Use Copy Constructor for JsonSerializerSettings

Fixes #29532

Fixes an issue where JsonSerializerSettings.DateFormatString overwrites DateFormatHandling. See #29532 for details

Author: MatthewSteeples

src/Mvc/Mvc.NewtonsoftJson/src/NewtonsoftJsonOutputFormatter.cs

@@ -113,7 +113,7 @@ protected virtual JsonSerializer CreateJsonSerializer()
         if (_serializerSettings == null)
         {
             // Lock the serializer settings once the first serialization has been initiated.
-            _serializerSettings = ShallowCopy(SerializerSettings);
+            _serializerSettings = new JsonSerializerSettings(SerializerSettings);
         }
 
         return JsonSerializer.Create(_serializerSettings);
@@ -190,44 +190,6 @@ public override async Task WriteResponseBodyAsync(OutputFormatterWriteContext co
         }
     }
 
-    private static JsonSerializerSettings ShallowCopy(JsonSerializerSettings settings)
-    {
-        var copiedSettings = new JsonSerializerSettings
-        {
-            FloatParseHandling = settings.FloatParseHandling,
-            FloatFormatHandling = settings.FloatFormatHandling,
-            DateParseHandling = settings.DateParseHandling,
-            DateTimeZoneHandling = settings.DateTimeZoneHandling,
-            DateFormatHandling = settings.DateFormatHandling,
-            Formatting = settings.Formatting,
-            MaxDepth = settings.MaxDepth,
-            DateFormatString = settings.DateFormatString,
-            Context = settings.Context,
-            Error = settings.Error,
-            SerializationBinder = settings.SerializationBinder,
-            TraceWriter = settings.TraceWriter,
-            Culture = settings.Culture,
-            ReferenceResolverProvider = settings.ReferenceResolverProvider,
-            EqualityComparer = settings.EqualityComparer,
-            ContractResolver = settings.ContractResolver,
-            ConstructorHandling = settings.ConstructorHandling,
-            TypeNameAssemblyFormatHandling = settings.TypeNameAssemblyFormatHandling,
-            MetadataPropertyHandling = settings.MetadataPropertyHandling,
-            TypeNameHandling = settings.TypeNameHandling,
-            PreserveReferencesHandling = settings.PreserveReferencesHandling,
-            Converters = settings.Converters,
-            DefaultValueHandling = settings.DefaultValueHandling,
-            NullValueHandling = settings.NullValueHandling,
-            ObjectCreationHandling = settings.ObjectCreationHandling,
-            MissingMemberHandling = settings.MissingMemberHandling,
-            ReferenceLoopHandling = settings.ReferenceLoopHandling,
-            CheckAdditionalContent = settings.CheckAdditionalContent,
-            StringEscapeHandling = settings.StringEscapeHandling,
-        };
-
-        return copiedSettings;
-    }
-
     private static partial class Log
     {
         [LoggerMessage(1, LogLevel.Debug, "Buffering IAsyncEnumerable instance of type '{Type}'.", EventName = "BufferingAsyncEnumerable", SkipEnabledCheck = true)]

src/Mvc/Mvc.NewtonsoftJson/test/NewtonsoftJsonOutputFormatterTest.cs

@@ -549,6 +549,23 @@ async IAsyncEnumerable<int> AsyncEnumerableThrows([EnumeratorCancellation] Cance
         }
     }
 
+    [Fact]
+    public void JsonSerializerSettingsCopyConstructor_DoesNotOverrideDateFormatHandling()
+    {
+        // Arrange
+        var originalSettings = new JsonSerializerSettings
+        {
+            DateFormatHandling = DateFormatHandling.MicrosoftDateFormat,
+        };
+
+        // Act
+        var copiedSettings = new JsonSerializerSettings(originalSettings);
+
+        // Assert
+        Assert.Equal(originalSettings.DateFormatHandling, copiedSettings.DateFormatHandling);
+        Assert.Equal(originalSettings.DateFormatString, copiedSettings.DateFormatString);
+    }
+
     private class TestableJsonOutputFormatter : NewtonsoftJsonOutputFormatter
     {
         public TestableJsonOutputFormatter(JsonSerializerSettings serializerSettings)