I'm getting Call to undefined function wp_parse_list() out of the blue

Question

I woke up this morning and started getting the following error:

Fatal error: Uncaught Error: Call to undefined function wp_parse_list() in /app/public.built/wp-includes/class-wp-comment-query.php:485 Stack trace: #0 /app/public.built/wp-includes/class-wp-comment-query.php(395): WP_Comment_Query->get_comment_ids() #1 /app/public.built/wp-includes/class-wp-comment-query.php(346): WP_Comment_Query->get_comments() #2 /app/public.built/wp-includes/comment.php(242): WP_Comment_Query->query(Array) #3 /app/public.built/wp-admin/includes/class-wp-comments-list-table.php(147): get_comments(Array) #4 /app/public.built/wp-admin/edit-comments.php(140): WP_Comments_List_Table->prepare_items() #5 {main} thrown in /app/public.built/wp-includes/class-wp-comment-query.php on line 485

I upgraded from 5.0.3 to 5.1 yesterday evening. I use WP REST API and I'm not sure if its response was cached by the client being the reason of noticing this only today...

I don't even use the comments in WP. Can this be entirely turned off? Or has anyone experienced this? I'm afraid production cache will also expire and will go down soon. Thanks

UPDATE: After downgrading back to 5.0.3 this has been resolved. However the question is still open.

Answer 1

it looks like this is a new function since 5.1.0. see that info here: https://de.wpseek.com/function/wp_parse_list/

you could try to add this in your themes function.php temporarily, as a workaround.

function wp_parse_list( $list ) {
    if ( ! is_array( $list ) ) {
        return preg_split( '/[\s,]+/', $list, -1, PREG_SPLIT_NO_EMPTY );
    }

    return $list;
}

so as you guess: i think it's something related with caching, too.