Merge tag 'rust-6.5' of https://github.com/Rust-for-Linux/linux

Pull rust updates from Miguel Ojeda:
 "A fairly small one in terms of feature additions. Most of the changes
  in terms of lines come from the upgrade to the new version of the
  toolchain (which in turn is big due to the vendored 'alloc' crate).

  Upgrade to Rust 1.68.2:

   - This is the first such upgrade, and we will try to update it often
     from now on, in order to remain close to the latest release, until
     a minimum version (which is "in the future") can be established.

     The upgrade brings the stabilization of 4 features we used (and 2
     more that we used in our old 'rust' branch).

     Commit 3ed03f4da06e ("rust: upgrade to Rust 1.68.2") contains the
     details and rationale.

  pin-init API:

   - Several internal improvements and fixes to the pin-init API, e.g.
     allowing to use 'Self' in a struct definition with '#[pin_data]'.

  'error' module:

   - New 'name()' method for the 'Error' type (with 'errname()'
     integration), used to implement the 'Debug' trait for 'Error'.

   - Add error codes from 'include/linux/errno.h' to the list of Rust
     'Error' constants.

   - Allow specifying error type on the 'Result' type (with the default
     still being our usual 'Error' type).

  'str' module:

   - 'TryFrom' implementation for 'CStr', and new 'to_cstring()' method
     based on it.

  'sync' module:

   - Implement 'AsRef' trait for 'Arc', allowing to use 'Arc' in code
     that is generic over smart pointer types.

   - Add 'ptr_eq' method to 'Arc' for easier, less error prone
     comparison between two 'Arc' pointers.

   - Reword the 'Send' safety comment for 'Arc', and avoid referencing
     it from the 'Sync' one.

  'task' module:

   - Implement 'Send' marker for 'Task'.

  'types' module:

   - Implement 'Send' and 'Sync' markers for 'ARef<T>' when 'T' is
     'AlwaysRefCounted', 'Send' and 'Sync'.

  Other changes:

   - Documentation improvements and '.gitattributes' change to start
     using the Rust diff driver"

* tag 'rust-6.5' of https://github.com/Rust-for-Linux/linux:
  rust: error: `impl Debug` for `Error` with `errname()` integration
  rust: task: add `Send` marker to `Task`
  rust: specify when `ARef` is thread safe
  rust: sync: reword the `Arc` safety comment for `Sync`
  rust: sync: reword the `Arc` safety comment for `Send`
  rust: sync: implement `AsRef<T>` for `Arc<T>`
  rust: sync: add `Arc::ptr_eq`
  rust: error: add missing error codes
  rust: str: add conversion from `CStr` to `CString`
  rust: error: allow specifying error type on `Result`
  rust: init: update macro expansion example in docs
  rust: macros: replace Self with the concrete type in #[pin_data]
  rust: macros: refactor generics parsing of `#[pin_data]` into its own function
  rust: macros: fix usage of `#[allow]` in `quote!`
  docs: rust: point directly to the standalone installers
  .gitattributes: set diff driver for Rust source code files
  rust: upgrade to Rust 1.68.2
  rust: arc: fix intra-doc link in `Arc<T>::init`
  rust: alloc: clarify what is the upstream version

7 files changed, 685 insertions, 209 deletions

diff --git a/rust/alloc/vec/drain.rs b/rust/alloc/vec/drain.rs
index b6a5f98e4fcd..d503d2f478ce 100644
--- a/rust/alloc/vec/drain.rs
+++ b/rust/alloc/vec/drain.rs
@@ -3,7 +3,7 @@
 use crate::alloc::{Allocator, Global};
 use core::fmt;
 use core::iter::{FusedIterator, TrustedLen};
-use core::mem;
+use core::mem::{self, ManuallyDrop, SizedTypeProperties};
 use core::ptr::{self, NonNull};
 use core::slice::{self};
 
@@ -67,6 +67,77 @@ impl<'a, T, A: Allocator> Drain<'a, T, A> {
     pub fn allocator(&self) -> &A {
         unsafe { self.vec.as_ref().allocator() }
     }
+
+    /// Keep unyielded elements in the source `Vec`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(drain_keep_rest)]
+    ///
+    /// let mut vec = vec!['a', 'b', 'c'];
+    /// let mut drain = vec.drain(..);
+    ///
+    /// assert_eq!(drain.next().unwrap(), 'a');
+    ///
+    /// // This call keeps 'b' and 'c' in the vec.
+    /// drain.keep_rest();
+    ///
+    /// // If we wouldn't call `keep_rest()`,
+    /// // `vec` would be empty.
+    /// assert_eq!(vec, ['b', 'c']);
+    /// ```
+    #[unstable(feature = "drain_keep_rest", issue = "101122")]
+    pub fn keep_rest(self) {
+        // At this moment layout looks like this:
+        //
+        // [head] [yielded by next] [unyielded] [yielded by next_back] [tail]
+        //        ^-- start         \_________/-- unyielded_len        \____/-- self.tail_len
+        //                          ^-- unyielded_ptr                  ^-- tail
+        //
+        // Normally `Drop` impl would drop [unyielded] and then move [tail] to the `start`.
+        // Here we want to
+        // 1. Move [unyielded] to `start`
+        // 2. Move [tail] to a new start at `start + len(unyielded)`
+        // 3. Update length of the original vec to `len(head) + len(unyielded) + len(tail)`
+        //    a. In case of ZST, this is the only thing we want to do
+        // 4. Do *not* drop self, as everything is put in a consistent state already, there is nothing to do
+        let mut this = ManuallyDrop::new(self);
+
+        unsafe {
+            let source_vec = this.vec.as_mut();
+
+            let start = source_vec.len();
+            let tail = this.tail_start;
+
+            let unyielded_len = this.iter.len();
+            let unyielded_ptr = this.iter.as_slice().as_ptr();
+
+            // ZSTs have no identity, so we don't need to move them around.
+            let needs_move = mem::size_of::<T>() != 0;
+
+            if needs_move {
+                let start_ptr = source_vec.as_mut_ptr().add(start);
+
+                // memmove back unyielded elements
+                if unyielded_ptr != start_ptr {
+                    let src = unyielded_ptr;
+                    let dst = start_ptr;
+
+                    ptr::copy(src, dst, unyielded_len);
+                }
+
+                // memmove back untouched tail
+                if tail != (start + unyielded_len) {
+                    let src = source_vec.as_ptr().add(tail);
+                    let dst = start_ptr.add(unyielded_len);
+                    ptr::copy(src, dst, this.tail_len);
+                }
+            }
+
+            source_vec.set_len(start + unyielded_len + this.tail_len);
+        }
+    }
 }
 
 #[stable(feature = "vec_drain_as_slice", since = "1.46.0")]
@@ -133,7 +204,7 @@ impl<T, A: Allocator> Drop for Drain<'_, T, A> {
 
         let mut vec = self.vec;
 
-        if mem::size_of::<T>() == 0 {
+        if T::IS_ZST {
             // ZSTs have no identity, so we don't need to move them around, we only need to drop the correct amount.
             // this can be achieved by manipulating the Vec length instead of moving values out from `iter`.
             unsafe {
@@ -154,9 +225,9 @@ impl<T, A: Allocator> Drop for Drain<'_, T, A> {
         }
 
         // as_slice() must only be called when iter.len() is > 0 because
-        // vec::Splice modifies vec::Drain fields and may grow the vec which would invalidate
-        // the iterator's internal pointers. Creating a reference to deallocated memory
-        // is invalid even when it is zero-length
+        // it also gets touched by vec::Splice which may turn it into a dangling pointer
+        // which would make it and the vec pointer point to different allocations which would
+        // lead to invalid pointer arithmetic below.
         let drop_ptr = iter.as_slice().as_ptr();
 
         unsafe {
diff --git a/rust/alloc/vec/drain_filter.rs b/rust/alloc/vec/drain_filter.rs
index b04fce041622..4b019220657d 100644
--- a/rust/alloc/vec/drain_filter.rs
+++ b/rust/alloc/vec/drain_filter.rs
@@ -1,8 +1,9 @@
 // SPDX-License-Identifier: Apache-2.0 OR MIT
 
 use crate::alloc::{Allocator, Global};
-use core::ptr::{self};
-use core::slice::{self};
+use core::mem::{self, ManuallyDrop};
+use core::ptr;
+use core::slice;
 
 use super::Vec;
 
@@ -56,6 +57,61 @@ where
     pub fn allocator(&self) -> &A {
         self.vec.allocator()
     }
+
+    /// Keep unyielded elements in the source `Vec`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(drain_filter)]
+    /// #![feature(drain_keep_rest)]
+    ///
+    /// let mut vec = vec!['a', 'b', 'c'];
+    /// let mut drain = vec.drain_filter(|_| true);
+    ///
+    /// assert_eq!(drain.next().unwrap(), 'a');
+    ///
+    /// // This call keeps 'b' and 'c' in the vec.
+    /// drain.keep_rest();
+    ///
+    /// // If we wouldn't call `keep_rest()`,
+    /// // `vec` would be empty.
+    /// assert_eq!(vec, ['b', 'c']);
+    /// ```
+    #[unstable(feature = "drain_keep_rest", issue = "101122")]
+    pub fn keep_rest(self) {
+        // At this moment layout looks like this:
+        //
+        //  _____________________/-- old_len
+        // /                     \
+        // [kept] [yielded] [tail]
+        //        \_______/ ^-- idx
+        //                \-- del
+        //
+        // Normally `Drop` impl would drop [tail] (via .for_each(drop), ie still calling `pred`)
+        //
+        // 1. Move [tail] after [kept]
+        // 2. Update length of the original vec to `old_len - del`
+        //    a. In case of ZST, this is the only thing we want to do
+        // 3. Do *not* drop self, as everything is put in a consistent state already, there is nothing to do
+        let mut this = ManuallyDrop::new(self);
+
+        unsafe {
+            // ZSTs have no identity, so we don't need to move them around.
+            let needs_move = mem::size_of::<T>() != 0;
+
+            if needs_move && this.idx < this.old_len && this.del > 0 {
+                let ptr = this.vec.as_mut_ptr();
+                let src = ptr.add(this.idx);
+                let dst = src.sub(this.del);
+                let tail_len = this.old_len - this.idx;
+                src.copy_to(dst, tail_len);
+            }
+
+            let new_len = this.old_len - this.del;
+            this.vec.set_len(new_len);
+        }
+    }
 }
 
 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
diff --git a/rust/alloc/vec/into_iter.rs b/rust/alloc/vec/into_iter.rs
index f7a50e76691e..34a2a70d6ded 100644
--- a/rust/alloc/vec/into_iter.rs
+++ b/rust/alloc/vec/into_iter.rs
@@ -3,14 +3,16 @@
 #[cfg(not(no_global_oom_handling))]
 use super::AsVecIntoIter;
 use crate::alloc::{Allocator, Global};
+#[cfg(not(no_global_oom_handling))]
+use crate::collections::VecDeque;
 use crate::raw_vec::RawVec;
+use core::array;
 use core::fmt;
-use core::intrinsics::arith_offset;
 use core::iter::{
     FusedIterator, InPlaceIterable, SourceIter, TrustedLen, TrustedRandomAccessNoCoerce,
 };
 use core::marker::PhantomData;
-use core::mem::{self, ManuallyDrop};
+use core::mem::{self, ManuallyDrop, MaybeUninit, SizedTypeProperties};
 #[cfg(not(no_global_oom_handling))]
 use core::ops::Deref;
 use core::ptr::{self, NonNull};
@@ -40,7 +42,9 @@ pub struct IntoIter<
     // to avoid dropping the allocator twice we need to wrap it into ManuallyDrop
     pub(super) alloc: ManuallyDrop<A>,
     pub(super) ptr: *const T,
-    pub(super) end: *const T,
+    pub(super) end: *const T, // If T is a ZST, this is actually ptr+len. This encoding is picked so that
+                              // ptr == end is a quick test for the Iterator being empty, that works
+                              // for both ZST and non-ZST.
 }
 
 #[stable(feature = "vec_intoiter_debug", since = "1.13.0")]
@@ -97,13 +101,16 @@ impl<T, A: Allocator> IntoIter<T, A> {
     }
 
     /// Drops remaining elements and relinquishes the backing allocation.
+    /// This method guarantees it won't panic before relinquishing
+    /// the backing allocation.
     ///
     /// This is roughly equivalent to the following, but more efficient
     ///
     /// ```
     /// # let mut into_iter = Vec::<u8>::with_capacity(10).into_iter();
+    /// let mut into_iter = std::mem::replace(&mut into_iter, Vec::new().into_iter());
     /// (&mut into_iter).for_each(core::mem::drop);
-    /// unsafe { core::ptr::write(&mut into_iter, Vec::new().into_iter()); }
+    /// std::mem::forget(into_iter);
     /// ```
     ///
     /// This method is used by in-place iteration, refer to the vec::in_place_collect
@@ -120,15 +127,45 @@ impl<T, A: Allocator> IntoIter<T, A> {
         self.ptr = self.buf.as_ptr();
         self.end = self.buf.as_ptr();
 
+        // Dropping the remaining elements can panic, so this needs to be
+        // done only after updating the other fields.
         unsafe {
             ptr::drop_in_place(remaining);
         }
     }
 
     /// Forgets to Drop the remaining elements while still allowing the backing allocation to be freed.
-    #[allow(dead_code)]
     pub(crate) fn forget_remaining_elements(&mut self) {
-        self.ptr = self.end;
+        // For th ZST case, it is crucial that we mutate `end` here, not `ptr`.
+        // `ptr` must stay aligned, while `end` may be unaligned.
+        self.end = self.ptr;
+    }
+
+    #[cfg(not(no_global_oom_handling))]
+    #[inline]
+    pub(crate) fn into_vecdeque(self) -> VecDeque<T, A> {
+        // Keep our `Drop` impl from dropping the elements and the allocator
+        let mut this = ManuallyDrop::new(self);
+
+        // SAFETY: This allocation originally came from a `Vec`, so it passes
+        // all those checks. We have `this.buf` ≤ `this.ptr` ≤ `this.end`,
+        // so the `sub_ptr`s below cannot wrap, and will produce a well-formed
+        // range. `end` ≤ `buf + cap`, so the range will be in-bounds.
+        // Taking `alloc` is ok because nothing else is going to look at it,
+        // since our `Drop` impl isn't going to run so there's no more code.
+        unsafe {
+            let buf = this.buf.as_ptr();
+            let initialized = if T::IS_ZST {
+                // All the pointers are the same for ZSTs, so it's fine to
+                // say that they're all at the beginning of the "allocation".
+                0..this.len()
+            } else {
+                this.ptr.sub_ptr(buf)..this.end.sub_ptr(buf)
+            };
+            let cap = this.cap;
+            let alloc = ManuallyDrop::take(&mut this.alloc);
+            VecDeque::from_contiguous_raw_parts_in(buf, initialized, cap, alloc)
+        }
     }
 }
 
@@ -150,19 +187,18 @@ impl<T, A: Allocator> Iterator for IntoIter<T, A> {
 
     #[inline]
     fn next(&mut self) -> Option<T> {
-        if self.ptr as *const _ == self.end {
+        if self.ptr == self.end {
             None
-        } else if mem::size_of::<T>() == 0 {
-            // purposefully don't use 'ptr.offset' because for
-            // vectors with 0-size elements this would return the
-            // same pointer.
-            self.ptr = unsafe { arith_offset(self.ptr as *const i8, 1) as *mut T };
+        } else if T::IS_ZST {
+            // `ptr` has to stay where it is to remain aligned, so we reduce the length by 1 by
+            // reducing the `end`.
+            self.end = self.end.wrapping_byte_sub(1);
 
             // Make up a value of this ZST.
             Some(unsafe { mem::zeroed() })
         } else {
             let old = self.ptr;
-            self.ptr = unsafe { self.ptr.offset(1) };
+            self.ptr = unsafe { self.ptr.add(1) };
 
             Some(unsafe { ptr::read(old) })
         }
@@ -170,7 +206,7 @@ impl<T, A: Allocator> Iterator for IntoIter<T, A> {
 
     #[inline]
     fn size_hint(&self) -> (usize, Option<usize>) {
-        let exact = if mem::size_of::<T>() == 0 {
+        let exact = if T::IS_ZST {
             self.end.addr().wrapping_sub(self.ptr.addr())
         } else {
             unsafe { self.end.sub_ptr(self.ptr) }
@@ -182,11 +218,9 @@ impl<T, A: Allocator> Iterator for IntoIter<T, A> {
     fn advance_by(&mut self, n: usize) -> Result<(), usize> {
         let step_size = self.len().min(n);
         let to_drop = ptr::slice_from_raw_parts_mut(self.ptr as *mut T, step_size);
-        if mem::size_of::<T>() == 0 {
-            // SAFETY: due to unchecked casts of unsigned amounts to signed offsets the wraparound
-            // effectively results in unsigned pointers representing positions 0..usize::MAX,
-            // which is valid for ZSTs.
-            self.ptr = unsafe { arith_offset(self.ptr as *const i8, step_size as isize) as *mut T }
+        if T::IS_ZST {
+            // See `next` for why we sub `end` here.
+            self.end = self.end.wrapping_byte_sub(step_size);
         } else {
             // SAFETY: the min() above ensures that step_size is in bounds
             self.ptr = unsafe { self.ptr.add(step_size) };
@@ -206,6 +240,43 @@ impl<T, A: Allocator> Iterator for IntoIter<T, A> {
         self.len()
     }
 
+    #[inline]
+    fn next_chunk<const N: usize>(&mut self) -> Result<[T; N], core::array::IntoIter<T, N>> {
+        let mut raw_ary = MaybeUninit::uninit_array();
+
+        let len = self.len();
+
+        if T::IS_ZST {
+            if len < N {
+                self.forget_remaining_elements();
+                // Safety: ZSTs can be conjured ex nihilo, only the amount has to be correct
+                return Err(unsafe { array::IntoIter::new_unchecked(raw_ary, 0..len) });
+            }
+
+            self.end = self.end.wrapping_byte_sub(N);
+            // Safety: ditto
+            return Ok(unsafe { raw_ary.transpose().assume_init() });
+        }
+
+        if len < N {
+            // Safety: `len` indicates that this many elements are available and we just checked that
+            // it fits into the array.
+            unsafe {
+                ptr::copy_nonoverlapping(self.ptr, raw_ary.as_mut_ptr() as *mut T, len);
+                self.forget_remaining_elements();
+                return Err(array::IntoIter::new_unchecked(raw_ary, 0..len));
+            }
+        }
+
+        // Safety: `len` is larger than the array size. Copy a fixed amount here to fully initialize
+        // the array.
+        return unsafe {
+            ptr::copy_nonoverlapping(self.ptr, raw_ary.as_mut_ptr() as *mut T, N);
+            self.ptr = self.ptr.add(N);
+            Ok(raw_ary.transpose().assume_init())
+        };
+    }
+
     unsafe fn __iterator_get_unchecked(&mut self, i: usize) -> Self::Item
     where
         Self: TrustedRandomAccessNoCoerce,
@@ -219,7 +290,7 @@ impl<T, A: Allocator> Iterator for IntoIter<T, A> {
         // that `T: Copy` so reading elements from the buffer doesn't invalidate
         // them for `Drop`.
         unsafe {
-            if mem::size_of::<T>() == 0 { mem::zeroed() } else { ptr::read(self.ptr.add(i)) }
+            if T::IS_ZST { mem::zeroed() } else { ptr::read(self.ptr.add(i)) }
         }
     }
 }
@@ -230,14 +301,14 @@ impl<T, A: Allocator> DoubleEndedIterator for IntoIter<T, A> {
     fn next_back(&mut self) -> Option<T> {
         if self.end == self.ptr {
             None
-        } else if mem::size_of::<T>() == 0 {
+        } else if T::IS_ZST {
             // See above for why 'ptr.offset' isn't used
-            self.end = unsafe { arith_offset(self.end as *const i8, -1) as *mut T };
+            self.end = self.end.wrapping_byte_sub(1);
 
             // Make up a value of this ZST.
             Some(unsafe { mem::zeroed() })
         } else {
-            self.end = unsafe { self.end.offset(-1) };
+            self.end = unsafe { self.end.sub(1) };
 
             Some(unsafe { ptr::read(self.end) })
         }
@@ -246,14 +317,12 @@ impl<T, A: Allocator> DoubleEndedIterator for IntoIter<T, A> {
     #[inline]
     fn advance_back_by(&mut self, n: usize) -> Result<(), usize> {
         let step_size = self.len().min(n);
-        if mem::size_of::<T>() == 0 {
+        if T::IS_ZST {
             // SAFETY: same as for advance_by()
-            self.end = unsafe {
-                arith_offset(self.end as *const i8, step_size.wrapping_neg() as isize) as *mut T
-            }
+            self.end = self.end.wrapping_byte_sub(step_size);
         } else {
             // SAFETY: same as for advance_by()
-            self.end = unsafe { self.end.offset(step_size.wrapping_neg() as isize) };
+            self.end = unsafe { self.end.sub(step_size) };
         }
         let to_drop = ptr::slice_from_raw_parts_mut(self.end as *mut T, step_size);
         // SAFETY: same as for advance_by()
diff --git a/rust/alloc/vec/is_zero.rs b/rust/alloc/vec/is_zero.rs
index 377f3d172777..d928dcf90e80 100644
--- a/rust/alloc/vec/is_zero.rs
+++ b/rust/alloc/vec/is_zero.rs
@@ -1,10 +1,13 @@
 // SPDX-License-Identifier: Apache-2.0 OR MIT
 
+use core::num::{Saturating, Wrapping};
+
 use crate::boxed::Box;
 
 #[rustc_specialization_trait]
 pub(super) unsafe trait IsZero {
-    /// Whether this value's representation is all zeros
+    /// Whether this value's representation is all zeros,
+    /// or can be represented with all zeroes.
     fn is_zero(&self) -> bool;
 }
 
@@ -19,12 +22,14 @@ macro_rules! impl_is_zero {
     };
 }
 
+impl_is_zero!(i8, |x| x == 0); // It is needed to impl for arrays and tuples of i8.
 impl_is_zero!(i16, |x| x == 0);
 impl_is_zero!(i32, |x| x == 0);
 impl_is_zero!(i64, |x| x == 0);
 impl_is_zero!(i128, |x| x == 0);
 impl_is_zero!(isize, |x| x == 0);
 
+impl_is_zero!(u8, |x| x == 0); // It is needed to impl for arrays and tuples of u8.
 impl_is_zero!(u16, |x| x == 0);
 impl_is_zero!(u32, |x| x == 0);
 impl_is_zero!(u64, |x| x == 0);
@@ -55,16 +60,42 @@ unsafe impl<T: IsZero, const N: usize> IsZero for [T; N] {
     #[inline]
     fn is_zero(&self) -> bool {
         // Because this is generated as a runtime check, it's not obvious that
-        // it's worth doing if the array is really long.  The threshold here
-        // is largely arbitrary, but was picked because as of 2022-05-01 LLVM
-        // can const-fold the check in `vec![[0; 32]; n]` but not in
-        // `vec![[0; 64]; n]`: https://godbolt.org/z/WTzjzfs5b
+        // it's worth doing if the array is really long. The threshold here
+        // is largely arbitrary, but was picked because as of 2022-07-01 LLVM
+        // fails to const-fold the check in `vec![[1; 32]; n]`
+        // See https://github.com/rust-lang/rust/pull/97581#issuecomment-1166628022
         // Feel free to tweak if you have better evidence.
 
-        N <= 32 && self.iter().all(IsZero::is_zero)
+        N <= 16 && self.iter().all(IsZero::is_zero)
+    }
+}
+
+// This is recursive macro.
+macro_rules! impl_for_tuples {
+    // Stopper
+    () => {
+        // No use for implementing for empty tuple because it is ZST.
+    };
+    ($first_arg:ident $(,$rest:ident)*) => {
+        unsafe impl <$first_arg: IsZero, $($rest: IsZero,)*> IsZero for ($first_arg, $($rest,)*){
+            #[inline]
+            fn is_zero(&self) -> bool{
+                // Destructure tuple to N references
+                // Rust allows to hide generic params by local variable names.
+                #[allow(non_snake_case)]
+                let ($first_arg, $($rest,)*) = self;
+
+                $first_arg.is_zero()
+                    $( && $rest.is_zero() )*
+            }
+        }
+
+        impl_for_tuples!($($rest),*);
     }
 }
 
+impl_for_tuples!(A, B, C, D, E, F, G, H);
+
 // `Option<&T>` and `Option<Box<T>>` are guaranteed to represent `None` as null.
 // For fat pointers, the bytes that would be the pointer metadata in the `Some`
 // variant are padding in the `None` variant, so ignoring them and
@@ -118,3 +149,56 @@ impl_is_zero_option_of_nonzero!(
     NonZeroUsize,
     NonZeroIsize,
 );
+
+macro_rules! impl_is_zero_option_of_num {
+    ($($t:ty,)+) => {$(
+        unsafe impl IsZero for Option<$t> {
+            #[inline]
+            fn is_zero(&self) -> bool {
+                const {
+                    let none: Self = unsafe { core::mem::MaybeUninit::zeroed().assume_init() };
+                    assert!(none.is_none());
+                }
+                self.is_none()
+            }
+        }
+    )+};
+}
+
+impl_is_zero_option_of_num!(u8, u16, u32, u64, u128, i8, i16, i32, i64, i128, usize, isize,);
+
+unsafe impl<T: IsZero> IsZero for Wrapping<T> {
+    #[inline]
+    fn is_zero(&self) -> bool {
+        self.0.is_zero()
+    }
+}
+
+unsafe impl<T: IsZero> IsZero for Saturating<T> {
+    #[inline]
+    fn is_zero(&self) -> bool {
+        self.0.is_zero()
+    }
+}
+
+macro_rules! impl_for_optional_bool {
+    ($($t:ty,)+) => {$(
+        unsafe impl IsZero for $t {
+            #[inline]
+            fn is_zero(&self) -> bool {
+                // SAFETY: This is *not* a stable layout guarantee, but
+                // inside `core` we're allowed to rely on the current rustc
+                // behaviour that options of bools will be one byte with
+                // no padding, so long as they're nested less than 254 deep.
+                let raw: u8 = unsafe { core::mem::transmute(*self) };
+                raw == 0
+            }
+        }
+    )+};
+}
+impl_for_optional_bool! {
+    Option<bool>,
+    Option<Option<bool>>,
+    Option<Option<Option<bool>>>,
+    // Could go further, but not worth the metadata overhead
+}
diff --git a/rust/alloc/vec/mod.rs b/rust/alloc/vec/mod.rs
index fe4fff5064bc..94995913566b 100644
--- a/rust/alloc/vec/mod.rs
+++ b/rust/alloc/vec/mod.rs
@@ -61,12 +61,12 @@ use core::cmp::Ordering;
 use core::convert::TryFrom;
 use core::fmt;
 use core::hash::{Hash, Hasher};
-use core::intrinsics::{arith_offset, assume};
+use core::intrinsics::assume;
 use core::iter;
 #[cfg(not(no_global_oom_handling))]
 use core::iter::FromIterator;
 use core::marker::PhantomData;
-use core::mem::{self, ManuallyDrop, MaybeUninit};
+use core::mem::{self, ManuallyDrop, MaybeUninit, SizedTypeProperties};
 use core::ops::{self, Index, IndexMut, Range, RangeBounds};
 use core::ptr::{self, NonNull};
 use core::slice::{self, SliceIndex};
@@ -75,7 +75,7 @@ use crate::alloc::{Allocator, Global};
 #[cfg(not(no_borrow))]
 use crate::borrow::{Cow, ToOwned};
 use crate::boxed::Box;
-use crate::collections::TryReserveError;
+use crate::collections::{TryReserveError, TryReserveErrorKind};
 use crate::raw_vec::RawVec;
 
 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
@@ -127,7 +127,7 @@ use self::set_len_on_drop::SetLenOnDrop;
 mod set_len_on_drop;
 
 #[cfg(not(no_global_oom_handling))]
-use self::in_place_drop::InPlaceDrop;
+use self::in_place_drop::{InPlaceDrop, InPlaceDstBufDrop};
 
 #[cfg(not(no_global_oom_handling))]
 mod in_place_drop;
@@ -169,7 +169,7 @@ mod spec_extend;
 /// vec[0] = 7;
 /// assert_eq!(vec[0], 7);
 ///
-/// vec.extend([1, 2, 3].iter().copied());
+/// vec.extend([1, 2, 3]);
 ///
 /// for x in &vec {
 ///     println!("{x}");
@@ -428,17 +428,25 @@ impl<T> Vec<T> {
         Vec { buf: RawVec::NEW, len: 0 }
     }
 
-    /// Constructs a new, empty `Vec<T>` with the specified capacity.
+    /// Constructs a new, empty `Vec<T>` with at least the specified capacity.
     ///
-    /// The vector will be able to hold exactly `capacity` elements without
-    /// reallocating. If `capacity` is 0, the vector will not allocate.
+    /// The vector will be able to hold at least `capacity` elements without
+    /// reallocating. This method is allowed to allocate for more elements than
+    /// `capacity`. If `capacity` is 0, the vector will not allocate.
     ///
     /// It is important to note that although the returned vector has the
-    /// *capacity* specified, the vector will have a zero *length*. For an
-    /// explanation of the difference between length and capacity, see
+    /// minimum *capacity* specified, the vector will have a zero *length*. For
+    /// an explanation of the difference between length and capacity, see
     /// *[Capacity and reallocation]*.
     ///
+    /// If it is important to know the exact allocated capacity of a `Vec`,
+    /// always use the [`capacity`] method after construction.
+    ///
+    /// For `Vec<T>` where `T` is a zero-sized type, there will be no allocation
+    /// and the capacity will always be `usize::MAX`.
+    ///
     /// [Capacity and reallocation]: #capacity-and-reallocation
+    /// [`capacity`]: Vec::capacity
     ///
     /// # Panics
     ///
@@ -451,19 +459,24 @@ 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);
+    /// assert!(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);
+    /// assert!(vec.capacity() >= 10);
     ///
     /// // ...but this may make the vector reallocate
     /// vec.push(11);
     /// assert_eq!(vec.len(), 11);
     /// assert!(vec.capacity() >= 11);
+    ///
+    /// // A vector of a zero-sized type will always over-allocate, since no
+    /// // allocation is necessary
+    /// let vec_units = Vec::<()>::with_capacity(10);
+    /// assert_eq!(vec_units.capacity(), usize::MAX);
     /// ```
     #[cfg(not(no_global_oom_handling))]
     #[inline]
@@ -473,17 +486,25 @@ impl<T> Vec<T> {
         Self::with_capacity_in(capacity, Global)
     }
 
-    /// Tries to construct a new, empty `Vec<T>` with the specified capacity.
+    /// Tries to construct a new, empty `Vec<T>` with at least the specified capacity.
     ///
-    /// The vector will be able to hold exactly `capacity` elements without
-    /// reallocating. If `capacity` is 0, the vector will not allocate.
+    /// The vector will be able to hold at least `capacity` elements without
+    /// reallocating. This method is allowed to allocate for more elements than
+    /// `capacity`. If `capacity` is 0, the vector will not allocate.
     ///
     /// It is important to note that although the returned vector has the
-    /// *capacity* specified, the vector will have a zero *length*. For an
-    /// explanation of the difference between length and capacity, see
+    /// minimum *capacity* specified, the vector will have a zero *length*. For
+    /// an explanation of the difference between length and capacity, see
     /// *[Capacity and reallocation]*.
     ///
+    /// If it is important to know the exact allocated capacity of a `Vec`,
+    /// always use the [`capacity`] method after construction.
+    ///
+    /// For `Vec<T>` where `T` is a zero-sized type, there will be no allocation
+    /// and the capacity will always be `usize::MAX`.
+    ///
     /// [Capacity and reallocation]: #capacity-and-reallocation
+    /// [`capacity`]: Vec::capacity
     ///
     /// # Examples
     ///
@@ -492,14 +513,14 @@ 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);
+    /// assert!(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);
+    /// assert!(vec.capacity() >= 10);
     ///
     /// // ...but this may make the vector reallocate
     /// vec.push(11);
@@ -508,6 +529,11 @@ impl<T> Vec<T> {
     ///
     /// let mut result = Vec::try_with_capacity(usize::MAX);
     /// assert!(result.is_err());
+    ///
+    /// // A vector of a zero-sized type will always over-allocate, since no
+    /// // allocation is necessary
+    /// let vec_units = Vec::<()>::try_with_capacity(10).unwrap();
+    /// assert_eq!(vec_units.capacity(), usize::MAX);
     /// ```
     #[inline]
     #[stable(feature = "kernel", since = "1.0.0")]
@@ -515,15 +541,15 @@ impl<T> Vec<T> {
         Self::try_with_capacity_in(capacity, Global)
     }
 
-    /// Creates a `Vec<T>` directly from the raw components of another vector.
+    /// Creates a `Vec<T>` directly from a pointer, a capacity, and a length.
     ///
     /// # Safety
     ///
     /// This is highly unsafe, due to the number of invariants that aren't
     /// checked:
     ///
-    /// * `ptr` needs to have been previously allocated via [`String`]/`Vec<T>`
-    ///   (at least, it's highly likely to be incorrect if it wasn't).
+    /// * `ptr` must have been allocated using the global allocator, such as via
+    ///   the [`alloc::alloc`] function.
     /// * `T` needs to have the same alignment as what `ptr` was allocated with.
     ///   (`T` having a less strict alignment is not sufficient, the alignment really
     ///   needs to be equal to satisfy the [`dealloc`] requirement that memory must be
@@ -532,6 +558,14 @@ impl<T> Vec<T> {
     ///   to be the same size as the pointer was allocated with. (Because similar to
     ///   alignment, [`dealloc`] must be called with the same layout `size`.)
     /// * `length` needs to be less than or equal to `capacity`.
+    /// * The first `length` values must be properly initialized values of type `T`.
+    /// * `capacity` needs to be the capacity that the pointer was allocated with.
+    /// * The allocated size in bytes must be no larger than `isize::MAX`.
+    ///   See the safety documentation of [`pointer::offset`].
+    ///
+    /// These requirements are always upheld by any `ptr` that has been allocated
+    /// via `Vec<T>`. Other allocation sources are allowed if the invariants are
+    /// upheld.
     ///
     /// Violating these may cause problems like corrupting the allocator's
     /// internal data structures. For example it is normally **not** safe
@@ -552,6 +586,7 @@ impl<T> Vec<T> {
     /// function.
     ///
     /// [`String`]: crate::string::String
+    /// [`alloc::alloc`]: crate::alloc::alloc
     /// [`dealloc`]: crate::alloc::GlobalAlloc::dealloc
     ///
     /// # Examples
@@ -574,8 +609,8 @@ impl<T> Vec<T> {
     ///
     /// unsafe {
     ///     // Overwrite memory with 4, 5, 6
-    ///     for i in 0..len as isize {
-    ///         ptr::write(p.offset(i), 4 + i);
+    ///     for i in 0..len {
+    ///         ptr::write(p.add(i), 4 + i);
     ///     }
     ///
     ///     // Put everything back together into a Vec
@@ -583,6 +618,32 @@ impl<T> Vec<T> {
     ///     assert_eq!(rebuilt, [4, 5, 6]);
     /// }
     /// ```
+    ///
+    /// Using memory that was allocated elsewhere:
+    ///
+    /// ```rust
+    /// #![feature(allocator_api)]
+    ///
+    /// use std::alloc::{AllocError, Allocator, Global, Layout};
+    ///
+    /// fn main() {
+    ///     let layout = Layout::array::<u32>(16).expect("overflow cannot happen");
+    ///
+    ///     let vec = unsafe {
+    ///         let mem = match Global.allocate(layout) {
+    ///             Ok(mem) => mem.cast::<u32>().as_ptr(),
+    ///             Err(AllocError) => return,
+    ///         };
+    ///
+    ///         mem.write(1_000_000);</