From f67ea052283680855d6830e43597a70e48468aa8 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jo=C3=A3o=20Severo?= <severo@teialabs.com>
Date: Mon, 11 Dec 2023 16:03:44 -0300
Subject: [PATCH] Add function to support prehashed keys

---
 src/map.rs | 47 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 47 insertions(+)

diff --git a/src/map.rs b/src/map.rs
index 9cd768f20..89b2ba6da 100644
--- a/src/map.rs
+++ b/src/map.rs
@@ -1824,6 +1824,53 @@ where
         (k_ref, v_ref)
     }
 
+    /// Inserts a key-value pair into the map using pre-generated key hash value.
+    ///
+    /// This method is intended to be used by monads that overwrite the default
+    /// hash method of the inner type.
+    ///
+    /// No value is returned from this function, this functions intent is to be
+    /// a fast insertion path for container types.
+    ///
+    /// [`None`]: https://doc.rust-lang.org/std/option/enum.Option.html#variant.None
+    /// [`std::collections`]: https://doc.rust-lang.org/std/collections/index.html
+    /// [module-level documentation]: https://doc.rust-lang.org/std/collections/index.html#insert-and-complex-keys
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    /// use std::hash::{BuildHasher, Hash, Hasher};
+    ///
+    /// let mut map = HashMap::new();
+    /// let key: i32 = 37;
+    ///
+    /// let hasher = map.hasher();
+    /// let mut state = hasher.build_hasher();
+    /// key.hash(&mut state);
+    /// let hash = state.finish();
+    ///
+    /// map.insert_with_hash(hash, key, 'a');
+    /// assert_eq!(map[&37], 'a');
+    ///
+    /// map.insert_with_hash(hash, key, 'b');
+    /// assert_eq!(map[&37], 'b');
+    /// ```
+    pub fn insert_with_hash(&mut self, hash: u64, k: K, mut v: V) {
+        let hasher = make_hasher::<_, V, S>(&self.hash_builder);
+        match self
+            .table
+            .find_or_find_insert_slot(hash, equivalent_key(&k), hasher)
+        {
+            Ok(bucket) => unsafe {
+                mem::swap(&mut bucket.as_mut().1, &mut v);
+            },
+            Err(slot) => unsafe {
+                self.table.insert_in_slot(hash, slot, (k, v));
+            },
+        };
+    }
+
     /// Tries to insert a key-value pair into the map, and returns
     /// a mutable reference to the value in the entry.
     ///