Twenty Ten child themes and twentyten_the_page_number

Fatal error: Call to undefined function twentyten_the_page_number() in wp-content/themes/my-child-theme/header.php on line 8

Twenty Ten, the new default theme in WordPress 3.0, is a phenomenal theme that makes a great parent theme. This site indeed uses Twenty Ten, with a lightweight child theme that changes some of the styling and has a small functions.php file to add a few small touches of functionality.

When Twenty Ten was first committed to WordPress trunk, core contributors and committers swooped in and started making line-by-line incremental improvements. The new default theme was, by and large, why WordPress 3.0 had some incredible innovations for theme developers, with custom backgrounds, headers, and menus; get_template_part(); and other features. It’s because we became theme developers ourselves.

An pre-release version of Twenty Ten contained a function called twentyten_the_page_number(). It was redundant, and thus removed before WordPress 3.0 and Twenty Ten 1.1 were shipped. But a few child themes were already expecting this function to be available, causing them to break.

Today, 42 days after the release of 3.0, we’ve released WordPress 3.0.1. With it, we’ve packaged Twenty Ten 1.1. But there are still some individuals out there who want to leverage a child theme that still expects this function to exist. This a short plugin will fix it for you.