1 files changed, 75 insertions, 0 deletions
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..35a90c4723
--- /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 modification
+/// does not change the key’s hash and equality**.
+///
+/// If keys are modified erroneously, 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 {}
+    }
+}