anchor.diff:   */
   class BottomTypeImpl extends TypeImpl {
     /**
  -   * The unique instance of this class, with indeterminate nullability.
  -   */
  -  static final BottomTypeImpl instance = instanceIndeterminate;
  -
  -  /**
  -   * The unique instance of this class, nullable.
  -   */
  -  static final BottomTypeImpl instanceNullable =
  -      new BottomTypeImpl._(NullabilitySuffix.question);
  -
  -  /**
  -   * The unique instance of this class, with indeterminate nullability.
  -   */
  -  static final BottomTypeImpl instanceIndeterminate =
  -      new BottomTypeImpl._(NullabilitySuffix.star);
  -
  -  /**
  -   * The unique instance of this class, non-nullable.
  -   */
  -  static final BottomTypeImpl instanceNonNullable =
  -      new BottomTypeImpl._(NullabilitySuffix.none);
  -
  -  @override
  -  final NullabilitySuffix nullabilitySuffix;
  +   * The unique instance of this class.
  +   */
  +  static final BottomTypeImpl instance = new BottomTypeImpl._();
   
     /**
      * Prevent the creation of instances of this class.
      */
  -  BottomTypeImpl._(this.nullabilitySuffix) : super(null, "<bottom>");
  +  BottomTypeImpl._() : super(null, "<bottom>");
   
     @override
     int get hashCode => 0;
   
     @override
     bool get isBottom => true;
  +
  +  @override
  +  NullabilitySuffix get nullabilitySuffix => NullabilitySuffix.none;
   
     @override
     bool operator ==(Object object) => identical(object, this);
  
positive.code:   /**
     * Constructor used by [CircularTypeImpl].
     */
    DynamicTypeImpl._circular(this.nullabilitySuffix)
        : super(instance.element, Keyword.DYNAMIC.lexeme);
  
    @override
    int get hashCode => 1;
  
    @override
    bool get isDynamic => true;
  
    @override
    bool operator ==(Object object) => identical(object, this);
  
negative.code:  */
  class CircularFunctionTypeImpl extends DynamicTypeImpl
      implements _FunctionTypeImplLazy {
    CircularFunctionTypeImpl() : super._circular();
  
    @override
    List<ParameterElement> get baseParameters => const <ParameterElement>[];
  