The issue with most breadcrumb functions is that it relies on the $post object on all pages. Not only is the $post global totally unreliable (see my post here), it might not even contain the data that we need, even if the $post global is not compromised
The $post global on archive pages (which includes category, tag, date, taxonomy term, author and custom post type archive) contains the first post in the loop before the loop. It is not always true that the first post is from the selected archive (the archive page you are on), which means that the info you are looking for might be incorrect, even though the $post global is not compromised. Conditions where the first post might not be from the selected archive is posts that are injected through custom stickies and the the_posts filter.
I have recently rewritten one of my very old breadcrumb functions which makes use of the $GLOBALS['wp_the_query'] object and the queried object saved in the $GLOBALS['wp_the_query'] global. This way, we have a 99.999% reliable breadcrumb that does not rely on the $post global or any compromised data.
Here is the function: (Requires PHP 5.4+. Also, feel free to alter as necessary)
function get_hansel_and_gretel_breadcrumbs()
{
// Set variables for later use
$here_text = __( 'You are currently here!' );
$home_link = home_url("https://wordpress.stackexchange.com/");
$home_text = __( 'Home' );
$link_before="<span typeof="v:Breadcrumb">";
$link_after="</span>";
$link_attr=" rel="v:url" property="v:title"";
$link = $link_before . '<a' . $link_attr . ' href="https://wordpress.stackexchange.com/questions/204738/%1$s">%2$s</a>' . $link_after;
$delimiter=" » "; // Delimiter between crumbs
$before="<span class="current">"; // Tag before the current crumb
$after="</span>"; // Tag after the current crumb
$page_addon = ''; // Adds the page number if the query is paged
$breadcrumb_trail="";
$category_links="";
/**
* Set our own $wp_the_query variable. Do not use the global variable version due to
* reliability
*/
$wp_the_query = $GLOBALS['wp_the_query'];
$queried_object = $wp_the_query->get_queried_object();
// Handle single post requests which includes single pages, posts and attatchments
if ( is_singular() )
{
/**
* Set our own $post variable. Do not use the global variable version due to
* reliability. We will set $post_object variable to $GLOBALS['wp_the_query']
*/
$post_object = sanitize_post( $queried_object );
// Set variables
$title = apply_filters( 'the_title', $post_object->post_title );
$parent = $post_object->post_parent;
$post_type = $post_object->post_type;
$post_id = $post_object->ID;
$post_link = $before . $title . $after;
$parent_string = '';
$post_type_link = '';
if ( 'post' === $post_type )
{
// Get the post categories
$categories = get_the_category( $post_id );
if ( $categories ) {
// Lets grab the first category
$category = $categories[0];
$category_links = get_category_parents( $category, true, $delimiter );
$category_links = str_replace( '<a', $link_before . '<a' . $link_attr, $category_links );
$category_links = str_replace( '</a>', '</a>' . $link_after, $category_links );
}
}
if ( !in_array( $post_type, ['post', 'page', 'attachment'] ) )
{
$post_type_object = get_post_type_object( $post_type );
$archive_link = esc_url( get_post_type_archive_link( $post_type ) );
$post_type_link = sprintf( $link, $archive_link, $post_type_object->labels->singular_name );
}
// Get post parents if $parent !== 0
if ( 0 !== $parent )
{
$parent_links = [];
while ( $parent ) {
$post_parent = get_post( $parent );
$parent_links[] = sprintf( $link, esc_url( get_permalink( $post_parent->ID ) ), get_the_title( $post_parent->ID ) );
$parent = $post_parent->post_parent;
}
$parent_links = array_reverse( $parent_links );
$parent_string = implode( $delimiter, $parent_links );
}
// Lets build the breadcrumb trail
if ( $parent_string ) {
$breadcrumb_trail = $parent_string . $delimiter . $post_link;
} else {
$breadcrumb_trail = $post_link;
}
if ( $post_type_link )
$breadcrumb_trail = $post_type_link . $delimiter . $breadcrumb_trail;
if ( $category_links )
$breadcrumb_trail = $category_links . $breadcrumb_trail;
}
// Handle archives which includes category-, tag-, taxonomy-, date-, custom post type archives and author archives
if( is_archive() )
{
if ( is_category()
|| is_tag()
|| is_tax()
) {
// Set the variables for this section
$term_object = get_term( $queried_object );
$taxonomy = $term_object->taxonomy;
$term_id = $term_object->term_id;
$term_name = $term_object->name;
$term_parent = $term_object->parent;
$taxonomy_object = get_taxonomy( $taxonomy );
$current_term_link = $before . $taxonomy_object->labels->singular_name . ': ' . $term_name . $after;
$parent_term_string = '';
if ( 0 !== $term_parent )
{
// Get all the current term ancestors
$parent_term_links = [];
while ( $term_parent ) {
$term = get_term( $term_parent, $taxonomy );
$parent_term_links[] = sprintf( $link, esc_url( get_term_link( $term ) ), $term->name );
$term_parent = $term->parent;
}
$parent_term_links = array_reverse( $parent_term_links );
$parent_term_string = implode( $delimiter, $parent_term_links );
}
if ( $parent_term_string ) {
$breadcrumb_trail = $parent_term_string . $delimiter . $current_term_link;
} else {
$breadcrumb_trail = $current_term_link;
}
} elseif ( is_author() ) {
$breadcrumb_trail = __( 'Author archive for ') . $before . $queried_object->data->display_name . $after;
} elseif ( is_date() ) {
// Set default variables
$year = $wp_the_query->query_vars['year'];
$monthnum = $wp_the_query->query_vars['monthnum'];
$day = $wp_the_query->query_vars['day'];
// Get the month name if $monthnum has a value
if ( $monthnum ) {
$date_time = DateTime::createFromFormat( '!m', $monthnum );
$month_name = $date_time->format( 'F' );
}
if ( is_year() ) {
$breadcrumb_trail = $before . $year . $after;
} elseif( is_month() ) {
$year_link = sprintf( $link, esc_url( get_year_link( $year ) ), $year );
$breadcrumb_trail = $year_link . $delimiter . $before . $month_name . $after;
} elseif( is_day() ) {
$year_link = sprintf( $link, esc_url( get_year_link( $year ) ), $year );
$month_link = sprintf( $link, esc_url( get_month_link( $year, $monthnum ) ), $month_name );
$breadcrumb_trail = $year_link . $delimiter . $month_link . $delimiter . $before . $day . $after;
}
} elseif ( is_post_type_archive() ) {
$post_type = $wp_the_query->query_vars['post_type'];
$post_type_object = get_post_type_object( $post_type );
$breadcrumb_trail = $before . $post_type_object->labels->singular_name . $after;
}
}
// Handle the search page
if ( is_search() ) {
$breadcrumb_trail = __( 'Search query for: ' ) . $before . get_search_query() . $after;
}
// Handle 404's
if ( is_404() ) {
$breadcrumb_trail = $before . __( 'Error 404' ) . $after;
}
// Handle paged pages
if ( is_paged() ) {
$current_page = get_query_var( 'paged' ) ? get_query_var( 'paged' ) : get_query_var( 'page' );
$page_addon = $before . sprintf( __( ' ( Page %s )' ), number_format_i18n( $current_page ) ) . $after;
}
$breadcrumb_output_link = '';
$breadcrumb_output_link .= '<div class="breadcrumb">';
if ( is_home()
|| is_front_page()
) {
// Do not show breadcrumbs on page one of home and frontpage
if ( is_paged() ) {
$breadcrumb_output_link .= $here_text . $delimiter;
$breadcrumb_output_link .= '<a href="' . $home_link . '">' . $home_text . '</a>';
$breadcrumb_output_link .= $page_addon;
}
} else {
$breadcrumb_output_link .= $here_text . $delimiter;
$breadcrumb_output_link .= '<a href="' . $home_link . '" rel="v:url" property="v:title">' . $home_text . '</a>';
$breadcrumb_output_link .= $delimiter;
$breadcrumb_output_link .= $breadcrumb_trail;
$breadcrumb_output_link .= $page_addon;
}
$breadcrumb_output_link .= '</div><!-- .breadcrumbs -->';
return $breadcrumb_output_link;
}
You can simply call it as follow
echo get_hansel_and_gretel_breadcrumbs();
where needed
This breadcrumb function takes care of custom post types as well