copyWith throws TypeError when built for web

[phr4fh]

Hi, thanks for your awesome library! I just encountered a bug that was extremely difficult to trace and I don't know what happens here exactly...

I'm using Message.copyWith in the process of creating my messages to diplay them in a chat UI. On Flutter Web, the following code throws a TypeError:

   flyerTypes.Message method1(flyerTypes.Message raw) {
    return raw.copyWith(id: "msg001"); // this throws TypeError: Instance of '_Type': type '_Type' is not a subtype of type 'Map<String, dynamic>?'
   }

I fixed it by passing metadata as parameter to copyWith:

   flyerTypes.Message method2(flyerTypes.Message raw) {
    return raw.copyWith(id: "msg002", metadata: raw.metadata); // this works fine
   }

• It is also fine (both ways) on Android, iOS and Windows.
• It is also fine when I debug it locally in the browser.
• Only when built and deployed to docker, it results in TypeError: Instance of '_Type': type '_Type' is not a subtype of type 'Map<String, dynamic>?'

Could it be something to do with dynamic metadata = _Unset in the copyWith implementation? Maybe minifying to JS optimizes the _Unset type away?

[demchenkoalex]

Hello. Oh man this looks hard haha.. the dynamic unset approach is the only way to make copyWith work with values and nulls without resetting all fields of the message. I already re-written this library for my upcoming v2 implementation and I used the same approach, cause there is literally no alternative. I wonder what can I even do here 🤔

[phr4fh]

Is something like the copy_with_extension not an option?

[demchenkoalex]

did not know about this package, let me test it :)

[demchenkoalex]

For the v2 types I was able to use freezed to generate pretty much everything, my final types would look something like this:

import 'package:freezed_annotation/freezed_annotation.dart';

import 'epoch_date_time_converter.dart';
import 'link_preview.dart';

part 'message.freezed.dart';
part 'message.g.dart';

@Freezed(unionKey: 'type', fallbackUnion: 'unsupported')
sealed class Message with _$Message {
  const factory Message.text({
    required String id,
    required String senderId,
    @EpochDateTimeConverter() required DateTime timestamp,
    Map<String, dynamic>? metadata,
    required String text,
    LinkPreview? linkPreview,
  }) = TextMessage;

  const factory Message.image({
    required String id,
    required String senderId,
    @EpochDateTimeConverter() required DateTime timestamp,
    Map<String, dynamic>? metadata,
    required String source,
    String? thumbhash,
    String? blurhash,
    double? width,
    double? height,
  }) = ImageMessage;

  const factory Message.unsupported({
    required String id,
    required String senderId,
    @EpochDateTimeConverter() required DateTime timestamp,
    Map<String, dynamic>? metadata,
  }) = UnsupportedMessage;

  factory Message.fromJson(Map<String, dynamic> json) =>
      _$MessageFromJson(json);
}