There might be duplicated enum values when allow_alias is true. Add…

There might be duplicated enum values when allow_alias is true. Add PreferredAlias into OriginalNameAttribute to remove the duplication (#2727)

csharp/src/Google.Protobuf.Test/JsonFormatterTest.cs

@@ -66,6 +66,18 @@ namespace Google.Protobuf
             AssertJson("{ 'c': 0 }", formatter.Format(new ForeignMessage()));
         }
 
+        [Test]
+        public void EnumAllowAlias()
+        {
+            var message = new TestEnumAllowAlias
+            {
+                Value = TestEnumWithDupValue.Foo2,
+            };
+            var actualText = JsonFormatter.Default.Format(message);
+            var expectedText = "{ 'value': 'FOO1' }";
+            AssertJson(expectedText, actualText);
+        }
+
         [Test]
         public void AllSingleFields()
         {

csharp/src/Google.Protobuf/JsonFormatter.cs

@@ -835,6 +835,9 @@ namespace Google.Protobuf
             // TODO: Consider adding functionality to TypeExtensions to avoid this difference.
             private static Dictionary<object, string> GetNameMapping(System.Type enumType) =>
                 enumType.GetFields(BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.Static)
+                    .Where(f => (f.GetCustomAttributes(typeof(OriginalNameAttribute), false)
+                                 .FirstOrDefault() as OriginalNameAttribute)
+                                 ?.PreferredAlias ?? true)
                     .ToDictionary(f => f.GetValue(null),
                                   f => (f.GetCustomAttributes(typeof(OriginalNameAttribute), false)
                                         .FirstOrDefault() as OriginalNameAttribute)
@@ -844,6 +847,8 @@ namespace Google.Protobuf
             private static Dictionary<object, string> GetNameMapping(System.Type enumType) =>
                 enumType.GetTypeInfo().DeclaredFields
                     .Where(f => f.IsStatic)
+                    .Where(f => f.GetCustomAttributes<OriginalNameAttribute>()
+                                 .FirstOrDefault()?.PreferredAlias ?? true)
                     .ToDictionary(f => f.GetValue(null),
                                   f => f.GetCustomAttributes<OriginalNameAttribute>()
                                         .FirstOrDefault()

csharp/src/Google.Protobuf/Reflection/OriginalNameAttribute.cs

@@ -46,6 +46,11 @@ namespace Google.Protobuf.Reflection
         /// </summary>
         public string Name { get; set; }
 
+        /// <summary>
+        /// If the name is preferred in the .proto file.
+        /// </summary>
+        public bool PreferredAlias { get; set; }
+
         /// <summary>
         /// Constructs a new attribute instance for the given name.
         /// </summary>
@@ -53,6 +58,8 @@ namespace Google.Protobuf.Reflection
         public OriginalNameAttribute(string name)
         {
             Name = ProtoPreconditions.CheckNotNull(name, nameof(name));
+            PreferredAlias = true;
         }
+	
     }
-}
+}
\ No newline at end of file

src/google/protobuf/compiler/csharp/csharp_enum.cc

@@ -65,6 +65,7 @@ void EnumGenerator::Generate(io::Printer* printer) {
                  "name", descriptor_->name());
   printer->Indent();
   std::set<string> used_names;
+  std::set<int> used_number;
   for (int i = 0; i < descriptor_->value_count(); i++) {
       WriteEnumValueDocComment(printer, descriptor_->value(i));
       string original_name = descriptor_->value(i)->name();
@@ -76,10 +77,18 @@ void EnumGenerator::Generate(io::Printer* printer) {
           << ") in " << descriptor_->name() << "; adding underscore to distinguish";
         name += "_";
       }
-      printer->Print("[pbr::OriginalName(\"$original_name$\")] $name$ = $number$,\n",
-         "original_name", original_name,
-         "name", name,
-         "number", SimpleItoa(descriptor_->value(i)->number()));         
+      int number = descriptor_->value(i)->number();
+      if (!used_number.insert(number).second) {
+          printer->Print("[pbr::OriginalName(\"$original_name$\", PreferredAlias = false)] $name$ = $number$,\n",
+             "original_name", original_name,
+             "name", name,
+             "number", SimpleItoa(number));
+      } else {
+          printer->Print("[pbr::OriginalName(\"$original_name$\")] $name$ = $number$,\n",
+             "original_name", original_name,
+             "name", name,
+             "number", SimpleItoa(number));
+      }
   }
   printer->Outdent();
   printer->Print("}\n");

src/google/protobuf/unittest_proto3.proto

@@ -200,6 +200,9 @@ message TestMutualRecursionB {
   int32 optional_int32 = 2;
 }
 
+message TestEnumAllowAlias {
+  TestEnumWithDupValue value = 1;
+}
 
 // Test an enum that has multiple values with the same number.
 enum TestEnumWithDupValue {