Merge pull request #1975 from riganti/fix-enum-custom-json-converter

Fix custom JSON converter on enum (or other type)

Author: exyi

src/Framework/Framework/Configuration/DefaultSerializerSettingsProvider.cs

@@ -34,6 +34,7 @@ private JsonSerializerOptions CreateSettings()
             return new JsonSerializerOptions()
             {
                 Converters = {
+                    new PreferTheJsonConverterAttribute(),
                     new DotvvmDateTimeConverter(),
                     new DotvvmObjectConverter(),
                     new DotvvmEnumConverter(),

src/Framework/Framework/ViewModel/Serialization/PreferTheJsonConverterAttribute.cs

@@ -0,0 +1,31 @@
+using System;
+using System.Reflection;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+using DotVVM.Framework.Utils;
+using FastExpressionCompiler;
+
+namespace DotVVM.Framework.ViewModel.Serialization
+{
+    public sealed class PreferTheJsonConverterAttribute : JsonConverterFactory
+    {
+        public override bool CanConvert(Type typeToConvert)
+        {
+            if (!typeToConvert.IsDefined(typeof(JsonConverterAttribute), inherit: false))
+                return false;
+            var attr = typeToConvert.GetCustomAttribute<JsonConverterAttribute>(inherit: false)!;
+            return attr.ConverterType is {} || attr.CreateConverter(typeToConvert) is {};
+        }
+
+        public override JsonConverter? CreateConverter(Type typeToConvert, JsonSerializerOptions options)
+        {
+            var attr = typeToConvert.GetCustomAttribute<JsonConverterAttribute>(inherit: false)!;
+            if (attr.CreateConverter(typeToConvert) is {} converter)
+                return converter;
+            if (attr.ConverterType is null)
+                throw new Exception($"Type {typeToConvert.ToCode()} has a [JsonConverter] attribute, but its CreateConverter returns null sometimes?");
+            return (JsonConverter)Activator.CreateInstance(attr.ConverterType)!;
+        }
+    }
+}
+

src/Tests/ViewModel/SerializerTests.cs

@@ -1437,6 +1437,14 @@ public void Serializer_CanDisableDotvvmSerializer()
             Assert.IsTrue(obj.ItsSerializedAnyway);
         }
 
+        [TestMethod]
+        public void Serializer_SupportCustomEnumConverter()
+        {
+            var (obj, json) = SerializeAndDeserialize<Tuple<TestEnumWithCustomConverter>>(new(TestEnumWithCustomConverter.Case5));
+
+            Assert.AreEqual(TestEnumWithCustomConverter.Case5, obj.Item1);
+            Assert.AreEqual("5esaC", (string)json["Item1"]);
+        }
 
         [TestMethod]
         public void Serializer_CanUseDefaultPolymorphismSupport_1()
@@ -1858,6 +1866,23 @@ public override void Write(Utf8JsonWriter writer, TestViewModelWithCustomConvert
         }
     }
 
+    [JsonConverter(typeof(TestEnumCustomConverter))]
+    public enum TestEnumWithCustomConverter { Case1, Case2, Case3, Case4, Case5, Case6, Case7 }
+
+    public class TestEnumCustomConverter : JsonConverter<TestEnumWithCustomConverter>
+    {
+        public override TestEnumWithCustomConverter Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+        {
+            var str = reader.GetString();
+            return (TestEnumWithCustomConverter)Enum.Parse(typeof(TestEnumWithCustomConverter), new string(str.Reverse().ToArray()));
+        }
+
+        public override void Write(Utf8JsonWriter writer, TestEnumWithCustomConverter value, JsonSerializerOptions options)
+        {
+            writer.WriteStringValue(new string(value.ToString().Reverse().ToArray()));
+        }
+    }
+
     class DynamicDispatchVMContainer<TStatic>
     {
         [Bind(AllowDynamicDispatch = true)]