如何让Visual Studio 2015 xproject（project.json）引用依赖项目的最高框架

Question

I'm creating a reusable library that targets several platforms (.NET 4.0, .NET 4.5, .NETStandard 1.0 and .NETStandard 1.3). The .NET 4.5 version of this project contains some features that are not available under the .NET 4.0 version.

The unit test project that references this library project has one single target platform, namely NET 4.5.1. This test project obviously contains some code that tests the .NET 4.5 specific features of the core library.

Unfortunately however, the test project does not compile, because Visual Studio seems to reference the .NETStandard 1.0 version, which obviously does not contain this feature.

To demonstrate my problem, I reduced this to the following two projects:

Core library:

{
  "version": "1.0.0-*",

  "frameworks": {
    "netstandard1.0": {
      "dependencies": {
        "NETStandard.Library": "1.6.0"
      }
    },
    "net40": {},
    "net45": {}
  }
}

Code file:

namespace CoreLibrary
{
#if NETSTANDARD1_0
    public class ClassNetStandard { }
#endif

#if NET40
    public class ClassNet40 { }
#endif

#if NET45
    public class ClassNet45 { }
#endif
}

Test library:

{
  "version": "1.0.0-*",

  "dependencies": {
    "CoreLibrary": { "target": "project" }
  },
  "frameworks": {
    "net451": {}
  }
}

Code:

// This compiles
new CoreLibrary.ClassNetStandard();

// This doesn't.
// error: Type or namespace 'ClassNet40' does not exist in namespace 'CoreLibrary'
new CoreLibrary.ClassNet40();
// error: Type or namespace 'ClassNet45' does not exist in namespace 'CoreLibrary'
new CoreLibrary.ClassNet45();

What should I change to allow my unit test project to compile and test the specific .NET 4.5 features?

Answer 1

There seems to be a bug in Visual Studio tools for .NET Core. When you reference multi-framework project from another one - Visual Studio only takes first listed framework from a list (in your case - "netstandard1.0") and treats that referenced project as single targeted for this framework. However, compiler handles this correctly, and while it seems that project builds correctly - in reality it does not. On the other hand, when you use ClassNet45 definition - it seems that it does not compile (Visual Studio shows errors) - it really does compile successfully.

It seems that Visual Studio tools for .NET Core are not polished enough yet, but probably this bug will be resolved in some near future.