class MockMenuBlockDeriver

class MockMenuBlockDeriver implements DeriverInterface {
    
    /**
     * {@inheritdoc}
     */
    public function getDerivativeDefinition($derivative_id, $base_plugin_definition) {
        $derivatives = $this->getDerivativeDefinitions($base_plugin_definition);
        if (isset($derivatives[$derivative_id])) {
            return $derivatives[$derivative_id];
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function getDerivativeDefinitions($base_plugin_definition) {
        // This isn't strictly necessary, but it helps reduce clutter in
        // DerivativePluginTest::testDerivativeDecorator()'s $expected variable.
        // Since derivative definitions don't need further deriving, we remove this
        // key from the returned definitions.
        unset($base_plugin_definition['deriver']);
        // Here, we create some mock menu block definitions for menus that might
        // exist in a typical Drupal site. In a real implementation, we would query
        // Drupal's configuration to find out which menus actually exist.
        $derivatives = [
            'main_menu' => [
                'label' => t('Main menu'),
            ] + $base_plugin_definition,
            'navigation' => [
                'label' => t('Navigation'),
            ] + $base_plugin_definition,
            'foo' => [
                // Instead of the derivative label, the specific label will be used.
'label' => t('Derivative label'),
                // This setting will be merged in.
'setting' => 'default',
            ] + $base_plugin_definition,
        ];
        return $derivatives;
    }

}