Macro API can't generate new types based on methods and properties from the base class

[tilucasoli]

I was trying to use the new dart feature Macro to generate the repetitive code in the Mix framework (@leoafarias). Initially, I aimed to simplify the API by generating new classes from a base class. For instance:

@GenerateModifier()
class OpacityModifier {
  final double opacity;

  const OpacityModifier(this.opacity);

  @override
  Widget build(Widget child) {
    assert(
      opacity >= 0.0 && opacity <= 1.0,
      'The opacity must be between 0.0 and 1.0 (inclusive).',
    );

    return Opacity(opacity: opacity, child: child);
  }
}

and then it will generate three more classes based on these properties and methods, OpacityModifierSpec, OpacityModifierAttribute, and OpacityUtility, they will be like:

class OpacityModifierSpec extends WidgetModifierSpec<OpacityModifierSpec> {
  final double opacity;
  const OpacityModifierSpec(this.opacity);

  @override
  OpacityModifierSpec lerp(OpacityModifierSpec? other, double t) {
    return OpacityModifierSpec(
      lerpDouble(opacity, other?.opacity, t) ?? opacity,
    );
  }

  @override
  OpacityModifierSpec copyWith({double? opacity}) {
    return OpacityModifierSpec(opacity ?? this.opacity);
  }

  @override
  get props => [opacity];

  @override
  Widget build(Widget child) {
    assert(
      opacity >= 0.0 && opacity <= 1.0,
      'The opacity must be between 0.0 and 1.0 (inclusive).',
    );

    return Opacity(opacity: opacity, child: child);
  }
}

class OpacityModifierAttribute extends WidgetModifierAttribute<
    OpacityModifierAttribute, OpacityModifierSpec> {
  final double opacity;
  const OpacityModifierAttribute(this.opacity);

  @override
  OpacityModifierAttribute merge(OpacityModifierAttribute? other) {
    return OpacityModifierAttribute(other?.opacity ?? opacity);
  }

  @override
  OpacityModifierSpec resolve(MixData mix) {
    return OpacityModifierSpec(opacity);
  }

  @override
  get props => [opacity];
}

class OpacityUtility<T extends Attribute>
    extends MixUtility<T, OpacityModifierAttribute> {
  const OpacityUtility(super.builder);
  T call(double value) => builder(OpacityModifierAttribute(value));
}

The problem is that the ClassTypeBuilder on ClassTypesMacro can't return the properties and methods. Why can't ClassTypesMacro access these values? What do you suggest to solve this?