Adding upstream version 115.7.0esr.upstream/115.7.0esrupstream

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

1 files changed, 2179 insertions, 0 deletions

diff --git a/third_party/rust/hashlink/src/linked_hash_map.rs b/third_party/rust/hashlink/src/linked_hash_map.rs
new file mode 100644
index 0000000000..b27c98b82b
--- /dev/null
+++ b/third_party/rust/hashlink/src/linked_hash_map.rs
@@ -0,0 +1,2179 @@
+use std::{
+    alloc::Layout,
+    borrow::Borrow,
+    cmp::Ordering,
+    fmt,
+    hash::{BuildHasher, Hash, Hasher},
+    iter::FromIterator,
+    marker::PhantomData,
+    mem::{self, MaybeUninit},
+    ops::{Index, IndexMut},
+    ptr::{self, NonNull},
+};
+
+use hashbrown::{hash_map, HashMap};
+
+pub enum TryReserveError {
+    CapacityOverflow,
+    AllocError { layout: Layout },
+}
+
+/// A version of `HashMap` that has a user controllable order for its entries.
+///
+/// It achieves this by keeping its entries in an internal linked list and using a `HashMap` to
+/// point at nodes in this linked list.
+///
+/// The order of entries defaults to "insertion order", but the user can also modify the order of
+/// existing entries by manually moving them to the front or back.
+///
+/// There are two kinds of methods that modify the order of the internal list:
+///
+/// * Methods that have names like `to_front` and `to_back` will unsurprisingly move an existing
+///   entry to the front or back
+/// * Methods that have the word `insert` will insert a new entry ot the back of the list, and if
+///   that method might replace an entry, that method will *also move that existing entry to the
+///   back*.
+pub struct LinkedHashMap<K, V, S = hash_map::DefaultHashBuilder> {
+    map: HashMap<NonNull<Node<K, V>>, (), NullHasher>,
+    // We need to keep any custom hash builder outside of the HashMap so we can access it alongside
+    // the entry API without mutable aliasing.
+    hash_builder: S,
+    // Circular linked list of nodes.  If `values` is non-null, it will point to a "guard node"
+    // which will never have an initialized key or value, `values.prev` will contain the last key /
+    // value in the list, `values.next` will contain the first key / value in the list.
+    values: Option<NonNull<Node<K, V>>>,
+    // *Singly* linked list of free nodes.  The `prev` pointers in the free list should be assumed
+    // invalid.
+    free: Option<NonNull<Node<K, V>>>,
+}
+
+impl<K, V> LinkedHashMap<K, V> {
+    #[inline]
+    pub fn new() -> Self {
+        Self {
+            hash_builder: hash_map::DefaultHashBuilder::default(),
+            map: HashMap::with_hasher(NullHasher),
+            values: None,
+            free: None,
+        }
+    }
+
+    #[inline]
+    pub fn with_capacity(capacity: usize) -> Self {
+        Self {
+            hash_builder: hash_map::DefaultHashBuilder::default(),
+            map: HashMap::with_capacity_and_hasher(capacity, NullHasher),
+            values: None,
+            free: None,
+        }
+    }
+}
+
+impl<K, V, S> LinkedHashMap<K, V, S> {
+    #[inline]
+    pub fn with_hasher(hash_builder: S) -> Self {
+        Self {
+            hash_builder,
+            map: HashMap::with_hasher(NullHasher),
+            values: None,
+            free: None,
+        }
+    }
+
+    #[inline]
+    pub fn with_capacity_and_hasher(capacity: usize, hash_builder: S) -> Self {
+        Self {
+            hash_builder,
+            map: HashMap::with_capacity_and_hasher(capacity, NullHasher),
+            values: None,
+            free: None,
+        }
+    }
+
+    #[inline]
+    pub fn reserve(&mut self, additional: usize) {
+        self.map.reserve(additional);
+    }
+
+    #[inline]
+    pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> {
+        self.map.try_reserve(additional).map_err(|e| match e {
+            hashbrown::TryReserveError::CapacityOverflow => TryReserveError::CapacityOverflow,
+            hashbrown::TryReserveError::AllocError { layout } => {
+                TryReserveError::AllocError { layout }
+            }
+        })
+    }
+
+    #[inline]
+    pub fn len(&self) -> usize {
+        self.map.len()
+    }
+
+    #[inline]
+    pub fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
+
+    #[inline]
+    pub fn clear(&mut self) {
+        self.map.clear();
+        if let Some(mut values) = self.values {
+            unsafe {
+                drop_value_nodes(values);
+                values.as_mut().links.value = ValueLinks {
+                    prev: values,
+                    next: values,
+                };
+            }
+        }
+    }
+
+    #[inline]
+    pub fn iter(&self) -> Iter<K, V> {
+        let (head, tail) = if let Some(values) = self.values {
+            unsafe {
+                let ValueLinks { next, prev } = values.as_ref().links.value;
+                (next.as_ptr(), prev.as_ptr())
+            }
+        } else {
+            (ptr::null_mut(), ptr::null_mut())
+        };
+
+        Iter {
+            head,
+            tail,
+            remaining: self.len(),
+            marker: PhantomData,
+        }
+    }
+
+    #[inline]
+    pub fn iter_mut(&mut self) -> IterMut<K, V> {
+        let (head, tail) = if let Some(values) = self.values {
+            unsafe {
+                let ValueLinks { next, prev } = values.as_ref().links.value;
+                (Some(next), Some(prev))
+            }
+        } else {
+            (None, None)
+        };
+
+        IterMut {
+            head,
+            tail,
+            remaining: self.len(),
+            marker: PhantomData,
+        }
+    }
+
+    #[inline]
+    pub fn drain(&mut self) -> Drain<'_, K, V> {
+        unsafe {
+            let (head, tail) = if let Some(mut values) = self.values {
+                let ValueLinks { next, prev } = values.as_ref().links.value;
+                values.as_mut().links.value = ValueLinks {
+                    next: values,
+                    prev: values,
+                };
+                (Some(next), Some(prev))
+            } else {
+                (None, None)
+            };
+            let len = self.len();
+
+            self.map.clear();
+
+            Drain {
+                free: (&mut self.free).into(),
+                head,
+                tail,
+                remaining: len,
+                marker: PhantomData,
+            }
+        }
+    }
+
+    #[inline]
+    pub fn keys(&self) -> Keys<K, V> {
+        Keys { inner: self.iter() }
+    }
+
+    #[inline]
+    pub fn values(&self) -> Values<K, V> {
+        Values { inner: self.iter() }
+    }
+
+    #[inline]
+    pub fn values_mut(&mut self) -> ValuesMut<K, V> {
+        ValuesMut {
+            inner: self.iter_mut(),
+        }
+    }
+
+    #[inline]
+    pub fn front(&self) -> Option<(&K, &V)> {
+        if self.is_empty() {
+            return None;
+        }
+        unsafe {
+            let front = (*self.values.as_ptr()).links.value.next.as_ptr();
+            let (key, value) = (*front).entry_ref();
+            Some((key, value))
+        }
+    }
+
+    #[inline]
+    pub fn back(&self) -> Option<(&K, &V)> {
+        if self.is_empty() {
+            return None;
+        }
+        unsafe {
+            let back = &*(*self.values.as_ptr()).links.value.prev.as_ptr();
+            let (key, value) = (*back).entry_ref();
+            Some((key, value))
+        }
+    }
+
+    #[inline]
+    pub fn retain<F>(&mut self, mut f: F)
+    where
+        F: FnMut(&K, &mut V) -> bool,
+    {
+        let free = self.free;
+        let mut drop_filtered_values = DropFilteredValues {
+            free: &mut self.free,
+            cur_free: free,
+        };
+
+        self.map.retain(|&node, _| unsafe {
+            let (k, v) = (*node.as_ptr()).entry_mut();
+            if f(k, v) {
+                true
+            } else {
+                drop_filtered_values.drop_later(node);
+                false
+            }
+        });
+    }
+
+    #[inline]
+    pub fn hasher(&self) -> &S {
+        &self.hash_builder
+    }
+
+    #[inline]
+    pub fn capacity(&self) -> usize {
+        self.map.capacity()
+    }
+}
+
+impl<K, V, S> LinkedHashMap<K, V, S>
+where
+    K: Eq + Hash,
+    S: BuildHasher,
+{
+    #[inline]
+    pub fn entry(&mut self, key: K) -> Entry<'_, K, V, S> {
+        match self.raw_entry_mut().from_key(&key) {
+            RawEntryMut::Occupied(occupied) => Entry::Occupied(OccupiedEntry {
+                key,
+                raw_entry: occupied,
+            }),
+            RawEntryMut::Vacant(vacant) => Entry::Vacant(VacantEntry {
+                key,
+                raw_entry: vacant,
+            }),
+        }
+    }
+
+    #[inline]
+    pub fn get<Q>(&self, k: &Q) -> Option<&V>
+    where
+        K: Borrow<Q>,
+        Q: Hash + Eq + ?Sized,
+    {
+        self.raw_entry().from_key(k).map(|(_, v)| v)
+    }
+
+    #[inline]
+    pub fn get_key_value<Q>(&self, k: &Q) -> Option<(&K, &V)>
+    where
+        K: Borrow<Q>,
+        Q: Hash + Eq + ?Sized,
+    {
+        self.raw_entry().from_key(k)
+    }
+
+    #[inline]
+    pub fn contains_key<Q>(&self, k: &Q) -> bool
+    where
+        K: Borrow<Q>,
+        Q: Hash + Eq + ?Sized,
+    {
+        self.get(k).is_some()
+    }
+
+    #[inline]
+    pub fn get_mut<Q>(&mut self, k: &Q) -> Option<&mut V>
+    where
+        K: Borrow<Q>,
+        Q: Hash + Eq + ?Sized,
+    {
+        match self.raw_entry_mut().from_key(k) {
+            RawEntryMut::Occupied(occupied) => Some(occupied.into_mut()),
+            RawEntryMut::Vacant(_) => None,
+        }
+    }
+
+    /// Inserts the given key / value pair at the *back* of the internal linked list.
+    ///
+    /// Returns the previously set value, if one existed prior to this call.  After this call,
+    /// calling `LinkedHashMap::back` will return a reference to this key / value pair.
+    #[inline]
+    pub fn insert(&mut self, k: K, v: V) -> Option<V> {
+        match self.raw_entry_mut().from_key(&k) {
+            RawEntryMut::Occupied(mut occupied) => {
+                occupied.to_back();
+                Some(occupied.replace_value(v))
+            }
+            RawEntryMut::Vacant(vacant) => {
+                vacant.insert(k, v);
+                None
+            }
+        }
+    }
+
+    /// If the given key is not in this map, inserts the key / value pair at the *back* of the
+    /// internal linked list and returns `None`, otherwise, replaces the existing value with the
+    /// given value *without* moving the entry in the internal linked list and returns the previous
+    /// value.
+    #[inline]
+    pub fn replace(&mut self, k: K, v: V) -> Option<V> {
+        match self.raw_entry_mut().from_key(&k) {
+            RawEntryMut::Occupied(mut occupied) => Some(occupied.replace_value(v)),
+            RawEntryMut::Vacant(vacant) => {
+                vacant.insert(k, v);
+                None
+            }
+        }
+    }
+
+    #[inline]
+    pub fn remove<Q>(&mut self, k: &Q) -> Option<V>
+    where
+        K: Borrow<Q>,
+        Q: Hash + Eq + ?Sized,
+    {
+        match self.raw_entry_mut().from_key(&k) {
+            RawEntryMut::Occupied(occupied) => Some(occupied.remove()),
+            RawEntryMut::Vacant(_) => None,
+        }
+    }
+
+    #[inline]
+    pub fn remove_entry<Q>(&mut self, k: &Q) -> Option<(K, V)>
+    where
+        K: Borrow<Q>,
+        Q: Hash + Eq + ?Sized,
+    {
+        match self.raw_entry_mut().from_key(&k) {
+            RawEntryMut::Occupied(occupied) => Some(occupied.remove_entry()),
+            RawEntryMut::Vacant(_) => None,
+        }
+    }
+
+    #[inline]
+    pub fn pop_front(&mut self) -> Option<(K, V)> {
+        if self.is_empty() {
+            return None;
+        }
+        unsafe {
+            let front = (*self.values.as_ptr()).links.value.next;
+            match self.map.raw_entry_mut().from_hash(
+                hash_key(&self.hash_builder, front.as_ref().key_ref()),
+                |k| (*k).as_ref().key_ref().eq(front.as_ref().key_ref()),
+            ) {
+                hash_map::RawEntryMut::Occupied(occupied) => {
+                    Some(remove_node(&mut self.free, occupied.remove_entry().0))
+                }
+                hash_map::RawEntryMut::Vacant(_) => None,
+            }
+        }
+    }
+
+    #[inline]
+    pub fn pop_back(&mut self) -> Option<(K, V)> {
+        if self.is_empty() {
+            return None;
+        }
+        unsafe {
+            let back = (*self.values.as_ptr()).links.value.prev;
+            match self
+                .map
+                .raw_entry_mut()
+                .from_hash(hash_key(&self.hash_builder, back.as_ref().key_ref()), |k| {
+                    (*k).as_ref().key_ref().eq(back.as_ref().key_ref())
+                }) {
+                hash_map::RawEntryMut::Occupied(occupied) => {
+                    Some(remove_node(&mut self.free, occupied.remove_entry().0))
+                }
+                hash_map::RawEntryMut::Vacant(_) => None,
+            }
+        }
+    }
+
+    /// If an entry with this key exists, move it to the front of the list and return a reference to
+    /// the value.
+    #[inline]
+    pub fn to_front<Q>(&mut self, k: &Q) -> Option<&mut V>
+    where
+        K: Borrow<Q>,
+        Q: Hash + Eq + ?Sized,
+    {
+        match self.raw_entry_mut().from_key(k) {
+            RawEntryMut::Occupied(mut occupied) => {
+                occupied.to_front();
+                Some(occupied.into_mut())
+            }
+            RawEntryMut::Vacant(_) => None,
+        }
+    }
+
+    /// If an entry with this key exists, move it to the back of the list and return a reference to
+    /// the value.
+    #[inline]
+    pub fn to_back<Q>(&mut self, k: &Q) -> Option<&mut V>
+    where
+        K: Borrow<Q>,
+        Q: Hash + Eq + ?Sized,
+    {
+        match self.raw_entry_mut().from_key(k) {
+            RawEntryMut::Occupied(mut occupied) => {
+                occupied.to_back();
+                Some(occupied.into_mut())
+            }
+            RawEntryMut::Vacant(_) => None,
+        }
+    }
+
+    #[inline]
+    pub fn shrink_to_fit(&mut self) {
+        unsafe {
+            let len = self.map.len();
+            if len != self.map.capacity() {
+                self.map = HashMap::with_hasher(NullHasher);
+                self.map.reserve(len);
+
+                if let Some(guard) = self.values {
+                    let mut cur = guard.as_ref().links.value.next;
+                    while cur != guard {
+                        let hash = hash_key(&self.hash_builder, cur.as_ref().key_ref());
+                        match self
+                            .map
+                            .raw_entry_mut()
+                            .from_hash(hash, |k| (*k).as_ref().key_ref().eq(cur.as_ref().key_ref()))
+                        {
+                            hash_map::RawEntryMut::Occupied(_) => unreachable!(),
+                            hash_map::RawEntryMut::Vacant(vacant) => {
+                                let hash_builder = &self.hash_builder;
+                                vacant.insert_with_hasher(hash, cur, (), |k| {
+                                    hash_key(hash_builder, (*k).as_ref().key_ref())
+                                });
+                            }
+                        }
+                        cur = cur.as_ref().links.value.next;
+                    }
+                }
+            }
+
+            drop_free_nodes(self.free);
+            self.free = None;
+        }
+    }
+
+    pub fn retain_with_order<F>(&mut self, mut f: F)
+    where
+        F: FnMut(&K, &mut V) -> bool,
+    {
+        let free = self.free;
+        let mut drop_filtered_values = DropFilteredValues {
+            free: &mut self.free,
+            cur_free: free,
+        };
+
+        if let Some(values) = self.values {
+            unsafe {
+                let mut cur = values.as_ref().links.value.next;
+                while cur != values {
+                    let next = cur.as_ref().links.value.next;
+                    let filter = {
+                        let (k, v) = (*cur.as_ptr()).entry_mut();
+                        !f(k, v)
+                    };
+                    if filter {
+                        let k = (*cur.as_ptr()).key_ref();
+                        let hash = hash_key(&self.hash_builder, k);
+                        match self
+                            .map
+                            .raw_entry_mut()
+                            .from_hash(hash, |o| (*o).as_ref().key_ref().eq(k))
+                        {
+                            hash_map::RawEntryMut::Occupied(entry) => {
+                                entry.remove();
+                                drop_filtered_values.drop_later(cur);
+                            }
+                            hash_map::RawEntryMut::Vacant(_) => unreachable!(),
+                        }
+                    }
+                    cur = next;
+                }
+            }
+        }
+    }
+}
+
+impl<K, V, S> LinkedHashMap<K, V, S>
+where
+    S: BuildHasher,
+{
+    #[inline]
+    pub fn raw_entry(&self) -> RawEntryBuilder<'_, K, V, S> {
+        RawEntryBuilder {
+            hash_builder: &self.hash_builder,
+            entry: self.map.raw_entry(),
+        }
+    }
+
+    #[inline]
+    pub fn raw_entry_mut(&mut self) -> RawEntryBuilderMut<'_, K, V, S> {
+        RawEntryBuilderMut {
+            hash_builder: &self.hash_builder,
+            values: &mut self.values,
+            free: &mut self.free,
+            entry: self.map.raw_entry_mut(),
+        }
+    }
+}
+
+impl<K, V, S> Default for LinkedHashMap<K, V, S>
+where
+    S: Default,
+{
+    #[inline]
+    fn default() -> Self {
+        Self::with_hasher(S::default())
+    }
+}
+
+impl<K: Hash + Eq, V, S: BuildHasher + Default> FromIterator<(K, V)> for LinkedHashMap<K, V, S> {
+    #[inline]
+    fn from_iter<I: IntoIterator<Item = (K, V)>>(iter: I) -> Self {
+        let iter = iter.into_iter();
+        let mut map = Self::with_capacity_and_hasher(iter.size_hint().0, S::default());
+        map.extend(iter);
+        map
+    }
+}
+
+impl<K, V, S> fmt::Debug for LinkedHashMap<K, V, S>
+where
+    K: fmt::Debug,
+    V: fmt::Debug,
+{
+    #[inline]
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_map().entries(self).finish()
+    }
+}
+
+impl<K: Hash + Eq, V: PartialEq, S: BuildHasher> PartialEq for LinkedHashMap<K, V, S> {
+    #[inline]
+    fn eq(&self, other: &Self) -> bool {
+        self.len() == other.len() && self.iter().eq(other)
+    }
+}
+
+impl<K: Hash + Eq, V: Eq, S: BuildHasher> Eq for LinkedHashMap<K, V, S> {}
+
+impl<K: Hash + Eq + PartialOrd, V: PartialOrd, S: BuildHasher> PartialOrd
+    for LinkedHashMap<K, V, S>
+{
+    #[inline]
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        self.iter().partial_cmp(other)
+    }
+
+    #[inline]
+    fn lt(&self, other: &Self) -> bool {
+        self.iter().lt(other)
+    }
+
+    #[inline]
+    fn le(&self, other: &Self) -> bool {
+        self.iter().le(other)
+    }
+
+    #[inline]
+    fn ge(&self, other: &Self) -> bool {
+        self.iter().ge(other)
+    }
+
+    #[inline]
+    fn gt(&self, other: &Self) -> bool {
+        self.iter().gt(other)
+    }
+}
+
+impl<K: Hash + Eq + Ord, V: Ord, S: BuildHasher> Ord for LinkedHashMap<K, V, S> {
+    #[inline]
+    fn cmp(&self, other: &Self) -> Ordering {
+        self.iter().cmp(other)
+    }
+}
+
+impl<K: Hash + Eq, V: Hash, S: BuildHasher> Hash for LinkedHashMap<K, V, S> {
+    #[inline]
+    fn hash<H: Hasher>(&self, h: &mut H) {
+        for e in self.iter() {
+            e.hash(h);
+        }
+    }
+}
+
+impl<K, V, S> Drop for LinkedHashMap<K, V, S> {
+    #[inline]
+    fn drop(&mut self) {
+        unsafe {
+            if let Some(values) = self.values {
+                drop_value_nodes(values);
+                let _ = Box::from_raw(values.as_ptr());
+            }
+            drop_free_nodes(self.free);
+        }
+    }
+}
+
+unsafe impl<K: Send, V: Send, S: Send> Send for LinkedHashMap<K, V, S> {}
+unsafe impl<K: Sync, V: Sync, S: Sync> Sync for LinkedHashMap<K, V, S> {}
+
+impl<'a, K, V, S, Q> Index<&'a Q> for LinkedHashMap<K, V, S>
+where
+    K: Hash + Eq + Borrow<Q>,
+    S: BuildHasher,
+    Q: Eq + Hash + ?Sized,
+{
+    type Output = V;
+
+    #[inline]
+    fn index(&self, index: &'a Q) -> &V {
+        self.get(index).expect("no entry found for key")
+    }
+}
+
+impl<'a, K, V, S, Q> IndexMut<&'a Q> for LinkedHashMap<K, V, S>
+where
+    K: Hash + Eq + Borrow<Q>,
+    S: BuildHasher,
+    Q: Eq + Hash + ?Sized,
+{
+    #[inline]
+    fn index_mut(&mut self, index: &'a Q) -> &mut V {
+        self.get_mut(index).expect("no entry found for key")
+    }
+}
+
+impl<K: Hash + Eq + Clone, V: Clone, S: BuildHasher + Clone> Clone for LinkedHashMap<K, V, S> {
+    #[inline]
+    fn clone(&self) -> Self {
+        let mut map = Self::with_hasher(self.hash_builder.clone());
+        map.extend(self.iter().map(|(k, v)| (k.clone(), v.clone())));
+        map
+    }
+}
+
+impl<K: Hash + Eq, V, S: BuildHasher> Extend<(K, V)> for LinkedHashMap<K, V, S> {
+    #[inline]
+    fn extend<I: IntoIterator<Item = (K, V)>>(&mut self, iter: I) {
+        for (k, v) in iter {
+            self.insert(k, v);
+        }
+    }
+}
+
+impl<'a, K, V, S> Extend<(&'a K, &'a V)> for LinkedHashMap<K, V, S>
+where
+    K: 'a + Hash + Eq + Copy,
+    V: 'a + Copy,
+    S: BuildHasher,
+{
+    #[inline]
+    fn extend<I: IntoIterator<Item = (&'a K, &'a V)>>(&mut self, iter: I) {
+        for (&k, &v) in iter {
+            self.insert(k, v);
+        }
+    }
+}
+
+pub enum Entry<'a, K, V, S> {
+    Occupied(OccupiedEntry<'a, K, V>),
+    Vacant(VacantEntry<'a, K, V, S>),
+}
+
+impl<K: fmt::Debug, V: fmt::Debug, S> fmt::Debug for Entry<'_, K, V, S> {
+    #[inline]
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match *self {
+            Entry::Vacant(ref v) => f.debug_tuple("Entry").field(v).finish(),
+            Entry::Occupied(ref o) => f.debug_tuple("Entry").field(o).finish(),
+        }
+    }
+}
+
+impl<'a, K, V, S> Entry<'a, K, V, S> {
+    /// If this entry is vacant, inserts a new entry with the given value and returns a reference to
+    /// it.
+    ///
+    /// If this entry is occupied, this method *moves the occupied entry to the back of the internal
+    /// linked list* and returns a reference to the existing value.
+    #[inline]
+    pub fn or_insert(self, default: V) -> &'a mut V
+    where
+        K: Hash,
+        S: BuildHasher,
+    {
+        match self {
+            Entry::Occupied(mut entry) => {
+                entry.to_back();
+                entry.into_mut()
+            }
+            Entry::Vacant(entry) => entry.insert(default),
+        }
+    }
+
+    /// Similar to `Entry::or_insert`, but accepts a function to construct a new value if this entry
+    /// is vacant.
+    #[inline]
+    pub fn or_insert_with<F: FnOnce() -> V>(self, default: F) -> &'a mut V
+    where
+        K: Hash,
+        S: BuildHasher,
+    {
+        match self {
+            Entry::Occupied(mut entry) => {
+                entry.to_back();
+                entry.into_mut()
+            }
+            Entry::Vacant(entry) => entry.insert(default()),
+        }
+    }
+
+    #[inline]
+    pub fn key(&self) -> &K {
+        match *self {
+            Entry::Occupied(ref entry) => entry.key(),
+            Entry::Vacant(ref entry) => entry.key(),
+        }
+    }
+
+    #[inline]
+    pub fn and_modify<F>(self, f: F) -> Self
+    where
+        F: FnOnce(&mut V),
+    {
+        match self {
+            Entry::Occupied(mut entry) => {
+                f(entry.get_mut());
+                Entry::Occupied(entry)
+            }
+            Entry::Vacant(entry) => Entry::Vacant(entry),
+        }
+    }
+}
+
+pub struct OccupiedEntry<'a, K, V> {
+    key: K,
+    raw_entry: RawOccupiedEntryMut<'a, K, V>,
+}
+
+impl<K: fmt::Debug, V: fmt::Debug> fmt::Debug for OccupiedEntry<'_, K, V> {
+    #[inline]
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("OccupiedEntry")
+            .field("key", self.key())
+            .field("value", self.get())
+            .finish()
+    }
+}
+
+impl<'a, K, V> OccupiedEntry<'a, K, V> {
+    #[inline]
+    pub fn key(&self) -> &K {
+        self.raw_entry.key()
+    }
+
+    #[inline]
+    pub fn remove_entry(self) -> (K, V) {
+        self.raw_entry.remove_entry()
+    }
+
+    #[inline]
+    pub fn get(&self) -> &V {
+        self.raw_entry.get()
+    }
+
+    #[inline]
+    pub fn get_mut(&mut self) -> &mut V {
+        self.raw_entry.get_mut()
+    }
+
+    #[inline]
+    pub fn into_mut(self) -> &'a mut V {
+        self.raw_entry.into_mut()
+    }
+
+    #[inline]
+    pub fn to_back(&mut self) {
+        self.raw_entry.to_back()
+    }
+
+    #[inline]
+    pub fn to_front(&mut self) {
+        self.raw_entry.to_front()
+    }
+
+    /// Replaces this entry's value with the provided value.
+    ///
+    /// Similarly to `LinkedHashMap::insert`, this moves the existing entry to the back of the
+    /// internal linked list.
+    #[inline]
+    pub fn insert(&mut self, value: V) -> V {
+        self.raw_entry.to_back();
+        self.raw_entry.replace_value(value)
+    }
+
+    #[inline]
+    pub fn remove(self) -> V {
+        self.raw_entry.remove()
+    }
+
+    /// Similar to `OccupiedEntry::replace_entry`, but *does* move the entry to the back of the
+    /// internal linked list.
+    #[inline]
+    pub fn insert_entry(mut self, value: V) -> (K, V) {
+        self.raw_entry.to_back();
+        self.replace_entry(value)
+    }
+
+    /// Replaces the entry's key with the key provided to `LinkedHashMap::entry`, and replaces the
+    /// entry's value with the given `value` parameter.
+    ///
+    /// Does *not* move the entry to the back of the internal linked list.
+    pub fn replace_entry(mut self, value: V) -> (K, V) {
+        let old_key = mem::replace(self.raw_entry.key_mut(), self.key);
+        let old_value = mem::replace(self.raw_entry.get_mut(), value);
+        (old_key, old_value)
+    }
+
+    /// Replaces this entry's key with the key provided to `LinkedHashMap::entry`.
+    ///
+    /// Does *not* move the entry to the back of the internal linked list.
+    #[inline]
+    pub fn replace_key(mut self) -> K {
+        mem::replace(self.raw_entry.key_mut(), self.key)
+    }
+}
+
+pub struct VacantEntry<'a, K, V, S> {
+    key: K,
+    raw_entry: RawVacantEntryMut<'a, K, V, S>,
+}
+
+impl<K: fmt::Debug, V, S> fmt::Debug for VacantEntry<'_, K, V, S> {
+    #[inline]
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_tuple("VacantEntry").field(self.key()).finish()
+    }
+}
+
+impl<'a, K, V, S> VacantEntry<'a, K, V, S> {
+    #[inline]
+    pub fn key(&self) -> &K {
+        &self.key
+    }
+
+    #[inline]
+    pub fn into_key(self) -> K {
+        self.key
+    }
+
+    /// Insert's the key for this vacant entry paired with the given value as a new entry at the
+    /// *back* of the internal linked list.
+    #[inline]
+    pub fn insert(self, value: V) -> &'a mut V
+    where
+        K: Hash,
+        S: BuildHasher,
+    {
+        self.raw_entry.insert(self.key, value).1
+    }
+}
+
+pub struct RawEntryBuilder<'a, K, V, S> {
+    hash_builder: &'a S,
+    entry: hash_map::RawEntryBuilder<'a, NonNull<Node<K, V>>, (), NullHasher>,
+}
+
+impl<'a, K, V, S> RawEntryBuilder<'a, K, V, S>
+where
+    S: BuildHasher,
+{
+    #[inline]
+    pub fn from_key<Q>(self, k: &Q) -> Option<(&'a K, &'a V)>
+    where
+        K: Borrow<Q>,
+        Q: Hash + Eq + ?Sized,
+    {
+        let hash = hash_key(self.hash_builder, k);
+        self.from_key_hashed_nocheck(hash, k)
+    }
+
+    #[inline]
+    pub fn from_key_hashed_nocheck<Q>(self, hash: u64, k: &Q) -> Option<(&'a K, &'a V)>
+    where
+        K: Borrow<Q>,
+        Q: Hash + Eq + ?Sized,
+    {
+        self.from_hash(hash, move |o| k.eq(o.borrow()))
+    }
+
+    #[inline]
+    pub fn from_hash(
+        self,
+        hash: u64,
+        mut is_match: impl FnMut(&K) -> bool,
+    ) -> Option<(&'a K, &'a V)> {
+        unsafe {
+            let node = *self
+                .entry
+                .from_hash(hash, move |k| is_match((*k).as_ref().key_ref()))?
+                .0;
+
+            let (key, value) = (*node.as_ptr()).entry_ref();
+            Some((key, value))
+        }
+    }
+}
+
+unsafe impl<'a, K, V, S> Send for RawEntryBuilder<'a, K, V, S>
+where
+    K: Send,
+    V: Send,
+    S: Send,
+{
+}
+
+unsafe impl<'a, K, V, S> Sync for RawEntryBuilder<'a, K, V, S>
+where
+    K: Sync,
+    V: Sync,
+    S: Sync,
+{
+}
+
+pub struct RawEntryBuilderMut<'a, K, V, S> {
+    hash_builder: &'a S,
+    values: &'a mut Option<NonNull<Node<K, V>>>,
+    free: &'a mut Option<NonNull<Node<K, V>>>,
+    entry: hash_map::RawEntryBuilderMut<'a, NonNull<Node<K, V>>, (), NullHasher>,
+}
+
+impl<'a, K, V, S> RawEntryBuilderMut<'a, K, V, S>
+where
+    S: BuildHasher,
+{
+    #[inline]
+    pub fn from_key<Q>(self, k: &Q) -> RawEntryMut<'a, K, V, S>
+    where
+        K: Borrow<Q>,
+        Q: Hash + Eq + ?Sized,
+    {
+        let hash = hash_key(self.hash_builder, k);
+        self.from_key_hashed_nocheck(hash, k)
+    }
+
+    #[inline]
+    pub fn from_key_hashed_nocheck<Q>(self, hash: u64, k: &Q) -> RawEntryMut<'a, K, V, S>
+    where
+        K: Borrow<Q>,
+        Q: Hash + Eq + ?Sized,
+    {
+        self.from_hash(hash, move |o| k.eq(o.borrow()))
+    }
+
+    #[inline]
+    pub fn from_hash(
+        self,
+        hash: u64,
+        mut is_match: impl FnMut(&K) -> bool,
+    ) -> RawEntryMut<'a, K, V, S> {
+        let entry = self
+            .entry
+            .from_hash(hash, move |k| is_match(unsafe { (*k).as_ref().key_ref() }));
+
+        match entry {
+            hash_map::RawEntryMut::Occupied(occupied) => {
+                RawEntryMut::Occupied(RawOccupiedEntryMut {
+                    free: self.free,
+                    values: self.values,
+                    entry: occupied,
+                })
+            }
+            hash_map::RawEntryMut::Vacant(vacant) => RawEntryMut::Vacant(RawVacantEntryMut {
+                hash_builder: self.hash_builder,
+                values: self.values,
+                free: self.free,
+                entry: vacant,
+            }),
+        }
+    }
+}
+
+unsafe impl<'a, K, V, S> Send for RawEntryBuilderMut<'a, K, V, S>
+where
+    K: Send,
+    V: Send,
+    S: Send,
+{
+}
+
+unsafe impl<'a, K, V, S> Sync for RawEntryBuilderMut<'a, K, V, S>
+where
+    K: Sync,
+    V: Sync,
+    S: Sync,
+{
+}
+
+pub enum RawEntryMut<'a, K, V, S> {
+    Occupied(RawOccupiedEntryMut<'a, K, V>),
+    Vacant(RawVacantEntryMut<'a, K, V, S>),
+}
+
+impl<'a, K, V, S> RawEntryMut<'a, K, V, S> {
+    /// Similarly to `Entry::or_insert`, if this entry is occupied, it will move the existing entry
+    /// to the back of the internal linked list.
+    #[inline]
+    pub fn or_insert(self, default_key: K, default_val: V) -> (&'a mut K, &'a mut V)
+    where
+        K: Hash,
+        S: BuildHasher,
+    {
+        match self {
+            RawEntryMut::Occupied(mut entry) => {
+                entry.to_back();
+                entry.into_key_value()
+            }
+            RawEntryMut::Vacant(entry) => entry.insert(default_key, default_val),
+        }
+    }
+
+    /// Similarly to `Entry::or_insert_with`, if this entry is occupied, it will move the existing
+    /// entry to the back of the internal linked list.
+    #[inline]
+    pub fn or_insert_with<F>(self, default: F) -> (&'a mut K, &'a mut V)
+    where
+        F: FnOnce() -> (K, V),
+        K: Hash,
+        S: BuildHasher,
+    {
+        match self {
+            RawEntryMut::Occupied(mut entry) => {
+                entry.to_back();
+                entry.into_key_value()
+            }
+            RawEntryMut::Vacant(entry) => {
+                let (k, v) = default();
+                entry.insert(k, v)
+            }
+        }
+    }
+
+    #[inline]
+    pub fn and_modify<F>(self, f: F) -> Self
+    where
+        F: FnOnce(&mut K, &mut V),
+    {
+        match self {
+            RawEntryMut::Occupied(mut entry) => {
+                {
+                    let (k, v) = entry.get_key_value_mut();
+                    f(k, v);
+                }
+                RawEntryMut::Occupied(entry)
+            }
+            RawEntryMut::Vacant(entry) => RawEntryMut::Vacant(entry),
+        }
+    }
+}
+
+pub struct RawOccupiedEntryMut<'a, K, V> {
+    free: &'a mut Option<NonNull<Node<K, V>>>,
+    values: &'a mut Option<NonNull<Node<K, V>>>,
+    entry: hash_map::RawOccupiedEntryMut<'a, NonNull<Node<K, V>>, (), NullHasher>,
+}
+
+impl<'a, K, V> RawOccupiedEntryMut<'a, K, V> {
+    #[inline]
+    pub fn key(&self) -> &K {
+        self.get_key_value().0
+    }
+
+    #[inline]
+    pub fn key_mut(&mut self) -> &mut K {
+        self.get_key_value_mut().0
+    }
+
+    #[inline]
+    pub fn into_key(self) -> &'a mut K {
+        self.into_key_value().0
+    }
+
+    #[inline]
+    pub fn get(&self) -> &V {
+        self.get_key_value().1
+    }
+
+    #[inline]
+    pub fn get_mut(&mut self) -> &mut V {
+        self.get_key_value_mut().1
+    }
+
+    #[inline]
+    pub fn into_mut(self) -> &'a mut V {
+        self.into_key_value().1
+    }
+
+    #[inline]
+    pub fn get_key_value(&self) -> (&K, &V) {
+        unsafe {
+            let node = *self.entry.key();
+            let (key, value) = (*node.as_ptr()).entry_ref();
+            (key, value)
+        }
+    }
+
+    #[inline]
+    pub fn get_key_value_mut(&mut self) -> (&mut K, &mut V) {
+        unsafe {
+            let node = *self.entry.key_mut();
+            let (key, value) = (*node.as_ptr()).entry_mut();
+            (key, value)
+        }
+    }
+
+    #[inline]
+    pub fn into_key_value(self) -> (&'a mut K, &'a mut V) {
+        unsafe {
+            let node = *self.entry.into_key();
+            let (key, value) = (*node.as_ptr()).entry_mut();
+            (key, value)
+        }
+    }
+
+    #[inline]
+    pub fn to_back(&mut self) {
+        unsafe {
+            let node = *self.entry.key_mut();
+            detach_node(node);
+            attach_before(node, NonNull::new_unchecked(self.values.as_ptr()));
+        }
+    }
+
+    #[inline]
+    pub fn to_front(&mut self) {
+        unsafe {
+            let node = *self.entry.key_mut();
+            detach_node(node);
+            attach_before(node, (*self.values.as_ptr()).links.value.next);
+        }
+    }
+
+    #[inline]
+    pub fn replace_value(&mut self, value: V) -> V {
+        unsafe {
+            let mut node = *self.entry.key_mut();
+            mem::replace(&mut node.as_mut().entry_mut().1, value)
+        }
+    }
+
+    #[inline]
+    pub fn replace_key(&mut self, key: K) -> K {
+        unsafe {
+            let mut node = *self.entry.key_mut();
+            mem::replace(&mut node.as_mut().entry_mut().0, key)
+        }
+    }
+
+    #[inline]
+    pub fn remove(self) -> V {
+        self.remove_entry().1
+    }
+
+    #[inline]
+    pub fn remove_entry(self) -> (K, V) {
+        let node = self.entry.remove_entry().0;
+        unsafe { remove_node(self.free, node) }
+    }
+}
+
+pub struct RawVacantEntryMut<'a, K, V, S> {
+    hash_builder: &'a S,
+    values: &'a mut Option<NonNull<Node<K, V>>>,
+    free: &'a mut Option<NonNull<Node<K, V>>>,
+    entry: hash_map::RawVacantEntryMut<'a, NonNull<Node<K, V>>, (), NullHasher>,
+}
+
+impl<'a, K, V, S> RawVacantEntryMut<'a, K, V, S> {
+    #[inline]
+    pub fn insert(self, key: K, value: V) -> (&'a mut K, &'a mut V)
+    where
+        K: Hash,
+        S: BuildHasher,
+    {
+        let hash = hash_key(self.hash_builder, &key);
+        self.insert_hashed_nocheck(hash, key, value)
+    }
+
+    #[inline]
+    pub fn insert_hashed_nocheck(self, hash: u64, key: K, value: V) -> (&'a mut K, &'a mut V)
+    where
+        K: Hash,
+        S: BuildHasher,
+    {
+        let hash_builder = self.hash_builder;
+        self.insert_with_hasher(hash, key, value, |k| hash_key(hash_builder, k))
+    }
+
+    #[inline]
+    pub fn insert_with_hasher(
+        self,
+        hash: u64,
+        key: K,
+        value: V,
+        hasher: impl Fn(&K) -> u64,
+    ) -> (&'a mut K, &'a mut V)
+    where
+        S: BuildHasher,
+    {
+        unsafe {
+            ensure_guard_node(self.values);
+            let mut new_node = allocate_node(self.free);
+            new_node.as_mut().put_entry((key, value));
+            attach_before(new_node, NonNull::new_unchecked(self.values.as_ptr()));
+
+            let node = *self
+                .entry
+                .insert_with_hasher(hash, new_node, (), move |k| hasher((*k).as_ref().key_ref()))
+                .0;
+
+            let (key, value) = (*node.as_ptr()).entry_mut();
+            (key, value)
+        }
+    }
+}
+
+impl<K, V, S> fmt::Debug for RawEntryBuilderMut<'_, K, V, S> {
+    #[inline]
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("RawEntryBuilder").finish()
+    }
+}
+
+impl<K: fmt::Debug, V: fmt::Debug, S> fmt::Debug for RawEntryMut<'_, K, V, S> {
+    #[inline]
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match *self {
+            RawEntryMut::Vacant(ref v) => f.debug_tuple("RawEntry").field(v).finish(),
+            RawEntryMut::Occupied(ref o) => f.debug_tuple("RawEntry").field(o).finish(),
+        }
+    }
+}
+
+impl<K: fmt::Debug, V: fmt::Debug> fmt::Debug for RawOccupiedEntryMut<'_, K, V> {
+    #[inline]
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("RawOccupiedEntryMut")
+            .field("key", self.key())
+            .field("value", self.get())
+            .finish()
+    }
+}
+
+impl<K, V, S> fmt::Debug for RawVacantEntryMut<'_, K, V, S> {
+    #[inline]
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("RawVacantEntryMut").finish()
+    }
+}
+
+impl<K, V, S> fmt::Debug for RawEntryBuilder<'_, K, V, S> {
+    #[inline]
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("RawEntryBuilder").finish()
+    }
+}
+
+unsafe impl<'a, K, V> Send for RawOccupiedEntryMut<'a, K, V>
+where
+    K: Send,
+    V: Send,
+{
+}
+
+unsafe impl<'a, K, V> Sync for RawOccupiedEntryMut<'a, K, V>
+where
+    K: Sync,
+    V: Sync,
+{
+}
+
+unsafe impl<'a, K, V, S> Send for RawVacantEntryMut<'a, K, V, S>
+where
+    K: Send,
+    V: Send,
+    S: Send,
+{
+}
+
+unsafe impl<'a, K, V, S> Sync for RawVacantEntryMut<'a, K, V, S>
+where
+    K: Sync,
+    V: Sync,
+    S: Sync,
+{
+}
+
+pub struct Iter<'a, K, V> {
+    head: *const Node<K, V>,
+    tail: *const Node<K, V>,
+    remaining: usize,
+    marker: PhantomData<(&'a K, &'a V)>,
+}
+
+pub struct IterMut<'a, K, V> {
+    head: Option<NonNull<Node<K, V>>>,
+    tail: Option<NonNull<Node<K, V>>>,
+    remaining: usize,
+    marker: PhantomData<(&'a K, &'a mut V)>,
+}
+
+pub struct IntoIter<K, V> {
+    head: Option<NonNull<Node<K, V>>>,
+    tail: Option<NonNull<Node<K, V>>>,
+    remaining: usize,
+    marker: PhantomData<(K, V)>,
+}
+
+pub struct Drain<'a, K, V> {
+    free: NonNull<Option<NonNull<Node<K, V>>>>,
+    head: Option<NonNull<Node<K, V>>>,
+    tail: Option<NonNull<Node<K, V>>>,
+    remaining: usize,
+    // We want `Drain` to be covariant
+    marker: PhantomData<(K, V, &'a LinkedHashMap<K, V>)>,
+}
+
+impl<K, V> IterMut<'_, K, V> {
+    #[inline]
+    pub(crate) fn iter(&self) -> Iter<'_, K, V> {
+        Iter {
+            head: self.head.as_ptr(),
+            tail: self.tail.as_ptr(),
+            remaining: self.remaining,
+            marker: PhantomData,
+        }
+    }
+}
+
+impl<K, V> IntoIter<K, V> {
+    #[inline]
+    pub(crate) fn iter(&self) -> Iter<'_, K, V> {
+        Iter {
+            head: self.head.as_ptr(),
+            tail: self.tail.as_ptr(),
+            remaining: self.remaining,
+            marker: PhantomData,
+        }
+    }
+}
+
+impl<K, V> Drain<'_, K, V> {
+    #[inline]
+    pub(crate) fn iter(&self) -> Iter<'_, K, V> {
+        Iter {
+            head: self.head.as_ptr(),
+            tail: self.tail.as_ptr(),
+            remaining: self.remaining,
+            marker: PhantomData,
+        }
+    }
+}
+
+unsafe impl<'a, K, V> Send for Iter<'a, K, V>
+where
+    K: Send,
+    V: Send,
+{
+}
+
+unsafe impl<'a, K, V> Send for IterMut<'a, K, V>
+where
+    K: Send,
+    V: Send,
+{
+}
+
+unsafe impl<K, V> Send for IntoIter<K, V>
+where
+    K: Send,
+    V: Send,
+{
+}
+
+unsafe impl<'a, K, V> Send for Drain<'a, K, V>
+where
+    K: Send,
+    V: Send,
+{
+}
+
+unsafe impl<'a, K, V> Sync for Iter<'a, K, V>
+where
+    K: Sync,
+    V: Sync,
+{
+}
+
+unsafe impl<'a, K, V> Sync for IterMut<'a, K, V>
+where
+    K: Sync,
+    V: Sync,
+{
+}
+
+unsafe impl<K, V> Sync for IntoIter<K, V>
+where
+    K: Sync,
+    V: Sync,
+{
+}
+
+unsafe impl<'a, K, V> Sync for Drain<'a, K, V>
+where
+    K: Sync,
+    V: Sync,
+{
+}
+
+impl<'a, K, V> Clone for Iter<'a, K, V> {
+    #[inline]
+    fn clone(&self) -> Self {
+        Iter { ..*self }
+    }
+}
+
+impl<K: fmt::Debug, V: fmt::Debug> fmt::Debug for Iter<'_, K, V> {
+    #[inline]
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_list().entries(self.clone()).finish()
+    }
+}
+
+impl<K, V> fmt::Debug for IterMut<'_, K, V>
+where
+    K: fmt::Debug,
+    V: fmt::Debug,
+{
+    #[inline]
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_list().entries(self.iter()).finish()
+    }
+}
+
+impl<K, V> fmt::Debug for IntoIter<K, V>
+where
+    K: fmt::Debug,
+    V: fmt::Debug,
+{
+    #[inline]
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_list().entries(self.iter()).finish()
+    }
+}
+
+impl<K, V> fmt::Debug for Drain<'_, K, V>
+where
+    K: fmt::Debug,
+    V: fmt::Debug,
+{
+    #[inline]
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_list().entries(self.iter()).finish()
+    }
+}
+
+impl<'a, K, V> Iterator for Iter<'a, K, V> {
+    type Item = (&'a K, &'a V);
+
+    #[inline]
+    fn next(&mut self) -> Option<(&'a K, &'a V)> {
+        if self.remaining == 0 {
+            None
+        } else {
+            self.remaining -= 1;
+            unsafe {
+                let (key, value) = (*self.head).entry_ref();
+                self.head = (*self.head).links.value.next.as_ptr();
+                Some((key, value))
+            }
+        }
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (self.remaining, Some(self.remaining))
+    }
+}
+
+impl<'a, K, V> Iterator for IterMut<'a, K, V> {
+    type Item = (&'a K, &'a mut V);
+
+    #[inline]
+    fn next(&mut self) -> Option<(&'a K, &'a mut V)> {
+        if self.remaining == 0 {
+            None
+        } else {
+            self.remaining -= 1;
+            unsafe {
+                let head = self.head.as_ptr();
+                let (key, value) = (*head).entry_mut();
+                self.head = Some((*head).links.value.next);
+                Some((key, value))
+            }
+        }
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (self.remaining, Some(self.remaining))
+    }
+}
+
+impl<K, V> Iterator for IntoIter<K, V> {
+    type Item = (K, V);
+
+    #[inline]
+    fn next(&mut self) -> Option<(K, V)> {
+        if self.remaining == 0 {
+            return None;
+        }
+        self.remaining -= 1;
+        unsafe {
+            let head = self.head.as_ptr();
+            self.head = Some((*head).links.value.next);
+            let mut e = Box::from_raw(head);
+            Some(e.take_entry())
+        }
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (self.remaining, Some(self.remaining))
+    }
+}
+
+impl<'a, K, V> Iterator for Drain<'a, K, V> {
+    type Item = (K, V);
+
+    #[inline]
+    fn next(&mut self) -> Option<(K, V)> {
+        if self.remaining == 0 {
+            return None;
+        }
+        self.remaining -= 1;
+        unsafe {
+            let mut head = NonNull::new_unchecked(self.head.as_ptr());
+            self.head = Some(head.as_ref().links.value.next);
+            let entry = head.as_mut().take_entry();
+            push_free(self.free.as_mut(), head);
+            Some(entry)
+        }
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (self.remaining, Some(self.remaining))
+    }
+}
+
+impl<'a, K, V> DoubleEndedIterator for Iter<'a, K, V> {
+    #[inline]
+    fn next_back(&mut self) -> Option<(&'a K, &'a V)> {
+        if self.remaining == 0 {
+            None
+        } else {
+            self.remaining -= 1;
+            unsafe {
+                let tail = self.tail;
+                self.tail = (*tail).links.value.prev.as_ptr();
+                let (key, value) = (*tail).entry_ref();
+                Some((key, value))
+            }
+        }
+    }
+}
+
+impl<'a, K, V> DoubleEndedIterator for IterMut<'a, K, V> {
+    #[inline]
+    fn next_back(&mut self) -> Option<(&'a K, &'a mut V)> {
+        if self.remaining == 0 {
+            None
+        } else {
+            self.remaining -= 1;
+            unsafe {
+                let tail = self.tail.as_ptr();
+                self.tail = Some((*tail).links.value.prev);
+                let (key, value) = (*tail).entry_mut();
+                Some((key, value))
+            }
+        }
+    }
+}
+
+impl<K, V> DoubleEndedIterator for IntoIter<K, V> {
+    #[inline]
+    fn next_back(&mut self) -> Option<(K, V)> {
+        if self.remaining == 0 {
+            return None;
+        }
+        self.remaining -= 1;
+        unsafe {
+            let mut e = *Box::from_raw(self.tail.as_ptr());
+            self.tail = Some(e.links.value.prev);
+            Some(e.take_entry())
+        }
+    }
+}
+
+impl<'a, K, V> DoubleEndedIterator for Drain<'a, K, V> {
+    #[inline]
+    fn next_back(&mut self) -> Option<(K, V)> {
+        if self.remaining == 0 {
+            return None;
+        }
+        self.remaining -= 1;
+        unsafe {
+            let mut tail = NonNull::new_unchecked(self.tail.as_ptr());
+            self.tail = Some(tail.as_ref().links.value.prev);
+            let entry = tail.as_mut().take_entry();
+            push_free(&mut *self.free.as_ptr(), tail);
+            Some(entry)
+        }
+    }
+}
+
+impl<'a, K, V> ExactSizeIterator for Iter<'a, K, V> {}
+
+impl<'a, K, V> ExactSizeIterator for IterMut<'a, K, V> {}
+
+impl<K, V> ExactSizeIterator for IntoIter<K, V> {}
+
+impl<K, V> Drop for IntoIter<K, V> {
+    #[inline]
+    fn drop(&mut self) {
+        for _ in 0..self.remaining {
+            unsafe {
+                let tail = self.tail.as_ptr();
+                self.tail = Some((*tail).links.value.prev);
+                (*tail).take_entry();
+                let _ = Box::from_raw(tail);
+            }
+        }
+    }
+}
+
+impl<'a, K, V> Drop for Drain<'a, K, V> {
+    #[inline]
+    fn drop(&mut self) {
+        for _ in 0..self.remaining {
+            unsafe {
+                let mut tail = NonNull::new_unchecked(self.tail.as_ptr());
+                self.tail = Some(tail.as_ref().links.value.prev);
+                tail.as_mut().take_entry();
+                push_free(&mut *self.free.as_ptr(), tail);
+            }
+        }
+    }
+}
+
+pub struct Keys<'a, K, V> {
+    inner: Iter<'a, K, V>,
+}
+
+impl<K: fmt::Debug, V> fmt::Debug for Keys<'_, K, V> {
+    #[inline]
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_list().entries(self.clone()).finish()
+    }
+}
+
+impl<'a, K, V> Clone for Keys<'a, K, V> {
+    #[inline]
+    fn clone(&self) -> Keys<'a, K, V> {
+        Keys {
+            inner: self.inner.clone(),
+        }
+    }
+}
+
+impl<'a, K, V> Iterator for Keys<'a, K, V> {
+    type Item = &'a K;
+
+    #[inline]
+    fn next(&mut self) -> Option<&'a K> {
+        self.inner.next().map(|e| e.0)
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.inner.size_hint()
+    }
+}
+
+impl<'a, K, V> DoubleEndedIterator for Keys<'a, K, V> {
+    #[inline]
+    fn next_back(&mut self) -> Option<&'a K> {
+        self.inner.next_back().map(|e| e.0)
+    }
+}
+
+impl<'a, K, V> ExactSizeIterator for Keys<'a, K, V> {
+    #[inline]
+    fn len(&self) -> usize {
+        self.inner.len()
+    }
+}
+
+pub struct Values<'a, K, V> {
+    inner: Iter<'a, K, V>,
+}
+
+impl<K, V> Clone for Values<'_, K, V> {
+    #[inline]
+    fn clone(&self) -> Self {
+        Values {
+            inner: self.inner.clone(),
+        }
+    }
+}
+
+impl<K, V: fmt::Debug> fmt::Debug for Values<'_, K, V> {
+    #[inline]
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_list().entries(self.clone()).finish()
+    }
+}
+
+impl<'a, K, V> Iterator for Values<'a, K, V> {
+    type Item = &'a V;
+
+    #[inline]
+    fn next(&mut self) -> Option<&'a V> {
+        self.inner.next().map(|e| e.1)
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.inner.size_hint()
+    }
+}
+
+impl<'a, K, V> DoubleEndedIterator for Values<'a, K, V> {
+    #[inline]
+    fn next_back(&mut self) -> Option<&'a V> {
+        self.inner.next_back().map(|e| e.1)
+    }
+}
+
+impl<'a, K, V> ExactSizeIterator for Values<'a, K, V> {
+    #[inline]
+    fn len(&self) -> usize {
+        self.inner.len()
+    }
+}
+
+pub struct ValuesMut<'a, K, V> {
+    inner: IterMut<'a, K, V>,
+}
+
+impl<K, V> fmt::Debug for ValuesMut<'_, K, V>
+where
+    K: fmt::Debug,
+    V: fmt::Debug,
+{
+    #[inline]
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_list().entries(self.inner.iter()).finish()
+    }
+}
+
+impl<'a, K, V> Iterator for ValuesMut<'a, K, V> {
+    type Item = &'a mut V;
+
+    #[inline]
+    fn next(&mut self) -> Option<&'a mut V> {
+        self.inner.next().map(|e| e.1)
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.inner.size_hint()
+    }
+}
+
+impl<'a, K, V> DoubleEndedIterator for ValuesMut<'a, K, V> {
+    #[inline]
+    fn next_back(&mut self) -> Option<&'a mut V> {
+        self.inner.next_back().map(|e| e.1)
+    }
+}
+
+impl<'a, K, V> ExactSizeIterator for ValuesMut<'a, K, V> {
+    #[inline]
+    fn len(&self) -> usize {
+        self.inner.len()
+    }
+}
+
+impl<'a, K, V, S> IntoIterator for &'a LinkedHashMap<K, V, S> {
+    type Item = (&'a K, &'a V);
+    type IntoIter = Iter<'a, K, V>;
+
+    #[inline]
+    fn into_iter(self) -> Iter<'a, K, V> {
+        self.iter()
+    }
+}
+
+impl<'a, K, V, S> IntoIterator for &'a mut LinkedHashMap<K, V, S> {
+    type Item = (&'a K, &'a mut V);
+    type IntoIter = IterMut<'a, K, V>;
+
+    #[inline]
+    fn into_iter(self) -> IterMut<'a, K, V> {
+        self.iter_mut()
+    }
+}
+
+impl<K, V, S> IntoIterator for LinkedHashMap<K, V, S> {
+    type Item = (K, V);
+    type IntoIter = IntoIter<K, V>;
+
+    #[inline]
+    fn into_iter(mut self) -> IntoIter<K, V> {
+        unsafe {
+            let (head, tail) = if let Some(values) = self.values {
+                let ValueLinks {
+                    next: head,
+                    prev: tail,
+                } = values.as_ref().links.value;
+
+                let _ = Box::from_raw(self.values.as_ptr());
+                self.values = None;
+
+                (Some(head), Some(tail))
+            } else {
+                (None, None)
+            };
+            let len = self.len();
+
+            drop_free_nodes(self.free);
+            self.free = None;
+
+            self.map.clear();
+
+            IntoIter {
+                head,
+                tail,
+                remaining: len,
+                marker: PhantomData,
+            }
+        }
+    }
+}
+
+// A ZST that asserts that the inner HashMap will not do its own key hashing
+struct NullHasher;
+
+impl BuildHasher for NullHasher {
+    type Hasher = Self;
+
+    #[inline]
+    fn build_hasher(&self) -> Self {
+        Self
+    }
+}
+
+impl Hasher for NullHasher {
+    #[inline]
+    fn write(&mut self, _bytes: &[u8]) {
+        unreachable!("inner map should not be using its built-in hasher")
+    }
+
+    #[inline]
+    fn finish(&self) -> u64 {
+        unreachable!("inner map should not be using its built-in hasher")
+    }
+}
+
+struct ValueLinks<K, V> {
+    next: NonNull<Node<K, V>>,
+    prev: NonNull<Node<K, V>>,
+}
+
+impl<K, V> Clone for ValueLinks<K, V> {
+    #[inline]
+    fn clone(&self) -> Self {
+        ValueLinks {
+            next: self.next,
+            prev: self.prev,
+        }
+    }
+}
+
+impl<K, V> Copy for ValueLinks<K, V> {}
+
+struct FreeLink<K, V> {
+    next: Option<NonNull<Node<K, V>>>,
+}
+
+impl<K, V> Clone for FreeLink<K, V> {
+    #[inline]
+    fn clone(&self) -> Self {
+        FreeLink { next: self.next }
+    }
+}
+
+impl<K, V> Copy for FreeLink<K, V> {}
+
+union Links<K, V> {
+    value: ValueLinks<K, V>,
+    free: FreeLink<K, V>,
+}
+
+struct Node<K, V> {
+    entry: MaybeUninit<(K, V)>,
+    links: Links<K, V>,
+}
+
+impl<K, V> Node<K, V> {
+    #[inline]
+    unsafe fn put_entry(&mut self, entry: (K, V)) {
+        self.entry.as_mut_ptr().write(entry)
+    }
+
+    #[inline]
+    unsafe fn entry_ref(&self) -> &(K, V) {
+        &*self.entry.as_ptr()
+    }
+
+    #[inline]
+    unsafe fn key_ref(&self) -> &K {
+        &(*self.entry.as_ptr()).0
+    }
+
+    #[inline]
+    unsafe fn entry_mut(&mut self) -> &mut (K, V) {
+        &mut *self.entry.as_mut_ptr()
+    }
+
+    #[inline]
+    unsafe fn take_entry(&mut self) -> (K, V) {
+        self.entry.as_ptr().read()
+    }
+}
+
+trait OptNonNullExt<T> {
+    fn as_ptr(self) -> *mut T;
+}
+
+impl<T> OptNonNullExt<T> for Option<NonNull<T>> {
+    #[inline]
+    fn as_ptr(self) -> *mut T {
+        match self {
+            Some(ptr) => ptr.as_ptr(),
+            None => ptr::null_mut(),
+        }
+    }
+}
+
+// Allocate a circular list guard node if not present.
+#[inline]
+unsafe fn ensure_guard_node<K, V>(head: &mut Option<NonNull<Node<K, V>>>) {
+    if head.is_none() {
+        let mut p = NonNull::new_unchecked(Box::into_raw(Box::new(Node {
+            entry: MaybeUninit::uninit(),
+            links: Links {
+                value: ValueLinks {
+                    next: NonNull::dangling(),
+                    prev: NonNull::dangling(),
+                },
+            },
+        })));
+        p.as_mut().links.value = ValueLinks { next: p, prev: p };
+        *head = Some(p);
+    }
+}
+
+// Attach the `to_attach` node to the existing circular list *before* `node`.
+#[inline]
+unsafe fn attach_before<K, V>(mut to_attach: NonNull<Node<K, V>>, mut node: NonNull<Node<K, V>>) {
+    to_attach.as_mut().links.value = ValueLinks {
+        prev: node.as_ref().links.value.prev,
+        next: node,
+    };
+    node.as_mut().links.value.prev = to_attach;
+    (*to_attach.as_mut().links.value.prev.as_ptr())
+        .links
+        .value
+        .next = to_attach;
+}
+
+#[inline]
+unsafe fn detach_node<K, V>(mut node: NonNull<Node<K, V>>) {
+    node.as_mut().links.value.prev.as_mut().links.value.next = node.as_ref().links.value.next;
+    node.as_mut().links.value.next.as_mut().links.value.prev = node.as_ref().links.value.prev;
+}
+
+#[inline]
+unsafe fn push_free<K, V>(
+    free_list: &mut Option<NonNull<Node<K, V>>>,
+    mut node: NonNull<Node<K, V>>,
+) {
+    node.as_mut().links.free.next = *free_list;
+    *free_list = Some(node);
+}
+
+#[inline]
+unsafe fn pop_free<K, V>(
+    free_list: &mut Option<NonNull<Node<K, V>>>,
+) -> Option<NonNull<Node<K, V>>> {
+    if let Some(free) = *free_list {
+        *free_list = free.as_ref().links.free.next;
+        Some(free)
+    } else {
+        None
+    }
+}
+
+#[inline]
+unsafe fn allocate_node<K, V>(free_list: &mut Option<NonNull<Node<K, V>>>) -> NonNull<Node<K, V>> {
+    if let Some(mut free) = pop_free(free_list) {
+        free.as_mut().links.value = ValueLinks {
+            next: NonNull::dangling(),
+            prev: NonNull::dangling(),
+        };
+        free
+    } else {
+        NonNull::new_unchecked(Box::into_raw(Box::new(Node {
+            entry: MaybeUninit::uninit(),
+            links: Links {
+                value: ValueLinks {
+                    next: NonNull::dangling(),
+                    prev: NonNull::dangling(),
+                },
+            },
+        })))
+    }
+}
+
+// Given node is assumed to be the guard node and is *not* dropped.
+#[inline]
+unsafe fn drop_value_nodes<K, V>(guard: NonNull<Node<K, V>>) {
+    let mut cur = guard.as_ref().links.value.prev;
+    while cur != guard {
+        let prev = cur.as_ref().links.value.prev;
+        cur.as_mut().take_entry();
+        let _ = Box::from_raw(cur.as_ptr());
+        cur = prev;
+    }
+}
+
+// Drops all linked free nodes starting with the given node.  Free nodes are only non-circular
+// singly linked, and should have uninitialized keys / values.
+#[inline]
+unsafe fn drop_free_nodes<K, V>(mut free: Option<NonNull<Node<K, V>>>) {
+    while let Some(some_free) = free {
+        let next_free = some_free.as_ref().links.free.next;
+        let _ = Box::from_raw(some_free.as_ptr());
+        free = next_free;
+    }
+}
+
+#[inline]
+unsafe fn remove_node<K, V>(
+    free_list: &mut Option<NonNull<Node<K, V>>>,
+    mut node: NonNull<Node<K, V>>,
+) -> (K, V) {
+    detach_node(node);
+    push_free(free_list, node);
+    node.as_mut().take_entry()
+}
+
+#[inline]
+fn hash_key<S, Q>(s: &S, k: &Q) -> u64
+where
+    S: BuildHasher,
+    Q: Hash + ?Sized,
+{
+    let mut hasher = s.build_hasher();
+    k.hash(&mut hasher);
+    hasher.finish()
+}
+
+// We do not drop the key and value when a value is filtered from the map during the call to
+// `retain`.  We need to be very careful not to have a live `HashMap` entry pointing to
+// either a dangling `Node` or a `Node` with dropped keys / values.  Since the key and value
+// types may panic on drop, they may short-circuit the entry in the map actually being
+// removed.  Instead, we push the removed nodes onto the free list eagerly, then try and
+// drop the keys and values for any newly freed nodes *after* `HashMap::retain` has
+// completely finished.
+struct DropFilteredValues<'a, K, V> {
+    free: &'a mut Option<NonNull<Node<K, V>>>,
+    cur_free: Option<NonNull<Node<K, V>>>,
+}
+
+impl<'a, K, V> DropFilteredValues<'a, K, V> {
+    #[inline]
+    fn drop_later(&mut self, node: NonNull<Node<K, V>>) {
+        unsafe {
+            detach_node(node);
+            push_free(&mut self.cur_free, node);
+        }
+    }
+}
+
+impl<'a, K, V> Drop for DropFilteredValues<'a, K, V> {
+    fn drop(&mut self) {
+        unsafe {
+            let end_free = self.cur_free;
+            while self.cur_free != *self.free {
+                let cur_free = self.cur_free.as_ptr();
+                (*cur_free).take_entry();
+                self.cur_free = (*cur_free).links.free.next;
+            }
+            *self.free = end_free;
+        }
+    }
+}