WordPress 3.1 Taxonomy Feeds

taxonomy-feeds.php

<?php
/** 
 * WordPress 3.1 Taxonomy Feeds Plugin (Must-Use)
 *
 * Copyright (C) 2011  hakre <http://hakre.wordpress.com/>
 * 
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 * 
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 * 
 * USAGE: 
 * 
 * http://example.net/feed?taxonomy=people
 * 
 * @author hakre <http://hakre.wordpress.com>
 * @see http://wordpress.stackexchange.com/questions/3720/rss-feed-for-posts-containing-any-term-from-a-taxonomy
 */

/* feel free to uncomment / remove the next hook as it's only in here for demo */
add_filter('init', function() {
	# register demo "people" taxonomy
	register_taxonomy(
		'people',
		'post',
		array(
			'label' => __('People'),
			'sort' => true,
			'args' => array('orderby' => 'term_order'),
			'rewrite' => array('slug' => 'person')
		)
	);
}); /* end of demo hook */

add_filter('pre_get_posts', function(WP_query $query) {	
	if (!($taxonomyName = $query->get('taxonomy')) && !$query->is_feed)
		return; # quick return if not a feed and parameter missing.	
	$taxonomyIds = get_terms($taxonomyName, array('fields' => 'ids'));
	if (is_wp_error($taxonomyIds))
		return; # quick return if taxonomy does not exists
	$taxonomyQuery = array(
		'taxonomy' => $taxonomyName,
		'terms' => $taxonomyIds,
	);	
	isset($query->query_vars['tax_query']) 
	    || $query->query_vars['tax_query'] = array()
		;
	$query->query_vars['tax_query'][] = $taxonomyQuery;
});