error[E0276]: impl has stricter requirements than trait
  --> $DIR/issue-18937.rs:19:5
   |
LL | /     fn foo<F>(&mut self, f: F)
LL | |         where F: fmt::Debug + 'a,
LL | |               Self: Sized;
   | |__________________________- definition of `foo` from trait
...
LL | /     fn foo<F>(&mut self, f: F)
LL | |         where F: fmt::Debug + 'static,
LL | |     {
LL | |         self.list.push(Box::new(f));
LL | |     }
   | |_____^ impl has extra requirement `F: 'static`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0276`.