function class_declaration() {
    $line = '';
    $line .= "interface {$this->component_data['plain_class_name']}";
    if ($this->component_data['parent_interface_names']) {
      $line .= ' extends ';
      $line .= implode(', ', $this->component_data['parent_interface_names']);
    }
    $line .= ' {';

    return [
      $line,
    ];
  }