Normalize associated types when checking global bounds

src/librustc_typeck/check/wfcheck.rs

@@ -711,6 +711,7 @@ fn check_false_global_bounds<'a, 'gcx, 'tcx>(
     for pred in implied_obligations {
         // Match the existing behavior.
         if pred.is_global() && !pred.has_late_bound_regions() {
+            let pred = fcx.normalize_associated_types_in(span, &pred);
             let obligation = traits::Obligation::new(
                 traits::ObligationCause::new(
                     span,

src/test/ui/issue-51044.rs

@@ -0,0 +1,40 @@
+// Copyright 2018 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.
+
+// run-pass
+// regression test for issue #50825
+// Check that the feature gate normalizes associated types.
+
+#![allow(dead_code)]
+struct Foo<T>(T);
+struct Duck;
+struct Quack;
+
+trait Hello<A> where A: Animal {
+}
+
+trait Animal {
+    type Noise;
+}
+
+trait Loud<R>  {
+}
+
+impl Loud<Quack> for f32 {
+}
+
+impl Animal for Duck {
+    type Noise = Quack;
+}
+
+impl Hello<Duck> for Foo<f32> where f32: Loud<<Duck as Animal>::Noise> {
+}
+
+fn main() {}