Fix multiple cursors inserting repeated text in multibuffers

crates/editor/src/editor.rs

@@ -9801,7 +9801,17 @@ mod tests {
     #[gpui::test]
     fn test_editing_overlapping_excerpts(cx: &mut gpui::MutableAppContext) {
         cx.set_global(Settings::test(cx));
-        let buffer = cx.add_model(|cx| Buffer::new(0, sample_text(3, 4, 'a'), cx));
+        let buffer = cx.add_model(|cx| {
+            Buffer::new(
+                0,
+                indoc! {"
+                    aaaa
+                    bbbb
+                    cccc"},
+                cx,
+            )
+        });
+
         let multibuffer = cx.add_model(|cx| {
             let mut multibuffer = MultiBuffer::new(0);
             multibuffer.push_excerpts(

crates/editor/src/multi_buffer.rs

@@ -378,13 +378,11 @@ impl MultiBuffer {
                     let mut insertions = Vec::new();
                     let mut deletions = Vec::new();
                     let empty_str: Arc<str> = "".into();
-                    while let Some((mut range, mut new_text, mut is_insertion)) = edits.next() {
+                    while let Some((mut range, new_text, mut is_insertion)) = edits.next() {
-                        while let Some((next_range, next_new_text, next_is_insertion)) =
+                        while let Some((next_range, _, next_is_insertion)) = edits.peek() {
-                            edits.peek()
-                        {
                             if range.end >= next_range.start {
                                 range.end = cmp::max(next_range.end, range.end);
-                                new_text = format!("{new_text}{next_new_text}").into();
+
                                 is_insertion |= *next_is_insertion;
                                 edits.next();
                             } else {
@@ -395,7 +393,7 @@ impl MultiBuffer {
                         if is_insertion {
                             insertions.push((
                                 buffer.anchor_before(range.start)..buffer.anchor_before(range.end),
-                                new_text,
+                                new_text.clone(),
                             ));
                         } else if !range.is_empty() {
                             deletions.push((