Source

File: wp-includes/nav-menu.php

function wp_get_nav_menu_items( $menu, $args = array() ) {
	$menu = wp_get_nav_menu_object( $menu );

	if ( ! $menu ) {
		return false;
	}

	static $fetched = array();

	$items = get_objects_in_term( $menu->term_id, 'nav_menu' );
	if ( is_wp_error( $items ) ) {
		return false;
	}

	$defaults        = array(
		'order'       => 'ASC',
		'orderby'     => 'menu_order',
		'post_type'   => 'nav_menu_item',
		'post_status' => 'publish',
		'output'      => ARRAY_A,
		'output_key'  => 'menu_order',
		'nopaging'    => true,
	);
	$args            = wp_parse_args( $args, $defaults );
	$args['include'] = $items;

	if ( ! empty( $items ) ) {
		$items = get_posts( $args );
	} else {
		$items = array();
	}

	// Get all posts and terms at once to prime the caches.
	if ( empty( $fetched[ $menu->term_id ] ) && ! wp_using_ext_object_cache() ) {
		$fetched[ $menu->term_id ] = true;
		$posts                     = array();
		$terms                     = array();
		foreach ( $items as $item ) {
			$object_id = get_post_meta( $item->ID, '_menu_item_object_id', true );
			$object    = get_post_meta( $item->ID, '_menu_item_object', true );
			$type      = get_post_meta( $item->ID, '_menu_item_type', true );

			if ( 'post_type' === $type ) {
				$posts[ $object ][] = $object_id;
			} elseif ( 'taxonomy' === $type ) {
				$terms[ $object ][] = $object_id;
			}
		}

		if ( ! empty( $posts ) ) {
			foreach ( array_keys( $posts ) as $post_type ) {
				get_posts(
					array(
						'post__in'               => $posts[ $post_type ],
						'post_type'              => $post_type,
						'nopaging'               => true,
						'update_post_term_cache' => false,
					)
				);
			}
		}
		unset( $posts );

		if ( ! empty( $terms ) ) {
			foreach ( array_keys( $terms ) as $taxonomy ) {
				get_terms(
					array(
						'taxonomy'     => $taxonomy,
						'include'      => $terms[ $taxonomy ],
						'hierarchical' => false,
					)
				);
			}
		}
		unset( $terms );
	}

	$items = array_map( 'wp_setup_nav_menu_item', $items );

	if ( ! is_admin() ) { // Remove invalid items only on front end.
		$items = array_filter( $items, '_is_valid_nav_menu_item' );
	}

	if ( ARRAY_A == $args['output'] ) {
		$items = wp_list_sort(
			$items,
			array(
				$args['output_key'] => 'ASC',
			)
		);
		$i     = 1;
		foreach ( $items as $k => $item ) {
			$items[ $k ]->{$args['output_key']} = $i++;
		}
	}

	/**
	 * Filters the navigation menu items being returned.
	 *
	 * @since 3.0.0
	 *
	 * @param array  $items An array of menu item post objects.
	 * @param object $menu  The menu object.
	 * @param array  $args  An array of arguments used to retrieve menu item objects.
	 */
	return apply_filters( 'wp_get_nav_menu_items', $items, $menu, $args );
}