Mahara Class ‘HTMLPurifier_Config’ not found

This error relates to a call to the clean_html function in lib/web.php which loads HTMLPurifier. Turns out that due to a bad .gitignore file where all files with the name config.php were being ignored, the file:

lib/htmlpurifier/HTMLPurifier/Config.php

Wasn’t in the install and caused this error. Fixing up the .gitignore file to only ignore the root level config.php (/config.php/) resolved the issue and allowed the missing config.php file to be deployed on the target install.