error[E0371]: the object type `(dyn Foo + 'a)` automatically implements the trait `Foo`
  --> $DIR/issue-20939.rs:13:1
   |
LL | impl<'a> Foo for Foo+'a {}
   | ^^^^^^^^^^^^^^^^^^^^^^^ `(dyn Foo + 'a)` automatically implements trait `Foo`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0371`.