diff --git a/zed/src/sum_tree/mod.rs b/zed/src/sum_tree/mod.rs
index 413f0e7ddc..03a9430ef5 100644
--- a/zed/src/sum_tree/mod.rs
+++ b/zed/src/sum_tree/mod.rs
@@ -337,7 +337,7 @@ impl<T: KeyedItem> SumTree<T> {
             return Vec::new();
         }
 
-        let mut replaced = Vec::new();
+        let mut removed = Vec::new();
         edits.sort_unstable_by_key(|item| item.key());
 
         *self = {
@@ -362,7 +362,7 @@ impl<T: KeyedItem> SumTree<T> {
 
                 if let Some(old_item) = old_item {
                     if old_item.key() == new_key {
-                        replaced.push(old_item.clone());
+                        removed.push(old_item.clone());
                         cursor.next();
                     }
                 }
@@ -380,7 +380,7 @@ impl<T: KeyedItem> SumTree<T> {
             new_tree
         };
 
-        replaced
+        removed
     }
 
     pub fn get(&self, key: &T::Key) -> Option<&T> {
@@ -497,6 +497,7 @@ where
 #[cfg(test)]
 mod tests {
     use super::*;
+    use std::cmp;
     use std::ops::Add;
 
     #[test]
@@ -780,11 +781,33 @@ mod tests {
         assert_eq!(cursor.slice(&Count(6), SeekBias::Right).items(), vec![6]);
     }
 
+    #[test]
+    fn test_edit() {
+        let mut tree = SumTree::<u8>::new();
+
+        let removed = tree.edit(vec![Edit::Insert(1), Edit::Insert(2), Edit::Insert(0)]);
+        assert_eq!(tree.items(), vec![0, 1, 2]);
+        assert_eq!(removed, Vec::<u8>::new());
+        assert_eq!(tree.get(&0), Some(&0));
+        assert_eq!(tree.get(&1), Some(&1));
+        assert_eq!(tree.get(&2), Some(&2));
+        assert_eq!(tree.get(&4), None);
+
+        let removed = tree.edit(vec![Edit::Insert(2), Edit::Insert(4), Edit::Remove(0)]);
+        assert_eq!(tree.items(), vec![1, 2, 4]);
+        assert_eq!(removed, vec![0, 2]);
+        assert_eq!(tree.get(&0), None);
+        assert_eq!(tree.get(&1), Some(&1));
+        assert_eq!(tree.get(&2), Some(&2));
+        assert_eq!(tree.get(&4), Some(&4));
+    }
+
     #[derive(Clone, Default, Debug)]
     pub struct IntegersSummary {
         count: Count,
         sum: Sum,
         contains_even: bool,
+        max: u8,
     }
 
     #[derive(Ord, PartialOrd, Default, Eq, PartialEq, Clone, Debug)]
@@ -801,15 +824,31 @@ mod tests {
                 count: Count(1),
                 sum: Sum(*self as usize),
                 contains_even: (*self & 1) == 0,
+                max: *self,
             }
         }
     }
 
+    impl KeyedItem for u8 {
+        type Key = u8;
+
+        fn key(&self) -> Self::Key {
+            *self
+        }
+    }
+
+    impl<'a> Dimension<'a, IntegersSummary> for u8 {
+        fn add_summary(&mut self, summary: &IntegersSummary) {
+            *self = summary.max;
+        }
+    }
+
     impl<'a> AddAssign<&'a Self> for IntegersSummary {
         fn add_assign(&mut self, other: &Self) {
             self.count.0 += &other.count.0;
             self.sum.0 += &other.sum.0;
             self.contains_even |= other.contains_even;
+            self.max = cmp::max(self.max, other.max);
         }
     }
 
@@ -819,15 +858,6 @@ mod tests {
         }
     }
 
-    // impl<'a> Add<&'a Self> for Count {
-    //     type Output = Self;
-    //
-    //     fn add(mut self, other: &Self) -> Self {
-    //         self.0 += other.0;
-    //         self
-    //     }
-    // }
-
     impl<'a> Dimension<'a, IntegersSummary> for Sum {
         fn add_summary(&mut self, summary: &IntegersSummary) {
             self.0 += summary.sum.0;