Adding upstream version 124.0.1.upstream/124.0.1

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

8 files changed, 723 insertions, 0 deletions

diff --git a/third_party/rust/rayon/src/collections/binary_heap.rs b/third_party/rust/rayon/src/collections/binary_heap.rs
new file mode 100644
index 0000000000..fa903121af
--- /dev/null
+++ b/third_party/rust/rayon/src/collections/binary_heap.rs
@@ -0,0 +1,120 @@
+//! This module contains the parallel iterator types for heaps
+//! (`BinaryHeap<T>`). You will rarely need to interact with it directly
+//! unless you have need to name one of the iterator types.
+
+use std::collections::BinaryHeap;
+
+use crate::iter::plumbing::*;
+use crate::iter::*;
+
+use crate::vec;
+
+/// Parallel iterator over a binary heap
+#[derive(Debug, Clone)]
+pub struct IntoIter<T: Ord + Send> {
+    inner: vec::IntoIter<T>,
+}
+
+impl<T: Ord + Send> IntoParallelIterator for BinaryHeap<T> {
+    type Item = T;
+    type Iter = IntoIter<T>;
+
+    fn into_par_iter(self) -> Self::Iter {
+        IntoIter {
+            inner: Vec::from(self).into_par_iter(),
+        }
+    }
+}
+
+delegate_indexed_iterator! {
+    IntoIter<T> => T,
+    impl<T: Ord + Send>
+}
+
+/// Parallel iterator over an immutable reference to a binary heap
+#[derive(Debug)]
+pub struct Iter<'a, T: Ord + Sync> {
+    inner: vec::IntoIter<&'a T>,
+}
+
+impl<'a, T: Ord + Sync> Clone for Iter<'a, T> {
+    fn clone(&self) -> Self {
+        Iter {
+            inner: self.inner.clone(),
+        }
+    }
+}
+
+into_par_vec! {
+    &'a BinaryHeap<T> => Iter<'a, T>,
+    impl<'a, T: Ord + Sync>
+}
+
+delegate_indexed_iterator! {
+    Iter<'a, T> => &'a T,
+    impl<'a, T: Ord + Sync + 'a>
+}
+
+// `BinaryHeap` doesn't have a mutable `Iterator`
+
+/// Draining parallel iterator that moves out of a binary heap,
+/// but keeps the total capacity.
+#[derive(Debug)]
+pub struct Drain<'a, T: Ord + Send> {
+    heap: &'a mut BinaryHeap<T>,
+}
+
+impl<'a, T: Ord + Send> ParallelDrainFull for &'a mut BinaryHeap<T> {
+    type Iter = Drain<'a, T>;
+    type Item = T;
+
+    fn par_drain(self) -> Self::Iter {
+        Drain { heap: self }
+    }
+}
+
+impl<'a, T: Ord + Send> ParallelIterator for Drain<'a, T> {
+    type Item = T;
+
+    fn drive_unindexed<C>(self, consumer: C) -> C::Result
+    where
+        C: UnindexedConsumer<Self::Item>,
+    {
+        bridge(self, consumer)
+    }
+
+    fn opt_len(&self) -> Option<usize> {
+        Some(self.len())
+    }
+}
+
+impl<'a, T: Ord + Send> IndexedParallelIterator for Drain<'a, T> {
+    fn drive<C>(self, consumer: C) -> C::Result
+    where
+        C: Consumer<Self::Item>,
+    {
+        bridge(self, consumer)
+    }
+
+    fn len(&self) -> usize {
+        self.heap.len()
+    }
+
+    fn with_producer<CB>(self, callback: CB) -> CB::Output
+    where
+        CB: ProducerCallback<Self::Item>,
+    {
+        super::DrainGuard::new(self.heap)
+            .par_drain(..)
+            .with_producer(callback)
+    }
+}
+
+impl<'a, T: Ord + Send> Drop for Drain<'a, T> {
+    fn drop(&mut self) {
+        if !self.heap.is_empty() {
+            // We must not have produced, so just call a normal drain to remove the items.
+            self.heap.drain();
+        }
+    }
+}
diff --git a/third_party/rust/rayon/src/collections/btree_map.rs b/third_party/rust/rayon/src/collections/btree_map.rs
new file mode 100644
index 0000000000..12436dca1c
--- /dev/null
+++ b/third_party/rust/rayon/src/collections/btree_map.rs
@@ -0,0 +1,66 @@
+//! This module contains the parallel iterator types for B-Tree maps
+//! (`BTreeMap<K, V>`). You will rarely need to interact with it directly
+//! unless you have need to name one of the iterator types.
+
+use std::collections::BTreeMap;
+
+use crate::iter::plumbing::*;
+use crate::iter::*;
+
+use crate::vec;
+
+/// Parallel iterator over a B-Tree map
+#[derive(Debug)] // std doesn't Clone
+pub struct IntoIter<K: Ord + Send, V: Send> {
+    inner: vec::IntoIter<(K, V)>,
+}
+
+into_par_vec! {
+    BTreeMap<K, V> => IntoIter<K, V>,
+    impl<K: Ord + Send, V: Send>
+}
+
+delegate_iterator! {
+    IntoIter<K, V> => (K, V),
+    impl<K: Ord + Send, V: Send>
+}
+
+/// Parallel iterator over an immutable reference to a B-Tree map
+#[derive(Debug)]
+pub struct Iter<'a, K: Ord + Sync, V: Sync> {
+    inner: vec::IntoIter<(&'a K, &'a V)>,
+}
+
+impl<'a, K: Ord + Sync, V: Sync> Clone for Iter<'a, K, V> {
+    fn clone(&self) -> Self {
+        Iter {
+            inner: self.inner.clone(),
+        }
+    }
+}
+
+into_par_vec! {
+    &'a BTreeMap<K, V> => Iter<'a, K, V>,
+    impl<'a, K: Ord + Sync, V: Sync>
+}
+
+delegate_iterator! {
+    Iter<'a, K, V> => (&'a K, &'a V),
+    impl<'a, K: Ord + Sync + 'a, V: Sync + 'a>
+}
+
+/// Parallel iterator over a mutable reference to a B-Tree map
+#[derive(Debug)]
+pub struct IterMut<'a, K: Ord + Sync, V: Send> {
+    inner: vec::IntoIter<(&'a K, &'a mut V)>,
+}
+
+into_par_vec! {
+    &'a mut BTreeMap<K, V> => IterMut<'a, K, V>,
+    impl<'a, K: Ord + Sync, V: Send>
+}
+
+delegate_iterator! {
+    IterMut<'a, K, V> => (&'a K, &'a mut V),
+    impl<'a, K: Ord + Sync + 'a, V: Send + 'a>
+}
diff --git a/third_party/rust/rayon/src/collections/btree_set.rs b/third_party/rust/rayon/src/collections/btree_set.rs
new file mode 100644
index 0000000000..061d37c7ea
--- /dev/null
+++ b/third_party/rust/rayon/src/collections/btree_set.rs
@@ -0,0 +1,52 @@
+//! This module contains the parallel iterator types for B-Tree sets
+//! (`BTreeSet<T>`). You will rarely need to interact with it directly
+//! unless you have need to name one of the iterator types.
+
+use std::collections::BTreeSet;
+
+use crate::iter::plumbing::*;
+use crate::iter::*;
+
+use crate::vec;
+
+/// Parallel iterator over a B-Tree set
+#[derive(Debug)] // std doesn't Clone
+pub struct IntoIter<T: Ord + Send> {
+    inner: vec::IntoIter<T>,
+}
+
+into_par_vec! {
+    BTreeSet<T> => IntoIter<T>,
+    impl<T: Ord + Send>
+}
+
+delegate_iterator! {
+    IntoIter<T> => T,
+    impl<T: Ord + Send>
+}
+
+/// Parallel iterator over an immutable reference to a B-Tree set
+#[derive(Debug)]
+pub struct Iter<'a, T: Ord + Sync> {
+    inner: vec::IntoIter<&'a T>,
+}
+
+impl<'a, T: Ord + Sync + 'a> Clone for Iter<'a, T> {
+    fn clone(&self) -> Self {
+        Iter {
+            inner: self.inner.clone(),
+        }
+    }
+}
+
+into_par_vec! {
+    &'a BTreeSet<T> => Iter<'a, T>,
+    impl<'a, T: Ord + Sync>
+}
+
+delegate_iterator! {
+    Iter<'a, T> => &'a T,
+    impl<'a, T: Ord + Sync + 'a>
+}
+
+// `BTreeSet` doesn't have a mutable `Iterator`
diff --git a/third_party/rust/rayon/src/collections/hash_map.rs b/third_party/rust/rayon/src/collections/hash_map.rs
new file mode 100644
index 0000000000..b657851d89
--- /dev/null
+++ b/third_party/rust/rayon/src/collections/hash_map.rs
@@ -0,0 +1,96 @@
+//! This module contains the parallel iterator types for hash maps
+//! (`HashMap<K, V>`). You will rarely need to interact with it directly
+//! unless you have need to name one of the iterator types.
+
+use std::collections::HashMap;
+use std::hash::{BuildHasher, Hash};
+use std::marker::PhantomData;
+
+use crate::iter::plumbing::*;
+use crate::iter::*;
+
+use crate::vec;
+
+/// Parallel iterator over a hash map
+#[derive(Debug)] // std doesn't Clone
+pub struct IntoIter<K: Hash + Eq + Send, V: Send> {
+    inner: vec::IntoIter<(K, V)>,
+}
+
+into_par_vec! {
+    HashMap<K, V, S> => IntoIter<K, V>,
+    impl<K: Hash + Eq + Send, V: Send, S: BuildHasher>
+}
+
+delegate_iterator! {
+    IntoIter<K, V> => (K, V),
+    impl<K: Hash + Eq + Send, V: Send>
+}
+
+/// Parallel iterator over an immutable reference to a hash map
+#[derive(Debug)]
+pub struct Iter<'a, K: Hash + Eq + Sync, V: Sync> {
+    inner: vec::IntoIter<(&'a K, &'a V)>,
+}
+
+impl<'a, K: Hash + Eq + Sync, V: Sync> Clone for Iter<'a, K, V> {
+    fn clone(&self) -> Self {
+        Iter {
+            inner: self.inner.clone(),
+        }
+    }
+}
+
+into_par_vec! {
+    &'a HashMap<K, V, S> => Iter<'a, K, V>,
+    impl<'a, K: Hash + Eq + Sync, V: Sync, S: BuildHasher>
+}
+
+delegate_iterator! {
+    Iter<'a, K, V> => (&'a K, &'a V),
+    impl<'a, K: Hash + Eq + Sync + 'a, V: Sync + 'a>
+}
+
+/// Parallel iterator over a mutable reference to a hash map
+#[derive(Debug)]
+pub struct IterMut<'a, K: Hash + Eq + Sync, V: Send> {
+    inner: vec::IntoIter<(&'a K, &'a mut V)>,
+}
+
+into_par_vec! {
+    &'a mut HashMap<K, V, S> => IterMut<'a, K, V>,
+    impl<'a, K: Hash + Eq + Sync, V: Send, S: BuildHasher>
+}
+
+delegate_iterator! {
+    IterMut<'a, K, V> => (&'a K, &'a mut V),
+    impl<'a, K: Hash + Eq + Sync + 'a, V: Send + 'a>
+}
+
+/// Draining parallel iterator that moves out of a hash map,
+/// but keeps the total capacity.
+#[derive(Debug)]
+pub struct Drain<'a, K: Hash + Eq + Send, V: Send> {
+    inner: vec::IntoIter<(K, V)>,
+    marker: PhantomData<&'a mut HashMap<K, V>>,
+}
+
+impl<'a, K: Hash + Eq + Send, V: Send, S: BuildHasher> ParallelDrainFull
+    for &'a mut HashMap<K, V, S>
+{
+    type Iter = Drain<'a, K, V>;
+    type Item = (K, V);
+
+    fn par_drain(self) -> Self::Iter {
+        let vec: Vec<_> = self.drain().collect();
+        Drain {
+            inner: vec.into_par_iter(),
+            marker: PhantomData,
+        }
+    }
+}
+
+delegate_iterator! {
+    Drain<'_, K, V> => (K, V),
+    impl<K: Hash + Eq + Send, V: Send>
+}
diff --git a/third_party/rust/rayon/src/collections/hash_set.rs b/third_party/rust/rayon/src/collections/hash_set.rs
new file mode 100644
index 0000000000..b6ee1c1109
--- /dev/null
+++ b/third_party/rust/rayon/src/collections/hash_set.rs
@@ -0,0 +1,80 @@
+//! This module contains the parallel iterator types for hash sets
+//! (`HashSet<T>`). You will rarely need to interact with it directly
+//! unless you have need to name one of the iterator types.
+
+use std::collections::HashSet;
+use std::hash::{BuildHasher, Hash};
+use std::marker::PhantomData;
+
+use crate::iter::plumbing::*;
+use crate::iter::*;
+
+use crate::vec;
+
+/// Parallel iterator over a hash set
+#[derive(Debug)] // std doesn't Clone
+pub struct IntoIter<T: Hash + Eq + Send> {
+    inner: vec::IntoIter<T>,
+}
+
+into_par_vec! {
+    HashSet<T, S> => IntoIter<T>,
+    impl<T: Hash + Eq + Send, S: BuildHasher>
+}
+
+delegate_iterator! {
+    IntoIter<T> => T,
+    impl<T: Hash + Eq + Send>
+}
+
+/// Parallel iterator over an immutable reference to a hash set
+#[derive(Debug)]
+pub struct Iter<'a, T: Hash + Eq + Sync> {
+    inner: vec::IntoIter<&'a T>,
+}
+
+impl<'a, T: Hash + Eq + Sync> Clone for Iter<'a, T> {
+    fn clone(&self) -> Self {
+        Iter {
+            inner: self.inner.clone(),
+        }
+    }
+}
+
+into_par_vec! {
+    &'a HashSet<T, S> => Iter<'a, T>,
+    impl<'a, T: Hash + Eq + Sync, S: BuildHasher>
+}
+
+delegate_iterator! {
+    Iter<'a, T> => &'a T,
+    impl<'a, T: Hash + Eq + Sync + 'a>
+}
+
+// `HashSet` doesn't have a mutable `Iterator`
+
+/// Draining parallel iterator that moves out of a hash set,
+/// but keeps the total capacity.
+#[derive(Debug)]
+pub struct Drain<'a, T: Hash + Eq + Send> {
+    inner: vec::IntoIter<T>,
+    marker: PhantomData<&'a mut HashSet<T>>,
+}
+
+impl<'a, T: Hash + Eq + Send, S: BuildHasher> ParallelDrainFull for &'a mut HashSet<T, S> {
+    type Iter = Drain<'a, T>;
+    type Item = T;
+
+    fn par_drain(self) -> Self::Iter {
+        let vec: Vec<_> = self.drain().collect();
+        Drain {
+            inner: vec.into_par_iter(),
+            marker: PhantomData,
+        }
+    }
+}
+
+delegate_iterator! {
+    Drain<'_, T> => T,
+    impl<T: Hash + Eq + Send>
+}
diff --git a/third_party/rust/rayon/src/collections/linked_list.rs b/third_party/rust/rayon/src/collections/linked_list.rs
new file mode 100644
index 0000000000..bddd2b0fce
--- /dev/null
+++ b/third_party/rust/rayon/src/collections/linked_list.rs
@@ -0,0 +1,66 @@
+//! This module contains the parallel iterator types for linked lists
+//! (`LinkedList<T>`). You will rarely need to interact with it directly
+//! unless you have need to name one of the iterator types.
+
+use std::collections::LinkedList;
+
+use crate::iter::plumbing::*;
+use crate::iter::*;
+
+use crate::vec;
+
+/// Parallel iterator over a linked list
+#[derive(Debug, Clone)]
+pub struct IntoIter<T: Send> {
+    inner: vec::IntoIter<T>,
+}
+
+into_par_vec! {
+    LinkedList<T> => IntoIter<T>,
+    impl<T: Send>
+}
+
+delegate_iterator! {
+    IntoIter<T> => T,
+    impl<T: Send>
+}
+
+/// Parallel iterator over an immutable reference to a linked list
+#[derive(Debug)]
+pub struct Iter<'a, T: Sync> {
+    inner: vec::IntoIter<&'a T>,
+}
+
+impl<'a, T: Sync> Clone for Iter<'a, T> {
+    fn clone(&self) -> Self {
+        Iter {
+            inner: self.inner.clone(),
+        }
+    }
+}
+
+into_par_vec! {
+    &'a LinkedList<T> => Iter<'a, T>,
+    impl<'a, T: Sync>
+}
+
+delegate_iterator! {
+    Iter<'a, T> => &'a T,
+    impl<'a, T: Sync + 'a>
+}
+
+/// Parallel iterator over a mutable reference to a linked list
+#[derive(Debug)]
+pub struct IterMut<'a, T: Send> {
+    inner: vec::IntoIter<&'a mut T>,
+}
+
+into_par_vec! {
+    &'a mut LinkedList<T> => IterMut<'a, T>,
+    impl<'a, T: Send>
+}
+
+delegate_iterator! {
+    IterMut<'a, T> => &'a mut T,
+    impl<'a, T: Send + 'a>
+}
diff --git a/third_party/rust/rayon/src/collections/mod.rs b/third_party/rust/rayon/src/collections/mod.rs
new file mode 100644
index 0000000000..3c99f32c4a
--- /dev/null
+++ b/third_party/rust/rayon/src/collections/mod.rs
@@ -0,0 +1,84 @@
+//! Parallel iterator types for [standard collections][std::collections]
+//!
+//! You will rarely need to interact with this module directly unless you need
+//! to name one of the iterator types.
+//!
+//! [std::collections]: https://doc.rust-lang.org/stable/std/collections/
+
+/// Convert an iterable collection into a parallel iterator by first
+/// collecting into a temporary `Vec`, then iterating that.
+macro_rules! into_par_vec {
+    ($t:ty => $iter:ident<$($i:tt),*>, impl $($args:tt)*) => {
+        impl $($args)* IntoParallelIterator for $t {
+            type Item = <$t as IntoIterator>::Item;
+            type Iter = $iter<$($i),*>;
+
+            fn into_par_iter(self) -> Self::Iter {
+                use std::iter::FromIterator;
+                $iter { inner: Vec::from_iter(self).into_par_iter() }
+            }
+        }
+    };
+}
+
+pub mod binary_heap;
+pub mod btree_map;
+pub mod btree_set;
+pub mod hash_map;
+pub mod hash_set;
+pub mod linked_list;
+pub mod vec_deque;
+
+use self::drain_guard::DrainGuard;
+
+mod drain_guard {
+    use crate::iter::ParallelDrainRange;
+    use std::mem;
+    use std::ops::RangeBounds;
+
+    /// A proxy for draining a collection by converting to a `Vec` and back.
+    ///
+    /// This is used for draining `BinaryHeap` and `VecDeque`, which both have
+    /// zero-allocation conversions to/from `Vec`, though not zero-cost:
+    /// - `BinaryHeap` will heapify from `Vec`, but at least that will be empty.
+    /// - `VecDeque` has to shift items to offset 0 when converting to `Vec`.
+    #[allow(missing_debug_implementations)]
+    pub(super) struct DrainGuard<'a, T, C: From<Vec<T>>> {
+        collection: &'a mut C,
+        vec: Vec<T>,
+    }
+
+    impl<'a, T, C> DrainGuard<'a, T, C>
+    where
+        C: Default + From<Vec<T>>,
+        Vec<T>: From<C>,
+    {
+        pub(super) fn new(collection: &'a mut C) -> Self {
+            Self {
+                // Temporarily steal the inner `Vec` so we can drain in place.
+                vec: Vec::from(mem::take(collection)),
+                collection,
+            }
+        }
+    }
+
+    impl<'a, T, C: From<Vec<T>>> Drop for DrainGuard<'a, T, C> {
+        fn drop(&mut self) {
+            // Restore the collection from the `Vec` with its original capacity.
+            *self.collection = C::from(mem::take(&mut self.vec));
+        }
+    }
+
+    impl<'a, T, C> ParallelDrainRange<usize> for &'a mut DrainGuard<'_, T, C>
+    where
+        T: Send,
+        C: From<Vec<T>>,
+    {
+        type Iter = crate::vec::Drain<'a, T>;
+        type Item = T;
+
+        fn par_drain<R: RangeBounds<usize>>(self, range: R) -> Self::Iter {
+            self.vec.par_drain(range)
+        }
+    }
+}
diff --git a/third_party/rust/rayon/src/collections/vec_deque.rs b/third_party/rust/rayon/src/collections/vec_deque.rs
new file mode 100644
index 0000000000..f87ce6b185
--- /dev/null
+++ b/third_party/rust/rayon/src/collections/vec_deque.rs
@@ -0,0 +1,159 @@
+//! This module contains the parallel iterator types for double-ended queues
+//! (`VecDeque<T>`). You will rarely need to interact with it directly
+//! unless you have need to name one of the iterator types.
+
+use std::collections::VecDeque;
+use std::ops::{Range, RangeBounds};
+
+use crate::iter::plumbing::*;
+use crate::iter::*;
+use crate::math::simplify_range;
+
+use crate::slice;
+use crate::vec;
+
+/// Parallel iterator over a double-ended queue
+#[derive(Debug, Clone)]
+pub struct IntoIter<T: Send> {
+    inner: vec::IntoIter<T>,
+}
+
+impl<T: Send> IntoParallelIterator for VecDeque<T> {
+    type Item = T;
+    type Iter = IntoIter<T>;
+
+    fn into_par_iter(self) -> Self::Iter {
+        // NOTE: requires data movement if the deque doesn't start at offset 0.
+        let inner = Vec::from(self).into_par_iter();
+        IntoIter { inner }
+    }
+}
+
+delegate_indexed_iterator! {
+    IntoIter<T> => T,
+    impl<T: Send>
+}
+
+/// Parallel iterator over an immutable reference to a double-ended queue
+#[derive(Debug)]
+pub struct Iter<'a, T: Sync> {
+    inner: Chain<slice::Iter<'a, T>, slice::Iter<'a, T>>,
+}
+
+impl<'a, T: Sync> Clone for Iter<'a, T> {
+    fn clone(&self) -> Self {
+        Iter {
+            inner: self.inner.clone(),
+        }
+    }
+}
+
+impl<'a, T: Sync> IntoParallelIterator for &'a VecDeque<T> {
+    type Item = &'a T;
+    type Iter = Iter<'a, T>;
+
+    fn into_par_iter(self) -> Self::Iter {
+        let (a, b) = self.as_slices();
+        Iter {
+            inner: a.into_par_iter().chain(b),
+        }
+    }
+}
+
+delegate_indexed_iterator! {
+    Iter<'a, T> => &'a T,
+    impl<'a, T: Sync + 'a>
+}
+
+/// Parallel iterator over a mutable reference to a double-ended queue
+#[derive(Debug)]
+pub struct IterMut<'a, T: Send> {
+    inner: Chain<slice::IterMut<'a, T>, slice::IterMut<'a, T>>,
+}
+
+impl<'a, T: Send> IntoParallelIterator for &'a mut VecDeque<T> {
+    type Item = &'a mut T;
+    type Iter = IterMut<'a, T>;
+
+    fn into_par_iter(self) -> Self::Iter {
+        let (a, b) = self.as_mut_slices();
+        IterMut {
+            inner: a.into_par_iter().chain(b),
+        }
+    }
+}
+
+delegate_indexed_iterator! {
+    IterMut<'a, T> => &'a mut T,
+    impl<'a, T: Send + 'a>
+}
+
+/// Draining parallel iterator that moves a range out of a double-ended queue,
+/// but keeps the total capacity.
+#[derive(Debug)]
+pub struct Drain<'a, T: Send> {
+    deque: &'a mut VecDeque<T>,
+    range: Range<usize>,
+    orig_len: usize,
+}
+
+impl<'a, T: Send> ParallelDrainRange<usize> for &'a mut VecDeque<T> {
+    type Iter = Drain<'a, T>;
+    type Item = T;
+
+    fn par_drain<R: RangeBounds<usize>>(self, range: R) -> Self::Iter {
+        Drain {
+            orig_len: self.len(),
+            range: simplify_range(range, self.len()),
+            deque: self,
+        }
+    }
+}
+
+impl<'a, T: Send> ParallelIterator for Drain<'a, T> {
+    type Item = T;
+
+    fn drive_unindexed<C>(self, consumer: C) -> C::Result
+    where
+        C: UnindexedConsumer<Self::Item>,
+    {
+        bridge(self, consumer)
+    }
+
+    fn opt_len(&self) -> Option<usize> {
+        Some(self.len())
+    }
+}
+
+impl<'a, T: Send> IndexedParallelIterator for Drain<'a, T> {
+    fn drive<C>(self, consumer: C) -> C::Result
+    where
+        C: Consumer<Self::Item>,
+    {
+        bridge(self, consumer)
+    }
+
+    fn len(&self) -> usize {
+        self.range.len()
+    }
+
+    fn with_producer<CB>(self, callback: CB) -> CB::Output
+    where
+        CB: ProducerCallback<Self::Item>,
+    {
+        // NOTE: requires data movement if the deque doesn't start at offset 0.
+        super::DrainGuard::new(self.deque)
+            .par_drain(self.range.clone())
+            .with_producer(callback)
+    }
+}
+
+impl<'a, T: Send> Drop for Drain<'a, T> {
+    fn drop(&mut self) {
+        if self.deque.len() != self.orig_len - self.range.len() {
+            // We must not have produced, so just call a normal drain to remove the items.
+            assert_eq!(self.deque.len(), self.orig_len);
+            self.deque.drain(self.range.clone());
+        }
+    }
+}