error[E0405]: cannot find trait `T` in this scope
  --> $DIR/issue-21221-4.rs:20:6
   |
LL | impl T for Foo {}
   |      ^ not found in this scope
help: possible candidate is found in another module, you can import it into scope
   |
18 | use issue_21221_4::T;
   |

error: cannot continue compilation due to previous error

If you want more information on this error, try using "rustc --explain E0405"