Rollup merge of #71168 - SimonSapin:into_raw_non_null, r=Amanieu

Deprecate `{Box,Rc,Arc}::into_raw_non_null`

Per ongoing FCP at https://github.com/rust-lang/rust/issues/47336#issuecomment-586589016
See also https://github.com/rust-lang/rust/issues/47336#issuecomment-614054164

5 files changed, 46 insertions, 31 deletions

diff --git a/src/liballoc/boxed.rs b/src/liballoc/boxed.rs
index db7420954a0..3d657396a9f 100644
--- a/src/liballoc/boxed.rs
+++ b/src/liballoc/boxed.rs
@@ -428,7 +428,12 @@ impl<T: ?Sized> Box<T> {
     #[stable(feature = "box_raw", since = "1.4.0")]
     #[inline]
     pub fn into_raw(b: Box<T>) -> *mut T {
-        Box::into_raw_non_null(b).as_ptr()
+        // Box is recognized as a "unique pointer" by Stacked Borrows, but internally it is a
+        // raw pointer for the type system. Turning it directly into a raw pointer would not be
+        // recognized as "releasing" the unique pointer to permit aliased raw accesses,
+        // so all raw pointer methods go through `leak` which creates a (unique)
+        // mutable reference. Turning *that* to a raw pointer behaves correctly.
+        Box::leak(b) as *mut T
     }
 
     /// Consumes the `Box`, returning the wrapped pointer as `NonNull<T>`.
@@ -451,6 +456,7 @@ impl<T: ?Sized> Box<T> {
     ///
     /// ```
     /// #![feature(box_into_raw_non_null)]
+    /// #![allow(deprecated)]
     ///
     /// let x = Box::new(5);
     /// let ptr = Box::into_raw_non_null(x);
@@ -460,24 +466,34 @@ impl<T: ?Sized> Box<T> {
     /// let x = unsafe { Box::from_raw(ptr.as_ptr()) };
     /// ```
     #[unstable(feature = "box_into_raw_non_null", issue = "47336")]
+    #[rustc_deprecated(
+        since = "1.44.0",
+        reason = "use `Box::leak(b).into()` or `NonNull::from(Box::leak(b))` instead"
+    )]
     #[inline]
     pub fn into_raw_non_null(b: Box<T>) -> NonNull<T> {
-        Box::into_unique(b).into()
-    }
-
-    #[unstable(feature = "ptr_internals", issue = "none", reason = "use into_raw_non_null instead")]
+        // Box is recognized as a "unique pointer" by Stacked Borrows, but internally it is a
+        // raw pointer for the type system. Turning it directly into a raw pointer would not be
+        // recognized as "releasing" the unique pointer to permit aliased raw accesses,
+        // so all raw pointer methods go through `leak` which creates a (unique)
+        // mutable reference. Turning *that* to a raw pointer behaves correctly.
+        Box::leak(b).into()
+    }
+
+    #[unstable(
+        feature = "ptr_internals",
+        issue = "none",
+        reason = "use `Box::leak(b).into()` or `Unique::from(Box::leak(b))` instead"
+    )]
     #[inline]
     #[doc(hidden)]
     pub fn into_unique(b: Box<T>) -> Unique<T> {
-        let b = mem::ManuallyDrop::new(b);
-        let mut unique = b.0;
-        // Box is kind-of a library type, but recognized as a "unique pointer" by
-        // Stacked Borrows.  This function here corresponds to "reborrowing to
-        // a raw pointer", but there is no actual reborrow here -- so
-        // without some care, the pointer we are returning here still carries
-        // the tag of `b`, with `Unique` permission.
-        // We round-trip through a mutable reference to avoid that.
-        unsafe { Unique::new_unchecked(unique.as_mut() as *mut T) }
+        // Box is recognized as a "unique pointer" by Stacked Borrows, but internally it is a
+        // raw pointer for the type system. Turning it directly into a raw pointer would not be
+        // recognized as "releasing" the unique pointer to permit aliased raw accesses,
+        // so all raw pointer methods go through `leak` which creates a (unique)
+        // mutable reference. Turning *that* to a raw pointer behaves correctly.
+        Box::leak(b).into()
     }
 
     /// Consumes and leaks the `Box`, returning a mutable reference,
@@ -523,7 +539,7 @@ impl<T: ?Sized> Box<T> {
     where
         T: 'a, // Technically not needed, but kept to be explicit.
     {
-        unsafe { &mut *Box::into_raw(b) }
+        unsafe { &mut *mem::ManuallyDrop::new(b).0.as_ptr() }
     }
 
     /// Converts a `Box<T>` into a `Pin<Box<T>>`
diff --git a/src/liballoc/collections/linked_list.rs b/src/liballoc/collections/linked_list.rs
index af341e6c1ca..5825bd306b6 100644
--- a/src/liballoc/collections/linked_list.rs
+++ b/src/liballoc/collections/linked_list.rs
@@ -143,7 +143,7 @@ impl<T> LinkedList<T> {
         unsafe {
             node.next = self.head;
             node.prev = None;
-            let node = Some(Box::into_raw_non_null(node));
+            let node = Some(Box::leak(node).into());
 
             match self.head {
                 None => self.tail = node,
@@ -184,7 +184,7 @@ impl<T> LinkedList<T> {
         unsafe {
             node.next = None;
             node.prev = self.tail;
-            let node = Some(Box::into_raw_non_null(node));
+            let node = Some(Box::leak(node).into());
 
             match self.tail {
                 None => self.head = node,
@@ -1133,11 +1133,9 @@ impl<T> IterMut<'_, T> {
                     Some(prev) => prev,
                 };
 
-                let node = Some(Box::into_raw_non_null(box Node {
-                    next: Some(head),
-                    prev: Some(prev),
-                    element,
-                }));
+                let node = Some(
+                    Box::leak(box Node { next: Some(head), prev: Some(prev), element }).into(),
+                );
 
                 // Not creating references to entire nodes to not invalidate the
                 // reference to `element` we handed to the user.
@@ -1450,7 +1448,7 @@ impl<'a, T> CursorMut<'a, T> {
     #[unstable(feature = "linked_list_cursors", issue = "58533")]
     pub fn insert_after(&mut self, item: T) {
         unsafe {
-            let spliced_node = Box::into_raw_non_null(Box::new(Node::new(item)));
+            let spliced_node = Box::leak(Box::new(Node::new(item))).into();
             let node_next = match self.current {
                 None => self.list.head,
                 Some(node) => node.as_ref().next,
@@ -1470,7 +1468,7 @@ impl<'a, T> CursorMut<'a, T> {
     #[unstable(feature = "linked_list_cursors", issue = "58533")]
     pub fn insert_before(&mut self, item: T) {
         unsafe {
-            let spliced_node = Box::into_raw_non_null(Box::new(Node::new(item)));
+            let spliced_node = Box::leak(Box::new(Node::new(item))).into();
             let node_prev = match self.current {
                 None => self.list.tail,
                 Some(node) => node.as_ref().prev,
diff --git a/src/liballoc/lib.rs b/src/liballoc/lib.rs
index a2071844d5d..be603d656f0 100644
--- a/src/liballoc/lib.rs
+++ b/src/liballoc/lib.rs
@@ -77,7 +77,6 @@
 #![feature(allocator_api)]
 #![feature(allow_internal_unstable)]
 #![feature(arbitrary_self_types)]
-#![feature(box_into_raw_non_null)]
 #![feature(box_patterns)]
 #![feature(box_syntax)]
 #![feature(cfg_sanitize)]
diff --git a/src/liballoc/rc.rs b/src/liballoc/rc.rs
index fb9f5faa018..dd225808878 100644
--- a/src/liballoc/rc.rs
+++ b/src/liballoc/rc.rs
@@ -324,11 +324,9 @@ impl<T> Rc<T> {
         // pointers, which ensures that the weak destructor never frees
         // the allocation while the strong destructor is running, even
         // if the weak pointer is stored inside the strong one.
-        Self::from_inner(Box::into_raw_non_null(box RcBox {
-            strong: Cell::new(1),
-            weak: Cell::new(1),
-            value,
-        }))
+        Self::from_inner(
+            Box::leak(box RcBox { strong: Cell::new(1), weak: Cell::new(1), value }).into(),
+        )
     }
 
     /// Constructs a new `Rc` with uninitialized contents.
@@ -662,6 +660,7 @@ impl<T: ?Sized> Rc<T> {
     ///
     /// ```
     /// #![feature(rc_into_raw_non_null)]
+    /// #![allow(deprecated)]
     ///
     /// use std::rc::Rc;
     ///
@@ -671,6 +670,7 @@ impl<T: ?Sized> Rc<T> {
     /// assert_eq!(deref, "hello");
     /// ```
     #[unstable(feature = "rc_into_raw_non_null", issue = "47336")]
+    #[rustc_deprecated(since = "1.44.0", reason = "use `Rc::into_raw` instead")]
     #[inline]
     pub fn into_raw_non_null(this: Self) -> NonNull<T> {
         // safe because Rc guarantees its pointer is non-null
diff --git a/src/liballoc/sync.rs b/src/liballoc/sync.rs
index cde412bee78..cb660b476c4 100644
--- a/src/liballoc/sync.rs
+++ b/src/liballoc/sync.rs
@@ -325,7 +325,7 @@ impl<T> Arc<T> {
             weak: atomic::AtomicUsize::new(1),
             data,
         };
-        Self::from_inner(Box::into_raw_non_null(x))
+        Self::from_inner(Box::leak(x).into())
     }
 
     /// Constructs a new `Arc` with uninitialized contents.
@@ -659,6 +659,7 @@ impl<T: ?Sized> Arc<T> {
     ///
     /// ```
     /// #![feature(rc_into_raw_non_null)]
+    /// #![allow(deprecated)]
     ///
     /// use std::sync::Arc;
     ///
@@ -668,6 +669,7 @@ impl<T: ?Sized> Arc<T> {
     /// assert_eq!(deref, "hello");
     /// ```
     #[unstable(feature = "rc_into_raw_non_null", issue = "47336")]
+    #[rustc_deprecated(since = "1.44.0", reason = "use `Arc::into_raw` instead")]
     #[inline]
     pub fn into_raw_non_null(this: Self) -> NonNull<T> {
         // safe because Arc guarantees its pointer is non-null