Rewrite endpoints don't work with taxonomies

[sillybean]

Adding a rewrite endpoint on category archives apparently confuses WP_Query and results in 404 errors. That is, according to all the documentation I have found on WP-Rewrite, this should work:

​http://example.com/category/slug/format/myformat/

But instead, you have to use:

​http://example.com/category/slug/?format=myformat

Excerpt from a sample plugin:

// Add permalink structure, flush rules on activation/deactivation
function uwc_ebook_activate() {
        uwc_ebook_add_rewrites();
        flush_rewrite_rules();
}
function uwc_ebook_deactivate() {
        flush_rewrite_rules();
}
register_activation_hook(__FILE__, 'uwc_ebook_activate');
register_deactivation_hook(__FILE__, 'uwc_ebook_deactivate');

// Add rewrite endpoint
function uwc_ebook_add_rewrites() {
        add_rewrite_endpoint('format', EP_CATEGORIES);
        // this doesn't work either:
        // add_rewrite_endpoint('format', EP_ALL);
}
add_filter('init', 'uwc_ebook_add_rewrites');

// Handle the endpoint display
function uwc_ebook_template_redirect() {
//      global $wp_query; var_dump($wp_query); exit;
        $format = get_query_var('format');
        $cat = get_query_var('cat');
        if ($format == 'epub' && isset($cat)) {
                $category = get_category($cat);
                if (!is_wp_error($category)) {
                        $uploads = wp_upload_dir();
                        $ebookurl = $uploads['baseurl'].'/ebooks/'.$category->slug.'/'.$category->slug.'.epub';
                        wp_redirect( $ebookurl, 301 );
                        exit;
                }
        } 
}
add_filter('template_redirect', 'uwc_ebook_template_redirect');

// the rest of the plugin generates the epub file containing all posts in that category

Uncommenting the $wp_query line shows what's going on. Relevant parts of the var dump, from the Science & Technical subcategory of How-To:

["category_name"]=>
    string(4) "epub"
["query"]=>
  array(1) {
    ["category_name"]=>
    string(36) "how-to/science-technical/format/epub"
  }

Using /how-to/science-technical/?format=epub instead, WP correctly recognizes the category and format as two different query vars.

I tested this in the latest nightly build, and it's broken there as well.

Bill Erickson had a similar problem a few weeks ago, in which he used EP_ALL and found that it worked everywhere except category archives:
​https://gist.github.com/1287996

The issue is a change in 3.1, which made taxonomies all be handled like any other permastruct. This means the endpoints are no longer properly checked. Surprised it was missed until now.

Unlike register_post_type(), register_taxonomy() does not provide a way to specify an endpoint. So fixing this also requires an API enhancement.

19275.diff​ standardizes on ep_mask being an optional argument for $argsrewrite? for either taxonomies or post types, and makes endpoints work for categories and tags.

Patch works perfectly. Thanks!

In [19738]:

Add 'ep_mask' as an argument to the 'rewrite' array for register_post_type() and register_taxonomy(). Keeps 'permalink_epmask' compatible as an argument for post type registrations. Fixes endpoints for category and tag pages. fixes #19275.

In [19740]:

Args is an object, not an array. props duck_, aaroncampbell. see #19275.

For the extra stuff in [19738], see [19739].

In [19741]:

Clean up and better document create_initial_taxonomies(). see #19275.

Just curious how does this effect #12779 (better support for custom post types in WP_Rewrite).