error[E0107]: trait takes 1 generic argument but 0 generic arguments were supplied
  --> $DIR/unable-fulfill-trait.rs:4:17
   |
LL |     field1: dyn Bar<'a, 'b,>,
   |                 ^^^ expected 1 generic argument
   |
note: trait defined here, with 1 generic parameter: `U`
  --> $DIR/unable-fulfill-trait.rs:9:11
   |
LL | pub trait Bar<'x, 's, U>
   |           ^^^         -
help: add missing generic argument
   |
LL |     field1: dyn Bar<'a, 'b, U,>,
   |                           +++

error[E0227]: ambiguous lifetime bound, explicit lifetime bound required
  --> $DIR/unable-fulfill-trait.rs:4:13
   |
LL |     field1: dyn Bar<'a, 'b,>,
   |             ^^^^^^^^^^^^^^^^

error: aborting due to 2 previous errors

Some errors have detailed explanations: E0107, E0227.
For more information about an error, try `rustc --explain E0107`.