Add test that shows how a cycle between the where-clauses on a type

and the type appearing in the trait would (previously) trigger an
error message. The code is now accepted. No reported issue that I am
aware of.

src/test/run-pass/astconv-cycle-between-trait-and-type.rs

@@ -0,0 +1,36 @@
+// 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.
+
+// Test that we are able to successfully compile a setup where a trait
+// (`Trait1`) references a struct (`SomeType<u32>`) which in turn
+// carries a predicate that references the trait (`u32 : Trait1`,
+// substituted).
+
+#![allow(dead_code)]
+
+trait Trait1 : Trait2<SomeType<u32>> {
+    fn dumb(&self) { }
+}
+
+trait Trait2<A> {
+    fn dumber(&self, _: A) { }
+}
+
+struct SomeType<A>
+    where A : Trait1
+{
+    a: A
+}
+
+impl Trait1 for u32 { }
+
+impl Trait2<SomeType<u32>> for u32 { }
+
+fn main() { }