1 files changed, 35 insertions, 0 deletions
diff --git a/src/test/ui/associated-types/associated-types-issue-20346.rs b/src/test/ui/associated-types/associated-types-issue-20346.rs
new file mode 100644
index 000000000..0cce847e1
--- /dev/null
+++ b/src/test/ui/associated-types/associated-types-issue-20346.rs
@@ -0,0 +1,35 @@
+// Test that we reliably check the value of the associated type.
+
+#![crate_type = "lib"]
+#![no_implicit_prelude]
+
+use std::option::Option::{self, None, Some};
+use std::vec::Vec;
+
+trait Iterator {
+    type Item;
+
+    fn next(&mut self) -> Option<Self::Item>;
+}
+
+fn is_iterator_of<A, I: Iterator<Item=A>>(_: &I) {}
+
+struct Adapter<I> {
+    iter: I,
+    found_none: bool,
+}
+
+impl<T, I> Iterator for Adapter<I> where I: Iterator<Item=Option<T>> {
+    type Item = T;
+
+    fn next(&mut self) -> Option<T> {
+        loop {}
+    }
+}
+
+fn test_adapter<T, I: Iterator<Item=Option<T>>>(it: I) {
+    is_iterator_of::<Option<T>, _>(&it);  // Sanity check
+    let adapter = Adapter { iter: it, found_none: false };
+    is_iterator_of::<T, _>(&adapter); // OK
+    is_iterator_of::<Option<T>, _>(&adapter); //~ ERROR type mismatch
+}