From a44abfdc29ee66ec1d51c2389405cbac479f35a7 Mon Sep 17 00:00:00 2001
From: Taylor Cramer <cramertj@google.com>
Date: Tue, 22 May 2018 17:09:49 -0700
Subject: [PATCH 1/4] Make `Unpin` safe to implement

---
 src/liballoc/boxed.rs | 2 +-
 src/libcore/marker.rs | 2 +-
 src/libcore/mem.rs    | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/liballoc/boxed.rs b/src/liballoc/boxed.rs
index a156734423551..a83ce7f379fbc 100644
--- a/src/liballoc/boxed.rs
+++ b/src/liballoc/boxed.rs
@@ -850,4 +850,4 @@ impl<T: ?Sized> fmt::Pointer for PinBox<T> {
 impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<PinBox<U>> for PinBox<T> {}
 
 #[unstable(feature = "pin", issue = "49150")]
-unsafe impl<T: ?Sized> Unpin for PinBox<T> {}
+impl<T: ?Sized> Unpin for PinBox<T> {}
diff --git a/src/libcore/marker.rs b/src/libcore/marker.rs
index 6c8ee0eda11e9..d4a87b13f04d2 100644
--- a/src/libcore/marker.rs
+++ b/src/libcore/marker.rs
@@ -605,7 +605,7 @@ unsafe impl<'a, T: ?Sized> Freeze for &'a mut T {}
 ///
 /// [`PinMut`]: ../mem/struct.PinMut.html
 #[unstable(feature = "pin", issue = "49150")]
-pub unsafe auto trait Unpin {}
+pub auto trait Unpin {}
 
 /// Implementations of `Copy` for primitive types.
 ///
diff --git a/src/libcore/mem.rs b/src/libcore/mem.rs
index 20445def634ec..116e56f4ae9fb 100644
--- a/src/libcore/mem.rs
+++ b/src/libcore/mem.rs
@@ -1207,4 +1207,4 @@ impl<'a, T: ?Sized> fmt::Pointer for PinMut<'a, T> {
 impl<'a, T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<PinMut<'a, U>> for PinMut<'a, T> {}
 
 #[unstable(feature = "pin", issue = "49150")]
-unsafe impl<'a, T: ?Sized> Unpin for PinMut<'a, T> {}
+impl<'a, T: ?Sized> Unpin for PinMut<'a, T> {}

From 640f6f07494ece4ebe7e4d9680fff9a83ab4b0d2 Mon Sep 17 00:00:00 2001
From: Taylor Cramer <cramertj@google.com>
Date: Tue, 22 May 2018 17:10:14 -0700
Subject: [PATCH 2/4] Add Pinned type for opting out of Unpin on stable

---
 src/libcore/marker.rs | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/src/libcore/marker.rs b/src/libcore/marker.rs
index d4a87b13f04d2..77db165bcbde3 100644
--- a/src/libcore/marker.rs
+++ b/src/libcore/marker.rs
@@ -607,6 +607,16 @@ unsafe impl<'a, T: ?Sized> Freeze for &'a mut T {}
 #[unstable(feature = "pin", issue = "49150")]
 pub auto trait Unpin {}
 
+/// A type which does not implement `Unpin`.
+///
+/// If a type contains a `Pinned`, it will not implement `Unpin` by default.
+#[unstable(feature = "pin", issue = "49150")]
+#[derive(Debug, Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash)]
+pub struct Pinned;
+
+#[unstable(feature = "pin", issue = "49150")]
+impl !Unpin for Pinned {}
+
 /// Implementations of `Copy` for primitive types.
 ///
 /// Implementations that cannot be described in Rust

From b7ccb248480918ae589756b585f4cdcae82a26b7 Mon Sep 17 00:00:00 2001
From: Taylor Cramer <cramertj@google.com>
Date: Tue, 22 May 2018 16:59:53 -0700
Subject: [PATCH 3/4] Add PinMut::set

---
 src/libcore/mem.rs | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/src/libcore/mem.rs b/src/libcore/mem.rs
index 116e56f4ae9fb..059c099d66b56 100644
--- a/src/libcore/mem.rs
+++ b/src/libcore/mem.rs
@@ -1164,6 +1164,14 @@ impl<'a, T: ?Sized> PinMut<'a, T> {
     {
         PinMut { inner: f(this.inner) }
     }
+
+    /// Assign a new value to the memory behind the pinned reference.
+    #[unstable(feature = "pin", issue = "49150")]
+    pub fn set(this: PinMut<'a, T>, value: T)
+        where T: Sized,
+    {
+        *this.inner = value;
+    }
 }
 
 #[unstable(feature = "pin", issue = "49150")]

From 15d2f965d83672dc8e7edc972ab256e587878332 Mon Sep 17 00:00:00 2001
From: Taylor Cramer <cramertj@google.com>
Date: Tue, 22 May 2018 17:07:51 -0700
Subject: [PATCH 4/4] Add Option::as_pin_mut

---
 src/libcore/lib.rs    |  1 +
 src/libcore/option.rs | 10 ++++++++++
 2 files changed, 11 insertions(+)

diff --git a/src/libcore/lib.rs b/src/libcore/lib.rs
index d37629ced11db..2121bc4438056 100644
--- a/src/libcore/lib.rs
+++ b/src/libcore/lib.rs
@@ -74,6 +74,7 @@
 #![deny(missing_debug_implementations)]
 
 #![feature(allow_internal_unstable)]
+#![feature(arbitrary_self_types)]
 #![feature(asm)]
 #![feature(associated_type_defaults)]
 #![feature(attr_literals)]
diff --git a/src/libcore/option.rs b/src/libcore/option.rs
index 28f37f72d6f9d..1e615042a6d88 100644
--- a/src/libcore/option.rs
+++ b/src/libcore/option.rs
@@ -147,6 +147,7 @@
 
 use iter::{FromIterator, FusedIterator, TrustedLen};
 use {mem, ops};
+use mem::PinMut;
 
 // Note that this is not a lang item per se, but it has a hidden dependency on
 // `Iterator`, which is one. The compiler assumes that the `next` method of
@@ -269,6 +270,15 @@ impl<T> Option<T> {
         }
     }
 
+    /// Converts from `Option<T>` to `Option<PinMut<'_, T>>`
+    #[inline]
+    #[unstable(feature = "pin", issue = "49150")]
+    pub fn as_pin_mut<'a>(self: PinMut<'a, Self>) -> Option<PinMut<'a, T>> {
+        unsafe {
+            PinMut::get_mut(self).as_mut().map(|x| PinMut::new_unchecked(x))
+        }
+    }
+
     /////////////////////////////////////////////////////////////////////////
     // Getting to contained values
     /////////////////////////////////////////////////////////////////////////