Move ProjectReference into a conditional import

[AArnott]

This makes the ProjectReference item itself completely undiscoverable for project systems that enumerate references using the MSBuild API that gets items regardless of condition, which appears to be how the legacy project system (csproj.dll) does it at least sometimes.

Fixes #1040

[AArnott]

@thomas-ravkilde Can you test this? You can download the nupkg from the PR build artifacts. Let me know if you need more instructions.

[thomas-ravkilde]

@AArnott Sorry for the delay. I'm afraid I need some more instructions. I thought I could just include prereleases in the VS NuGet Package Manager but that doesn't appear to be the case. I see v3.6.79-alpha as the latest prerelease on v3.6. Where do I find the PR build artifacts?

[AArnott]

Perfectly understandable, and thank you for trying. The instructions for consuming PR build artifacts is near the bottom of our README.
But even that only carries CI builds. For a PR build, you'd need to download the nupkg artifact from the PR build and then point your nuget.config file to the directory that contains the nupkg. You can get it from the deployables-Windows artifact here.

[thomas-ravkilde]

Ah, I see. Thanks, I couldn't figure out how to get to the PR build artifacts.

Unfortunately, the change doesn't fix the issue:

[AArnott]

Thanks for testing and reporting back.
I have no idea how it would be failing at this point unless there's something very peculiar in your setup.
Can you send me a minimal repro?

[thomas-ravkilde]

Hm... Very interesting.

• I created a new .NET Framework 4.8 Console project. --> No issue.
• I removed all projects in my solution to create a minimal repro. --> Still got the warning.
• Cleaned the solution and rebuilt. --> Still got the warning.
• Ran git clean -xdf, cleaned the solution and rebuilt. --> Now there's no warning.

So it appears that your change did actually fix the issue but that there was something sticky in the build process.

[AArnott]

Progress. Great.

Can you verify with one more step: roll back to the latest release of NB.GV and verify that even after git clean the warning comes back?