error[E0271]: type mismatch resolving `<Adapter<I> as Iterator>::Item == Option<T>`
  --> $DIR/associated-types-issue-20346.rs:34:36
   |
LL | fn test_adapter<T, I: Iterator<Item=Option<T>>>(it: I) {
   |                 - this type parameter
...
LL |     is_iterator_of::<Option<T>, _>(&adapter);
   |     ------------------------------ ^^^^^^^^ type mismatch resolving `<Adapter<I> as Iterator>::Item == Option<T>`
   |     |
   |     required by a bound introduced by this call
   |
note: expected this to be `Option<T>`
  --> $DIR/associated-types-issue-20346.rs:23:17
   |
LL |     type Item = T;
   |                 ^
   = note:        expected enum `Option<T>`
           found type parameter `T`
note: required by a bound in `is_iterator_of`
  --> $DIR/associated-types-issue-20346.rs:15:34
   |
LL | fn is_iterator_of<A, I: Iterator<Item=A>>(_: &I) {}
   |                                  ^^^^^^ required by this bound in `is_iterator_of`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0271`.