wp_get_nav_menu_to_edit

function wp_get_nav_menu_to_edit( $menu_id = 0 ) {
	$menu = wp_get_nav_menu_object( $menu_id );

	// If the menu exists, get its items.
	if ( is_nav_menu( $menu ) ) {
		$menu_items = wp_get_nav_menu_items( $menu->term_id, array( 'post_status' => 'any' ) );
		$result     = '<div id="menu-instructions" class="post-body-plain';
		$result    .= ( ! empty( $menu_items ) ) ? ' menu-instructions-inactive">' : '">';
		$result    .= '<p>' . __( 'Add menu items from the column on the left.' ) . '</p>';
		$result    .= '</div>';

		if ( empty( $menu_items ) ) {
			return $result . ' <ul class="menu" id="menu-to-edit"> </ul>';
		}

		/**
		 * Filters the Walker class used when adding nav menu items.
		 *
		 * @since 3.0.0
		 *
		 * @param string $class   The walker class to use. Default 'Walker_Nav_Menu_Edit'.
		 * @param int    $menu_id ID of the menu being rendered.
		 */
		$walker_class_name = apply_filters( 'wp_edit_nav_menu_walker', 'Walker_Nav_Menu_Edit', $menu_id );

		if ( class_exists( $walker_class_name ) ) {
			$walker = new $walker_class_name;
		} else {
			return new WP_Error(
				'menu_walker_not_exist',
				sprintf(
					/* translators: %s: Walker class name. */
					__( 'The Walker class named %s does not exist.' ),
					'<strong>' . $walker_class_name . '</strong>'
				)
			);
		}

		$some_pending_menu_items = false;
		$some_invalid_menu_items = false;
		foreach ( (array) $menu_items as $menu_item ) {
			if ( isset( $menu_item->post_status ) && 'draft' === $menu_item->post_status ) {
				$some_pending_menu_items = true;
			}
			if ( ! empty( $menu_item->_invalid ) ) {
				$some_invalid_menu_items = true;
			}
		}

		if ( $some_pending_menu_items ) {
			$result .= '<div class="notice notice-info notice-alt inline"><p>' . __( 'Click Save Menu to make pending menu items public.' ) . '</p></div>';
		}

		if ( $some_invalid_menu_items ) {
			$result .= '<div class="notice notice-error notice-alt inline"><p>' . __( 'There are some invalid menu items. Please check or delete them.' ) . '</p></div>';
		}

		$result .= '<ul class="menu" id="menu-to-edit"> ';
		$result .= walk_nav_menu_tree( array_map( 'wp_setup_nav_menu_item', $menu_items ), 0, (object) array( 'walker' => $walker ) );
		$result .= ' </ul> ';
		return $result;
	} elseif ( is_wp_error( $menu ) ) {
		return $menu;
	}

}