Adding case insensitive to enum based on loading JsonEnum config

json_annotation/lib/src/enum_helpers.dart

@@ -4,6 +4,19 @@
 
 import 'json_key.dart';
 
+/// Compare an enum value against a source using case-insensitive.
+///
+/// Exposed only for code generated by `package:json_serializable`.
+/// Not meant to be used directly by user code.
+bool $enumCompareCaseInsensitive(String arg1, Object arg2) => arg2 is String &&
+      (arg1.toLowerCase() == arg2.toLowerCase());
+
+/// Compare an enum value against a source.
+///
+/// Exposed only for code generated by `package:json_serializable`.
+/// Not meant to be used directly by user code.
+bool $enumCompareStandard<V>(V arg1, Object arg2) => arg1 == arg2;
+
 /// Returns the key associated with value [source] from [enumValues], if one
 /// exists.
 ///
@@ -18,13 +31,16 @@ K? $enumDecodeNullable<K extends Enum, V>(
   Map<K, V> enumValues,
   Object? source, {
   Enum? unknownValue,
+  bool Function(V arg1, Object arg2)? comparator,
 }) {
   if (source == null) {
     return null;
   }
 
+  comparator ??= $enumCompareStandard;
+
   for (var entry in enumValues.entries) {
-    if (entry.value == source) {
+    if (comparator(entry.value, source)) {
       return entry.key;
     }
   }
@@ -65,6 +81,7 @@ K $enumDecode<K extends Enum, V>(
   Map<K, V> enumValues,
   Object? source, {
   K? unknownValue,
+  bool Function(V arg1, Object arg2)? comparator,
 }) {
   if (source == null) {
     throw ArgumentError(
@@ -73,8 +90,9 @@ K $enumDecode<K extends Enum, V>(
     );
   }
 
+  comparator ??= $enumCompareStandard;
   for (var entry in enumValues.entries) {
-    if (entry.value == source) {
+    if (comparator(entry.value, source)) {
       return entry.key;
     }
   }

json_annotation/lib/src/json_enum.dart

@@ -13,6 +13,7 @@ class JsonEnum {
   const JsonEnum({
     this.alwaysCreate = false,
     this.fieldRename = FieldRename.none,
+    this.caseInsensitive = false,
   });
 
   /// If `true`, `_$[enum name]EnumMap` is generated for in library containing
@@ -34,4 +35,16 @@ class JsonEnum {
   /// Note: the value for [JsonValue.value] takes precedence over this option
   /// for entries annotated with [JsonValue].
   final FieldRename fieldRename;
+
+  /// if `true`, enum comparison will be done using case-insensitive.
+  ///
+  /// The default, `false`, means enum comparison will be done using
+  /// case-sensitive.
+  final bool caseInsensitive;
+
+  factory JsonEnum.fromJson(Map<String, dynamic> json) {
+    final caseInsensitive = json['case_insensitive'] as bool?;
+    return // caseInsensitive == null ? null :
+      JsonEnum(caseInsensitive: caseInsensitive ?? false);
+  }
 }

json_serializable/lib/src/enum_utils.dart

@@ -75,6 +75,7 @@ JsonEnum _fromAnnotation(DartObject? dartObject) {
   final reader = ConstantReader(dartObject);
   return JsonEnum(
       alwaysCreate: reader.read('alwaysCreate').literalValue as bool,
+      caseInsensitive: reader.read('caseInsensitive').literalValue as bool,
       fieldRename: enumValueForDartObject(
         reader.read('fieldRename').objectValue,
         FieldRename.values,

json_serializable/lib/src/json_key_utils.dart

@@ -30,11 +30,15 @@ KeyConfig _from(FieldElement element, ClassConfig classAnnotation) {
   final ctorParamDefault = classAnnotation.ctorParamDefaults[element.name];
 
   if (obj.isNull) {
+    final enumObj = jsonEnumAnnotation(element);
+
     return _populateJsonKey(
       classAnnotation,
       element,
       defaultValue: ctorParamDefault,
       ignore: classAnnotation.ignoreUnannotated,
+      caseInsensitive: enumObj.isNull ? null :
+        enumObj.read('caseInsensitive').literalValue as bool?,
     );
   }
 
@@ -241,6 +245,7 @@ KeyConfig _populateJsonKey(
   String? readValueFunctionName,
   bool? required,
   String? unknownEnumValue,
+  bool? caseInsensitive,
 }) {
   if (disallowNullValue == true) {
     if (includeIfNull == true) {
@@ -261,6 +266,7 @@ KeyConfig _populateJsonKey(
     readValueFunctionName: readValueFunctionName,
     required: required ?? false,
     unknownEnumValue: unknownEnumValue,
+    caseInsensitive: caseInsensitive,
   );
 }
 

json_serializable/lib/src/type_helpers/config_types.dart

@@ -21,6 +21,8 @@ class KeyConfig {
 
   final String? unknownEnumValue;
 
+  final bool? caseInsensitive;
+
   final String? readValueFunctionName;
 
   KeyConfig({
@@ -32,6 +34,7 @@ class KeyConfig {
     required this.readValueFunctionName,
     required this.required,
     required this.unknownEnumValue,
+    required this.caseInsensitive,
   });
 }
 

json_serializable/lib/src/type_helpers/enum_helper.dart

@@ -71,6 +71,8 @@ class EnumHelper extends TypeHelper<TypeHelperContextWithConfig> {
       expression,
       if (jsonKey.unknownEnumValue != null)
         'unknownValue: ${jsonKey.unknownEnumValue}',
+      if ((jsonKey.caseInsensitive ?? false) == true)
+        r'comparator: $enumCompareCaseInsensitive',
     ];
 
     return '$functionName(${args.join(', ')})';

json_serializable/lib/src/utils.dart

@@ -13,6 +13,8 @@ import 'type_helpers/config_types.dart';
 
 const _jsonKeyChecker = TypeChecker.fromRuntime(JsonKey);
 
+const _jsonEnumChecker = TypeChecker.fromRuntime(JsonEnum);
+
 DartObject? _jsonKeyAnnotation(FieldElement element) =>
     _jsonKeyChecker.firstAnnotationOf(element) ??
     (element.getter == null
@@ -22,6 +24,14 @@ DartObject? _jsonKeyAnnotation(FieldElement element) =>
 ConstantReader jsonKeyAnnotation(FieldElement element) =>
     ConstantReader(_jsonKeyAnnotation(element));
 
+DartObject? _jsonEnumAnnotation(Element? element) =>
+    (element != null && element is ClassElement) ?
+      _jsonEnumChecker.firstAnnotationOf(element)
+      : null;
+
+ConstantReader jsonEnumAnnotation(FieldElement element) =>
+  ConstantReader(_jsonEnumAnnotation(element.type.element));
+
 /// Returns `true` if [element] is annotated with [JsonKey].
 bool hasJsonKeyAnnotation(FieldElement element) =>
     _jsonKeyAnnotation(element) != null;

json_serializable/test/integration/integration_test.dart

@@ -88,6 +88,12 @@ void main() {
       roundTripOrder(order);
     });
 
+    test('case insensitive map', () {
+      final jsonOrder = {'category': 'CHaRmED'};
+      final order = Order.fromJson(jsonOrder);
+      expect(order.category, Category.charmed);
+    });
+
     test('required, but missing enum value fails', () {
       expect(
           () => Person.fromJson({

json_serializable/test/integration/json_test_common.dart

@@ -6,7 +6,7 @@ import 'dart:collection';
 
 import 'package:json_annotation/json_annotation.dart';
 
-@JsonEnum(fieldRename: FieldRename.kebab)
+@JsonEnum(fieldRename: FieldRename.kebab, caseInsensitive: true)
 enum Category {
   top,
   bottom,