Disable net461 build on non-Windows platforms

[roji]

When trying to work on EF Core on Linux, the build is complicated by the fact that some projects target net461. While various workarounds exist for targeting .NET Framework on non-Windows platforms with mono, this is complicated. In addition, while the test infrastructure does contain logic to skip .NET Framework on non-Windows platforms (see test/Directory.Build.props), 3 projects under src do not.

This PR conditionally adds net461 in these 3 projects, only when on Windows. I'm not sure what effects this could have (I don't know the EF Core build system well yet), but it does help me build the project. If this needs to be done in some other way (or is not possible for some reason), please let me know. This is not urgent.

[smitpatel]

What is exact issue you are seeing? We are just compiling on net461 and last I checked it was working fine on Linux /Mac

[ajcvickers]

Interestingly, whenever I dev I temporarily remove all but one TFM to make things faster. I have just been keeping a temporary Directory.Build.Props around for this, but maybe we can make it a configurable switch in some way such that anybody can easily develop just targeting on thing, since I believe this is the most efficient way to work in most cases.

[roji]

@smitpatel when trying to build one of these projects (e.g. EFCore.Design) with a simple dotnet build on Linux, I get the error described in dotnet/sdk#335:

/home/roji/.dotnet/sdk/2.2.100-preview2-009404/Microsoft.Common.CurrentVersion.targets(1179,5): error MSB3644: The reference assemblies for framework ".NETFramework,Version=v4.6.1" were not found. To resolve this, install the SDK or Targeting Pack for this framework version or retarget your application to a version of the framework for which you have the SDK or Targeting Pack installed. Note that assemblies will be resolved from the Global Assembly Cache (GAC) and will be used in place of reference assemblies. Therefore your assembly may not be correctly targeted for the framework you intend. [/home/roji/projects/EFCore/src/EFCore.Design/EFCore.Design.csproj]

FWIW I do have mono installed (5.6.0.179, on Ubuntu 18.10). As described in dotnet/sdk#335, there are some workarounds for getting around this and making dotnet SDK use the mono-provided reference assemblies for .NET Framework - but if any such workarounds exist in the EF Core build system they don't seem to be working for me... I wonder why you're not encountering the same error.

Regardless, as @ajcvickers wrote it seems like a good idea to at least disable building .NET Framework in dev mode to make it faster.

[roji]

Note: the Ubuntu/MacOS builds are failing because the Oracle provider tests are executed. As all other tests exclude net461 on non-Windows (via Directory.Build.props), it may make sense to do the same for the Oracle tests. I'll wait for your feedback...

[natemcmaster]

An alternative would be to add a reference to Microsoft.NETFramework.ReferenceAssemblies. We were planning on doing this anyways as a part of upgrading tests to .NET 4.7.2. You can see an example of this here: aspnet/HttpSysServer@3e08bf8. The important bit is this:

  <ItemGroup Condition="'$(TargetFrameworkIdentifier)' == '.NETFramework' ">
    <PackageReference Include="Microsoft.NETFramework.ReferenceAssemblies" Version="$(MicrosoftNETFrameworkReferenceAssemblies)" PrivateAssets="All" />
  </ItemGroup>

Also, if you upgrade KoreBuild, I added a fix a few days ago to completely skip .NET Framework tests on non-Windows platforms: aspnet/BuildTools@ee0ad5b

[bricelam]

master is using the NuGet package. Non-Windows machines should be able to build net461 now.