1 files changed, 23 insertions, 0 deletions
diff --git a/src/test/ui/traits/assoc-type-in-supertrait.rs b/src/test/ui/traits/assoc-type-in-supertrait.rs
new file mode 100644
index 000000000..7d6a754cc
--- /dev/null
+++ b/src/test/ui/traits/assoc-type-in-supertrait.rs
@@ -0,0 +1,23 @@
+// run-pass
+// Test case where an associated type is referenced from within the
+// supertrait definition. Issue #20220.
+
+
+use std::vec::IntoIter;
+
+pub trait Foo: Iterator<Item=<Self as Foo>::Key> {
+    type Key;
+}
+
+impl Foo for IntoIter<i32> {
+    type Key = i32;
+}
+
+fn sum_foo<F:Foo<Key=i32>>(f: F) -> i32 {
+    f.fold(0, |a,b| a + b)
+}
+
+fn main() {
+    let x = sum_foo(vec![11, 10, 1].into_iter());
+    assert_eq!(x, 22);
+}