Remove hardcoded limit in deserialization constructor arguments

src/libraries/System.Text.Json/Common/JsonConstants.cs

@@ -5,9 +5,6 @@ namespace System.Text.Json
 {
     internal static partial class JsonConstants
     {
-        // The maximum number of parameters a constructor can have where it can be supported by the serializer.
-        public const int MaxParameterCount = 64;
-
         // Standard format for double and single on non-inbox frameworks.
         public const string DoubleFormatString = "G17";
         public const string SingleFormatString = "G9";

src/libraries/System.Text.Json/gen/JsonSourceGenerator.Emitter.cs

@@ -951,11 +951,6 @@ private static string GetParameterizedCtorInvocationFunc(TypeGenerationSpec type
                 int paramCount = parameters.Length;
                 Debug.Assert(paramCount != 0);
 
-                if (paramCount > JsonConstants.MaxParameterCount)
-                {
-                    return "null";
-                }
-
                 const string ArgsVarName = "args";
                 int lastIndex = paramCount - 1;
 

src/libraries/System.Text.Json/src/Resources/Strings.resx

@@ -485,9 +485,6 @@
   <data name="ConstructorParamIncompleteBinding" xml:space="preserve">
     <value>Each parameter in the deserialization constructor on type '{0}' must bind to an object property or field on deserialization. Each parameter name must match with a property or field on the object. Fields are only considered when 'JsonSerializerOptions.IncludeFields' is enabled. The match can be case-insensitive.</value>
   </data>
-  <data name="ConstructorMaxOf64Parameters" xml:space="preserve">
-    <value>The deserialization constructor on type '{0}' may not have more than 64 parameters for deserialization.</value>
-  </data>
   <data name="ObjectWithParameterizedCtorRefMetadataNotSupported" xml:space="preserve">
     <value>Reference metadata is not supported when deserializing constructor parameters. See type '{0}'.</value>
   </data>

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Object/ObjectWithParameterizedConstructorConverter.Large.cs

@@ -34,16 +34,13 @@ protected sealed override bool ReadAndCacheConstructorArgument(scoped ref ReadSt
 
         protected sealed override object CreateObject(ref ReadStackFrame frame)
         {
-            object[] arguments = (object[])frame.CtorArgumentState!.Arguments;
-            frame.CtorArgumentState.Arguments = null!;
+            Debug.Assert(frame.CtorArgumentState != null);
+            Debug.Assert(frame.JsonTypeInfo.CreateObjectWithArgs != null);
 
-            var createObject = (Func<object[], T>?)frame.JsonTypeInfo.CreateObjectWithArgs;
+            object[] arguments = (object[])frame.CtorArgumentState.Arguments;
+            frame.CtorArgumentState.Arguments = null!;
 
-            if (createObject == null)
-            {
-                // This means this constructor has more than 64 parameters.
-                ThrowHelper.ThrowNotSupportedException_ConstructorMaxOf64Parameters(TypeToConvert);
-            }
+            Func<object[], T> createObject = (Func<object[], T>)frame.JsonTypeInfo.CreateObjectWithArgs;
 
             object obj = createObject(arguments);
 

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

@@ -12,7 +12,7 @@ internal abstract class MemberAccessor
         public abstract Func<object>? CreateConstructor(
             [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] Type classType);
 
-        public abstract Func<object[], T>? CreateParameterizedConstructor<T>(ConstructorInfo constructor);
+        public abstract Func<object[], T> CreateParameterizedConstructor<T>(ConstructorInfo constructor);
 
         public abstract JsonTypeInfo.ParameterizedConstructorDelegate<T, TArg0, TArg1, TArg2, TArg3>?
             CreateParameterizedConstructor<T, TArg0, TArg1, TArg2, TArg3>(ConstructorInfo constructor);

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

@@ -45,7 +45,7 @@ public override Func<IEnumerable<TElement>, TCollection> CreateImmutableEnumerab
             => s_cache.GetOrAdd((nameof(CreateImmutableEnumerableCreateRangeDelegate), typeof((TCollection, TElement)), null),
                 static (_) => s_sourceAccessor.CreateImmutableEnumerableCreateRangeDelegate<TCollection, TElement>());
 
-        public override Func<object[], T>? CreateParameterizedConstructor<T>(ConstructorInfo constructor)
+        public override Func<object[], T> CreateParameterizedConstructor<T>(ConstructorInfo constructor)
             => s_cache.GetOrAdd((nameof(CreateParameterizedConstructor), typeof(T), constructor), static key => s_sourceAccessor.CreateParameterizedConstructor<T>((ConstructorInfo)key.member!));
 
         public override JsonTypeInfo.ParameterizedConstructorDelegate<T, TArg0, TArg1, TArg2, TArg3>? CreateParameterizedConstructor<T, TArg0, TArg1, TArg2, TArg3>(ConstructorInfo constructor)

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

@@ -59,13 +59,13 @@ internal sealed class ReflectionEmitMemberAccessor : MemberAccessor
 
             generator.Emit(OpCodes.Ret);
 
-            return (Func<object>)dynamicMethod.CreateDelegate(typeof(Func<object>));
+            return CreateDelegate<Func<object>>(dynamicMethod);
         }
 
-        public override Func<object[], T>? CreateParameterizedConstructor<T>(ConstructorInfo constructor) =>
+        public override Func<object[], T> CreateParameterizedConstructor<T>(ConstructorInfo constructor) =>
             CreateDelegate<Func<object[], T>>(CreateParameterizedConstructor(constructor));
 
-        private static DynamicMethod? CreateParameterizedConstructor(ConstructorInfo constructor)
+        private static DynamicMethod CreateParameterizedConstructor(ConstructorInfo constructor)
         {
             Type? type = constructor.DeclaringType;
 
@@ -76,11 +76,6 @@ internal sealed class ReflectionEmitMemberAccessor : MemberAccessor
             ParameterInfo[] parameters = constructor.GetParameters();
             int parameterCount = parameters.Length;
 
-            if (parameterCount > JsonConstants.MaxParameterCount)
-            {
-                return null;
-            }
-
             var dynamicMethod = new DynamicMethod(
                 ConstructorInfo.ConstructorName,
                 type,
@@ -95,7 +90,7 @@ internal sealed class ReflectionEmitMemberAccessor : MemberAccessor
                 Type paramType = parameters[i].ParameterType;
 
                 generator.Emit(OpCodes.Ldarg_0);
-                generator.Emit(OpCodes.Ldc_I4_S, i);
+                generator.Emit(OpCodes.Ldc_I4, i);
                 generator.Emit(OpCodes.Ldelem_Ref);
                 generator.Emit(OpCodes.Unbox_Any, paramType);
             }

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

@@ -41,7 +41,7 @@ public ConstructorContext([DynamicallyAccessedMembers(DynamicallyAccessedMemberT
             return new ConstructorContext(type).CreateInstance!;
         }
 
-        public override Func<object[], T>? CreateParameterizedConstructor<T>(ConstructorInfo constructor)
+        public override Func<object[], T> CreateParameterizedConstructor<T>(ConstructorInfo constructor)
         {
             Type type = typeof(T);
 
@@ -50,11 +50,6 @@ public ConstructorContext([DynamicallyAccessedMembers(DynamicallyAccessedMemberT
 
             int parameterCount = constructor.GetParameters().Length;
 
-            if (parameterCount > JsonConstants.MaxParameterCount)
-            {
-                return null;
-            }
-
             return (arguments) =>
             {
                 // The input array was rented from the shared ArrayPool, so its size is likely to be larger than the param count.

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

@@ -40,12 +40,6 @@ public static void ThrowNotSupportedException_TypeRequiresAsyncSerialization(Typ
             throw new NotSupportedException(SR.Format(SR.TypeRequiresAsyncSerialization, propertyType));
         }
 
-        [DoesNotReturn]
-        public static void ThrowNotSupportedException_ConstructorMaxOf64Parameters(Type type)
-        {
-            throw new NotSupportedException(SR.Format(SR.ConstructorMaxOf64Parameters, type));
-        }
-
         [DoesNotReturn]
         public static void ThrowNotSupportedException_DictionaryKeyTypeNotSupported(Type keyType, JsonConverter converter)
         {

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

@@ -726,7 +726,7 @@ async Task RunTestAsync<T>()
         }
 
         [Fact]
-        public async Task Cannot_Deserialize_ObjectWith_Ctor_With_65_Params()
+        public async Task Can_Deserialize_ObjectWith_Ctor_With_65_Params()
         {
             async Task RunTestAsync<T>()
             {
@@ -752,11 +752,8 @@ async Task RunTestAsync<T>()
                 sb.Append("Int32");
                 sb.Append(")");
 
-                NotSupportedException ex = await Assert.ThrowsAsync<NotSupportedException>(() => Serializer.DeserializeWrapper<T>(input));
-                Assert.Contains(type.ToString(), ex.ToString());
-
-                ex = await Assert.ThrowsAsync<NotSupportedException>(() => Serializer.DeserializeWrapper<T>("{}"));
-                Assert.Contains(type.ToString(), ex.ToString());
+                T value = await Serializer.DeserializeWrapper<T>(input);
+                value = await Serializer.DeserializeWrapper<T>("{}");
             }
 
             await RunTestAsync<Class_With_Ctor_With_65_Params>();
@@ -1426,6 +1423,17 @@ public async Task TestClassWithDefaultCtorParams()
             JsonTestHelper.AssertJsonEqual(json, await Serializer.SerializeWrapper(obj));
         }
 
+        [Fact]
+        public async Task TestClassWithManyConstructorParameters()
+        {
+            ClassWithManyConstructorParameters value = ClassWithManyConstructorParameters.Create();
+            string json = JsonSerializer.Serialize(value);
+
+            ClassWithManyConstructorParameters result = await Serializer.DeserializeWrapper<ClassWithManyConstructorParameters>(json);
+
+            Assert.Equal(value, result); // Type is C# record that implements structural equality.
+        }
+
         public class ClassWithDefaultCtorParams
         {
             public Point_2D_Struct_WithAttribute Struct { get; }

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

@@ -118,7 +118,7 @@ async Task RunTestAsync<T>(string testData)
         }
 
         [Fact]
-        public async Task Cannot_DeserializeAsync_ObjectWith_Ctor_With_65_Params()
+        public async Task Can_DeserializeAsync_ObjectWith_Ctor_With_65_Params()
         {
             if (StreamingSerializer is null)
             {
@@ -137,6 +137,7 @@ async Task RunTestAsync<T>()
                 sb.Append("}");
 
                 string input = sb.ToString();
+                T value;
 
                 using (MemoryStream stream = new MemoryStream(Encoding.UTF8.GetBytes(input)))
                 {
@@ -145,7 +146,7 @@ async Task RunTestAsync<T>()
                         DefaultBufferSize = 1
                     };
 
-                    await Assert.ThrowsAsync<NotSupportedException>(async () => await StreamingSerializer.DeserializeWrapper<T>(stream, options));
+                    value = await StreamingSerializer.DeserializeWrapper<T>(stream, options);
                 }
 
                 using (MemoryStream stream = new MemoryStream("{}"u8.ToArray()))
@@ -155,7 +156,7 @@ async Task RunTestAsync<T>()
                         DefaultBufferSize = 1
                     };
 
-                    await Assert.ThrowsAsync<NotSupportedException>(async () => await StreamingSerializer.DeserializeWrapper<T>(stream, options));
+                    value = await StreamingSerializer.DeserializeWrapper<T>(stream, options);
                 }
             }