Omnisharp-roslyn: VS 2019 Preview 16.6 not being picked over 16.5 causes issues with net5.0

[alexrp]

In a solution I'm working on, I have a WPF project which references a library project. Both are currently targeting netcoreapp5.0 which works fine. If I change both to target net5.0 (the preferred TFM going forward), I get this error from OmniSharp:

Project '..\core\core.csproj' targets 'net5.0'. It cannot be referenced by a project that targets '.NETCoreApp,Version=v5.0'.

(Fwiw, I made absolutely sure there are no projects still using netcoreapp5.0 in the solution.)

[filipw]

OmniSharp will use msbuild from Visual Studio 2019 if it's found on your machine. is your VS2019 updated to handle net5.0 (so to VS 16.5+)?

[alexrp]

I have VS 2019 16.5.4 installed (according to Visual Studio Installer).

OmniSharp seems to be picking it up properly:

[info]: OmniSharp.MSBuild.Discovery.MSBuildLocator
        Located 2 MSBuild instance(s)
            1: Visual Studio Community 2019 16.5.30011.22 - "C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\MSBuild\Current\Bin"
            2: StandAlone 16.4 - "C:\Users\alex\.vscode\extensions\ms-dotnettools.csharp-1.21.18\.omnisharp\1.35.1\.msbuild\Current\Bin"
[info]: OmniSharp.MSBuild.Discovery.MSBuildLocator
        Registered MSBuild instance: Visual Studio Community 2019 16.5.30011.22 - "C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\MSBuild\Current\Bin"

[filipw]

then everything should work - can you post the full log at debug level?

[alexrp]

Mmh, ordinarily I would, but there's thousands of lines of output and this is a private project, so I probably can't just post it as-is. Is there a particular subset of the log I should grab?

By the way, I noticed that dotnet msbuild -version says:

Microsoft (R) Build Engine version 16.6.0-preview-20181-02+9f3e4e725 for .NET Core
Copyright (C) Microsoft Corporation. All rights reserved.

16.6.0.18102

Meanwhile msbuild -version in the VS 2019 developer command prompt says:

Microsoft (R) Build Engine version 16.5.0+d4cbfca49 for .NET Framework
Copyright (C) Microsoft Corporation. All rights reserved.

16.5.0.12403

I don't know if that would make any difference, but it seems worth noting since dotnet CLI has no problem with either netcoreapp5.0 or net5.0 while OmniSharp only accepts netcoreapp5.0.

[filipw]

you will have to provide a small repro of this and a log because otherwise it's unfortunately impossible to troubleshoot.
net5.0 should definitely be supported, we explicitly have a test that verifies net5.0 TFM as part of the CI build https://github.com/OmniSharp/omnisharp-roslyn/blob/v1.35.1/test-assets/test-projects/Net50Project/net50-lib/net50-lib.csproj#L4

[alexrp]

mkdir test && cd test
dotnet new classlib -n lib -f net5.0
dotnet new wpf -n wpf
sed -i 's/netcoreapp5.0/net5.0/' wpf/wpf.csproj
dotnet add wpf reference lib
dotnet new sln
dotnet sln add lib
dotnet sln add wpf
dotnet build # Will work fine.

Then open the folder in VS Code and you'll get the error I mentioned from OmniSharp.

[filipw]

I see. the minimum VS to handle this is 16.6 Preview 2
Once you install the latest 16.6 preview (16.6.30105.148) it should work (at least it does on my machine 😀)

[alexrp]

I don't suppose it would be possible to make OmniSharp pick up the MSBuild that .NET Core ships with?

[filipw]

you can do that by adding omnisharp.json with

{
   "msbuild" : {
         "UseLegacySdkResolver": true
    }
}

[alexrp]

Just out of curiosity, given the Legacy bit, what's the reason for not doing that by default?

[alexrp]

In any case, it seems that adding that setting to my project's omnisharp.json has no effect. It still locates the same MSBuild instances that I posted above.

[alexrp]

Also, a minimal installation of VS 2019 Preview with just Roslyn + MSBuild results in:

[info]: OmniSharp.MSBuild.Discovery.MSBuildLocator
        Located 3 MSBuild instance(s)
            1: Visual Studio Community 2019 16.5.30011.22 - "C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\MSBuild\Current\Bin"
            2: Visual Studio Community 2019 16.6.30105.148 - "C:\Program Files (x86)\Microsoft Visual Studio\2019\Preview\MSBuild\Current\Bin"
            3: StandAlone 16.4 - "C:\Users\alex\.vscode\extensions\ms-dotnettools.csharp-1.21.18\.omnisharp\1.35.1\.msbuild\Current\Bin"
[info]: OmniSharp.MSBuild.Discovery.MSBuildLocator
        Registered MSBuild instance: Visual Studio Community 2019 16.5.30011.22 - "C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\MSBuild\Current\Bin"

Can I tell OmniSharp which one to use? I'd rather not have to uninstall the stable version of VS 2019.

[filipw]

sorry, I thought you asked about how to use the SDK resolver that ships with dotnet SDK 🙈
you can force a custom msbuild using these settings https://github.com/OmniSharp/omnisharp-roslyn/pull/1545#issuecomment-510461836

however, 16.6 should be picked before 16.5 - it does so on my machine at least (and the sample you posted also works then), so looks like it's non deterministic. I will check that

[xtqqczze]

@filipw I am also having this issue with https://github.com/PowerShell/PowerShell project.

[info]: OmniSharp.MSBuild.Discovery.MSBuildLocator
        Located 3 MSBuild instance(s)
            1: Visual Studio Community 2019 16.5.30011.22 - "C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\MSBuild\Current\Bin"
            2: Visual Studio Community 2019 16.6.30105.148 - "C:\Program Files (x86)\Microsoft Visual Studio\2019\Preview\MSBuild\Current\Bin"
            3: StandAlone 16.4 - "C:\Users\MD\.vscode\extensions\ms-dotnettools.csharp-1.21.18\.omnisharp\1.35.1\.msbuild\Current\Bin"
[info]: OmniSharp.MSBuild.Discovery.MSBuildLocator
        Registered MSBuild instance: Visual Studio Community 2019 16.5.30011.22 - "C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\MSBuild\Current\Bin"

[xtqqczze]

Using instructions at https://github.com/OmniSharp/omnisharp-roslyn/pull/1545#issuecomment-510461836, I inserted the following in %USERPROFILE%\.omnisharp\omnisharp.json to resolve my issue:

{
  "MSBuild": {
    "MSBuildOverride": {
      "MSBuildPath": "C:\\Program Files (x86)\\Microsoft Visual Studio\\2019\\Preview\\MSBuild\\Current\\Bin",
      "Name": "Overridden MSBuild"
    }
  }
}