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;
     }