restrict_trait(_: impl Closure<'static>) {}

fn check(_: &'static ()) {}

fn main() {
    // OK 4/4
    restrict_fn(|r| check(r));
    restrict_fn(|r: &_| check(r));
    restrict_fn(|r: &()| check(r));
    restrict_fn(|r: &'static ()| check(r));

    // OK 2/4
    restrict_trait(|r| check(r));
    restrict_trait(|r: &_| check(r)); // FAIL: lifetime of reference outlives lifetime of borrowed content
    // restrict_trait(|r: &()| check(r)); // also FAIL
    restrict_trait(|r: &'static ()| check(r));
}