From 767c79beaee716fec8b79576ed0445d341ff6a96 Mon Sep 17 00:00:00 2001
From: Boog900 <54e72d8a-345f-4599-bd90-c6b9bc7d0ec5@aleeas.com>
Date: Tue, 18 Nov 2025 04:13:38 +0000
Subject: [PATCH] fix `last` on iterators with dup values

---
 heed/src/databases/database.rs |  1 +
 heed/src/iterator/iter.rs      | 48 +++-------------------------------
 heed/src/iterator/mod.rs       |  6 ++---
 3 files changed, 8 insertions(+), 47 deletions(-)

diff --git a/heed/src/databases/database.rs b/heed/src/databases/database.rs
index 46ccc902..0a79cac8 100644
--- a/heed/src/databases/database.rs
+++ b/heed/src/databases/database.rs
@@ -434,6 +434,7 @@ impl<KC, DC, C, CDUP> Database<KC, DC, C, CDUP> {
     /// drop(iter);
     ///
     /// let mut iter = db.get_duplicates(&wtxn, &68)?.expect("the key exists");
+    /// assert_eq!(iter.next().transpose()?, Some((68, 120)));
     /// assert_eq!(iter.last().transpose()?, Some((68, 123)));
     ///
     /// wtxn.commit()?;
diff --git a/heed/src/iterator/iter.rs b/heed/src/iterator/iter.rs
index 2f85fca5..17e3a97d 100644
--- a/heed/src/iterator/iter.rs
+++ b/heed/src/iterator/iter.rs
@@ -179,17 +179,7 @@ where
     }
 
     fn last(mut self) -> Option<Self::Item> {
-        let result = if self.move_on_first {
-            self.cursor.move_on_last(IM::MOVE_OPERATION)
-        } else {
-            match (self.cursor.current(), self.cursor.move_on_last(IM::MOVE_OPERATION)) {
-                (Ok(Some((ckey, _))), Ok(Some((key, data)))) if ckey != key => {
-                    Ok(Some((key, data)))
-                }
-                (Ok(_), Ok(_)) => Ok(None),
-                (Err(e), _) | (_, Err(e)) => Err(e),
-            }
-        };
+        let result = self.cursor.move_on_last(IM::MOVE_OPERATION);
 
         match result {
             Ok(Some((key, data))) => match (KC::bytes_decode(key), DC::bytes_decode(data)) {
@@ -408,17 +398,7 @@ where
     }
 
     fn last(mut self) -> Option<Self::Item> {
-        let result = if self.move_on_first {
-            self.cursor.move_on_last(IM::MOVE_OPERATION)
-        } else {
-            match (self.cursor.current(), self.cursor.move_on_last(IM::MOVE_OPERATION)) {
-                (Ok(Some((ckey, _))), Ok(Some((key, data)))) if ckey != key => {
-                    Ok(Some((key, data)))
-                }
-                (Ok(_), Ok(_)) => Ok(None),
-                (Err(e), _) | (_, Err(e)) => Err(e),
-            }
-        };
+        let result = self.cursor.move_on_last(IM::MOVE_OPERATION);
 
         match result {
             Ok(Some((key, data))) => match (KC::bytes_decode(key), DC::bytes_decode(data)) {
@@ -525,17 +505,7 @@ where
     }
 
     fn last(mut self) -> Option<Self::Item> {
-        let result = if self.move_on_last {
-            self.cursor.move_on_first(IM::MOVE_OPERATION)
-        } else {
-            match (self.cursor.current(), self.cursor.move_on_first(IM::MOVE_OPERATION)) {
-                (Ok(Some((ckey, _))), Ok(Some((key, data)))) if ckey != key => {
-                    Ok(Some((key, data)))
-                }
-                (Ok(_), Ok(_)) => Ok(None),
-                (Err(e), _) | (_, Err(e)) => Err(e),
-            }
-        };
+        let result = self.cursor.move_on_first(IM::MOVE_OPERATION);
 
         match result {
             Ok(Some((key, data))) => match (KC::bytes_decode(key), DC::bytes_decode(data)) {
@@ -756,17 +726,7 @@ where
     }
 
     fn last(mut self) -> Option<Self::Item> {
-        let result = if self.move_on_last {
-            self.cursor.move_on_first(IM::MOVE_OPERATION)
-        } else {
-            match (self.cursor.current(), self.cursor.move_on_first(IM::MOVE_OPERATION)) {
-                (Ok(Some((ckey, _))), Ok(Some((key, data)))) if ckey != key => {
-                    Ok(Some((key, data)))
-                }
-                (Ok(_), Ok(_)) => Ok(None),
-                (Err(e), _) | (_, Err(e)) => Err(e),
-            }
-        };
+        let result = self.cursor.move_on_first(IM::MOVE_OPERATION);
 
         match result {
             Ok(Some((key, data))) => match (KC::bytes_decode(key), DC::bytes_decode(data)) {
diff --git a/heed/src/iterator/mod.rs b/heed/src/iterator/mod.rs
index 9622fbe4..db118a98 100644
--- a/heed/src/iterator/mod.rs
+++ b/heed/src/iterator/mod.rs
@@ -227,7 +227,7 @@ mod tests {
         assert_eq!(iter.next().transpose().unwrap(), Some((2, ())));
         assert_eq!(iter.next().transpose().unwrap(), Some((3, ())));
         assert_eq!(iter.next().transpose().unwrap(), Some((4, ())));
-        assert_eq!(iter.last().transpose().unwrap(), None);
+        assert_eq!(iter.last().transpose().unwrap(), Some((4, ())));
 
         let mut iter = db.iter(&wtxn).unwrap();
         assert_eq!(iter.next().transpose().unwrap(), Some((1, ())));
@@ -235,7 +235,7 @@ mod tests {
         assert_eq!(iter.next().transpose().unwrap(), Some((3, ())));
         assert_eq!(iter.next().transpose().unwrap(), Some((4, ())));
         assert_eq!(iter.next().transpose().unwrap(), None);
-        assert_eq!(iter.last().transpose().unwrap(), None);
+        assert_eq!(iter.last().transpose().unwrap(), Some((4, ())));
 
         wtxn.abort();
 
@@ -249,7 +249,7 @@ mod tests {
 
         let mut iter = db.iter(&wtxn).unwrap();
         assert_eq!(iter.next().transpose().unwrap(), Some((1, ())));
-        assert_eq!(iter.last().transpose().unwrap(), None);
+        assert_eq!(iter.last().transpose().unwrap(), Some((1, ())));
 
         wtxn.abort();
     }