WordPress : Displays a location breadcrumb trail using WordPress navigation menus.

wp-nav_trail

<?php

/**
 * Displays a location breadcrumb trail.
 *
 * Uses WordPress nav menu items and theme locations to build
 * a breadcrumb trail. Overall, this template functon replicates
 * most of the procedures found in `wp_nav_menu()`.
 *
 * @param array $args {
 *     Optional. Array of nav menu arguments.
 *
 *     @type string        $menu            Desired menu. Accepts (matching in order) id, slug, name. Default empty.
 *     @type string        $theme_location  Theme location to be used. Must be registered with register_nav_menu()
 *                                          in order to be selectable by the user.
 *     @type string        $container       Whether to wrap the ul, and what to wrap it with. Default 'nav'.
 *     @type string        $container_class Class that is applied to the container. Default 'menu-{menu slug}-container'.
 *     @type string        $container_id    The ID that is applied to the container. Default empty.
 *     @type callback|bool $fallback_cb     If the menu doesn't exists, a callback function will fire.
 *                                          Default is 'wp_page_menu'. Set to false for no fallback.
 *     @type string        $title_home      Anchor text for the front page.
 *     @type bool          $include_home    Add front page crumb.
 *     @type bool          $include_single  Add single post crumb.
 *     @type string        $item_before     Text before the link text. Default empty.
 *     @type string        $item_after      Text after the link text. Default empty.
 *     @type string        $item_wrap       How the item should be rendered.
 *                                          Uses printf() format with numbered placeholders.
 *     @type string        $item_separator  How the list items should be separated. Default is an arrow.
 *     @type string        $link_before     Text before the label. Default empty.
 *     @type string        $link_after      Text after the label. Default empty.
 *     @type string        $link_wrap       How the link should be rendered. Default is an anchor with an id, class, and href attribute.
 *                                          Uses printf() format with numbered placeholders.
 *     @type string        $current_wrap    How the current label should be rendered.
 *                                          Uses printf() format with numbered placeholders.
 *                                          Same numbered placeholders as $link_wrap.
 *     @type bool          $echo            Whether to echo the menu or return it. Default true.
 * }
 * @return mixed Menu output if $echo is false, false if there are no items or no menu was found.
 */

function wp_nav_trail( $args = [] )
{
	$defaults = [
		'echo'            => true,
		'menu'            => '',
		'theme_location'  => '',
		'container'       => 'nav',
		'container_class' => '',
		'container_id'    => '',
		'fallback_cb'     => '',
		'title_home'      => __('Home'),
		'include_home'    => true,
		'include_single'  => false,
		'item_before'     => '',
		'item_after'      => '',
		'item_wrap'       => '<span id="%1$s" class="%2$s" typeof="v:Breadcrumb">%3$s</span>',
		'item_separator'  => ' &#8594; ',
		'link_before'     => '',
		'link_after'      => '',
		'link_wrap'       => '<a href="%1$s" rel="v:url" property="v:title">%2$s</a>',
		'current_wrap'    => '<span property="v:title">%2$s</span>'
	];

	$args = wp_parse_args( $args, $defaults );

	/**
	 * Filter the arguments used to display a breadcrumb trail.
	 *
	 * @see {function} WordPress\Nav_Menus\wp_nav_menu()
	 * @see {filter}   wp_nav_menu_args
	 *
	 * @param array $args Array of wp_nav_trail() arguments.
	 */

	$args = apply_filters( 'wp_nav_trail_args', $args );
	$args = (object) $args;

	/**
	 * Filter whether to short-circuit the wp_nav_trail() output.
	 *
	 * Returning a non-null value to the filter will short-circuit
	 * wp_nav_trail(), echoing that value if $args->echo is true,
	 * returning that value otherwise.
	 *
	 * @see {function} WordPress\Nav_Menus\wp_nav_menu()
	 * @see {filter}   pre_wp_nav_menu
	 *
	 * @param string|null $output Nav trail output to short-circuit with. Default null.
	 * @param object      $args   An object containing wp_nav_trail() arguments.
	 */

	$nav_menu = apply_filters( 'pre_wp_nav_trail', null, $args );

	if ( null !== $nav_menu ) {
		if ( $args->echo ) {
			echo $nav_menu;
			return;
		}

		return $nav_menu;
	}

	// Get the nav menu based on the requested menu
	$menu = wp_get_nav_menu_object( $args->menu );

	// Get the nav menu based on the theme_location
	if ( ! $menu && $args->theme_location && ( $locations = get_nav_menu_locations() ) && isset( $locations[ $args->theme_location ] ) ) {
		$menu = wp_get_nav_menu_object( $locations[ $args->theme_location ] );
	}

	// get the first menu that has items if we still can't find a menu
	if ( ! $menu && ! $args->theme_location ) {
		$menus = wp_get_nav_menus([ 'orderby' => 'name' ]);
		foreach ( $menus as $menu_maybe ) {
			if ( $menu_items = wp_get_nav_menu_items( $menu_maybe->term_id, [ 'update_post_term_cache' => false ] ) ) {
				$menu = $menu_maybe;
				break;
			}
		}
	}

	// If the menu exists, get its items.
	if ( $menu && ! is_wp_error( $menu ) && ! isset( $menu_items ) )
		$menu_items = wp_get_nav_menu_items( $menu->term_id, [ 'update_post_term_cache' => false ] );

	/*
	 * If no menu was found:
	 *  - Fall back (if one was specified), or bail.
	 *
	 * If no menu items were found:
	 *  - Fall back, but only if no theme location was specified.
	 *  - Otherwise, bail.
	 */
	if ( ( ! $menu || is_wp_error( $menu ) || ( isset( $menu_items ) && empty( $menu_items ) && ! $args->theme_location ) )
		&& $args->fallback_cb && is_callable( $args->fallback_cb ) ) {
			return call_user_func( $args->fallback_cb, (array) $args );
	}

	if ( ! $menu || is_wp_error( $menu ) ) {
		return false;
	}

	$nav_menu = $items = '';

	$show_container = false;
	if ( $args->container ) {

		/**
		 * Filter the list of HTML tags that are valid for use as breadcrumb containers.
		 *
		 * @see {function} WordPress\Nav_Menus\wp_nav_menu()
		 * @see {filter}   wp_nav_menu_container_allowedtags
		 *
		 * @param array $tags The acceptable HTML tags for use as breadcrumb containers.
		 *                    Default is array containing 'div' and 'nav'.
		 */

		$allowed_tags = apply_filters( 'wp_nav_trail_container_allowedtags', [ 'div', 'nav' ] );

		if ( in_array( $args->container, $allowed_tags ) ) {
			$show_container = true;

			$atts = [];
			$atts['id']     = ( $args->container_id ? esc_attr( $args->container_id ) : '' );
			$atts['class']  = ( $args->container_class ? esc_attr( $args->container_class ) : 'trail-' . $menu->slug . '-container' );
			$atts['prefix'] = 'v:http://rdf.data-vocabulary.org/#';

			/**
			 * Filter the HTML attributes applied to a trail's container.
			 *
			 * @see {method} WordPress\Nav_Menus\Walker_Nav_Menu::start_el()
			 * @see {filter} nav_menu_link_attributes
			 *
			 * @param array $atts {
			 *     The HTML attributes applied to the trail's container, empty strings are ignored.
			 *
			 *     @type string  $id      The ID attribute.
			 *     @type string  $class   The class names attribute.
			 *     @type string  $prefix  The prefix attribute.
			 * }
			 * @param array  $args  An array of wp_nav_trail() arguments.
			 */

			$atts = apply_filters( 'nav_trail_container_attributes', $atts, $args );

			$attributes = '';
			foreach ( $atts as $attr => $value ) {
				if ( ! empty( $value ) ) {
					$attributes .= ' ' . $attr . '="' . esc_attr( $value ) . '"';
				}
			}

			$nav_menu .= '<'. $args->container . $attributes . '>';
		}
	}

	// Set up the $menu_item variables
	_wp_menu_item_classes_by_context( $menu_items );

	$sorted_menu_items = [];
	foreach ( (array) $menu_items as $menu_item ) {
		$sorted_menu_items[ $menu_item->menu_order ] = $menu_item;
	}

	unset( $menu_items, $menu_item );

	/**
	 * Filter the sorted list of breadcrumb objects before generating the trail's HTML.
	 *
	 * @see {function} WordPress\Nav_Menus\wp_nav_menu()
	 * @see {filter}   wp_nav_menu_objects
	 *
	 * @param array  $sorted_menu_items The breadcrumnb items, sorted by each breadcrumb's menu order.
	 * @param object $args              An object containing wp_nav_trail() arguments.
	 */
	$sorted_menu_items = apply_filters( 'wp_nav_trail_objects', $sorted_menu_items, $args );

	$items = [];

	if ( $args->include_home ) {
		$show_on_front = get_option('show_on_front');
		$page_on_front = get_option('page_on_front');
		// $page_for_posts = get_option('page_for_posts');

		if ( ( $show_on_front === 'page' && is_front_page() ) || ( $show_on_front === 'posts' && is_home() ) ) {
			// Do nothing
		}
		else {

			$front_page = (object) [
				'ID'                    => $page_on_front,
				'db_id'                 => $page_on_front,
				'object_id'             => 0,
				'object'                => 'page',
				'post_parent'           => 0,
				'post_name'             => 'home',
				'menu_item_parent'      => 0,
				'type'                  => 'post_type',
				'title'                 => $args->title_home,
				'url'                   => home_url(),
				'description'           => '',
				'attr_title'            => '',
				'classes'               => [],
				'target'                => '',
				'xfn'                   => '',
				'current'               => is_front_page(),
				'current_item_parent'   => false,
				'current_item_ancestor' => true
			];

			array_unshift( $sorted_menu_items, $front_page );

		}
	}

	/** @todo $args->include_single */

	if ( $args->include_single ) {
	}

	foreach ( $sorted_menu_items as $item ) {
		if ( $item->current_item_ancestor || $item->current_item_parent || $item->current ) {

			$classes = ( empty( $item->classes ) ? [] : (array) $item->classes );

			/**
			 * Filter the CSS class(es) applied to a breadcrumb's <a>.
			 *
			 * @see {method} WordPress\Nav_Menus\Walker_Nav_Menu::start_el()
			 * @see {filter} nav_menu_css_class
			 *
			 * @param array   $classes  The CSS classes that are applied to the breadcrumb's <a>.
			 * @param object  $item     The current breadcrumb.
			 * @param array   $args     An array of wp_nav_trail() arguments.
			 */

			$class_names = implode( ' ', apply_filters( 'nav_trail_css_class', array_filter( $classes ), $item, $args ) );

			/**
			 * Filter the ID applied to a breadcrumb's <a>.
			 *
			 * @see {method} WordPress\Nav_Menus\Walker_Nav_Menu::start_el()
			 * @see {filter} nav_menu_item_id
			 *
			 * @param string  $item_id  The ID that is applied to the breadcrumb's <a>.
			 * @param object  $item     The current breadcrumb.
			 * @param array   $args     An array of wp_nav_trail() arguments.
			 */

			$id = apply_filters( 'nav_trail_item_id', 'crumb-item-' . $item->ID, $item, $args );

			/**
			 * Filter the URL applied to a breadcrumb's <a>.
			 *
			 * @param string  $item_id  The URL that is applied to the breadcrumb's <a>.
			 * @param object  $item     The current breadcrumb.
			 * @param array   $args     An array of wp_nav_trail() arguments.
			 */

			$url = apply_filters( 'nav_trail_item_url', $item->url, $item, $args );

			$title = $args->link_before . apply_filters( 'the_title', $item->title, $item->ID ) . $args->link_after;

			$format = ( $item->current ? $args->current_wrap : $args->link_wrap );

			/**
			 * Filter a breadcrumb's output format.
			 *
			 * @param string  $format  The breadcrumb's HTML output.
			 * @param object  $item    Trail item data object.
			 * @param object  $args    An object containing wp_nav_trail() arguments.
			 */

			$format = apply_filters( 'nav_trail_item_format', $format, $item, $args );

			$link_output  = $args->item_before;
			$link_output .= sprintf( $format, esc_url( $url ), $title );
			$link_output .= $args->item_after;

			$item_output  = sprintf( $args->item_wrap, esc_attr( $id ), esc_attr( $class_names ), $link_output );

			/**
			 * Filter a breadcrumb's output.
			 *
			 * @see {method} WordPress\Nav_Menus\Walker_Nav_Menu::start_el()
			 * @see {filter} walker_nav_menu_start_el
			 *
			 * @param string  $item_output  The breadcrumb's HTML output.
			 * @param object  $item         Trail item data object.
			 * @param object  $args         An object containing wp_nav_trail() arguments.
			 */

			$items[] = apply_filters( 'nav_trail_item', $item_output, $items, $args );
		}
	}

	if ( function_exists('first') ) {

		/**
		 * Filter the first item (most likely the root ancestor).
		 *
		 * @param string $item_output The breadcrumb's HTML output.
		 * @param object $item        Trail item data object.
		 * @param array  $args        An array of wp_nav_trail() arguments.
		 */

		apply_filters( 'nav_trail_start', first( $items ), reset( $sorted_menu_items ), $args );

	}

	if ( function_exists('last') ) {

		/**
		 * Filter the last item (most likely the active one).
		 *
		 * @param string $item_output The breadcrumb's HTML output.
		 * @param object $item        Trail item data object.
		 * @param array  $args        An array of wp_nav_trail() arguments.
		 */

		apply_filters( 'nav_trail_end', last( $items ), end( $sorted_menu_items ), $args );

	}

	/**
	 * Filter the separator applied between each item.
	 *
	 * @param string  $separator  The URL that is applied to the breadcrumb's <a>.
	 * @param array   $items      The trail's HTML output.
	 * @param array   $args       An array of wp_nav_trail() arguments.
	 */

	$separator = apply_filters( 'nav_trail_separator', $args->item_separator, $items, $args );

	$items = implode( $separator, $items );

	unset( $sorted_menu_items );

	/**
	 * Filter the HTML list content for navigation menus.
	 *
	 * @see {function} WordPress\Nav_Menus\wp_nav_menu()
	 * @see {filter}   wp_nav_menu_items
	 *
	 * @param string $items The HTML list content for the breadcrumbs.
	 * @param object $args  An object containing wp_nav_trail() arguments.
	 */

	$items = apply_filters( 'wp_nav_trail_items', $items, $args );

	/**
	 * Filter the HTML list content for a specific navigation menu.
	 *
	 * @see {function} WordPress\Nav_Menus\wp_nav_menu()
	 * @see {filter}   wp_nav_menu_{$menu->slug}_items
	 *
	 * @param string $items The HTML list content for the breadcrumbs.
	 * @param object $args  An object containing wp_nav_trail() arguments.
	 */

	$items = apply_filters( "wp_nav_trail_{$menu->slug}_items", $items, $args );

	// Don't print any markup if there are no items at this point.
	if ( empty( $items ) ) {
		return false;
	}

	$nav_menu .= $items;
	unset( $items );

	if ( $show_container ) {
		$nav_menu .= '</' . $args->container . '>';
	}

	/**
	 * Filter the HTML content for navigation breadcrumb trail.
	 *
	 * @see {function} WordPress\Nav_Menus\wp_nav_menu()
	 * @see {filter}   wp_nav_menu
	 *
	 * @param string $nav_menu The HTML content for the navigation breadcrumb trail.
	 * @param object $args     An object containing wp_nav_trail() arguments.
	 */
	$nav_menu = apply_filters( 'wp_nav_trail', $nav_menu, $args );

	if ( $args->echo ) {
		echo $nav_menu;
	}
	else {
		return $nav_menu;
	}
}