error[E0726]: implicit elided lifetime not allowed here
  --> $DIR/return-not-existing-pair.rs:9:20
   |
LL | impl<'a, 'b, T, U> MyTrait<T> for U {
   |                    ^^^^^^^^^^ expected lifetime parameters
   |
help: indicate the anonymous lifetimes
   |
LL | impl<'a, 'b, T, U> MyTrait<'_, '_, T> for U {
   |                            +++++++

error[E0412]: cannot find type `ConnImpl` in this scope
  --> $DIR/return-not-existing-pair.rs:5:48
   |
LL |     async fn foo(&'a self, key: &'b T) -> (&'a ConnImpl, &'b T);
   |                                                ^^^^^^^^ not found in this scope

error[E0308]: mismatched types
  --> $DIR/return-not-existing-pair.rs:11:42
   |
LL |     async fn foo(_: T) -> (&'a U, &'b T) {}
   |                                          ^^ expected `(&U, &T)`, found `()`
   |
   = note:  expected tuple `(&'a U, &'b T)`
           found unit type `()`

error: aborting due to 3 previous errors

Some errors have detailed explanations: E0308, E0412, E0726.
For more information about an error, try `rustc --explain E0308`.