fix: synchronize horizontal scrolling between diff panes

src/diff.rs

@@ -615,6 +615,11 @@ impl DiffState {
             Focus::After => self.max_after,
             Focus::Files => return 0,
         };
+        let columns = if self.pane_layout() == PaneLayout::Split {
+            self.max_before.max(self.max_after)
+        } else {
+            columns
+        };
         left.min(columns.saturating_add(1).saturating_sub(width.max(1)))
     }
 
@@ -630,10 +635,15 @@ impl DiffState {
             left.saturating_sub(3)
         };
         let left = self.bound_horizontal(focus, left, width);
-        match focus {
-            Focus::Before => self.left_before = left,
-            Focus::After => self.left_after = left,
-            Focus::Files => unreachable!(),
+        if self.pane_layout() == PaneLayout::Split {
+            self.left_before = left;
+            self.left_after = left;
+        } else {
+            match focus {
+                Focus::Before => self.left_before = left,
+                Focus::After => self.left_after = left,
+                Focus::Files => unreachable!(),
+            }
         }
         self.follow_caret = false;
     }

src/tui.rs

@@ -4317,16 +4317,16 @@ mod tests {
             .unwrap();
         assert!(screen_text(&terminal).contains("ore.before."));
         assert_eq!(session.editor().diff().unwrap().left_before, 3);
-        assert_eq!(session.editor().diff().unwrap().left_after, 0);
+        assert_eq!(session.editor().diff().unwrap().left_after, 3);
         let mut shift = document_wheel(MouseEventKind::ScrollDown, after.x + 1, after.y + 1);
         shift.modifiers = KeyModifiers::SHIFT;
         assert!(viewports.scroll(&mut session, shift));
         terminal
             .draw(|frame| viewports.draw_session(frame, &mut session))
             .unwrap();
-        assert!(screen_text(&terminal).contains("er.after."));
-        assert_eq!(session.editor().diff().unwrap().left_before, 3);
-        assert_eq!(session.editor().diff().unwrap().left_after, 3);
+        assert!(screen_text(&terminal).contains("after.after."));
+        assert_eq!(session.editor().diff().unwrap().left_before, 6);
+        assert_eq!(session.editor().diff().unwrap().left_after, 6);
         assert_eq!(session.editor().diff().unwrap().top, 0);
         assert_eq!(session.editor().diff().unwrap().focus, initial_focus);
         assert_eq!(session.editor().cursor(), initial_cursor);