Adding upstream version 86.0.1.upstream/86.0.1upstream

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

13 files changed, 5846 insertions, 0 deletions

diff --git a/third_party/rust/indexmap/src/equivalent.rs b/third_party/rust/indexmap/src/equivalent.rs
new file mode 100644
index 0000000000..ad6635ffac
--- /dev/null
+++ b/third_party/rust/indexmap/src/equivalent.rs
@@ -0,0 +1,27 @@
+use core::borrow::Borrow;
+
+/// Key equivalence trait.
+///
+/// This trait allows hash table lookup to be customized.
+/// It has one blanket implementation that uses the regular `Borrow` solution,
+/// just like `HashMap` and `BTreeMap` do, so that you can pass `&str` to lookup
+/// into a map with `String` keys and so on.
+///
+/// # Contract
+///
+/// The implementor **must** hash like `K`, if it is hashable.
+pub trait Equivalent<K: ?Sized> {
+    /// Compare self to `key` and return `true` if they are equal.
+    fn equivalent(&self, key: &K) -> bool;
+}
+
+impl<Q: ?Sized, K: ?Sized> Equivalent<K> for Q
+where
+    Q: Eq,
+    K: Borrow<Q>,
+{
+    #[inline]
+    fn equivalent(&self, key: &K) -> bool {
+        *self == *key.borrow()
+    }
+}
diff --git a/third_party/rust/indexmap/src/lib.rs b/third_party/rust/indexmap/src/lib.rs
new file mode 100644
index 0000000000..2df2ceed8a
--- /dev/null
+++ b/third_party/rust/indexmap/src/lib.rs
@@ -0,0 +1,191 @@
+// We *mostly* avoid unsafe code, but `map::core::raw` allows it to use `RawTable` buckets.
+#![deny(unsafe_code)]
+#![warn(rust_2018_idioms)]
+#![doc(html_root_url = "https://docs.rs/indexmap/1/")]
+#![no_std]
+
+//! [`IndexMap`] is a hash table where the iteration order of the key-value
+//! pairs is independent of the hash values of the keys.
+//!
+//! [`IndexSet`] is a corresponding hash set using the same implementation and
+//! with similar properties.
+//!
+//! [`IndexMap`]: map/struct.IndexMap.html
+//! [`IndexSet`]: set/struct.IndexSet.html
+//!
+//!
+//! ### Feature Highlights
+//!
+//! [`IndexMap`] and [`IndexSet`] are drop-in compatible with the std `HashMap`
+//! and `HashSet`, but they also have some features of note:
+//!
+//! - The ordering semantics (see their documentation for details)
+//! - Sorting methods and the [`.pop()`][IndexMap::pop] methods.
+//! - The [`Equivalent`] trait, which offers more flexible equality definitions
+//!   between borrowed and owned versions of keys.
+//! - The [`MutableKeys`][map::MutableKeys] trait, which gives opt-in mutable
+//!   access to hash map keys.
+//!
+//! ### Alternate Hashers
+//!
+//! [`IndexMap`] and [`IndexSet`] have a default hasher type `S = RandomState`,
+//! just like the standard `HashMap` and `HashSet`, which is resistant to
+//! HashDoS attacks but not the most performant. Type aliases can make it easier
+//! to use alternate hashers:
+//!
+//! ```
+//! use fnv::FnvBuildHasher;
+//! use fxhash::FxBuildHasher;
+//! use indexmap::{IndexMap, IndexSet};
+//!
+//! type FnvIndexMap<K, V> = IndexMap<K, V, FnvBuildHasher>;
+//! type FnvIndexSet<T> = IndexSet<T, FnvBuildHasher>;
+//!
+//! type FxIndexMap<K, V> = IndexMap<K, V, FxBuildHasher>;
+//! type FxIndexSet<T> = IndexSet<T, FxBuildHasher>;
+//!
+//! let std: IndexSet<i32> = (0..100).collect();
+//! let fnv: FnvIndexSet<i32> = (0..100).collect();
+//! let fx: FxIndexSet<i32> = (0..100).collect();
+//! assert_eq!(std, fnv);
+//! assert_eq!(std, fx);
+//! ```
+//!
+//! ### Rust Version
+//!
+//! This version of indexmap requires Rust 1.32 or later, or Rust 1.36+ for
+//! using with `alloc` (without `std`), see below.
+//!
+//! The indexmap 1.x release series will use a carefully considered version
+//! upgrade policy, where in a later 1.x version, we will raise the minimum
+//! required Rust version.
+//!
+//! ## No Standard Library Targets
+//!
+//! From Rust 1.36, this crate supports being built without `std`, requiring
+//! `alloc` instead. This is enabled automatically when it is detected that
+//! `std` is not available. There is no crate feature to enable/disable to
+//! trigger this. It can be tested by building for a std-less target.
+//!
+//! - Creating maps and sets using [`new`][IndexMap::new] and
+//! [`with_capacity`][IndexMap::with_capacity] is unavailable without `std`.  
+//!   Use methods [`IndexMap::default`][def],
+//!   [`with_hasher`][IndexMap::with_hasher],
+//!   [`with_capacity_and_hasher`][IndexMap::with_capacity_and_hasher] instead.
+//!   A no-std compatible hasher will be needed as well, for example
+//!   from the crate `twox-hash`.
+//! - Macros [`indexmap!`] and [`indexset!`] are unavailable without `std`.
+//!
+//! [def]: map/struct.IndexMap.html#impl-Default
+
+#[cfg(not(has_std))]
+extern crate alloc;
+
+#[cfg(has_std)]
+#[macro_use]
+extern crate std;
+
+#[cfg(not(has_std))]
+use alloc::vec::{self, Vec};
+
+#[cfg(has_std)]
+use std::vec::{self, Vec};
+
+#[macro_use]
+mod macros;
+mod equivalent;
+mod mutable_keys;
+#[cfg(feature = "serde-1")]
+mod serde;
+mod util;
+
+pub mod map;
+pub mod set;
+
+// Placed after `map` and `set` so new `rayon` methods on the types
+// are documented after the "normal" methods.
+#[cfg(feature = "rayon")]
+mod rayon;
+
+pub use crate::equivalent::Equivalent;
+pub use crate::map::IndexMap;
+pub use crate::set::IndexSet;
+
+// shared private items
+
+/// Hash value newtype. Not larger than usize, since anything larger
+/// isn't used for selecting position anyway.
+#[derive(Clone, Copy, Debug, PartialEq)]
+struct HashValue(usize);
+
+impl HashValue {
+    #[inline(always)]
+    fn get(self) -> u64 {
+        self.0 as u64
+    }
+}
+
+#[derive(Copy, Debug)]
+struct Bucket<K, V> {
+    hash: HashValue,
+    key: K,
+    value: V,
+}
+
+impl<K, V> Clone for Bucket<K, V>
+where
+    K: Clone,
+    V: Clone,
+{
+    fn clone(&self) -> Self {
+        Bucket {
+            hash: self.hash,
+            key: self.key.clone(),
+            value: self.value.clone(),
+        }
+    }
+
+    fn clone_from(&mut self, other: &Self) {
+        self.hash = other.hash;
+        self.key.clone_from(&other.key);
+        self.value.clone_from(&other.value);
+    }
+}
+
+impl<K, V> Bucket<K, V> {
+    // field accessors -- used for `f` instead of closures in `.map(f)`
+    fn key_ref(&self) -> &K {
+        &self.key
+    }
+    fn value_ref(&self) -> &V {
+        &self.value
+    }
+    fn value_mut(&mut self) -> &mut V {
+        &mut self.value
+    }
+    fn key(self) -> K {
+        self.key
+    }
+    fn key_value(self) -> (K, V) {
+        (self.key, self.value)
+    }
+    fn refs(&self) -> (&K, &V) {
+        (&self.key, &self.value)
+    }
+    fn ref_mut(&mut self) -> (&K, &mut V) {
+        (&self.key, &mut self.value)
+    }
+    fn muts(&mut self) -> (&mut K, &mut V) {
+        (&mut self.key, &mut self.value)
+    }
+}
+
+trait Entries {
+    type Entry;
+    fn into_entries(self) -> Vec<Self::Entry>;
+    fn as_entries(&self) -> &[Self::Entry];
+    fn as_entries_mut(&mut self) -> &mut [Self::Entry];
+    fn with_entries<F>(&mut self, f: F)
+    where
+        F: FnOnce(&mut [Self::Entry]);
+}
diff --git a/third_party/rust/indexmap/src/macros.rs b/third_party/rust/indexmap/src/macros.rs
new file mode 100644
index 0000000000..c4d84217d1
--- /dev/null
+++ b/third_party/rust/indexmap/src/macros.rs
@@ -0,0 +1,120 @@
+#[cfg(has_std)]
+#[macro_export]
+/// Create an `IndexMap` from a list of key-value pairs
+///
+/// ## Example
+///
+/// ```
+/// use indexmap::indexmap;
+///
+/// let map = indexmap!{
+///     "a" => 1,
+///     "b" => 2,
+/// };
+/// assert_eq!(map["a"], 1);
+/// assert_eq!(map["b"], 2);
+/// assert_eq!(map.get("c"), None);
+///
+/// // "a" is the first key
+/// assert_eq!(map.keys().next(), Some(&"a"));
+/// ```
+macro_rules! indexmap {
+    (@single $($x:tt)*) => (());
+    (@count $($rest:expr),*) => (<[()]>::len(&[$($crate::indexmap!(@single $rest)),*]));
+
+    ($($key:expr => $value:expr,)+) => { $crate::indexmap!($($key => $value),+) };
+    ($($key:expr => $value:expr),*) => {
+        {
+            let _cap = $crate::indexmap!(@count $($key),*);
+            let mut _map = $crate::IndexMap::with_capacity(_cap);
+            $(
+                _map.insert($key, $value);
+            )*
+            _map
+        }
+    };
+}
+
+#[cfg(has_std)]
+#[macro_export]
+/// Create an `IndexSet` from a list of values
+///
+/// ## Example
+///
+/// ```
+/// use indexmap::indexset;
+///
+/// let set = indexset!{
+///     "a",
+///     "b",
+/// };
+/// assert!(set.contains("a"));
+/// assert!(set.contains("b"));
+/// assert!(!set.contains("c"));
+///
+/// // "a" is the first value
+/// assert_eq!(set.iter().next(), Some(&"a"));
+/// ```
+macro_rules! indexset {
+    (@single $($x:tt)*) => (());
+    (@count $($rest:expr),*) => (<[()]>::len(&[$($crate::indexset!(@single $rest)),*]));
+
+    ($($value:expr,)+) => { $crate::indexset!($($value),+) };
+    ($($value:expr),*) => {
+        {
+            let _cap = $crate::indexset!(@count $($value),*);
+            let mut _set = $crate::IndexSet::with_capacity(_cap);
+            $(
+                _set.insert($value);
+            )*
+            _set
+        }
+    };
+}
+
+// generate all the Iterator methods by just forwarding to the underlying
+// self.iter and mapping its element.
+macro_rules! iterator_methods {
+    // $map_elt is the mapping function from the underlying iterator's element
+    // same mapping function for both options and iterators
+    ($map_elt:expr) => {
+        fn next(&mut self) -> Option<Self::Item> {
+            self.iter.next().map($map_elt)
+        }
+
+        fn size_hint(&self) -> (usize, Option<usize>) {
+            self.iter.size_hint()
+        }
+
+        fn count(self) -> usize {
+            self.iter.len()
+        }
+
+        fn nth(&mut self, n: usize) -> Option<Self::Item> {
+            self.iter.nth(n).map($map_elt)
+        }
+
+        fn last(mut self) -> Option<Self::Item> {
+            self.next_back()
+        }
+
+        fn collect<C>(self) -> C
+        where
+            C: FromIterator<Self::Item>,
+        {
+            // NB: forwarding this directly to standard iterators will
+            // allow it to leverage unstable traits like `TrustedLen`.
+            self.iter.map($map_elt).collect()
+        }
+    };
+}
+
+macro_rules! double_ended_iterator_methods {
+    // $map_elt is the mapping function from the underlying iterator's element
+    // same mapping function for both options and iterators
+    ($map_elt:expr) => {
+        fn next_back(&mut self) -> Option<Self::Item> {
+            self.iter.next_back().map($map_elt)
+        }
+    };
+}
diff --git a/third_party/rust/indexmap/src/map.rs b/third_party/rust/indexmap/src/map.rs
new file mode 100644
index 0000000000..6829ef94b8
--- /dev/null
+++ b/third_party/rust/indexmap/src/map.rs
@@ -0,0 +1,1627 @@
+//! `IndexMap` is a hash table where the iteration order of the key-value
+//! pairs is independent of the hash values of the keys.
+
+mod core;
+
+pub use crate::mutable_keys::MutableKeys;
+
+#[cfg(feature = "rayon")]
+pub use crate::rayon::map as rayon;
+
+use crate::vec::{self, Vec};
+use ::core::cmp::Ordering;
+use ::core::fmt;
+use ::core::hash::{BuildHasher, Hash, Hasher};
+use ::core::iter::FromIterator;
+use ::core::ops::{Index, IndexMut, RangeBounds};
+use ::core::slice::{Iter as SliceIter, IterMut as SliceIterMut};
+
+#[cfg(has_std)]
+use std::collections::hash_map::RandomState;
+
+use self::core::IndexMapCore;
+use crate::equivalent::Equivalent;
+use crate::util::third;
+use crate::{Bucket, Entries, HashValue};
+
+pub use self::core::{Entry, OccupiedEntry, VacantEntry};
+
+/// A hash table where the iteration order of the key-value pairs is independent
+/// of the hash values of the keys.
+///
+/// The interface is closely compatible with the standard `HashMap`, but also
+/// has additional features.
+///
+/// # Order
+///
+/// The key-value pairs have a consistent order that is determined by
+/// the sequence of insertion and removal calls on the map. The order does
+/// not depend on the keys or the hash function at all.
+///
+/// All iterators traverse the map in *the order*.
+///
+/// The insertion order is preserved, with **notable exceptions** like the
+/// `.remove()` or `.swap_remove()` methods. Methods such as `.sort_by()` of
+/// course result in a new order, depending on the sorting order.
+///
+/// # Indices
+///
+/// The key-value pairs are indexed in a compact range without holes in the
+/// range `0..self.len()`. For example, the method `.get_full` looks up the
+/// index for a key, and the method `.get_index` looks up the key-value pair by
+/// index.
+///
+/// # Examples
+///
+/// ```
+/// use indexmap::IndexMap;
+///
+/// // count the frequency of each letter in a sentence.
+/// let mut letters = IndexMap::new();
+/// for ch in "a short treatise on fungi".chars() {
+///     *letters.entry(ch).or_insert(0) += 1;
+/// }
+///
+/// assert_eq!(letters[&'s'], 2);
+/// assert_eq!(letters[&'t'], 3);
+/// assert_eq!(letters[&'u'], 1);
+/// assert_eq!(letters.get(&'y'), None);
+/// ```
+#[cfg(has_std)]
+pub struct IndexMap<K, V, S = RandomState> {
+    core: IndexMapCore<K, V>,
+    hash_builder: S,
+}
+#[cfg(not(has_std))]
+pub struct IndexMap<K, V, S> {
+    core: IndexMapCore<K, V>,
+    hash_builder: S,
+}
+
+impl<K, V, S> Clone for IndexMap<K, V, S>
+where
+    K: Clone,
+    V: Clone,
+    S: Clone,
+{
+    fn clone(&self) -> Self {
+        IndexMap {
+            core: self.core.clone(),
+            hash_builder: self.hash_builder.clone(),
+        }
+    }
+
+    fn clone_from(&mut self, other: &Self) {
+        self.core.clone_from(&other.core);
+        self.hash_builder.clone_from(&other.hash_builder);
+    }
+}
+
+impl<K, V, S> Entries for IndexMap<K, V, S> {
+    type Entry = Bucket<K, V>;
+
+    #[inline]
+    fn into_entries(self) -> Vec<Self::Entry> {
+        self.core.into_entries()
+    }
+
+    #[inline]
+    fn as_entries(&self) -> &[Self::Entry] {
+        self.core.as_entries()
+    }
+
+    #[inline]
+    fn as_entries_mut(&mut self) -> &mut [Self::Entry] {
+        self.core.as_entries_mut()
+    }
+
+    fn with_entries<F>(&mut self, f: F)
+    where
+        F: FnOnce(&mut [Self::Entry]),
+    {
+        self.core.with_entries(f);
+    }
+}
+
+impl<K, V, S> fmt::Debug for IndexMap<K, V, S>
+where
+    K: fmt::Debug,
+    V: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        if cfg!(not(feature = "test_debug")) {
+            f.debug_map().entries(self.iter()).finish()
+        } else {
+            // Let the inner `IndexMapCore` print all of its details
+            f.debug_struct("IndexMap")
+                .field("core", &self.core)
+                .finish()
+        }
+    }
+}
+
+#[cfg(has_std)]
+impl<K, V> IndexMap<K, V> {
+    /// Create a new map. (Does not allocate.)
+    #[inline]
+    pub fn new() -> Self {
+        Self::with_capacity(0)
+    }
+
+    /// Create a new map with capacity for `n` key-value pairs. (Does not
+    /// allocate if `n` is zero.)
+    ///
+    /// Computes in **O(n)** time.
+    #[inline]
+    pub fn with_capacity(n: usize) -> Self {
+        Self::with_capacity_and_hasher(n, <_>::default())
+    }
+}
+
+impl<K, V, S> IndexMap<K, V, S> {
+    /// Create a new map with capacity for `n` key-value pairs. (Does not
+    /// allocate if `n` is zero.)
+    ///
+    /// Computes in **O(n)** time.
+    #[inline]
+    pub fn with_capacity_and_hasher(n: usize, hash_builder: S) -> Self {
+        if n == 0 {
+            IndexMap {
+                core: IndexMapCore::new(),
+                hash_builder,
+            }
+        } else {
+            IndexMap {
+                core: IndexMapCore::with_capacity(n),
+                hash_builder,
+            }
+        }
+    }
+
+    /// Create a new map with `hash_builder`
+    pub fn with_hasher(hash_builder: S) -> Self {
+        Self::with_capacity_and_hasher(0, hash_builder)
+    }
+
+    /// Computes in **O(1)** time.
+    pub fn capacity(&self) -> usize {
+        self.core.capacity()
+    }
+
+    /// Return a reference to the map's `BuildHasher`.
+    pub fn hasher(&self) -> &S {
+        &self.hash_builder
+    }
+
+    /// Return the number of key-value pairs in the map.
+    ///
+    /// Computes in **O(1)** time.
+    #[inline]
+    pub fn len(&self) -> usize {
+        self.core.len()
+    }
+
+    /// Returns true if the map contains no elements.
+    ///
+    /// Computes in **O(1)** time.
+    #[inline]
+    pub fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
+
+    /// Return an iterator over the key-value pairs of the map, in their order
+    pub fn iter(&self) -> Iter<'_, K, V> {
+        Iter {
+            iter: self.as_entries().iter(),
+        }
+    }
+
+    /// Return an iterator over the key-value pairs of the map, in their order
+    pub fn iter_mut(&mut self) -> IterMut<'_, K, V> {
+        IterMut {
+            iter: self.as_entries_mut().iter_mut(),
+        }
+    }
+
+    /// Return an iterator over the keys of the map, in their order
+    pub fn keys(&self) -> Keys<'_, K, V> {
+        Keys {
+            iter: self.as_entries().iter(),
+        }
+    }
+
+    /// Return an iterator over the values of the map, in their order
+    pub fn values(&self) -> Values<'_, K, V> {
+        Values {
+            iter: self.as_entries().iter(),
+        }
+    }
+
+    /// Return an iterator over mutable references to the the values of the map,
+    /// in their order
+    pub fn values_mut(&mut self) -> ValuesMut<'_, K, V> {
+        ValuesMut {
+            iter: self.as_entries_mut().iter_mut(),
+        }
+    }
+
+    /// Remove all key-value pairs in the map, while preserving its capacity.
+    ///
+    /// Computes in **O(n)** time.
+    pub fn clear(&mut self) {
+        self.core.clear();
+    }
+
+    /// Clears the `IndexMap` in the given index range, returning those
+    /// key-value pairs as a drain iterator.
+    ///
+    /// The range may be any type that implements `RangeBounds<usize>`,
+    /// including all of the `std::ops::Range*` types, or even a tuple pair of
+    /// `Bound` start and end values. To drain the map entirely, use `RangeFull`
+    /// like `map.drain(..)`.
+    ///
+    /// This shifts down all entries following the drained range to fill the
+    /// gap, and keeps the allocated memory for reuse.
+    ///
+    /// ***Panics*** if the starting point is greater than the end point or if
+    /// the end point is greater than the length of the map.
+    pub fn drain<R>(&mut self, range: R) -> Drain<'_, K, V>
+    where
+        R: RangeBounds<usize>,
+    {
+        Drain {
+            iter: self.core.drain(range),
+        }
+    }
+}
+
+impl<K, V, S> IndexMap<K, V, S>
+where
+    K: Hash + Eq,
+    S: BuildHasher,
+{
+    /// Reserve capacity for `additional` more key-value pairs.
+    ///
+    /// Computes in **O(n)** time.
+    pub fn reserve(&mut self, additional: usize) {
+        self.core.reserve(additional);
+    }
+
+    /// Shrink the capacity of the map as much as possible.
+    ///
+    /// Computes in **O(n)** time.
+    pub fn shrink_to_fit(&mut self) {
+        self.core.shrink_to_fit();
+    }
+
+    fn hash<Q: ?Sized + Hash>(&self, key: &Q) -> HashValue {
+        let mut h = self.hash_builder.build_hasher();
+        key.hash(&mut h);
+        HashValue(h.finish() as usize)
+    }
+
+    /// Insert a key-value pair in the map.
+    ///
+    /// If an equivalent key already exists in the map: the key remains and
+    /// retains in its place in the order, its corresponding value is updated
+    /// with `value` and the older value is returned inside `Some(_)`.
+    ///
+    /// If no equivalent key existed in the map: the new key-value pair is
+    /// inserted, last in order, and `None` is returned.
+    ///
+    /// Computes in **O(1)** time (amortized average).
+    ///
+    /// See also [`entry`](#method.entry) if you you want to insert *or* modify
+    /// or if you need to get the index of the corresponding key-value pair.
+    pub fn insert(&mut self, key: K, value: V) -> Option<V> {
+        self.insert_full(key, value).1
+    }
+
+    /// Insert a key-value pair in the map, and get their index.
+    ///
+    /// If an equivalent key already exists in the map: the key remains and
+    /// retains in its place in the order, its corresponding value is updated
+    /// with `value` and the older value is returned inside `(index, Some(_))`.
+    ///
+    /// If no equivalent key existed in the map: the new key-value pair is
+    /// inserted, last in order, and `(index, None)` is returned.
+    ///
+    /// Computes in **O(1)** time (amortized average).
+    ///
+    /// See also [`entry`](#method.entry) if you you want to insert *or* modify
+    /// or if you need to get the index of the corresponding key-value pair.
+    pub fn insert_full(&mut self, key: K, value: V) -> (usize, Option<V>) {
+        let hash = self.hash(&key);
+        self.core.insert_full(hash, key, value)
+    }
+
+    /// Get the given key’s corresponding entry in the map for insertion and/or
+    /// in-place manipulation.
+    ///
+    /// Computes in **O(1)** time (amortized average).
+    pub fn entry(&mut self, key: K) -> Entry<'_, K, V> {
+        let hash = self.hash(&key);
+        self.core.entry(hash, key)
+    }
+
+    /// Return `true` if an equivalent to `key` exists in the map.
+    ///
+    /// Computes in **O(1)** time (average).
+    pub fn contains_key<Q: ?Sized>(&self, key: &Q) -> bool
+    where
+        Q: Hash + Equivalent<K>,
+    {
+        self.get_index_of(key).is_some()
+    }
+
+    /// Return a reference to the value stored for `key`, if it is present,
+    /// else `None`.
+    ///
+    /// Computes in **O(1)** time (average).
+    pub fn get<Q: ?Sized>(&self, key: &Q) -> Option<&V>
+    where
+        Q: Hash + Equivalent<K>,
+    {
+        if let Some(i) = self.get_index_of(key) {
+            let entry = &self.as_entries()[i];
+            Some(&entry.value)
+        } else {
+            None
+        }
+    }
+
+    /// Return references to the key-value pair stored for `key`,
+    /// if it is present, else `None`.
+    ///
+    /// Computes in **O(1)** time (average).
+    pub fn get_key_value<Q: ?Sized>(&self, key: &Q) -> Option<(&K, &V)>
+    where
+        Q: Hash + Equivalent<K>,
+    {
+        if let Some(i) = self.get_index_of(key) {
+            let entry = &self.as_entries()[i];
+            Some((&entry.key, &entry.value))
+        } else {
+            None
+        }
+    }
+
+    /// Return item index, key and value
+    pub fn get_full<Q: ?Sized>(&self, key: &Q) -> Option<(usize, &K, &V)>
+    where
+        Q: Hash + Equivalent<K>,
+    {
+        if let Some(i) = self.get_index_of(key) {
+            let entry = &self.as_entries()[i];
+            Some((i, &entry.key, &entry.value))
+        } else {
+            None
+        }
+    }
+
+    /// Return item index, if it exists in the map
+    pub fn get_index_of<Q: ?Sized>(&self, key: &Q) -> Option<usize>
+    where
+        Q: Hash + Equivalent<K>,
+    {
+        if self.is_empty() {
+            None
+        } else {
+            let hash = self.hash(key);
+            self.core.get_index_of(hash, key)
+        }
+    }
+
+    pub fn get_mut<Q: ?Sized>(&mut self, key: &Q) -> Option<&mut V>
+    where
+        Q: Hash + Equivalent<K>,
+    {
+        if let Some(i) = self.get_index_of(key) {
+            let entry = &mut self.as_entries_mut()[i];
+            Some(&mut entry.value)
+        } else {
+            None
+        }
+    }
+
+    pub fn get_full_mut<Q: ?Sized>(&mut self, key: &Q) -> Option<(usize, &K, &mut V)>
+    where
+        Q: Hash + Equivalent<K>,
+    {
+        if let Some(i) = self.get_index_of(key) {
+            let entry = &mut self.as_entries_mut()[i];
+            Some((i, &entry.key, &mut entry.value))
+        } else {
+            None
+        }
+    }
+
+    pub(crate) fn get_full_mut2_impl<Q: ?Sized>(
+        &mut self,
+        key: &Q,
+    ) -> Option<(usize, &mut K, &mut V)>
+    where
+        Q: Hash + Equivalent<K>,
+    {
+        if let Some(i) = self.get_index_of(key) {
+            let entry = &mut self.as_entries_mut()[i];
+            Some((i, &mut entry.key, &mut entry.value))
+        } else {
+            None
+        }
+    }
+
+    /// Remove the key-value pair equivalent to `key` and return
+    /// its value.
+    ///
+    /// **NOTE:** This is equivalent to `.swap_remove(key)`, if you need to
+    /// preserve the order of the keys in the map, use `.shift_remove(key)`
+    /// instead.
+    ///
+    /// Computes in **O(1)** time (average).
+    pub fn remove<Q: ?Sized>(&mut self, key: &Q) -> Option<V>
+    where
+        Q: Hash + Equivalent<K>,
+    {
+        self.swap_remove(key)
+    }
+
+    /// Remove and return the key-value pair equivalent to `key`.
+    ///
+    /// **NOTE:** This is equivalent to `.swap_remove_entry(key)`, if you need to
+    /// preserve the order of the keys in the map, use `.shift_remove_entry(key)`
+    /// instead.
+    ///
+    /// Computes in **O(1)** time (average).
+    pub fn remove_entry<Q: ?Sized>(&mut self, key: &Q) -> Option<(K, V)>
+    where
+        Q: Hash + Equivalent<K>,
+    {
+        self.swap_remove_entry(key)
+    }
+
+    /// Remove the key-value pair equivalent to `key` and return
+    /// its value.
+    ///
+    /// Like `Vec::swap_remove`, the pair is removed by swapping it with the
+    /// last element of the map and popping it off. **This perturbs
+    /// the postion of what used to be the last element!**
+    ///
+    /// Return `None` if `key` is not in map.
+    ///
+    /// Computes in **O(1)** time (average).
+    pub fn swap_remove<Q: ?Sized>(&mut self, key: &Q) -> Option<V>
+    where
+        Q: Hash + Equivalent<K>,
+    {
+        self.swap_remove_full(key).map(third)
+    }
+
+    /// Remove and return the key-value pair equivalent to `key`.
+    ///
+    /// Like `Vec::swap_remove`, the pair is removed by swapping it with the
+    /// last element of the map and popping it off. **This perturbs
+    /// the postion of what used to be the last element!**
+    ///
+    /// Return `None` if `key` is not in map.
+    ///
+    /// Computes in **O(1)** time (average).
+    pub fn swap_remove_entry<Q: ?Sized>(&mut self, key: &Q) -> Option<(K, V)>
+    where
+        Q: Hash + Equivalent<K>,
+    {
+        match self.swap_remove_full(key) {
+            Some((_, key, value)) => Some((key, value)),
+            None => None,
+        }
+    }
+
+    /// Remove the key-value pair equivalent to `key` and return it and
+    /// the index it had.
+    ///
+    /// Like `Vec::swap_remove`, the pair is removed by swapping it with the
+    /// last element of the map and popping it off. **This perturbs
+    /// the postion of what used to be the last element!**
+    ///
+    /// Return `None` if `key` is not in map.
+    ///
+    /// Computes in **O(1)** time (average).
+    pub fn swap_remove_full<Q: ?Sized>(&mut self, key: &Q) -> Option<(usize, K, V)>
+    where
+        Q: Hash + Equivalent<K>,
+    {
+        if self.is_empty() {
+            return None;
+        }
+        let hash = self.hash(key);
+        self.core.swap_remove_full(hash, key)
+    }
+
+    /// Remove the key-value pair equivalent to `key` and return
+    /// its value.
+    ///
+    /// Like `Vec::remove`, the pair is removed by shifting all of the
+    /// elements that follow it, preserving their relative order.
+    /// **This perturbs the index of all of those elements!**
+    ///
+    /// Return `None` if `key` is not in map.
+    ///
+    /// Computes in **O(n)** time (average).
+    pub fn shift_remove<Q: ?Sized>(&mut self, key: &Q) -> Option<V>
+    where
+        Q: Hash + Equivalent<K>,
+    {
+        self.shift_remove_full(key).map(third)
+    }
+
+    /// Remove and return the key-value pair equivalent to `key`.
+    ///
+    /// Like `Vec::remove`, the pair is removed by shifting all of the
+    /// elements that follow it, preserving their relative order.
+    /// **This perturbs the index of all of those elements!**
+    ///
+    /// Return `None` if `key` is not in map.
+    ///
+    /// Computes in **O(n)** time (average).
+    pub fn shift_remove_entry<Q: ?Sized>(&mut self, key: &Q) -> Option<(K, V)>
+    where
+        Q: Hash + Equivalent<K>,
+    {
+        match self.shift_remove_full(key) {
+            Some((_, key, value)) => Some((key, value)),
+            None => None,
+        }
+    }
+
+    /// Remove the key-value pair equivalent to `key` and return it and
+    /// the index it had.
+    ///
+    /// Like `Vec::remove`, the pair is removed by shifting all of the
+    /// elements that follow it, preserving their relative order.
+    /// **This perturbs the index of all of those elements!**
+    ///
+    /// Return `None` if `key` is not in map.
+    ///
+    /// Computes in **O(n)** time (average).
+    pub fn shift_remove_full<Q: ?Sized>(&mut self, key: &Q) -> Option<(usize, K, V)>
+    where
+        Q: Hash + Equivalent<K>,
+    {
+        if self.is_empty() {
+            return None;
+        }
+        let hash = self.hash(key);
+        self.core.shift_remove_full(hash, key)
+    }
+
+    /// Remove the last key-value pair
+    ///
+    /// Computes in **O(1)** time (average).
+    pub fn pop(&mut self) -> Option<(K, V)> {
+        self.core.pop()
+    }
+
+    /// Scan through each key-value pair in the map and keep those where the
+    /// closure `keep` returns `true`.
+    ///
+    /// The elements are visited in order, and remaining elements keep their
+    /// order.
+    ///
+    /// Computes in **O(n)** time (average).
+    pub fn retain<F>(&mut self, mut keep: F)
+    where
+        F: FnMut(&K, &mut V) -> bool,
+    {
+        self.core.retain_in_order(move |k, v| keep(k, v));
+    }
+
+    pub(crate) fn retain_mut<F>(&mut self, keep: F)
+    where
+        F: FnMut(&mut K, &mut V) -> bool,
+    {
+        self.core.retain_in_order(keep);
+    }
+
+    /// Sort the map’s key-value pairs by the default ordering of the keys.
+    ///
+    /// See `sort_by` for details.
+    pub fn sort_keys(&mut self)
+    where
+        K: Ord,
+    {
+        self.with_entries(|entries| {
+            entries.sort_by(|a, b| Ord::cmp(&a.key, &b.key));
+        });
+    }
+
+    /// Sort the map’s key-value pairs in place using the comparison
+    /// function `compare`.
+    ///
+    /// The comparison function receives two key and value pairs to compare (you
+    /// can sort by keys or values or their combination as needed).
+    ///
+    /// Computes in **O(n log n + c)** time and **O(n)** space where *n* is
+    /// the length of the map and *c* the capacity. The sort is stable.
+    pub fn sort_by<F>(&mut self, mut cmp: F)
+    where
+        F: FnMut(&K, &V, &K, &V) -> Ordering,
+    {
+        self.with_entries(move |entries| {
+            entries.sort_by(move |a, b| cmp(&a.key, &a.value, &b.key, &b.value));
+        });
+    }
+
+    /// Sort the key-value pairs of the map and return a by value iterator of
+    /// the key-value pairs with the result.
+    ///
+    /// The sort is stable.
+    pub fn sorted_by<F>(self, mut cmp: F) -> IntoIter<K, V>
+    where
+        F: FnMut(&K, &V, &K, &V) -> Ordering,
+    {
+        let mut entries = self.into_entries();
+        entries.sort_by(move |a, b| cmp(&a.key, &a.value, &b.key, &b.value));
+        IntoIter {
+            iter: entries.into_iter(),
+        }
+    }
+
+    /// Reverses the order of the map’s key-value pairs in place.
+    ///
+    /// Computes in **O(n)** time and **O(1)** space.
+    pub fn reverse(&mut self) {
+        self.core.reverse()
+    }
+}
+
+impl<K, V, S> IndexMap<K, V, S> {
+    /// Get a key-value pair by index
+    ///
+    /// Valid indices are *0 <= index < self.len()*
+    ///
+    /// Computes in **O(1)** time.
+    pub fn get_index(&self, index: usize) -> Option<(&K, &V)> {
+        self.as_entries().get(index).map(Bucket::refs)
+    }
+
+    /// Get a key-value pair by index
+    ///
+    /// Valid indices are *0 <= index < self.len()*
+    ///
+    /// Computes in **O(1)** time.
+    pub fn get_index_mut(&mut self, index: usize) -> Option<(&mut K, &mut V)> {
+        self.as_entries_mut().get_mut(index).map(Bucket::muts)
+    }
+
+    /// Remove the key-value pair by index
+    ///
+    /// Valid indices are *0 <= index < self.len()*
+    ///
+    /// Like `Vec::swap_remove`, the pair is removed by swapping it with the
+    /// last element of the map and popping it off. **This perturbs
+    /// the postion of what used to be the last element!**
+    ///
+    /// Computes in **O(1)** time (average).
+    pub fn swap_remove_index(&mut self, index: usize) -> Option<(K, V)> {
+        self.core.swap_remove_index(index)
+    }
+
+    /// Remove the key-value pair by index
+    ///
+    /// Valid indices are *0 <= index < self.len()*
+    ///
+    /// Like `Vec::remove`, the pair is removed by shifting all of the
+    /// elements that follow it, preserving their relative order.
+    /// **This perturbs the index of all of those elements!**
+    ///
+    /// Computes in **O(n)** time (average).
+    pub fn shift_remove_index(&mut self, index: usize) -> Option<(K, V)> {
+        self.core.shift_remove_index(index)
+    }
+}
+
+/// An iterator over the keys of a `IndexMap`.
+///
+/// This `struct` is created by the [`keys`] method on [`IndexMap`]. See its
+/// documentation for more.
+///
+/// [`keys`]: struct.IndexMap.html#method.keys
+/// [`IndexMap`]: struct.IndexMap.html
+pub struct Keys<'a, K, V> {
+    pub(crate) iter: SliceIter<'a, Bucket<K, V>>,
+}
+
+impl<'a, K, V> Iterator for Keys<'a, K, V> {
+    type Item = &'a K;
+
+    iterator_methods!(Bucket::key_ref);
+}
+
+impl<K, V> DoubleEndedIterator for Keys<'_, K, V> {
+    fn next_back(&mut self) -> Option<Self::Item> {
+        self.iter.next_back().map(Bucket::key_ref)
+    }
+}
+
+impl<K, V> ExactSizeIterator for Keys<'_, K, V> {
+    fn len(&self) -> usize {
+        self.iter.len()
+    }
+}
+
+// FIXME(#26925) Remove in favor of `#[derive(Clone)]`
+impl<K, V> Clone for Keys<'_, K, V> {
+    fn clone(&self) -> Self {
+        Keys {
+            iter: self.iter.clone(),
+        }
+    }
+}
+
+impl<K: fmt::Debug, V> fmt::Debug for Keys<'_, K, V> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_list().entries(self.clone()).finish()
+    }
+}
+
+/// An iterator over the values of a `IndexMap`.
+///
+/// This `struct` is created by the [`values`] method on [`IndexMap`]. See its
+/// documentation for more.
+///
+/// [`values`]: struct.IndexMap.html#method.values
+/// [`IndexMap`]: struct.IndexMap.html
+pub struct Values<'a, K, V> {
+    iter: SliceIter<'a, Bucket<K, V>>,
+}
+
+impl<'a, K, V> Iterator for Values<'a, K, V> {
+    type Item = &'a V;
+
+    iterator_methods!(Bucket::value_ref);
+}
+
+impl<K, V> DoubleEndedIterator for Values<'_, K, V> {
+    fn next_back(&mut self) -> Option<Self::Item> {
+        self.iter.next_back().map(Bucket::value_ref)
+    }
+}
+
+impl<K, V> ExactSizeIterator for Values<'_, K, V> {
+    fn len(&self) -> usize {
+        self.iter.len()
+    }
+}
+
+// FIXME(#26925) Remove in favor of `#[derive(Clone)]`
+impl<K, V> Clone for Values<'_, K, V> {
+    fn clone(&self) -> Self {
+        Values {
+            iter: self.iter.clone(),
+        }
+    }
+}
+
+impl<K, V: fmt::Debug> fmt::Debug for Values<'_, K, V> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_list().entries(self.clone()).finish()
+    }
+}
+
+/// A mutable iterator over the values of a `IndexMap`.
+///
+/// This `struct` is created by the [`values_mut`] method on [`IndexMap`]. See its
+/// documentation for more.
+///
+/// [`values_mut`]: struct.IndexMap.html#method.values_mut
+/// [`IndexMap`]: struct.IndexMap.html
+pub struct ValuesMut<'a, K, V> {
+    iter: SliceIterMut<'a, Bucket<K, V>>,
+}
+
+impl<'a, K, V> Iterator for ValuesMut<'a, K, V> {
+    type Item = &'a mut V;
+
+    iterator_methods!(Bucket::value_mut);
+}
+
+impl<K, V> DoubleEndedIterator for ValuesMut<'_, K, V> {
+    fn next_back(&mut self) -> Option<Self::Item> {
+        self.iter.next_back().map(Bucket::value_mut)
+    }
+}
+
+impl<K, V> ExactSizeIterator for ValuesMut<'_, K, V> {
+    fn len(&self) -> usize {
+        self.iter.len()
+    }
+}
+
+/// An iterator over the entries of a `IndexMap`.
+///
+/// This `struct` is created by the [`iter`] method on [`IndexMap`]. See its
+/// documentation for more.
+///
+/// [`iter`]: struct.IndexMap.html#method.iter
+/// [`IndexMap`]: struct.IndexMap.html
+pub struct Iter<'a, K, V> {
+    iter: SliceIter<'a, Bucket<K, V>>,
+}
+
+impl<'a, K, V> Iterator for Iter<'a, K, V> {
+    type Item = (&'a K, &'a V);
+
+    iterator_methods!(Bucket::refs);
+}
+
+impl<K, V> DoubleEndedIterator for Iter<'_, K, V> {
+    fn next_back(&mut self) -> Option<Self::Item> {
+        self.iter.next_back().map(Bucket::refs)
+    }
+}
+
+impl<K, V> ExactSizeIterator for Iter<'_, K, V> {
+    fn len(&self) -> usize {
+        self.iter.len()
+    }
+}
+
+// FIXME(#26925) Remove in favor of `#[derive(Clone)]`
+impl<K, V> Clone for Iter<'_, K, V> {
+    fn clone(&self) -> Self {
+        Iter {
+            iter: self.iter.clone(),
+        }
+    }
+}
+
+impl<K: fmt::Debug, V: fmt::Debug> fmt::Debug for Iter<'_, K, V> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_list().entries(self.clone()).finish()
+    }
+}
+
+/// A mutable iterator over the entries of a `IndexMap`.
+///
+/// This `struct` is created by the [`iter_mut`] method on [`IndexMap`]. See its
+/// documentation for more.
+///
+/// [`iter_mut`]: struct.IndexMap.html#method.iter_mut
+/// [`IndexMap`]: struct.IndexMap.html
+pub struct IterMut<'a, K, V> {
+    iter: SliceIterMut<'a, Bucket<K, V>>,
+}
+
+impl<'a, K, V> Iterator for IterMut<'a, K, V> {
+    type Item = (&'a K, &'a mut V);
+
+    iterator_methods!(Bucket::ref_mut);
+}
+
+impl<K, V> DoubleEndedIterator for IterMut<'_, K, V> {
+    fn next_back(&mut self) -> Option<Self::Item> {
+        self.iter.next_back().map(Bucket::ref_mut)
+    }
+}
+
+impl<K, V> ExactSizeIterator for IterMut<'_, K, V> {
+    fn len(&self) -> usize {
+        self.iter.len()
+    }
+}
+
+/// An owning iterator over the entries of a `IndexMap`.
+///
+/// This `struct` is created by the [`into_iter`] method on [`IndexMap`]
+/// (provided by the `IntoIterator` trait). See its documentation for more.
+///
+/// [`into_iter`]: struct.IndexMap.html#method.into_iter
+/// [`IndexMap`]: struct.IndexMap.html
+pub struct IntoIter<K, V> {
+    pub(crate) iter: vec::IntoIter<Bucket<K, V>>,
+}
+
+impl<K, V> Iterator for IntoIter<K, V> {
+    type Item = (K, V);
+
+    iterator_methods!(Bucket::key_value);
+}
+
+impl<K, V> DoubleEndedIterator for IntoIter<K, V> {
+    fn next_back(&mut self) -> Option<Self::Item> {
+        self.iter.next_back().map(Bucket::key_value)
+    }
+}
+
+impl<K, V> ExactSizeIterator for IntoIter<K, V> {
+    fn len(&self) -> usize {
+        self.iter.len()
+    }
+}
+
+impl<K: fmt::Debug, V: fmt::Debug> fmt::Debug for IntoIter<K, V> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let iter = self.iter.as_slice().iter().map(Bucket::refs);
+        f.debug_list().entries(iter).finish()
+    }
+}
+
+/// A draining iterator over the entries of a `IndexMap`.
+///
+/// This `struct` is created by the [`drain`] method on [`IndexMap`]. See its
+/// documentation for more.
+///
+/// [`drain`]: struct.IndexMap.html#method.drain
+/// [`IndexMap`]: struct.IndexMap.html
+pub struct Drain<'a, K, V> {
+    pub(crate) iter: vec::Drain<'a, Bucket<K, V>>,
+}
+
+impl<K, V> Iterator for Drain<'_, K, V> {
+    type Item = (K, V);
+
+    iterator_methods!(Bucket::key_value);
+}
+
+impl<K, V> DoubleEndedIterator for Drain<'_, K, V> {
+    double_ended_iterator_methods!(Bucket::key_value);
+}
+
+impl<'a, K, V, S> IntoIterator for &'a IndexMap<K, V, S> {
+    type Item = (&'a K, &'a V);
+    type IntoIter = Iter<'a, K, V>;
+    fn into_iter(self) -> Self::IntoIter {
+        self.iter()
+    }
+}
+
+impl<'a, K, V, S> IntoIterator for &'a mut IndexMap<K, V, S> {
+    type Item = (&'a K, &'a mut V);
+    type IntoIter = IterMut<'a, K, V>;
+    fn into_iter(self) -> Self::IntoIter {
+        self.iter_mut()
+    }
+}
+
+impl<K, V, S> IntoIterator for IndexMap<K, V, S> {
+    type Item = (K, V);
+    type IntoIter = IntoIter<K, V>;
+    fn into_iter(self) -> Self::IntoIter {
+        IntoIter {
+            iter: self.into_entries().into_iter(),
+        }
+    }
+}
+
+/// Access `IndexMap` values corresponding to a key.
+///
+/// # Examples
+///
+/// ```
+/// use indexmap::IndexMap;
+///
+/// let mut map = IndexMap::new();
+/// for word in "Lorem ipsum dolor sit amet".split_whitespace() {
+///     map.insert(word.to_lowercase(), word.to_uppercase());
+/// }
+/// assert_eq!(map["lorem"], "LOREM");
+/// assert_eq!(map["ipsum"], "IPSUM");
+/// ```
+///
+/// ```should_panic
+/// use indexmap::IndexMap;
+///
+/// let mut map = IndexMap::new();
+/// map.insert("foo", 1);
+/// println!("{:?}", map["bar"]); // panics!
+/// ```
+impl<K, V, Q: ?Sized, S> Index<&Q> for IndexMap<K, V, S>
+where
+    Q: Hash + Equivalent<K>,
+    K: Hash + Eq,
+    S: BuildHasher,
+{
+    type Output = V;
+
+    /// Returns a reference to the value corresponding to the supplied `key`.
+    ///
+    /// ***Panics*** if `key` is not present in the map.
+    fn index(&self, key: &Q) -> &V {
+        self.get(key).expect("IndexMap: key not found")
+    }
+}
+
+/// Access `IndexMap` values corresponding to a key.
+///
+/// Mutable indexing allows changing / updating values of key-value
+/// pairs that are already present.
+///
+/// You can **not** insert new pairs with index syntax, use `.insert()`.
+///
+/// # Examples
+///
+/// ```
+/// use indexmap::IndexMap;
+///
+/// let mut map = IndexMap::new();
+/// for word in "Lorem ipsum dolor sit amet".split_whitespace() {
+///     map.insert(word.to_lowercase(), word.to_string());
+/// }
+/// let lorem = &mut map["lorem"];
+/// assert_eq!(lorem, "Lorem");
+/// lorem.retain(char::is_lowercase);
+/// assert_eq!(map["lorem"], "orem");
+/// ```
+///
+/// ```should_panic
+/// use indexmap::IndexMap;
+///
+/// let mut map = IndexMap::new();
+/// map.insert("foo", 1);
+/// map["bar"] = 1; // panics!
+/// ```
+impl<K, V, Q: ?Sized, S> IndexMut<&Q> for IndexMap<K, V, S>
+where
+    Q: Hash + Equivalent<K>,
+    K: Hash + Eq,
+    S: BuildHasher,
+{
+    /// Returns a mutable reference to the value corresponding to the supplied `key`.
+    ///
+    /// ***Panics*** if `key` is not present in the map.
+    fn index_mut(&mut self, key: &Q) -> &mut V {
+        self.get_mut(key).expect("IndexMap: key not found")
+    }
+}
+
+/// Access `IndexMap` values at indexed positions.
+///
+/// # Examples
+///
+/// ```
+/// use indexmap::IndexMap;
+///
+/// let mut map = IndexMap::new();
+/// for word in "Lorem ipsum dolor sit amet".split_whitespace() {
+///     map.insert(word.to_lowercase(), word.to_uppercase());
+/// }
+/// assert_eq!(map[0], "LOREM");
+/// assert_eq!(map[1], "IPSUM");
+/// map.reverse();
+/// assert_eq!(map[0], "AMET");
+/// assert_eq!(map[1], "SIT");
+/// map.sort_keys();
+/// assert_eq!(map[0], "AMET");
+/// assert_eq!(map[1], "DOLOR");
+/// ```
+///
+/// ```should_panic
+/// use indexmap::IndexMap;
+///
+/// let mut map = IndexMap::new();
+/// map.insert("foo", 1);
+/// println!("{:?}", map[10]); // panics!
+/// ```
+impl<K, V, S> Index<usize> for IndexMap<K, V, S> {
+    type Output = V;
+
+    /// Returns a reference to the value at the supplied `index`.
+    ///
+    /// ***Panics*** if `index` is out of bounds.
+    fn index(&self, index: usize) -> &V {
+        self.get_index(index)
+            .expect("IndexMap: index out of bounds")
+            .1
+    }
+}
+
+/// Access `IndexMap` values at indexed positions.
+///
+/// Mutable indexing allows changing / updating indexed values
+/// that are already present.
+///
+/// You can **not** insert new values with index syntax, use `.insert()`.
+///
+/// # Examples
+///
+/// ```
+/// use indexmap::IndexMap;
+///
+/// let mut map = IndexMap::new();
+/// for word in "Lorem ipsum dolor sit amet".split_whitespace() {
+///     map.insert(word.to_lowercase(), word.to_string());
+/// }
+/// let lorem = &mut map[0];
+/// assert_eq!(lorem, "Lorem");
+/// lorem.retain(char::is_lowercase);
+/// assert_eq!(map["lorem"], "orem");
+/// ```
+///
+/// ```should_panic
+/// use indexmap::IndexMap;
+///
+/// let mut map = IndexMap::new();
+/// map.insert("foo", 1);
+/// map[10] = 1; // panics!
+/// ```
+impl<K, V, S> IndexMut<usize> for IndexMap<K, V, S> {
+    /// Returns a mutable reference to the value at the supplied `index`.
+    ///
+    /// ***Panics*** if `index` is out of bounds.
+    fn index_mut(&mut self, index: usize) -> &mut V {
+        self.get_index_mut(index)
+            .expect("IndexMap: index out of bounds")
+            .1
+    }
+}
+
+impl<K, V, S> FromIterator<(K, V)> for IndexMap<K, V, S>
+where
+    K: Hash + Eq,
+    S: BuildHasher + Default,
+{
+    /// Create an `IndexMap` from the sequence of key-value pairs in the
+    /// iterable.
+    ///
+    /// `from_iter` uses the same logic as `extend`. See
+    /// [`extend`](#method.extend) for more details.
+    fn from_iter<I: IntoIterator<Item = (K, V)>>(iterable: I) -> Self {
+        let iter = iterable.into_iter();
+        let (low, _) = iter.size_hint();
+        let mut map = Self::with_capacity_and_hasher(low, <_>::default());
+        map.extend(iter);
+        map
+    }
+}
+
+impl<K, V, S> Extend<(K, V)> for IndexMap<K, V, S>
+where
+    K: Hash + Eq,
+    S: BuildHasher,
+{
+    /// Extend the map with all key-value pairs in the iterable.
+    ///
+    /// This is equivalent to calling [`insert`](#method.insert) for each of
+    /// them in order, which means that for keys that already existed
+    /// in the map, their value is updated but it keeps the existing order.
+    ///
+    /// New keys are inserted in the order they appear in the sequence. If
+    /// equivalents of a key occur more than once, the last corresponding value
+    /// prevails.
+    fn extend<I: IntoIterator<Item = (K, V)>>(&mut self, iterable: I) {
+        // (Note: this is a copy of `std`/`hashbrown`'s reservation logic.)
+        // Keys may be already present or show multiple times in the iterator.
+        // Reserve the entire hint lower bound if the map is empty.
+        // Otherwise reserve half the hint (rounded up), so the map
+        // will only resize twice in the worst case.
+        let iter = iterable.into_iter();
+        let reserve = if self.is_empty() {
+            iter.size_hint().0
+        } else {
+            (iter.size_hint().0 + 1) / 2
+        };
+        self.reserve(reserve);
+        iter.for_each(move |(k, v)| {
+            self.insert(k, v);
+        });
+    }
+}
+
+impl<'a, K, V, S> Extend<(&'a K, &'a V)> for IndexMap<K, V, S>
+where
+    K: Hash + Eq + Copy,
+    V: Copy,
+    S: BuildHasher,
+{
+    /// Extend the map with all key-value pairs in the iterable.
+    ///
+    /// See the first extend method for more details.
+    fn extend<I: IntoIterator<Item = (&'a K, &'a V)>>(&mut self, iterable: I) {
+        self.extend(iterable.into_iter().map(|(&key, &value)| (key, value)));
+    }
+}
+
+impl<K, V, S> Default for IndexMap<K, V, S>
+where
+    S: Default,
+{
+    /// Return an empty `IndexMap`
+    fn default() -> Self {
+        Self::with_capacity_and_hasher(0, S::default())
+    }
+}
+
+impl<K, V1, S1, V2, S2> PartialEq<IndexMap<K, V2, S2>> for IndexMap<K, V1, S1>
+where
+    K: Hash + Eq,
+    V1: PartialEq<V2>,
+    S1: BuildHasher,
+    S2: BuildHasher,
+{
+    fn eq(&self, other: &IndexMap<K, V2, S2>) -> bool {
+        if self.len() != other.len() {
+            return false;
+        }
+
+        self.iter()
+            .all(|(key, value)| other.get(key).map_or(false, |v| *value == *v))
+    }
+}
+
+impl<K, V, S> Eq for IndexMap<K, V, S>
+where
+    K: Eq + Hash,
+    V: Eq,
+    S: BuildHasher,
+{
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::util::enumerate;
+    use std::string::String;
+
+    #[test]
+    fn it_works() {
+        let mut map = IndexMap::new();
+        assert_eq!(map.is_empty(), true);
+        map.insert(1, ());
+        map.insert(1, ());
+        assert_eq!(map.len(), 1);
+        assert!(map.get(&1).is_some());
+        assert_eq!(map.is_empty(), false);
+    }
+
+    #[test]
+    fn new() {
+        let map = IndexMap::<String, String>::new();
+        println!("{:?}", map);
+        assert_eq!(map.capacity(), 0);
+        assert_eq!(map.len(), 0);
+        assert_eq!(map.is_empty(), true);
+    }
+
+    #[test]
+    fn insert() {
+        let insert = [0, 4, 2, 12, 8, 7, 11, 5];
+        let not_present = [1, 3, 6, 9, 10];
+        let mut map = IndexMap::with_capacity(insert.len());
+
+        for (i, &elt) in enumerate(&insert) {
+            assert_eq!(map.len(), i);
+            map.insert(elt, elt);
+            assert_eq!(map.len(), i + 1);
+            assert_eq!(map.get(&elt), Some(&elt));
+            assert_eq!(map[&elt], elt);
+        }
+        println!("{:?}", map);
+
+        for &elt in &not_present {
+            assert!(map.get(&elt).is_none());
+        }
+    }
+
+    #[test]
+    fn insert_full() {
+        let insert = vec![9, 2, 7, 1, 4, 6, 13];
+        let present = vec![1, 6, 2];
+        let mut map = IndexMap::with_capacity(insert.len());
+
+        for (i, &elt) in enumerate(&insert) {
+            assert_eq!(map.len(), i);
+            let (index, existing) = map.insert_full(elt, elt);
+            assert_eq!(existing, None);
+            assert_eq!(Some(index), map.get_full(&elt).map(|x| x.0));
+            assert_eq!(map.len(), i + 1);
+        }
+
+        let len = map.len();
+        for &elt in &present {
+            let (index, existing) = map.insert_full(elt, elt);
+            assert_eq!(existing, Some(elt));
+            assert_eq!(Some(index), map.get_full(&elt).map(|x| x.0));
+            assert_eq!(map.len(), len);
+        }
+    }
+
+    #[test]
+    fn insert_2() {
+        let mut map = IndexMap::with_capacity(16);
+
+        let mut keys = vec![];
+        keys.extend(0..16);
+        keys.extend(128..267);
+
+        for &i in &keys {
+            let old_map = map.clone();
+            map.insert(i, ());
+            for key in old_map.keys() {
+                if map.get(key).is_none() {
+                    println!("old_map: {:?}", old_map);
+                    println!("map: {:?}", map);
+                    panic!("did not find {} in map", key);
+                }
+            }
+        }
+
+        for &i in &keys {
+            assert!(map.get(&i).is_some(), "did not find {}", i);
+        }
+    }
+
+    #[test]
+    fn insert_order() {
+        let insert = [0, 4, 2, 12, 8, 7, 11, 5, 3, 17, 19, 22, 23];
+        let mut map = IndexMap::new();
+
+        for &elt in &insert {
+            map.insert(elt, ());
+        }
+
+        assert_eq!(map.keys().count(), map.len());
+        assert_eq!(map.keys().count(), insert.len());
+        for (a, b) in insert.iter().zip(map.keys()) {
+            assert_eq!(a, b);
+        }
+        for (i, k) in (0..insert.len()).zip(map.keys()) {
+            assert_eq!(map.get_index(i).unwrap().0, k);
+        }
+    }
+
+    #[test]
+    fn grow() {
+        let insert = [0, 4, 2, 12, 8, 7, 11];
+        let not_present = [1, 3, 6, 9, 10];
+        let mut map = IndexMap::with_capacity(insert.len());
+
+        for (i, &elt) in enumerate(&insert) {
+            assert_eq!(map.len(), i);
+            map.insert(elt, elt);
+            assert_eq!(map.len(), i + 1);
+            assert_eq!(map.get(&elt), Some(&elt));
+            assert_eq!(map[&elt], elt);
+        }
+
+        println!("{:?}", map);
+        for &elt in &insert {
+            map.insert(elt * 10, elt);
+        }
+        for &elt in &insert {
+            map.insert(elt * 100, elt);
+        }
+        for (i, &elt) in insert.iter().cycle().enumerate().take(100) {
+            map.insert(elt * 100 + i as i32, elt);
+        }
+        println!("{:?}", map);
+        for &elt in &not_present {
+            assert!(map.get(&elt).is_none());
+        }
+    }
+
+    #[test]
+    fn reserve() {
+        let mut map = IndexMap::<usize, usize>::new();
+        assert_eq!(map.capacity(), 0);
+        map.reserve(100);
+        let capacity = map.capacity();
+        assert!(capacity >= 100);
+        for i in 0..capacity {
+            assert_eq!(map.len(), i);
+            map.insert(i, i * i);
+            assert_eq!(map.len(), i + 1);
+            assert_eq!(map.capacity(), capacity);
+            assert_eq!(map.get(&i), Some(&(i * i)));
+        }
+        map.insert(capacity, std::usize::MAX);
+        assert_eq!(map.len(), capacity + 1);
+        assert!(map.capacity() > capacity);
+        assert_eq!(map.get(&capacity), Some(&std::usize::MAX));
+    }
+
+    #[test]
+    fn shrink_to_fit() {
+        let mut map = IndexMap::<usize, usize>::new();
+        assert_eq!(map.capacity(), 0);
+        for i in 0..100 {
+            assert_eq!(map.len(), i);
+            map.insert(i, i * i);
+            assert_eq!(map.len(), i + 1);
+            assert!(map.capacity() >= i + 1);
+            assert_eq!(map.get(&i), Some(&(i * i)));
+            map.shrink_to_fit();
+            assert_eq!(map.len(), i + 1);
+            assert_eq!(map.capacity(), i + 1);
+            assert_eq!(map.get(&i), Some(&(i * i)));
+        }
+    }
+
+    #[test]
+    fn remove() {
+        let insert = [0, 4, 2, 12, 8, 7, 11, 5, 3, 17, 19, 22, 23];
+        let mut map = IndexMap::new();
+
+        for &elt in &insert {
+            map.insert(elt, elt);
+        }
+
+        assert_eq!(map.keys().count(), map.len());
+        assert_eq!(map.keys().count(), insert.len());
+        for (a, b) in insert.iter().zip(map.keys()) {
+            assert_eq!(a, b);
+        }
+
+        let remove_fail = [99, 77];
+        let remove = [4, 12, 8, 7];
+
+        for &key in &remove_fail {
+            assert!(map.swap_remove_full(&key).is_none());
+        }
+        println!("{:?}", map);
+        for &key in &remove {
+            //println!("{:?}", map);
+            let index = map.get_full(&key).unwrap().0;
+            assert_eq!(map.swap_remove_full(&key), Some((index, key, key)));
+        }
+        println!("{:?}", map);
+
+        for key in &insert {
+            assert_eq!(map.get(key).is_some(), !remove.contains(key));
+        }
+        assert_eq!(map.len(), insert.len() - remove.len());
+        assert_eq!(map.keys().count(), insert.len() - remove.len());
+    }
+
+    #[test]
+    fn remove_to_empty() {
+        let mut map = indexmap! { 0 => 0, 4 => 4, 5 => 5 };
+        map.swap_remove(&5).unwrap();
+        map.swap_remove(&4).unwrap();
+        map.swap_remove(&0).unwrap();
+        assert!(map.is_empty());
+    }
+
+    #[test]
+    fn swap_remove_index() {
+        let insert = [0, 4, 2, 12, 8, 7, 11, 5, 3, 17, 19, 22, 23];
+        let mut map = IndexMap::new();
+
+        for &elt in &insert {
+            map.insert(elt, elt * 2);
+        }
+
+        let mut vector = insert.to_vec();
+        let remove_sequence = &[3, 3, 10, 4, 5, 4, 3, 0, 1];
+
+        // check that the same swap remove sequence on vec and map
+        // have the same result.
+        for &rm in remove_sequence {
+            let out_vec = vector.swap_remove(rm);
+            let (out_map, _) = map.swap_remove_index(rm).unwrap();
+            assert_eq!(out_vec, out_map);
+        }
+        assert_eq!(vector.len(), map.len());
+        for (a, b) in vector.iter().zip(map.keys()) {
+            assert_eq!(a, b);
+        }
+    }
+
+    #[test]
+    fn partial_eq_and_eq() {
+        let mut map_a = IndexMap::new();
+        map_a.insert(1, "1");
+        map_a.insert(2, "2");
+        let mut map_b = map_a.clone();
+        assert_eq!(map_a, map_b);
+        map_b.swap_remove(&1);
+        assert_ne!(map_a, map_b);
+
+        let map_c: IndexMap<_, String> = map_b.into_iter().map(|(k, v)| (k, v.into())).collect();
+        assert_ne!(map_a, map_c);
+        assert_ne!(map_c, map_a);
+    }
+
+    #[test]
+    fn extend() {
+        let mut map = IndexMap::new();
+        map.extend(vec![(&1, &2), (&3, &4)]);
+        map.extend(vec![(5, 6)]);
+        assert_eq!(
+            map.into_iter().collect::<Vec<_>>(),
+            vec![(1, 2), (3, 4), (5, 6)]
+        );
+    }
+
+    #[test]
+    fn entry() {
+        let mut map = IndexMap::new();
+
+        map.insert(1, "1");
+        map.insert(2, "2");
+        {
+            let e = map.entry(3);
+            assert_eq!(e.index(), 2);
+            let e = e.or_insert("3");
+            assert_eq!(e, &"3");
+        }
+
+        let e = map.entry(2);
+        assert_eq!(e.index(), 1);
+        assert_eq!(e.key(), &2);
+        match e {
+            Entry::Occupied(ref e) => assert_eq!(e.get(), &"2"),
+            Entry::Vacant(_) => panic!(),
+        }
+        assert_eq!(e.or_insert("4"), &"2");
+    }
+
+    #[test]
+    fn entry_and_modify() {
+        let mut map = IndexMap::new();
+
+        map.insert(1, "1");
+        map.entry(1).and_modify(|x| *x = "2");
+        assert_eq!(Some(&"2"), map.get(&1));
+
+        map.entry(2).and_modify(|x| *x = "doesn't exist");
+        assert_eq!(None, map.get(&2));
+    }
+
+    #[test]
+    fn entry_or_default() {
+        let mut map = IndexMap::new();
+
+        #[derive(Debug, PartialEq)]
+        enum TestEnum {
+            DefaultValue,
+            NonDefaultValue,
+        }
+
+        impl Default for TestEnum {
+            fn default() -> Self {
+                TestEnum::DefaultValue
+            }
+        }
+
+        map.insert(1, TestEnum::NonDefaultValue);
+        assert_eq!(&mut TestEnum::NonDefaultValue, map.entry(1).or_default());
+
+        assert_eq!(&mut TestEnum::DefaultValue, map.entry(2).or_default());
+    }
+
+    #[test]
+    fn keys() {
+        let vec = vec![(1, 'a'), (2, 'b'), (3, 'c')];
+        let map: IndexMap<_, _> = vec.into_iter().collect();
+        let keys: Vec<_> = map.keys().cloned().collect();
+        assert_eq!(keys.len(), 3);
+        assert!(keys.contains(&1));
+        assert!(keys.contains(&2));
+        assert!(keys.contains(&3));
+    }
+
+    #[test]
+    fn values() {
+        let vec = vec![(1, 'a'), (2, 'b'), (3, 'c')];
+        let map: IndexMap<_, _> = vec.into_iter().collect();
+        let values: Vec<_> = map.values().cloned().collect();
+        assert_eq!(values.len(), 3);
+        assert!(values.contains(&'a'));
+        assert!(values.contains(&'b'));
+        assert!(values.contains(&'c'));
+    }
+
+    #[test]
+    fn values_mut() {
+        let vec = vec![(1, 1), (2, 2), (3, 3)];
+        let mut map: IndexMap<_, _> = vec.into_iter().collect();
+        for value in map.values_mut() {
+            *value *= 2
+        }
+        let values: Vec<_> = map.values().cloned().collect();
+        assert_eq!(values.len(), 3);
+        assert!(values.contains(&2));
+        assert!(values.contains(&4));
+        assert!(values.contains(&6));
+    }
+}
diff --git a/third_party/rust/indexmap/src/map/core.rs b/third_party/rust/indexmap/src/map/core.rs
new file mode 100644
index 0000000000..7adb69a133
--- /dev/null
+++ b/third_party/rust/indexmap/src/map/core.rs
@@ -0,0 +1,410 @@
+//! This is the core implementation that doesn't depend on the hasher at all.
+//!
+//! The methods of `IndexMapCore` don't use any Hash properties of K.
+//!
+//! It's cleaner to separate them out, then the compiler checks that we are not
+//! using Hash at all in these methods.
+//!
+//! However, we should probably not let this show in the public API or docs.
+
+mod raw;
+
+use hashbrown::raw::RawTable;
+
+use crate::vec::{Drain, Vec};
+use core::cmp;
+use core::fmt;
+use core::mem::replace;
+use core::ops::RangeBounds;
+
+use crate::equivalent::Equivalent;
+use crate::util::{enumerate, simplify_range};
+use crate::{Bucket, Entries, HashValue};
+
+/// Core of the map that does not depend on S
+pub(crate) struct IndexMapCore<K, V> {
+    /// indices mapping from the entry hash to its index.
+    indices: RawTable<usize>,
+    /// entries is a dense vec of entries in their order.
+    entries: Vec<Bucket<K, V>>,
+}
+
+#[inline(always)]
+fn get_hash<K, V>(entries: &[Bucket<K, V>]) -> impl Fn(&usize) -> u64 + '_ {
+    move |&i| entries[i].hash.get()
+}
+
+impl<K, V> Clone for IndexMapCore<K, V>
+where
+    K: Clone,
+    V: Clone,
+{
+    fn clone(&self) -> Self {
+        let indices = self.indices.clone();
+        let mut entries = Vec::with_capacity(indices.capacity());
+        entries.clone_from(&self.entries);
+        IndexMapCore { indices, entries }
+    }
+
+    fn clone_from(&mut self, other: &Self) {
+        let hasher = get_hash(&other.entries);
+        self.indices.clone_from_with_hasher(&other.indices, hasher);
+        if self.entries.capacity() < other.entries.len() {
+            // If we must resize, match the indices capacity
+            self.reserve_entries();
+        }
+        self.entries.clone_from(&other.entries);
+    }
+}
+
+impl<K, V> fmt::Debug for IndexMapCore<K, V>
+where
+    K: fmt::Debug,
+    V: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("IndexMapCore")
+            .field("indices", &raw::DebugIndices(&self.indices))
+            .field("entries", &self.entries)
+            .finish()
+    }
+}
+
+impl<K, V> Entries for IndexMapCore<K, V> {
+    type Entry = Bucket<K, V>;
+
+    #[inline]
+    fn into_entries(self) -> Vec<Self::Entry> {
+        self.entries
+    }
+
+    #[inline]
+    fn as_entries(&self) -> &[Self::Entry] {
+        &self.entries
+    }
+
+    #[inline]
+    fn as_entries_mut(&mut self) -> &mut [Self::Entry] {
+        &mut self.entries
+    }
+
+    fn with_entries<F>(&mut self, f: F)
+    where
+        F: FnOnce(&mut [Self::Entry]),
+    {
+        f(&mut self.entries);
+        self.rebuild_hash_table();
+    }
+}
+
+impl<K, V> IndexMapCore<K, V> {
+    #[inline]
+    pub(crate) fn new() -> Self {
+        IndexMapCore {
+            indices: RawTable::new(),
+            entries: Vec::new(),
+        }
+    }
+
+    #[inline]
+    pub(crate) fn with_capacity(n: usize) -> Self {
+        IndexMapCore {
+            indices: RawTable::with_capacity(n),
+            entries: Vec::with_capacity(n),
+        }
+    }
+
+    #[inline]
+    pub(crate) fn len(&self) -> usize {
+        self.indices.len()
+    }
+
+    #[inline]
+    pub(crate) fn capacity(&self) -> usize {
+        cmp::min(self.indices.capacity(), self.entries.capacity())
+    }
+
+    pub(crate) fn clear(&mut self) {
+        self.indices.clear();
+        self.entries.clear();
+    }
+
+    pub(crate) fn drain<R>(&mut self, range: R) -> Drain<'_, Bucket<K, V>>
+    where
+        R: RangeBounds<usize>,
+    {
+        let range = simplify_range(range, self.entries.len());
+        self.erase_indices(range.start, range.end);
+        self.entries.drain(range)
+    }
+
+    /// Reserve capacity for `additional` more key-value pairs.
+    pub(crate) fn reserve(&mut self, additional: usize) {
+        self.indices.reserve(additional, get_hash(&self.entries));
+        self.reserve_entries();
+    }
+
+    /// Reserve entries capacity to match the indices
+    fn reserve_entries(&mut self) {
+        let additional = self.indices.capacity() - self.entries.len();
+        self.entries.reserve_exact(additional);
+    }
+
+    /// Shrink the capacity of the map as much as possible.
+    pub(crate) fn shrink_to_fit(&mut self) {
+        self.indices.shrink_to(0, get_hash(&self.entries));
+        self.entries.shrink_to_fit();
+    }
+
+    /// Remove the last key-value pair
+    pub(crate) fn pop(&mut self) -> Option<(K, V)> {
+        if let Some(entry) = self.entries.pop() {
+            let last = self.entries.len();
+            self.erase_index(entry.hash, last);
+            Some((entry.key, entry.value))
+        } else {
+            None
+        }
+    }
+
+    /// Append a key-value pair, *without* checking whether it already exists,
+    /// and return the pair's new index.
+    fn push(&mut self, hash: HashValue, key: K, value: V) -> usize {
+        let i = self.entries.len();
+        self.indices.insert(hash.get(), i, get_hash(&self.entries));
+        if i == self.entries.capacity() {
+            // Reserve our own capacity synced to the indices,
+            // rather than letting `Vec::push` just double it.
+            self.reserve_entries();
+        }
+        self.entries.push(Bucket { hash, key, value });
+        i
+    }
+
+    pub(crate) fn insert_full(&mut self, hash: HashValue, key: K, value: V) -> (usize, Option<V>)
+    where
+        K: Eq,
+    {
+        match self.get_index_of(hash, &key) {
+            Some(i) => (i, Some(replace(&mut self.entries[i].value, value))),
+            None => (self.push(hash, key, value), None),
+        }
+    }
+
+    pub(crate) fn retain_in_order<F>(&mut self, mut keep: F)
+    where
+        F: FnMut(&mut K, &mut V) -> bool,
+    {
+        // Like Vec::retain in self.entries, but with mutable K and V.
+        // We swap-shift all the items we want to keep, truncate the rest,
+        // then rebuild the raw hash table with the new indexes.
+        let len = self.entries.len();
+        let mut n_deleted = 0;
+        for i in 0..len {
+            let will_keep = {
+                let entry = &mut self.entries[i];
+                keep(&mut entry.key, &mut entry.value)
+            };
+            if !will_keep {
+                n_deleted += 1;
+            } else if n_deleted > 0 {
+                self.entries.swap(i - n_deleted, i);
+            }
+        }
+        if n_deleted > 0 {
+            self.entries.truncate(len - n_deleted);
+            self.rebuild_hash_table();
+        }
+    }
+
+    fn rebuild_hash_table(&mut self) {
+        self.indices.clear();
+        debug_assert!(self.indices.capacity() >= self.entries.len());
+        for (i, entry) in enumerate(&self.entries) {
+            // We should never have to reallocate, so there's no need for a real hasher.
+            self.indices.insert_no_grow(entry.hash.get(), i);
+        }
+    }
+}
+
+/// Entry for an existing key-value pair or a vacant location to
+/// insert one.
+pub enum Entry<'a, K, V> {
+    /// Existing slot with equivalent key.
+    Occupied(OccupiedEntry<'a, K, V>),
+    /// Vacant slot (no equivalent key in the map).
+    Vacant(VacantEntry<'a, K, V>),
+}
+
+impl<'a, K, V> Entry<'a, K, V> {
+    /// Computes in **O(1)** time (amortized average).
+    pub fn or_insert(self, default: V) -> &'a mut V {
+        match self {
+            Entry::Occupied(entry) => entry.into_mut(),
+            Entry::Vacant(entry) => entry.insert(default),
+        }
+    }
+
+    /// Computes in **O(1)** time (amortized average).
+    pub fn or_insert_with<F>(self, call: F) -> &'a mut V
+    where
+        F: FnOnce() -> V,
+    {
+        match self {
+            Entry::Occupied(entry) => entry.into_mut(),
+            Entry::Vacant(entry) => entry.insert(call()),
+        }
+    }
+
+    pub fn key(&self) -> &K {
+        match *self {
+            Entry::Occupied(ref entry) => entry.key(),
+            Entry::Vacant(ref entry) => entry.key(),
+        }
+    }
+
+    /// Return the index where the key-value pair exists or will be inserted.
+    pub fn index(&self) -> usize {
+        match *self {
+            Entry::Occupied(ref entry) => entry.index(),
+            Entry::Vacant(ref entry) => entry.index(),
+        }
+    }
+
+    /// Modifies the entry if it is occupied.
+    pub fn and_modify<F>(self, f: F) -> Self
+    where
+        F: FnOnce(&mut V),
+    {
+        match self {
+            Entry::Occupied(mut o) => {
+                f(o.get_mut());
+                Entry::Occupied(o)
+            }
+            x => x,
+        }
+    }
+
+    /// Inserts a default-constructed value in the entry if it is vacant and returns a mutable
+    /// reference to it. Otherwise a mutable reference to an already existent value is returned.
+    ///
+    /// Computes in **O(1)** time (amortized average).
+    pub fn or_default(self) -> &'a mut V
+    where
+        V: Default,
+    {
+        match self {
+            Entry::Occupied(entry) => entry.into_mut(),
+            Entry::Vacant(entry) => entry.insert(V::default()),
+        }
+    }
+}
+
+impl<K: fmt::Debug, V: fmt::Debug> fmt::Debug for Entry<'_, K, V> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match *self {
+            Entry::Vacant(ref v) => f.debug_tuple(stringify!(Entry)).field(v).finish(),
+            Entry::Occupied(ref o) => f.debug_tuple(stringify!(Entry)).field(o).finish(),
+        }
+    }
+}
+
+pub use self::raw::OccupiedEntry;
+
+// Extra methods that don't threaten the unsafe encapsulation.
+impl<K, V> OccupiedEntry<'_, K, V> {
+    /// Sets the value of the entry to `value`, and returns the entry's old value.
+    pub fn insert(&mut self, value: V) -> V {
+        replace(self.get_mut(), value)
+    }
+
+    /// Remove the key, value pair stored in the map for this entry, and return the value.
+    ///
+    /// **NOTE:** This is equivalent to `.swap_remove()`.
+    pub fn remove(self) -> V {
+        self.swap_remove()
+    }
+
+    /// Remove the key, value pair stored in the map for this entry, and return the value.
+    ///
+    /// Like `Vec::swap_remove`, the pair is removed by swapping it with the
+    /// last element of the map and popping it off. **This perturbs
+    /// the postion of what used to be the last element!**
+    ///
+    /// Computes in **O(1)** time (average).
+    pub fn swap_remove(self) -> V {
+        self.swap_remove_entry().1
+    }
+
+    /// Remove the key, value pair stored in the map for this entry, and return the value.
+    ///
+    /// Like `Vec::remove`, the pair is removed by shifting all of the
+    /// elements that follow it, preserving their relative order.
+    /// **This perturbs the index of all of those elements!**
+    ///
+    /// Computes in **O(n)** time (average).
+    pub fn shift_remove(self) -> V {
+        self.shift_remove_entry().1
+    }
+
+    /// Remove and return the key, value pair stored in the map for this entry
+    ///
+    /// **NOTE:** This is equivalent to `.swap_remove_entry()`.
+    pub fn remove_entry(self) -> (K, V) {
+        self.swap_remove_entry()
+    }
+}
+
+impl<K: fmt::Debug, V: fmt::Debug> fmt::Debug for OccupiedEntry<'_, K, V> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct(stringify!(OccupiedEntry))
+            .field("key", self.key())
+            .field("value", self.get())
+            .finish()
+    }
+}
+
+/// A view into a vacant entry in a `IndexMap`.
+/// It is part of the [`Entry`] enum.
+///
+/// [`Entry`]: enum.Entry.html
+pub struct VacantEntry<'a, K, V> {
+    map: &'a mut IndexMapCore<K, V>,
+    hash: HashValue,
+    key: K,
+}
+
+impl<'a, K, V> VacantEntry<'a, K, V> {
+    pub fn key(&self) -> &K {
+        &self.key
+    }
+
+    pub fn into_key(self) -> K {
+        self.key
+    }
+
+    /// Return the index where the key-value pair will be inserted.
+    pub fn index(&self) -> usize {
+        self.map.len()
+    }
+
+    pub fn insert(self, value: V) -> &'a mut V {
+        let i = self.map.push(self.hash, self.key, value);
+        &mut self.map.entries[i].value
+    }
+}
+
+impl<K: fmt::Debug, V> fmt::Debug for VacantEntry<'_, K, V> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_tuple(stringify!(VacantEntry))
+            .field(self.key())
+            .finish()
+    }
+}
+
+#[test]
+fn assert_send_sync() {
+    fn assert_send_sync<T: Send + Sync>() {}
+    assert_send_sync::<IndexMapCore<i32, i32>>();
+    assert_send_sync::<Entry<'_, i32, i32>>();
+}
diff --git a/third_party/rust/indexmap/src/map/core/raw.rs b/third_party/rust/indexmap/src/map/core/raw.rs
new file mode 100644
index 0000000000..fdfadb91c1
--- /dev/null
+++ b/third_party/rust/indexmap/src/map/core/raw.rs
@@ -0,0 +1,335 @@
+#![allow(unsafe_code)]
+//! This module encapsulates the `unsafe` access to `hashbrown::raw::RawTable`,
+//! mostly in dealing with its bucket "pointers".
+
+use super::{Entry, Equivalent, HashValue, IndexMapCore, VacantEntry};
+use crate::util::enumerate;
+use core::fmt;
+use core::mem::replace;
+use hashbrown::raw::RawTable;
+
+type RawBucket = hashbrown::raw::Bucket<usize>;
+
+pub(super) struct DebugIndices<'a>(pub &'a RawTable<usize>);
+impl fmt::Debug for DebugIndices<'_> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let indices = unsafe { self.0.iter().map(|raw_bucket| raw_bucket.read()) };
+        f.debug_list().entries(indices).finish()
+    }
+}
+
+impl<K, V> IndexMapCore<K, V> {
+    /// Return the raw bucket with an equivalent key
+    fn find_equivalent<Q>(&self, hash: HashValue, key: &Q) -> Option<RawBucket>
+    where
+        Q: ?Sized + Equivalent<K>,
+    {
+        self.indices.find(hash.get(), {
+            move |&i| Q::equivalent(key, &self.entries[i].key)
+        })
+    }
+
+    /// Return the raw bucket for the given index
+    fn find_index(&self, hash: HashValue, index: usize) -> Option<RawBucket> {
+        self.indices.find(hash.get(), move |&i| i == index)
+    }
+
+    /// Return the index in `entries` where an equivalent key can be found
+    pub(crate) fn get_index_of<Q>(&self, hash: HashValue, key: &Q) -> Option<usize>
+    where
+        Q: ?Sized + Equivalent<K>,
+    {
+        match self.find_equivalent(hash, key) {
+            Some(raw_bucket) => Some(unsafe { raw_bucket.read() }),
+            None => None,
+        }
+    }
+
+    /// Erase the given index from `indices`.
+    ///
+    /// The index doesn't need to be valid in `entries` while calling this.  No other index
+    /// adjustments are made -- this is only used by `pop` for the greatest index.
+    pub(super) fn erase_index(&mut self, hash: HashValue, index: usize) {
+        debug_assert_eq!(index, self.indices.len() - 1);
+        let raw_bucket = self.find_index(hash, index).unwrap();
+        unsafe { self.indices.erase(raw_bucket) };
+    }
+
+    /// Erase `start..end` from `indices`, and shift `end..` indices down to `start..`
+    ///
+    /// All of these items should still be at their original location in `entries`.
+    /// This is used by `drain`, which will let `Vec::drain` do the work on `entries`.
+    pub(super) fn erase_indices(&mut self, start: usize, end: usize) {
+        let (init, shifted_entries) = self.entries.split_at(end);
+        let (start_entries, erased_entries) = init.split_at(start);
+
+        let erased = erased_entries.len();
+        let shifted = shifted_entries.len();
+        let half_capacity = self.indices.buckets() / 2;
+
+        // Use a heuristic between different strategies
+        if erased == 0 {
+            // Degenerate case, nothing to do
+        } else if start + shifted < half_capacity && start < erased {
+            // Reinsert everything, as there are few kept indices
+            self.indices.clear();
+
+            // Reinsert stable indices
+            for (i, entry) in enumerate(start_entries) {
+                self.indices.insert_no_grow(entry.hash.get(), i);
+            }
+
+            // Reinsert shifted indices
+            for (i, entry) in (start..).zip(shifted_entries) {
+                self.indices.insert_no_grow(entry.hash.get(), i);
+            }
+        } else if erased + shifted < half_capacity {
+            // Find each affected index, as there are few to adjust
+
+            // Find erased indices
+            for (i, entry) in (start..).zip(erased_entries) {
+                let bucket = self.find_index(entry.hash, i).unwrap();
+                unsafe { self.indices.erase(bucket) };
+            }
+
+            // Find shifted indices
+            for ((new, old), entry) in (start..).zip(end..).zip(shifted_entries) {
+                let bucket = self.find_index(entry.hash, old).unwrap();
+                unsafe { bucket.write(new) };
+            }
+        } else {
+            // Sweep the whole table for adjustments
+            unsafe {
+                for bucket in self.indices.iter() {
+                    let i = bucket.read();
+                    if i >= end {
+                        bucket.write(i - erased);
+                    } else if i >= start {
+                        self.indices.erase(bucket);
+                    }
+                }
+            }
+        }
+
+        debug_assert_eq!(self.indices.len(), start + shifted);
+    }
+
+    pub(crate) fn entry(&mut self, hash: HashValue, key: K) -> Entry<'_, K, V>
+    where
+        K: Eq,
+    {
+        match self.find_equivalent(hash, &key) {
+            // Safety: The entry is created with a live raw bucket, at the same time we have a &mut
+            // reference to the map, so it can not be modified further.
+            Some(raw_bucket) => Entry::Occupied(OccupiedEntry {
+                map: self,
+                raw_bucket,
+                key,
+            }),
+            None => Entry::Vacant(VacantEntry {
+                map: self,
+                hash,
+                key,
+            }),
+        }
+    }
+
+    /// Remove an entry by shifting all entries that follow it
+    pub(crate) fn shift_remove_full<Q>(&mut self, hash: HashValue, key: &Q) -> Option<(usize, K, V)>
+    where
+        Q: ?Sized + Equivalent<K>,
+    {
+        match self.find_equivalent(hash, key) {
+            Some(raw_bucket) => unsafe { Some(self.shift_remove_bucket(raw_bucket)) },
+            None => None,
+        }
+    }
+
+    /// Remove an entry by shifting all entries that follow it
+    pub(crate) fn shift_remove_index(&mut self, index: usize) -> Option<(K, V)> {
+        let raw_bucket = match self.entries.get(index) {
+            Some(entry) => self.find_index(entry.hash, index).unwrap(),
+            None => return None,
+        };
+        unsafe {
+            let (_, key, value) = self.shift_remove_bucket(raw_bucket);
+            Some((key, value))
+        }
+    }
+
+    /// Remove an entry by shifting all entries that follow it
+    ///
+    /// Safety: The caller must pass a live `raw_bucket`.
+    #[allow(unused_unsafe)]
+    unsafe fn shift_remove_bucket(&mut self, raw_bucket: RawBucket) -> (usize, K, V) {
+        // use Vec::remove, but then we need to update the indices that point
+        // to all of the other entries that have to move
+        let index = unsafe { self.indices.remove(raw_bucket) };
+        let entry = self.entries.remove(index);
+
+        // correct indices that point to the entries that followed the removed entry.
+        // use a heuristic between a full sweep vs. a `find()` for every shifted item.
+        let raw_capacity = self.indices.buckets();
+        let shifted_entries = &self.entries[index..];
+        if shifted_entries.len() > raw_capacity / 2 {
+            // shift all indices greater than `index`
+            unsafe {
+                for bucket in self.indices.iter() {
+                    let i = bucket.read();
+                    if i > index {
+                        bucket.write(i - 1);
+                    }
+                }
+            }
+        } else {
+            // find each following entry to shift its index
+            for (i, entry) in (index + 1..).zip(shifted_entries) {
+                let shifted_bucket = self.find_index(entry.hash, i).unwrap();
+                unsafe { shifted_bucket.write(i - 1) };
+            }
+        }
+
+        (index, entry.key, entry.value)
+    }
+
+    /// Remove an entry by swapping it with the last
+    pub(crate) fn swap_remove_full<Q>(&mut self, hash: HashValue, key: &Q) -> Option<(usize, K, V)>
+    where
+        Q: ?Sized + Equivalent<K>,
+    {
+        match self.find_equivalent(hash, key) {
+            Some(raw_bucket) => unsafe { Some(self.swap_remove_bucket(raw_bucket)) },
+            None => None,
+        }
+    }
+
+    /// Remove an entry by swapping it with the last
+    pub(crate) fn swap_remove_index(&mut self, index: usize) -> Option<(K, V)> {
+        let raw_bucket = match self.entries.get(index) {
+            Some(entry) => self.find_index(entry.hash, index).unwrap(),
+            None => return None,
+        };
+        unsafe {
+            let (_, key, value) = self.swap_remove_bucket(raw_bucket);
+            Some((key, value))
+        }
+    }
+
+    /// Remove an entry by swapping it with the last
+    ///
+    /// Safety: The caller must pass a live `raw_bucket`.
+    #[allow(unused_unsafe)]
+    unsafe fn swap_remove_bucket(&mut self, raw_bucket: RawBucket) -> (usize, K, V) {
+        // use swap_remove, but then we need to update the index that points
+        // to the other entry that has to move
+        let index = unsafe { self.indices.remove(raw_bucket) };
+        let entry = self.entries.swap_remove(index);
+
+        // correct index that points to the entry that had to swap places
+        if let Some(entry) = self.entries.get(index) {
+            // was not last element
+            // examine new element in `index` and find it in indices
+            let last = self.entries.len();
+            let swapped_bucket = self.find_index(entry.hash, last).unwrap();
+            unsafe { swapped_bucket.write(index) };
+        }
+
+        (index, entry.key, entry.value)
+    }
+
+    pub(crate) fn reverse(&mut self) {
+        self.entries.reverse();
+
+        // No need to save hash indices, can easily calculate what they should
+        // be, given that this is an in-place reversal.
+        let len = self.entries.len();
+        unsafe {
+            for raw_bucket in self.indices.iter() {
+                let i = raw_bucket.read();
+                raw_bucket.write(len - i - 1);
+            }
+        }
+    }
+}
+
+/// A view into an occupied entry in a `IndexMap`.
+/// It is part of the [`Entry`] enum.
+///
+/// [`Entry`]: enum.Entry.html
+// SAFETY: The lifetime of the map reference also constrains the raw bucket,
+// which is essentially a raw pointer into the map indices.
+pub struct OccupiedEntry<'a, K, V> {
+    map: &'a mut IndexMapCore<K, V>,
+    raw_bucket: RawBucket,
+    key: K,
+}
+
+// `hashbrown::raw::Bucket` is only `Send`, not `Sync`.
+// SAFETY: `&self` only accesses the bucket to read it.
+unsafe impl<K: Sync, V: Sync> Sync for OccupiedEntry<'_, K, V> {}
+
+// The parent module also adds methods that don't threaten the unsafe encapsulation.
+impl<'a, K, V> OccupiedEntry<'a, K, V> {
+    pub fn key(&self) -> &K {
+        &self.key
+    }
+
+    pub fn get(&self) -> &V {
+        &self.map.entries[self.index()].value
+    }
+
+    pub fn get_mut(&mut self) -> &mut V {
+        let index = self.index();
+        &mut self.map.entries[index].value
+    }
+
+    /// Put the new key in the occupied entry's key slot
+    pub(crate) fn replace_key(self) -> K {
+        let index = self.index();
+        let old_key = &mut self.map.entries[index].key;
+        replace(old_key, self.key)
+    }
+
+    /// Return the index of the key-value pair
+    #[inline]
+    pub fn index(&self) -> usize {
+        unsafe { self.raw_bucket.read() }
+    }
+
+    pub fn into_mut(self) -> &'a mut V {
+        let index = self.index();
+        &mut self.map.entries[index].value
+    }
+
+    /// Remove and return the key, value pair stored in the map for this entry
+    ///
+    /// Like `Vec::swap_remove`, the pair is removed by swapping it with the
+    /// last element of the map and popping it off. **This perturbs
+    /// the postion of what used to be the last element!**
+    ///
+    /// Computes in **O(1)** time (average).
+    pub fn swap_remove_entry(self) -> (K, V) {
+        // This is safe because it can only happen once (self is consumed)
+        // and map.indices have not been modified since entry construction
+        unsafe {
+            let (_, key, value) = self.map.swap_remove_bucket(self.raw_bucket);
+            (key, value)
+        }
+    }
+
+    /// Remove and return the key, value pair stored in the map for this entry
+    ///
+    /// Like `Vec::remove`, the pair is removed by shifting all of the
+    /// elements that follow it, preserving their relative order.
+    /// **This perturbs the index of all of those elements!**
+    ///
+    /// Computes in **O(n)** time (average).
+    pub fn shift_remove_entry(self) -> (K, V) {
+        // This is safe because it can only happen once (self is consumed)
+        // and map.indices have not been modified since entry construction
+        unsafe {
+            let (_, key, value) = self.map.shift_remove_bucket(self.raw_bucket);
+            (key, value)
+        }
+    }
+}
diff --git a/third_party/rust/indexmap/src/mutable_keys.rs b/third_party/rust/indexmap/src/mutable_keys.rs
new file mode 100644
index 0000000000..0688441ee9
--- /dev/null
+++ b/third_party/rust/indexmap/src/mutable_keys.rs
@@ -0,0 +1,75 @@
+use core::hash::{BuildHasher, Hash};
+
+use super::{Equivalent, IndexMap};
+
+pub struct PrivateMarker {}
+
+/// Opt-in mutable access to keys.
+///
+/// These methods expose `&mut K`, mutable references to the key as it is stored
+/// in the map.
+/// You are allowed to modify the keys in the hashmap **if the modifcation
+/// does not change the key’s hash and equality**.
+///
+/// If keys are modified erronously, you can no longer look them up.
+/// This is sound (memory safe) but a logical error hazard (just like
+/// implementing PartialEq, Eq, or Hash incorrectly would be).
+///
+/// `use` this trait to enable its methods for `IndexMap`.
+pub trait MutableKeys {
+    type Key;
+    type Value;
+
+    /// Return item index, mutable reference to key and value
+    fn get_full_mut2<Q: ?Sized>(
+        &mut self,
+        key: &Q,
+    ) -> Option<(usize, &mut Self::Key, &mut Self::Value)>
+    where
+        Q: Hash + Equivalent<Self::Key>;
+
+    /// Scan through each key-value pair in the map and keep those where the
+    /// closure `keep` returns `true`.
+    ///
+    /// The elements are visited in order, and remaining elements keep their
+    /// order.
+    ///
+    /// Computes in **O(n)** time (average).
+    fn retain2<F>(&mut self, keep: F)
+    where
+        F: FnMut(&mut Self::Key, &mut Self::Value) -> bool;
+
+    /// This method is not useful in itself – it is there to “seal” the trait
+    /// for external implementation, so that we can add methods without
+    /// causing breaking changes.
+    fn __private_marker(&self) -> PrivateMarker;
+}
+
+/// Opt-in mutable access to keys.
+///
+/// See [`MutableKeys`](trait.MutableKeys.html) for more information.
+impl<K, V, S> MutableKeys for IndexMap<K, V, S>
+where
+    K: Eq + Hash,
+    S: BuildHasher,
+{
+    type Key = K;
+    type Value = V;
+    fn get_full_mut2<Q: ?Sized>(&mut self, key: &Q) -> Option<(usize, &mut K, &mut V)>
+    where
+        Q: Hash + Equivalent<K>,
+    {
+        self.get_full_mut2_impl(key)
+    }
+
+    fn retain2<F>(&mut self, keep: F)
+    where
+        F: FnMut(&mut K, &mut V) -> bool,
+    {
+        self.retain_mut(keep)
+    }
+
+    fn __private_marker(&self) -> PrivateMarker {
+        PrivateMarker {}
+    }
+}
diff --git a/third_party/rust/indexmap/src/rayon/map.rs b/third_party/rust/indexmap/src/rayon/map.rs
new file mode 100644
index 0000000000..ed4c74e438
--- /dev/null
+++ b/third_party/rust/indexmap/src/rayon/map.rs
@@ -0,0 +1,496 @@
+//! Parallel iterator types for `IndexMap` with [rayon](https://docs.rs/rayon/1.0/rayon).
+//!
+//! You will rarely need to interact with this module directly unless you need to name one of the
+//! iterator types.
+//!
+//! Requires crate feature `"rayon"`
+
+use super::collect;
+use rayon::iter::plumbing::{Consumer, ProducerCallback, UnindexedConsumer};
+use rayon::prelude::*;
+
+use crate::vec::Vec;
+use core::cmp::Ordering;
+use core::fmt;
+use core::hash::{BuildHasher, Hash};
+
+use crate::Bucket;
+use crate::Entries;
+use crate::IndexMap;
+
+/// Requires crate feature `"rayon"`.
+impl<K, V, S> IntoParallelIterator for IndexMap<K, V, S>
+where
+    K: Send,
+    V: Send,
+{
+    type Item = (K, V);
+    type Iter = IntoParIter<K, V>;
+
+    fn into_par_iter(self) -> Self::Iter {
+        IntoParIter {
+            entries: self.into_entries(),
+        }
+    }
+}
+
+/// A parallel owning iterator over the entries of a `IndexMap`.
+///
+/// This `struct` is created by the [`into_par_iter`] method on [`IndexMap`]
+/// (provided by rayon's `IntoParallelIterator` trait). See its documentation for more.
+///
+/// [`into_par_iter`]: ../struct.IndexMap.html#method.into_par_iter
+/// [`IndexMap`]: ../struct.IndexMap.html
+pub struct IntoParIter<K, V> {
+    entries: Vec<Bucket<K, V>>,
+}
+
+impl<K: fmt::Debug, V: fmt::Debug> fmt::Debug for IntoParIter<K, V> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let iter = self.entries.iter().map(Bucket::refs);
+        f.debug_list().entries(iter).finish()
+    }
+}
+
+impl<K: Send, V: Send> ParallelIterator for IntoParIter<K, V> {
+    type Item = (K, V);
+
+    parallel_iterator_methods!(Bucket::key_value);
+}
+
+impl<K: Send, V: Send> IndexedParallelIterator for IntoParIter<K, V> {
+    indexed_parallel_iterator_methods!(Bucket::key_value);
+}
+
+/// Requires crate feature `"rayon"`.
+impl<'a, K, V, S> IntoParallelIterator for &'a IndexMap<K, V, S>
+where
+    K: Sync,
+    V: Sync,
+{
+    type Item = (&'a K, &'a V);
+    type Iter = ParIter<'a, K, V>;
+
+    fn into_par_iter(self) -> Self::Iter {
+        ParIter {
+            entries: self.as_entries(),
+        }
+    }
+}
+
+/// A parallel iterator over the entries of a `IndexMap`.
+///
+/// This `struct` is created by the [`par_iter`] method on [`IndexMap`]
+/// (provided by rayon's `IntoParallelRefIterator` trait). See its documentation for more.
+///
+/// [`par_iter`]: ../struct.IndexMap.html#method.par_iter
+/// [`IndexMap`]: ../struct.IndexMap.html
+pub struct ParIter<'a, K, V> {
+    entries: &'a [Bucket<K, V>],
+}
+
+impl<K, V> Clone for ParIter<'_, K, V> {
+    fn clone(&self) -> Self {
+        ParIter { ..*self }
+    }
+}
+
+impl<K: fmt::Debug, V: fmt::Debug> fmt::Debug for ParIter<'_, K, V> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let iter = self.entries.iter().map(Bucket::refs);
+        f.debug_list().entries(iter).finish()
+    }
+}
+
+impl<'a, K: Sync, V: Sync> ParallelIterator for ParIter<'a, K, V> {
+    type Item = (&'a K, &'a V);
+
+    parallel_iterator_methods!(Bucket::refs);
+}
+
+impl<K: Sync, V: Sync> IndexedParallelIterator for ParIter<'_, K, V> {
+    indexed_parallel_iterator_methods!(Bucket::refs);
+}
+
+/// Requires crate feature `"rayon"`.
+impl<'a, K, V, S> IntoParallelIterator for &'a mut IndexMap<K, V, S>
+where
+    K: Sync + Send,
+    V: Send,
+{
+    type Item = (&'a K, &'a mut V);
+    type Iter = ParIterMut<'a, K, V>;
+
+    fn into_par_iter(self) -> Self::Iter {
+        ParIterMut {
+            entries: self.as_entries_mut(),
+        }
+    }
+}
+
+/// A parallel mutable iterator over the entries of a `IndexMap`.
+///
+/// This `struct` is created by the [`par_iter_mut`] method on [`IndexMap`]
+/// (provided by rayon's `IntoParallelRefMutIterator` trait). See its documentation for more.
+///
+/// [`par_iter_mut`]: ../struct.IndexMap.html#method.par_iter_mut
+/// [`IndexMap`]: ../struct.IndexMap.html
+pub struct ParIterMut<'a, K, V> {
+    entries: &'a mut [Bucket<K, V>],
+}
+
+impl<'a, K: Sync + Send, V: Send> ParallelIterator for ParIterMut<'a, K, V> {
+    type Item = (&'a K, &'a mut V);
+
+    parallel_iterator_methods!(Bucket::ref_mut);
+}
+
+impl<K: Sync + Send, V: Send> IndexedParallelIterator for ParIterMut<'_, K, V> {
+    indexed_parallel_iterator_methods!(Bucket::ref_mut);
+}
+
+/// Parallel iterator methods and other parallel methods.
+///
+/// The following methods **require crate feature `"rayon"`**.
+///
+/// See also the `IntoParallelIterator` implementations.
+impl<K, V, S> IndexMap<K, V, S>
+where
+    K: Sync,
+    V: Sync,
+{
+    /// Return a parallel iterator over the keys of the map.
+    ///
+    /// While parallel iterators can process items in any order, their relative order
+    /// in the map is still preserved for operations like `reduce` and `collect`.
+    pub fn par_keys(&self) -> ParKeys<'_, K, V> {
+        ParKeys {
+            entries: self.as_entries(),
+        }
+    }
+
+    /// Return a parallel iterator over the values of the map.
+    ///
+    /// While parallel iterators can process items in any order, their relative order
+    /// in the map is still preserved for operations like `reduce` and `collect`.
+    pub fn par_values(&self) -> ParValues<'_, K, V> {
+        ParValues {
+            entries: self.as_entries(),
+        }
+    }
+}
+
+impl<K, V, S> IndexMap<K, V, S>
+where
+    K: Hash + Eq + Sync,
+    V: Sync,
+    S: BuildHasher,
+{
+    /// Returns `true` if `self` contains all of the same key-value pairs as `other`,
+    /// regardless of each map's indexed order, determined in parallel.
+    pub fn par_eq<V2, S2>(&self, other: &IndexMap<K, V2, S2>) -> bool
+    where
+        V: PartialEq<V2>,
+        V2: Sync,
+        S2: BuildHasher + Sync,
+    {
+        self.len() == other.len()
+            && self
+                .par_iter()
+                .all(move |(key, value)| other.get(key).map_or(false, |v| *value == *v))
+    }
+}
+
+/// A parallel iterator over the keys of a `IndexMap`.
+///
+/// This `struct` is created by the [`par_keys`] method on [`IndexMap`]. See its
+/// documentation for more.
+///
+/// [`par_keys`]: ../struct.IndexMap.html#method.par_keys
+/// [`IndexMap`]: ../struct.IndexMap.html
+pub struct ParKeys<'a, K, V> {
+    entries: &'a [Bucket<K, V>],
+}
+
+impl<K, V> Clone for ParKeys<'_, K, V> {
+    fn clone(&self) -> Self {
+        ParKeys { ..*self }
+    }
+}
+
+impl<K: fmt::Debug, V> fmt::Debug for ParKeys<'_, K, V> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let iter = self.entries.iter().map(Bucket::key_ref);
+        f.debug_list().entries(iter).finish()
+    }
+}
+
+impl<'a, K: Sync, V: Sync> ParallelIterator for ParKeys<'a, K, V> {
+    type Item = &'a K;
+
+    parallel_iterator_methods!(Bucket::key_ref);
+}
+
+impl<K: Sync, V: Sync> IndexedParallelIterator for ParKeys<'_, K, V> {
+    indexed_parallel_iterator_methods!(Bucket::key_ref);
+}
+
+/// A parallel iterator over the values of a `IndexMap`.
+///
+/// This `struct` is created by the [`par_values`] method on [`IndexMap`]. See its
+/// documentation for more.
+///
+/// [`par_values`]: ../struct.IndexMap.html#method.par_values
+/// [`IndexMap`]: ../struct.IndexMap.html
+pub struct ParValues<'a, K, V> {
+    entries: &'a [Bucket<K, V>],
+}
+
+impl<K, V> Clone for ParValues<'_, K, V> {
+    fn clone(&self) -> Self {
+        ParValues { ..*self }
+    }
+}
+
+impl<K, V: fmt::Debug> fmt::Debug for ParValues<'_, K, V> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let iter = self.entries.iter().map(Bucket::value_ref);
+        f.debug_list().entries(iter).finish()
+    }
+}
+
+impl<'a, K: Sync, V: Sync> ParallelIterator for ParValues<'a, K, V> {
+    type Item = &'a V;
+
+    parallel_iterator_methods!(Bucket::value_ref);
+}
+
+impl<K: Sync, V: Sync> IndexedParallelIterator for ParValues<'_, K, V> {
+    indexed_parallel_iterator_methods!(Bucket::value_ref);
+}
+
+/// Requires crate feature `"rayon"`.
+impl<K, V, S> IndexMap<K, V, S>
+where
+    K: Send,
+    V: Send,
+{
+    /// Return a parallel iterator over mutable references to the the values of the map
+    ///
+    /// While parallel iterators can process items in any order, their relative order
+    /// in the map is still preserved for operations like `reduce` and `collect`.
+    pub fn par_values_mut(&mut self) -> ParValuesMut<'_, K, V> {
+        ParValuesMut {
+            entries: self.as_entries_mut(),
+        }
+    }
+}
+
+impl<K, V, S> IndexMap<K, V, S>
+where
+    K: Hash + Eq + Send,
+    V: Send,
+    S: BuildHasher,
+{
+    /// Sort the map’s key-value pairs in parallel, by the default ordering of the keys.
+    pub fn par_sort_keys(&mut self)
+    where
+        K: Ord,
+    {
+        self.with_entries(|entries| {
+            entries.par_sort_by(|a, b| K::cmp(&a.key, &b.key));
+        });
+    }
+
+    /// Sort the map’s key-value pairs in place and in parallel, using the comparison
+    /// function `compare`.
+    ///
+    /// The comparison function receives two key and value pairs to compare (you
+    /// can sort by keys or values or their combination as needed).
+    pub fn par_sort_by<F>(&mut self, cmp: F)
+    where
+        F: Fn(&K, &V, &K, &V) -> Ordering + Sync,
+    {
+        self.with_entries(|entries| {
+            entries.par_sort_by(move |a, b| cmp(&a.key, &a.value, &b.key, &b.value));
+        });
+    }
+
+    /// Sort the key-value pairs of the map in parallel and return a by value parallel
+    /// iterator of the key-value pairs with the result.
+    pub fn par_sorted_by<F>(self, cmp: F) -> IntoParIter<K, V>
+    where
+        F: Fn(&K, &V, &K, &V) -> Ordering + Sync,
+    {
+        let mut entries = self.into_entries();
+        entries.par_sort_by(move |a, b| cmp(&a.key, &a.value, &b.key, &b.value));
+        IntoParIter { entries }
+    }
+}
+
+/// A parallel mutable iterator over the values of a `IndexMap`.
+///
+/// This `struct` is created by the [`par_values_mut`] method on [`IndexMap`]. See its
+/// documentation for more.
+///
+/// [`par_values_mut`]: ../struct.IndexMap.html#method.par_values_mut
+/// [`IndexMap`]: ../struct.IndexMap.html
+pub struct ParValuesMut<'a, K, V> {
+    entries: &'a mut [Bucket<K, V>],
+}
+
+impl<'a, K: Send, V: Send> ParallelIterator for ParValuesMut<'a, K, V> {
+    type Item = &'a mut V;
+
+    parallel_iterator_methods!(Bucket::value_mut);
+}
+
+impl<K: Send, V: Send> IndexedParallelIterator for ParValuesMut<'_, K, V> {
+    indexed_parallel_iterator_methods!(Bucket::value_mut);
+}
+
+/// Requires crate feature `"rayon"`.
+impl<K, V, S> FromParallelIterator<(K, V)> for IndexMap<K, V, S>
+where
+    K: Eq + Hash + Send,
+    V: Send,
+    S: BuildHasher + Default + Send,
+{
+    fn from_par_iter<I>(iter: I) -> Self
+    where
+        I: IntoParallelIterator<Item = (K, V)>,
+    {
+        let list = collect(iter);
+        let len = list.iter().map(Vec::len).sum();
+        let mut map = Self::with_capacity_and_hasher(len, S::default());
+        for vec in list {
+            map.extend(vec);
+        }
+        map
+    }
+}
+
+/// Requires crate feature `"rayon"`.
+impl<K, V, S> ParallelExtend<(K, V)> for IndexMap<K, V, S>
+where
+    K: Eq + Hash + Send,
+    V: Send,
+    S: BuildHasher + Send,
+{
+    fn par_extend<I>(&mut self, iter: I)
+    where
+        I: IntoParallelIterator<Item = (K, V)>,
+    {
+        for vec in collect(iter) {
+            self.extend(vec);
+        }
+    }
+}
+
+/// Requires crate feature `"rayon"`.
+impl<'a, K: 'a, V: 'a, S> ParallelExtend<(&'a K, &'a V)> for IndexMap<K, V, S>
+where
+    K: Copy + Eq + Hash + Send + Sync,
+    V: Copy + Send + Sync,
+    S: BuildHasher + Send,
+{
+    fn par_extend<I>(&mut self, iter: I)
+    where
+        I: IntoParallelIterator<Item = (&'a K, &'a V)>,
+    {
+        for vec in collect(iter) {
+            self.extend(vec);
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::string::String;
+
+    #[test]
+    fn insert_order() {
+        let insert = [0, 4, 2, 12, 8, 7, 11, 5, 3, 17, 19, 22, 23];
+        let mut map = IndexMap::new();
+
+        for &elt in &insert {
+            map.insert(elt, ());
+        }
+
+        assert_eq!(map.par_keys().count(), map.len());
+        assert_eq!(map.par_keys().count(), insert.len());
+        insert.par_iter().zip(map.par_keys()).for_each(|(a, b)| {
+            assert_eq!(a, b);
+        });
+        (0..insert.len())
+            .into_par_iter()
+            .zip(map.par_keys())
+            .for_each(|(i, k)| {
+                assert_eq!(map.get_index(i).unwrap().0, k);
+            });
+    }
+
+    #[test]
+    fn partial_eq_and_eq() {
+        let mut map_a = IndexMap::new();
+        map_a.insert(1, "1");
+        map_a.insert(2, "2");
+        let mut map_b = map_a.clone();
+        assert!(map_a.par_eq(&map_b));
+        map_b.swap_remove(&1);
+        assert!(!map_a.par_eq(&map_b));
+        map_b.insert(3, "3");
+        assert!(!map_a.par_eq(&map_b));
+
+        let map_c: IndexMap<_, String> =
+            map_b.into_par_iter().map(|(k, v)| (k, v.into())).collect();
+        assert!(!map_a.par_eq(&map_c));
+        assert!(!map_c.par_eq(&map_a));
+    }
+
+    #[test]
+    fn extend() {
+        let mut map = IndexMap::new();
+        map.par_extend(vec![(&1, &2), (&3, &4)]);
+        map.par_extend(vec![(5, 6)]);
+        assert_eq!(
+            map.into_par_iter().collect::<Vec<_>>(),
+            vec![(1, 2), (3, 4), (5, 6)]
+        );
+    }
+
+    #[test]
+    fn keys() {
+        let vec = vec![(1, 'a'), (2, 'b'), (3, 'c')];
+        let map: IndexMap<_, _> = vec.into_par_iter().collect();
+        let keys: Vec<_> = map.par_keys().cloned().collect();
+        assert_eq!(keys.len(), 3);
+        assert!(keys.contains(&1));
+        assert!(keys.contains(&2));
+        assert!(keys.contains(&3));
+    }
+
+    #[test]
+    fn values() {
+        let vec = vec![(1, 'a'), (2, 'b'), (3, 'c')];
+        let map: IndexMap<_, _> = vec.into_par_iter().collect();
+        let values: Vec<_> = map.par_values().cloned().collect();
+        assert_eq!(values.len(), 3);
+        assert!(values.contains(&'a'));
+        assert!(values.contains(&'b'));
+        assert!(values.contains(&'c'));
+    }
+
+    #[test]
+    fn values_mut() {
+        let vec = vec![(1, 1), (2, 2), (3, 3)];
+        let mut map: IndexMap<_, _> = vec.into_par_iter().collect();
+        map.par_values_mut().for_each(|value| *value *= 2);
+        let values: Vec<_> = map.par_values().cloned().collect();
+        assert_eq!(values.len(), 3);
+        assert!(values.contains(&2));
+        assert!(values.contains(&4));
+        assert!(values.contains(&6));
+    }
+}
diff --git a/third_party/rust/indexmap/src/rayon/mod.rs b/third_party/rust/indexmap/src/rayon/mod.rs
new file mode 100644
index 0000000000..57c810beea
--- /dev/null
+++ b/third_party/rust/indexmap/src/rayon/mod.rs
@@ -0,0 +1,83 @@
+use rayon::prelude::*;
+
+#[cfg(not(has_std))]
+use alloc::collections::LinkedList;
+
+#[cfg(has_std)]
+use std::collections::LinkedList;
+
+use crate::vec::Vec;
+
+// generate `ParallelIterator` methods by just forwarding to the underlying
+// self.entries and mapping its elements.
+macro_rules! parallel_iterator_methods {
+    // $map_elt is the mapping function from the underlying iterator's element
+    ($map_elt:expr) => {
+        fn drive_unindexed<C>(self, consumer: C) -> C::Result
+        where
+            C: UnindexedConsumer<Self::Item>,
+        {
+            self.entries
+                .into_par_iter()
+                .map($map_elt)
+                .drive_unindexed(consumer)
+        }
+
+        // NB: This allows indexed collection, e.g. directly into a `Vec`, but the
+        // underlying iterator must really be indexed.  We should remove this if we
+        // start having tombstones that must be filtered out.
+        fn opt_len(&self) -> Option<usize> {
+            Some(self.entries.len())
+        }
+    };
+}
+
+// generate `IndexedParallelIterator` methods by just forwarding to the underlying
+// self.entries and mapping its elements.
+macro_rules! indexed_parallel_iterator_methods {
+    // $map_elt is the mapping function from the underlying iterator's element
+    ($map_elt:expr) => {
+        fn drive<C>(self, consumer: C) -> C::Result
+        where
+            C: Consumer<Self::Item>,
+        {
+            self.entries.into_par_iter().map($map_elt).drive(consumer)
+        }
+
+        fn len(&self) -> usize {
+            self.entries.len()
+        }
+
+        fn with_producer<CB>(self, callback: CB) -> CB::Output
+        where
+            CB: ProducerCallback<Self::Item>,
+        {
+            self.entries
+                .into_par_iter()
+                .map($map_elt)
+                .with_producer(callback)
+        }
+    };
+}
+
+pub mod map;
+pub mod set;
+
+// This form of intermediate collection is also how Rayon collects `HashMap`.
+// Note that the order will also be preserved!
+fn collect<I: IntoParallelIterator>(iter: I) -> LinkedList<Vec<I::Item>> {
+    iter.into_par_iter()
+        .fold(Vec::new, |mut vec, elem| {
+            vec.push(elem);
+            vec
+        })
+        .map(|vec| {
+            let mut list = LinkedList::new();
+            list.push_back(vec);
+            list
+        })
+        .reduce(LinkedList::new, |mut list1, mut list2| {
+            list1.append(&mut list2);
+            list1
+        })
+}
diff --git a/third_party/rust/indexmap/src/rayon/set.rs b/third_party/rust/indexmap/src/rayon/set.rs
new file mode 100644
index 0000000000..f6e08d4837
--- /dev/null
+++ b/third_party/rust/indexmap/src/rayon/set.rs
@@ -0,0 +1,673 @@
+//! Parallel iterator types for `IndexSet` with [rayon](https://docs.rs/rayon/1.0/rayon).
+//!
+//! You will rarely need to interact with this module directly unless you need to name one of the
+//! iterator types.
+//!
+//! Requires crate feature `"rayon"`.
+
+use super::collect;
+use rayon::iter::plumbing::{Consumer, ProducerCallback, UnindexedConsumer};
+use rayon::prelude::*;
+
+use crate::vec::Vec;
+use core::cmp::Ordering;
+use core::fmt;
+use core::hash::{BuildHasher, Hash};
+
+use crate::Entries;
+use crate::IndexSet;
+
+type Bucket<T> = crate::Bucket<T, ()>;
+
+/// Requires crate feature `"rayon"`.
+impl<T, S> IntoParallelIterator for IndexSet<T, S>
+where
+    T: Send,
+{
+    type Item = T;
+    type Iter = IntoParIter<T>;
+
+    fn into_par_iter(self) -> Self::Iter {
+        IntoParIter {
+            entries: self.into_entries(),
+        }
+    }
+}
+
+/// A parallel owning iterator over the items of a `IndexSet`.
+///
+/// This `struct` is created by the [`into_par_iter`] method on [`IndexSet`]
+/// (provided by rayon's `IntoParallelIterator` trait). See its documentation for more.
+///
+/// [`IndexSet`]: ../struct.IndexSet.html
+/// [`into_par_iter`]: ../struct.IndexSet.html#method.into_par_iter
+pub struct IntoParIter<T> {
+    entries: Vec<Bucket<T>>,
+}
+
+impl<T: fmt::Debug> fmt::Debug for IntoParIter<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let iter = self.entries.iter().map(Bucket::key_ref);
+        f.debug_list().entries(iter).finish()
+    }
+}
+
+impl<T: Send> ParallelIterator for IntoParIter<T> {
+    type Item = T;
+
+    parallel_iterator_methods!(Bucket::key);
+}
+
+impl<T: Send> IndexedParallelIterator for IntoParIter<T> {
+    indexed_parallel_iterator_methods!(Bucket::key);
+}
+
+/// Requires crate feature `"rayon"`.
+impl<'a, T, S> IntoParallelIterator for &'a IndexSet<T, S>
+where
+    T: Sync,
+{
+    type Item = &'a T;
+    type Iter = ParIter<'a, T>;
+
+    fn into_par_iter(self) -> Self::Iter {
+        ParIter {
+            entries: self.as_entries(),
+        }
+    }
+}
+
+/// A parallel iterator over the items of a `IndexSet`.
+///
+/// This `struct` is created by the [`par_iter`] method on [`IndexSet`]
+/// (provided by rayon's `IntoParallelRefIterator` trait). See its documentation for more.
+///
+/// [`IndexSet`]: ../struct.IndexSet.html
+/// [`par_iter`]: ../struct.IndexSet.html#method.par_iter
+pub struct ParIter<'a, T> {
+    entries: &'a [Bucket<T>],
+}
+
+impl<T> Clone for ParIter<'_, T> {
+    fn clone(&self) -> Self {
+        ParIter { ..*self }
+    }
+}
+
+impl<T: fmt::Debug> fmt::Debug for ParIter<'_, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let iter = self.entries.iter().map(Bucket::key_ref);
+        f.debug_list().entries(iter).finish()
+    }
+}
+
+impl<'a, T: Sync> ParallelIterator for ParIter<'a, T> {
+    type Item = &'a T;
+
+    parallel_iterator_methods!(Bucket::key_ref);
+}
+
+impl<T: Sync> IndexedParallelIterator for ParIter<'_, T> {
+    indexed_parallel_iterator_methods!(Bucket::key_ref);
+}
+
+/// Parallel iterator methods and other parallel methods.
+///
+/// The following methods **require crate feature `"rayon"`**.
+///
+/// See also the `IntoParallelIterator` implementations.
+impl<T, S> IndexSet<T, S>
+where
+    T: Hash + Eq + Sync,
+    S: BuildHasher + Sync,
+{
+    /// Return a parallel iterator over the values that are in `self` but not `other`.
+    ///
+    /// While parallel iterators can process items in any order, their relative order
+    /// in the `self` set is still preserved for operations like `reduce` and `collect`.
+    pub fn par_difference<'a, S2>(
+        &'a self,
+        other: &'a IndexSet<T, S2>,
+    ) -> ParDifference<'a, T, S, S2>
+    where
+        S2: BuildHasher + Sync,
+    {
+        ParDifference {
+            set1: self,
+            set2: other,
+        }
+    }
+
+    /// Return a parallel iterator over the values that are in `self` or `other`,
+    /// but not in both.
+    ///
+    /// While parallel iterators can process items in any order, their relative order
+    /// in the sets is still preserved for operations like `reduce` and `collect`.
+    /// Values from `self` are produced in their original order, followed by
+    /// values from `other` in their original order.
+    pub fn par_symmetric_difference<'a, S2>(
+        &'a self,
+        other: &'a IndexSet<T, S2>,
+    ) -> ParSymmetricDifference<'a, T, S, S2>
+    where
+        S2: BuildHasher + Sync,
+    {
+        ParSymmetricDifference {
+            set1: self,
+            set2: other,
+        }
+    }
+
+    /// Return a parallel iterator over the values that are in both `self` and `other`.
+    ///
+    /// While parallel iterators can process items in any order, their relative order
+    /// in the `self` set is still preserved for operations like `reduce` and `collect`.
+    pub fn par_intersection<'a, S2>(
+        &'a self,
+        other: &'a IndexSet<T, S2>,
+    ) -> ParIntersection<'a, T, S, S2>
+    where
+        S2: BuildHasher + Sync,
+    {
+        ParIntersection {
+            set1: self,
+            set2: other,
+        }
+    }
+
+    /// Return a parallel iterator over all values that are in `self` or `other`.
+    ///
+    /// While parallel iterators can process items in any order, their relative order
+    /// in the sets is still preserved for operations like `reduce` and `collect`.
+    /// Values from `self` are produced in their original order, followed by
+    /// values that are unique to `other` in their original order.
+    pub fn par_union<'a, S2>(&'a self, other: &'a IndexSet<T, S2>) -> ParUnion<'a, T, S, S2>
+    where
+        S2: BuildHasher + Sync,
+    {
+        ParUnion {
+            set1: self,
+            set2: other,
+        }
+    }
+
+    /// Returns `true` if `self` contains all of the same values as `other`,
+    /// regardless of each set's indexed order, determined in parallel.
+    pub fn par_eq<S2>(&self, other: &IndexSet<T, S2>) -> bool
+    where
+        S2: BuildHasher + Sync,
+    {
+        self.len() == other.len() && self.par_is_subset(other)
+    }
+
+    /// Returns `true` if `self` has no elements in common with `other`,
+    /// determined in parallel.
+    pub fn par_is_disjoint<S2>(&self, other: &IndexSet<T, S2>) -> bool
+    where
+        S2: BuildHasher + Sync,
+    {
+        if self.len() <= other.len() {
+            self.par_iter().all(move |value| !other.contains(value))
+        } else {
+            other.par_iter().all(move |value| !self.contains(value))
+        }
+    }
+
+    /// Returns `true` if all elements of `other` are contained in `self`,
+    /// determined in parallel.
+    pub fn par_is_superset<S2>(&self, other: &IndexSet<T, S2>) -> bool
+    where
+        S2: BuildHasher + Sync,
+    {
+        other.par_is_subset(self)
+    }
+
+    /// Returns `true` if all elements of `self` are contained in `other`,
+    /// determined in parallel.
+    pub fn par_is_subset<S2>(&self, other: &IndexSet<T, S2>) -> bool
+    where
+        S2: BuildHasher + Sync,
+    {
+        self.len() <= other.len() && self.par_iter().all(move |value| other.contains(value))
+    }
+}
+
+/// A parallel iterator producing elements in the difference of `IndexSet`s.
+///
+/// This `struct` is created by the [`par_difference`] method on [`IndexSet`].
+/// See its documentation for more.
+///
+/// [`IndexSet`]: ../struct.IndexSet.html
+/// [`par_difference`]: ../struct.IndexSet.html#method.par_difference
+pub struct ParDifference<'a, T, S1, S2> {
+    set1: &'a IndexSet<T, S1>,
+    set2: &'a IndexSet<T, S2>,
+}
+
+impl<T, S1, S2> Clone for ParDifference<'_, T, S1, S2> {
+    fn clone(&self) -> Self {
+        ParDifference { ..*self }
+    }
+}
+
+impl<T, S1, S2> fmt::Debug for ParDifference<'_, T, S1, S2>
+where
+    T: fmt::Debug + Eq + Hash,
+    S1: BuildHasher,
+    S2: BuildHasher,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_list()
+            .entries(self.set1.difference(&self.set2))
+            .finish()
+    }
+}
+
+impl<'a, T, S1, S2> ParallelIterator for ParDifference<'a, T, S1, S2>
+where
+    T: Hash + Eq + Sync,
+    S1: BuildHasher + Sync,
+    S2: BuildHasher + Sync,
+{
+    type Item = &'a T;
+
+    fn drive_unindexed<C>(self, consumer: C) -> C::Result
+    where
+        C: UnindexedConsumer<Self::Item>,
+    {
+        let Self { set1, set2 } = self;
+
+        set1.par_iter()
+            .filter(move |&item| !set2.contains(item))
+            .drive_unindexed(consumer)
+    }
+}
+
+/// A parallel iterator producing elements in the intersection of `IndexSet`s.
+///
+/// This `struct` is created by the [`par_intersection`] method on [`IndexSet`].
+/// See its documentation for more.
+///
+/// [`IndexSet`]: ../struct.IndexSet.html
+/// [`par_intersection`]: ../struct.IndexSet.html#method.par_intersection
+pub struct ParIntersection<'a, T, S1, S2> {
+    set1: &'a IndexSet<T, S1>,
+    set2: &'a IndexSet<T, S2>,
+}
+
+impl<T, S1, S2> Clone for ParIntersection<'_, T, S1, S2> {
+    fn clone(&self) -> Self {
+        ParIntersection { ..*self }
+    }
+}
+
+impl<T, S1, S2> fmt::Debug for ParIntersection<'_, T, S1, S2>
+where
+    T: fmt::Debug + Eq + Hash,
+    S1: BuildHasher,
+    S2: BuildHasher,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_list()
+            .entries(self.set1.intersection(&self.set2))
+            .finish()
+    }
+}
+
+impl<'a, T, S1, S2> ParallelIterator for ParIntersection<'a, T, S1, S2>
+where
+    T: Hash + Eq + Sync,
+    S1: BuildHasher + Sync,
+    S2: BuildHasher + Sync,
+{
+    type Item = &'a T;
+
+    fn drive_unindexed<C>(self, consumer: C) -> C::Result
+    where
+        C: UnindexedConsumer<Self::Item>,
+    {
+        let Self { set1, set2 } = self;
+
+        set1.par_iter()
+            .filter(move |&item| set2.contains(item))
+            .drive_unindexed(consumer)
+    }
+}
+
+/// A parallel iterator producing elements in the symmetric difference of `IndexSet`s.
+///
+/// This `struct` is created by the [`par_symmetric_difference`] method on
+/// [`IndexSet`]. See its documentation for more.
+///
+/// [`IndexSet`]: ../struct.IndexSet.html
+/// [`par_symmetric_difference`]: ../struct.IndexSet.html#method.par_symmetric_difference
+pub struct ParSymmetricDifference<'a, T, S1, S2> {
+    set1: &'a IndexSet<T, S1>,
+    set2: &'a IndexSet<T, S2>,
+}
+
+impl<T, S1, S2> Clone for ParSymmetricDifference<'_, T, S1, S2> {
+    fn clone(&self) -> Self {
+        ParSymmetricDifference { ..*self }
+    }
+}
+
+impl<T, S1, S2> fmt::Debug for ParSymmetricDifference<'_, T, S1, S2>
+where
+    T: fmt::Debug + Eq + Hash,
+    S1: BuildHasher,
+    S2: BuildHasher,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_list()
+            .entries(self.set1.symmetric_difference(&self.set2))
+            .finish()
+    }
+}
+
+impl<'a, T, S1, S2> ParallelIterator for ParSymmetricDifference<'a, T, S1, S2>
+where
+    T: Hash + Eq + Sync,
+    S1: BuildHasher + Sync,
+    S2: BuildHasher + Sync,
+{
+    type Item = &'a T;
+
+    fn drive_unindexed<C>(self, consumer: C) -> C::Result
+    where
+        C: UnindexedConsumer<Self::Item>,
+    {
+        let Self { set1, set2 } = self;
+
+        set1.par_difference(set2)
+            .chain(set2.par_difference(set1))
+            .drive_unindexed(consumer)
+    }
+}
+
+/// A parallel iterator producing elements in the union of `IndexSet`s.
+///
+/// This `struct` is created by the [`par_union`] method on [`IndexSet`].
+/// See its documentation for more.
+///
+/// [`IndexSet`]: ../struct.IndexSet.html
+/// [`par_union`]: ../struct.IndexSet.html#method.par_union
+pub struct ParUnion<'a, T, S1, S2> {
+    set1: &'a IndexSet<T, S1>,
+    set2: &'a IndexSet<T, S2>,
+}
+
+impl<T, S1, S2> Clone for ParUnion<'_, T, S1, S2> {
+    fn clone(&self) -> Self {
+        ParUnion { ..*self }
+    }
+}
+
+impl<T, S1, S2> fmt::Debug for ParUnion<'_, T, S1, S2>
+where
+    T: fmt::Debug + Eq + Hash,
+    S1: BuildHasher,
+    S2: BuildHasher,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_list().entries(self.set1.union(&self.set2)).finish()
+    }
+}
+
+impl<'a, T, S1, S2> ParallelIterator for ParUnion<'a, T, S1, S2>
+where
+    T: Hash + Eq + Sync,
+    S1: BuildHasher + Sync,
+    S2: BuildHasher + Sync,
+{
+    type Item = &'a T;
+
+    fn drive_unindexed<C>(self, consumer: C) -> C::Result
+    where
+        C: UnindexedConsumer<Self::Item>,
+    {
+        let Self { set1, set2 } = self;
+
+        set1.par_iter()
+            .chain(set2.par_difference(set1))
+            .drive_unindexed(consumer)
+    }
+}
+
+/// Parallel sorting methods.
+///
+/// The following methods **require crate feature `"rayon"`**.
+impl<T, S> IndexSet<T, S>
+where
+    T: Hash + Eq + Send,
+    S: BuildHasher + Send,
+{
+    /// Sort the set’s values in parallel by their default ordering.
+    pub fn par_sort(&mut self)
+    where
+        T: Ord,
+    {
+        self.with_entries(|entries| {
+            entries.par_sort_by(|a, b| T::cmp(&a.key, &b.key));
+        });
+    }
+
+    /// Sort the set’s values in place and in parallel, using the comparison function `compare`.
+    pub fn par_sort_by<F>(&mut self, cmp: F)
+    where
+        F: Fn(&T, &T) -> Ordering + Sync,
+    {
+        self.with_entries(|entries| {
+            entries.par_sort_by(move |a, b| cmp(&a.key, &b.key));
+        });
+    }
+
+    /// Sort the values of the set in parallel and return a by value parallel iterator of
+    /// the values with the result.
+    pub fn par_sorted_by<F>(self, cmp: F) -> IntoParIter<T>
+    where
+        F: Fn(&T, &T) -> Ordering + Sync,
+    {
+        let mut entries = self.into_entries();
+        entries.par_sort_by(move |a, b| cmp(&a.key, &b.key));
+        IntoParIter { entries }
+    }
+}
+
+/// Requires crate feature `"rayon"`.
+impl<T, S> FromParallelIterator<T> for IndexSet<T, S>
+where
+    T: Eq + Hash + Send,
+    S: BuildHasher + Default + Send,
+{
+    fn from_par_iter<I>(iter: I) -> Self
+    where
+        I: IntoParallelIterator<Item = T>,
+    {
+        let list = collect(iter);
+        let len = list.iter().map(Vec::len).sum();
+        let mut set = Self::with_capacity_and_hasher(len, S::default());
+        for vec in list {
+            set.extend(vec);
+        }
+        set
+    }
+}
+
+/// Requires crate feature `"rayon"`.
+impl<T, S> ParallelExtend<T> for IndexSet<T, S>
+where
+    T: Eq + Hash + Send,
+    S: BuildHasher + Send,
+{
+    fn par_extend<I>(&mut self, iter: I)
+    where
+        I: IntoParallelIterator<Item = T>,
+    {
+        for vec in collect(iter) {
+            self.extend(vec);
+        }
+    }
+}
+
+/// Requires crate feature `"rayon"`.
+impl<'a, T: 'a, S> ParallelExtend<&'a T> for IndexSet<T, S>
+where
+    T: Copy + Eq + Hash + Send + Sync,
+    S: BuildHasher + Send,
+{
+    fn par_extend<I>(&mut self, iter: I)
+    where
+        I: IntoParallelIterator<Item = &'a T>,
+    {
+        for vec in collect(iter) {
+            self.extend(vec);
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn insert_order() {
+        let insert = [0, 4, 2, 12, 8, 7, 11, 5, 3, 17, 19, 22, 23];
+        let mut set = IndexSet::new();
+
+        for &elt in &insert {
+            set.insert(elt);
+        }
+
+        assert_eq!(set.par_iter().count(), set.len());
+        assert_eq!(set.par_iter().count(), insert.len());
+        insert.par_iter().zip(&set).for_each(|(a, b)| {
+            assert_eq!(a, b);
+        });
+        (0..insert.len())
+            .into_par_iter()
+            .zip(&set)
+            .for_each(|(i, v)| {
+                assert_eq!(set.get_index(i).unwrap(), v);
+            });
+    }
+
+    #[test]
+    fn partial_eq_and_eq() {
+        let mut set_a = IndexSet::new();
+        set_a.insert(1);
+        set_a.insert(2);
+        let mut set_b = set_a.clone();
+        assert!(set_a.par_eq(&set_b));
+        set_b.swap_remove(&1);
+        assert!(!set_a.par_eq(&set_b));
+        set_b.insert(3);
+        assert!(!set_a.par_eq(&set_b));
+
+        let set_c: IndexSet<_> = set_b.into_par_iter().collect();
+        assert!(!set_a.par_eq(&set_c));
+        assert!(!set_c.par_eq(&set_a));
+    }
+
+    #[test]
+    fn extend() {
+        let mut set = IndexSet::new();
+        set.par_extend(vec![&1, &2, &3, &4]);
+        set.par_extend(vec![5, 6]);
+        assert_eq!(
+            set.into_par_iter().collect::<Vec<_>>(),
+            vec![1, 2, 3, 4, 5, 6]
+        );
+    }
+
+    #[test]
+    fn comparisons() {
+        let set_a: IndexSet<_> = (0..3).collect();
+        let set_b: IndexSet<_> = (3..6).collect();
+        let set_c: IndexSet<_> = (0..6).collect();
+        let set_d: IndexSet<_> = (3..9).collect();
+
+        assert!(!set_a.par_is_disjoint(&set_a));
+        assert!(set_a.par_is_subset(&set_a));
+        assert!(set_a.par_is_superset(&set_a));
+
+        assert!(set_a.par_is_disjoint(&set_b));
+        assert!(set_b.par_is_disjoint(&set_a));
+        assert!(!set_a.par_is_subset(&set_b));
+        assert!(!set_b.par_is_subset(&set_a));
+        assert!(!set_a.par_is_superset(&set_b));
+        assert!(!set_b.par_is_superset(&set_a));
+
+        assert!(!set_a.par_is_disjoint(&set_c));
+        assert!(!set_c.par_is_disjoint(&set_a));
+        assert!(set_a.par_is_subset(&set_c));
+        assert!(!set_c.par_is_subset(&set_a));
+        assert!(!set_a.par_is_superset(&set_c));
+        assert!(set_c.par_is_superset(&set_a));
+
+        assert!(!set_c.par_is_disjoint(&set_d));
+        assert!(!set_d.par_is_disjoint(&set_c));
+        assert!(!set_c.par_is_subset(&set_d));
+        assert!(!set_d.par_is_subset(&set_c));
+        assert!(!set_c.par_is_superset(&set_d));
+        assert!(!set_d.par_is_superset(&set_c));
+    }
+
+    #[test]
+    fn iter_comparisons() {
+        use std::iter::empty;
+
+        fn check<'a, I1, I2>(iter1: I1, iter2: I2)
+        where
+            I1: ParallelIterator<Item = &'a i32>,
+            I2: Iterator<Item = i32>,
+        {
+            let v1: Vec<_> = iter1.cloned().collect();
+            let v2: Vec<_> = iter2.collect();
+            assert_eq!(v1, v2);
+        }
+
+        let set_a: IndexSet<_> = (0..3).collect();
+        let set_b: IndexSet<_> = (3..6).collect();
+        let set_c: IndexSet<_> = (0..6).collect();
+        let set_d: IndexSet<_> = (3..9).rev().collect();
+
+        check(set_a.par_difference(&set_a), empty());
+        check(set_a.par_symmetric_difference(&set_a), empty());
+        check(set_a.par_intersection(&set_a), 0..3);
+        check(set_a.par_union(&set_a), 0..3);
+
+        check(set_a.par_difference(&set_b), 0..3);
+        check(set_b.par_difference(&set_a), 3..6);
+        check(set_a.par_symmetric_difference(&set_b), 0..6);
+        check(set_b.par_symmetric_difference(&set_a), (3..6).chain(0..3));
+        check(set_a.par_intersection(&set_b), empty());
+        check(set_b.par_intersection(&set_a), empty());
+        check(set_a.par_union(&set_b), 0..6);
+        check(set_b.par_union(&set_a), (3..6).chain(0..3));
+
+        check(set_a.par_difference(&set_c), empty());
+        check(set_c.par_difference(&set_a), 3..6);
+        check(set_a.par_symmetric_difference(&set_c), 3..6);
+        check(set_c.par_symmetric_difference(&set_a), 3..6);
+        check(set_a.par_intersection(&set_c), 0..3);
+        check(set_c.par_intersection(&set_a), 0..3);
+        check(set_a.par_union(&set_c), 0..6);
+        check(set_c.par_union(&set_a), 0..6);
+
+        check(set_c.par_difference(&set_d), 0..3);
+        check(set_d.par_difference(&set_c), (6..9).rev());
+        check(
+            set_c.par_symmetric_difference(&set_d),
+            (0..3).chain((6..9).rev()),
+        );
+        check(
+            set_d.par_symmetric_difference(&set_c),
+            (6..9).rev().chain(0..3),
+        );
+        check(set_c.par_intersection(&set_d), 3..6);
+        check(set_d.par_intersection(&set_c), (3..6).rev());
+        check(set_c.par_union(&set_d), (0..6).chain((6..9).rev()));
+        check(set_d.par_union(&set_c), (3..9).rev().chain(0..3));
+    }
+}
diff --git a/third_party/rust/indexmap/src/serde.rs b/third_party/rust/indexmap/src/serde.rs
new file mode 100644
index 0000000000..853c6b9aa3
--- /dev/null
+++ b/third_party/rust/indexmap/src/serde.rs
@@ -0,0 +1,163 @@
+use serde::de::value::{MapDeserializer, SeqDeserializer};
+use serde::de::{
+    Deserialize, Deserializer, Error, IntoDeserializer, MapAccess, SeqAccess, Visitor,
+};
+use serde::ser::{Serialize, SerializeMap, SerializeSeq, Serializer};
+
+use core::fmt::{self, Formatter};
+use core::hash::{BuildHasher, Hash};
+use core::marker::PhantomData;
+
+use crate::IndexMap;
+
+/// Requires crate feature `"serde-1"`
+impl<K, V, S> Serialize for IndexMap<K, V, S>
+where
+    K: Serialize + Hash + Eq,
+    V: Serialize,
+    S: BuildHasher,
+{
+    fn serialize<T>(&self, serializer: T) -> Result<T::Ok, T::Error>
+    where
+        T: Serializer,
+    {
+        let mut map_serializer = serializer.serialize_map(Some(self.len()))?;
+        for (key, value) in self {
+            map_serializer.serialize_entry(key, value)?;
+        }
+        map_serializer.end()
+    }
+}
+
+struct IndexMapVisitor<K, V, S>(PhantomData<(K, V, S)>);
+
+impl<'de, K, V, S> Visitor<'de> for IndexMapVisitor<K, V, S>
+where
+    K: Deserialize<'de> + Eq + Hash,
+    V: Deserialize<'de>,
+    S: Default + BuildHasher,
+{
+    type Value = IndexMap<K, V, S>;
+
+    fn expecting(&self, formatter: &mut Formatter<'_>) -> fmt::Result {
+        write!(formatter, "a map")
+    }
+
+    fn visit_map<A>(self, mut map: A) -> Result<Self::Value, A::Error>
+    where
+        A: MapAccess<'de>,
+    {
+        let mut values =
+            IndexMap::with_capacity_and_hasher(map.size_hint().unwrap_or(0), S::default());
+
+        while let Some((key, value)) = map.next_entry()? {
+            values.insert(key, value);
+        }
+
+        Ok(values)
+    }
+}
+
+/// Requires crate feature `"serde-1"`
+impl<'de, K, V, S> Deserialize<'de> for IndexMap<K, V, S>
+where
+    K: Deserialize<'de> + Eq + Hash,
+    V: Deserialize<'de>,
+    S: Default + BuildHasher,
+{
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        deserializer.deserialize_map(IndexMapVisitor(PhantomData))
+    }
+}
+
+impl<'de, K, V, S, E> IntoDeserializer<'de, E> for IndexMap<K, V, S>
+where
+    K: IntoDeserializer<'de, E> + Eq + Hash,
+    V: IntoDeserializer<'de, E>,
+    S: BuildHasher,
+    E: Error,
+{
+    type Deserializer = MapDeserializer<'de, <Self as IntoIterator>::IntoIter, E>;
+
+    fn into_deserializer(self) -> Self::Deserializer {
+        MapDeserializer::new(self.into_iter())
+    }
+}
+
+use crate::IndexSet;
+
+/// Requires crate feature `"serde-1"`
+impl<T, S> Serialize for IndexSet<T, S>
+where
+    T: Serialize + Hash + Eq,
+    S: BuildHasher,
+{
+    fn serialize<Se>(&self, serializer: Se) -> Result<Se::Ok, Se::Error>
+    where
+        Se: Serializer,
+    {
+        let mut set_serializer = serializer.serialize_seq(Some(self.len()))?;
+        for value in self {
+            set_serializer.serialize_element(value)?;
+        }
+        set_serializer.end()
+    }
+}
+
+struct IndexSetVisitor<T, S>(PhantomData<(T, S)>);
+
+impl<'de, T, S> Visitor<'de> for IndexSetVisitor<T, S>
+where
+    T: Deserialize<'de> + Eq + Hash,
+    S: Default + BuildHasher,
+{
+    type Value = IndexSet<T, S>;
+
+    fn expecting(&self, formatter: &mut Formatter<'_>) -> fmt::Result {
+        write!(formatter, "a set")
+    }
+
+    fn visit_seq<A>(self, mut seq: A) -> Result<Self::Value, A::Error>
+    where
+        A: SeqAccess<'de>,
+    {
+        let mut values =
+            IndexSet::with_capacity_and_hasher(seq.size_hint().unwrap_or(0), S::default());
+
+        while let Some(value) = seq.next_element()? {
+            values.insert(value);
+        }
+
+        Ok(values)
+    }
+}
+
+/// Requires crate feature `"serde-1"`
+impl<'de, T, S> Deserialize<'de> for IndexSet<T, S>
+where
+    T: Deserialize<'de> + Eq + Hash,
+    S: Default + BuildHasher,
+{
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        deserializer.deserialize_seq(IndexSetVisitor(PhantomData))
+    }
+}
+
+impl<'de, T, S, E> IntoDeserializer<'de, E> for IndexSet<T, S>
+where
+    T: IntoDeserializer<'de, E> + Eq + Hash,
+    S: BuildHasher,
+    E: Error,
+{
+    type Deserializer = SeqDeserializer<<Self as IntoIterator>::IntoIter, E>;
+
+    fn into_deserializer(self) -> Self::Deserializer {
+        SeqDeserializer::new(self.into_iter())
+    }
+}
diff --git a/third_party/rust/indexmap/src/set.rs b/third_party/rust/indexmap/src/set.rs
new file mode 100644
index 0000000000..9949389187
--- /dev/null
+++ b/third_party/rust/indexmap/src/set.rs
@@ -0,0 +1,1607 @@
+//! A hash set implemented using `IndexMap`
+
+#[cfg(feature = "rayon")]
+pub use crate::rayon::set as rayon;
+
+#[cfg(has_std)]
+use std::collections::hash_map::RandomState;
+
+use crate::vec::{self, Vec};
+use core::cmp::Ordering;
+use core::fmt;
+use core::hash::{BuildHasher, Hash};
+use core::iter::{Chain, FromIterator};
+use core::ops::{BitAnd, BitOr, BitXor, Index, RangeBounds, Sub};
+use core::slice;
+
+use super::{Entries, Equivalent, IndexMap};
+
+type Bucket<T> = super::Bucket<T, ()>;
+
+/// A hash set where the iteration order of the values is independent of their
+/// hash values.
+///
+/// The interface is closely compatible with the standard `HashSet`, but also
+/// has additional features.
+///
+/// # Order
+///
+/// The values have a consistent order that is determined by the sequence of
+/// insertion and removal calls on the set. The order does not depend on the
+/// values or the hash function at all. Note that insertion order and value
+/// are not affected if a re-insertion is attempted once an element is
+/// already present.
+///
+/// All iterators traverse the set *in order*.  Set operation iterators like
+/// `union` produce a concatenated order, as do their matching "bitwise"
+/// operators.  See their documentation for specifics.
+///
+/// The insertion order is preserved, with **notable exceptions** like the
+/// `.remove()` or `.swap_remove()` methods. Methods such as `.sort_by()` of
+/// course result in a new order, depending on the sorting order.
+///
+/// # Indices
+///
+/// The values are indexed in a compact range without holes in the range
+/// `0..self.len()`. For example, the method `.get_full` looks up the index for
+/// a value, and the method `.get_index` looks up the value by index.
+///
+/// # Examples
+///
+/// ```
+/// use indexmap::IndexSet;
+///
+/// // Collects which letters appear in a sentence.
+/// let letters: IndexSet<_> = "a short treatise on fungi".chars().collect();
+///
+/// assert!(letters.contains(&'s'));
+/// assert!(letters.contains(&'t'));
+/// assert!(letters.contains(&'u'));
+/// assert!(!letters.contains(&'y'));
+/// ```
+#[cfg(has_std)]
+pub struct IndexSet<T, S = RandomState> {
+    map: IndexMap<T, (), S>,
+}
+#[cfg(not(has_std))]
+pub struct IndexSet<T, S> {
+    map: IndexMap<T, (), S>,
+}
+
+impl<T, S> Clone for IndexSet<T, S>
+where
+    T: Clone,
+    S: Clone,
+{
+    fn clone(&self) -> Self {
+        IndexSet {
+            map: self.map.clone(),
+        }
+    }
+
+    fn clone_from(&mut self, other: &Self) {
+        self.map.clone_from(&other.map);
+    }
+}
+
+impl<T, S> Entries for IndexSet<T, S> {
+    type Entry = Bucket<T>;
+
+    #[inline]
+    fn into_entries(self) -> Vec<Self::Entry> {
+        self.map.into_entries()
+    }
+
+    #[inline]
+    fn as_entries(&self) -> &[Self::Entry] {
+        self.map.as_entries()
+    }
+
+    #[inline]
+    fn as_entries_mut(&mut self) -> &mut [Self::Entry] {
+        self.map.as_entries_mut()
+    }
+
+    fn with_entries<F>(&mut self, f: F)
+    where
+        F: FnOnce(&mut [Self::Entry]),
+    {
+        self.map.with_entries(f);
+    }
+}
+
+impl<T, S> fmt::Debug for IndexSet<T, S>
+where
+    T: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        if cfg!(not(feature = "test_debug")) {
+            f.debug_set().entries(self.iter()).finish()
+        } else {
+            // Let the inner `IndexMap` print all of its details
+            f.debug_struct("IndexSet").field("map", &self.map).finish()
+        }
+    }
+}
+
+#[cfg(has_std)]
+impl<T> IndexSet<T> {
+    /// Create a new set. (Does not allocate.)
+    pub fn new() -> Self {
+        IndexSet {
+            map: IndexMap::new(),
+        }
+    }
+
+    /// Create a new set with capacity for `n` elements.
+    /// (Does not allocate if `n` is zero.)
+    ///
+    /// Computes in **O(n)** time.
+    pub fn with_capacity(n: usize) -> Self {
+        IndexSet {
+            map: IndexMap::with_capacity(n),
+        }
+    }
+}
+
+impl<T, S> IndexSet<T, S> {
+    /// Create a new set with capacity for `n` elements.
+    /// (Does not allocate if `n` is zero.)
+    ///
+    /// Computes in **O(n)** time.
+    pub fn with_capacity_and_hasher(n: usize, hash_builder: S) -> Self {
+        IndexSet {
+            map: IndexMap::with_capacity_and_hasher(n, hash_builder),
+        }
+    }
+
+    /// Create a new set with `hash_builder`
+    pub fn with_hasher(hash_builder: S) -> Self {
+        IndexSet {
+            map: IndexMap::with_hasher(hash_builder),
+        }
+    }
+
+    /// Computes in **O(1)** time.
+    pub fn capacity(&self) -> usize {
+        self.map.capacity()
+    }
+
+    /// Return a reference to the set's `BuildHasher`.
+    pub fn hasher(&self) -> &S {
+        self.map.hasher()
+    }
+
+    /// Return the number of elements in the set.
+    ///
+    /// Computes in **O(1)** time.
+    pub fn len(&self) -> usize {
+        self.map.len()
+    }
+
+    /// Returns true if the set contains no elements.
+    ///
+    /// Computes in **O(1)** time.
+    pub fn is_empty(&self) -> bool {
+        self.map.is_empty()
+    }
+
+    /// Return an iterator over the values of the set, in their order
+    pub fn iter(&self) -> Iter<'_, T> {
+        Iter {
+            iter: self.map.keys().iter,
+        }
+    }
+
+    /// Remove all elements in the set, while preserving its capacity.
+    ///
+    /// Computes in **O(n)** time.
+    pub fn clear(&mut self) {
+        self.map.clear();
+    }
+
+    /// Clears the `IndexSet` in the given index range, returning those values
+    /// as a drain iterator.
+    ///
+    /// The range may be any type that implements `RangeBounds<usize>`,
+    /// including all of the `std::ops::Range*` types, or even a tuple pair of
+    /// `Bound` start and end values. To drain the set entirely, use `RangeFull`
+    /// like `set.drain(..)`.
+    ///
+    /// This shifts down all entries following the drained range to fill the
+    /// gap, and keeps the allocated memory for reuse.
+    ///
+    /// ***Panics*** if the starting point is greater than the end point or if
+    /// the end point is greater than the length of the set.
+    pub fn drain<R>(&mut self, range: R) -> Drain<'_, T>
+    where
+        R: RangeBounds<usize>,
+    {
+        Drain {
+            iter: self.map.drain(range).iter,
+        }
+    }
+}
+
+impl<T, S> IndexSet<T, S>
+where
+    T: Hash + Eq,
+    S: BuildHasher,
+{
+    /// Reserve capacity for `additional` more values.
+    ///
+    /// Computes in **O(n)** time.
+    pub fn reserve(&mut self, additional: usize) {
+        self.map.reserve(additional);
+    }
+
+    /// Shrink the capacity of the set as much as possible.
+    ///
+    /// Computes in **O(n)** time.
+    pub fn shrink_to_fit(&mut self) {
+        self.map.shrink_to_fit();
+    }
+
+    /// Insert the value into the set.
+    ///
+    /// If an equivalent item already exists in the set, it returns
+    /// `false` leaving the original value in the set and without
+    /// altering its insertion order. Otherwise, it inserts the new
+    /// item and returns `true`.
+    ///
+    /// Computes in **O(1)** time (amortized average).
+    pub fn insert(&mut self, value: T) -> bool {
+        self.map.insert(value, ()).is_none()
+    }
+
+    /// Insert the value into the set, and get its index.
+    ///
+    /// If an equivalent item already exists in the set, it returns
+    /// the index of the existing item and `false`, leaving the
+    /// original value in the set and without altering its insertion
+    /// order. Otherwise, it inserts the new item and returns the index
+    /// of the inserted item and `true`.
+    ///
+    /// Computes in **O(1)** time (amortized average).
+    pub fn insert_full(&mut self, value: T) -> (usize, bool) {
+        use super::map::Entry::*;
+
+        match self.map.entry(value) {
+            Occupied(e) => (e.index(), false),
+            Vacant(e) => {
+                let index = e.index();
+                e.insert(());
+                (index, true)
+            }
+        }
+    }
+
+    /// Return an iterator over the values that are in `self` but not `other`.
+    ///
+    /// Values are produced in the same order that they appear in `self`.
+    pub fn difference<'a, S2>(&'a self, other: &'a IndexSet<T, S2>) -> Difference<'a, T, S2>
+    where
+        S2: BuildHasher,
+    {
+        Difference {
+            iter: self.iter(),
+            other,
+        }
+    }
+
+    /// Return an iterator over the values that are in `self` or `other`,
+    /// but not in both.
+    ///
+    /// Values from `self` are produced in their original order, followed by
+    /// values from `other` in their original order.
+    pub fn symmetric_difference<'a, S2>(
+        &'a self,
+        other: &'a IndexSet<T, S2>,
+    ) -> SymmetricDifference<'a, T, S, S2>
+    where
+        S2: BuildHasher,
+    {
+        SymmetricDifference {
+            iter: self.difference(other).chain(other.difference(self)),
+        }
+    }
+
+    /// Return an iterator over the values that are in both `self` and `other`.
+    ///
+    /// Values are produced in the same order that they appear in `self`.
+    pub fn intersection<'a, S2>(&'a self, other: &'a IndexSet<T, S2>) -> Intersection<'a, T, S2>
+    where
+        S2: BuildHasher,
+    {
+        Intersection {
+            iter: self.iter(),
+            other,
+        }
+    }
+
+    /// Return an iterator over all values that are in `self` or `other`.
+    ///
+    /// Values from `self` are produced in their original order, followed by
+    /// values that are unique to `other` in their original order.
+    pub fn union<'a, S2>(&'a self, other: &'a IndexSet<T, S2>) -> Union<'a, T, S>
+    where
+        S2: BuildHasher,
+    {
+        Union {
+            iter: self.iter().chain(other.difference(self)),
+        }
+    }
+
+    /// Return `true` if an equivalent to `value` exists in the set.
+    ///
+    /// Computes in **O(1)** time (average).
+    pub fn contains<Q: ?Sized>(&self, value: &Q) -> bool
+    where
+        Q: Hash + Equivalent<T>,
+    {
+        self.map.contains_key(value)
+    }
+
+    /// Return a reference to the value stored in the set, if it is present,
+    /// else `None`.
+    ///
+    /// Computes in **O(1)** time (average).
+    pub fn get<Q: ?Sized>(&self, value: &Q) -> Option<&T>
+    where
+        Q: Hash + Equivalent<T>,
+    {
+        self.map.get_key_value(value).map(|(x, &())| x)
+    }
+
+    /// Return item index and value
+    pub fn get_full<Q: ?Sized>(&self, value: &Q) -> Option<(usize, &T)>
+    where
+        Q: Hash + Equivalent<T>,
+    {
+        self.map.get_full(value).map(|(i, x, &())| (i, x))
+    }
+
+    /// Return item index, if it exists in the set
+    pub fn get_index_of<Q: ?Sized>(&self, value: &Q) -> Option<usize>
+    where
+        Q: Hash + Equivalent<T>,
+    {
+        self.map.get_index_of(value)
+    }
+
+    /// Adds a value to the set, replacing the existing value, if any, that is
+    /// equal to the given one. Returns the replaced value.
+    ///
+    /// Computes in **O(1)** time (average).
+    pub fn replace(&mut self, value: T) -> Option<T> {
+        use super::map::Entry::*;
+
+        match self.map.entry(value) {
+            Vacant(e) => {
+                e.insert(());
+                None
+            }
+            Occupied(e) => Some(e.replace_key()),
+        }
+    }
+
+    /// Remove the value from the set, and return `true` if it was present.
+    ///
+    /// **NOTE:** This is equivalent to `.swap_remove(value)`, if you want
+    /// to preserve the order of the values in the set, use `.shift_remove(value)`.
+    ///
+    /// Computes in **O(1)** time (average).
+    pub fn remove<Q: ?Sized>(&mut self, value: &Q) -> bool
+    where
+        Q: Hash + Equivalent<T>,
+    {
+        self.swap_remove(value)
+    }
+
+    /// Remove the value from the set, and return `true` if it was present.
+    ///
+    /// Like `Vec::swap_remove`, the value is removed by swapping it with the
+    /// last element of the set and popping it off. **This perturbs
+    /// the postion of what used to be the last element!**
+    ///
+    /// Return `false` if `value` was not in the set.
+    ///
+    /// Computes in **O(1)** time (average).
+    pub fn swap_remove<Q: ?Sized>(&mut self, value: &Q) -> bool
+    where
+        Q: Hash + Equivalent<T>,
+    {
+        self.map.swap_remove(value).is_some()
+    }
+
+    /// Remove the value from the set, and return `true` if it was present.
+    ///
+    /// Like `Vec::remove`, the value is removed by shifting all of the
+    /// elements that follow it, preserving their relative order.
+    /// **This perturbs the index of all of those elements!**
+    ///
+    /// Return `false` if `value` was not in the set.
+    ///
+    /// Computes in **O(n)** time (average).
+    pub fn shift_remove<Q: ?Sized>(&mut self, value: &Q) -> bool
+    where
+        Q: Hash + Equivalent<T>,
+    {
+        self.map.shift_remove(value).is_some()
+    }
+
+    /// Removes and returns the value in the set, if any, that is equal to the
+    /// given one.
+    ///
+    /// **NOTE:** This is equivalent to `.swap_take(value)`, if you need to
+    /// preserve the order of the values in the set, use `.shift_take(value)`
+    /// instead.
+    ///
+    /// Computes in **O(1)** time (average).
+    pub fn take<Q: ?Sized>(&mut self, value: &Q) -> Option<T>
+    where
+        Q: Hash + Equivalent<T>,
+    {
+        self.swap_take(value)
+    }
+
+    /// Removes and returns the value in the set, if any, that is equal to the
+    /// given one.
+    ///
+    /// Like `Vec::swap_remove`, the value is removed by swapping it with the
+    /// last element of the set and popping it off. **This perturbs
+    /// the postion of what used to be the last element!**
+    ///
+    /// Return `None` if `value` was not in the set.
+    ///
+    /// Computes in **O(1)** time (average).
+    pub fn swap_take<Q: ?Sized>(&mut self, value: &Q) -> Option<T>
+    where
+        Q: Hash + Equivalent<T>,
+    {
+        self.map.swap_remove_entry(value).map(|(x, ())| x)
+    }
+
+    /// Removes and returns the value in the set, if any, that is equal to the
+    /// given one.
+    ///
+    /// Like `Vec::remove`, the value is removed by shifting all of the
+    /// elements that follow it, preserving their relative order.
+    /// **This perturbs the index of all of those elements!**
+    ///
+    /// Return `None` if `value` was not in the set.
+    ///
+    /// Computes in **O(n)** time (average).
+    pub fn shift_take<Q: ?Sized>(&mut self, value: &Q) -> Option<T>
+    where
+        Q: Hash + Equivalent<T>,
+    {
+        self.map.shift_remove_entry(value).map(|(x, ())| x)
+    }
+
+    /// Remove the value from the set return it and the index it had.
+    ///
+    /// Like `Vec::swap_remove`, the value is removed by swapping it with the
+    /// last element of the set and popping it off. **This perturbs
+    /// the postion of what used to be the last element!**
+    ///
+    /// Return `None` if `value` was not in the set.
+    pub fn swap_remove_full<Q: ?Sized>(&mut self, value: &Q) -> Option<(usize, T)>
+    where
+        Q: Hash + Equivalent<T>,
+    {
+        self.map.swap_remove_full(value).map(|(i, x, ())| (i, x))
+    }
+
+    /// Remove the value from the set return it and the index it had.
+    ///
+    /// Like `Vec::remove`, the value is removed by shifting all of the
+    /// elements that follow it, preserving their relative order.
+    /// **This perturbs the index of all of those elements!**
+    ///
+    /// Return `None` if `value` was not in the set.
+    pub fn shift_remove_full<Q: ?Sized>(&mut self, value: &Q) -> Option<(usize, T)>
+    where
+        Q: Hash + Equivalent<T>,
+    {
+        self.map.shift_remove_full(value).map(|(i, x, ())| (i, x))
+    }
+
+    /// Remove the last value
+    ///
+    /// Computes in **O(1)** time (average).
+    pub fn pop(&mut self) -> Option<T> {
+        self.map.pop().map(|(x, ())| x)
+    }
+
+    /// Scan through each value in the set and keep those where the
+    /// closure `keep` returns `true`.
+    ///
+    /// The elements are visited in order, and remaining elements keep their
+    /// order.
+    ///
+    /// Computes in **O(n)** time (average).
+    pub fn retain<F>(&mut self, mut keep: F)
+    where
+        F: FnMut(&T) -> bool,
+    {
+        self.map.retain(move |x, &mut ()| keep(x))
+    }
+
+    /// Sort the set’s values by their default ordering.
+    ///
+    /// See `sort_by` for details.
+    pub fn sort(&mut self)
+    where
+        T: Ord,
+    {
+        self.map.sort_keys()
+    }
+
+    /// Sort the set’s values in place using the comparison function `compare`.
+    ///
+    /// Computes in **O(n log n)** time and **O(n)** space. The sort is stable.
+    pub fn sort_by<F>(&mut self, mut compare: F)
+    where
+        F: FnMut(&T, &T) -> Ordering,
+    {
+        self.map.sort_by(move |a, _, b, _| compare(a, b));
+    }
+
+    /// Sort the values of the set and return a by value iterator of
+    /// the values with the result.
+    ///
+    /// The sort is stable.
+    pub fn sorted_by<F>(self, mut cmp: F) -> IntoIter<T>
+    where
+        F: FnMut(&T, &T) -> Ordering,
+    {
+        IntoIter {
+            iter: self.map.sorted_by(move |a, &(), b, &()| cmp(a, b)).iter,
+        }
+    }
+
+    /// Reverses the order of the set’s values in place.
+    ///
+    /// Computes in **O(n)** time and **O(1)** space.
+    pub fn reverse(&mut self) {
+        self.map.reverse()
+    }
+}
+
+impl<T, S> IndexSet<T, S> {
+    /// Get a value by index
+    ///
+    /// Valid indices are *0 <= index < self.len()*
+    ///
+    /// Computes in **O(1)** time.
+    pub fn get_index(&self, index: usize) -> Option<&T> {
+        self.map.get_index(index).map(|(x, &())| x)
+    }
+
+    /// Remove the key-value pair by index
+    ///
+    /// Valid indices are *0 <= index < self.len()*
+    ///
+    /// Like `Vec::swap_remove`, the value is removed by swapping it with the
+    /// last element of the set and popping it off. **This perturbs
+    /// the postion of what used to be the last element!**
+    ///
+    /// Computes in **O(1)** time (average).
+    pub fn swap_remove_index(&mut self, index: usize) -> Option<T> {
+        self.map.swap_remove_index(index).map(|(x, ())| x)
+    }
+
+    /// Remove the key-value pair by index
+    ///
+    /// Valid indices are *0 <= index < self.len()*
+    ///
+    /// Like `Vec::remove`, the value is removed by shifting all of the
+    /// elements that follow it, preserving their relative order.
+    /// **This perturbs the index of all of those elements!**
+    ///
+    /// Computes in **O(n)** time (average).
+    pub fn shift_remove_index(&mut self, index: usize) -> Option<T> {
+        self.map.shift_remove_index(index).map(|(x, ())| x)
+    }
+}
+
+/// Access `IndexSet` values at indexed positions.
+///
+/// # Examples
+///
+/// ```
+/// use indexmap::IndexSet;
+///
+/// let mut set = IndexSet::new();
+/// for word in "Lorem ipsum dolor sit amet".split_whitespace() {
+///     set.insert(word.to_string());
+/// }
+/// assert_eq!(set[0], "Lorem");
+/// assert_eq!(set[1], "ipsum");
+/// set.reverse();
+/// assert_eq!(set[0], "amet");
+/// assert_eq!(set[1], "sit");
+/// set.sort();
+/// assert_eq!(set[0], "Lorem");
+/// assert_eq!(set[1], "amet");
+/// ```
+///
+/// ```should_panic
+/// use indexmap::IndexSet;
+///
+/// let mut set = IndexSet::new();
+/// set.insert("foo");
+/// println!("{:?}", set[10]); // panics!
+/// ```
+impl<T, S> Index<usize> for IndexSet<T, S> {
+    type Output = T;
+
+    /// Returns a reference to the value at the supplied `index`.
+    ///
+    /// ***Panics*** if `index` is out of bounds.
+    fn index(&self, index: usize) -> &T {
+        self.get_index(index)
+            .expect("IndexSet: index out of bounds")
+    }
+}
+
+/// An owning iterator over the items of a `IndexSet`.
+///
+/// This `struct` is created by the [`into_iter`] method on [`IndexSet`]
+/// (provided by the `IntoIterator` trait). See its documentation for more.
+///
+/// [`IndexSet`]: struct.IndexSet.html
+/// [`into_iter`]: struct.IndexSet.html#method.into_iter
+pub struct IntoIter<T> {
+    iter: vec::IntoIter<Bucket<T>>,
+}
+
+impl<T> Iterator for IntoIter<T> {
+    type Item = T;
+
+    iterator_methods!(Bucket::key);
+}
+
+impl<T> DoubleEndedIterator for IntoIter<T> {
+    fn next_back(&mut self) -> Option<Self::Item> {
+        self.iter.next_back().map(Bucket::key)
+    }
+}
+
+impl<T> ExactSizeIterator for IntoIter<T> {
+    fn len(&self) -> usize {
+        self.iter.len()
+    }
+}
+
+impl<T: fmt::Debug> fmt::Debug for IntoIter<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let iter = self.iter.as_slice().iter().map(Bucket::key_ref);
+        f.debug_list().entries(iter).finish()
+    }
+}
+
+/// An iterator over the items of a `IndexSet`.
+///
+/// This `struct` is created by the [`iter`] method on [`IndexSet`].
+/// See its documentation for more.
+///
+/// [`IndexSet`]: struct.IndexSet.html
+/// [`iter`]: struct.IndexSet.html#method.iter
+pub struct Iter<'a, T> {
+    iter: slice::Iter<'a, Bucket<T>>,
+}
+
+impl<'a, T> Iterator for Iter<'a, T> {
+    type Item = &'a T;
+
+    iterator_methods!(Bucket::key_ref);
+}
+
+impl<T> DoubleEndedIterator for Iter<'_, T> {
+    fn next_back(&mut self) -> Option<Self::Item> {
+        self.iter.next_back().map(Bucket::key_ref)
+    }
+}
+
+impl<T> ExactSizeIterator for Iter<'_, T> {
+    fn len(&self) -> usize {
+        self.iter.len()
+    }
+}
+
+impl<T> Clone for Iter<'_, T> {
+    fn clone(&self) -> Self {
+        Iter {
+            iter: self.iter.clone(),
+        }
+    }
+}
+
+impl<T: fmt::Debug> fmt::Debug for Iter<'_, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_list().entries(self.clone()).finish()
+    }
+}
+
+/// A draining iterator over the items of a `IndexSet`.
+///
+/// This `struct` is created by the [`drain`] method on [`IndexSet`].
+/// See its documentation for more.
+///
+/// [`IndexSet`]: struct.IndexSet.html
+/// [`drain`]: struct.IndexSet.html#method.drain
+pub struct Drain<'a, T> {
+    iter: vec::Drain<'a, Bucket<T>>,
+}
+
+impl<T> Iterator for Drain<'_, T> {
+    type Item = T;
+
+    iterator_methods!(Bucket::key);
+}
+
+impl<T> DoubleEndedIterator for Drain<'_, T> {
+    double_ended_iterator_methods!(Bucket::key);
+}
+
+impl<'a, T, S> IntoIterator for &'a IndexSet<T, S> {
+    type Item = &'a T;
+    type IntoIter = Iter<'a, T>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.iter()
+    }
+}
+
+impl<T, S> IntoIterator for IndexSet<T, S> {
+    type Item = T;
+    type IntoIter = IntoIter<T>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        IntoIter {
+            iter: self.map.into_iter().iter,
+        }
+    }
+}
+
+impl<T, S> FromIterator<T> for IndexSet<T, S>
+where
+    T: Hash + Eq,
+    S: BuildHasher + Default,
+{
+    fn from_iter<I: IntoIterator<Item = T>>(iterable: I) -> Self {
+        let iter = iterable.into_iter().map(|x| (x, ()));
+        IndexSet {
+            map: IndexMap::from_iter(iter),
+        }
+    }
+}
+
+impl<T, S> Extend<T> for IndexSet<T, S>
+where
+    T: Hash + Eq,
+    S: BuildHasher,
+{
+    fn extend<I: IntoIterator<Item = T>>(&mut self, iterable: I) {
+        let iter = iterable.into_iter().map(|x| (x, ()));
+        self.map.extend(iter);
+    }
+}
+
+impl<'a, T, S> Extend<&'a T> for IndexSet<T, S>
+where
+    T: Hash + Eq + Copy + 'a,
+    S: BuildHasher,
+{
+    fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iterable: I) {
+        let iter = iterable.into_iter().cloned(); // FIXME: use `copied` in Rust 1.36
+        self.extend(iter);
+    }
+}
+
+impl<T, S> Default for IndexSet<T, S>
+where
+    S: Default,
+{
+    /// Return an empty `IndexSet`
+    fn default() -> Self {
+        IndexSet {
+            map: IndexMap::default(),
+        }
+    }
+}
+
+impl<T, S1, S2> PartialEq<IndexSet<T, S2>> for IndexSet<T, S1>
+where
+    T: Hash + Eq,
+    S1: BuildHasher,
+    S2: BuildHasher,
+{
+    fn eq(&self, other: &IndexSet<T, S2>) -> bool {
+        self.len() == other.len() && self.is_subset(other)
+    }
+}
+
+impl<T, S> Eq for IndexSet<T, S>
+where
+    T: Eq + Hash,
+    S: BuildHasher,
+{
+}
+
+impl<T, S> IndexSet<T, S>
+where
+    T: Eq + Hash,
+    S: BuildHasher,
+{
+    /// Returns `true` if `self` has no elements in common with `other`.
+    pub fn is_disjoint<S2>(&self, other: &IndexSet<T, S2>) -> bool
+    where
+        S2: BuildHasher,
+    {
+        if self.len() <= other.len() {
+            self.iter().all(move |value| !other.contains(value))
+        } else {
+            other.iter().all(move |value| !self.contains(value))
+        }
+    }
+
+    /// Returns `true` if all elements of `self` are contained in `other`.
+    pub fn is_subset<S2>(&self, other: &IndexSet<T, S2>) -> bool
+    where
+        S2: BuildHasher,
+    {
+        self.len() <= other.len() && self.iter().all(move |value| other.contains(value))
+    }
+
+    /// Returns `true` if all elements of `other` are contained in `self`.
+    pub fn is_superset<S2>(&self, other: &IndexSet<T, S2>) -> bool
+    where
+        S2: BuildHasher,
+    {
+        other.is_subset(self)
+    }
+}
+
+/// A lazy iterator producing elements in the difference of `IndexSet`s.
+///
+/// This `struct` is created by the [`difference`] method on [`IndexSet`].
+/// See its documentation for more.
+///
+/// [`IndexSet`]: struct.IndexSet.html
+/// [`difference`]: struct.IndexSet.html#method.difference
+pub struct Difference<'a, T, S> {
+    iter: Iter<'a, T>,
+    other: &'a IndexSet<T, S>,
+}
+
+impl<'a, T, S> Iterator for Difference<'a, T, S>
+where
+    T: Eq + Hash,
+    S: BuildHasher,
+{
+    type Item = &'a T;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        while let Some(item) = self.iter.next() {
+            if !self.other.contains(item) {
+                return Some(item);
+            }
+        }
+        None
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (0, self.iter.size_hint().1)
+    }
+}
+
+impl<T, S> DoubleEndedIterator for Difference<'_, T, S>
+where
+    T: Eq + Hash,
+    S: BuildHasher,
+{
+    fn next_back(&mut self) -> Option<Self::Item> {
+        while let Some(item) = self.iter.next_back() {
+            if !self.other.contains(item) {
+                return Some(item);
+            }
+        }
+        None
+    }
+}
+
+impl<T, S> Clone for Difference<'_, T, S> {
+    fn clone(&self) -> Self {
+        Difference {
+            iter: self.iter.clone(),
+            ..*self
+        }
+    }
+}
+
+impl<T, S> fmt::Debug for Difference<'_, T, S>
+where
+    T: fmt::Debug + Eq + Hash,
+    S: BuildHasher,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_list().entries(self.clone()).finish()
+    }
+}
+
+/// A lazy iterator producing elements in the intersection of `IndexSet`s.
+///
+/// This `struct` is created by the [`intersection`] method on [`IndexSet`].
+/// See its documentation for more.
+///
+/// [`IndexSet`]: struct.IndexSet.html
+/// [`intersection`]: struct.IndexSet.html#method.intersection
+pub struct Intersection<'a, T, S> {
+    iter: Iter<'a, T>,
+    other: &'a IndexSet<T, S>,
+}
+
+impl<'a, T, S> Iterator for Intersection<'a, T, S>
+where
+    T: Eq + Hash,
+    S: BuildHasher,
+{
+    type Item = &'a T;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        while let Some(item) = self.iter.next() {
+            if self.other.contains(item) {
+                return Some(item);
+            }
+        }
+        None
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (0, self.iter.size_hint().1)
+    }
+}
+
+impl<T, S> DoubleEndedIterator for Intersection<'_, T, S>
+where
+    T: Eq + Hash,
+    S: BuildHasher,
+{
+    fn next_back(&mut self) -> Option<Self::Item> {
+        while let Some(item) = self.iter.next_back() {
+            if self.other.contains(item) {
+                return Some(item);
+            }
+        }
+        None
+    }
+}
+
+impl<T, S> Clone for Intersection<'_, T, S> {
+    fn clone(&self) -> Self {
+        Intersection {
+            iter: self.iter.clone(),
+            ..*self
+        }
+    }
+}
+
+impl<T, S> fmt::Debug for Intersection<'_, T, S>
+where
+    T: fmt::Debug + Eq + Hash,
+    S: BuildHasher,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_list().entries(self.clone()).finish()
+    }
+}
+
+/// A lazy iterator producing elements in the symmetric difference of `IndexSet`s.
+///
+/// This `struct` is created by the [`symmetric_difference`] method on
+/// [`IndexSet`]. See its documentation for more.
+///
+/// [`IndexSet`]: struct.IndexSet.html
+/// [`symmetric_difference`]: struct.IndexSet.html#method.symmetric_difference
+pub struct SymmetricDifference<'a, T, S1, S2> {
+    iter: Chain<Difference<'a, T, S2>, Difference<'a, T, S1>>,
+}
+
+impl<'a, T, S1, S2> Iterator for SymmetricDifference<'a, T, S1, S2>
+where
+    T: Eq + Hash,
+    S1: BuildHasher,
+    S2: BuildHasher,
+{
+    type Item = &'a T;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.iter.next()
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.iter.size_hint()
+    }
+
+    fn fold<B, F>(self, init: B, f: F) -> B
+    where
+        F: FnMut(B, Self::Item) -> B,
+    {
+        self.iter.fold(init, f)
+    }
+}
+
+impl<T, S1, S2> DoubleEndedIterator for SymmetricDifference<'_, T, S1, S2>
+where
+    T: Eq + Hash,
+    S1: BuildHasher,
+    S2: BuildHasher,
+{
+    fn next_back(&mut self) -> Option<Self::Item> {
+        self.iter.next_back()
+    }
+}
+
+impl<T, S1, S2> Clone for SymmetricDifference<'_, T, S1, S2> {
+    fn clone(&self) -> Self {
+        SymmetricDifference {
+            iter: self.iter.clone(),
+        }
+    }
+}
+
+impl<T, S1, S2> fmt::Debug for SymmetricDifference<'_, T, S1, S2>
+where
+    T: fmt::Debug + Eq + Hash,
+    S1: BuildHasher,
+    S2: BuildHasher,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_list().entries(self.clone()).finish()
+    }
+}
+
+/// A lazy iterator producing elements in the union of `IndexSet`s.
+///
+/// This `struct` is created by the [`union`] method on [`IndexSet`].
+/// See its documentation for more.
+///
+/// [`IndexSet`]: struct.IndexSet.html
+/// [`union`]: struct.IndexSet.html#method.union
+pub struct Union<'a, T, S> {
+    iter: Chain<Iter<'a, T>, Difference<'a, T, S>>,
+}
+
+impl<'a, T, S> Iterator for Union<'a, T, S>
+where
+    T: Eq + Hash,
+    S: BuildHasher,
+{
+    type Item = &'a T;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.iter.next()
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.iter.size_hint()
+    }
+
+    fn fold<B, F>(self, init: B, f: F) -> B
+    where
+        F: FnMut(B, Self::Item) -> B,
+    {
+        self.iter.fold(init, f)
+    }
+}
+
+impl<T, S> DoubleEndedIterator for Union<'_, T, S>
+where
+    T: Eq + Hash,
+    S: BuildHasher,
+{
+    fn next_back(&mut self) -> Option<Self::Item> {
+        self.iter.next_back()
+    }
+}
+
+impl<T, S> Clone for Union<'_, T, S> {
+    fn clone(&self) -> Self {
+        Union {
+            iter: self.iter.clone(),
+        }
+    }
+}
+
+impl<T, S> fmt::Debug for Union<'_, T, S>
+where
+    T: fmt::Debug + Eq + Hash,
+    S: BuildHasher,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_list().entries(self.clone()).finish()
+    }
+}
+
+impl<T, S1, S2> BitAnd<&IndexSet<T, S2>> for &IndexSet<T, S1>
+where
+    T: Eq + Hash + Clone,
+    S1: BuildHasher + Default,
+    S2: BuildHasher,
+{
+    type Output = IndexSet<T, S1>;
+
+    /// Returns the set intersection, cloned into a new set.
+    ///
+    /// Values are collected in the same order that they appear in `self`.
+    fn bitand(self, other: &IndexSet<T, S2>) -> Self::Output {
+        self.intersection(other).cloned().collect()
+    }
+}
+
+impl<T, S1, S2> BitOr<&IndexSet<T, S2>> for &IndexSet<T, S1>
+where
+    T: Eq + Hash + Clone,
+    S1: BuildHasher + Default,
+    S2: BuildHasher,
+{
+    type Output = IndexSet<T, S1>;
+
+    /// Returns the set union, cloned into a new set.
+    ///
+    /// Values from `self` are collected in their original order, followed by
+    /// values that are unique to `other` in their original order.
+    fn bitor(self, other: &IndexSet<T, S2>) -> Self::Output {
+        self.union(other).cloned().collect()
+    }
+}
+
+impl<T, S1, S2> BitXor<&IndexSet<T, S2>> for &IndexSet<T, S1>
+where
+    T: Eq + Hash + Clone,
+    S1: BuildHasher + Default,
+    S2: BuildHasher,
+{
+    type Output = IndexSet<T, S1>;
+
+    /// Returns the set symmetric-difference, cloned into a new set.
+    ///
+    /// Values from `self` are collected in their original order, followed by
+    /// values from `other` in their original order.
+    fn bitxor(self, other: &IndexSet<T, S2>) -> Self::Output {
+        self.symmetric_difference(other).cloned().collect()
+    }
+}
+
+impl<T, S1, S2> Sub<&IndexSet<T, S2>> for &IndexSet<T, S1>
+where
+    T: Eq + Hash + Clone,
+    S1: BuildHasher + Default,
+    S2: BuildHasher,
+{
+    type Output = IndexSet<T, S1>;
+
+    /// Returns the set difference, cloned into a new set.
+    ///
+    /// Values are collected in the same order that they appear in `self`.
+    fn sub(self, other: &IndexSet<T, S2>) -> Self::Output {
+        self.difference(other).cloned().collect()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::util::enumerate;
+    use std::string::String;
+
+    #[test]
+    fn it_works() {
+        let mut set = IndexSet::new();
+        assert_eq!(set.is_empty(), true);
+        set.insert(1);
+        set.insert(1);
+        assert_eq!(set.len(), 1);
+        assert!(set.get(&1).is_some());
+        assert_eq!(set.is_empty(), false);
+    }
+
+    #[test]
+    fn new() {
+        let set = IndexSet::<String>::new();
+        println!("{:?}", set);
+        assert_eq!(set.capacity(), 0);
+        assert_eq!(set.len(), 0);
+        assert_eq!(set.is_empty(), true);
+    }
+
+    #[test]
+    fn insert() {
+        let insert = [0, 4, 2, 12, 8, 7, 11, 5];
+        let not_present = [1, 3, 6, 9, 10];
+        let mut set = IndexSet::with_capacity(insert.len());
+
+        for (i, &elt) in enumerate(&insert) {
+            assert_eq!(set.len(), i);
+            set.insert(elt);
+            assert_eq!(set.len(), i + 1);
+            assert_eq!(set.get(&elt), Some(&elt));
+        }
+        println!("{:?}", set);
+
+        for &elt in &not_present {
+            assert!(set.get(&elt).is_none());
+        }
+    }
+
+    #[test]
+    fn insert_full() {
+        let insert = vec![9, 2, 7, 1, 4, 6, 13];
+        let present = vec![1, 6, 2];
+        let mut set = IndexSet::with_capacity(insert.len());
+
+        for (i, &elt) in enumerate(&insert) {
+            assert_eq!(set.len(), i);
+            let (index, success) = set.insert_full(elt);
+            assert!(success);
+            assert_eq!(Some(index), set.get_full(&elt).map(|x| x.0));
+            assert_eq!(set.len(), i + 1);
+        }
+
+        let len = set.len();
+        for &elt in &present {
+            let (index, success) = set.insert_full(elt);
+            assert!(!success);
+            assert_eq!(Some(index), set.get_full(&elt).map(|x| x.0));
+            assert_eq!(set.len(), len);
+        }
+    }
+
+    #[test]
+    fn insert_2() {
+        let mut set = IndexSet::with_capacity(16);
+
+        let mut values = vec![];
+        values.extend(0..16);
+        values.extend(128..267);
+
+        for &i in &values {
+            let old_set = set.clone();
+            set.insert(i);
+            for value in old_set.iter() {
+                if set.get(value).is_none() {
+                    println!("old_set: {:?}", old_set);
+                    println!("set: {:?}", set);
+                    panic!("did not find {} in set", value);
+                }
+            }
+        }
+
+        for &i in &values {
+            assert!(set.get(&i).is_some(), "did not find {}", i);
+        }
+    }
+
+    #[test]
+    fn insert_dup() {
+        let mut elements = vec![0, 2, 4, 6, 8];
+        let mut set: IndexSet<u8> = elements.drain(..).collect();
+        {
+            let (i, v) = set.get_full(&0).unwrap();
+            assert_eq!(set.len(), 5);
+            assert_eq!(i, 0);
+            assert_eq!(*v, 0);
+        }
+        {
+            let inserted = set.insert(0);
+            let (i, v) = set.get_full(&0).unwrap();
+            assert_eq!(set.len(), 5);
+            assert_eq!(inserted, false);
+            assert_eq!(i, 0);
+            assert_eq!(*v, 0);
+        }
+    }
+
+    #[test]
+    fn insert_order() {
+        let insert = [0, 4, 2, 12, 8, 7, 11, 5, 3, 17, 19, 22, 23];
+        let mut set = IndexSet::new();
+
+        for &elt in &insert {
+            set.insert(elt);
+        }
+
+        assert_eq!(set.iter().count(), set.len());
+        assert_eq!(set.iter().count(), insert.len());
+        for (a, b) in insert.iter().zip(set.iter()) {
+            assert_eq!(a, b);
+        }
+        for (i, v) in (0..insert.len()).zip(set.iter()) {
+            assert_eq!(set.get_index(i).unwrap(), v);
+        }
+    }
+
+    #[test]
+    fn grow() {
+        let insert = [0, 4, 2, 12, 8, 7, 11];
+        let not_present = [1, 3, 6, 9, 10];
+        let mut set = IndexSet::with_capacity(insert.len());
+
+        for (i, &elt) in enumerate(&insert) {
+            assert_eq!(set.len(), i);
+            set.insert(elt);
+            assert_eq!(set.len(), i + 1);
+            assert_eq!(set.get(&elt), Some(&elt));
+        }
+
+        println!("{:?}", set);
+        for &elt in &insert {
+            set.insert(elt * 10);
+        }
+        for &elt in &insert {
+            set.insert(elt * 100);
+        }
+        for (i, &elt) in insert.iter().cycle().enumerate().take(100) {
+            set.insert(elt * 100 + i as i32);
+        }
+        println!("{:?}", set);
+        for &elt in &not_present {
+            assert!(set.get(&elt).is_none());
+        }
+    }
+
+    #[test]
+    fn reserve() {
+        let mut set = IndexSet::<usize>::new();
+        assert_eq!(set.capacity(), 0);
+        set.reserve(100);
+        let capacity = set.capacity();
+        assert!(capacity >= 100);
+        for i in 0..capacity {
+            assert_eq!(set.len(), i);
+            set.insert(i);
+            assert_eq!(set.len(), i + 1);
+            assert_eq!(set.capacity(), capacity);
+            assert_eq!(set.get(&i), Some(&i));
+        }
+        set.insert(capacity);
+        assert_eq!(set.len(), capacity + 1);
+        assert!(set.capacity() > capacity);
+        assert_eq!(set.get(&capacity), Some(&capacity));
+    }
+
+    #[test]
+    fn shrink_to_fit() {
+        let mut set = IndexSet::<usize>::new();
+        assert_eq!(set.capacity(), 0);
+        for i in 0..100 {
+            assert_eq!(set.len(), i);
+            set.insert(i);
+            assert_eq!(set.len(), i + 1);
+            assert!(set.capacity() >= i + 1);
+            assert_eq!(set.get(&i), Some(&i));
+            set.shrink_to_fit();
+            assert_eq!(set.len(), i + 1);
+            assert_eq!(set.capacity(), i + 1);
+            assert_eq!(set.get(&i), Some(&i));
+        }
+    }
+
+    #[test]
+    fn remove() {
+        let insert = [0, 4, 2, 12, 8, 7, 11, 5, 3, 17, 19, 22, 23];
+        let mut set = IndexSet::new();
+
+        for &elt in &insert {
+            set.insert(elt);
+        }
+
+        assert_eq!(set.iter().count(), set.len());
+        assert_eq!(set.iter().count(), insert.len());
+        for (a, b) in insert.iter().zip(set.iter()) {
+            assert_eq!(a, b);
+        }
+
+        let remove_fail = [99, 77];
+        let remove = [4, 12, 8, 7];
+
+        for &value in &remove_fail {
+            assert!(set.swap_remove_full(&value).is_none());
+        }
+        println!("{:?}", set);
+        for &value in &remove {
+            //println!("{:?}", set);
+            let index = set.get_full(&value).unwrap().0;
+            assert_eq!(set.swap_remove_full(&value), Some((index, value)));
+        }
+        println!("{:?}", set);
+
+        for value in &insert {
+            assert_eq!(set.get(value).is_some(), !remove.contains(value));
+        }
+        assert_eq!(set.len(), insert.len() - remove.len());
+        assert_eq!(set.iter().count(), insert.len() - remove.len());
+    }
+
+    #[test]
+    fn swap_remove_index() {
+        let insert = [0, 4, 2, 12, 8, 7, 11, 5, 3, 17, 19, 22, 23];
+        let mut set = IndexSet::new();
+
+        for &elt in &insert {
+            set.insert(elt);
+        }
+
+        let mut vector = insert.to_vec();
+        let remove_sequence = &[3, 3, 10, 4, 5, 4, 3, 0, 1];
+
+        // check that the same swap remove sequence on vec and set
+        // have the same result.
+        for &rm in remove_sequence {
+            let out_vec = vector.swap_remove(rm);
+            let out_set = set.swap_remove_index(rm).unwrap();
+            assert_eq!(out_vec, out_set);
+        }
+        assert_eq!(vector.len(), set.len());
+        for (a, b) in vector.iter().zip(set.iter()) {
+            assert_eq!(a, b);
+        }
+    }
+
+    #[test]
+    fn partial_eq_and_eq() {
+        let mut set_a = IndexSet::new();
+        set_a.insert(1);
+        set_a.insert(2);
+        let mut set_b = set_a.clone();
+        assert_eq!(set_a, set_b);
+        set_b.swap_remove(&1);
+        assert_ne!(set_a, set_b);
+
+        let set_c: IndexSet<_> = set_b.into_iter().collect();
+        assert_ne!(set_a, set_c);
+        assert_ne!(set_c, set_a);
+    }
+
+    #[test]
+    fn extend() {
+        let mut set = IndexSet::new();
+        set.extend(vec![&1, &2, &3, &4]);
+        set.extend(vec![5, 6]);
+        assert_eq!(set.into_iter().collect::<Vec<_>>(), vec![1, 2, 3, 4, 5, 6]);
+    }
+
+    #[test]
+    fn comparisons() {
+        let set_a: IndexSet<_> = (0..3).collect();
+        let set_b: IndexSet<_> = (3..6).collect();
+        let set_c: IndexSet<_> = (0..6).collect();
+        let set_d: IndexSet<_> = (3..9).collect();
+
+        assert!(!set_a.is_disjoint(&set_a));
+        assert!(set_a.is_subset(&set_a));
+        assert!(set_a.is_superset(&set_a));
+
+        assert!(set_a.is_disjoint(&set_b));
+        assert!(set_b.is_disjoint(&set_a));
+        assert!(!set_a.is_subset(&set_b));
+        assert!(!set_b.is_subset(&set_a));
+        assert!(!set_a.is_superset(&set_b));
+        assert!(!set_b.is_superset(&set_a));
+
+        assert!(!set_a.is_disjoint(&set_c));
+        assert!(!set_c.is_disjoint(&set_a));
+        assert!(set_a.is_subset(&set_c));
+        assert!(!set_c.is_subset(&set_a));
+        assert!(!set_a.is_superset(&set_c));
+        assert!(set_c.is_superset(&set_a));
+
+        assert!(!set_c.is_disjoint(&set_d));
+        assert!(!set_d.is_disjoint(&set_c));
+        assert!(!set_c.is_subset(&set_d));
+        assert!(!set_d.is_subset(&set_c));
+        assert!(!set_c.is_superset(&set_d));
+        assert!(!set_d.is_superset(&set_c));
+    }
+
+    #[test]
+    fn iter_comparisons() {
+        use std::iter::empty;
+
+        fn check<'a, I1, I2>(iter1: I1, iter2: I2)
+        where
+            I1: Iterator<Item = &'a i32>,
+            I2: Iterator<Item = i32>,
+        {
+            assert!(iter1.cloned().eq(iter2));
+        }
+
+        let set_a: IndexSet<_> = (0..3).collect();
+        let set_b: IndexSet<_> = (3..6).collect();
+        let set_c: IndexSet<_> = (0..6).collect();
+        let set_d: IndexSet<_> = (3..9).rev().collect();
+
+        check(set_a.difference(&set_a), empty());
+        check(set_a.symmetric_difference(&set_a), empty());
+        check(set_a.intersection(&set_a), 0..3);
+        check(set_a.union(&set_a), 0..3);
+
+        check(set_a.difference(&set_b), 0..3);
+        check(set_b.difference(&set_a), 3..6);
+        check(set_a.symmetric_difference(&set_b), 0..6);
+        check(set_b.symmetric_difference(&set_a), (3..6).chain(0..3));
+        check(set_a.intersection(&set_b), empty());
+        check(set_b.intersection(&set_a), empty());
+        check(set_a.union(&set_b), 0..6);
+        check(set_b.union(&set_a), (3..6).chain(0..3));
+
+        check(set_a.difference(&set_c), empty());
+        check(set_c.difference(&set_a), 3..6);
+        check(set_a.symmetric_difference(&set_c), 3..6);
+        check(set_c.symmetric_difference(&set_a), 3..6);
+        check(set_a.intersection(&set_c), 0..3);
+        check(set_c.intersection(&set_a), 0..3);
+        check(set_a.union(&set_c), 0..6);
+        check(set_c.union(&set_a), 0..6);
+
+        check(set_c.difference(&set_d), 0..3);
+        check(set_d.difference(&set_c), (6..9).rev());
+        check(
+            set_c.symmetric_difference(&set_d),
+            (0..3).chain((6..9).rev()),
+        );
+        check(set_d.symmetric_difference(&set_c), (6..9).rev().chain(0..3));
+        check(set_c.intersection(&set_d), 3..6);
+        check(set_d.intersection(&set_c), (3..6).rev());
+        check(set_c.union(&set_d), (0..6).chain((6..9).rev()));
+        check(set_d.union(&set_c), (3..9).rev().chain(0..3));
+    }
+
+    #[test]
+    fn ops() {
+        let empty = IndexSet::<i32>::new();
+        let set_a: IndexSet<_> = (0..3).collect();
+        let set_b: IndexSet<_> = (3..6).collect();
+        let set_c: IndexSet<_> = (0..6).collect();
+        let set_d: IndexSet<_> = (3..9).rev().collect();
+
+        // FIXME: #[allow(clippy::eq_op)] in Rust 1.31
+        #[cfg_attr(feature = "cargo-clippy", allow(renamed_and_removed_lints, eq_op))]
+        {
+            assert_eq!(&set_a & &set_a, set_a);
+            assert_eq!(&set_a | &set_a, set_a);
+            assert_eq!(&set_a ^ &set_a, empty);
+            assert_eq!(&set_a - &set_a, empty);
+        }
+
+        assert_eq!(&set_a & &set_b, empty);
+        assert_eq!(&set_b & &set_a, empty);
+        assert_eq!(&set_a | &set_b, set_c);
+        assert_eq!(&set_b | &set_a, set_c);
+        assert_eq!(&set_a ^ &set_b, set_c);
+        assert_eq!(&set_b ^ &set_a, set_c);
+        assert_eq!(&set_a - &set_b, set_a);
+        assert_eq!(&set_b - &set_a, set_b);
+
+        assert_eq!(&set_a & &set_c, set_a);
+        assert_eq!(&set_c & &set_a, set_a);
+        assert_eq!(&set_a | &set_c, set_c);
+        assert_eq!(&set_c | &set_a, set_c);
+        assert_eq!(&set_a ^ &set_c, set_b);
+        assert_eq!(&set_c ^ &set_a, set_b);
+        assert_eq!(&set_a - &set_c, empty);
+        assert_eq!(&set_c - &set_a, set_b);
+
+        assert_eq!(&set_c & &set_d, set_b);
+        assert_eq!(&set_d & &set_c, set_b);
+        assert_eq!(&set_c | &set_d, &set_a | &set_d);
+        assert_eq!(&set_d | &set_c, &set_a | &set_d);
+        assert_eq!(&set_c ^ &set_d, &set_a | &(&set_d - &set_b));
+        assert_eq!(&set_d ^ &set_c, &set_a | &(&set_d - &set_b));
+        assert_eq!(&set_c - &set_d, set_a);
+        assert_eq!(&set_d - &set_c, &set_d - &set_b);
+    }
+}
diff --git a/third_party/rust/indexmap/src/util.rs b/third_party/rust/indexmap/src/util.rs
new file mode 100644
index 0000000000..5388f470cf
--- /dev/null
+++ b/third_party/rust/indexmap/src/util.rs
@@ -0,0 +1,39 @@
+use core::iter::Enumerate;
+use core::ops::{Bound, Range, RangeBounds};
+
+pub(crate) fn third<A, B, C>(t: (A, B, C)) -> C {
+    t.2
+}
+
+pub(crate) fn enumerate<I>(iterable: I) -> Enumerate<I::IntoIter>
+where
+    I: IntoIterator,
+{
+    iterable.into_iter().enumerate()
+}
+
+pub(crate) fn simplify_range<R>(range: R, len: usize) -> Range<usize>
+where
+    R: RangeBounds<usize>,
+{
+    let start = match range.start_bound() {
+        Bound::Unbounded => 0,
+        Bound::Included(&i) if i <= len => i,
+        Bound::Excluded(&i) if i < len => i + 1,
+        bound => panic!("range start {:?} should be <= length {}", bound, len),
+    };
+    let end = match range.end_bound() {
+        Bound::Unbounded => len,
+        Bound::Excluded(&i) if i <= len => i,
+        Bound::Included(&i) if i < len => i + 1,
+        bound => panic!("range end {:?} should be <= length {}", bound, len),
+    };
+    if start > end {
+        panic!(
+            "range start {:?} should be <= range end {:?}",
+            range.start_bound(),
+            range.end_bound()
+        );
+    }
+    start..end
+}