Classes not being generated with class-modifiers

[JosephNK]

flutter doctor

Doctor summary (to see all details, run flutter doctor -v):
[✓] Flutter (Channel stable, 3.19.0, on macOS 13.4 22F66 darwin-x64, locale ko-KR)
... ...
...

Dependency Info
- built_value: ^8.9.1
- build_runner: ^2.4.8
- built_value_generator: ^8.9.1
- analyzer: ^6.4.1

api_service_response.dart

part 'api_service_response.g.dart';

@BuiltValue(instantiable: false)
abstract class APIServiceResponse extends Object with APIServiceResponseValues {
  APIServiceResponse rebuild(void Function(APIServiceResponseBuilder) updates);
  APIServiceResponseBuilder toBuilder();
}

mixin APIServiceResponseValues {
  @BuiltValueField(wireName: 'status_cd')
  String? get statusCd;
  ...
}

$ dart pub run build_runner build --delete-conflicting-outputs

[SEVERE] built_value_generator:built_value on lib/src/services/response/base/api_service_response.dart (cached):
An error `FormatterException` occurred while formatting the generated source for
  `package:flutter_nano_chatbot/src/services/response/base/api_service_response.dart`
which was output to
  `lib/src/services/response/base/api_service_response.built_value.g.part`.
This may indicate an issue in the generator, the input source code, or in the
source formatter.
Could not format because the source could not be parsed:

line 7, column 10 of .: This requires the 'class-modifiers' language feature to be enabled.
  ╷
7 │ abstract mixin class APIServiceResponseBuilder {
  │          ^^^^^

Is there a solution?

[JosephNK]

I succeeded by using the @dart directive as shown below.
I don't know if this is the right way.
Is there any other way?

// @dart = 2.18
import 'package:built_value/built_value.dart';

part 'api_service_response.g.dart';

@BuiltValue(instantiable: false)
abstract class APIServiceResponse extends Object with APIServiceResponseValues {
  APIServiceResponse rebuild(void Function(APIServiceResponseBuilder) updates);
  APIServiceResponseBuilder toBuilder();
}
... ...
...

[JosephNK]

I tried again after removing the pubspec.lock file and it worked.
There seems to have been an issue with dart 3.0 in pubspec dependencies.

[davidmorgan]

Interesting! Not sure how that happened. If you (or anyone else reading this) figure out a way to repro, please let me know. Thanks.