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RegisterTypes will attempt to register abstract types (undocumented breaking change in v6.5.0)

See original GitHub issue

Describe the Bug

In Autofac v6.4.0, a scanning registration using RegisterTypes that includes types that cannot be constructed (e.g. interfaces, abstract classes) will work fine.

In Autofac v6.5.0 onwards, it will attempt to register those non-constructible types resulting in an Autofac.Core.Activators.Reflection.NoConstructorsFoundException upon building the container.

This is a breaking change that I couldn’t find documented anywhere.

Steps to Reproduce

public class ReproTest
{
    interface IInterface { }

    class Class : IInterface
    {
    }

    [Fact]
    public void Repro()
    {
        var containerBuilder = new ContainerBuilder();

        containerBuilder
            .RegisterTypes(typeof(IInterface), typeof(Class))
            .AssignableTo<IInterface>();

        var exception = Record.Exception(() => containerBuilder.Build());

        Assert.Null(exception);
    }
}

Expected Behavior

No exception, test passes (v6.4.0 behaviour)

Exception with Stack Trace

v6.5.0 onwards throws:

Autofac.Core.Activators.Reflection.NoConstructorsFoundException: No accessible constructors were found for the type 'ReproTestProject.ReproTest+IInterface'.
   at Autofac.Core.Activators.Reflection.DefaultConstructorFinder.GetDefaultPublicConstructors(Type type)
   at Autofac.Core.Activators.Reflection.DefaultConstructorFinder.FindConstructors(Type targetType)
   at Autofac.Core.Activators.Reflection.ReflectionActivator.ConfigurePipeline(IComponentRegistryServices componentRegistryServices, IResolvePipelineBuilder pipelineBuilder)
   at Autofac.Core.Registration.ComponentRegistration.BuildResolvePipeline(IComponentRegistryServices registryServices, IResolvePipelineBuilder pipelineBuilder)
   at Autofac.Core.Registration.ComponentRegistration.BuildResolvePipeline(IComponentRegistryServices registryServices)
   at Autofac.Core.Registration.ComponentRegistryBuilder.Build()
   at Autofac.ContainerBuilder.Build(ContainerBuildOptions options)
   at ReproTestProject.ReproTest.<>c__DisplayClass2_0.<Repro>b__0()

Dependency Versions

Autofac: v6.5.0

Additional Info

A workaround is for the user to filter out abstract types from the types passed to RegisterTypes themselves.

In trying to figure out why I was getting this exception after upgrading to v6.5.0 from v6.4.0 I took a look at the diff between the two versions, and the removal of !t.IsAbstract in CanBeRegistered in this commit was something that stood out to me that might be the cause.