From 5fac991bf6bc4b07df9b4b4eb3fcb0c5487973c4 Mon Sep 17 00:00:00 2001
From: CDirkx <christiaan@dirkx.com>
Date: Sun, 30 Aug 2020 19:40:00 +0200
Subject: [PATCH] Add unstable `const_ordering` feature, and some tests.

---
 library/core/src/cmp.rs              |  2 ++
 library/core/src/lib.rs              |  1 +
 src/test/ui/consts/const-ordering.rs | 17 +++++++++++++++++
 3 files changed, 20 insertions(+)
 create mode 100644 src/test/ui/consts/const-ordering.rs

diff --git a/library/core/src/cmp.rs b/library/core/src/cmp.rs
index b66a6409b9cf..ddc9f7b8cbad 100644
--- a/library/core/src/cmp.rs
+++ b/library/core/src/cmp.rs
@@ -356,6 +356,7 @@ impl Ordering {
     /// ```
     #[inline]
     #[must_use]
+    #[rustc_const_unstable(feature = "const_ordering", issue = "76113")]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub const fn reverse(self) -> Ordering {
         match self {
@@ -394,6 +395,7 @@ impl Ordering {
     /// ```
     #[inline]
     #[must_use]
+    #[rustc_const_unstable(feature = "const_ordering", issue = "76113")]
     #[stable(feature = "ordering_chaining", since = "1.17.0")]
     pub const fn then(self, other: Ordering) -> Ordering {
         match self {
diff --git a/library/core/src/lib.rs b/library/core/src/lib.rs
index fcf5454308b4..745c46e08684 100644
--- a/library/core/src/lib.rs
+++ b/library/core/src/lib.rs
@@ -86,6 +86,7 @@
 #![feature(const_ptr_offset_from)]
 #![feature(const_raw_ptr_comparison)]
 #![feature(const_result)]
+#![feature(const_ordering)]
 #![feature(const_slice_from_raw_parts)]
 #![feature(const_slice_ptr_len)]
 #![feature(const_size_of_val)]
diff --git a/src/test/ui/consts/const-ordering.rs b/src/test/ui/consts/const-ordering.rs
new file mode 100644
index 000000000000..9feb2b27dadb
--- /dev/null
+++ b/src/test/ui/consts/const-ordering.rs
@@ -0,0 +1,17 @@
+// run-pass
+
+#![feature(const_ordering)]
+
+use std::cmp::Ordering;
+
+// the following methods of core::cmp::Ordering are const:
+//  - reverse
+//  - then
+
+fn main() {
+    const REVERSE : Ordering = Ordering::Greater.reverse();
+    assert_eq!(REVERSE, Ordering::Less);
+
+    const THEN : Ordering = Ordering::Equal.then(REVERSE);
+    assert_eq!(THEN, Ordering::Less);
+}