MessagePack.Generator - Issues with generic

[RAORelewise]

I am currently trying to use the MessagePack.Generator tool to pre-create all formatters for our project. Our project uses a bunch of generics and i am wondering how to approach this, maybe i am doing something wrong.

So for the following code:

[Union(0, typeof(Dog))]
public abstract class Animal
{
}

[MessagePackObject]
public sealed class Dog : Animal
{
    
}

Everything works fine. But if i add generics:

[Union(0, typeof(Dog))]
public abstract class Animal<T>
{
}

[MessagePackObject]
public sealed class Dog : Animal<double>
{
    
}

I am getting this error:

PS C:\Projects\MessagePackGeneratorTest\MessagePackGeneratorTest> mpc -i .\MessagePackGeneratorTest.csproj -o MessagePackGenerated.cs
Project Compilation Start:MessagePackGeneratorTest
Project Compilation Complete:00:00:00.4858938
Method Collect Start
Fail in application running on MessagepackCompiler.RunAsync
MessagePackCompiler.CodeAnalysis.MessagePackGeneratorResolveFailedException: Serialization Object must mark MessagePackObjectAttribute. type: global::MessagePackGeneratorTest.Animal<T>
   at MessagePackCompiler.CodeAnalysis.TypeCollector.GetObjectInfo(INamedTypeSymbol type) in D:\a\1\s\src\MessagePack.GeneratorCore\CodeAnalysis\TypeCollector.cs:line 609
   at MessagePackCompiler.CodeAnalysis.TypeCollector.CollectObject(INamedTypeSymbol type) in D:\a\1\s\src\MessagePack.GeneratorCore\CodeAnalysis\TypeCollector.cs:line 600
   at MessagePackCompiler.CodeAnalysis.TypeCollector.CollectGeneric(INamedTypeSymbol type) in D:\a\1\s\src\MessagePack.GeneratorCore\CodeAnalysis\TypeCollector.cs:line 550
   at MessagePackCompiler.CodeAnalysis.TypeCollector.CollectCore(ITypeSymbol typeSymbol) in D:\a\1\s\src\MessagePack.GeneratorCore\CodeAnalysis\TypeCollector.cs:line 364
   at MessagePackCompiler.CodeAnalysis.TypeCollector.Collect() in D:\a\1\s\src\MessagePack.GeneratorCore\CodeAnalysis\TypeCollector.cs:line 305
   at MessagePackCompiler.CodeGenerator.GenerateFileAsync(Compilation compilation, String output, String resolverName, String namespace, Boolean useMapMode, String multipleIfDirectiveOutputSymbols, String[] externalIgnoreTypeNames) in D:\a\1\s\src\MessagePack.GeneratorCore\CodeGenerator.cs:line 67
   at MessagePack.Generator.MessagepackCompiler.RunAsync(String input, String output, String conditionalSymbol, String resolverName, String namespace, Boolean useMapMode, String multipleIfDirectiveOutputSymbols, String[] externalIgnoreTypeNames) in D:\a\1\s\src\MessagePack.Generator\MessagepackCompiler.cs:line 
66
   at ConsoleAppFramework.WithFilterInvoker.RunCore(ConsoleAppContext _)
   at ConsoleAppFramework.WithFilterInvoker.InvokeAsync()
   at ConsoleAppFramework.ConsoleAppEngine.RunCore(Type type, MethodInfo methodInfo, Object instance, String[] args, Int32 argsOffset)
   at ConsoleAppFramework.ConsoleAppEngine.RunCore(Type type, MethodInfo methodInfo, Object instance, String[] args, Int32 argsOffset)

Why is it now required to add a MessagePackObject attribute? And even if i do add it. The next error is now that i do not have any public ctor, why is this now required?

[Union(0, typeof(Dog))]
[MessagePackObject]
public abstract class Animal<T>
{
}

MessagePackCompiler.CodeAnalysis.MessagePackGeneratorResolveFailedException: can't find public constructor. type:global::MessagePackGeneratorTest.Animal<T>

Alright.. so now i add the public ctor (side question, why doesnt it work using protected parameterless ctors in abstract classes either?):

[Union(0, typeof(Dog))]
[MessagePackObject]
public abstract class Animal<T>
{
    public Animal()
    {
        
    }
}

[MessagePackObject]
public sealed class Dog : Animal<double>
{
    public Dog()
    {
        
    }
}

Doing this the generator succeeded. BUT. It wont compile.

It is generating this formatter:

    public sealed class AnimalFormatter<T> : global::MessagePack.Formatters.IMessagePackFormatter<global::MessagePackGeneratorTest.Animal<T>>
    {

        public void Serialize(ref global::MessagePack.MessagePackWriter writer, global::MessagePackGeneratorTest.Animal<T> value, global::MessagePack.MessagePackSerializerOptions options)
        {
            if (value == null)
            {
                writer.WriteNil();
                return;
            }

            writer.WriteArrayHeader(0);
        }

        public global::MessagePackGeneratorTest.Animal<T> Deserialize(ref global::MessagePack.MessagePackReader reader, global::MessagePack.MessagePackSerializerOptions options)
        {
            if (reader.TryReadNil())
            {
                return null;
            }

            reader.Skip();
            return new global::MessagePackGeneratorTest.Animal<T>();
        }
    }

Where it fails as you cant create an instance of an abstract type -> return new global::MessagePackGeneratorTest.Animal();

Why is it creating a formatter for this base type now? It looks completely different without the generics.

• Version used: 2.5.140
• Runtime: .net 7 class library