error[E0277]: the trait bound `(): Bar` is not satisfied
  --> $DIR/impl-trait-return-trailing-semicolon.rs:3:13
   |
LL | fn foo() -> impl Bar {
   |             ^^^^^^^^ the trait `Bar` is not implemented for `()`
LL |     5;
   |      - consider removing this semicolon

error: aborting due to previous error

For more information about this error, try `rustc --explain E0277`.