error[E0106]: missing lifetime specifier
  --> $DIR/issue-63388-2.rs:12:10
   |
LL |         foo: &dyn Foo, bar: &'a dyn Foo
   |              --------       -----------
LL |     ) -> &dyn Foo
   |          ^ expected named lifetime parameter
   |
   = help: this function's return type contains a borrowed value, but the signature does not say whether it is borrowed from `foo` or `bar`
help: consider using the `'a` lifetime
   |
LL |     ) -> &'a dyn Foo
   |           ++

error[E0621]: explicit lifetime required in the type of `foo`
  --> $DIR/issue-63388-2.rs:13:5
   |
LL |           foo: &dyn Foo, bar: &'a dyn Foo
   |                -------- help: add explicit lifetime `'a` to the type of `foo`: `&'a (dyn Foo + 'a)`
LL |       ) -> &dyn Foo
LL | /     {
LL | |
LL | |         foo
LL | |     }
   | |_____^ lifetime `'a` required

error: aborting due to 2 previous errors

Some errors have detailed explanations: E0106, E0621.
For more information about an error, try `rustc --explain E0106`.