Merging upstream version 1.66.0+dfsg1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

8 files changed, 243 insertions, 78 deletions

diff --git a/library/core/src/slice/index.rs b/library/core/src/slice/index.rs
index 3403a5a86..6d2f7330d 100644
--- a/library/core/src/slice/index.rs
+++ b/library/core/src/slice/index.rs
@@ -139,6 +139,8 @@ mod private_slice_index {
     impl Sealed for ops::RangeToInclusive<usize> {}
     #[stable(feature = "slice_index_with_ops_bound_pair", since = "1.53.0")]
     impl Sealed for (ops::Bound<usize>, ops::Bound<usize>) {}
+
+    impl Sealed for ops::IndexRange {}
 }
 
 /// A helper trait used for indexing operations.
@@ -158,6 +160,7 @@ mod private_slice_index {
     message = "the type `{T}` cannot be indexed by `{Self}`",
     label = "slice indices are of type `usize` or ranges of `usize`"
 )]
+#[const_trait]
 pub unsafe trait SliceIndex<T: ?Sized>: private_slice_index::Sealed {
     /// The output type returned by methods.
     #[stable(feature = "slice_get_slice", since = "1.28.0")]
@@ -229,7 +232,10 @@ unsafe impl<T> const SliceIndex<[T]> for usize {
         // `self` is in bounds of `slice` so `self` cannot overflow an `isize`,
         // so the call to `add` is safe.
         unsafe {
-            assert_unsafe_precondition!([T](this: usize, slice: *const [T]) => this < slice.len());
+            assert_unsafe_precondition!(
+                "slice::get_unchecked requires that the index is within the slice",
+                [T](this: usize, slice: *const [T]) => this < slice.len()
+            );
             slice.as_ptr().add(self)
         }
     }
@@ -239,7 +245,10 @@ unsafe impl<T> const SliceIndex<[T]> for usize {
         let this = self;
         // SAFETY: see comments for `get_unchecked` above.
         unsafe {
-            assert_unsafe_precondition!([T](this: usize, slice: *mut [T]) => this < slice.len());
+            assert_unsafe_precondition!(
+                "slice::get_unchecked_mut requires that the index is within the slice",
+                [T](this: usize, slice: *mut [T]) => this < slice.len()
+            );
             slice.as_mut_ptr().add(self)
         }
     }
@@ -257,6 +266,83 @@ unsafe impl<T> const SliceIndex<[T]> for usize {
     }
 }
 
+/// Because `IndexRange` guarantees `start <= end`, fewer checks are needed here
+/// than there are for a general `Range<usize>` (which might be `100..3`).
+#[rustc_const_unstable(feature = "const_index_range_slice_index", issue = "none")]
+unsafe impl<T> const SliceIndex<[T]> for ops::IndexRange {
+    type Output = [T];
+
+    #[inline]
+    fn get(self, slice: &[T]) -> Option<&[T]> {
+        if self.end() <= slice.len() {
+            // SAFETY: `self` is checked to be valid and in bounds above.
+            unsafe { Some(&*self.get_unchecked(slice)) }
+        } else {
+            None
+        }
+    }
+
+    #[inline]
+    fn get_mut(self, slice: &mut [T]) -> Option<&mut [T]> {
+        if self.end() <= slice.len() {
+            // SAFETY: `self` is checked to be valid and in bounds above.
+            unsafe { Some(&mut *self.get_unchecked_mut(slice)) }
+        } else {
+            None
+        }
+    }
+
+    #[inline]
+    unsafe fn get_unchecked(self, slice: *const [T]) -> *const [T] {
+        let end = self.end();
+        // SAFETY: the caller guarantees that `slice` is not dangling, so it
+        // cannot be longer than `isize::MAX`. They also guarantee that
+        // `self` is in bounds of `slice` so `self` cannot overflow an `isize`,
+        // so the call to `add` is safe.
+
+        unsafe {
+            assert_unsafe_precondition!(
+                "slice::get_unchecked requires that the index is within the slice",
+                [T](end: usize, slice: *const [T]) => end <= slice.len()
+            );
+            ptr::slice_from_raw_parts(slice.as_ptr().add(self.start()), self.len())
+        }
+    }
+
+    #[inline]
+    unsafe fn get_unchecked_mut(self, slice: *mut [T]) -> *mut [T] {
+        let end = self.end();
+        // SAFETY: see comments for `get_unchecked` above.
+        unsafe {
+            assert_unsafe_precondition!(
+                "slice::get_unchecked_mut requires that the index is within the slice",
+                [T](end: usize, slice: *mut [T]) => end <= slice.len()
+            );
+            ptr::slice_from_raw_parts_mut(slice.as_mut_ptr().add(self.start()), self.len())
+        }
+    }
+
+    #[inline]
+    fn index(self, slice: &[T]) -> &[T] {
+        if self.end() <= slice.len() {
+            // SAFETY: `self` is checked to be valid and in bounds above.
+            unsafe { &*self.get_unchecked(slice) }
+        } else {
+            slice_end_index_len_fail(self.end(), slice.len())
+        }
+    }
+
+    #[inline]
+    fn index_mut(self, slice: &mut [T]) -> &mut [T] {
+        if self.end() <= slice.len() {
+            // SAFETY: `self` is checked to be valid and in bounds above.
+            unsafe { &mut *self.get_unchecked_mut(slice) }
+        } else {
+            slice_end_index_len_fail(self.end(), slice.len())
+        }
+    }
+}
+
 #[stable(feature = "slice_get_slice_impls", since = "1.15.0")]
 #[rustc_const_unstable(feature = "const_slice_index", issue = "none")]
 unsafe impl<T> const SliceIndex<[T]> for ops::Range<usize> {
@@ -291,8 +377,11 @@ unsafe impl<T> const SliceIndex<[T]> for ops::Range<usize> {
         // so the call to `add` is safe.
 
         unsafe {
-            assert_unsafe_precondition!([T](this: ops::Range<usize>, slice: *const [T]) =>
-            this.end >= this.start && this.end <= slice.len());
+            assert_unsafe_precondition!(
+                "slice::get_unchecked requires that the range is within the slice",
+                [T](this: ops::Range<usize>, slice: *const [T]) =>
+                this.end >= this.start && this.end <= slice.len()
+            );
             ptr::slice_from_raw_parts(slice.as_ptr().add(self.start), self.end - self.start)
         }
     }
@@ -302,8 +391,11 @@ unsafe impl<T> const SliceIndex<[T]> for ops::Range<usize> {
         let this = ops::Range { start: self.start, end: self.end };
         // SAFETY: see comments for `get_unchecked` above.
         unsafe {
-            assert_unsafe_precondition!([T](this: ops::Range<usize>, slice: *mut [T]) =>
-                this.end >= this.start && this.end <= slice.len());
+            assert_unsafe_precondition!(
+                "slice::get_unchecked_mut requires that the range is within the slice",
+                [T](this: ops::Range<usize>, slice: *mut [T]) =>
+                this.end >= this.start && this.end <= slice.len()
+            );
             ptr::slice_from_raw_parts_mut(slice.as_mut_ptr().add(self.start), self.end - self.start)
         }
     }
diff --git a/library/core/src/slice/iter.rs b/library/core/src/slice/iter.rs
index 395c56784..8a8962828 100644
--- a/library/core/src/slice/iter.rs
+++ b/library/core/src/slice/iter.rs
@@ -9,7 +9,7 @@ use crate::fmt;
 use crate::intrinsics::{assume, exact_div, unchecked_sub};
 use crate::iter::{FusedIterator, TrustedLen, TrustedRandomAccess, TrustedRandomAccessNoCoerce};
 use crate::marker::{PhantomData, Send, Sized, Sync};
-use crate::mem;
+use crate::mem::{self, SizedTypeProperties};
 use crate::num::NonZeroUsize;
 use crate::ptr::NonNull;
 
@@ -91,11 +91,8 @@ impl<'a, T> Iter<'a, T> {
         unsafe {
             assume(!ptr.is_null());
 
-            let end = if mem::size_of::<T>() == 0 {
-                ptr.wrapping_byte_add(slice.len())
-            } else {
-                ptr.add(slice.len())
-            };
+            let end =
+                if T::IS_ZST { ptr.wrapping_byte_add(slice.len()) } else { ptr.add(slice.len()) };
 
             Self { ptr: NonNull::new_unchecked(ptr as *mut T), end, _marker: PhantomData }
         }
@@ -127,6 +124,7 @@ impl<'a, T> Iter<'a, T> {
     /// ```
     #[must_use]
     #[stable(feature = "iter_to_slice", since = "1.4.0")]
+    #[inline]
     pub fn as_slice(&self) -> &'a [T] {
         self.make_slice()
     }
@@ -146,6 +144,7 @@ iterator! {struct Iter -> *const T, &'a T, const, {/* no mut */}, {
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T> Clone for Iter<'_, T> {
+    #[inline]
     fn clone(&self) -> Self {
         Iter { ptr: self.ptr, end: self.end, _marker: self._marker }
     }
@@ -153,6 +152,7 @@ impl<T> Clone for Iter<'_, T> {
 
 #[stable(feature = "slice_iter_as_ref", since = "1.13.0")]
 impl<T> AsRef<[T]> for Iter<'_, T> {
+    #[inline]
     fn as_ref(&self) -> &[T] {
         self.as_slice()
     }
@@ -227,11 +227,8 @@ impl<'a, T> IterMut<'a, T> {
         unsafe {
             assume(!ptr.is_null());
 
-            let end = if mem::size_of::<T>() == 0 {
-                ptr.wrapping_byte_add(slice.len())
-            } else {
-                ptr.add(slice.len())
-            };
+            let end =
+                if T::IS_ZST { ptr.wrapping_byte_add(slice.len()) } else { ptr.add(slice.len()) };
 
             Self { ptr: NonNull::new_unchecked(ptr), end, _marker: PhantomData }
         }
@@ -303,6 +300,7 @@ impl<'a, T> IterMut<'a, T> {
     /// ```
     #[must_use]
     #[stable(feature = "slice_iter_mut_as_slice", since = "1.53.0")]
+    #[inline]
     pub fn as_slice(&self) -> &[T] {
         self.make_slice()
     }
@@ -351,6 +349,7 @@ impl<'a, T> IterMut<'a, T> {
 
 #[stable(feature = "slice_iter_mut_as_slice", since = "1.53.0")]
 impl<T> AsRef<[T]> for IterMut<'_, T> {
+    #[inline]
     fn as_ref(&self) -> &[T] {
         self.as_slice()
     }
diff --git a/library/core/src/slice/iter/macros.rs b/library/core/src/slice/iter/macros.rs
index 6c9e7574e..ce51d48e3 100644
--- a/library/core/src/slice/iter/macros.rs
+++ b/library/core/src/slice/iter/macros.rs
@@ -100,7 +100,7 @@ macro_rules! iterator {
             // Unsafe because the offset must not exceed `self.len()`.
             #[inline(always)]
             unsafe fn pre_dec_end(&mut self, offset: usize) -> * $raw_mut T {
-                if mem::size_of::<T>() == 0 {
+                if T::IS_ZST {
                     zst_shrink!(self, offset);
                     self.ptr.as_ptr()
                 } else {
@@ -140,7 +140,7 @@ macro_rules! iterator {
                 // since we check if the iterator is empty first.
                 unsafe {
                     assume(!self.ptr.as_ptr().is_null());
-                    if mem::size_of::<T>() != 0 {
+                    if !<T>::IS_ZST {
                         assume(!self.end.is_null());
                     }
                     if is_empty!(self) {
@@ -166,7 +166,7 @@ macro_rules! iterator {
             fn nth(&mut self, n: usize) -> Option<$elem> {
                 if n >= len!(self) {
                     // This iterator is now empty.
-                    if mem::size_of::<T>() == 0 {
+                    if T::IS_ZST {
                         // We have to do it this way as `ptr` may never be 0, but `end`
                         // could be (due to wrapping).
                         self.end = self.ptr.as_ptr();
@@ -355,7 +355,7 @@ macro_rules! iterator {
                 // empty first.
                 unsafe {
                     assume(!self.ptr.as_ptr().is_null());
-                    if mem::size_of::<T>() != 0 {
+                    if !<T>::IS_ZST {
                         assume(!self.end.is_null());
                     }
                     if is_empty!(self) {
diff --git a/library/core/src/slice/memchr.rs b/library/core/src/slice/memchr.rs
index 7de1f48e6..c848c2e18 100644
--- a/library/core/src/slice/memchr.rs
+++ b/library/core/src/slice/memchr.rs
@@ -141,8 +141,8 @@ pub fn memrchr(x: u8, text: &[u8]) -> Option<usize> {
         // SAFETY: offset starts at len - suffix.len(), as long as it is greater than
         // min_aligned_offset (prefix.len()) the remaining distance is at least 2 * chunk_bytes.
         unsafe {
-            let u = *(ptr.offset(offset as isize - 2 * chunk_bytes as isize) as *const Chunk);
-            let v = *(ptr.offset(offset as isize - chunk_bytes as isize) as *const Chunk);
+            let u = *(ptr.add(offset - 2 * chunk_bytes) as *const Chunk);
+            let v = *(ptr.add(offset - chunk_bytes) as *const Chunk);
 
             // Break if there is a matching byte.
             let zu = contains_zero_byte(u ^ repeated_x);
diff --git a/library/core/src/slice/mod.rs b/library/core/src/slice/mod.rs
index 6a7150d29..4f1bb1734 100644
--- a/library/core/src/slice/mod.rs
+++ b/library/core/src/slice/mod.rs
@@ -9,7 +9,7 @@
 use crate::cmp::Ordering::{self, Greater, Less};
 use crate::intrinsics::{assert_unsafe_precondition, exact_div};
 use crate::marker::Copy;
-use crate::mem;
+use crate::mem::{self, SizedTypeProperties};
 use crate::num::NonZeroUsize;
 use crate::ops::{Bound, FnMut, OneSidedRange, Range, RangeBounds};
 use crate::option::Option;
@@ -123,18 +123,11 @@ impl<T> [T] {
     #[lang = "slice_len_fn"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[rustc_const_stable(feature = "const_slice_len", since = "1.39.0")]
+    #[rustc_allow_const_fn_unstable(ptr_metadata)]
     #[inline]
     #[must_use]
-    // SAFETY: const sound because we transmute out the length field as a usize (which it must be)
     pub const fn len(&self) -> usize {
-        // FIXME: Replace with `crate::ptr::metadata(self)` when that is const-stable.
-        // As of this writing this causes a "Const-stable functions can only call other
-        // const-stable functions" error.
-
-        // SAFETY: Accessing the value from the `PtrRepr` union is safe since *const T
-        // and PtrComponents<T> have the same memory layouts. Only std can make this
-        // guarantee.
-        unsafe { crate::ptr::PtrRepr { const_ptr: self }.components.metadata }
+        ptr::metadata(self)
     }
 
     /// Returns `true` if the slice has a length of 0.
@@ -660,7 +653,10 @@ impl<T> [T] {
         let ptr = this.as_mut_ptr();
         // SAFETY: caller has to guarantee that `a < self.len()` and `b < self.len()`
         unsafe {
-            assert_unsafe_precondition!([T](a: usize, b: usize, this: &mut [T]) => a < this.len() && b < this.len());
+            assert_unsafe_precondition!(
+                "slice::swap_unchecked requires that the indices are within the slice",
+                [T](a: usize, b: usize, this: &mut [T]) => a < this.len() && b < this.len()
+            );
             ptr::swap(ptr.add(a), ptr.add(b));
         }
     }
@@ -976,7 +972,10 @@ impl<T> [T] {
         let this = self;
         // SAFETY: Caller must guarantee that `N` is nonzero and exactly divides the slice length
         let new_len = unsafe {
-            assert_unsafe_precondition!([T](this: &[T], N: usize) => N != 0 && this.len() % N == 0);
+            assert_unsafe_precondition!(
+                "slice::as_chunks_unchecked requires `N != 0` and the slice to split exactly into `N`-element chunks",
+                [T](this: &[T], N: usize) => N != 0 && this.len() % N == 0
+            );
             exact_div(self.len(), N)
         };
         // SAFETY: We cast a slice of `new_len * N` elements into
@@ -1116,7 +1115,10 @@ impl<T> [T] {
         let this = &*self;
         // SAFETY: Caller must guarantee that `N` is nonzero and exactly divides the slice length
         let new_len = unsafe {
-            assert_unsafe_precondition!([T](this: &[T], N: usize) => N != 0 && this.len() % N == 0);
+            assert_unsafe_precondition!(
+                "slice::as_chunks_unchecked_mut requires `N != 0` and the slice to split exactly into `N`-element chunks",
+                [T](this: &[T], N: usize) => N != 0 && this.len() % N == 0
+            );
             exact_div(this.len(), N)
         };
         // SAFETY: We cast a slice of `new_len * N` elements into
@@ -1580,7 +1582,8 @@ impl<T> [T] {
     #[inline]
     #[track_caller]
     #[must_use]
-    pub fn split_at_mut(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
+    #[rustc_const_unstable(feature = "const_slice_split_at_mut", issue = "101804")]
+    pub const fn split_at_mut(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
         assert!(mid <= self.len());
         // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
         // fulfills the requirements of `from_raw_parts_mut`.
@@ -1679,9 +1682,10 @@ impl<T> [T] {
     /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
     /// ```
     #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
+    #[rustc_const_unstable(feature = "const_slice_split_at_mut", issue = "101804")]
     #[inline]
     #[must_use]
-    pub unsafe fn split_at_mut_unchecked(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
+    pub const unsafe fn split_at_mut_unchecked(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
         let len = self.len();
         let ptr = self.as_mut_ptr();
 
@@ -1690,7 +1694,10 @@ impl<T> [T] {
         // `[ptr; mid]` and `[mid; len]` are not overlapping, so returning a mutable reference
         // is fine.
         unsafe {
-            assert_unsafe_precondition!((mid: usize, len: usize) => mid <= len);
+            assert_unsafe_precondition!(
+                "slice::split_at_mut_unchecked requires the index to be within the slice",
+                (mid: usize, len: usize) => mid <= len
+            );
             (from_raw_parts_mut(ptr, mid), from_raw_parts_mut(ptr.add(mid), len - mid))
         }
     }
@@ -2074,7 +2081,7 @@ impl<T> [T] {
         SplitN::new(self.split(pred), n)
     }
 
-    /// Returns an iterator over subslices separated by elements that match
+    /// Returns an iterator over mutable subslices separated by elements that match
     /// `pred`, limited to returning at most `n` items. The matched element is
     /// not contained in the subslices.
     ///
@@ -2357,6 +2364,28 @@ impl<T> [T] {
     /// assert!(match r { Ok(1..=4) => true, _ => false, });
     /// ```
     ///
+    /// If you want to find that whole *range* of matching items, rather than
+    /// an arbitrary matching one, that can be done using [`partition_point`]:
+    /// ```
+    /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
+    ///
+    /// let low = s.partition_point(|x| x < &1);
+    /// assert_eq!(low, 1);
+    /// let high = s.partition_point(|x| x <= &1);
+    /// assert_eq!(high, 5);
+    /// let r = s.binary_search(&1);
+    /// assert!((low..high).contains(&r.unwrap()));
+    ///
+    /// assert!(s[..low].iter().all(|&x| x < 1));
+    /// assert!(s[low..high].iter().all(|&x| x == 1));
+    /// assert!(s[high..].iter().all(|&x| x > 1));
+    ///
+    /// // For something not found, the "range" of equal items is empty
+    /// assert_eq!(s.partition_point(|x| x < &11), 9);
+    /// assert_eq!(s.partition_point(|x| x <= &11), 9);
+    /// assert_eq!(s.binary_search(&11), Err(9));
+    /// ```
+    ///
     /// If you want to insert an item to a sorted vector, while maintaining
     /// sort order, consider using [`partition_point`]:
     ///
@@ -2424,15 +2453,20 @@ impl<T> [T] {
     where
         F: FnMut(&'a T) -> Ordering,
     {
+        // INVARIANTS:
+        // - 0 <= left <= left + size = right <= self.len()
+        // - f returns Less for everything in self[..left]
+        // - f returns Greater for everything in self[right..]
         let mut size = self.len();
         let mut left = 0;
         let mut right = size;
         while left < right {
             let mid = left + size / 2;
 
-            // SAFETY: the call is made safe by the following invariants:
-            // - `mid >= 0`
-            // - `mid < size`: `mid` is limited by `[left; right)` bound.
+            // SAFETY: the while condition means `size` is strictly positive, so
+            // `size/2 < size`.  Thus `left + size/2 < left + size`, which
+            // coupled with the `left + size <= self.len()` invariant means
+            // we have `left + size/2 < self.len()`, and this is in-bounds.
             let cmp = f(unsafe { self.get_unchecked(mid) });
 
             // The reason why we use if/else control flow rather than match
@@ -2450,6 +2484,10 @@ impl<T> [T] {
 
             size = right - left;
         }
+
+        // SAFETY: directly true from the overall invariant.
+        // Note that this is `<=`, unlike the assume in the `Ok` path.
+        unsafe { crate::intrinsics::assume(left <= self.len()) };
         Err(left)
     }
 
@@ -2540,7 +2578,7 @@ impl<T> [T] {
     where
         T: Ord,
     {
-        sort::quicksort(self, |a, b| a.lt(b));
+        sort::quicksort(self, T::lt);
     }
 
     /// Sorts the slice with a comparator function, but might not preserve the order of equal
@@ -2643,9 +2681,10 @@ impl<T> [T] {
     /// less than or equal to any value at a position `j > index`. Additionally, this reordering is
     /// unstable (i.e. any number of equal elements may end up at position `index`), in-place
     /// (i.e. does not allocate), and *O*(*n*) worst-case. This function is also/ known as "kth
-    /// element" in other libraries. It returns a triplet of the following values: all elements less
-    /// than the one at the given index, the value at the given index, and all elements greater than
-    /// the one at the given index.
+    /// element" in other libraries. It returns a triplet of the following from the reordered slice:
+    /// the subslice prior to `index`, the element at `index`, and the subslice after `index`;
+    /// accordingly, the values in those two subslices will respectively all be less-than-or-equal-to
+    /// and greater-than-or-equal-to the value of the element at `index`.
     ///
     /// # Current implementation
     ///
@@ -2679,8 +2718,7 @@ impl<T> [T] {
     where
         T: Ord,
     {
-        let mut f = |a: &T, b: &T| a.lt(b);
-        sort::partition_at_index(self, index, &mut f)
+        sort::partition_at_index(self, index, T::lt)
     }
 
     /// Reorder the slice with a comparator function such that the element at `index` is at its
@@ -2690,10 +2728,11 @@ impl<T> [T] {
     /// less than or equal to any value at a position `j > index` using the comparator function.
     /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
     /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
-    /// is also known as "kth element" in other libraries. It returns a triplet of the following
-    /// values: all elements less than the one at the given index, the value at the given index,
-    /// and all elements greater than the one at the given index, using the provided comparator
-    /// function.
+    /// is also known as "kth element" in other libraries. It returns a triplet of the following from
+    /// the slice reordered according to the provided comparator function: the subslice prior to
+    /// `index`, the element at `index`, and the subslice after `index`; accordingly, the values in
+    /// those two subslices will respectively all be less-than-or-equal-to and greater-than-or-equal-to
+    /// the value of the element at `index`.
     ///
     /// # Current implementation
     ///
@@ -2731,8 +2770,7 @@ impl<T> [T] {
     where
         F: FnMut(&T, &T) -> Ordering,
     {
-        let mut f = |a: &T, b: &T| compare(a, b) == Less;
-        sort::partition_at_index(self, index, &mut f)
+        sort::partition_at_index(self, index, |a: &T, b: &T| compare(a, b) == Less)
     }
 
     /// Reorder the slice with a key extraction function such that the element at `index` is at its
@@ -2742,10 +2780,11 @@ impl<T> [T] {
     /// less than or equal to any value at a position `j > index` using the key extraction function.
     /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
     /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
-    /// is also known as "kth element" in other libraries. It returns a triplet of the following
-    /// values: all elements less than the one at the given index, the value at the given index, and
-    /// all elements greater than the one at the given index, using the provided key extraction
-    /// function.
+    /// is also known as "kth element" in other libraries. It returns a triplet of the following from
+    /// the slice reordered according to the provided key extraction function: the subslice prior to
+    /// `index`, the element at `index`, and the subslice after `index`; accordingly, the values in
+    /// those two subslices will respectively all be less-than-or-equal-to and greater-than-or-equal-to
+    /// the value of the element at `index`.
     ///
     /// # Current implementation
     ///
@@ -2784,8 +2823,7 @@ impl<T> [T] {
         F: FnMut(&T) -> K,
         K: Ord,
     {
-        let mut g = |a: &T, b: &T| f(a).lt(&f(b));
-        sort::partition_at_index(self, index, &mut g)
+        sort::partition_at_index(self, index, |a: &T, b: &T| f(a).lt(&f(b)))
     }
 
     /// Moves all consecutive repeated elements to the end of the slice according to the
@@ -3459,7 +3497,7 @@ impl<T> [T] {
     #[must_use]
     pub unsafe fn align_to<U>(&self) -> (&[T], &[U], &[T]) {
         // Note that most of this function will be constant-evaluated,
-        if mem::size_of::<U>() == 0 || mem::size_of::<T>() == 0 {
+        if U::IS_ZST || T::IS_ZST {
             // handle ZSTs specially, which is – don't handle them at all.
             return (self, &[], &[]);
         }
@@ -3520,7 +3558,7 @@ impl<T> [T] {
     #[must_use]
     pub unsafe fn align_to_mut<U>(&mut self) -> (&mut [T], &mut [U], &mut [T]) {
         // Note that most of this function will be constant-evaluated,
-        if mem::size_of::<U>() == 0 || mem::size_of::<T>() == 0 {
+        if U::IS_ZST || T::IS_ZST {
             // handle ZSTs specially, which is – don't handle them at all.
             return (self, &mut [], &mut []);
         }
@@ -3776,6 +3814,16 @@ impl<T> [T] {
     /// assert!(v[i..].iter().all(|&x| !(x < 5)));
     /// ```
     ///
+    /// If all elements of the slice match the predicate, including if the slice
+    /// is empty, then the length of the slice will be returned:
+    ///
+    /// ```
+    /// let a = [2, 4, 8];
+    /// assert_eq!(a.partition_point(|x| x < &100), a.len());
+    /// let a: [i32; 0] = [];
+    /// assert_eq!(a.partition_point(|x| x < &100), 0);
+    /// ```
+    ///
     /// If you want to insert an item to a sorted vector, while maintaining
     /// sort order:
     ///
@@ -4066,7 +4114,7 @@ impl<T, const N: usize> [[T; N]] {
     /// ```
     #[unstable(feature = "slice_flatten", issue = "95629")]
     pub fn flatten(&self) -> &[T] {
-        let len = if crate::mem::size_of::<T>() == 0 {
+        let len = if T::IS_ZST {
             self.len().checked_mul(N).expect("slice len overflow")
         } else {
             // SAFETY: `self.len() * N` cannot overflow because `self` is
@@ -4104,7 +4152,7 @@ impl<T, const N: usize> [[T; N]] {
     /// ```
     #[unstable(feature = "slice_flatten", issue = "95629")]
     pub fn flatten_mut(&mut self) -> &mut [T] {
-        let len = if crate::mem::size_of::<T>() == 0 {
+        let len = if T::IS_ZST {
             self.len().checked_mul(N).expect("slice len overflow")
         } else {
             // SAFETY: `self.len() * N` cannot overflow because `self` is
diff --git a/library/core/src/slice/raw.rs b/library/core/src/slice/raw.rs
index f1e8bc79b..052fd34d0 100644
--- a/library/core/src/slice/raw.rs
+++ b/library/core/src/slice/raw.rs
@@ -1,7 +1,9 @@
 //! Free functions to create `&[T]` and `&mut [T]`.
 
 use crate::array;
-use crate::intrinsics::{assert_unsafe_precondition, is_aligned_and_not_null};
+use crate::intrinsics::{
+    assert_unsafe_precondition, is_aligned_and_not_null, is_valid_allocation_size,
+};
 use crate::ops::Range;
 use crate::ptr;
 
@@ -90,9 +92,10 @@ use crate::ptr;
 pub const unsafe fn from_raw_parts<'a, T>(data: *const T, len: usize) -> &'a [T] {
     // SAFETY: the caller must uphold the safety contract for `from_raw_parts`.
     unsafe {
-        assert_unsafe_precondition!([T](data: *const T, len: usize) =>
-            is_aligned_and_not_null(data)
-                && crate::mem::size_of::<T>().saturating_mul(len) <= isize::MAX as usize
+        assert_unsafe_precondition!(
+            "slice::from_raw_parts requires the pointer to be aligned and non-null, and the total size of the slice not to exceed `isize::MAX`",
+            [T](data: *const T, len: usize) => is_aligned_and_not_null(data)
+                && is_valid_allocation_size::<T>(len)
         );
         &*ptr::slice_from_raw_parts(data, len)
     }
@@ -134,9 +137,10 @@ pub const unsafe fn from_raw_parts<'a, T>(data: *const T, len: usize) -> &'a [T]
 pub const unsafe fn from_raw_parts_mut<'a, T>(data: *mut T, len: usize) -> &'a mut [T] {
     // SAFETY: the caller must uphold the safety contract for `from_raw_parts_mut`.
     unsafe {
-        assert_unsafe_precondition!([T](data: *mut T, len: usize) =>
-            is_aligned_and_not_null(data)
-                && crate::mem::size_of::<T>().saturating_mul(len) <= isize::MAX as usize
+        assert_unsafe_precondition!(
+            "slice::from_raw_parts_mut requires the pointer to be aligned and non-null, and the total size of the slice not to exceed `isize::MAX`",
+            [T](data: *mut T, len: usize) => is_aligned_and_not_null(data)
+                && is_valid_allocation_size::<T>(len)
         );
         &mut *ptr::slice_from_raw_parts_mut(data, len)
     }
@@ -188,6 +192,10 @@ pub const fn from_mut<T>(s: &mut T) -> &mut [T] {
 ///
 /// Note that a range created from [`slice::as_ptr_range`] fulfills these requirements.
 ///
+/// # Panics
+///
+/// This function panics if `T` is a Zero-Sized Type (“ZST”).
+///
 /// # Caveat
 ///
 /// The lifetime for the returned slice is inferred from its usage. To
@@ -219,9 +227,15 @@ pub const unsafe fn from_ptr_range<'a, T>(range: Range<*const T>) -> &'a [T] {
     unsafe { from_raw_parts(range.start, range.end.sub_ptr(range.start)) }
 }
 
-/// Performs the same functionality as [`from_ptr_range`], except that a
+/// Forms a mutable slice from a pointer range.
+///
+/// This is the same functionality as [`from_ptr_range`], except that a
 /// mutable slice is returned.
 ///
+/// This function is useful for interacting with foreign interfaces which
+/// use two pointers to refer to a range of elements in memory, as is
+/// common in C++.
+///
 /// # Safety
 ///
 /// Behavior is undefined if any of the following conditions are violated:
@@ -247,6 +261,18 @@ pub const unsafe fn from_ptr_range<'a, T>(range: Range<*const T>) -> &'a [T] {
 ///
 /// Note that a range created from [`slice::as_mut_ptr_range`] fulfills these requirements.
 ///
+/// # Panics
+///
+/// This function panics if `T` is a Zero-Sized Type (“ZST”).
+///
+/// # Caveat
+///
+/// The lifetime for the returned slice is inferred from its usage. To
+/// prevent accidental misuse, it's suggested to tie the lifetime to whichever
+/// source lifetime is safe in the context, such as by providing a helper
+/// function taking the lifetime of a host value for the slice, or by explicit
+/// annotation.
+///
 /// # Examples
 ///
 /// ```
diff --git a/library/core/src/slice/rotate.rs b/library/core/src/slice/rotate.rs
index 4589c6c0f..fa8c238f8 100644
--- a/library/core/src/slice/rotate.rs
+++ b/library/core/src/slice/rotate.rs
@@ -1,5 +1,5 @@
 use crate::cmp;
-use crate::mem::{self, MaybeUninit};
+use crate::mem::{self, MaybeUninit, SizedTypeProperties};
 use crate::ptr;
 
 /// Rotates the range `[mid-left, mid+right)` such that the element at `mid` becomes the first
@@ -63,7 +63,7 @@ use crate::ptr;
 /// when `left < right` the swapping happens from the left instead.
 pub unsafe fn ptr_rotate<T>(mut left: usize, mut mid: *mut T, mut right: usize) {
     type BufType = [usize; 32];
-    if mem::size_of::<T>() == 0 {
+    if T::IS_ZST {
         return;
     }
     loop {
diff --git a/library/core/src/slice/sort.rs b/library/core/src/slice/sort.rs
index c6c03c0b0..87f77b7f2 100644
--- a/library/core/src/slice/sort.rs
+++ b/library/core/src/slice/sort.rs
@@ -7,7 +7,7 @@
 //! stable sorting implementation.
 
 use crate::cmp;
-use crate::mem::{self, MaybeUninit};
+use crate::mem::{self, MaybeUninit, SizedTypeProperties};
 use crate::ptr;
 
 /// When dropped, copies from `src` into `dest`.
@@ -813,7 +813,7 @@ where
     F: FnMut(&T, &T) -> bool,
 {
     // Sorting has no meaningful behavior on zero-sized types.
-    if mem::size_of::<T>() == 0 {
+    if T::IS_ZST {
         return;
     }
 
@@ -898,7 +898,7 @@ where
         panic!("partition_at_index index {} greater than length of slice {}", index, v.len());
     }
 
-    if mem::size_of::<T>() == 0 {
+    if T::IS_ZST {
         // Sorting has no meaningful behavior on zero-sized types. Do nothing.
     } else if index == v.len() - 1 {
         // Find max element and place it in the last position of the array. We're free to use