Fix lag when large diff hunk intersects the viewport (#26088)

Max Brunsfeld created 10 months ago

We were iterating over the row range of a hunk, and inserting into a
hash map for every row.

Release Notes:

- Fixed a performance problem when a large diff hunk was displayed in an
editor.

Change summary

crates/editor/src/element.rs | 55 ++++++++++++++++---------------------
1 file changed, 24 insertions(+), 31 deletions(-)

Detailed changes

crates/editor/src/element.rs

@@ -2018,7 +2018,7 @@ impl EditorElement {
         scroll_pixel_position: gpui::Point<Pixels>,
         gutter_dimensions: &GutterDimensions,
         gutter_hitbox: &Hitbox,
-        rows_with_hunk_bounds: &HashMap<DisplayRow, Bounds<Pixels>>,
+        display_hunks: &[(DisplayDiffHunk, Option<Hitbox>)],
         snapshot: &EditorSnapshot,
         window: &mut Window,
         cx: &mut App,
@@ -2094,7 +2094,7 @@ impl EditorElement {
                         gutter_dimensions,
                         scroll_pixel_position,
                         gutter_hitbox,
-                        rows_with_hunk_bounds,
+                        display_hunks,
                         window,
                         cx,
                     );
@@ -2112,7 +2112,7 @@ impl EditorElement {
         scroll_pixel_position: gpui::Point<Pixels>,
         gutter_dimensions: &GutterDimensions,
         gutter_hitbox: &Hitbox,
-        rows_with_hunk_bounds: &HashMap<DisplayRow, Bounds<Pixels>>,
+        display_hunks: &[(DisplayDiffHunk, Option<Hitbox>)],
         window: &mut Window,
         cx: &mut App,
     ) -> Option<AnyElement> {
@@ -2137,7 +2137,7 @@ impl EditorElement {
             gutter_dimensions,
             scroll_pixel_position,
             gutter_hitbox,
-            rows_with_hunk_bounds,
+            display_hunks,
             window,
             cx,
         );
@@ -5689,7 +5689,7 @@ fn prepaint_gutter_button(
     gutter_dimensions: &GutterDimensions,
     scroll_pixel_position: gpui::Point<Pixels>,
     gutter_hitbox: &Hitbox,
-    rows_with_hunk_bounds: &HashMap<DisplayRow, Bounds<Pixels>>,
+    display_hunks: &[(DisplayDiffHunk, Option<Hitbox>)],
     window: &mut Window,
     cx: &mut App,
 ) -> AnyElement {
@@ -5701,9 +5701,23 @@ fn prepaint_gutter_button(
     let indicator_size = button.layout_as_root(available_space, window, cx);
 
     let blame_width = gutter_dimensions.git_blame_entries_width;
-    let gutter_width = rows_with_hunk_bounds
-        .get(&row)
-        .map(|bounds| bounds.size.width);
+    let gutter_width = display_hunks
+        .binary_search_by(|(hunk, _)| match hunk {
+            DisplayDiffHunk::Folded { display_row } => display_row.cmp(&row),
+            DisplayDiffHunk::Unfolded {
+                display_row_range, ..
+            } => {
+                if display_row_range.end <= row {
+                    Ordering::Less
+                } else if display_row_range.start > row {
+                    Ordering::Greater
+                } else {
+                    Ordering::Equal
+                }
+            }
+        })
+        .ok()
+        .and_then(|ix| Some(display_hunks[ix].1.as_ref()?.size.width));
     let left_offset = blame_width.max(gutter_width).unwrap_or_default();
 
     let mut x = left_offset;
@@ -7219,27 +7233,6 @@ impl Element for EditorElement {
 
                     let gutter_settings = EditorSettings::get_global(cx).gutter;
 
-                    let rows_with_hunk_bounds = display_hunks
-                        .iter()
-                        .filter_map(|(hunk, hitbox)| Some((hunk, hitbox.as_ref()?.bounds)))
-                        .fold(
-                            HashMap::default(),
-                            |mut rows_with_hunk_bounds, (hunk, bounds)| {
-                                match hunk {
-                                    DisplayDiffHunk::Folded { display_row } => {
-                                        rows_with_hunk_bounds.insert(*display_row, bounds);
-                                    }
-                                    DisplayDiffHunk::Unfolded {
-                                        display_row_range, ..
-                                    } => {
-                                        for display_row in display_row_range.iter_rows() {
-                                            rows_with_hunk_bounds.insert(display_row, bounds);
-                                        }
-                                    }
-                                }
-                                rows_with_hunk_bounds
-                            },
-                        );
                     let mut code_actions_indicator = None;
                     if let Some(newest_selection_head) = newest_selection_head {
                         let newest_selection_point =
@@ -7289,7 +7282,7 @@ impl Element for EditorElement {
                                                     scroll_pixel_position,
                                                     &gutter_dimensions,
                                                     &gutter_hitbox,
-                                                    &rows_with_hunk_bounds,
+                                                    &display_hunks,
                                                     window,
                                                     cx,
                                                 );
@@ -7317,7 +7310,7 @@ impl Element for EditorElement {
                             scroll_pixel_position,
                             &gutter_dimensions,
                             &gutter_hitbox,
-                            &rows_with_hunk_bounds,
+                            &display_hunks,
                             &snapshot,
                             window,
                             cx,