WP_Error not displaying errors

Question

I am trying to utilize WP_Error for my plugin, but nothing happens. Is this too late for WP_Error? Too early? Or am I doing something else wrong?

function cpt_pre_post_publish(){
    return new WP_Error('error', __('Error!' ));
}

add_action('pre_get_posts', 'cpt_pre_post_publish');

Answer 1

Actions don't typically return data, so I doubt you will get this working the way you are trying to. Something like...

function cpt_pre_post_publish(){
  global $my_error;
  $my_error = new WP_Error('error', __('Error!' ));
}
add_action('pre_get_posts', 'cpt_pre_post_publish');

... should set a variable that you could access in a template file with...

global $my_error;
var_dump($my_error);

It is really not clear exactly what you are trying to do though.

Answer 2

Please see the example on the Codex, which indicates that you can return the WP_Error from a function, later use the function is_wp_error() (essentially the same as checking instanceof WP_Error), and display the error message.

s_ha_dum is right that actions shouldn't really return -- there's nothing to catch the information being returned.