How to enable hierarchical permalinks for hierarchical taxonomies

If you have a category called “term” and a subcategory called “subterm”, your can access subterm posts at /cat/subcat. But this doesn’t work out of the box with custom taxonomies. They are accessible at /taxonomy/subterm, but not /taxonomy/term/subterm.

They’ve gone over this in the WordPress Trac (http://core.trac.wordpress.org/ticket/12659), and it kind of looks like they have a solution, but as I’ve never used the Trac and don’t fully understand its language (diffs, etc), I need someone more experienced to actually tell me how to implement this. Is there code there that I have to paste into WordPress core files? Is this already implemented and I can add something to my theme’s functions.php?

If possible I’d prefer not to modify any core files. Help!

This is implemented in WordPress now as of 3.1.

When you register your taxonomy, make sure to set rewrite hierarchical to true as well as the taxonomy itself:

<?php
register_taxonomy('genre',array('book'), array(
'hierarchical' => true, // this makes it hierarchical in the UI
'labels' => $labels,
'show_ui' => true,
'query_var' => true,
'rewrite' => array( 'hierarchical' => true ), // this makes hierarchical URLs
));