Test use of impl Trait in an impl as the value for an associated type in an impl trait

src/test/ui/type-alias-impl-trait/type-alias-impl-trait-assoc-impl-trait.rs

+// check-pass
+
+#![feature(type_alias_impl_trait)]
+#![allow(dead_code)]
+
+type Foo = impl Iterator<Item = impl Send>;
+
+fn make_foo() -> Foo {
+    vec![1, 2].into_iter()
+}
+
+type Bar = impl Send;
+type Baz = impl Iterator<Item = Bar>;
+
+fn make_baz() -> Baz {
+    vec!["1", "2"].into_iter()
+}
+
+fn main() {}