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.

  • and where do you get that error? Commented Feb 26, 2019 at 9:04
  • 2
    It sounds like there was an issue with the install of 5.1. Try reinstalling it. Commented Feb 26, 2019 at 9:06

1 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.

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