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.

[ryan]

Isolated to an MU change.

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

[ryan]

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().

[donncha]

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?

[anonymized_218323]

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.