Remove new concurrent dictionary for generic method holders

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

@@ -600,9 +600,7 @@ internal JsonTypeInfo GetOrAddClass(Type type)
         {
             _haveTypesBeenCreated = true;
 
-            // todo: for performance and reduced instances, consider using the converters and JsonTypeInfo from s_defaultOptions by cloning (or reference directly if no changes).
-            // https://github.com/dotnet/runtime/issues/32357
-            if (!_classes.TryGetValue(type, out JsonTypeInfo? result))
+            if (!TryGetClass(type, out JsonTypeInfo? result))
             {
                 result = _classes.GetOrAdd(type, GetClassFromContextOrCreate(type));
             }
@@ -644,6 +642,20 @@ internal JsonTypeInfo GetOrAddClassForRootType(Type type)
             return jsonTypeInfo;
         }
 
+        internal bool TryGetClass(Type type, [NotNullWhen(true)] out JsonTypeInfo? jsonTypeInfo)
+        {
+            // todo: for performance and reduced instances, consider using the converters and JsonTypeInfo from s_defaultOptions by cloning (or reference directly if no changes).
+            // https://github.com/dotnet/runtime/issues/32357
+            if (!_classes.TryGetValue(type, out JsonTypeInfo? result))
+            {
+                jsonTypeInfo = null;
+                return false;
+            }
+
+            jsonTypeInfo = result;
+            return true;
+        }
+
         internal bool TypeIsCached(Type type)
         {
             return _classes.ContainsKey(type);

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Metadata/GenericMethodHolder.cs

@@ -13,8 +13,6 @@ namespace System.Text.Json.Serialization.Metadata
     /// </summary>
     internal abstract class GenericMethodHolder
     {
-        private static ConcurrentDictionary<Type, GenericMethodHolder>? s_holders;
-
         /// <summary>
         /// Returns the default value for the specified type.
         /// </summary>
@@ -26,33 +24,12 @@ internal abstract class GenericMethodHolder
         public abstract bool IsDefaultValue(object value);
 
         /// <summary>
-        /// Returns a holder instance representing a type.
+        /// Creates a holder instance representing a type.
         /// </summary>
-        public static GenericMethodHolder GetHolder(Type type)
+        public static GenericMethodHolder CreateHolder(Type type)
         {
-            if (s_holders == null)
-            {
-                s_holders = new ConcurrentDictionary<Type, GenericMethodHolder>();
-                return CreateAndCacheHolder();
-            }
-            else
-            {
-                if (!s_holders.TryGetValue(type, out GenericMethodHolder? holder))
-                {
-                    holder = CreateAndCacheHolder();
-                }
-
-                return holder;
-            }
-
-            GenericMethodHolder CreateAndCacheHolder()
-            {
-                Type holderType = typeof(GenericMethodHolder<>).MakeGenericType(type);
-                GenericMethodHolder holderInstance = (GenericMethodHolder)Activator.CreateInstance(holderType)!;
-                Debug.Assert(s_holders != null);
-                s_holders[type] = holderInstance;
-                return holderInstance;
-            }
+            Type holderType = typeof(GenericMethodHolder<>).MakeGenericType(type);
+            return (GenericMethodHolder)Activator.CreateInstance(holderType)!;
         }
     }
 

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Metadata/JsonParameterInfo.cs

@@ -100,7 +100,18 @@ public static JsonParameterInfo CreateIgnoredParameterPlaceholder(
             {
                 // The <T> value in the created JsonPropertyInfo<T> instance (sbyte)
                 // doesn't match the parameter type, use reflection to get the default value.
-                GenericMethodHolder holder = GenericMethodHolder.GetHolder(parameterInfo.ParameterType);
+                Type parameterType = parameterInfo.ParameterType;
+
+                GenericMethodHolder holder;
+                if (matchingProperty.Options.TryGetClass(parameterType, out JsonTypeInfo? typeInfo))
+                {
+                    holder = typeInfo.GenericMethods;
+                }
+                else
+                {
+                    holder = GenericMethodHolder.CreateHolder(parameterInfo.ParameterType);
+                }
+
                 jsonParameterInfo.DefaultValue = holder.DefaultValue;
             }
 

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Metadata/JsonTypeInfo.cs

@@ -130,7 +130,7 @@ internal GenericMethodHolder GenericMethods
         {
             get
             {
-                _genericMethods ??= GenericMethodHolder.GetHolder(Type);
+                _genericMethods ??= GenericMethodHolder.CreateHolder(Type);
                 return _genericMethods;
             }
         }

src/libraries/System.Text.Json/tests/Common/ConstructorTests/ConstructorTests.ParameterMatching.cs

@@ -1307,5 +1307,20 @@ public class TypeWith_RefStringProp_ParamCtor
 
             public TypeWith_RefStringProp_ParamCtor(ref string nameRef) => _name = nameRef;
         }
+
+        [Fact]
+        public async Task BindToIgnoredPropOfSameType()
+        {
+            string json = @"{""Prop"":{}}";
+            Assert.NotNull(await JsonSerializerWrapperForString.DeserializeWrapper<ClassWithIgnoredSameType>(json));
+        }
+
+        public class ClassWithIgnoredSameType
+        {
+            [JsonIgnore]
+            public ClassWithIgnoredSameType Prop { get; }
+
+            public ClassWithIgnoredSameType(ClassWithIgnoredSameType prop) { }
+        }
     }
 }

src/libraries/System.Text.Json/tests/System.Text.Json.SourceGeneration.Tests/Serialization/ConstructorTests.cs

@@ -129,6 +129,7 @@ protected ConstructorTests_Metadata(JsonSerializerWrapperForString stringWrapper
         [JsonSerializable(typeof(SmallType_IgnoredProp_Bind_Param))]
         [JsonSerializable(typeof(LargeType_IgnoredProp_Bind_ParamWithDefaultValue))]
         [JsonSerializable(typeof(LargeType_IgnoredProp_Bind_Param))]
+        [JsonSerializable(typeof(ClassWithIgnoredSameType))]
         internal sealed partial class ConstructorTestsContext_Metadata : JsonSerializerContext
         {
         }
@@ -249,6 +250,7 @@ public ConstructorTests_Default()
         [JsonSerializable(typeof(SmallType_IgnoredProp_Bind_Param))]
         [JsonSerializable(typeof(LargeType_IgnoredProp_Bind_ParamWithDefaultValue))]
         [JsonSerializable(typeof(LargeType_IgnoredProp_Bind_Param))]
+        [JsonSerializable(typeof(ClassWithIgnoredSameType))]
         internal sealed partial class ConstructorTestsContext_Default : JsonSerializerContext
         {
         }