Debugging Drupal 8 module upgrades

This page is still under development.

• Read the error message! :)
• debug($var);
• If WSOD, tail your PHP error log.
  

     tail -f /path/to/php_error.log
    

• Comment out hook_install()/hook_uninstall().
• Remove stale compiled PHP files. (new!)
  

  sudo rm -rf sites/default/files/php
    

• Clear the cache.
• drush cr (Requires the "8.x" drush version).
• Uninstall/reinstall your module.
• Reinstall your site. (There are no 8.x->8.x upgrades yet.)