backport opportunistic bugfixes

Author: eiriktsarpalis

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Object/ObjectDefaultConverter.cs

@@ -312,7 +312,9 @@ internal sealed override bool OnTryWrite(
 
                         if (!jsonPropertyInfo.GetMemberAndWriteJson(objectValue!, ref state, writer))
                         {
-                            Debug.Assert(jsonPropertyInfo.ConverterBase.ConverterStrategy != ConverterStrategy.Value);
+                            Debug.Assert(jsonPropertyInfo.ConverterBase.ConverterStrategy != ConverterStrategy.Value ||
+                                         jsonPropertyInfo.ConverterBase.TypeToConvert == JsonTypeInfo.ObjectType);
+
                             return false;
                         }
 

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

@@ -476,6 +476,7 @@ internal bool TryWriteDataExtensionProperty(Utf8JsonWriter writer, T value, Json
 
             // Ignore the naming policy for extension data.
             state.Current.IgnoreDictionaryKeyPolicy = true;
+            state.Current.DeclaredJsonPropertyInfo = state.Current.JsonTypeInfo.ElementTypeInfo!.PropertyInfoForTypeInfo;
 
             success = dictionaryConverter.OnWriteResume(writer, value, options, ref state);
             if (success)

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Write.String.cs

@@ -125,9 +125,6 @@ private static string WriteUsingMetadata<TValue>(in TValue value, JsonTypeInfo?
                 throw new ArgumentNullException(nameof(jsonTypeInfo));
             }
 
-            WriteStack state = default;
-            state.Initialize(jsonTypeInfo, supportContinuation: false);
-
             JsonSerializerOptions options = jsonTypeInfo.Options;
 
             using (var output = new PooledByteBufferWriter(options.DefaultBufferSize))

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

@@ -258,8 +258,7 @@ static void AppendStackFrame(StringBuilder sb, in ReadStackFrame frame)
 
                 if (frame.JsonTypeInfo != null && frame.IsProcessingEnumerable())
                 {
-                    IEnumerable? enumerable = (IEnumerable?)frame.ReturnValue;
-                    if (enumerable == null)
+                    if (frame.ReturnValue is not IEnumerable enumerable)
                     {
                         return;
                     }

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

@@ -253,13 +253,10 @@ public void DisposePendingDisposablesOnException()
             DisposeFrame(Current.CollectionEnumerator, ref exception);
 
             int stackSize = Math.Max(_count, _continuationCount);
-            if (stackSize > 1)
+            for (int i = 0; i < stackSize - 1; i++)
             {
-                for (int i = 0; i < stackSize - 1; i++)
-                {
-                    Debug.Assert(_previous[i].AsyncEnumerator is null);
-                    DisposeFrame(_previous[i].CollectionEnumerator, ref exception);
-                }
+                Debug.Assert(_previous[i].AsyncEnumerator is null);
+                DisposeFrame(_previous[i].CollectionEnumerator, ref exception);
             }
 
             if (exception is not null)
@@ -294,12 +291,9 @@ public async ValueTask DisposePendingDisposablesOnExceptionAsync()
             exception = await DisposeFrame(Current.CollectionEnumerator, Current.AsyncEnumerator, exception).ConfigureAwait(false);
 
             int stackSize = Math.Max(_count, _continuationCount);
-            if (stackSize > 1)
+            for (int i = 0; i < stackSize - 1; i++)
             {
-                for (int i = 0; i < stackSize - 1; i++)
-                {
-                    exception = await DisposeFrame(_previous[i].CollectionEnumerator, _previous[i].AsyncEnumerator, exception).ConfigureAwait(false);
-                }
+                exception = await DisposeFrame(_previous[i].CollectionEnumerator, _previous[i].AsyncEnumerator, exception).ConfigureAwait(false);
             }
 
             if (exception is not null)
@@ -353,7 +347,7 @@ public string PropertyPath()
 
             return sb.ToString();
 
-            void AppendStackFrame(StringBuilder sb, in WriteStackFrame frame)
+            static void AppendStackFrame(StringBuilder sb, in WriteStackFrame frame)
             {
                 // Append the property name.
                 string? propertyName = frame.DeclaredJsonPropertyInfo?.MemberInfo?.Name;
@@ -366,7 +360,7 @@ void AppendStackFrame(StringBuilder sb, in WriteStackFrame frame)
                 AppendPropertyName(sb, propertyName);
             }
 
-            void AppendPropertyName(StringBuilder sb, string? propertyName)
+            static void AppendPropertyName(StringBuilder sb, string? propertyName)
             {
                 if (propertyName != null)
                 {

src/libraries/System.Text.Json/tests/System.Text.Json.Tests/Serialization/ReferenceHandlerTests.IgnoreCycles.cs

@@ -14,7 +14,7 @@ namespace System.Text.Json.Serialization.Tests
     public class ReferenceHandlerTests_IgnoreCycles
     {
         private static readonly JsonSerializerOptions s_optionsIgnoreCycles =
-            new JsonSerializerOptions { ReferenceHandler = ReferenceHandler.IgnoreCycles };
+            new JsonSerializerOptions { ReferenceHandler = ReferenceHandler.IgnoreCycles, DefaultBufferSize = 1 };
 
         [Fact]
         public async Task IgnoreCycles_OnObject()
@@ -401,6 +401,25 @@ public async void IgnoreCycles_BoxedValueShouldNotBeIgnored()
             await Test_Serialize_And_SerializeAsync_Contains(root, expectedSubstring: @"""DayOfBirth"":15", expectedTimes: 2, s_optionsIgnoreCycles);
         }
 
+        [Fact]
+        public async Task CycleDetectionStatePersistsAcrossContinuations()
+        {
+            string expectedValueJson = @"{""LargePropertyName"":""A large-ish string to force continuations"",""Nested"":null}";
+            var recVal = new RecursiveValue { LargePropertyName = "A large-ish string to force continuations" };
+            recVal.Nested = recVal;
+
+            var value = new List<RecursiveValue> { recVal, recVal };
+            string expectedJson = $"[{expectedValueJson},{expectedValueJson}]";
+
+            await Test_Serialize_And_SerializeAsync(value, expectedJson, s_optionsIgnoreCycles);
+        }
+
+        public class RecursiveValue
+        {
+            public string LargePropertyName { get; set; }
+            public RecursiveValue? Nested { get; set; }
+        }
+
         private async Task Test_Serialize_And_SerializeAsync<T>(T obj, string expected, JsonSerializerOptions options)
         {
             string json;