Bug: dart_mappable_plugin generates concrete class conflicting with freezed v3+ abstract requirement

[YaminMahdi]

Bug Report

Summary

dart_mappable_plugin generates a concrete class definition that conflicts with the required abstract or sealed modifier introduced in freezed v3+. This causes build errors when using both packages together.

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Following dependencies in my pubspec.yaml:

dependencies:
  freezed_annotation: ^3.1.0
  json_annotation: ^4.9.0

dev_dependencies:
  build_runner: ^2.5.4
  freezed: ^3.1.0
  json_serializable: ^6.9.5

❌ Actual Behavior

The dart_mappable_plugin generates a concrete class Person, which clashes with the expected abstract base class for freezed v3+. This leads to build errors like:

Error: Missing concrete implementations of 'getter mixin _$Person on Object.firstName',
       'getter mixin _$Person on Object.lastName',
       'getter mixin _$Person on Object.age',
       and 'mixin _$Person on Object.toJson'.

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✅ Expected Behavior

The generated code should respect the freezed requirement for abstract classes and avoid conflicting with them.

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💡 Solution

Simply add the abstract keyword to the class definition.
This resolves the conflict and satisfies both code generators:

@freezed
-class Person with _$Person {
+abstract class Person with _$Person {
  const factory Person({
    required String firstName,
    required String lastName,
    required int age,
  }) = _Person;

  factory Person.fromJson(Map<String, Object?> json) => _$PersonFromJson(json);
}

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Reference

• freezed v3 Migration Guide