Serializing type which hides inherited property with both properties ignored throws ArgumentException

[AndersWangRask]

Description

With System.Text.Json when trying to serialize a class that is inheriting from a class and is using the new keyword for a property and the new property and the hidden property return different types that has the same name (e.g. "Class1") and both properties are set to [JsonIgnore] an exception is thrown with the following message:

An item with the same key has already been added. Key: class1

It looks like there are actual two problems:

First that two types cannot have the same name apparently.

Second that it only looks at both types when both properties are set to [JsonIgnore]. All other combinations seems to work.

I have identified the issue in both .Net 6 and .Net 7 Preview 2.

Reproduction Steps

Run following code as a Console app in .Net 6 or 7:

using System.Text.Json.Serialization;

Console.WriteLine("Hello, World!");

MyNamespace.Class2 class2 = new MyNamespace.Class2();

string jsonText;

try
{
    jsonText = System.Text.Json.JsonSerializer.Serialize(class2);
}
catch (Exception ex)
{
    jsonText = "EXCEPTION: " + ex.Message;
}

Console.WriteLine(jsonText);

namespace MyNamespace
{
    public class Class1
    {

    }

    public class Class2 : MyNamespaceBase.Class2
    {
        [JsonIgnore]
        public new Class1 class1 => new Class1();
    }
}

namespace MyNamespaceBase
{
    public class Class1
    {

    }

    public class Class2
    {
        [JsonIgnore]
        public Class1 class1 => new Class1();
    }
}

Expected behavior

Should not throw exception. Should serialize the object.

Actual behavior

Following exception is thrown:

System.ArgumentException: An item with the same key has already been added. Key: class1
   at System.Collections.Generic.Dictionary`2.TryInsert(TKey key, TValue value, InsertionBehavior behavior)
   at System.Collections.Generic.Dictionary`2.Add(TKey key, TValue value)
   at System.Text.Json.Serialization.Metadata.JsonTypeInfo.CacheMember(Type declaringType, Type memberType, MemberInfo memberInfo, Boolean isVirtual, Nullable`1 typeNumberHandling, Boolean& propertyOrderSpecified, Dictionary`2& ignoredMembers)
   at System.Text.Json.Serialization.Metadata.JsonTypeInfo..ctor(Type type, JsonConverter converter, Type runtimeType, JsonSerializerOptions options)
   at System.Text.Json.JsonSerializerOptions.<InitializeForReflectionSerializer>g__CreateJsonTypeInfo|120_0(Type type, JsonSerializerOptions options)
   at System.Collections.Concurrent.ConcurrentDictionary`2.GetOrAdd(TKey key, Func`2 valueFactory)
   at System.Text.Json.JsonSerializer.GetTypeInfo(JsonSerializerOptions options, Type runtimeType)
   at System.Text.Json.JsonSerializer.Serialize[TValue](TValue value, JsonSerializerOptions options)
   at Program.<Main>$(String[] args) in C:\GitHubRepos\DotNetTextJsonSerializerProblem\ConsoleApp1\Program.cs:line 12The program '[42624] ConsoleApp1.exe: Program Trace' has exited with code 0 (0x0).

Regression?

I have identified the issue in both .Net 6 and .Net 7 Preview 2. I have not tested other versions.

Known Workarounds

No response

Configuration

No response

Other information

No response

EDIT @krwq: fixed code formatting and call stack

[ghost]

Tagging subscribers to this area: @dotnet/area-system-text-json
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Description

With System.Text.Json when trying to serialize a class that is inheriting from a class and is using the new keyword for a property and the new property and the hidden property return different types that has the same name (e.g. "Class1") and both properties are set to [JsonIgnore] an exception is thrown with the following message:

An item with the same key has already been added. Key: class1

It looks like there are actual two problems:

First that two types cannot have the same name apparently.

Second that it only looks at both types when both properties are set to [JsonIgnore]. All other combinations seems to work.

I have identified the issue in both .Net 6 and .Net 7 Preview 2.

Reproduction Steps

Run following code as a Console app in .Net 6 or 7:

`using System.Text.Json.Serialization;

Console.WriteLine("Hello, World!");

MyNamespace.Class2 class2 = new MyNamespace.Class2();

string jsonText;

try
{
jsonText = System.Text.Json.JsonSerializer.Serialize(class2);
}
catch (Exception ex)
{
jsonText = "EXCEPTION: " + ex.Message;
}

Console.WriteLine(jsonText);

namespace MyNamespace
{
public class Class1
{

}

public class Class2 : MyNamespaceBase.Class2
{
    [JsonIgnore]
    public new Class1 class1 => new Class1();
}

}

namespace MyNamespaceBase
{
public class Class1
{

}

public class Class2
{
    [JsonIgnore]
    public Class1 class1 => new Class1();
}

}`

Expected behavior

Should not throw exception. Should serialize the object.

Actual behavior

Following exception is thrown:

System.ArgumentException: An item with the same key has already been added. Key: class1
at System.Collections.Generic.Dictionary2.TryInsert(TKey key, TValue value, InsertionBehavior behavior) at System.Collections.Generic.Dictionary2.Add(TKey key, TValue value)
at System.Text.Json.Serialization.Metadata.JsonTypeInfo.CacheMember(Type declaringType, Type memberType, MemberInfo memberInfo, Boolean isVirtual, Nullable1 typeNumberHandling, Boolean& propertyOrderSpecified, Dictionary2& ignoredMembers)
at System.Text.Json.Serialization.Metadata.JsonTypeInfo..ctor(Type type, JsonConverter converter, Type runtimeType, JsonSerializerOptions options)
at System.Text.Json.JsonSerializerOptions.g__CreateJsonTypeInfo|120_0(Type type, JsonSerializerOptions options)
at System.Collections.Concurrent.ConcurrentDictionary2.GetOrAdd(TKey key, Func2 valueFactory)
at System.Text.Json.JsonSerializer.GetTypeInfo(JsonSerializerOptions options, Type runtimeType)
at System.Text.Json.JsonSerializer.Serialize[TValue](TValue value, JsonSerializerOptions options)
at Program.

$(String[] args) in C:\GitHubRepos\DotNetTextJsonSerializerProblem\ConsoleApp1\Program.cs:line 12The program '[42624] ConsoleApp1.exe: Program Trace' has exited with code 0 (0x0).

Regression?

I have identified the issue in both .Net 6 and .Net 7 Preview 2. I have not tested other versions.

Known Workarounds

No response

Configuration

No response

Other information

No response

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

[krwq]

I'm putting it in 7.0.0 milestone for now so it doesn't disappear from our radar. I do not promise it will be fixed in this timeline though. We have a set of issues related to JsonIgnore and this is another one.