Ran into a funny thing today. If you're performing a wordpress search with WPQuery, and you're using the post__in parameter to specify an array of ID's to retrieve and your array is _empty then you end up with the post__in field ignore entirely and the other parameters taking precedence.
This is rather strange, as I'd expect it to show 0 posts since no ID's would match an empty list.
Specifically, my arguments to WP_Query were along these lines:
$query_args = array( 'post_type' => 'redacted', 'post_status' => 'publish', 'posts_per_page' => $limit, 'paged' => $page, 'post__in' => $ids, 'meta_key' => '_expiration_date', 'meta_value' => time(), 'meta_compare' => '>=', 'ignore_sticky_posts'= > true );
ids array was empty, then I'd just get everything back.
Which isn't what I wanted at all, so to fix the problem I just
initialized the array with -1 and it all worked the way I expected it
Well, weirder things have happend. I wonder if this is a WordPress bug or intentional?