feat: implement first version of sealed class serialization

example/lib/complex_sealed_class_examples.dart

@@ -0,0 +1,36 @@
+import 'package:json_annotation/json_annotation.dart';
+
+part 'complex_sealed_class_examples.g.dart';
+
+@JsonSerializable(unionDiscriminator: 'organization')
+sealed class Organization {
+  final String name;
+
+  Organization({required this.name});
+
+  factory Organization.fromJson(Map<String, dynamic> json) =>
+      _$OrganizationFromJson(json);
+
+  Map<String, dynamic> toJson() => _$OrganizationToJson(this);
+}
+
+@JsonSerializable(unionDiscriminator: 'department')
+sealed class Department extends Organization {
+  final String departmentHead;
+
+  Department({required this.departmentHead, required super.name});
+
+  factory Department.fromJson(Map<String, dynamic> json) =>
+      _$DepartmentFromJson(json);
+}
+
+@JsonSerializable()
+class Team extends Department {
+  final String teamLead;
+
+  Team({
+    required this.teamLead,
+    required super.departmentHead,
+    required super.name,
+  });
+}

example/lib/sealed_class_example.dart

@@ -0,0 +1,32 @@
+import 'package:json_annotation/json_annotation.dart';
+
+part 'sealed_class_example.g.dart';
+
+@JsonSerializable(
+  unionDiscriminator: 'vehicle_type',
+  unionRename: FieldRename.snake,
+)
+sealed class Vehicle {
+  final String vehicleID;
+
+  Vehicle({required this.vehicleID});
+
+  factory Vehicle.fromJson(Map<String, dynamic> json) =>
+      _$VehicleFromJson(json);
+
+  Map<String, dynamic> toJson() => _$VehicleToJson(this);
+}
+
+@JsonSerializable()
+class Car extends Vehicle {
+  final int numberOfDoors;
+
+  Car({required this.numberOfDoors, required super.vehicleID});
+}
+
+@JsonSerializable()
+class Bicycle extends Vehicle {
+  final bool hasBell;
+
+  Bicycle({required this.hasBell, required super.vehicleID});
+}

example/pubspec.yaml

@@ -7,7 +7,7 @@ environment:
 resolution: workspace
 
 dependencies:
-  json_annotation: ^4.9.0
+  json_annotation: ^4.11.0-wip
 
 dev_dependencies:
   # Used by tests. Not required to use `json_serializable`.

json_annotation/CHANGELOG.md

@@ -1,7 +1,9 @@
-## 4.11.0
+## 4.11.0-wip
 
 - Add `JsonSerializable.dateTimeUtc` configuration option. 
   ([#1371](https://github.com/google/json_serializable.dart/issues/1371))
+- Add `JsonSerializable.unionRename` and `JsonSerializable.unionDiscriminator`
+  to support sealed class serialization.
 
 ## 4.10.0
 
@@ -10,6 +12,8 @@
   (Huge thanks to [Chris Sells](https://sellsbrothers.com/) for the PR!)
 - Require `meta: ^1.16.0`
 - Require `sdk: ^3.9.0`
+- Require Dart 3.8
+- Deprecated `FieldRename` in favor of `RenameType`
 
 ## 4.9.0
 

json_annotation/lib/src/allowed_keys_helpers.dart

@@ -79,6 +79,24 @@ class UnrecognizedKeysException extends BadKeyException {
     : super._(map);
 }
 
+/// Exception thrown if there is an unrecognized union type in a JSON map
+/// that was provided during deserialization.
+class UnrecognizedUnionTypeException extends BadKeyException {
+  /// The discriminator that was not recognized.
+  final String unrecognizedType;
+
+  /// The type of the union that was being deserialized.
+  final Type unionType;
+
+  @override
+  String get message =>
+      'Unrecognized type: $unrecognizedType '
+      'for union: $unionType.';
+
+  UnrecognizedUnionTypeException(this.unrecognizedType, this.unionType, Map map)
+    : super._(map);
+}
+
 /// Exception thrown if there are missing required keys in a JSON map that was
 /// provided during deserialization.
 class MissingRequiredKeysException extends BadKeyException {

json_annotation/lib/src/json_serializable.dart

@@ -237,6 +237,20 @@ class JsonSerializable {
   /// `includeIfNull`, that value takes precedent.
   final bool? includeIfNull;
 
+  /// The discriminator key used to identify the union type.
+  ///
+  /// Defaults to `type`.
+  final String? unionDiscriminator;
+
+  /// Defines the automatic naming strategy when converting class names
+  /// to union type names.
+  ///
+  /// With a value [FieldRename.none] (the default), the name of the class is
+  /// used without modification.
+  ///
+  /// See [FieldRename] for details on the other options.
+  final FieldRename? unionRename;
+
   /// A list of [JsonConverter] to apply to this class.
   ///
   /// Writing:
@@ -291,6 +305,8 @@ class JsonSerializable {
     this.genericArgumentFactories,
     this.createPerFieldToJson,
     this.dateTimeUtc,
+    this.unionDiscriminator,
+    this.unionRename,
   });
 
   factory JsonSerializable.fromJson(Map<String, dynamic> json) =>
@@ -311,6 +327,9 @@ class JsonSerializable {
     ignoreUnannotated: false,
     includeIfNull: true,
     genericArgumentFactories: false,
+    dateTimeUtc: false,
+    unionDiscriminator: 'type',
+    unionRename: FieldRename.none,
   );
 
   /// Returns a new [JsonSerializable] instance with fields equal to the
@@ -333,6 +352,9 @@ class JsonSerializable {
     includeIfNull: includeIfNull ?? defaults.includeIfNull,
     genericArgumentFactories:
         genericArgumentFactories ?? defaults.genericArgumentFactories,
+    dateTimeUtc: dateTimeUtc ?? defaults.dateTimeUtc,
+    unionDiscriminator: unionDiscriminator ?? defaults.unionDiscriminator,
+    unionRename: unionRename ?? defaults.unionRename,
   );
 
   Map<String, dynamic> toJson() => _$JsonSerializableToJson(this);

json_annotation/pubspec.yaml

@@ -1,5 +1,5 @@
 name: json_annotation
-version: 4.11.0
+version: 4.11.0-wip
 description: >-
   Classes and helper functions that support JSON code generation via the
   `json_serializable` package.

json_serializable/CHANGELOG.md

@@ -1,3 +1,8 @@
+## 6.14.0-wip
+
+- Add support for deserializing union json to sealed class
+- Add support for serializing sealed class to union json
+
 ## 6.13.1
 
 - Improve error message when generating code for `Record` types with unsupported
@@ -9,24 +14,6 @@
 - Require `source_gen: ^4.1.2`
 - Require `source_helper: ^1.3.10`
 
-## 6.13.0
-
-- Fix schema generation for many different types of fields. 
-  ([#1549](https://github.com/google/json_serializable.dart/issues/1549))
-- Support `JsonSerializable.dateTimeUtc` configuration option. 
-  ([#1371](https://github.com/google/json_serializable.dart/issues/1371))
-- Remove `json_schema` from `dependencies` (it is only used in tests).
-
-## 6.12.0
-
-- Support `JsonKey` annotation on constructor parameters.
-- Add support for `JsonSerializable(createJsonSchema: true)`.
-  (Huge thanks to [Chris Sells](https://sellsbrothers.com/) for the PR!)
-
-## 6.11.4
-
-- Allow `analyzer: >=9.0.0 <11.0.0`
-
 ## 6.11.3
 
 - Require `analyzer: ^9.0.0`
@@ -61,8 +48,6 @@
 
 ## 6.10.0
 
-- Required `analyzer: ^7.4.0`.
-- Switch to analyzer element2 model and `build: ^3.0.0-dev`.
 - Move `package:collection` to a dev dependency.
 - Use new `null-aware element` feature in generated code.
 - Require Dart 3.8