IDE0065 (Using directives must be placed outside of a namespace declaration) is noisy for alias declarations inside namespace

[mavasani]

Version Used: Latest

Steps to Reproduce:

using System;

namespace N
{
    using GenericInt = GenericClass<int>;

    public static class A
    {
        public static void M(GenericInt g)
        {
            Console.WriteLine("Hello");
        }
    }

    public static class GenericClass<T>
    { 
    }
}

Expected Behavior:
Either IDE0065 does not fire or it has a code style option to allow alias declarations inside namespace. This is a very common pattern and is sometimes essential for correct type resolution.

Actual Behavior:
IDE0065 fires. This makes it very difficult to enforce this rule on CI.

[mavasani]

@JoeRobich @sharwell

[sharwell]

... is sometimes essential for correct type resolution

I don't mind requiring a suppression for this case. It means you've already introduced a naming ambiguity (though it's sometimes accidental or unavoidable in XML comments).

I'd love to have #27712 for this.

[mavasani]

I don't mind requiring a suppression for this case.

This had 60+ violations in just the analyzers repo, and I suspect would have many more in Roslyn. This makes me feel like it would be noisy enough to warrant an additional option for aliases. We can wait for more customer feedback and decide though.

[sharwell]

@mavasani I was only calling out the case where the alias must appear inside the namespace for correctness. I would be surprised if that was a majority case; generally the alias can be moved outside the namespace as long as the types are fully-qualified at the same time.

[CyrusNajmabadi]

I would be surprised if that was a majority case; generally the alias can be moved outside the namespace as long as the types are fully-qualified at the same time.

tihs is true, but is often undesirably verbose.

I agree that using aliases should not necessarily be under the same purview as using directives. The directive is a global style on where people should place the namespaces they are pulling in.

The latter is used commonly for:

1. disambiguation (in which case, grouping with the rest is appropriate)
2. typedefs (in which case, there's no relation to the directives, and they should be placeable where conveinent).

[sharwell]

I've had pull requests rejected from projects because I placed a using alias directive inside the namespace to avoid unnecessary verbosity. This analyzer and refactoring eliminated the tedious work of moving and qualifying it. It would be unfortunate to take that help away.

[mavasani]

Can we add an option to exclude alias declarations from this rule? I think this is a classic case where there would be a proportionately divided group on whether or not they should be included in the rule, and it seems to justify an end user option.

[mavasani]

Marking for design review.

[allisonchou]

This issue was discussed during today's design meeting (4/13). It was decided that we will add an option to exclude using alias declarations, however the default configuration will be kept the same (i.e. applies to everything).