From 2843e648c236c0ed31f0155f0805f43f3ee7ed95 Mon Sep 17 00:00:00 2001
From: Jorge Aparicio <jorge@japaric.io>
Date: Sat, 21 Apr 2018 23:22:27 +0200
Subject: [PATCH 1/2] turn `ManuallyDrop::new` into a constant function

---
 src/libcore/mem.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/libcore/mem.rs b/src/libcore/mem.rs
index e3f08926610..6d64d91312e 100644
--- a/src/libcore/mem.rs
+++ b/src/libcore/mem.rs
@@ -960,7 +960,7 @@ impl<T> ManuallyDrop<T> {
     /// ```
     #[stable(feature = "manually_drop", since = "1.20.0")]
     #[inline]
-    pub fn new(value: T) -> ManuallyDrop<T> {
+    pub const fn new(value: T) -> ManuallyDrop<T> {
         ManuallyDrop { value: value }
     }
 

From b61a4c20c6acd963070adb083b12d5e21a5843d3 Mon Sep 17 00:00:00 2001
From: Jorge Aparicio <jorge@japaric.io>
Date: Mon, 7 May 2018 12:11:22 +0200
Subject: [PATCH 2/2] make the const constructor unstable

---
 src/libcore/mem.rs | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/libcore/mem.rs b/src/libcore/mem.rs
index 6d64d91312e..6836f8622b0 100644
--- a/src/libcore/mem.rs
+++ b/src/libcore/mem.rs
@@ -959,6 +959,7 @@ impl<T> ManuallyDrop<T> {
     /// ManuallyDrop::new(Box::new(()));
     /// ```
     #[stable(feature = "manually_drop", since = "1.20.0")]
+    #[rustc_const_unstable(feature = "const_manually_drop_new")]
     #[inline]
     pub const fn new(value: T) -> ManuallyDrop<T> {
         ManuallyDrop { value: value }