apply_filters_ref_array bug

[jfarthing84]

I believe (unless I am not using it correctly) that there is a bug with the new apply_filters_ref_array() function. Particularly, I am applying two different functions certain 'posts_' filters in the query, and only the one with the highest priority is processed. Small example:

function posts_where_filter_one($where) {
  global $wpdb;
  $where .= " AND $wpdb->posts.post_type = 'post'";
}
add_filter('posts_where', 'posts_where_filter_one');

function posts_where_filter_two($where) {
  global $wpdb;
  $where .= " AND $wpdb->posts.post_status = 'publish'";
}
add_filter('posts_where', 'posts_where_filter_two');

You would expect $where to end up as:

AND wp_posts.post_type = 'post' AND wp_posts.post_status = 'publish'

But instead it end up as:

AND wp_posts.post_status = 'publish'

Erm, you forgot to do return $where in both cases.

On a closer look, bug confirmed.

Huh, oops. I sure did. I didn'tforget in my code though, just on typing the example here.

jfarthing84, can you confirm that the patch fixes the problem?

Yes, it does.

Good enough. :)

Your filters are not written correctly.

A filter hooked into a WordPress filter must return something to be passed back out.

By default the first argument passed to apply_filters / apply_filters_ref_array is returned unless a function is hooked in.

If something is hooked in then the result of that function is returned instead.

If there are a number of filters then the result of one gets passed to the next as an argument.

Your examples should be:

function posts_where_filter_one($where) {
  global $wpdb;
  $where .= " AND $wpdb->posts.post_type = 'post'";
  return $where;
}
add_filter('posts_where', 'posts_where_filter_one');

function posts_where_filter_two($where) {
  global $wpdb;
  $where .= " AND $wpdb->posts.post_status = 'publish'";
  return $where;
}
add_filter('posts_where', 'posts_where_filter_two');

Closing as invalid

Wow, if you look up I said that I just forgot to type the return in my mockup examples here, not in my code. It is a bug. Try it yourself.

Ok I missed the subtlety of the bug and the need for multiple filters.

Sorry.

I've added a test case for this now to wordpress-tests so it won't reappear in the future.

(In [13906]) Ensure that apply_filters_ref_array passes the result of the filter to the next filter. Fixes #12723 props scribue.