error[E0405]: unresolved trait `T`
  --> $DIR/issue-21221-4.rs:20:6
   |
20 | impl T for Foo {}
   |      ^ no resolution found
   |
   = help: possible candidate is found in another module, you can import it into scope:
   = help:   `use issue_21221_4::T;`

error: cannot continue compilation due to previous error