error[E0308]: mismatched types
  --> $DIR/type-parameter-names.rs:5:5
   |
LL | fn foo<Foo, Bar>(x: Foo) -> Bar {
   |                             --- expected `Bar` because of return type
LL |     x
   |     ^ expected type parameter, found a different type parameter
   |
   = note: expected type `Bar`
              found type `Foo`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0308`.