query_posts() kills is_404 flag

[donncha]

Repeated usage of query_posts() destroys the 404 status flag for a page.

This probably hasn't been noticed before because the 404.php theme file will have been selected by the time query_posts() is used (say in a theme).

How to reproduce:

Add this code to your sidebar: (or any other query_posts() call that generates posts) query_posts("cat=23&posts_per_page=12");

In the footer of your theme's index.php (or 404.php if it's there) add this code: <?php if( is_404() ) { echo "<p>" . $_SERVER[ 'REQUEST_URI' ] . " is a 404</p>"; } ?>

Add and remove the query_posts() call. The "is a 404" message will disappear and reappear. query_posts() creates a new global WP_Query and all status flags get overwritten.

I discovered this bug while trying to figure out why wp-super-cache was caching 404 pages. Eventually I used the template_redirect action to remember the 404 status for use later on. People have complained about wp-super-cache caching 404 pages for quite some time so this is probably a long standing bug.

Isolated to an MU change.

 http://trac.mu.wordpress.org/ticket/626

Oops, that's slightly different, but I'm not sure what there is to do here anyway. query_posts() uses the global query. If you don't want to stomp the global query, don't use query_posts().

Apparently plenty of themes use it in the sidebar and the Codex doesn't mention the 404 side effect. Perhaps the documentation should be updated?

I'm pretty sure it does say something about screwing up the main Loop. It also says that the alternative is to use get_posts() or create your own WP_Query object. You just can't go around overriding globals and expecting stuff to work.

It isn't WordPress's fault.