[wp-trac] [WordPress Trac] #32632: Update wp_setup_nav_menu_item() to stop overriding empty properties from supplied $menu_item

[WordPress Trac]

#32632: Update wp_setup_nav_menu_item() to stop overriding empty properties from
supplied $menu_item
-------------------------+-----------------
 Reporter:  westonruter  |      Owner:
     Type:  enhancement  |     Status:  new
 Priority:  normal       |  Milestone:  4.3
Component:  Menus        |    Version:  3.0
 Severity:  normal       |   Keywords:
  Focuses:               |
-------------------------+-----------------
 For Menu Customizer (#32576) we take a previewed menu item and create a
 mock `WP_Post` object out of it, and then pass it into
 `wp_get_nav_menu_items()` to get the proper properties added. See
 [https://github.com/voldemortensen/menu-
 customizer/blob/981c82cad7effd1c8bb84ded0c1cc04f204e74cb/class-wp-
 customize-nav-menu-item-setting.php#L327-L348 class-wp-customize-nav-menu-
 item-setting.php].

 However, `wp_setup_nav_menu_item()` is currently written in a way that it
 uses `! empty(...)` checks as opposed to `isset()` checks. This means that
 if the menu item is Customized to preview a change where the
 `menu_item_parent` is changed from the DB-saved value `1` to the new value
 `0`, this will get overwritten by `wp_setup_nav_menu_item()` because
 `$menu_item->parent_menu_item` as `0` will be considered empty in:

 {{{
 $menu_item->menu_item_parent = empty( $menu_item->menu_item_parent ) ?
 get_post_meta( $menu_item->ID, '_menu_item_menu_item_parent', true ) :
 $menu_item->menu_item_parent;
 }}}

 So I suggest that the `! empty()` checks be replaced with `isset()`
 checks.

 Also, I suggest that the `WP_Post` constructor to be updated to indicate
 that `WP_Post|object` can be the supplied param, as opposed to just
 `WP_Post`.

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Ticket URL: <https://core.trac.wordpress.org/ticket/32632>
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