error[E0700]: hidden type for `impl Swap + 'a` captures lifetime that does not appear in bounds
  --> $DIR/hidden-lifetimes.rs:29:5
   |
LL | fn hide_ref<'a, 'b, T: 'static>(x: &'a mut &'b T) -> impl Swap + 'a {
   |                 --                                   -------------- opaque type defined here
   |                 |
   |                 hidden type `&'a mut &'b T` captures the lifetime `'b` as defined here
LL |     x
   |     ^
   |
help: add a `use<...>` bound to explicitly capture `'b`
   |
LL | fn hide_ref<'a, 'b, T: 'static>(x: &'a mut &'b T) -> impl Swap + 'a + use<'a, 'b, T> {
   |                                                                     ++++++++++++++++

error[E0700]: hidden type for `impl Swap + 'a` captures lifetime that does not appear in bounds
  --> $DIR/hidden-lifetimes.rs:46:5
   |
LL | fn hide_rc_refcell<'a, 'b: 'a, T: 'static>(x: Rc<RefCell<&'b T>>) -> impl Swap + 'a {
   |                        --                                            -------------- opaque type defined here
   |                        |
   |                        hidden type `Rc<RefCell<&'b T>>` captures the lifetime `'b` as defined here
LL |     x
   |     ^
   |
help: add a `use<...>` bound to explicitly capture `'b`
   |
LL | fn hide_rc_refcell<'a, 'b: 'a, T: 'static>(x: Rc<RefCell<&'b T>>) -> impl Swap + 'a + use<'a, 'b, T> {
   |                                                                                     ++++++++++++++++

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0700`.