Allow new pages to be assigned to a menu

Could you elaborate?

(In [14738]) Rename wp_save_nav_menu_item to wp_save_nav_menu_items. Though it could handle one item, it expects a mess of post data containing an array of menu items. see #13447.

Add an "Automatically add new pages to this menu" checkbox to each menu tab. When new pages are created, they are added to the end of any menu that has this checked. Also considered was having a dropdown or list of menus in the edit page form, but since adding new pages to a menu is a one time action rather than a state the UX for that would be cumbersome.

Checkbox is done on my local install. Just need to get the right callback in place on the publish_page hook.

(In [14878]) Allow pages to be added automattically to menus. see #13447.

I'm finding that this reveals a bug (I think) in automatic positioning handled in wp_update_nav_menu_item, but we can iterate. (It adds them to the bottom, but above ones added previously through auto-add.)

We're also not removing old menus from the auto_add list. We can do that either on save or on the publish hook by doing a get_objects_in_term and intersecting them.

(In [14934]) Don't store nonexistent (deleted) menus in the auto-add option. see #13447.

Add post_status to wp_update_nav_menu_item, allowing us to directly publish a new menu item. Also, check for draft menu items too when deciding menu order.

(In [14937]) Ensure auto-added pages are both published and sent to the end of the menu. Tiny enhancement and optimization to wp_update_nav_menu_item come with it. fixes #13447.

Thanks to filosofo for helping me review that.

We're going to handle UX for this in #13525, where discussion has already started on the exact placement of the checkbox added here. Thus, resolved as fixed.

Forgot about post_parent.

(In [15111]) Ensure we're only auto-adding root pages to menus. fixes #13447.