wp_check_for_changed_slugs

Source code

function wp_check_for_changed_slugs($post_id, $post, $post_before) {

	// dont bother if it hasnt changed

	if ( $post->post_name == $post_before->post_name )

		return;



	// we're only concerned with published, non-hierarchical objects

	if ( $post->post_status != 'publish' || is_post_type_hierarchical( $post->post_type ) )

		return;



	$old_slugs = (array) get_post_meta($post_id, '_wp_old_slug');



	// if we haven't added this old slug before, add it now

	if ( !empty( $post_before->post_name ) && !in_array($post_before->post_name, $old_slugs) )

		add_post_meta($post_id, '_wp_old_slug', $post_before->post_name);



	// if the new slug was used previously, delete it from the list

	if ( in_array($post->post_name, $old_slugs) )

		delete_post_meta($post_id, '_wp_old_slug', $post->post_name);

}