1 files changed, 25 insertions, 0 deletions
diff --git a/src/test/ui/associated-types/associated-types-issue-20346.stderr b/src/test/ui/associated-types/associated-types-issue-20346.stderr
new file mode 100644
index 000000000..a67cf9928
--- /dev/null
+++ b/src/test/ui/associated-types/associated-types-issue-20346.stderr
@@ -0,0 +1,25 @@
+error[E0271]: type mismatch resolving `<Adapter<I> as Iterator>::Item == Option<T>`
+  --> $DIR/associated-types-issue-20346.rs:34:5
+   |
+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>`
+   |
+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`.