diff --git a/library/alloc/src/vec/mod.rs b/library/alloc/src/vec/mod.rs
index 9a66e69bdc061..1ca5ee5537582 100644
--- a/library/alloc/src/vec/mod.rs
+++ b/library/alloc/src/vec/mod.rs
@@ -479,12 +479,14 @@ impl<T> Vec<T> {
     ///
     /// * `ptr` needs to have been previously allocated via [`String`]/`Vec<T>`
     ///   (at least, it's highly likely to be incorrect if it wasn't).
-    /// * `T` needs to have the same size and alignment as what `ptr` was allocated with.
+    /// * `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
     ///   allocated and deallocated with the same layout.)
+    /// * The size of `T` times the `capacity` (ie. the allocated size in bytes) needs
+    ///   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`.
-    /// * `capacity` needs to be the capacity that the pointer was allocated with.
     ///
     /// Violating these may cause problems like corrupting the allocator's
     /// internal data structures. For example it is **not** safe
@@ -492,7 +494,9 @@ impl<T> Vec<T> {
     /// It's also not safe to build one from a `Vec<u16>` and its length, because
     /// the allocator cares about the alignment, and these two types have different
     /// alignments. The buffer was allocated with alignment 2 (for `u16`), but after
-    /// turning it into a `Vec<u8>` it'll be deallocated with alignment 1.
+    /// turning it into a `Vec<u8>` it'll be deallocated with alignment 1. To avoid
+    /// these issues, it is often preferable to do casting/transmuting using
+    /// [`slice::from_raw_parts`] instead.
     ///
     /// The ownership of `ptr` is effectively transferred to the
     /// `Vec<T>` which may then deallocate, reallocate or change the
@@ -2929,6 +2933,48 @@ impl<T, const N: usize> From<[T; N]> for Vec<T> {
     }
 }
 
+#[cfg(not(no_global_oom_handling))]
+#[stable(feature = "vec_from_array_ref", since = "1.61.0")]
+impl<T: Clone, const N: usize> From<&[T; N]> for Vec<T> {
+    /// Allocate a `Vec<T>` and fill it by cloning `s`'s items.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// assert_eq!(Vec::from(b"raw"), vec![b'r', b'a', b'w']);
+    /// ```
+    #[cfg(not(test))]
+    fn from(s: &[T; N]) -> Vec<T> {
+        s.to_vec()
+    }
+
+    #[cfg(test)]
+    fn from(s: &[T; N]) -> Vec<T> {
+        crate::slice::to_vec(s, Global)
+    }
+}
+
+#[cfg(not(no_global_oom_handling))]
+#[stable(feature = "vec_from_array_ref", since = "1.61.0")]
+impl<T: Clone, const N: usize> From<&mut [T; N]> for Vec<T> {
+    /// Allocate a `Vec<T>` and fill it by cloning `s`'s items.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// assert_eq!(Vec::from(&mut [1, 2, 3]), vec![1, 2, 3]);
+    /// ```
+    #[cfg(not(test))]
+    fn from(s: &mut [T; N]) -> Vec<T> {
+        s.to_vec()
+    }
+
+    #[cfg(test)]
+    fn from(s: &mut [T; N]) -> Vec<T> {
+        crate::slice::to_vec(s, Global)
+    }
+}
+
 #[stable(feature = "vec_from_cow_slice", since = "1.14.0")]
 impl<'a, T> From<Cow<'a, [T]>> for Vec<T>
 where
diff --git a/library/alloc/src/vec/partial_eq.rs b/library/alloc/src/vec/partial_eq.rs
index 50e1409610507..b0cf72577a1be 100644
--- a/library/alloc/src/vec/partial_eq.rs
+++ b/library/alloc/src/vec/partial_eq.rs
@@ -20,7 +20,7 @@ macro_rules! __impl_slice_eq1 {
     }
 }
 
-__impl_slice_eq1! { [A: Allocator] Vec<T, A>, Vec<U, A>, #[stable(feature = "rust1", since = "1.0.0")] }
+__impl_slice_eq1! { [A1: Allocator, A2: Allocator] Vec<T, A1>, Vec<U, A2>, #[stable(feature = "rust1", since = "1.0.0")] }
 __impl_slice_eq1! { [A: Allocator] Vec<T, A>, &[U], #[stable(feature = "rust1", since = "1.0.0")] }
 __impl_slice_eq1! { [A: Allocator] Vec<T, A>, &mut [U], #[stable(feature = "rust1", since = "1.0.0")] }
 __impl_slice_eq1! { [A: Allocator] &[T], Vec<U, A>, #[stable(feature = "partialeq_vec_for_ref_slice", since = "1.46.0")] }
diff --git a/library/core/src/mem/manually_drop.rs b/library/core/src/mem/manually_drop.rs
index f577f102e8db2..3d719afe49e4a 100644
--- a/library/core/src/mem/manually_drop.rs
+++ b/library/core/src/mem/manually_drop.rs
@@ -4,11 +4,12 @@ use crate::ptr;
 /// A wrapper to inhibit compiler from automatically calling `T`’s destructor.
 /// This wrapper is 0-cost.
 ///
-/// `ManuallyDrop<T>` is subject to the same layout optimizations as `T`.
-/// As a consequence, it has *no effect* on the assumptions that the compiler makes
-/// about its contents. For example, initializing a `ManuallyDrop<&mut T>`
-/// with [`mem::zeroed`] is undefined behavior.
-/// If you need to handle uninitialized data, use [`MaybeUninit<T>`] instead.
+/// `ManuallyDrop<T>` is guaranteed to have the same layout as `T`, and is subject
+/// to the same layout optimizations as `T`. As a consequence, it has *no effect*
+/// on the assumptions that the compiler makes about its contents. For example,
+/// initializing a `ManuallyDrop<&mut T>` with [`mem::zeroed`] is undefined
+/// behavior. If you need to handle uninitialized data, use [`MaybeUninit<T>`]
+/// instead.
 ///
 /// Note that accessing the value inside a `ManuallyDrop<T>` is safe.
 /// This means that a `ManuallyDrop<T>` whose content has been dropped must not