Static classes with identical names and namespaces into different referenced projects

[CSharpLanguage]

Scenario

Try to extend by new methods a existing static class from another referenced library (project)

Steps to reproduce

1. Create library Project A and add a static class with some methods

namespace AnyLibrary
{
    public static class AnyExtensions
    {
        public static T Method_A<T>(this T o) => o;

        public static T Method_B<T>(T o) => o;
    }
}

2. Create Project B and add into references Project A

3. Add into Project B a static class with the same name and namespace but another methods

namespace AnyLibrary
{
    public static class AnyExtensions
    {
        public static T Method_C<T>(this T o) => o;

        public static T Method_D<T>(T o) => o;
    }
}

4. Try to use all methods

using AnyLibrary;

var x = "abc";
Console.WriteLine(x.Method_A()); // Compiled !!! But show Error CS1061 if there are another fatal errors into project	 string' does not contain a definition for 'Method_A' and no extension method 'Method_A' accepting a first argument of type 'string' could be found (are you missing a using directive or an assembly reference?)
//Console.WriteLine(AnyExtensions.Method_A(x)); // Error	CS0117 'AnyExtensions' does not contain a definition for 'Method_A'
//Console.WriteLine(AnyExtensions.Method_B(x)); // Error	CS0117 'AnyExtensions' does not contain a definition for 'Method_B'

Console.WriteLine(x.Method_C()); // Compiled
Console.WriteLine(AnyExtensions.Method_C(x)); // Compiled
Console.WriteLine(AnyExtensions.Method_D(x)); // Compiled

5. Remarkable at a current situation that it is possible to use extension method like x.Method_A() but not possible like AnyExtensions.Method_A(x). Seems that

AnyExtensions.Method_A(x);
AnyExtensions.Method_B(x)

should be allowed too by compiler because it is possible to resolve a path conflict by method names.

[theunrepentantgeek]

Using directives allow specifying an alias, explicitly to work around this issue.

I'd conjecture that the reason for method resolution not doing this disambiguation is because it would introduce inconsistency. If both methods declared Method_Z(), then only can be called - with your demo, I think it would be the second one but would have to test. Having both Method_Z() and Method_A() work at the same time, even though they're resident in different classes, would be very odd.

[jnm2]

Such a conflict is extremely undesirable. When it exists, switching back and forth in the same file should be minimized. A good design will not require extern aliases.
(Aside: applying aliases to assemblies from NuGet package references requires painful hacks.)

[CSharpLanguage]

@tannergooding @jnm2
Maybe described steps are not clear.

The real situation looks like:

1. There is a common library which had used into different solutions

2. The library contains a similar static class with some methods

namespace AnyLibrary
{
    public static class AnyExtensions
    {
        public static T Method_A<T>(this T o) => ... ;

        public static T Method_B<T>(T o) => ... ;

        public static T Method_C<T>(this T o) => ... ;

        public static T Method_D<T>(T o) => ... ;
    }
}

3. Implementation of methods C and D require external dependency. But this dependency is not important for some solutions and may be avoided

4. By this reason I try to split AnyLibrary on two parts: the first contains

namespace AnyLibrary
{
    public static class AnyExtensions
    {
        public static T Method_A<T>(this T o) => ... ;

        public static T Method_B<T>(T o) => ... ;
    }
}

and not require the external dependency,
the second optional part

namespace AnyLibrary
{
    public static class AnyExtensions
    {
        public static T Method_C<T>(this T o) => ... ;

        public static T Method_D<T>(T o) => ... ;
    }
}

contains the external dependency

5. Now I expect that if both parts referenced to the any project I can use all following variations

x.Method_A()
AnyExtensions.Method_A(x)
AnyExtensions.Method_B(x)

x.Method_C()
AnyExtensions.Method_C(x)
AnyExtensions.Method_D(x)

But currently situation looks very strange

1. I can use extension methods like

x.Method_A()
x.Method_C()

but can't use the same methods via class name

AnyExtensions.Method_A(x)
AnyExtensions.Method_C(x)

2. If I try to define the second part inside the project and add the first part a like external dependency I can use

AnyExtensions.Method_C(x)
AnyExtensions.Method_D(x)

but can't

AnyExtensions.Method_A(x)
AnyExtensions.Method_B(x)

If a compiler can resolve this path conflict for implicit extension methods call [x.Method_A()], why it can not resolve the same conflict for the explicit extension method call [AnyExtensions.Method_A(x)] and a simple static methods too [AnyExtensions.Method_B(x)] ?

[jnm2]

@CyrusNajmabadi Can we reopen when conversion to discussion fails so that it doesn't appear that the issue is being rejected without a response?

[CyrusNajmabadi]

:(