Merge pull request #2 from rust-lang/master

update from origin 2020-06-10

14 files changed, 319 insertions, 191 deletions

diff --git a/src/liballoc/boxed.rs b/src/liballoc/boxed.rs
index 8ef6090c743..22c344323a2 100644
--- a/src/liballoc/boxed.rs
+++ b/src/liballoc/boxed.rs
@@ -865,6 +865,25 @@ impl From<Box<str>> for Box<[u8]> {
     }
 }
 
+#[stable(feature = "box_from_array", since = "1.45.0")]
+impl<T, const N: usize> From<[T; N]> for Box<[T]>
+where
+    [T; N]: LengthAtMost32,
+{
+    /// Converts a `[T; N]` into a `Box<[T]>`
+    ///
+    /// This conversion moves the array to newly heap-allocated memory.
+    ///
+    /// # Examples
+    /// ```rust
+    /// let boxed: Box<[u8]> = Box::from([4, 2]);
+    /// println!("{:?}", boxed);
+    /// ```
+    fn from(array: [T; N]) -> Box<[T]> {
+        box array
+    }
+}
+
 #[stable(feature = "boxed_slice_try_from", since = "1.43.0")]
 impl<T, const N: usize> TryFrom<Box<[T]>> for Box<[T; N]>
 where
@@ -1090,6 +1109,14 @@ impl<T: Clone> Clone for Box<[T]> {
     fn clone(&self) -> Self {
         self.to_vec().into_boxed_slice()
     }
+
+    fn clone_from(&mut self, other: &Self) {
+        if self.len() == other.len() {
+            self.clone_from_slice(&other);
+        } else {
+            *self = other.clone();
+        }
+    }
 }
 
 #[stable(feature = "box_borrow", since = "1.1.0")]
diff --git a/src/liballoc/collections/binary_heap.rs b/src/liballoc/collections/binary_heap.rs
index a3ef9989184..c2fe4691b34 100644
--- a/src/liballoc/collections/binary_heap.rs
+++ b/src/liballoc/collections/binary_heap.rs
@@ -1376,6 +1376,16 @@ impl<T: Ord> Extend<T> for BinaryHeap<T> {
     fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
         <Self as SpecExtend<I>>::spec_extend(self, iter);
     }
+
+    #[inline]
+    fn extend_one(&mut self, item: T) {
+        self.push(item);
+    }
+
+    #[inline]
+    fn extend_reserve(&mut self, additional: usize) {
+        self.reserve(additional);
+    }
 }
 
 impl<T: Ord, I: IntoIterator<Item = T>> SpecExtend<I> for BinaryHeap<T> {
@@ -1406,4 +1416,14 @@ impl<'a, T: 'a + Ord + Copy> Extend<&'a T> for BinaryHeap<T> {
     fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
         self.extend(iter.into_iter().cloned());
     }
+
+    #[inline]
+    fn extend_one(&mut self, &item: &'a T) {
+        self.push(item);
+    }
+
+    #[inline]
+    fn extend_reserve(&mut self, additional: usize) {
+        self.reserve(additional);
+    }
 }
diff --git a/src/liballoc/collections/btree/map.rs b/src/liballoc/collections/btree/map.rs
index c6cb39b1bf5..fa1c09d9ece 100644
--- a/src/liballoc/collections/btree/map.rs
+++ b/src/liballoc/collections/btree/map.rs
@@ -1901,6 +1901,11 @@ impl<K: Ord, V> Extend<(K, V)> for BTreeMap<K, V> {
             self.insert(k, v);
         });
     }
+
+    #[inline]
+    fn extend_one(&mut self, (k, v): (K, V)) {
+        self.insert(k, v);
+    }
 }
 
 #[stable(feature = "extend_ref", since = "1.2.0")]
@@ -1908,6 +1913,11 @@ impl<'a, K: Ord + Copy, V: Copy> Extend<(&'a K, &'a V)> for BTreeMap<K, V> {
     fn extend<I: IntoIterator<Item = (&'a K, &'a V)>>(&mut self, iter: I) {
         self.extend(iter.into_iter().map(|(&key, &value)| (key, value)));
     }
+
+    #[inline]
+    fn extend_one(&mut self, (&k, &v): (&'a K, &'a V)) {
+        self.insert(k, v);
+    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
diff --git a/src/liballoc/collections/btree/set.rs b/src/liballoc/collections/btree/set.rs
index dee5fb878ff..525ef38c32f 100644
--- a/src/liballoc/collections/btree/set.rs
+++ b/src/liballoc/collections/btree/set.rs
@@ -1152,6 +1152,11 @@ impl<T: Ord> Extend<T> for BTreeSet<T> {
             self.insert(elem);
         });
     }
+
+    #[inline]
+    fn extend_one(&mut self, elem: T) {
+        self.insert(elem);
+    }
 }
 
 #[stable(feature = "extend_ref", since = "1.2.0")]
@@ -1159,6 +1164,11 @@ impl<'a, T: 'a + Ord + Copy> Extend<&'a T> for BTreeSet<T> {
     fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
         self.extend(iter.into_iter().cloned());
     }
+
+    #[inline]
+    fn extend_one(&mut self, &elem: &'a T) {
+        self.insert(elem);
+    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
diff --git a/src/liballoc/collections/linked_list.rs b/src/liballoc/collections/linked_list.rs
index cc0f07b8227..85f2505f756 100644
--- a/src/liballoc/collections/linked_list.rs
+++ b/src/liballoc/collections/linked_list.rs
@@ -1748,6 +1748,11 @@ impl<T> Extend<T> for LinkedList<T> {
     fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
         <Self as SpecExtend<I>>::spec_extend(self, iter);
     }
+
+    #[inline]
+    fn extend_one(&mut self, elem: T) {
+        self.push_back(elem);
+    }
 }
 
 impl<I: IntoIterator> SpecExtend<I> for LinkedList<I::Item> {
@@ -1767,6 +1772,11 @@ impl<'a, T: 'a + Copy> Extend<&'a T> for LinkedList<T> {
     fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
         self.extend(iter.into_iter().cloned());
     }
+
+    #[inline]
+    fn extend_one(&mut self, &elem: &'a T) {
+        self.push_back(elem);
+    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
diff --git a/src/liballoc/collections/vec_deque.rs b/src/liballoc/collections/vec_deque.rs
index 540649c61b3..ae54d3971ba 100644
--- a/src/liballoc/collections/vec_deque.rs
+++ b/src/liballoc/collections/vec_deque.rs
@@ -2881,6 +2881,16 @@ impl<A> Extend<A> for VecDeque<A> {
             }
         }
     }
+
+    #[inline]
+    fn extend_one(&mut self, elem: A) {
+        self.push_back(elem);
+    }
+
+    #[inline]
+    fn extend_reserve(&mut self, additional: usize) {
+        self.reserve(additional);
+    }
 }
 
 #[stable(feature = "extend_ref", since = "1.2.0")]
@@ -2888,6 +2898,16 @@ impl<'a, T: 'a + Copy> Extend<&'a T> for VecDeque<T> {
     fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
         self.extend(iter.into_iter().cloned());
     }
+
+    #[inline]
+    fn extend_one(&mut self, &elem: &T) {
+        self.push_back(elem);
+    }
+
+    #[inline]
+    fn extend_reserve(&mut self, additional: usize) {
+        self.reserve(additional);
+    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
diff --git a/src/liballoc/lib.rs b/src/liballoc/lib.rs
index 7aaa91ee10d..9bcfc9457f5 100644
--- a/src/liballoc/lib.rs
+++ b/src/liballoc/lib.rs
@@ -93,6 +93,7 @@
 #![feature(container_error_extra)]
 #![feature(dropck_eyepatch)]
 #![feature(exact_size_is_empty)]
+#![feature(extend_one)]
 #![feature(fmt_internals)]
 #![feature(fn_traits)]
 #![feature(fundamental)]
diff --git a/src/liballoc/raw_vec.rs b/src/liballoc/raw_vec.rs
index 2bd4733db42..805dbfe2775 100644
--- a/src/liballoc/raw_vec.rs
+++ b/src/liballoc/raw_vec.rs
@@ -9,7 +9,7 @@ use core::ptr::{NonNull, Unique};
 use core::slice;
 
 use crate::alloc::{
-    handle_alloc_error, AllocErr,
+    handle_alloc_error,
     AllocInit::{self, *},
     AllocRef, Global, Layout,
     ReallocPlacement::{self, *},
@@ -118,6 +118,30 @@ impl<T> RawVec<T, Global> {
             RawVec::from_raw_parts(slice.as_mut_ptr(), slice.len())
         }
     }
+
+    /// Converts the entire buffer into `Box<[MaybeUninit<T>]>` with the specified `len`.
+    ///
+    /// Note that this will correctly reconstitute any `cap` changes
+    /// that may have been performed. (See description of type for details.)
+    ///
+    /// # Safety
+    ///
+    /// * `len` must be greater than or equal to the most recently requested capacity, and
+    /// * `len` must be less than or equal to `self.capacity()`.
+    ///
+    /// Note, that the requested capacity and `self.capacity()` could differ, as
+    /// an allocator could overallocate and return a greater memory block than requested.
+    pub unsafe fn into_box(self, len: usize) -> Box<[MaybeUninit<T>]> {
+        // Sanity-check one half of the safety requirement (we cannot check the other half).
+        debug_assert!(
+            len <= self.capacity(),
+            "`len` must be smaller than or equal to `self.capacity()`"
+        );
+
+        let me = ManuallyDrop::new(self);
+        let slice = slice::from_raw_parts_mut(me.ptr() as *mut MaybeUninit<T>, len);
+        Box::from_raw(slice)
+    }
 }
 
 impl<T, A: AllocRef> RawVec<T, A> {
@@ -211,13 +235,13 @@ impl<T, A: AllocRef> RawVec<T, A> {
         }
     }
 
-    /// Ensures that the buffer contains at least enough space to hold
-    /// `used_capacity + needed_extra_capacity` elements. If it doesn't already have
-    /// enough capacity, will reallocate enough space plus comfortable slack
-    /// space to get amortized `O(1)` behavior. Will limit this behavior
-    /// if it would needlessly cause itself to panic.
+    /// Ensures that the buffer contains at least enough space to hold `len +
+    /// additional` elements. If it doesn't already have enough capacity, will
+    /// reallocate enough space plus comfortable slack space to get amortized
+    /// `O(1)` behavior. Will limit this behavior if it would needlessly cause
+    /// itself to panic.
     ///
-    /// If `used_capacity` exceeds `self.capacity()`, this may fail to actually allocate
+    /// If `len` exceeds `self.capacity()`, this may fail to actually allocate
     /// the requested space. This is not really unsafe, but the unsafe
     /// code *you* write that relies on the behavior of this function may break.
     ///
@@ -263,8 +287,8 @@ impl<T, A: AllocRef> RawVec<T, A> {
     /// #   vector.push_all(&[1, 3, 5, 7, 9]);
     /// # }
     /// ```
-    pub fn reserve(&mut self, used_capacity: usize, needed_extra_capacity: usize) {
-        match self.try_reserve(used_capacity, needed_extra_capacity) {
+    pub fn reserve(&mut self, len: usize, additional: usize) {
+        match self.try_reserve(len, additional) {
             Err(CapacityOverflow) => capacity_overflow(),
             Err(AllocError { layout, .. }) => handle_alloc_error(layout),
             Ok(()) => { /* yay */ }
@@ -272,55 +296,23 @@ impl<T, A: AllocRef> RawVec<T, A> {
     }
 
     /// The same as `reserve`, but returns on errors instead of panicking or aborting.
-    pub fn try_reserve(
-        &mut self,
-        used_capacity: usize,
-        needed_extra_capacity: usize,
-    ) -> Result<(), TryReserveError> {
-        if self.needs_to_grow(used_capacity, needed_extra_capacity) {
-            self.grow_amortized(used_capacity, needed_extra_capacity, MayMove)
+    pub fn try_reserve(&mut self, len: usize, additional: usize) -> Result<(), TryReserveError> {
+        if self.needs_to_grow(len, additional) {
+            self.grow_amortized(len, additional)
         } else {
             Ok(())
         }
     }
 
-    /// Attempts to ensure that the buffer contains at least enough space to hold
-    /// `used_capacity + needed_extra_capacity` elements. If it doesn't already have
-    /// enough capacity, will reallocate in place enough space plus comfortable slack
-    /// space to get amortized `O(1)` behavior. Will limit this behaviour
-    /// if it would needlessly cause itself to panic.
+    /// Ensures that the buffer contains at least enough space to hold `len +
+    /// additional` elements. If it doesn't already, will reallocate the
+    /// minimum possible amount of memory necessary. Generally this will be
+    /// exactly the amount of memory necessary, but in principle the allocator
+    /// is free to give back more than we asked for.
     ///
-    /// If `used_capacity` exceeds `self.capacity()`, this may fail to actually allocate
-    /// the requested space. This is not really unsafe, but the unsafe
-    /// code *you* write that relies on the behavior of this function may break.
-    ///
-    /// Returns `true` if the reallocation attempt has succeeded.
-    ///
-    /// # Panics
-    ///
-    /// * Panics if the requested capacity exceeds `usize::MAX` bytes.
-    /// * Panics on 32-bit platforms if the requested capacity exceeds
-    ///   `isize::MAX` bytes.
-    pub fn reserve_in_place(&mut self, used_capacity: usize, needed_extra_capacity: usize) -> bool {
-        // This is more readable than putting this in one line:
-        // `!self.needs_to_grow(...) || self.grow(...).is_ok()`
-        if self.needs_to_grow(used_capacity, needed_extra_capacity) {
-            self.grow_amortized(used_capacity, needed_extra_capacity, InPlace).is_ok()
-        } else {
-            true
-        }
-    }
-
-    /// Ensures that the buffer contains at least enough space to hold
-    /// `used_capacity + needed_extra_capacity` elements. If it doesn't already,
-    /// will reallocate the minimum possible amount of memory necessary.
-    /// Generally this will be exactly the amount of memory necessary,
-    /// but in principle the allocator is free to give back more than
-    /// we asked for.
-    ///
-    /// If `used_capacity` exceeds `self.capacity()`, this may fail to actually allocate
-    /// the requested space. This is not really unsafe, but the unsafe
-    /// code *you* write that relies on the behavior of this function may break.
+    /// If `len` exceeds `self.capacity()`, this may fail to actually allocate
+    /// the requested space. This is not really unsafe, but the unsafe code
+    /// *you* write that relies on the behavior of this function may break.
     ///
     /// # Panics
     ///
@@ -331,8 +323,8 @@ impl<T, A: AllocRef> RawVec<T, A> {
     /// # Aborts
     ///
     /// Aborts on OOM.
-    pub fn reserve_exact(&mut self, used_capacity: usize, needed_extra_capacity: usize) {
-        match self.try_reserve_exact(used_capacity, needed_extra_capacity) {
+    pub fn reserve_exact(&mut self, len: usize, additional: usize) {
+        match self.try_reserve_exact(len, additional) {
             Err(CapacityOverflow) => capacity_overflow(),
             Err(AllocError { layout, .. }) => handle_alloc_error(layout),
             Ok(()) => { /* yay */ }
@@ -342,14 +334,10 @@ impl<T, A: AllocRef> RawVec<T, A> {
     /// The same as `reserve_exact`, but returns on errors instead of panicking or aborting.
     pub fn try_reserve_exact(
         &mut self,
-        used_capacity: usize,
-        needed_extra_capacity: usize,
+        len: usize,
+        additional: usize,
     ) -> Result<(), TryReserveError> {
-        if self.needs_to_grow(used_capacity, needed_extra_capacity) {
-            self.grow_exact(used_capacity, needed_extra_capacity)
-        } else {
-            Ok(())
-        }
+        if self.needs_to_grow(len, additional) { self.grow_exact(len, additional) } else { Ok(()) }
     }
 
     /// Shrinks the allocation down to the specified amount. If the given amount
@@ -374,8 +362,8 @@ impl<T, A: AllocRef> RawVec<T, A> {
 impl<T, A: AllocRef> RawVec<T, A> {
     /// Returns if the buffer needs to grow to fulfill the needed extra capacity.
     /// Mainly used to make inlining reserve-calls possible without inlining `grow`.
-    fn needs_to_grow(&self, used_capacity: usize, needed_extra_capacity: usize) -> bool {
-        needed_extra_capacity > self.capacity().wrapping_sub(used_capacity)
+    fn needs_to_grow(&self, len: usize, additional: usize) -> bool {
+        additional > self.capacity().wrapping_sub(len)
     }
 
     fn capacity_from_bytes(excess: usize) -> usize {
@@ -395,14 +383,9 @@ impl<T, A: AllocRef> RawVec<T, A> {
     // so that all of the code that depends on `T` is within it, while as much
     // of the code that doesn't depend on `T` as possible is in functions that
     // are non-generic over `T`.
-    fn grow_amortized(
-        &mut self,
-        used_capacity: usize,
-        needed_extra_capacity: usize,
-        placement: ReallocPlacement,
-    ) -> Result<(), TryReserveError> {
+    fn grow_amortized(&mut self, len: usize, additional: usize) -> Result<(), TryReserveError> {
         // This is ensured by the calling contexts.
-        debug_assert!(needed_extra_capacity > 0);
+        debug_assert!(additional > 0);
 
         if mem::size_of::<T>() == 0 {
             // Since we return a capacity of `usize::MAX` when `elem_size` is
@@ -411,8 +394,7 @@ impl<T, A: AllocRef> RawVec<T, A> {
         }
 
         // Nothing we can really do about these checks, sadly.
-        let required_cap =
-            used_capacity.checked_add(needed_extra_capacity).ok_or(CapacityOverflow)?;
+        let required_cap = len.checked_add(additional).ok_or(CapacityOverflow)?;
 
         // This guarantees exponential growth. The doubling cannot overflow
         // because `cap <= isize::MAX` and the type of `cap` is `usize`.
@@ -437,7 +419,7 @@ impl<T, A: AllocRef> RawVec<T, A> {
         let new_layout = Layout::array::<T>(cap);
 
         // `finish_grow` is non-generic over `T`.
-        let memory = finish_grow(new_layout, placement, self.current_memory(), &mut self.alloc)?;
+        let memory = finish_grow(new_layout, self.current_memory(), &mut self.alloc)?;
         self.set_memory(memory);
         Ok(())
     }
@@ -445,22 +427,18 @@ impl<T, A: AllocRef> RawVec<T, A> {
     // The constraints on this method are much the same as those on
     // `grow_amortized`, but this method is usually instantiated less often so
     // it's less critical.
-    fn grow_exact(
-        &mut self,
-        used_capacity: usize,
-        needed_extra_capacity: usize,
-    ) -> Result<(), TryReserveError> {
+    fn grow_exact(&mut self, len: usize, additional: usize) -> Result<(), TryReserveError> {
         if mem::size_of::<T>() == 0 {
             // Since we return a capacity of `usize::MAX` when the type size is
             // 0, getting to here necessarily means the `RawVec` is overfull.
             return Err(CapacityOverflow);
         }
 
-        let cap = used_capacity.checked_add(needed_extra_capacity).ok_or(CapacityOverflow)?;
+        let cap = len.checked_add(additional).ok_or(CapacityOverflow)?;
         let new_layout = Layout::array::<T>(cap);
 
         // `finish_grow` is non-generic over `T`.
-        let memory = finish_grow(new_layout, MayMove, self.current_memory(), &mut self.alloc)?;
+        let memory = finish_grow(new_layout, self.current_memory(), &mut self.alloc)?;
         self.set_memory(memory);
         Ok(())
     }
@@ -494,7 +472,6 @@ impl<T, A: AllocRef> RawVec<T, A> {
 // much smaller than the number of `T` types.)
 fn finish_grow<A>(
     new_layout: Result<Layout, LayoutErr>,
-    placement: ReallocPlacement,
     current_memory: Option<(NonNull<u8>, Layout)>,
     alloc: &mut A,
 ) -> Result<MemoryBlock, TryReserveError>
@@ -508,44 +485,15 @@ where
 
     let memory = if let Some((ptr, old_layout)) = current_memory {
         debug_assert_eq!(old_layout.align(), new_layout.align());
-        unsafe { alloc.grow(ptr, old_layout, new_layout.size(), placement, Uninitialized) }
+        unsafe { alloc.grow(ptr, old_layout, new_layout.size(), MayMove, Uninitialized) }
     } else {
-        match placement {
-            MayMove => alloc.alloc(new_layout, Uninitialized),
-            InPlace => Err(AllocErr),
-        }
+        alloc.alloc(new_layout, Uninitialized)
     }
     .map_err(|_| AllocError { layout: new_layout, non_exhaustive: () })?;
 
     Ok(memory)
 }
 
-impl<T> RawVec<T, Global> {
-    /// Converts the entire buffer into `Box<[MaybeUninit<T>]>` with the specified `len`.
-    ///
-    /// Note that this will correctly reconstitute any `cap` changes
-    /// that may have been performed. (See description of type for details.)
-    ///
-    /// # Safety
-    ///
-    /// * `len` must be greater than or equal to the most recently requested capacity, and
-    /// * `len` must be less than or equal to `self.capacity()`.
-    ///
-    /// Note, that the requested capacity and `self.capacity()` could differ, as
-    /// an allocator could overallocate and return a greater memory block than requested.
-    pub unsafe fn into_box(self, len: usize) -> Box<[MaybeUninit<T>]> {
-        // Sanity-check one half of the safety requirement (we cannot check the other half).
-        debug_assert!(
-            len <= self.capacity(),
-            "`len` must be smaller than or equal to `self.capacity()`"
-        );
-
-        let me = ManuallyDrop::new(self);
-        let slice = slice::from_raw_parts_mut(me.ptr() as *mut MaybeUninit<T>, len);
-        Box::from_raw(slice)
-    }
-}
-
 unsafe impl<#[may_dangle] T, A: AllocRef> Drop for RawVec<T, A> {
     /// Frees the memory owned by the `RawVec` *without* trying to drop its contents.
     fn drop(&mut self) {
diff --git a/src/liballoc/rc.rs b/src/liballoc/rc.rs
index ad96a138d7e..925bc7d3c02 100644
--- a/src/liballoc/rc.rs
+++ b/src/liballoc/rc.rs
@@ -580,8 +580,6 @@ impl<T: ?Sized> Rc<T> {
     /// # Examples
     ///
     /// ```
-    /// #![feature(weak_into_raw)]
-    ///
     /// use std::rc::Rc;
     ///
     /// let x = Rc::new("hello".to_owned());
@@ -590,7 +588,7 @@ impl<T: ?Sized> Rc<T> {
     /// assert_eq!(x_ptr, Rc::as_ptr(&y));
     /// assert_eq!(unsafe { &*x_ptr }, "hello");
     /// ```
-    #[unstable(feature = "weak_into_raw", issue = "60728")]
+    #[stable(feature = "weak_into_raw", since = "1.45.0")]
     pub fn as_ptr(this: &Self) -> *const T {
         let ptr: *mut RcBox<T> = NonNull::as_ptr(this.ptr);
         let fake_ptr = ptr as *mut T;
@@ -1681,8 +1679,6 @@ impl<T> Weak<T> {
     /// # Examples
     ///
     /// ```
-    /// #![feature(weak_into_raw)]
-    ///
     /// use std::rc::Rc;
     /// use std::ptr;
     ///
@@ -1700,7 +1696,7 @@ impl<T> Weak<T> {
     /// ```
     ///
     /// [`null`]: ../../std/ptr/fn.null.html
-    #[unstable(feature = "weak_into_raw", issue = "60728")]
+    #[stable(feature = "weak_into_raw", since = "1.45.0")]
     pub fn as_ptr(&self) -> *const T {
         let offset = data_offset_sized::<T>();
         let ptr = self.ptr.cast::<u8>().as_ptr().wrapping_offset(offset);
@@ -1718,8 +1714,6 @@ impl<T> Weak<T> {
     /// # Examples
     ///
     /// ```
-    /// #![feature(weak_into_raw)]
-    ///
     /// use std::rc::{Rc, Weak};
     ///
     /// let strong = Rc::new("hello".to_owned());
@@ -1735,7 +1729,7 @@ impl<T> Weak<T> {
     ///
     /// [`from_raw`]: struct.Weak.html#method.from_raw
     /// [`as_ptr`]: struct.Weak.html#method.as_ptr
-    #[unstable(feature = "weak_into_raw", issue = "60728")]
+    #[stable(feature = "weak_into_raw", since = "1.45.0")]
     pub fn into_raw(self) -> *const T {
         let result = self.as_ptr();
         mem::forget(self);
@@ -1762,8 +1756,6 @@ impl<T> Weak<T> {
     /// # Examples
     ///
     /// ```
-    /// #![feature(weak_into_raw)]
-    ///
     /// use std::rc::{Rc, Weak};
     ///
     /// let strong = Rc::new("hello".to_owned());
@@ -1788,7 +1780,7 @@ impl<T> Weak<T> {
     /// [`Weak`]: struct.Weak.html
     /// [`new`]: struct.Weak.html#method.new
     /// [`forget`]: ../../std/mem/fn.forget.html
-    #[unstable(feature = "weak_into_raw", issue = "60728")]
+    #[stable(feature = "weak_into_raw", since = "1.45.0")]
     pub unsafe fn from_raw(ptr: *const T) -> Self {
         if ptr.is_null() {
             Self::new()
@@ -2043,11 +2035,7 @@ trait RcBoxPtr<T: ?Sized> {
         // nevertheless, we insert an abort here to hint LLVM at
         // an otherwise missed optimization.
         if strong == 0 || strong == usize::max_value() {
-            // remove `unsafe` on bootstrap bump
-            #[cfg_attr(not(bootstrap), allow(unused_unsafe))]
-            unsafe {
-                abort();
-            }
+            abort();
         }
         self.inner().strong.set(strong + 1);
     }
@@ -2071,11 +2059,7 @@ trait RcBoxPtr<T: ?Sized> {
         // nevertheless, we insert an abort here to hint LLVM at
         // an otherwise missed optimization.
         if weak == 0 || weak == usize::max_value() {
-            // remove `unsafe` on bootstrap bump
-            #[cfg_attr(not(bootstrap), allow(unused_unsafe))]
-            unsafe {
-                abort();
-            }
+            abort();
         }
         self.inner().weak.set(weak + 1);
     }
diff --git a/src/liballoc/string.rs b/src/liballoc/string.rs
index f3fe1adebb1..0378ff5362a 100644
--- a/src/liballoc/string.rs
+++ b/src/liballoc/string.rs
@@ -1799,6 +1799,16 @@ impl Extend<char> for String {
         self.reserve(lower_bound);
         iterator.for_each(move |c| self.push(c));
     }
+
+    #[inline]
+    fn extend_one(&mut self, c: char) {
+        self.push(c);
+    }
+
+    #[inline]
+    fn extend_reserve(&mut self, additional: usize) {
+        self.reserve(additional);
+    }
 }
 
 #[stable(feature = "extend_ref", since = "1.2.0")]
@@ -1806,6 +1816,16 @@ impl<'a> Extend<&'a char> for String {
     fn extend<I: IntoIterator<Item = &'a char>>(&mut self, iter: I) {
         self.extend(iter.into_iter().cloned());
     }
+
+    #[inline]
+    fn extend_one(&mut self, &c: &'a char) {
+        self.push(c);
+    }
+
+    #[inline]
+    fn extend_reserve(&mut self, additional: usize) {
+        self.reserve(additional);
+    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -1813,6 +1833,11 @@ impl<'a> Extend<&'a str> for String {
     fn extend<I: IntoIterator<Item = &'a str>>(&mut self, iter: I) {
         iter.into_iter().for_each(move |s| self.push_str(s));
     }
+
+    #[inline]
+    fn extend_one(&mut self, s: &'a str) {
+        self.push_str(s);
+    }
 }
 
 #[stable(feature = "extend_string", since = "1.4.0")]
@@ -1820,6 +1845,11 @@ impl Extend<String> for String {
     fn extend<I: IntoIterator<Item = String>>(&mut self, iter: I) {
         iter.into_iter().for_each(move |s| self.push_str(&s));
     }
+
+    #[inline]
+    fn extend_one(&mut self, s: String) {
+        self.push_str(&s);
+    }
 }
 
 #[stable(feature = "herd_cows", since = "1.19.0")]
@@ -1827,6 +1857,11 @@ impl<'a> Extend<Cow<'a, str>> for String {
     fn extend<I: IntoIterator<Item = Cow<'a, str>>>(&mut self, iter: I) {
         iter.into_iter().for_each(move |s| self.push_str(&s));
     }
+
+    #[inline]
+    fn extend_one(&mut self, s: Cow<'a, str>) {
+        self.push_str(&s);
+    }
 }
 
 /// A convenience impl that delegates to the impl for `&str`.
diff --git a/src/liballoc/sync.rs b/src/liballoc/sync.rs
index b7be8042ea4..cd4172d6a2d 100644
--- a/src/liballoc/sync.rs
+++ b/src/liballoc/sync.rs
@@ -579,8 +579,6 @@ impl<T: ?Sized> Arc<T> {
     /// # Examples
     ///
     /// ```
-    /// #![feature(weak_into_raw)]
-    ///
     /// use std::sync::Arc;
     ///
     /// let x = Arc::new("hello".to_owned());
@@ -589,7 +587,7 @@ impl<T: ?Sized> Arc<T> {
     /// assert_eq!(x_ptr, Arc::as_ptr(&y));
     /// assert_eq!(unsafe { &*x_ptr }, "hello");
     /// ```
-    #[unstable(feature = "weak_into_raw", issue = "60728")]
+    #[stable(feature = "weak_into_raw", since = "1.45.0")]
     pub fn as_ptr(this: &Self) -> *const T {
         let ptr: *mut ArcInner<T> = NonNull::as_ptr(this.ptr);
         let fake_ptr = ptr as *mut T;
@@ -867,12 +865,10 @@ impl<T: ?Sized> Arc<T> {
     unsafe fn drop_slow(&mut self) {
         // Destroy the data at this time, even though we may not free the box
         // allocation itself (there may still be weak pointers lying around).
-        ptr::drop_in_place(&mut self.ptr.as_mut().data);
+        ptr::drop_in_place(Self::get_mut_unchecked(self));
 
-        if self.inner().weak.fetch_sub(1, Release) == 1 {
-            acquire!(self.inner().weak);
-            Global.dealloc(self.ptr.cast(), Layout::for_value(self.ptr.as_ref()))
-        }
+        // Drop the weak ref collectively held by all strong references
+        drop(Weak { ptr: self.ptr });
     }
 
     #[inline]
@@ -1097,11 +1093,7 @@ impl<T: ?Sized> Clone for Arc<T> {
         // We abort because such a program is incredibly degenerate, and we
         // don't care to support it.
         if old_size > MAX_REFCOUNT {
-            // remove `unsafe` on bootstrap bump
-            #[cfg_attr(not(bootstrap), allow(unused_unsafe))]
-            unsafe {
-                abort();
-            }
+            abort();
         }
 
         Self::from_inner(self.ptr)
@@ -1204,7 +1196,7 @@ impl<T: Clone> Arc<T> {
 
         // As with `get_mut()`, the unsafety is ok because our reference was
         // either unique to begin with, or became one upon cloning the contents.
-        unsafe { &mut this.ptr.as_mut().data }
+        unsafe { Self::get_mut_unchecked(this) }
     }
 }
 
@@ -1280,7 +1272,9 @@ impl<T: ?Sized> Arc<T> {
     #[inline]
     #[unstable(feature = "get_mut_unchecked", issue = "63292")]
     pub unsafe fn get_mut_unchecked(this: &mut Self) -> &mut T {
-        &mut this.ptr.as_mut().data
+        // We are careful to *not* create a reference covering the "count" fields, as
+        // this would alias with concurrent access to the reference counts (e.g. by `Weak`).
+        &mut (*this.ptr.as_ptr()).data
     }
 
     /// Determine whether this is the unique reference (including weak refs) to
@@ -1449,8 +1443,6 @@ impl<T> Weak<T> {
     /// # Examples
     ///
     /// ```
-    /// #![feature(weak_into_raw)]
-    ///
     /// use std::sync::Arc;
     /// use std::ptr;
     ///
@@ -1468,7 +1460,7 @@ impl<T> Weak<T> {
     /// ```
     ///
     /// [`null`]: ../../std/ptr/fn.null.html
-    #[unstable(feature = "weak_into_raw", issue = "60728")]
+    #[stable(feature = "weak_into_raw", since = "1.45.0")]
     pub fn as_ptr(&self) -> *const T {
         let offset = data_offset_sized::<T>();
         let ptr = self.ptr.cast::<u8>().as_ptr().wrapping_offset(offset);
@@ -1486,8 +1478,6 @@ impl<T> Weak<T> {
     /// # Examples
     ///
     /// ```
-    /// #![feature(weak_into_raw)]
-    ///
     /// use std::sync::{Arc, Weak};
     ///
     /// let strong = Arc::new("hello".to_owned());
@@ -1503,7 +1493,7 @@ impl<T> Weak<T> {
     ///
     /// [`from_raw`]: struct.Weak.html#method.from_raw
     /// [`as_ptr`]: struct.Weak.html#method.as_ptr
-    #[unstable(feature = "weak_into_raw", issue = "60728")]
+    #[stable(feature = "weak_into_raw", since = "1.45.0")]
     pub fn into_raw(self) -> *const T {
         let result = self.as_ptr();
         mem::forget(self);
@@ -1531,8 +1521,6 @@ impl<T> Weak<T> {
     /// # Examples
     ///
     /// ```
-    /// #![feature(weak_into_raw)]
-    ///
     /// use std::sync::{Arc, Weak};
     ///
     /// let strong = Arc::new("hello".to_owned());
@@ -1557,7 +1545,7 @@ impl<T> Weak<T> {
     /// [`Weak`]: struct.Weak.html
     /// [`Arc`]: struct.Arc.html
     /// [`forget`]: ../../std/mem/fn.forget.html
-    #[unstable(feature = "weak_into_raw", issue = "60728")]
+    #[stable(feature = "weak_into_raw", since = "1.45.0")]
     pub unsafe fn from_raw(ptr: *const T) -> Self {
         if ptr.is_null() {
             Self::new()
@@ -1571,6 +1559,13 @@ impl<T> Weak<T> {
     }
 }
 
+/// Helper type to allow accessing the reference counts without
+/// making any assertions about the data field.
+struct WeakInner<'a> {
+    weak: &'a atomic::AtomicUsize,
+    strong: &'a atomic::AtomicUsize,
+}
+
 impl<T: ?Sized> Weak<T> {
     /// Attempts to upgrade the `Weak` pointer to an [`Arc`], delaying
     /// dropping of the inner value if successful.
@@ -1617,11 +1612,7 @@ impl<T: ?Sized> Weak<T> {
 
             // See comments in `Arc::clone` for why we do this (for `mem::forget`).
             if n > MAX_REFCOUNT {
-                // remove `unsafe` on bootstrap bump
-                #[cfg_attr(not(bootstrap), allow(unused_unsafe))]
-                unsafe {
-                    abort();
-                }
+                abort();
             }
 
             // Relaxed is valid for the same reason it is on Arc's Clone impl
@@ -1678,8 +1669,18 @@ impl<T: ?Sized> Weak<T> {
     /// Returns `None` when the pointer is dangling and there is no allocated `ArcInner`,
     /// (i.e., when this `Weak` was created by `Weak::new`).
     #[inline]
-    fn inner(&self) -> Option<&ArcInner<T>> {
-        if is_dangling(self.ptr) { None } else { Some(unsafe { self.ptr.as_ref() }) }
+    fn inner(&self) -> Option<WeakInner<'_>> {
+        if is_dangling(self.ptr) {
+            None
+        } else {
+            // We are careful to *not* create a reference covering the "data" field, as
+            // the field may be mutated concurrently (for example, if the last `Arc`
+            // is dropped, the data field will be dropped in-place).
+            Some(unsafe {
+                let ptr = self.ptr.as_ptr();
+                WeakInner { strong: &(*ptr).strong, weak: &(*ptr).weak }
+            })
+        }
     }
 
     /// Returns `true` if the two `Weak`s point to the same allocation (similar to
@@ -1758,10 +1759,7 @@ impl<T: ?Sized> Clone for Weak<T> {
 
         // See comments in Arc::clone() for why we do this (for mem::forget).
         if old_size > MAX_REFCOUNT {
-            #[cfg_attr(not(bootstrap), allow(unused_unsafe))] // remove `unsafe` on bootstrap bump
-            unsafe {
-                abort();
-            }
+            abort();
         }
 
         Weak { ptr: self.ptr }
diff --git a/src/liballoc/tests/boxed.rs b/src/liballoc/tests/boxed.rs
index 66782ecbeb7..5377485da8f 100644
--- a/src/liballoc/tests/boxed.rs
+++ b/src/liballoc/tests/boxed.rs
@@ -16,3 +16,36 @@ fn unitialized_zero_size_box() {
         NonNull::<MaybeUninit<String>>::dangling().as_ptr(),
     );
 }
+
+#[derive(Clone, PartialEq, Eq, Debug)]
+struct Dummy {
+    _data: u8,
+}
+
+#[test]
+fn box_clone_and_clone_from_equivalence() {
+    for size in (0..8).map(|i| 2usize.pow(i)) {
+        let control = vec![Dummy { _data: 42 }; size].into_boxed_slice();
+        let clone = control.clone();
+        let mut copy = vec![Dummy { _data: 84 }; size].into_boxed_slice();
+        copy.clone_from(&control);
+        assert_eq!(control, clone);
+        assert_eq!(control, copy);
+    }
+}
+
+/// This test might give a false positive in case the box realocates, but the alocator keeps the
+/// original pointer.
+///
+/// On the other hand it won't give a false negative, if it fails than the memory was definitly not
+/// reused
+#[test]
+fn box_clone_from_ptr_stability() {
+    for size in (0..8).map(|i| 2usize.pow(i)) {
+        let control = vec![Dummy { _data: 42 }; size].into_boxed_slice();
+        let mut copy = vec![Dummy { _data: 84 }; size].into_boxed_slice();
+        let copy_raw = copy.as_ptr() as usize;
+        copy.clone_from(&control);
+        assert_eq!(copy.as_ptr() as usize, copy_raw);
+    }
+}
diff --git a/src/liballoc/tests/vec.rs b/src/liballoc/tests/vec.rs
index b16044d9640..b73fd95ab6a 100644
--- a/src/liballoc/tests/vec.rs
+++ b/src/liballoc/tests/vec.rs
@@ -16,7 +16,7 @@ impl Drop for DropCounter<'_> {
 
 #[test]
 fn test_small_vec_struct() {
-    assert!(size_of::<Vec<u8>>() == size_of::<usize>() * 3);
+    assert_eq!(size_of::<Vec<u8>>(), size_of::<usize>() * 3);
 }
 
 #[test]
diff --git a/src/liballoc/vec.rs b/src/liballoc/vec.rs
index d26cd77aae4..2226737757b 100644
--- a/src/liballoc/vec.rs
+++ b/src/liballoc/vec.rs
@@ -343,14 +343,19 @@ impl<T> Vec<T> {
     ///
     /// // The vector contains no items, even though it has capacity for more
     /// assert_eq!(vec.len(), 0);
+    /// assert_eq!(vec.capacity(), 10);
     ///
     /// // These are all done without reallocating...
     /// for i in 0..10 {
     ///     vec.push(i);
     /// }
+    /// assert_eq!(vec.len(), 10);
+    /// assert_eq!(vec.capacity(), 10);
     ///
     /// // ...but this may make the vector reallocate
     /// vec.push(11);
+    /// assert_eq!(vec.len(), 11);
+    /// assert!(vec.capacity() >= 11);
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
@@ -979,7 +984,7 @@ impl<T> Vec<T> {
             // bounds check above succeeds there must be a last element (which
             // can be self[index] itself).
             let last = ptr::read(self.as_ptr().add(len - 1));
-            let hole: *mut T = self.as_mut_ptr().add(index);
+            let hole = self.as_mut_ptr().add(index);
             self.set_len(len - 1);
             ptr::replace(hole, last)
         }
@@ -1901,6 +1906,22 @@ unsafe impl<T: ?Sized> IsZero for Option<Box<T>> {
 ////////////////////////////////////////////////////////////////////////////////
 
 #[stable(feature = "rust1", since = "1.0.0")]
+impl<T> ops::Deref for Vec<T> {
+    type Target = [T];
+
+    fn deref(&self) -> &[T] {
+        unsafe { slice::from_raw_parts(self.as_ptr(), self.len) }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> ops::DerefMut for Vec<T> {
+    fn deref_mut(&mut self) -> &mut [T] {
+        unsafe { slice::from_raw_parts_mut(self.as_mut_ptr(), self.len) }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
 impl<T: Clone> Clone for Vec<T> {
     #[cfg(not(test))]
     fn clone(&self) -> Vec<T> {
@@ -1956,22 +1977,6 @@ impl<T, I: SliceIndex<[T]>> IndexMut<I> for Vec<T> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T> ops::Deref for Vec<T> {
-    type Target = [T];
-
-    fn deref(&self) -> &[T] {
-        unsafe { slice::from_raw_parts(self.as_ptr(), self.len) }
-    }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T> ops::DerefMut for Vec<T> {
-    fn deref_mut(&mut self) -> &mut [T] {
-        unsafe { slice::from_raw_parts_mut(self.as_mut_ptr(), self.len) }
-    }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
 impl<T> FromIterator<T> for Vec<T> {
     #[inline]
     fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Vec<T> {
@@ -2045,6 +2050,16 @@ impl<T> Extend<T> for Vec<T> {
     fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
         <Self as SpecExtend<T, I::IntoIter>>::spec_extend(self, iter.into_iter())
     }
+
+    #[inline]
+    fn extend_one(&mut self, item: T) {
+        self.push(item);
+    }
+
+    #[inline]
+    fn extend_reserve(&mut self, additional: usize) {
+        self.reserve(additional);
+    }
 }
 
 // Specialization trait used for Vec::from_iter and Vec::extend
@@ -2316,6 +2331,16 @@ impl<'a, T: 'a + Copy> Extend<&'a T> for Vec<T> {
     fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
         self.spec_extend(iter.into_iter())
     }
+
+    #[inline]
+    fn extend_one(&mut self, &item: &'a T) {
+        self.push(item);
+    }
+
+    #[inline]
+    fn extend_reserve(&mut self, additional: usize) {
+        self.reserve(additional);
+    }
 }
 
 macro_rules! __impl_slice_eq1 {
@@ -2603,6 +2628,13 @@ impl<T> IntoIter<T> {
     }
 }
 
+#[stable(feature = "vec_intoiter_as_ref", since = "1.46.0")]
+impl<T> AsRef<[T]> for IntoIter<T> {
+    fn as_ref(&self) -> &[T] {
+        self.as_slice()
+    }
+}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 unsafe impl<T: Send> Send for IntoIter<T> {}
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -2945,12 +2977,12 @@ impl<T> Drain<'_, T> {
     }
 
     /// Makes room for inserting more elements before the tail.
-    unsafe fn move_tail(&mut self, extra_capacity: usize) {
+    unsafe fn move_tail(&mut self, additional: usize) {
         let vec = self.vec.as_mut();
-        let used_capacity = self.tail_start + self.tail_len;
-        vec.buf.reserve(used_capacity, extra_capacity);
+        let len = self.tail_start + self.tail_len;
+        vec.buf.reserve(len, additional);
 
-        let new_tail_start = self.tail_start + extra_capacity;
+        let new_tail_start = self.tail_start + additional;
         let src = vec.as_ptr().add(self.tail_start);
         let dst = vec.as_mut_ptr().add(new_tail_start);
         ptr::copy(src, dst, self.tail_len);