Added feature gate.

src/test/ui/feature-gates/feature-gate-self-in-typedefs.rs

@@ -0,0 +1,18 @@
+// 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.
+
+enum StackList<'a, T: 'a> {
+    Nil,
+    Cons(T, &'a Self)
+    //~^ ERROR cannot find type `Self` in this scope
+    //~| `Self` is only available in traits and impls
+}
+
+fn main() {}

src/test/ui/feature-gates/feature-gate-self-in-typedefs.stderr

@@ -0,0 +1,9 @@
+error[E0411]: cannot find type `Self` in this scope
+  --> $DIR/feature-gate-self-in-typedefs.rs:13:17
+   |
+LL |     Cons(T, &'a Self)
+   |                 ^^^^ `Self` is only available in traits and impls
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0411`.