error: missing `fn`, `type`, `const`, or `static` for item declaration
  --> $DIR/issue-21153.rs:1:29
   |
LL |   trait MyTrait<T>: Iterator {
   |  _____________________________^
LL | |
LL | |     Item = T;
   | |____^ missing `fn`, `type`, `const`, or `static`

error: aborting due to previous error