Mutable Union types not mutable

[Var1377]

When using @unfreezed, union types don't allow mutation

Example:

@unfreezed
class ExampleADT with _$ExampleADT {
  const ExampleADT._();

  factory ExampleADT.firstVariant({required int arg1}) = _ExampleFirstVariant;
  factory ExampleADT.secondVariant({required String arg2}) = _ExampleSecondVariant;

  factory ExampleADT.fromJson(Map<String, dynamic> json) => _$ExampleADTFromJson(json);

  void mutate() => this.map(firstVariant: (value) => value.arg1 = 2, secondVariant: (value) => value.arg2 = "1");
}

Expected Behaviour: Mutation

Actual Behaviour:

There isn’t a setter named 'arg1' in class '_ExampleFirstVariant'.
Try correcting the name to reference an existing setter, or declare the setter.

There isn’t a setter named 'arg2' in class '_ExampleSecondVariant'.
Try correcting the name to reference an existing setter, or declare the setter.