Remove &[T] from vec_deque::Drain

Author: saethlin

Diff for: library/alloc/src/collections/vec_deque/iter.rs

@@ -1,7 +1,9 @@
 use core::fmt;
 use core::iter::{FusedIterator, TrustedLen, TrustedRandomAccess, TrustedRandomAccessNoCoerce};
+use core::marker::PhantomData;
 use core::mem::MaybeUninit;
 use core::ops::Try;
+use core::ptr::NonNull;
 
 use super::{count, wrap_index, RingSlices};
 
@@ -13,38 +15,53 @@ use super::{count, wrap_index, RingSlices};
 /// [`iter`]: super::VecDeque::iter
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct Iter<'a, T: 'a> {
-    ring: &'a [MaybeUninit<T>],
+    ring: NonNull<[T]>,
     tail: usize,
     head: usize,
+    _marker: PhantomData<&'a T>,
 }
 
 impl<'a, T> Iter<'a, T> {
     pub(super) fn new(ring: &'a [MaybeUninit<T>], tail: usize, head: usize) -> Self {
-        Iter { ring, tail, head }
+        Iter {
+            ring: unsafe { NonNull::new_unchecked(ring as *const [MaybeUninit<T>] as *mut _) },
+            tail,
+            head,
+            _marker: PhantomData,
+        }
+    }
+
+    unsafe fn ring(&self) -> &'a [MaybeUninit<T>] {
+        unsafe {
+            core::slice::from_raw_parts(
+                self.ring.as_ptr() as *const MaybeUninit<T>,
+                self.ring.len(),
+            )
+        }
     }
 }
 
+#[stable(feature = "rust1", since = "1.0.0")]
+unsafe impl<T: Sync> Sync for Iter<'_, T> {}
+#[stable(feature = "rust1", since = "1.0.0")]
+unsafe impl<T: Sync> Send for Iter<'_, T> {}
+
 #[stable(feature = "collection_debug", since = "1.17.0")]
 impl<T: fmt::Debug> fmt::Debug for Iter<'_, T> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        let (front, back) = RingSlices::ring_slices(self.ring, self.head, self.tail);
+        let (front, back) = unsafe { RingSlices::ring_slices(self.ring(), self.head, self.tail) };
         // Safety:
         // - `self.head` and `self.tail` in a ring buffer are always valid indices.
         // - `RingSlices::ring_slices` guarantees that the slices split according to `self.head` and `self.tail` are initialized.
-        unsafe {
-            f.debug_tuple("Iter")
-                .field(&MaybeUninit::slice_assume_init_ref(front))
-                .field(&MaybeUninit::slice_assume_init_ref(back))
-                .finish()
-        }
+        f.debug_tuple("Iter").field(&front).field(&back).finish()
     }
 }
 
 // FIXME(#26925) Remove in favor of `#[derive(Clone)]`
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T> Clone for Iter<'_, T> {
     fn clone(&self) -> Self {
-        Iter { ring: self.ring, tail: self.tail, head: self.head }
+        Iter { ring: self.ring, tail: self.tail, head: self.head, _marker: PhantomData }
     }
 }
 
@@ -62,7 +79,7 @@ impl<'a, T> Iterator for Iter<'a, T> {
         // Safety:
         // - `self.tail` in a ring buffer is always a valid index.
         // - `self.head` and `self.tail` equality is checked above.
-        unsafe { Some(self.ring.get_unchecked(tail).assume_init_ref()) }
+        unsafe { Some(self.ring().get_unchecked(tail).assume_init_ref()) }
     }
 
     #[inline]
@@ -75,11 +92,11 @@ impl<'a, T> Iterator for Iter<'a, T> {
     where
         F: FnMut(Acc, Self::Item) -> Acc,
     {
-        let (front, back) = RingSlices::ring_slices(self.ring, self.head, self.tail);
         // Safety:
         // - `self.head` and `self.tail` in a ring buffer are always valid indices.
         // - `RingSlices::ring_slices` guarantees that the slices split according to `self.head` and `self.tail` are initialized.
         unsafe {
+            let (front, back) = RingSlices::ring_slices(self.ring(), self.head, self.tail);
             accum = MaybeUninit::slice_assume_init_ref(front).iter().fold(accum, &mut f);
             MaybeUninit::slice_assume_init_ref(back).iter().fold(accum, &mut f)
         }
@@ -94,12 +111,13 @@ impl<'a, T> Iterator for Iter<'a, T> {
         let (mut iter, final_res);
         if self.tail <= self.head {
             // Safety: single slice self.ring[self.tail..self.head] is initialized.
-            iter = unsafe { MaybeUninit::slice_assume_init_ref(&self.ring[self.tail..self.head]) }
-                .iter();
+            iter =
+                unsafe { MaybeUninit::slice_assume_init_ref(&self.ring()[self.tail..self.head]) }
+                    .iter();
             final_res = iter.try_fold(init, &mut f);
         } else {
-            // Safety: two slices: self.ring[self.tail..], self.ring[..self.head] both are initialized.
-            let (front, back) = self.ring.split_at(self.tail);
+            // Safety: two slices: self.ring()[self.tail..], self.ring()[..self.head] both are initialized.
+            let (front, back) = unsafe { self.ring().split_at(self.tail) };
 
             let mut back_iter = unsafe { MaybeUninit::slice_assume_init_ref(back).iter() };
             let res = back_iter.try_fold(init, &mut f);
@@ -133,7 +151,7 @@ impl<'a, T> Iterator for Iter<'a, T> {
         // that is in bounds.
         unsafe {
             let idx = wrap_index(self.tail.wrapping_add(idx), self.ring.len());
-            self.ring.get_unchecked(idx).assume_init_ref()
+            self.ring().get_unchecked(idx).assume_init_ref()
         }
     }
 }
@@ -149,18 +167,18 @@ impl<'a, T> DoubleEndedIterator for Iter<'a, T> {
         // Safety:
         // - `self.head` in a ring buffer is always a valid index.
         // - `self.head` and `self.tail` equality is checked above.
-        unsafe { Some(self.ring.get_unchecked(self.head).assume_init_ref()) }
+        unsafe { Some(self.ring().get_unchecked(self.head).assume_init_ref()) }
     }
 
     fn rfold<Acc, F>(self, mut accum: Acc, mut f: F) -> Acc
     where
         F: FnMut(Acc, Self::Item) -> Acc,
     {
-        let (front, back) = RingSlices::ring_slices(self.ring, self.head, self.tail);
         // Safety:
         // - `self.head` and `self.tail` in a ring buffer are always valid indices.
         // - `RingSlices::ring_slices` guarantees that the slices split according to `self.head` and `self.tail` are initialized.
         unsafe {
+            let (front, back) = RingSlices::ring_slices(self.ring(), self.head, self.tail);
             accum = MaybeUninit::slice_assume_init_ref(back).iter().rfold(accum, &mut f);
             MaybeUninit::slice_assume_init_ref(front).iter().rfold(accum, &mut f)
         }
@@ -174,14 +192,14 @@ impl<'a, T> DoubleEndedIterator for Iter<'a, T> {
     {
         let (mut iter, final_res);
         if self.tail <= self.head {
-            // Safety: single slice self.ring[self.tail..self.head] is initialized.
+            // Safety: single slice self.ring()[self.tail..self.head] is initialized.
             iter = unsafe {
-                MaybeUninit::slice_assume_init_ref(&self.ring[self.tail..self.head]).iter()
+                MaybeUninit::slice_assume_init_ref(&self.ring()[self.tail..self.head]).iter()
             };
             final_res = iter.try_rfold(init, &mut f);
         } else {
-            // Safety: two slices: self.ring[self.tail..], self.ring[..self.head] both are initialized.
-            let (front, back) = self.ring.split_at(self.tail);
+            // Safety: two slices: self.ring()[self.tail..], self.ring()[..self.head] both are initialized.
+            let (front, back) = unsafe { self.ring().split_at(self.tail) };
 
             let mut front_iter =
                 unsafe { MaybeUninit::slice_assume_init_ref(&front[..self.head]).iter() };