WordPress enable prev/next link for CPT / Taxonomy

wp-cpt-prev-next-links.php

<?php

// Enables $in_same_cat for any taxonomy
add_filter( 'get_previous_post_join', 'taxonomical_prev_next', 10, 3 );
add_filter( 'get_previous_post_where', 'taxonomical_prev_next', 10, 3 );

add_filter( 'get_next_post_join', 'taxonomical_prev_next', 10, 3 );
add_filter( 'get_next_post_where', 'taxonomical_prev_next', 10, 3 );

function taxonomical_prev_next( $sql, $in_same_cat, $excluded_categories ) {
	global $post;
	if ( $post->post_type != 'post' && $in_same_cat ) {
		$taxonomies = get_object_taxonomies( $post->post_type );
		$cat_array = wp_get_object_terms($post->ID, $taxonomies, array('fields' => 'ids'));
		if ( count( $cat_array ) )
			$sql = str_replace( "tt.term_id IN ()", "tt.term_id IN (". implode( ",", $cat_array ) . ") ", $sql );
		else
			$sql = str_replace( "AND tt.term_id IN ()", "", $sql );
		$sql = str_replace( "tt.taxonomy = 'category'", "tt.taxonomy IN ('" . implode( "','", $taxonomies ) . "') ", $sql );
	}
	return $sql;
}