Add filter to search available menu items query

[TimothyBlynJacobs]

The customize_nav_menu_available_items filter in combination with the customize_nav_menu_available_item_types allow us to add custom menu items to the customizer. But there is no corresponding filter in the search method search_available_items_query. So when a user searches for menu items, we can't make ours appear.

[TimothyBlynJacobs]

Patch added.

[westonruter]

@TimothyBlynJacobs: I think I actually came across this exact issue last week. I wanted to include private pages in my available items, so what I did (somewhat of a hack) is like:

<?php
add_action( 'pre_get_posts', function( \WP_Query $query ) {
        if ( ! doing_action( 'wp_ajax_load-available-menu-items-customizer' ) ) {
                return;
        }
        $post_type = $query->get( 'post_type' );
        if ( ! $post_type ) {
                return;
        }
        $post_type_obj = get_post_type_object( $post_type );
        if ( ! $post_type_obj ) {
                return;
        }
        if ( current_user_can( $post_type_obj->cap->read_private_posts ) ) {
                $query->set( 'post_status', array_merge( array( 'private' ), (array) $query->get( 'post_status' ) ) );
        }
} );

The same approach could be used to modify the query for searching, by looking to see if: doing_action( 'wp_ajax_search-available-menu-items-customizer' ).

[TimothyBlynJacobs]

@westonruter The problem is that the custom menu items we want to add aren't post objects. They are a custom menu type, so we can't retrieve them by modifying the query.

[westonruter]

I'm going to rename this filter to customize_nav_menu_searched_items.

[westonruter]

In 36676:

Customize: Introduce customize_nav_menu_searched_items filter for modifying results of nav menu item searches.

This new filter can be used in conjunction with the customize_nav_menu_available_items and customize_nav_menu_available_item_types filters.

Props TimothyBlynJacobs, westonruter.
Fixes #34947.