error[E0491]: in type `&'a &'b usize`, reference has a longer lifetime than the data it references
  --> $DIR/regions-free-region-ordering-callee-4.rs:5:1
   |
LL | / fn ordering4<'a, 'b, F>(a: &'a usize, b: &'b usize, x: F) where F: FnOnce(&'a &'b usize) {
LL | |
LL | |     // Do not infer ordering from closure argument types.
LL | |     let z: Option<&'a &'b usize> = None;
LL | | }
   | |_^
   |
note: the pointer is valid for the lifetime 'a as defined on the function body at 5:14
  --> $DIR/regions-free-region-ordering-callee-4.rs:5:14
   |
LL | fn ordering4<'a, 'b, F>(a: &'a usize, b: &'b usize, x: F) where F: FnOnce(&'a &'b usize) {
   |              ^^
note: but the referenced data is only valid for the lifetime 'b as defined on the function body at 5:18
  --> $DIR/regions-free-region-ordering-callee-4.rs:5:18
   |
LL | fn ordering4<'a, 'b, F>(a: &'a usize, b: &'b usize, x: F) where F: FnOnce(&'a &'b usize) {
   |                  ^^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0491`.