error[E0271]: type mismatch resolving `<impl Bar as Foo>::Item == i32`
  --> $DIR/impl-trait-return-missing-constraint.rs:25:13
   |
LL | fn bar() -> impl Bar {
   |             -------- the found opaque type
...
LL | fn baz() -> impl Bar<Item = i32> {
   |             ^^^^^^^^^^^^^^^^^^^^ expected `i32`, found associated type
   |
   = note:         expected type `i32`
           found associated type `<impl Bar as Foo>::Item`
help: consider constraining the associated type `<impl Bar as Foo>::Item` to `i32`
   |
LL | fn bar() -> impl Bar<Item = i32> {
   |                     ^^^^^^^^^^^^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0271`.