Summary

To get around some B/C issues with using Composer's autoloader, we created a fork of the full Composer\Autoload\ClassLoader class and modified its loadClass() method to hook into Joomla's own autoloader.

Issues

1) A complete fork of the class is not necessary for the single method call. We should be able to safely extend Composer's ClassLoader and just override the method we need to. From my testing, this is possible and works without issue.

2) If you have packages installed via a Composer global installation, for example composer global require phpunit/phpunit (to install PHPUnit globally instead of a per-project dependency), executing those global scripts on the Joomla installation fails due to a redeclared class (ClassLoader) and function (includeFile). Now that our loader is extending ClassLoader, we can make our class wise and only import the class/file included with Joomla if another script has already imported ClassLoader.

Testing Instructions

Within the CMS, testing is simple - Apply the patch

If you have packages Composer packages globally installed and are executing those on a Joomla installation, pre-patch you should get a failure due to the redeclared class/function. Post-patch, scripts should function properly.