Disallow impl Trait in unsupported position

src/test/compile-fail/issue-47715.rs

@@ -0,0 +1,38 @@
+// 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.
+
+trait Foo {}
+
+trait Bar<T> {}
+
+trait Iterable {
+    type Item;
+}
+
+struct Container<T: Iterable<Item = impl Foo>> {
+    //~^ ERROR `impl Trait` not allowed
+    field: T
+}
+
+enum Enum<T: Iterable<Item = impl Foo>> {
+    //~^ ERROR `impl Trait` not allowed
+    A(T),
+}
+
+union Union<T: Iterable<Item = impl Foo> + Copy> {
+    //~^ ERROR `impl Trait` not allowed
+    x: T,
+}
+
+type Type<T: Iterable<Item = impl Foo>> = T;
+//~^ ERROR `impl Trait` not allowed
+
+fn main() {
+}