feat: Add JsonSerializable(createJsonMeta)

json_annotation/lib/src/json_serializable.dart

@@ -6,6 +6,7 @@ import 'package:meta/meta_meta.dart';
 
 import 'allowed_keys_helpers.dart';
 import 'checked_helpers.dart';
+import 'enum_helpers.dart';
 import 'json_converter.dart';
 import 'json_key.dart';
 
@@ -64,6 +65,13 @@ class JsonSerializable {
   /// This setting has no effect if [createFactory] is `false`.
   final String? constructor;
 
+  /// If `true` (defaults to false), a private, static `_$ExampleJsonMeta`
+  /// constant is created in the generated part file.
+  ///
+  /// This constant can be used by other code-generators to support features
+  /// such as [fieldRename].
+  final bool? createJsonMeta;
+
   /// If `true` (the default), a private, static `_$ExampleFromJson` method
   /// is created in the generated part file.
   ///
@@ -231,6 +239,7 @@ class JsonSerializable {
     this.anyMap,
     this.checked,
     this.constructor,
+    this.createJsonMeta,
     this.createFactory,
     this.createToJson,
     this.disallowUnrecognizedKeys,

json_serializable/lib/src/encoder_helper.dart

@@ -16,6 +16,26 @@ import 'unsupported_type_error.dart';
 abstract class EncodeHelper implements HelperCore {
   String _fieldAccess(FieldElement field) => '$_toJsonParamName.${field.name}';
 
+  /// Generates an object containing metadatas related to the encoding,
+  /// destined to be used by other code-generators.
+  String createJsonMeta(Set<FieldElement> accessibleFieldSet) {
+    assert(config.createJsonMeta);
+
+    final buffer =
+        StringBuffer('const _\$${element.name}JsonMeta = <String, String> {');
+
+    for (final field in accessibleFieldSet) {
+      buffer.writeln(
+        '${escapeDartString(field.name)}: '
+        '${escapeDartString(nameAccess(field))},',
+      );
+    }
+
+    buffer.write('};');
+
+    return buffer.toString();
+  }
+
   Iterable<String> createToJson(Set<FieldElement> accessibleFields) sync* {
     assert(config.createToJson);
 

json_serializable/lib/src/generator_helper.dart

@@ -108,6 +108,10 @@ class GeneratorHelper extends HelperCore with EncodeHelper, DecodeHelper {
       },
     );
 
+    if (config.createJsonMeta) {
+      yield createJsonMeta(accessibleFieldSet);
+    }
+
     if (config.createToJson) {
       yield* createToJson(accessibleFieldSet);
     }

json_serializable/lib/src/type_helpers/config_types.dart

@@ -45,6 +45,7 @@ class ClassConfig {
   final String constructor;
   final bool createFactory;
   final bool createToJson;
+  final bool createJsonMeta;
   final bool disallowUnrecognizedKeys;
   final bool explicitToJson;
   final FieldRename fieldRename;
@@ -60,6 +61,7 @@ class ClassConfig {
     required this.constructor,
     required this.createFactory,
     required this.createToJson,
+    required this.createJsonMeta,
     required this.disallowUnrecognizedKeys,
     required this.explicitToJson,
     required this.fieldRename,
@@ -76,6 +78,8 @@ class ClassConfig {
         checked: config.checked ?? ClassConfig.defaults.checked,
         anyMap: config.anyMap ?? ClassConfig.defaults.anyMap,
         constructor: config.constructor ?? ClassConfig.defaults.constructor,
+        createJsonMeta:
+            config.createJsonMeta ?? ClassConfig.defaults.createJsonMeta,
         createFactory:
             config.createFactory ?? ClassConfig.defaults.createFactory,
         createToJson: config.createToJson ?? ClassConfig.defaults.createToJson,
@@ -101,6 +105,7 @@ class ClassConfig {
     constructor: '',
     createFactory: true,
     createToJson: true,
+    createJsonMeta: false,
     disallowUnrecognizedKeys: false,
     explicitToJson: false,
     fieldRename: FieldRename.none,
@@ -115,6 +120,7 @@ class ClassConfig {
         constructor: constructor,
         createFactory: createFactory,
         createToJson: createToJson,
+        createJsonMeta: createJsonMeta,
         ignoreUnannotated: ignoreUnannotated,
         explicitToJson: explicitToJson,
         includeIfNull: includeIfNull,

json_serializable/lib/src/utils.dart

@@ -56,6 +56,7 @@ JsonSerializable _valueForAnnotation(ConstantReader reader) => JsonSerializable(
       constructor: reader.read('constructor').literalValue as String?,
       createFactory: reader.read('createFactory').literalValue as bool?,
       createToJson: reader.read('createToJson').literalValue as bool?,
+      createJsonMeta: reader.read('createJsonMeta').literalValue as bool?,
       disallowUnrecognizedKeys:
           reader.read('disallowUnrecognizedKeys').literalValue as bool?,
       explicitToJson: reader.read('explicitToJson').literalValue as bool?,
@@ -101,6 +102,7 @@ ClassConfig mergeConfig(
     constructor: constructor,
     createFactory: annotation.createFactory ?? config.createFactory,
     createToJson: annotation.createToJson ?? config.createToJson,
+    createJsonMeta: annotation.createJsonMeta ?? config.createJsonMeta,
     disallowUnrecognizedKeys:
         annotation.disallowUnrecognizedKeys ?? config.disallowUnrecognizedKeys,
     explicitToJson: annotation.explicitToJson ?? config.explicitToJson,

json_serializable/test/config_test.dart

@@ -126,6 +126,10 @@ void main() {
             lastLine = "type 'int' is not a subtype of type 'String?' in type "
                 'cast';
             break;
+          case 'create_to_json':
+            lastLine = "type 'int' is not a subtype of type 'bool?' in type "
+                'cast';
+            break;
           default:
             lastLine =
                 "type 'int' is not a subtype of type 'bool?' in type cast";
@@ -152,6 +156,7 @@ const _invalidConfig = {
   'checked': 42,
   'constructor': 42,
   'create_factory': 42,
+  'create_json_meta': 42,
   'create_to_json': 42,
   'disallow_unrecognized_keys': 42,
   'explicit_to_json': 42,

json_serializable/test/integration/integration_test.dart

@@ -7,6 +7,7 @@ import 'package:test/test.dart';
 
 import '../test_utils.dart';
 import 'json_enum_example.dart';
+import 'json_meta_example.dart';
 import 'json_test_common.dart' show Category, Platform, StatusCode;
 import 'json_test_example.dart';
 
@@ -322,4 +323,14 @@ void main() {
       isNull,
     );
   });
+
+  test(r'_$ModelJsonMeta', () {
+    expect(
+      modelMeta,
+      {
+        'firstName': 'first-name',
+        'lastName': 'LAST_NAME',
+      },
+    );
+  });
 }

json_serializable/test/integration/json_meta_example.dart

@@ -0,0 +1,28 @@
+import 'package:json_annotation/json_annotation.dart';
+
+part 'json_meta_example.g.dart';
+
+@JsonSerializable(createJsonMeta: true, fieldRename: FieldRename.kebab)
+class Model {
+  Model({
+    required this.firstName,
+    required this.lastName,
+    this.ignoredName,
+  });
+
+  factory Model.fromJson(Map<String, Object?> json) => _$ModelFromJson(json);
+
+  final String firstName;
+
+  @JsonKey(name: 'LAST_NAME')
+  final String lastName;
+
+  @JsonKey(ignore: true)
+  final String? ignoredName;
+
+  String get fullName => '$firstName $lastName';
+
+  Map<String, Object?> toJson() => _$ModelToJson(this);
+}
+
+const modelMeta = _$ModelJsonMeta;

json_serializable/test/shared_config.dart

@@ -19,6 +19,7 @@ final generatorConfigNonDefaultJson =
   constructor: 'something',
   createFactory: false,
   createToJson: false,
+  createJsonMeta: true,
   disallowUnrecognizedKeys: true,
   explicitToJson: true,
   fieldRename: FieldRename.kebab,

json_serializable/test/test_sources/test_sources.dart

@@ -15,6 +15,7 @@ class ConfigurationImplicitDefaults {
   constructor: '',
   createFactory: true,
   createToJson: true,
+  createJsonMeta: false,
   disallowUnrecognizedKeys: false,
   explicitToJson: false,
   fieldRename: FieldRename.none,