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:5:68
   |
LL | fn ordering4<'a, 'b, F>(a: &'a usize, b: &'b usize, x: F) where F: FnOnce(&'a &'b usize) {
   |                                                                    ^^^^^^^^^^^^^^^^^^^^^
   |
note: the pointer is valid for the lifetime `'a` as defined here
  --> $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 here
  --> $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`.