From 2c6bc186100df68ba6dc7e7388e3708af7ba1539 Mon Sep 17 00:00:00 2001
From: Andrew Cann <shum@canndrew.org>
Date: Wed, 18 Jan 2017 15:05:28 +0800
Subject: [PATCH] Feature gate `&Void`'s uninhabitedness.

References to empty types are only considered empty if feature(never_type) is
enabled.
---
 src/librustc/ty/inhabitedness/mod.rs          |  8 +++++++-
 ...ninhabited-reference-type-feature-gated.rs | 19 +++++++++++++++++++
 src/test/run-pass/empty-types-in-patterns.rs  |  5 +++++
 3 files changed, 31 insertions(+), 1 deletion(-)
 create mode 100644 src/test/compile-fail/uninhabited-reference-type-feature-gated.rs

diff --git a/src/librustc/ty/inhabitedness/mod.rs b/src/librustc/ty/inhabitedness/mod.rs
index c5b75839e99b7..92395e3c381aa 100644
--- a/src/librustc/ty/inhabitedness/mod.rs
+++ b/src/librustc/ty/inhabitedness/mod.rs
@@ -190,7 +190,13 @@ impl<'a, 'gcx, 'tcx> TyS<'tcx> {
                     ty.uninhabited_from(visited, tcx)
                 }
             }
-            TyRef(_, ref tm) => tm.ty.uninhabited_from(visited, tcx),
+            TyRef(_, ref tm) => {
+                if tcx.sess.features.borrow().never_type {
+                    tm.ty.uninhabited_from(visited, tcx)
+                } else {
+                    DefIdForest::empty()
+                }
+            }
 
             _ => DefIdForest::empty(),
         }
diff --git a/src/test/compile-fail/uninhabited-reference-type-feature-gated.rs b/src/test/compile-fail/uninhabited-reference-type-feature-gated.rs
new file mode 100644
index 0000000000000..8f246eddbcde4
--- /dev/null
+++ b/src/test/compile-fail/uninhabited-reference-type-feature-gated.rs
@@ -0,0 +1,19 @@
+// Copyright 2016 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 Void {}
+
+fn main() {
+    let x: Result<u32, &'static Void> = Ok(23);
+    let _ = match x {   //~ ERROR non-exhaustive
+        Ok(n) => n,
+    };
+}
+
diff --git a/src/test/run-pass/empty-types-in-patterns.rs b/src/test/run-pass/empty-types-in-patterns.rs
index 23705d36e3de2..033b185a0ef06 100644
--- a/src/test/run-pass/empty-types-in-patterns.rs
+++ b/src/test/run-pass/empty-types-in-patterns.rs
@@ -55,6 +55,11 @@ fn main() {
         Err(e) => match e {},
     };
 
+    let x: Result<u32, &!> = Ok(123);
+    match x {
+        Ok(y) => y,
+    };
+
     bar(&[]);
 }