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I have seen other extensions by that developer having badly written plugins which break Joomla's API application.

If you could attach the extension's ZIP installation file in your next reply I could check. It's okay that this is a public ticket; attachments are always private, even in public tickets, meaning that only you and me will be able to download them.

The attachment failed. I made this ticket private. Please upload the extension's ZIP file to Dropbox, OneDrive, or Google Drive and paste me a share link here.

The problem is caused by the System - Joom Donation plugin. When it is enabled, any access to the Joomla! API application (api/index.php on your site) results in the error Class "DonationHelper" not found.

This comes from plugins/system/jdonation/jdonation.php line 56 which tries to load administrator/components/com_jdonation/loader.php. In that file they use JLoader::registerPrefix to register Donation as a class prefix. However, they have made an important mistake on that line. They are using JPATH_ROOT instead of JPATH_SITE. This mistake is repeated further down that file.

There is a subtle difference between JPATH_ROOT and JPATH_SITE:

• JPATH_ROOT is the absolute path to the root of the current application. In the frontend and backend applications it's the root path to the site, e.g. /var/www/mysite. In the API application it's the absolute path to the api folder e.g. /var/www/mysite/api.
• JPATH_SITE on the contrary is always the absolute path to the site's root, e.g. /var/www/mysite. That's what they wanted to use.

I can see why they are confused. The difference between JPATH_SITE and JPATH_ROOT was never documented in Joomla. If you haven't tracked its development very closely you'd never know about it.

For what it's worth, JPATH_ROOT being identical to JPATH_SITE in the administrator application has always been wrong and the core maintainers knew it. However, this mistake was made early in the Joomla! 1.5 development and by the time Joomla! 1.6 was underway there was a lot of code written which would've broken if the mistake was fixed. Therefore, the wrong definition for JPATH_ROOT was left in the code. When Joomla! 4 added two more applications, api and cli, the new applications did not carry the mistake forward. Instead, the JPATH_ROOT is now correctly set to the absolute path pointing to the root of each of these new Joomla! applications. Yeah, quite the mess.

If you edit the file administrator/components/com_jdonation/loader.php and replace JPATH_ROOT with JPATH_SITE everything works. This change is backwards compatible all the way to Joomla! 3.0 released back in 2012.

Please copy this entire message to a ticket to the JoomDonation people so they can fix their code.

Ah, on a similar note, there is another way to deal with that in plugins/system/jdonation/jdonation.php itself.

In the __construct method, right before calling parent::__construct they can add the following code:

if (!\Joomla\CMS\Factory::getApplication()->isClient('administrator') && !\Joomla\CMS\Factory::getApplication()->isClient('site')) return;

I have explained the reasoning in detail in my blog post https://www.dionysopoulos.me/common-mistakes-writing-joomla-plugins.html under the heading "There is more to Joomla than the frontend and backend".

Please add that note to your ticket to the JoomDonation people.

So, let me see if I get this straight.

The author of JoomDonation EXPLICITLY STATED that despite being notified about the exact way his plugin breaks the Joomla! API application and the Joomla! CLI application, and the one line he needs to add, he has decided to NOT fix his code? In other words, he explicitly stated that even though he knows his plugin breaks Joomla! he will not fix it?

Good. I'll report him to the Joomla! Extensions Directory. If he wants to be the asshole breaking sites he has no right to get traffic from the JED.

I reported the extension. Let's see what happens :)