How do I solve a .NET PackageReference and ProjectReference dependency conflict

Question

I have a dependency problem integrating three .NET projects. Here goes:

I have 3 different projects:

• Project A
• Project B
• Project C

In two separate solutions:

• Solution 1 contains Project A and Project B
• Solution 2 contains Project C

Now these three Project B and C both reference Project A:

• Project B uses a ProjectReference for that
• Project C uses a PackageReference for that

So far so good.

Now I want to use Project C inside Project B, so I want to create a NuGet package out of project C and use a PackageReference to that in Project B.

So we have:

Project B  ------PackageReference---->  Project C
   |                                       |
   | ProjectReference                      |
   |                                       |
   |                                       |
  \/                                       |
Project A <--------PackageReference---------

Still everything builds.

Now when I write a function in Project B that comes from Project C, that uses a Project A type as a parameter I get a compile error. Example of a piece of code I wrote in Project B:

var foo = ProjectCFunction( ProjectAEnum );

Results in:

Error CS0012 The type 'ProjectAEnum' is defined in an assembly that is not referenced. You must add a reference to assembly 'ProjectA, Version=1.0.0.0, Culture=neutral, PublicKeyToken=d706911480550fc3'.

I only get this error when calling a Project C function that also has a Project C type in it's public signature. If I don't everything is fine, and everything runs smoothly. Which feels weird.

Also, I have considered splitting Solution 1 up, and having a solution for each project and using only PackageReferences between the three projects. But this requires a huge effort, and refactoring, and will require a shift in my team's way of working.

Another consideration was to add Project C to Solution 1 and using only ProjectReferences between the three. But this doesn't feel good as well, since both solutions have very different release cycles.

Does anyone know of a third option? Would really appreciate it.