@Default using static const and fromJson will generate code that does not compile

[mono0926]

I've tested this at 0.9.1 , supported by #75.

---

As tested here, this works well:

@freezed
abstract class StaticConstDefault with _$StaticConstDefault {
  factory StaticConstDefault([@Default(Duration.zero) Duration value]) =
      _StaticConstDefault;
}

But, if fromJson line is added, it failed to compile.

@freezed
abstract class StaticConstDefault with _$StaticConstDefault {
  factory StaticConstDefault([@Default(Duration.zero) Duration value]) =
      _StaticConstDefault;
  // This failed to compile
  factory StaticConstDefault.fromJson(Map<String, dynamic> json) =>
      _$StaticConstDefaultFromJson(json);
}

Error log:

[SEVERE] json_serializable:json_serializable on x.dart:
Error running JsonSerializableGenerator
Error with `@JsonKey` on `value`. `defaultValue` is `Duration`, it must be a literal.
package:anycommu/model/entity/kpt/kpt.freezed.dart:45:18
   ╷
45 │   final Duration value;
   │                  ^^^^^
   ╵

[rrousselGit]

Duration is not serializable. You need to deserialize it into a timestamp

[rrousselGit]

Actually it doesn't sound to be related to if Duration is serializable or not (as no default value works).

It sounds like JsonKey just doesn't support Duration as a value. Maybe make an issue on json_serializable? I can't do anything about it.

[mono0926]

@rrousselGit

json_serializable supports Duration serialization(google/json_serializable.dart#336).

This is generated automatically and if @Default(Duration.zero) is omitted, everything works well.

_$_StaticConstDefault _$_$_StaticConstDefaultFromJson(
    Map<String, dynamic> json) {
  return _$_StaticConstDefault(
    json['value'] == null ? null : Duration(microseconds: json['value'] as int),
  );
}

Map<String, dynamic> _$_$_StaticConstDefaultToJson(
        _$_StaticConstDefault instance) =>
    <String, dynamic>{
      'value': instance.value?.inMicroseconds,
    };

---

It sounds like JsonKey just doesn't support Duration as a value. Maybe make an issue on json_serializable? I can't do anything about it.

Okay, thanks 👍
I'll investigate it a little more, and I might make an issue on json_serializable.

[rrousselGit]

In the mean time you could add an extra @JsonKey() next to the @Default.

But this means deserializing the json will not add the default value

[gysipos]

Just to add my experience with the issue: List of enums as @default value will cause the same error, for example:

    @Default([PoliKind.ESTATE]) 
    List<PoliKind> kinds, //always ESTATE

The enum:

  enum PoliKind {
    @JsonValue("AD")
    AD,
    @JsonValue("ESTATE")
    ESTATE
  }

the result:

Error with `@JsonKey` on `kinds`. `defaultValue` is `List > PoliKind`, it must be a literal.

[rrousselGit]

Unfortunately I don't think there's anything I can do here. It's json_serializable that is rejecting the default value.

But the @Default(...) @JsonKey() workaround seem to be enough. So I'll close this

[PiN73]

Starting from freezed 2, this will work

@freezed
class Cart with _$Cart {
  const factory Cart({
    @Default([]) List<int> items,
  }) = _Cart;

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

@freezed
class User with _$User {
  const factory User({
    @Default(Cart()) Cart cart,
  }) = _User;

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

Then Cart.fromJson({}).items or User.fromJson({}).cart.items will give you []

---

Before freezed 2, use this workaround:

@Default(const Cart()) @JsonKey(fromJson: _CartFromNullableJson) Cart cart,

Cart _CartFromNullableJson(Map<String, dynamic>? json) =>
    json == null ? Cart() : Cart.fromJson(json);