Ticket #49628: 49628.8.diff

src/wp-includes/post.php

@@ -2135 +2135 @@
         /**
          * Filters whether a post type is considered "viewable".
          *
+         * The returned filtered value must be a boolean type to ensure
+         * `is_post_type_viewable()` only returns a boolean. This strictness
+         * is by design to maintain backwards-compatibility and guard against
+         * potential type errors in PHP 8.1+. Non-boolean values (even falsey
+         * and truthy values) will result in the function returning false.
+         *
          * @since 5.9.0
          *
-         * @param bool         $is_viewable Whether the post type is "viewable".
+         * @param bool         $is_viewable Whether the post type is "viewable" (strict type).
          * @param WP_Post_Type $post_type   Post type object.
          */
-        $is_viewable = apply_filters( 'is_post_type_viewable', $is_viewable, $post_type );
-
-        // Make sure the filtered value is a boolean type before returning it.
-        if ( ! is_bool( $is_viewable ) ) {
-                return false;
-        }
-
-        return $is_viewable;
+        return true === apply_filters( 'is_post_type_viewable', $is_viewable, $post_type );
 }
 
 /**