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: lifetime may not live long enough --> $DIR/regions-free-region-ordering-callee-4.rs:8:12 | LL | fn ordering4<'a, 'b, F>(a: &'a usize, b: &'b usize, x: F) where F: FnOnce(&'a &'b usize) { | -- -- lifetime `'b` defined here | | | lifetime `'a` defined here ... LL | let z: Option<&'a &'b usize> = None; | ^^^^^^^^^^^^^^^^^^^^^ requires that `'b` must outlive `'a` | = help: consider adding the following bound: `'b: 'a` error: aborting due to 2 previous errors For more information about this error, try `rustc --explain E0491`.