error: unused implementer of `Iterator` that must be used
  --> $DIR/unused-supertrait.rs:9:5
   |
LL |     it();
   |     ^^^^
   |
   = note: iterators are lazy and do nothing unless consumed
note: the lint level is defined here
  --> $DIR/unused-supertrait.rs:1:9
   |
LL | #![deny(unused_must_use)]
   |         ^^^^^^^^^^^^^^^

error: aborting due to previous error