layout/scrolling: Fix add_column() skipping activate_column() sometimes

When the column was added immediately to the left of the current column
and activated, the new idx would be equal to active_column_idx, which
would skip activate_column() with its variable resets.

src/layout/scrolling.rs

@@ -986,6 +986,10 @@ impl<W: LayoutElement> ScrollingSpace<W> {
         self.data.insert(idx, ColumnData::new(&column));
         self.columns.insert(idx, column);
 
+        if !was_empty && idx <= self.active_column_idx {
+            self.active_column_idx += 1;
+        }
+
         if activate {
             // If this is the first window on an empty workspace, remove the effect of whatever
             // view_offset was left over and skip the animation.
@@ -1002,8 +1006,6 @@ impl<W: LayoutElement> ScrollingSpace<W> {
                 anim_config.unwrap_or(self.options.animations.horizontal_view_movement.0);
             self.activate_column_with_anim_config(idx, anim_config);
             self.activate_prev_column_on_removal = prev_offset;
-        } else if !was_empty && idx <= self.active_column_idx {
-            self.active_column_idx += 1;
         }
 
         // Animate movement of other columns.

src/layout/tests.rs

@@ -3674,6 +3674,34 @@ fn tabs_with_different_border() {
     check_ops_with_options(options, ops);
 }
 
+#[test]
+fn expel_pending_left_from_fullscreen_tabbed_column() {
+    let ops = [
+        Op::AddOutput(1),
+        Op::AddWindow {
+            params: TestWindowParams::new(1),
+        },
+        Op::FullscreenWindow(1),
+        Op::Communicate(1),
+        // 1 is now fullscreen, view_offset_to_restore is set.
+        Op::ToggleColumnTabbedDisplay,
+        Op::AddWindow {
+            params: TestWindowParams::new(2),
+        },
+        Op::ConsumeOrExpelWindowLeft { id: Some(2) },
+        // 2 is consumed into a fullscreen column, fullscreen is requested but not applied.
+        //
+        // Now, get it back out while keeping it focused.
+        //
+        // Importantly, we expel it *left*, which results in adding a new column with the exact
+        // same active_column_idx.
+        Op::FocusWindow(2),
+        Op::ConsumeOrExpelWindowLeft { id: None },
+    ];
+
+    check_ops(ops);
+}
+
 fn parent_id_causes_loop(layout: &Layout<TestWindow>, id: usize, mut parent_id: usize) -> bool {
     if parent_id == id {
         return true;