Add aliases to JsonValue to enum value to be decoded from different JSON values

json_annotation/lib/src/enum_helpers.dart

@@ -51,6 +51,53 @@ K? $enumDecodeNullable<K extends Enum, V>(
   return unknownValue;
 }
 
+/// Returns the key associated with value [source] from [decodeMap], if one
+/// exists.
+///
+/// If [unknownValue] is not `null` and [source] is not a value in [decodeMap],
+/// [unknownValue] is returned. Otherwise, an [ArgumentError] is thrown.
+///
+/// If [source] is `null`, `null` is returned.
+///
+/// Exposed only for code generated by `package:json_serializable`.
+/// Not meant to be used directly by user code.
+V? $enumDecodeNullableWithDecodeMap<K, V extends Enum>(
+  Map<K, V> decodeMap,
+  Object? source, {
+  Enum? unknownValue,
+}) {
+  if (source == null) {
+    return null;
+  }
+
+  final decodedValue = decodeMap[source];
+
+  if (decodedValue != null) {
+    return decodedValue;
+  }
+
+  if (unknownValue == JsonKey.nullForUndefinedEnumValue) {
+    return null;
+  }
+
+  if (unknownValue == null) {
+    throw ArgumentError(
+      '`$source` is not one of the supported values: '
+      '${decodeMap.keys.join(', ')}',
+    );
+  }
+
+  if (unknownValue is! V) {
+    throw ArgumentError.value(
+      unknownValue,
+      'unknownValue',
+      'Must by of type `$K` or `JsonKey.nullForUndefinedEnumValue`.',
+    );
+  }
+
+  return unknownValue;
+}
+
 /// Returns the key associated with value [source] from [enumValues], if one
 /// exists.
 ///
@@ -88,3 +135,41 @@ K $enumDecode<K extends Enum, V>(
 
   return unknownValue;
 }
+
+/// Returns the key associated with value [source] from [decodeMap], if one
+/// exists.
+///
+/// If [unknownValue] is not `null` and [source] is not a value in [decodeMap],
+/// [unknownValue] is returned. Otherwise, an [ArgumentError] is thrown.
+///
+/// If [source] is `null`, an [ArgumentError] is thrown.
+///
+/// Exposed only for code generated by `package:json_serializable`.
+/// Not meant to be used directly by user code.
+V $enumDecodeWithDecodeMap<K, V extends Enum>(
+  Map<K, V> decodeMap,
+  Object? source, {
+  V? unknownValue,
+}) {
+  if (source == null) {
+    throw ArgumentError(
+      'A value must be provided. Supported values: '
+      '${decodeMap.keys.join(', ')}',
+    );
+  }
+
+  final decodedValue = decodeMap[source];
+
+  if (decodedValue != null) {
+    return decodedValue;
+  }
+
+  if (unknownValue == null) {
+    throw ArgumentError(
+      '`$source` is not one of the supported values: '
+      '${decodeMap.keys.join(', ')}',
+    );
+  }
+
+  return unknownValue;
+}

json_annotation/lib/src/json_value.dart

@@ -9,5 +9,10 @@ class JsonValue {
   /// Can be a [String] or an [int].
   final dynamic value;
 
-  const JsonValue(this.value);
+  /// Optional values that can be used when deserializing.
+  ///
+  /// The elements of [aliases] must be either [String] or [int].
+  final Set<Object> aliases;
+
+  const JsonValue(this.value, {this.aliases = const {}});
 }

json_serializable/lib/src/enum_utils.dart

@@ -15,6 +15,9 @@ import 'utils.dart';
 String constMapName(DartType targetType) =>
     '_\$${targetType.element!.name}EnumMap';
 
+String constDecodeMapName(DartType targetType) =>
+    '_\$${targetType.element!.name}EnumDecodeMap';
+
 /// If [targetType] is not an enum, return `null`.
 ///
 /// Otherwise, returns `true` if [targetType] is nullable OR if one of the
@@ -38,14 +41,38 @@ String? enumValueMapFromType(
   final enumMap =
       _enumMap(targetType, nullWithNoAnnotation: nullWithNoAnnotation);
 
-  if (enumMap == null) return null;
-
-  final items = enumMap.entries
-      .map((e) => '  ${targetType.element!.name}.${e.key.name}: '
-          '${jsonLiteralAsDart(e.value)},')
-      .join();
-
-  return 'const ${constMapName(targetType)} = {\n$items\n};';
+  final enumAliases =
+      _enumAliases(targetType, nullWithNoAnnotation: nullWithNoAnnotation);
+
+  final valuesItems = enumMap == null
+      ? null
+      : [
+          for (final MapEntry(:key, :value) in enumMap.entries)
+            '  ${targetType.element3!.name3}.${key.name}: '
+                '${jsonLiteralAsDart(value)},',
+        ].join();
+
+  final valuesMap = valuesItems == null
+      ? null
+      : '// ignore: unused_element\n'
+          'const ${constMapName(targetType)} = {\n$valuesItems\n};';
+
+  final decodeItems = enumAliases == null
+      ? null
+      : [
+          for (final MapEntry(:key, :value) in enumAliases.entries)
+            '  ${jsonLiteralAsDart(key)}: '
+                '${targetType.element!.name}.${value.name},',
+        ].join();
+
+  final decodeMap = decodeItems == null
+      ? null
+      : '// ignore: unused_element\n'
+          'const ${constDecodeMapName(targetType)} = {\n$decodeItems\n};';
+
+  return valuesMap == null && decodeMap == null
+      ? null
+      : [valuesMap, decodeMap].join('\n\n');
 }
 
 Map<FieldElement, Object?>? _enumMap(
@@ -73,6 +100,34 @@ Map<FieldElement, Object?>? _enumMap(
   };
 }
 
+Map<Object?, FieldElement>? _enumAliases(
+  DartType targetType, {
+  bool nullWithNoAnnotation = false,
+}) {
+  final targetTypeElement = targetType.element;
+  if (targetTypeElement == null) return null;
+  final annotation = _jsonEnumChecker.firstAnnotationOf(targetTypeElement);
+  final jsonEnum = _fromAnnotation(annotation);
+
+  final enumFields = iterateEnumFields(targetType);
+
+  if (enumFields == null || (nullWithNoAnnotation && !jsonEnum.alwaysCreate)) {
+    return null;
+  }
+
+  return {
+    for (var field in enumFields) ...{
+      _generateEntry(
+        field: field,
+        jsonEnum: jsonEnum,
+        targetType: targetType,
+      ): field,
+      for (var alias in _generateAliases(field: field, targetType: targetType))
+        alias: field,
+    },
+  };
+}
+
 Object? _generateEntry({
   required FieldElement field,
   required JsonEnum jsonEnum,
@@ -138,6 +193,36 @@ Object? _generateEntry({
   }
 }
 
+List<Object?> _generateAliases({
+  required FieldElement field,
+  required DartType targetType,
+}) {
+  final annotation =
+      const TypeChecker.fromRuntime(JsonValue).firstAnnotationOfExact(field);
+
+  if (annotation == null) {
+    return const [];
+  } else {
+    final reader = ConstantReader(annotation);
+
+    final valueReader = reader.read('aliases');
+
+    if (valueReader.validAliasesType) {
+      return [
+        for (final value in valueReader.setValue)
+          ConstantReader(value).literalValue,
+      ];
+    } else {
+      final targetTypeCode = typeToCode(targetType);
+      throw InvalidGenerationSourceError(
+        'The `JsonValue` annotation on `$targetTypeCode.${field.name}` aliases '
+        'should all be of type String or int.',
+        element: field,
+      );
+    }
+  }
+}
+
 const _jsonEnumChecker = TypeChecker.fromRuntime(JsonEnum);
 
 JsonEnum _fromAnnotation(DartObject? dartObject) {
@@ -154,4 +239,10 @@ JsonEnum _fromAnnotation(DartObject? dartObject) {
 
 extension on ConstantReader {
   bool get validValueType => isString || isNull || isInt;
+
+  bool get validAliasesType =>
+      isSet &&
+      setValue.every((element) =>
+          (element.type?.isDartCoreString ?? false) ||
+          (element.type?.isDartCoreInt ?? false));
 }

json_serializable/lib/src/type_helpers/enum_helper.dart

@@ -64,15 +64,15 @@ class EnumHelper extends TypeHelper<TypeHelperContextWithConfig> {
 
     String functionName;
     if (targetType.isNullableType || defaultProvided) {
-      functionName = r'$enumDecodeNullable';
+      functionName = r'$enumDecodeNullableWithDecodeMap';
     } else {
-      functionName = r'$enumDecode';
+      functionName = r'$enumDecodeWithDecodeMap';
     }
 
     context.addMember(memberContent);
 
     final args = [
-      constMapName(targetType),
+      constDecodeMapName(targetType),
       expression,
       if (jsonKey.unknownEnumValue != null)
         'unknownValue: ${jsonKey.unknownEnumValue}',