ThemeEngineExtensionList.php

<?php

namespace Drupal\Core\Extension;


/**
 * Provides a list of available theme engines.
 *
 * @internal
 *   This class is not yet stable and therefore there are no guarantees that the
 *   internal implementations including constructor signature and protected
 *   properties / methods will not change over time. This will be reviewed after
 *   https://www.drupal.org/project/drupal/issues/2940481
 */
class ThemeEngineExtensionList extends ExtensionList {
    
    /**
     * {@inheritdoc}
     */
    protected $defaults = [
        'dependencies' => [],
        'description' => '',
        'package' => 'Other',
        'version' => NULL,
        'php' => \Drupal::MINIMUM_PHP,
    ];
    
    /**
     * {@inheritdoc}
     */
    protected function getInstalledExtensionNames() {
        // Theme engines do not have an 'install' state, so return names of all
        // discovered theme engines.
        return array_keys($this->extensions);
    }

}