Use System.Text.Json's copy ctor (#21016)

Author: pranavkm

src/Mvc/Mvc.Core/src/Formatters/SystemTextJsonOutputFormatter.cs

@@ -40,7 +40,10 @@ internal static SystemTextJsonOutputFormatter CreateFormatter(JsonOptions jsonOp
             if (jsonSerializerOptions.Encoder is null)
             {
                 // If the user hasn't explicitly configured the encoder, use the less strict encoder that does not encode all non-ASCII characters.
-                jsonSerializerOptions = jsonSerializerOptions.Copy(JavaScriptEncoder.UnsafeRelaxedJsonEscaping);
+                jsonSerializerOptions = new JsonSerializerOptions(jsonSerializerOptions)
+                {
+                    Encoder = JavaScriptEncoder.UnsafeRelaxedJsonEscaping,
+                };
             }
 
             return new SystemTextJsonOutputFormatter(jsonSerializerOptions);

src/Mvc/Mvc.Core/src/Infrastructure/JsonSerializerOptionsCopyConstructor.cs

@@ -1,6 +1,14 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
+using System.IO;
+using System.Text;
+using System.Text.Json.Serialization;
+using System.Threading.Tasks;
+using Microsoft.Extensions.Primitives;
+using Microsoft.Net.Http.Headers;
+using Xunit;
+
 namespace Microsoft.AspNetCore.Mvc.Formatters
 {
     public class SystemTextJsonOutputFormatterTest : JsonOutputFormatterTestBase
@@ -9,5 +17,51 @@ protected override TextOutputFormatter GetOutputFormatter()
         {
             return SystemTextJsonOutputFormatter.CreateFormatter(new JsonOptions());
         }
+
+        [Fact]
+        public async Task WriteResponseBodyAsync_AllowsConfiguringPreserveReferenceHandling()
+        {
+            // Arrange
+            var formatter = GetOutputFormatter();
+            ((SystemTextJsonOutputFormatter)formatter).SerializerOptions.ReferenceHandling = ReferenceHandling.Preserve;
+            var expectedContent = "{\"$id\":\"1\",\"name\":\"Person\",\"child\":{\"$id\":\"2\",\"name\":\"Child\",\"child\":null,\"parent\":{\"$ref\":\"1\"}},\"parent\":null}";
+            var person = new Person
+            {
+                Name = "Person",
+                Child = new Person { Name = "Child", },
+            };
+            person.Child.Parent = person;
+
+            var mediaType = MediaTypeHeaderValue.Parse("application/json; charset=utf-8");
+            var encoding = CreateOrGetSupportedEncoding(formatter, "utf-8", isDefaultEncoding: true);
+
+            var body = new MemoryStream();
+            var actionContext = GetActionContext(mediaType, body);
+
+            var outputFormatterContext = new OutputFormatterWriteContext(
+                actionContext.HttpContext,
+                new TestHttpResponseStreamWriterFactory().CreateWriter,
+                typeof(Person),
+                person)
+            {
+                ContentType = new StringSegment(mediaType.ToString()),
+            };
+
+            // Act
+            await formatter.WriteResponseBodyAsync(outputFormatterContext, Encoding.GetEncoding("utf-8"));
+
+            // Assert
+            var actualContent = encoding.GetString(body.ToArray());
+            Assert.Equal(expectedContent, actualContent);
+        }
+
+        private class Person
+        {
+            public string Name { get; set; }
+
+            public Person Child { get; set; }
+
+            public Person Parent { get; set; }
+        }
     }
 }

src/Mvc/Mvc.Core/test/Formatters/SystemTextJsonOutputFormatterTest.cs

@@ -33,7 +33,10 @@ private static JsonSerializerOptions GetHtmlSafeSerializerOptions(JsonSerializer
                 return serializerOptions;
             }
 
-            return serializerOptions.Copy(JavaScriptEncoder.Default);
+            return new JsonSerializerOptions(serializerOptions)
+            {
+                Encoder = JavaScriptEncoder.Default,
+            };
         }
     }
 }