Fix JsonSerializerOptions.GetConverter recreating built-in converters

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializerOptions.Converters.cs

@@ -159,7 +159,10 @@ internal JsonConverter GetConverterFromMember(Type? parentClassType, Type proper
         [RequiresUnreferencedCode("Getting a converter for a type may require reflection which depends on unreferenced code.")]
         public JsonConverter GetConverter(Type typeToConvert!!)
         {
-            RootBuiltInConverters();
+            if (!IsInitializedForReflectionSerializer)
+            {
+                InitializeForReflectionSerializer();
+            }
             return GetConverterInternal(typeToConvert);
         }
 

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/WriteStack.cs

@@ -99,7 +99,6 @@ private void EnsurePushCapacity()
         public JsonConverter Initialize(Type type, JsonSerializerOptions options, bool supportContinuation)
         {
             JsonTypeInfo jsonTypeInfo = options.GetOrAddJsonTypeInfoForRootType(type);
-            Debug.Assert(options == jsonTypeInfo.Options);
             return Initialize(jsonTypeInfo, supportContinuation);
         }
 

src/libraries/System.Text.Json/tests/Common/TestClasses/TestClasses.Constructor.cs

@@ -456,6 +456,8 @@ public class Point_2D : ITestClass
         [JsonConstructor]
         public Point_2D(int x, int y) => (X, Y) = (x, y);
 
+        public Point_2D() : this(0, 0) { }
+
         public void Initialize() { }
 
         public void Verify()

src/libraries/System.Text.Json/tests/System.Text.Json.Tests/Serialization/CustomConverterTests/CustomConverterTests.cs

@@ -1,6 +1,8 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.IO;
+using Microsoft.DotNet.RemoteExecutor;
 using Xunit;
 
 namespace System.Text.Json.Serialization.Tests
@@ -161,19 +163,29 @@ public static void VerifyObjectConverterWithPreservedReferences()
             Assert.Equal(true, obj);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(RemoteExecutor), nameof(RemoteExecutor.IsSupported))]
         public static void GetConverterRootsBuiltInConverters()
         {
-            JsonSerializerOptions options = new();
-            RunTest<DateTime>();
-            RunTest<Point_2D>();
-
-            void RunTest<TConverterReturn>()
+            RemoteExecutor.Invoke(static () =>
             {
-                JsonConverter converter = options.GetConverter(typeof(TConverterReturn));
-                Assert.NotNull(converter);
-                Assert.True(converter is JsonConverter<TConverterReturn>);
-            }
+                JsonSerializerOptions options = new();
+                RunTest<DateTime>();
+                RunTest<Point_2D>();
+
+                void RunTest<T>() where T : new()
+                {
+                    JsonConverter<T> converter = options.GetConverter(typeof(T)) as JsonConverter<T>;
+                    Assert.NotNull(converter);
+
+                    // Should be possible to call into converters that require
+                    // reflection-based metadata
+                    T value = new();
+                    using var writer = new Utf8JsonWriter(new MemoryStream());
+                    converter.Write(writer, value, options);
+                    writer.Flush();
+                    Assert.True(writer.BytesCommitted > 0);
+                }
+            }).Dispose();
         }
 
         [Fact]