From edf9174e09ad2385ef50db5a5ea1fecf6d5b3830 Mon Sep 17 00:00:00 2001
From: Eirik Tsarpalis <eirik.tsarpalis@gmail.com>
Date: Wed, 23 Feb 2022 18:40:09 +0000
Subject: [PATCH] Fix JsonSerializerOptions.GetConverter reallocating default
 converters on each call.

---
 .../JsonSerializerOptions.Converters.cs       |  5 ++-
 .../Text/Json/Serialization/WriteStack.cs     |  1 -
 .../TestClasses/TestClasses.Constructor.cs    |  2 ++
 .../CustomConverterTests.cs                   | 32 +++++++++++++------
 4 files changed, 28 insertions(+), 12 deletions(-)

diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializerOptions.Converters.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializerOptions.Converters.cs
index 6d3a3c88d61647..d30f675462dc32 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializerOptions.Converters.cs
+++ b/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);
         }
 
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/WriteStack.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/WriteStack.cs
index f966a1a77cb7a0..4b861f31d40676 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/WriteStack.cs
+++ b/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);
         }
 
diff --git a/src/libraries/System.Text.Json/tests/Common/TestClasses/TestClasses.Constructor.cs b/src/libraries/System.Text.Json/tests/Common/TestClasses/TestClasses.Constructor.cs
index 890d61f97245d1..ce3ddf1da9a5eb 100644
--- a/src/libraries/System.Text.Json/tests/Common/TestClasses/TestClasses.Constructor.cs
+++ b/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()
diff --git a/src/libraries/System.Text.Json/tests/System.Text.Json.Tests/Serialization/CustomConverterTests/CustomConverterTests.cs b/src/libraries/System.Text.Json/tests/System.Text.Json.Tests/Serialization/CustomConverterTests/CustomConverterTests.cs
index 80067292399c46..30852afa0556d1 100644
--- a/src/libraries/System.Text.Json/tests/System.Text.Json.Tests/Serialization/CustomConverterTests/CustomConverterTests.cs
+++ b/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]