Correct category attribute for inclusion in Topmenu -- is_active vs. include_in_menu?

Question

Two attributes on the Category model seem possibly relevant to determining whether a category should be shown in the Topmenu: Is Active (is_active) and Include in Navigation Menu (include_in_menu).

Despite the seemingly obvious intended purpose for Include in Navigation Menu, a review of the code shows that Magento doesn't even check it when adding categories to the Topmenu--it only checks the is_active attribute.

Am I missing the point of the Include in Navigation Menu attribute, or is this potentially a bug?

For completeness, here's an overview of how I understand Magento's process of rendering the Topmenu:

1. The top.menu block's getHtml() method is called.
2. The page_block_html_topmenu_gethtml_before event is fired to get items added to the block's $_menu attribute.
3. Mage_Catalog_Model_Observer::addCatalogToTopmenuItems observes the event, retrieves the store's top-level categories, and calls its sibling method _addCategoriesToMenu() to add them to the menu.
4. _addCategoriesToMenu() recursively adds the categories and their subcategories to the menu, using if (!$category->getIsActive()) { continue; } to pass on categories that are not active, but does not check include_in_menu at all.
5. Back in the top.Menu block's getHtml method, the menu is rendered, either using a renderer class (if a catalog.topnav.renderer block is configured), or otherwise the default rendering method.

Aside from the question of whether categories must also be Active in order to appear, shouldn't _addCategoriesToMenu use if (!$category->getIncludeInMenu()) { continue; } instead?

Answer 1

Mage_Catalog_Model_Resource_Category_Tree::addCollectionData already sends only active and included in menu categories.

So in Mage_Catalog_Model_Observer::_addCategoriesToMenu the $categories array is only formed by items that are active and included in the menu.

You can try in Mage_Catalog_Model_Resource_Category_Tree to remove the line 159 $collection->addAttributeToFilter('include_in_menu', 1); to disregard the filter if this is what you want.

At least, this is how I understand it.