From b3d2346230736b253d8f2a9df461901b7de67abd Mon Sep 17 00:00:00 2001
From: Ralf Jung <post@ralfj.de>
Date: Fri, 3 Aug 2018 18:02:34 +0200
Subject: [PATCH 1/4] unsized ManuallyDrop

---
 src/libcore/mem.rs                 | 11 ++++++++---
 src/libcore/tests/manually_drop.rs |  4 ++++
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/src/libcore/mem.rs b/src/libcore/mem.rs
index 8a74e7c6f1cc6..1eec4def1bbff 100644
--- a/src/libcore/mem.rs
+++ b/src/libcore/mem.rs
@@ -956,7 +956,7 @@ pub fn discriminant<T>(v: &T) -> Discriminant<T> {
 #[stable(feature = "manually_drop", since = "1.20.0")]
 #[lang = "manually_drop"]
 #[derive(Copy, Clone, Debug, Default, PartialEq, Eq, PartialOrd, Ord, Hash)]
-pub struct ManuallyDrop<T> {
+pub struct ManuallyDrop<T: ?Sized> {
     value: T,
 }
 
@@ -990,7 +990,9 @@ impl<T> ManuallyDrop<T> {
     pub fn into_inner(slot: ManuallyDrop<T>) -> T {
         slot.value
     }
+}
 
+impl<T: ?Sized> ManuallyDrop<T> {
     /// Manually drops the contained value.
     ///
     /// # Safety
@@ -1006,7 +1008,7 @@ impl<T> ManuallyDrop<T> {
 }
 
 #[stable(feature = "manually_drop", since = "1.20.0")]
-impl<T> Deref for ManuallyDrop<T> {
+impl<T: ?Sized> Deref for ManuallyDrop<T> {
     type Target = T;
     #[inline]
     fn deref(&self) -> &Self::Target {
@@ -1015,13 +1017,16 @@ impl<T> Deref for ManuallyDrop<T> {
 }
 
 #[stable(feature = "manually_drop", since = "1.20.0")]
-impl<T> DerefMut for ManuallyDrop<T> {
+impl<T: ?Sized> DerefMut for ManuallyDrop<T> {
     #[inline]
     fn deref_mut(&mut self) -> &mut Self::Target {
         &mut self.value
     }
 }
 
+#[unstable(feature = "coerce_unsized", issue = "27732")]
+impl<T: CoerceUnsized<U>, U> CoerceUnsized<ManuallyDrop<U>> for ManuallyDrop<T> {}
+
 /// A pinned reference.
 ///
 /// A pinned reference is a lot like a mutable reference, except that it is not
diff --git a/src/libcore/tests/manually_drop.rs b/src/libcore/tests/manually_drop.rs
index 96bc9247da6e7..b8826ad408761 100644
--- a/src/libcore/tests/manually_drop.rs
+++ b/src/libcore/tests/manually_drop.rs
@@ -21,4 +21,8 @@ fn smoke() {
 
     let x = ManuallyDrop::new(TypeWithDrop);
     drop(x);
+
+    // also test unsizing
+    let x : Box<ManuallyDrop<[TypeWithDrop]>> = Box::new(ManuallyDrop::new([TypeWithDrop]));
+    drop(x);
 }

From 3dcdb8a83e953bfa033349e07c0f62b4230ea514 Mon Sep 17 00:00:00 2001
From: Ralf Jung <post@ralfj.de>
Date: Mon, 6 Aug 2018 15:52:27 +0200
Subject: [PATCH 2/4] remove unnecessary CoerceUnsized impl

---
 src/libcore/mem.rs | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/src/libcore/mem.rs b/src/libcore/mem.rs
index 1eec4def1bbff..9efac3e8d4cb2 100644
--- a/src/libcore/mem.rs
+++ b/src/libcore/mem.rs
@@ -1024,9 +1024,6 @@ impl<T: ?Sized> DerefMut for ManuallyDrop<T> {
     }
 }
 
-#[unstable(feature = "coerce_unsized", issue = "27732")]
-impl<T: CoerceUnsized<U>, U> CoerceUnsized<ManuallyDrop<U>> for ManuallyDrop<T> {}
-
 /// A pinned reference.
 ///
 /// A pinned reference is a lot like a mutable reference, except that it is not

From d865adcf1eea0772be93a2b330073238b0803e17 Mon Sep 17 00:00:00 2001
From: Ralf Jung <post@ralfj.de>
Date: Mon, 6 Aug 2018 15:52:36 +0200
Subject: [PATCH 3/4] unconfuse @eddyb

---
 src/libcore/tests/manually_drop.rs | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/libcore/tests/manually_drop.rs b/src/libcore/tests/manually_drop.rs
index b8826ad408761..82dfb8d4c0b2a 100644
--- a/src/libcore/tests/manually_drop.rs
+++ b/src/libcore/tests/manually_drop.rs
@@ -23,6 +23,7 @@ fn smoke() {
     drop(x);
 
     // also test unsizing
-    let x : Box<ManuallyDrop<[TypeWithDrop]>> = Box::new(ManuallyDrop::new([TypeWithDrop]));
+    let x : Box<ManuallyDrop<[TypeWithDrop]>> =
+        Box::new(ManuallyDrop::new([TypeWithDrop, TypeWithDrop]));
     drop(x);
 }

From 5ee5a7eb5568011b29a9fee16b00e2b576603da3 Mon Sep 17 00:00:00 2001
From: Ralf Jung <post@ralfj.de>
Date: Thu, 9 Aug 2018 11:56:01 +0200
Subject: [PATCH 4/4] repr(transparent)

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

diff --git a/src/libcore/mem.rs b/src/libcore/mem.rs
index 9efac3e8d4cb2..ea711c69393a4 100644
--- a/src/libcore/mem.rs
+++ b/src/libcore/mem.rs
@@ -956,6 +956,7 @@ pub fn discriminant<T>(v: &T) -> Discriminant<T> {
 #[stable(feature = "manually_drop", since = "1.20.0")]
 #[lang = "manually_drop"]
 #[derive(Copy, Clone, Debug, Default, PartialEq, Eq, PartialOrd, Ord, Hash)]
+#[repr(transparent)]
 pub struct ManuallyDrop<T: ?Sized> {
     value: T,
 }