Upgrade from 4.2.2 to 5.0.1 breaks decoration

[lukasvavrek]

Hi, while playing around updating and upgrading my app I run into a compatibility issue.

Here is an example of the registration code:

public static class DependencyInjection
{
    public static IServiceCollection AddApplication(this IServiceCollection services)
    {
        services.Scan(scan =>
            scan.FromCallingAssembly()
                .AddClasses(classes => classes
                    .AssignableTo(typeof(IRequestHandler<,>))
                    .NotInNamespaceOf<IRequestHandlerBehavior>())
                .AsImplementedInterfaces()
                .WithTransientLifetime()
        );
        
        services.Decorate(typeof(IRequestHandler<,>), typeof(RequestExceptionHandler<,>));

        return services;
    }
}

While this works as expected in version 4.2.2, in 5.0.1 I am running into:

System.NullReferenceException: Object reference not set to an instance of an object.
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.Populate()
   at Microsoft.Extensions.DependencyInjection.ServiceProvider..ctor(ICollection`1 serviceDescriptors, ServiceProviderOptions options)
   at Microsoft.Extensions.DependencyInjection.ServiceCollectionContainerBuilderExtensions.BuildServiceProvider(IServiceCollection services, ServiceProviderOptions options)
   at Microsoft.Extensions.Hosting.HostApplicationBuilder.Build()
   at Microsoft.AspNetCore.Builder.WebApplicationBuilder.Build()
   at Program.<Main>$(String[] args) in /XXX/Program.cs:line 15

Let me please know if I can provide some useful information!

[khellang]

Thanks for the bug report! Looks like it comes from deep within the container code. Need to dig a bit here 😅

[Mike-E-angelo]

Related: #235

[ajdean]

From what I have found if you are targeting net8.0 then decoration works fine.

If you are targeting something below that (e.g. net6.0 or net7.0), then you will need to ensure you have added Microsoft.Extensions.DependencyInjection version >= 8.0.0 otherwise I think it fails due to keyed services not being supported.

[martynas-m]

We're using .net 8, and tried to upgrade to 5.0.2- it crashes with same Object reference not set to an object error. But we migrated DependencyInjection package to 9th version.

[khellang]

I have tests covering pretty much this exact scenario, which passes on latest Scrutor main, targeting .NET 9 with Microsoft.Extensions.DependencyInjection v9.0.0.

Does anyone have any additional details that could help pin this down?