why aspnet serviceprovider return wrong result?

Question

I have a problem in regard to understand asp net core service provider. I register a service type with a non-generic concrete and an open generic registration,

AddTransient(typeof(IBase<Config>), typeof(Base));
AddTransient(typeof(IBase<>), typeof(BaseGeneric<>));

when I try to resolve all services, the behavior is not what I expected.

I create an empty web app with:

dotnet new web

and change the program.cs like following

ServiceCollection sc = new ServiceCollection();

sc.AddTransient(typeof(IBase<Config>), typeof(Base));
sc.AddTransient(typeof(IBase<>), typeof(BaseGeneric<>));
var serviceProvider = sc.BuildServiceProvider();
var services2 = serviceProvider.GetServices(typeof(IBase<Config>));

foreach (var s in services2){
   Console.WriteLine(s.GetType());
}
Console.WriteLine();
var builder = WebApplication.CreateBuilder(args);

builder.Services.AddTransient(typeof(IBase<Config>), typeof(Base));
builder.Services.AddTransient(typeof(IBase<>), typeof(BaseGeneric<>));

var app = builder.Build();

var services = app.Services.GetServices(typeof(IBase<Config>));

foreach (var s in services){
   Console.WriteLine(s.GetType());
}
app.MapGet("/", () => "Hello World!");

app.Run();

public class Config { }
public interface IBase<T> { }
public class BaseGeneric<T> : IBase<T> { }
public class Base : IBase<Config> { }

the output of two foreach is

Base
BaseGeneric`1[Config]

Base
Base

I expect two foreach print same result.but as you can see they return different results. Is this a valid assumption that they should work like each other? if yes so what is the problem here? and another thing that I found is if you change the order of builder.Services registration the result is OK.

Answer 1

It's a bug in "Microsoft.Extensions.DependencyInjection" from version 6.0.0 :

https://github.com/dotnet/runtime/issues/65145

When the option ValidateOnBuild is enable in the service provider, this produce a weird behavior to retrieve generic dependency.

The correction is planned to .NET 8.

---

It's reproducing with :

>dotnet new console -f net7.0
>dotnet add package Microsoft.Extensions.DependencyInjection --version 6.0.0

Modify "Program.cs" by :

using Microsoft.Extensions.DependencyInjection;

ServiceCollection sc = new ServiceCollection();

sc.AddTransient(typeof(IBase<Config>), typeof(Base));
sc.AddTransient(typeof(IBase<>), typeof(BaseGeneric<>));

LogServices(sc, false);
LogServices(sc, true);

void LogServices(ServiceCollection sc, bool validate)
{
    Console.WriteLine("ValidateOnBuild: " + validate);
    var serviceProvider = sc.BuildServiceProvider(new ServiceProviderOptions { ValidateOnBuild = validate });
    var services = serviceProvider.GetServices(typeof(IBase<Config>));

    foreach (var s in services)
    {
        Console.WriteLine(s.GetType());
    }
}

public class Config { }
public interface IBase<T> { }
public class BaseGeneric<T> : IBase<T> { }
public class Base : IBase<Config> { }

This bug is reproduced :

dotnet run
ValidateOnBuild: False
Base
BaseGeneric`1[Config]
ValidateOnBuild: True
Base
Base

If we downgrade the "Microsoft.Extensions.DependencyInjection" version to the precedent :

>dotnet add package Microsoft.Extensions.DependencyInjection --version 5.0.2
>dotnet run
ValidateOnBuild: False
Base
BaseGeneric`1[Config]
ValidateOnBuild: True
Base
BaseGeneric`1[Config]

This is the expected behavior.

---

In ASP.NET Core, when the environment is "Development", the service builder is build witht the option ValidateOnBuild and you have this behavior. Test in production and you have the expected behavior.