“Call to undefined method JApplicationSite::isClient()” when Updating to Joomla 3.8

A new client approached us yesterday and told us that they were seeing a blank page on the frontend and on the backend of their Joomla website after updating it to 3.8.0. Since a blank page is a sign of a fatal error, we set the error reporting on the client’s site to “maximum” in the configuration.php file, and then checked the frontend of the website, which was displaying the following:

Fatal error: Call to undefined method JApplicationSite::isClient() in /home/[cpanel-user]/public_html/plugins/system/languagefilter/languagefilter.php on line 94

The backend of the website was displaying the following error:

Fatal error: Call to undefined method JApplicationAdministrator::isClient() in /home/[cpanel-user]/public_html/plugins/system/languagefilter/languagefilter.php on line 94

(Note: Enabling debugging displayed the following error on the backend and on the fronted of the Joomla website: Fatal error: Call to undefined method JProfiler::setStart() in /home/[cpanel-user]/public_html/administrator/index.php on line 45)

If you look closely at the above errors, you will notice that the problem is that 2 basic Joomla classes, JApplicationSite and JApplicationAdministrator, are not being loaded. But why?

We investigated the problem very thoroughly. We looked at all the files that were used to load core classes or support the loading of core classes, notably, the following 2 files:

• The file loader.php which is located under the libraries/cms/class/ folder.
• The file ClassLoader.php which is located under the libraries/vendor/composer folder.

We couldn’t find anything.

We then thought it could be a problem with the PHP version that the client was using, which was PHP 5.4, and so we switched to 5.6, and then 7.0, and then 7.1. None worked!

We then started thinking about the hosting environment, could it be? Well, the client was using GoDaddy, which should cause any decent developer to become a bit skeptical at the very least (in fact, we could just blame GoDaddy for the heat wave we’re having right now in Montreal and everyone would believe us!). So, we copied the website over to one of our servers, and we tested it there. Same exact problem!

Eventually, we decided to copy a fresh copy of Joomla 3.8 onto the website. So, we downloaded Joomla 3.8, we then removed the images and the templates folder from the downloaded zip file, we extracted the zip file onto the website, and we tried loading the website, still, the same error.

Then it suddenly hit us, what if the problem is similar to this other problem that we resolved a while ago which was caused by Joomla loading old library files instead of the new ones? So, we renamed the existing libraries folder to libraries_old, and we copied a fresh copy of the libraries folder onto the website (from the Joomla 3.8 zip file that we just downloaded) and then we tested it. This time it worked!

Aha! So, the problem was caused by the wrong library file(s) being loaded? But which one(s)? We were determined to find out the answer to our question, so, we printed out all the included files on the fixed site, and then, we reverted back and printed out all the included files on the broken site, and we compared the list of files.

There were, in fact, many, many files that were included from the wrong places on the broken Joomla website. For example, the factory.php file was included from the libraries/joomla folder instead of the libraries/src folder. There were also many files included from the libraries/cms folder, and these files were included from folders that should no longer exist under the libraries/cms folder. In fact, the libraries/cms folder in Joomla 3.8 has only 3 folders inside it (Joomla 3.7.5 has 30 folders inside the libraries/cms folder).

It seems that the client has either updated the site manually (e.g. by overwriting the files from a fresh Joomla install), or the client has updated the site from the backend but from an old Joomla website where the update process does not include removing these old library files/folders. In any case, we think the problem is really caused by Joomla, which should take into consideration any update scenario. The problem is also ironic, since it highlights the fact that there is a huge change in the file structure in Joomla 3.8, completely contradicting a statement by a core Joomla developer that the “the difference from 3.7.5 is relatively minor”.

So, if you are seeing the Call to undefined method JApplicationSite::isClient() error on your Joomla website, then try renaming the libraries folder to libraries_old and then copying the libraries folder from a fresh Joomla 3.8 install. If it doesn’t work, or if you are seeing a different error, then please contact us. We are always ready to help, our fees are very reasonable, and we really love working on Joomla websites!