GrumPHP\Configuration\Compiler\ExtensionCompilerPass::process PHP Method

    public function process(ContainerBuilder $container)
    {
        $extensions = $container->getParameter('extensions');
        $extensions = is_array($extensions) ? $extensions : [];
        foreach ($extensions as $extensionClass) {
            if (!class_exists($extensionClass)) {
                throw new RuntimeException(sprintf('Invalid extension class specified: %s', $extensionClass));
            }
            $extension = new $extensionClass();
            if (!$extension instanceof ExtensionInterface) {
                throw new RuntimeException(sprintf('Extension class must implement ExtensionInterface. But `%s` is not.', $extensionClass));
            }
            $extension->load($container);
        }
    }