gistfile1.php

<?php

function woo_custom_breadcrumbs_trail_add_product_categories ( $trail ) {
  if ( ( get_post_type() == 'product' ) && is_singular() ) {

    global $post;
    
    $taxonomy = 'product_cat';
    
    $terms = get_the_terms( $post->ID, $taxonomy );
    $links = array();

    if ( $terms && ! is_wp_error( $terms ) ) {
    
      foreach ( $terms as $c ) {
      
        $parents = woo_get_term_parents( $c->term_id, $taxonomy, true, ', ', false, array( $c->term_id ) );
        if ( $parents != '' ) {
          $parents_arr = explode( ', ', $parents );
          
          foreach ( $parents_arr as $p ) {
            if ( $p != '' ) { $links[] = $p; }
          }
        }
      }
      
      // Add the trail back on to the end.
      $links[] = $trail['trail_end'];
      
      // Add the new links, and the original trail's end, back into the trail.
      array_splice( $trail, 1, count( $trail ) - 1, $links );
    
    }
  }

  return $trail;
} // End woo_custom_breadcrumbs_trail_add_product_categories()
add_filter( 'woo_breadcrumbs_trail', 'woo_custom_breadcrumbs_trail_add_product_categories', 10 );

function woo_get_term_parents( $id, $taxonomy, $link = false, $separator = '/', $nicename = false, $visited = array() ) {
  $chain = '';
  $parent = &get_term( $id, $taxonomy );

  if ( is_wp_error( $parent ) )
    return $parent;

  if ( $nicename )
    $name = $parent->slug;
  else
    $name = $parent->name;


  if ( $parent->parent && ( $parent->parent != $parent->term_id ) && ! in_array( $parent->parent, $visited ) && ! in_array( $parent->term_id, $visited ) ) {
    $visited[] = $parent->parent;
    $visited[] = $parent->term_id;
    $chain .= woo_get_term_parents( $parent->parent, $taxonomy, $link, $separator, $nicename, $visited );
  }

  if ( $link ) {
    $chain .= '<a href="' . get_term_link( $parent, $taxonomy ) . '" title="' . esc_attr( sprintf( __( "View all posts in %s" ), $parent->name ) ) . '">'.$name.'</a>' . $separator;
  } else {
    $chain .= $name.$separator;
  }
  
  return $chain;
} // End woo_get_term_parents()

This does not give me a trail of categories in breadcrumbs. What could be possible cause of error?

The error is that the filter doesn't exist: woo_breadcrumbs_trail