wp_list_filter() and supports

Question

I'm testing the function wp_list_filter(), basically I want to know if post_type has some specific feature before making stuffs.

So I end up with this:

public static function get_post_types_with_support( $feature ) {
   global $_wp_post_type_features;
   $post_types = wp_list_filter( $_wp_post_type_features, array( $feature => 1 ) );

   return $post_types;
}

The problem is I do not understand why I can't get it working with custom post type while I gave some specific support to them.

For example, book post_type supports thumbnails, but I do not have it in my array when I display it. Where am I wrong?

EDIT : by feature I mean support. If my post_type supports this feature then I can use it. My function is supposed to return array with post_types that support my feature e.g thumbnail

Answer 1

As I noted on a comment and @toscho wrote in his answer, your code works if used after wp_loaded hook. The reason why it works for core post types if used on earlier hooks is WordPress register core post types 2 times: first time just after 'mu_plugins_loaded' hook and then again on 'init' hook (reference).

That said, if you want to use a solution that make no use of pseudo-private variables you can rely on the functions that WordPress has for the scope: get_post_types and post_type_supports, possibly using a sort of cache to improve performance on subsequents calls on same request, something like this:

function get_post_types_with_support( $feature ) {
  static $supports;
  if ( ! isset( $supports[$feature] ) ) {
    if ( ! did_action( 'wp_loaded' ) && current_filter() !== 'wp_loaded' ) {
      return new WP_Error( 'too-early', 'Are you in a hurry?' );
    }
    $supports[$feature] = array_filter( array_map( function( $type ) use( $feature )  {
      if ( post_type_supports( $type, $feature ) ) return $type;
    }, array_values( get_post_types() ) ) );
  }
  return $supports[$feature];
}

Answer 2

Post types are registered on wp_loaded or init – after plugins and the theme are loaded.

Searching in $_wp_post_type_features list on plugins_loaded is too early. Be also aware that variable might change in the future. In WordPress, where almost everything is global, pseudo-private variables are marked with a leading underscore. Read that as a sign not to access these variables directly.