Error using the generated class: Expecting a fromJson constructor with exactly one positional parameter

[bsr203]

Hello,

I have issue using a generated class as the json code generator gives below error.

Expecting a `fromJson` constructor with exactly one positional parameter. The only extra parameters allowed are functions of the form `T Function(Object?) fromJsonT` where `T` is a type parameter of the target type.
package:proj/gen/v1/proj/api/core.pb.dart:179:21
    ╷
179 │   factory TimeRange.fromJson($core.String i, [$pb.ExtensionRegistry r = $pb.ExtensionRegistry.EMPTY]) => create()..mergeFromJson(i, r);
    │                     ^^^^^^^^
    ╵
[INFO] Running build completed, took 3.7s

Message:

message TimeRange {
  int32 lower = 1;
  int32 upper = 2;
  TimeUnit unit = 3;
}

enum TimeUnit {
  TIME_UNIT_UNSPECIFIED = 0;
  TIME_UNIT_DAY = 1;
  TIME_UNIT_YEAR = 2;
}

relevant part of the the generated code

TimeRange._() : super();
  ....
  factory TimeRange.fromBuffer($core.List<$core.int> i, [$pb.ExtensionRegistry r = $pb.ExtensionRegistry.EMPTY]) => create()..mergeFromBuffer(i, r);
  factory TimeRange.fromJson($core.String i, [$pb.ExtensionRegistry r = $pb.ExtensionRegistry.EMPTY]) => create()..mergeFromJson(i, r);
  @$core.Deprecated(

I am using the generated type like,

@freezed
class Entity with _$Entity {
  const factory Entity({
    ...
    required api_core.TimeRange dur,
  }) = _Entity;

and the json_serializable is throwing above error.

I use the latest protoc_plugin

Is it possible to provide a constructor with one positional parameter?

Please let me know for any details. Thanks.

[osa1]

Are you adding @JsonSerializable() to a protoc_plugin generated class?

[bsr203]

Sorry for the late response. My class is generated with protoc plugin, so not adding@JsonSerializable() . Seems like there is no easy way to do it. see google/json_serializable.dart#1017. Please close it if it is not possible easily.