Test that associated types are not required as type parameters

Closes #18173

src/test/run-pass/issue18173.rs

@@ -0,0 +1,21 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+trait Foo {
+    type T;
+}
+
+// should be able to use a trait with an associated type without specifying it as an argument
+trait Bar<F: Foo> {
+    fn bar(foo: &F);
+}
+
+pub fn main() {
+}