Normalize types in supertraits when checking that impls are valid during wf.

Fixes #20559.

src/test/run-pass/associated-types-projection-in-supertrait.rs

@@ -0,0 +1,50 @@
+// 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 handle to correctly handle a projection type
+// that appears in a supertrait bound. Issue #20559.
+
+trait A
+{
+    type TA;
+}
+
+trait B<TB>
+{
+    fn foo (&self, t : TB) -> String;
+}
+
+trait C<TC : A> : B<<TC as A>::TA> { }
+
+struct X;
+
+impl A for X
+{
+    type TA = i32;
+}
+
+struct Y;
+
+impl C<X> for Y { }
+
+// Both of these impls are required for successful compilation
+impl B<i32> for Y
+{
+    fn foo (&self, t : i32) -> String
+    {
+        format!("First {}", t)
+    }
+}
+
+fn main ()
+{
+    let y = Y;
+    assert_eq!(y.foo(5), format!("First 5"));
+}