Fix unknown enum handling

protobuf/lib/src/protobuf/proto3_json.dart

@@ -174,6 +174,8 @@ void _mergeFromProto3Json(
   );
 
   void recursionHelper(Object? json, FieldSet fieldSet) {
+    // Convert a JSON object to proto object. Returns `null` on unknown enum
+    // values when [ignoreUnknownFields] is [true].
     Object? convertProto3JsonValue(Object value, FieldInfo fieldInfo) {
       final fieldType = fieldInfo.type;
       switch (PbFieldType.baseType(fieldType)) {
@@ -184,16 +186,14 @@ void _mergeFromProto3Json(
           throw context.parseException('Expected bool value', json);
         case PbFieldType.BYTES_BIT:
           if (value is String) {
-            Uint8List result;
             try {
-              result = base64Decode(value);
+              return base64Decode(value);
             } on FormatException {
               throw context.parseException(
                 'Expected bytes encoded as base64 String',
                 json,
               );
             }
-            return result;
           }
           throw context.parseException(
             'Expected bytes encoded as base64 String',
@@ -294,16 +294,14 @@ void _mergeFromProto3Json(
         case PbFieldType.SFIXED64_BIT:
           if (value is int) return Int64(value);
           if (value is String) {
-            Int64 result;
             try {
-              result = Int64.parseInt(value);
+              return Int64.parseInt(value);
             } on FormatException {
               throw context.parseException(
                 'Expected int or stringified int',
                 value,
               );
             }
-            return result;
           }
           throw context.parseException(
             'Expected int or stringified int',
@@ -409,13 +407,14 @@ void _mergeFromProto3Json(
                   throw context.parseException('Expected a String key', subKey);
                 }
                 context.addMapIndex(subKey);
-                fieldValues[decodeMapKey(
-                  subKey,
-                  mapFieldInfo.keyFieldType,
-                )] = convertProto3JsonValue(
+                final key = decodeMapKey(subKey, mapFieldInfo.keyFieldType);
+                final value = convertProto3JsonValue(
                   subValue,
                   mapFieldInfo.valueFieldInfo,
                 );
+                if (value != null) {
+                  fieldValues[key] = value;
+                }
                 context.popIndex();
               });
             } else {
@@ -427,7 +426,10 @@ void _mergeFromProto3Json(
               for (var i = 0; i < value.length; i++) {
                 final entry = value[i];
                 context.addListIndex(i);
-                values.add(convertProto3JsonValue(entry, fieldInfo));
+                final parsedValue = convertProto3JsonValue(entry, fieldInfo);
+                if (parsedValue != null) {
+                  values.add(parsedValue);
+                }
                 context.popIndex();
               }
             } else {

protoc_plugin/Makefile

@@ -31,6 +31,7 @@ TEST_PROTO_LIST = \
 	entity \
 	enum_extension \
 	enum_name \
+	enum_test \
 	enums \
 	extend_unittest \
 	ExtensionEnumNameConflict \

protoc_plugin/test/protos/enum_test.proto

@@ -0,0 +1,16 @@
+// Copyright (c) 2023, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+syntax = "proto3";
+
+enum A {
+  X = 0;
+  Y = 1;
+}
+
+message Message {
+  A enum_field = 1;
+  map<int32, A> map_value_field = 2;
+  repeated A repeated_enum_field = 3;
+}

protoc_plugin/test/unknown_enums_test.dart

@@ -0,0 +1,44 @@
+// Copyright (c) 2023, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:test/test.dart';
+import 'package:collection/collection.dart';
+
+import 'gen/enum_test.pb.dart';
+
+void main() {
+  group('Enum parsing in maps, lists, messages', () {
+    test('Parse known fields', () {
+      final json = {
+        'enumField': 'Y',
+        'mapValueField': {'1': 'Y'},
+        'repeatedEnumField': ['Y'],
+      };
+
+      final msg = Message();
+      msg.mergeFromProto3Json(json);
+      expect(msg.enumField, A.Y);
+      expect(msg.mapValueField.values.toList(), [A.Y]);
+      expect(msg.repeatedEnumField, [A.Y]);
+    });
+
+    test('Skip unknown fields', () {
+      final json = {
+        'enumField': 'Z',
+        'mapValueField': {'1': 'X', '2': 'Z', '3': 'Y'},
+        'repeatedEnumField': ['X', 'Z', 'Y'],
+      };
+
+      final msg = Message();
+      msg.enumField = A.Y;
+      msg.mergeFromProto3Json(json, ignoreUnknownFields: true);
+      expect(msg.enumField, A.X); // unknown value defaults the enum value
+      expect(msg.mapValueField.values.toList()..sortBy((e) => e.value), [
+        A.X,
+        A.Y,
+      ]);
+      expect(msg.repeatedEnumField..sortBy((e) => e.value), [A.X, A.Y]);
+    });
+  });
+}