Fix #66727. (#67041)

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Read.HandleMetadata.cs

@@ -336,6 +336,11 @@ public static partial class JsonSerializer
 
             if (state.Current.ObjectState == StackFrameObjectState.ReadValuesStartArray)
             {
+                // Temporary workaround for the state machine accidentally
+                // erasing the JsonPropertyName property in certain async
+                // re-entrancy patterns.
+                state.Current.JsonPropertyName = s_valuesPropertyName;
+
                 if (reader.TokenType != JsonTokenType.StartArray)
                 {
                     ThrowHelper.ThrowJsonException_MetadataValuesInvalidToken(reader.TokenType);

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

@@ -208,15 +208,19 @@ public string JsonPath()
         {
             StringBuilder sb = new StringBuilder("$");
 
-            // If a continuation, always report back full stack which does not use Current for the last frame.
-            int count = Math.Max(_count, _continuationCount + 1);
+            (int frameCount, bool includeCurrentFrame) = _continuationCount switch
+            {
+                0 => (_count - 1, true), // Not a countinuation, report previous frames and Current.
+                1 => (0, true), // Continuation of depth 1, just report Current frame.
+                int c => (c, false) // Continuation of depth > 1, report the entire stack.
+            };
 
-            for (int i = 0; i < count - 1; i++)
+            for (int i = 0; i < frameCount; i++)
             {
                 AppendStackFrame(sb, ref _stack[i]);
             }
 
-            if (_continuationCount == 0)
+            if (includeCurrentFrame)
             {
                 AppendStackFrame(sb, ref Current);
             }

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

@@ -332,15 +332,19 @@ public string PropertyPath()
         {
             StringBuilder sb = new StringBuilder("$");
 
-            // If a continuation, always report back full stack which does not use Current for the last frame.
-            int count = Math.Max(_count, _continuationCount + 1);
+            (int frameCount, bool includeCurrentFrame) = _continuationCount switch
+            {
+                0 => (_count - 1, true), // Not a countinuation, report previous frames and Current.
+                1 => (0, true), // Continuation of depth 1, just report Current frame.
+                int c => (c, false) // Continuation of depth > 1, report the entire stack.
+            };
 
-            for (int i = 0; i < count - 1; i++)
+            for (int i = 0; i < frameCount; i++)
             {
                 AppendStackFrame(sb, ref _stack[i]);
             }
 
-            if (_continuationCount == 0)
+            if (includeCurrentFrame)
             {
                 AppendStackFrame(sb, ref Current);
             }

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

@@ -15,7 +15,6 @@ public sealed class ReferenceHandlerTestsDynamic_AsyncStream : ReferenceHandlerT
         public ReferenceHandlerTestsDynamic_AsyncStream() : base(JsonSerializerWrapper.AsyncStreamSerializer) { }
     }
 
-    [ActiveIssue("https://github.com/dotnet/runtime/issues/66727")]
     public sealed class ReferenceHandlerTestsDynamic_AsyncStreamWithSmallBuffer : ReferenceHandlerTests
     {
         public ReferenceHandlerTestsDynamic_AsyncStreamWithSmallBuffer() : base(JsonSerializerWrapper.AsyncStreamSerializerWithSmallBuffer) { }