Remove non-focused memory leaks in core doctests for Miri.

Author: zachs18

core/src/mem/maybe_uninit.rs

@@ -274,6 +274,8 @@ impl<T> MaybeUninit<T> {
     /// use std::mem::MaybeUninit;
     ///
     /// let v: MaybeUninit<Vec<u8>> = MaybeUninit::new(vec![42]);
+    /// # // Prevent leaks for Miri
+    /// # unsafe { let _ = MaybeUninit::assume_init(v); }
     /// ```
     ///
     /// [`assume_init`]: MaybeUninit::assume_init
@@ -506,6 +508,8 @@ impl<T> MaybeUninit<T> {
     /// // Create a reference into the `MaybeUninit<T>`. This is okay because we initialized it.
     /// let x_vec = unsafe { &*x.as_ptr() };
     /// assert_eq!(x_vec.len(), 3);
+    /// # // Prevent leaks for Miri
+    /// # unsafe { MaybeUninit::assume_init_drop(&mut x); }
     /// ```
     ///
     /// *Incorrect* usage of this method:
@@ -545,6 +549,8 @@ impl<T> MaybeUninit<T> {
     /// let x_vec = unsafe { &mut *x.as_mut_ptr() };
     /// x_vec.push(3);
     /// assert_eq!(x_vec.len(), 4);
+    /// # // Prevent leaks for Miri
+    /// # unsafe { MaybeUninit::assume_init_drop(&mut x); }
     /// ```
     ///
     /// *Incorrect* usage of this method:
@@ -746,6 +752,8 @@ impl<T> MaybeUninit<T> {
     /// use std::mem::MaybeUninit;
     ///
     /// let mut x = MaybeUninit::<Vec<u32>>::uninit();
+    /// # let mut x_mu = x;
+    /// # let mut x = &mut x_mu;
     /// // Initialize `x`:
     /// x.write(vec![1, 2, 3]);
     /// // Now that our `MaybeUninit<_>` is known to be initialized, it is okay to
@@ -755,6 +763,8 @@ impl<T> MaybeUninit<T> {
     ///     x.assume_init_ref()
     /// };
     /// assert_eq!(x, &vec![1, 2, 3]);
+    /// # // Prevent leaks for Miri
+    /// # unsafe { MaybeUninit::assume_init_drop(&mut x_mu); }
     /// ```
     ///
     /// ### *Incorrect* usages of this method:
@@ -1088,6 +1098,8 @@ impl<T> MaybeUninit<T> {
     /// let init = MaybeUninit::clone_from_slice(&mut dst, &src);
     ///
     /// assert_eq!(init, src);
+    /// # // Prevent leaks for Miri
+    /// # unsafe { std::ptr::drop_in_place(init); }
     /// ```
     ///
     /// ```

core/src/ptr/non_null.rs

@@ -1663,6 +1663,8 @@ impl<T> NonNull<[T]> {
     /// // Note that calling `memory.as_mut()` is not allowed here as the content may be uninitialized.
     /// # #[allow(unused_variables)]
     /// let slice: &mut [MaybeUninit<u8>] = unsafe { memory.as_uninit_slice_mut() };
+    /// # // Prevent leaks for Miri.
+    /// # unsafe { Global.deallocate(memory.cast(), Layout::new::<[u8; 32]>()); }
     /// # Ok::<_, std::alloc::AllocError>(())
     /// ```
     #[inline]