fix and test rust-lang#43475

Author: Twey

src/librustc/traits/select.rs

@@ -1420,8 +1420,21 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
                         -> bool
     {
         assert!(!skol_trait_ref.has_escaping_regions());
+        debug!("match_projection: obligation={:?}, trait_bound={:?}",
+               obligation, trait_bound);
+
+        let Normalized { value: normal_bound, obligations } =
+            project::normalize(
+                self, obligation.param_env.clone(), obligation.cause.clone(),
+                &trait_bound);
+        debug!("match_projection: \
+                obligation={:?}, normal_bound={:?}, \
+                additional inferred_obligations={:?}",
+               obligation, normal_bound, obligations);
+        self.inferred_obligations.extend(obligations);
+
         match self.infcx.at(&obligation.cause, obligation.param_env)
-                        .sup(ty::Binder(skol_trait_ref), trait_bound) {
+                        .sup(ty::Binder(skol_trait_ref), normal_bound) {
             Ok(InferOk { obligations, .. }) => {
                 self.inferred_obligations.extend(obligations);
             }

src/test/run-pass/issue-43475.rs

@@ -0,0 +1,31 @@
+// Copyright 2014 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 FooT: Foo;
+}
+
+impl Foo for () {
+    type FooT = ();
+}
+
+trait Bar<A: Foo> {
+    type BarT: Bar<A::FooT>;
+}
+
+impl Bar<()> for () {
+    type BarT = ();
+}
+
+fn test<C: Bar<()>>() {}
+
+fn main() {
+    test::<()>()
+}