System.Text.Json.JsonSerializer does not work with Dictionary<string, object>

[konarx]

Description

When a Dictionary<string, object> needs serialization, the .NET default System.Text.Json.JsonSerializer throws an exception:

System.InvalidOperationException: Method may only be called on a Type for which Type.IsGenericParameter is true.

I have provided a simple piece of code example to reproduce it. I tried with Newtonsoft.Json.JsonConvert and it works flawlessly.

Reproduction Steps

 public void TestDictionarySerialize()
        {
            var dictionary = new Dictionary<string, object> {
                {"Hello", typeof(string)}, 
                {"World", typeof(string)}
            };

            //This serialization fails
            System.Text.Json.JsonSerializer.Serialize(dictionary,
                typeof(Dictionary<string, object>));

           //This serialization fails
            System.Text.Json.JsonSerializer.Serialize(dictionary);

            //This serialization succeeds
            Newtonsoft.Json.JsonConvert.SerializeObject(dictionary);
        }

Expected behavior

System.Text.Json.JsonSerializer should not throw any Exception

Actual behavior

System.Text.Json.JsonSerializer throws:

System.InvalidOperationException: Method may only be called on a Type for which Type.IsGenericParameter is true.

Regression?

No response

Known Workarounds

Newtonsoft.Json.JsonConvert works flawlessly

Configuration

• .NET 6.0.200
• Windows 10 Enterprise 21H2 19044.1586
• x64

Other information

No response

[ghost]

Tagging subscribers to this area: @dotnet/area-system-text-json, @gregsdennis
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Issue Details

---

Description

When a Dictionary<string, object> needs serialization, the .NET default System.Text.Json.JsonSerializer throws an exception:

System.InvalidOperationException: Method may only be called on a Type for which Type.IsGenericParameter is true.

I have provided a simple piece of code example to reproduce it. I tried with Newtonsoft.Json.JsonConvert and it works flawlessly.

Reproduction Steps

 public void TestDictionarySerialize()
        {
            var dictionary = new Dictionary<string, object> {
                {"Hello", typeof(string)}, 
                {"World", typeof(string)}
            };

            //This serialization fails
            System.Text.Json.JsonSerializer.Serialize(dictionary,
                typeof(Dictionary<string, object>));

            //This serialization succeeds
            Newtonsoft.Json.JsonConvert.SerializeObject(dictionary);
        }

Expected behavior

System.Text.Json.JsonSerializer should not throw any Exception

Actual behavior

System.Text.Json.JsonSerializer throws:

System.InvalidOperationException: Method may only be called on a Type for which Type.IsGenericParameter is true.

Regression?

No response

Known Workarounds

Newtonsoft.Json.JsonConvert works flawlessly

Configuration

• .NET 6.0.200
• Windows 10 Enterprise 21H2 19044.1586
• x64

Other information

No response

Author:	konarx
Assignees:	-
Labels:	area-System.Text.Json, untriaged
Milestone:	-

[danmoseley]

 	System.Private.CoreLib.dll!System.RuntimeType.DeclaringMethod.get() Line 3214	C#
>	System.Text.Json.dll!System.Text.Json.Serialization.Metadata.JsonPropertyInfo<System.Reflection.MethodBase>.GetMemberAndWriteJson(object obj, ref System.Text.Json.WriteStack state, System.Text.Json.Utf8JsonWriter writer) Line 247	C#
 	System.Text.Json.dll!System.Text.Json.Serialization.Converters.ObjectDefaultConverter<System.RuntimeType>.OnTryWrite(System.Text.Json.Utf8JsonWriter writer, System.RuntimeType value, System.Text.Json.JsonSerializerOptions options, ref System.Text.Json.WriteStack state) Line 289	C#
 	System.Text.Json.dll!System.Text.Json.Serialization.JsonConverter<System.RuntimeType>.TryWrite(System.Text.Json.Utf8JsonWriter writer, System.RuntimeType value, System.Text.Json.JsonSerializerOptions options, ref System.Text.Json.WriteStack state) Line 473	C#
 	System.Text.Json.dll!System.Text.Json.Serialization.JsonConverter<System.RuntimeType>.TryWriteAsObject(System.Text.Json.Utf8JsonWriter writer, object value, System.Text.Json.JsonSerializerOptions options, ref System.Text.Json.WriteStack state) Line 118	C#
 	System.Text.Json.dll!System.Text.Json.Serialization.JsonConverter<System.__Canon>.TryWrite(System.Text.Json.Utf8JsonWriter writer, System.__Canon value, System.Text.Json.JsonSerializerOptions options, ref System.Text.Json.WriteStack state) Line 413	C#
 	System.Text.Json.dll!System.Text.Json.Serialization.Converters.DictionaryOfTKeyTValueConverter<System.Collections.Generic.Dictionary<string, object>, string, object>.OnWriteResume(System.Text.Json.Utf8JsonWriter writer, System.Collections.Generic.Dictionary<string, object> value, System.Text.Json.JsonSerializerOptions options, ref System.Text.Json.WriteStack state) Line 87	C#
 	System.Text.Json.dll!System.Text.Json.Serialization.JsonDictionaryConverter<System.__Canon, System.__Canon, System.__Canon>.OnTryWrite(System.Text.Json.Utf8JsonWriter writer, System.__Canon dictionary, System.Text.Json.JsonSerializerOptions options, ref System.Text.Json.WriteStack state) Line 302	C#
 	System.Text.Json.dll!System.Text.Json.Serialization.JsonConverter<System.Collections.Generic.Dictionary<string, object>>.TryWrite(System.Text.Json.Utf8JsonWriter writer, System.Collections.Generic.Dictionary<string, object> value, System.Text.Json.JsonSerializerOptions options, ref System.Text.Json.WriteStack state) Line 473	C#
 	System.Text.Json.dll!System.Text.Json.Serialization.JsonConverter<System.__Canon>.WriteCore(System.Text.Json.Utf8JsonWriter writer, System.__Canon value, System.Text.Json.JsonSerializerOptions options, ref System.Text.Json.WriteStack state) Line 41	C#
 	System.Text.Json.dll!System.Text.Json.Serialization.JsonConverter<System.Collections.Generic.Dictionary<string, object>>.WriteCoreAsObject(System.Text.Json.Utf8JsonWriter writer, object value, System.Text.Json.JsonSerializerOptions options, ref System.Text.Json.WriteStack state) Line 30	C#
 	System.Text.Json.dll!System.Text.Json.JsonSerializer.WriteUsingSerializer<object>(System.Text.Json.Utf8JsonWriter writer, object value, System.Text.Json.Serialization.Metadata.JsonTypeInfo jsonTypeInfo) Line 85	C#
 	System.Text.Json.dll!System.Text.Json.JsonSerializer.WriteStringUsingSerializer<object>(object value, System.Text.Json.Serialization.Metadata.JsonTypeInfo jsonTypeInfo) Line 155	C#
 	System.Text.Json.dll!System.Text.Json.JsonSerializer.Serialize(object value, System.Type inputType, System.Text.Json.JsonSerializerOptions options) Line 63	C#
 	ConsoleApp43.dll!Program.<Main>$(string[] args) Line 7	C#

[eiriktsarpalis]

This is a bug, our unsupported type detection for System.Type values is evaded in the case of polymorphism. Values are resolved as System.RuntimeType which is not caught by the relevant converter.

This example should have failed with NotSupportedException since System.Type serialization is not supported by default.