error[E0391]: cycle detected when computing the supertraits of `T`
  --> $DIR/issue-20772.rs:1:1
   |
LL | / trait T : Iterator<Item=Self::Item>
LL | | //~^ ERROR cycle detected
LL | | //~| ERROR associated type `Item` not found for `Self`
LL | | {}
   | |__^
   |
   = note: ...which again requires computing the supertraits of `T`, completing the cycle

error[E0220]: associated type `Item` not found for `Self`
  --> $DIR/issue-20772.rs:1:25
   |
LL | trait T : Iterator<Item=Self::Item>
   |                         ^^^^^^^^^^ associated type `Item` not found

error: aborting due to 2 previous errors

Some errors occurred: E0220, E0391.
For more information about an error, try `rustc --explain E0220`.