Resolving decorated service behavior changes when adding Named registration

[mchandschuh]

Version Information

$ autofac --version
    4.9.4

$ dotnet --version
    3.0.100

$ cat global.json
{
  "sdk":{
    "version": "2.2.103"
  }
}

Description

While working with decorators, I'm observing an unexpected change in behavior by adding a Named<TService>(serviceName). It appears that the addition of the named registration is causing the decorators to be applied twice, resuling in D2(D2(D1(D1(root)))) I suspect I may be misunderstanding the interplay between the various registration types.

This seems similar to #965 which was fixed in 4.9.2 per comments in the issue.

Questions

• How does adding multiple registrations for the same service impact service resolution?
• If this is not a bug, then decorator application appears to be more complex than I anticipated. Is there anything useful that would help me in understanding why autofac behaves the way it does in the below unit tests?

Reproduction

private interface IContract
{
    IContract Inner { get; }
}
private class Root1 : IContract
{
    public IContract Inner => null;
}
private class Decorator1 : IContract
{
    public IContract Inner { get; }
    public Decorator1(IContract inner) { Inner = inner; }
}
private class Decorator2 : IContract
{
    public IContract Inner { get; }
    public Decorator2(IContract inner) { Inner = inner; }
}


[Test]
public void RegisterType_As_AndRegisterDecorators_AppliesDecoratorsInOrder_ResolvedByType()
{
    // this test passes and produces the following output:
    // Decorator2
    // Decorator1
    // Root1

    var builder = new ContainerBuilder();
    builder.RegisterType<Root1>().As<IContract>();
    builder.RegisterDecorator(typeof(Decorator1), typeof(IContract));
    builder.RegisterDecorator(typeof(Decorator2), typeof(IContract));

    var container = builder.Build();
    var component = container.Resolve<IContract>();

    WriteInners(component);
    Assert.IsInstanceOf<Decorator2>(component);
    Assert.IsInstanceOf<Decorator1>(component.Inner);
    Assert.IsInstanceOf<Root1>(component.Inner.Inner);
}

[Test]
public void RegisterType_Named_As_AndRegisterDecorators_AppliesDecoratorsInOrder_ResolvedByType()
{
    // this test fails and produces the following output:
    // Decorator2
    // Decorator2
    // Decorator1
    // Decorator1
    // Root1

    var builder = new ContainerBuilder();
    builder.RegisterType<Root1>().Named<IContract>("root1").As<IContract>();
    builder.RegisterDecorator(typeof(Decorator1), typeof(IContract));
    builder.RegisterDecorator(typeof(Decorator2), typeof(IContract));

    var container = builder.Build();
    var component = container.Resolve<IContract>();

    WriteInners(component);
    Assert.IsInstanceOf<Decorator2>(component);
    Assert.IsInstanceOf<Decorator1>(component.Inner);
    Assert.IsInstanceOf<Root1>(component.Inner.Inner);
}

[Test]
public void RegisterType_Named_AndRegisterDecorators_AppliesDecoratorsInOrder_ResolvedByName()
{
    // this test passes and produces the following output:
    // Decorator2
    // Decorator1
    // Root1

    var builder = new ContainerBuilder();
    builder.RegisterType<Root1>().Named<IContract>("root1");
    builder.RegisterDecorator(typeof(Decorator1), typeof(IContract));
    builder.RegisterDecorator(typeof(Decorator2), typeof(IContract));

    var container = builder.Build();
    var component = container.ResolveNamed<IContract>("root1");

    WriteInners(component);
    Assert.IsInstanceOf<Decorator2>(component);
    Assert.IsInstanceOf<Decorator1>(component.Inner);
    Assert.IsInstanceOf<Root1>(component.Inner.Inner);
}

[Test]
public void RegisterType_Named_As_AndRegisterDecorators_AppliesDecoratorsInOrder_ResolvedByName()
{
    // this test fails and produces the following output:
    // Decorator2
    // Decorator2
    // Decorator1
    // Decorator1
    // Root1

    var builder = new ContainerBuilder();
    builder.RegisterType<Root1>().Named<IContract>("root1").As<IContract>();
    builder.RegisterDecorator(typeof(Decorator1), typeof(IContract));
    builder.RegisterDecorator(typeof(Decorator2), typeof(IContract));

    var container = builder.Build();
    var component = container.ResolveNamed<IContract>("root1");

    WriteInners(component);
    Assert.IsInstanceOf<Decorator2>(component);
    Assert.IsInstanceOf<Decorator1>(component.Inner);
    Assert.IsInstanceOf<Root1>(component.Inner.Inner);
}

[Test]
public void RegisterType_Keyed_As_AndRegisterDecorators_AppliesDecoratorsInOrder_ResolvedByType()
{
    // this test fails and produces the following output:
    // Decorator2
    // Decorator2
    // Decorator1
    // Decorator1
    // Root1

    var builder = new ContainerBuilder();
    builder.RegisterType<Root1>().Keyed<IContract>("root1").As<IContract>();
    builder.RegisterDecorator(typeof(Decorator1), typeof(IContract));
    builder.RegisterDecorator(typeof(Decorator2), typeof(IContract));

    var container = builder.Build();
    var component = container.Resolve<IContract>();

    WriteInners(component);
    Assert.IsInstanceOf<Decorator2>(component);
    Assert.IsInstanceOf<Decorator1>(component.Inner);
    Assert.IsInstanceOf<Root1>(component.Inner.Inner);
}

[Test]
public void RegisterType_Named_Keyed_As_AndRegisterDecorators_AppliesDecoratorsInOrder_ResolvedByType()
{
    // this test fails and produces the following output:
    // Decorator2
    // Decorator2
    // Decorator1
    // Decorator1
    // Root1

    var builder = new ContainerBuilder();
    builder.RegisterType<Root1>().Named<IContract>("root1").Keyed<IContract>("root1").As<IContract>();
    builder.RegisterDecorator(typeof(Decorator1), typeof(IContract));
    builder.RegisterDecorator(typeof(Decorator2), typeof(IContract));

    var container = builder.Build();
    var component = container.Resolve<IContract>();

    WriteInners(component);
    Assert.IsInstanceOf<Decorator2>(component);
    Assert.IsInstanceOf<Decorator1>(component.Inner);
    Assert.IsInstanceOf<Root1>(component.Inner.Inner);
}

private void WriteInners(IContract component)
{
    var current = component;
    do
    {
        Console.WriteLine(current.GetType().Name);
        current = current.Inner;
    }
    while (current != null);

[tillig]

@alexmg might want to look at this since it overlaps a bit with the new decorator syntax and possibly work that's going on in there.

[RaymondHuy]

Hi @tillig @mchandschuh I have run your reproduction on develop branch and I see that all test cases are passed. Is there anything wrong ?

[tillig]

Agreed. Testing against Autofac 5.0.0-develop-00640 from MyGet shows that this has been resolved for the 5.0.0 release.