Custom plugin doesn't even seem to load on Joomla 4

Question

As a sort of newbie developer with php/Joomla, I created a content plugin for Joomla 3 which pretty much did what I wanted and expected...

I then decided to migrate it to Joomla 4 following the very few examples that I could google here and there and nothing works. In fact, the plugin doesn't even seem to load.

So, I decided to get back to a very simple sort of helloworld type thing test and even this test doesn't do anything. I should add that install and activation work and no error message is ever displayed when setting to Maximum.

Here's the very simple thing I tried:

<?php
defined('_JEXEC') or die; 
use Joomla\CMS\Plugin\CMSPlugin; 
class PlgContentTest extends CMSPlugin 
{ 
    public function onContentPrepare($context, &$article, &$params, $page = 0) 
    { 
        if ($context !== 'com_content.article') 
        { 
            echo 'Wrong!'; 
            return; 
        } 
        echo 'Here!'; 
    }
}
?>

I cannot figure out what I've done wrong here, except maybe something about file naming?

My xml:

<?xml version="1.0" encoding="utf-8"?>
<extension type="plugin" version="4.0" method="upgrade" group="content">
<name>Test</name>
<author></author>
<creationDate>January 2022</creationDate>
<copyright>Copyright (C) 2022+ . All rights reserved.</copyright>
<license>GNU General Public License version 2 or later; see LICENSE.txt</license>
<version>1.5</version>
<description>PLG_CONTENT_TEST_DESCRIPTION</description>
<files>
<filename plugin="Test">Test.php</filename>
<filename>index.html</filename>
</files>
<languages folder="administrator/language">
<language tag="en-GB">language/en-GB/en-GB.plg_content_Test.ini</language>
<language tag="en-GB">language/en-GB/en-GB.plg_content_Test.sys.ini</language>
<language tag="fr-FR">language/fr-FR/fr-FR.plg_content_Test.ini</language>
<language tag="fr-FR">language/fr-FR/fr-FR.plg_content_Test.sys.ini</language>
<languages>
</extension>

Answer 1

Why do you use a capital in your filename? It's something you questioned yourself already.

Could you rename the file from Test.php to test.php?

And change

<filename plugin="Test">Test.php</filename>

to

<filename plugin="test">test.php</filename>

And do the same with language files.

btw: not related to your issue, but two thing to make it a bit easier:

1. you don't need to add the language in the file name:

language/en-GB/en-GB.plg_content_test.ini

can become

language/en-GB/plg_content_test.ini

and you can make it yourself easier: add

<folder>language</folder>

and remove the whole <languages folder="administrator/language"> [..] <languages> part

edit: Could you try changing your xml manifest to:

<?xml version="1.0" encoding="utf-8"?>
<extension version="4.0" type="plugin" group="content" method="upgrade">

    <name>plg_content_test</name>
    
    <files>
        <filename plugin="test">test.php</filename>
        <folder>language</folder>
    </files>

</extension>

and create a /language/en-GB/ in your plugin folder with files:

• plg_content_test.ini
• plg_content_test.sys.ini