Generate EnumMap without as a field of a class

Author: LichKing-2234

json_serializable/lib/src/json_serializable_generator.dart

@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:analyzer/dart/element/element.dart';
+import 'package:analyzer/dart/element/type.dart';
 import 'package:build/build.dart';
 import 'package:json_annotation/json_annotation.dart';
 import 'package:source_gen/source_gen.dart';
@@ -13,6 +14,7 @@ import 'type_helper.dart';
 import 'type_helpers/big_int_helper.dart';
 import 'type_helpers/date_time_helper.dart';
 import 'type_helpers/duration_helper.dart';
+import 'type_helpers/enum_helper.dart';
 import 'type_helpers/json_helper.dart';
 import 'type_helpers/uri_helper.dart';
 
@@ -76,6 +78,14 @@ class JsonSerializableGenerator
       );
     }
 
+    final targetType = element.thisType;
+    if (targetType is InterfaceType && targetType.element.isEnum) {
+      final memberContent = enumValueMapFromType(targetType);
+      if (memberContent != null) {
+        return [enumDecodeHelper, enumDecodeHelperNullable, memberContent];
+      }
+    }
+
     final helper = GeneratorHelper(_settings, element, annotation);
     return helper.generate();
   }

json_serializable/lib/src/type_helpers/enum_helper.dart

@@ -20,7 +20,7 @@ class EnumHelper extends TypeHelper<TypeHelperContextWithConfig> {
     String expression,
     TypeHelperContextWithConfig context,
   ) {
-    final memberContent = _enumValueMapFromType(targetType);
+    final memberContent = enumValueMapFromType(targetType);
 
     if (memberContent == null) {
       return null;
@@ -38,18 +38,18 @@ class EnumHelper extends TypeHelper<TypeHelperContextWithConfig> {
     TypeHelperContextWithConfig context,
     bool defaultProvided,
   ) {
-    final memberContent = _enumValueMapFromType(targetType);
+    final memberContent = enumValueMapFromType(targetType);
 
     if (memberContent == null) {
       return null;
     }
 
-    context.addMember(_enumDecodeHelper);
+    context.addMember(enumDecodeHelper);
 
     String functionName;
     if (targetType.isNullableType || defaultProvided) {
       functionName = r'_$enumDecodeNullable';
-      context.addMember(_enumDecodeHelperNullable);
+      context.addMember(enumDecodeHelperNullable);
     } else {
       functionName = r'_$enumDecode';
     }
@@ -71,7 +71,7 @@ class EnumHelper extends TypeHelper<TypeHelperContextWithConfig> {
 String _constMapName(DartType targetType) =>
     '_\$${targetType.element!.name}EnumMap';
 
-String? _enumValueMapFromType(DartType targetType) {
+String? enumValueMapFromType(DartType targetType) {
   final enumMap = enumFieldsMap(targetType);
 
   if (enumMap == null) {
@@ -86,7 +86,7 @@ String? _enumValueMapFromType(DartType targetType) {
   return 'const ${_constMapName(targetType)} = {\n$items\n};';
 }
 
-const _enumDecodeHelper = r'''
+const enumDecodeHelper = r'''
 K _$enumDecode<K, V>(
   Map<K, V> enumValues,
   Object? source, {
@@ -113,7 +113,7 @@ K _$enumDecode<K, V>(
   ).key;
 }''';
 
-const _enumDecodeHelperNullable = r'''
+const enumDecodeHelperNullable = r'''
 K? _$enumDecodeNullable<K, V>(
   Map<K, V> enumValues,
   dynamic source, {