OmniSharp doesn't work with latest .NET 6 SDK

[richlander]

I tried .NET 6 Preview 5 and 6, on Windows and macOS. I get this error in the O# logs. As a result, I cannot use VS Code for C#.

Microsoft.Build.Exceptions.InvalidProjectFileException: The SDK 'Microsoft.NET.SDK.WorkloadAutoImportPropsLocator' specified could not be found.  C:\Program Files\dotnet\sdk\6.0.100-preview.5.21269.7\Sdks\Microsoft.NET.Sdk\targets\Microsoft.NET.Sdk.ImportWorkloads.props

Is this an O# or SDK issue?

No repro in VS 16.10 P4.

[dotnet-issue-labeler]

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[richlander]

Related: dotnet/core#6278

[snickler]

From what I've been testing, the issue is with the Microsoft.DotNet.MSBuildSdkResolver.dll from .NET 6 Preview 3

OmniSharp/omnisharp-roslyn#2134

I can make things run again by using an older version of the MSBuildSDKResolver

[richlander]

/cc @rainersigwald

[richlander]

Are there test cases for this? I ran into this a couple years ago, too. I've seen plenty of other folks filing issues on this on GH and SO.

Example: dotnet/vscode-csharp#2937

[snickler]

I have it working with a later MSBuildSdkResolver.

1. Download and extract the latest omnisharp-roslyn release for your OS-arch and extract it to a directory
2. Grab Microsoft.DotNet.MSBuildSdkResolver 6.0.100-preview.4.21254.26 from the dnceng Azure Artifacts
3. Extract the contents from lib/net472/ inside the NuGet package to .msbuild/Current/Bin/SdkResolvers/Microsoft.DotNet.MSBuildSdkResolver inside of the directory where OmniSharp is extracted.
4. Edit the Omnisharp VSCode plugin settings and set "omnisharp.path": "path-to-omnisharp\\omnisharp.exe",
5. Restart the Omnisharp extension
6. Enjoy

[rainersigwald]

This is an OmniSharp issue. It packages tools including the .NET SDK resolver that's used to import the .NET SDK. The .NET 6 SDK is configured so that it can be loaded only in MSBuild 16.10 and newer, but there were "MSBuild 16.10.0-preview" releases that go with Microsoft.DotNet.MSBuildSdkResolver versions that needed some work to actually work, so that block isn't working in OmniSharp at the moment. dotnet/core#6278 (comment)

One thing I'm confused by though @richlander--on Windows, OmniSharp should default to using a Visual Studio copy of MSBuild and so not hit this if you have a VS installed. For instance in my log (toward the very top):

[info]: OmniSharp.MSBuild.Discovery.MSBuildLocator
        Located 5 MSBuild instance(s)
            1: Visual Studio Enterprise 2017 15.9.28307.1525 - "C:\Program Files (x86)\Microsoft Visual Studio\2017\Enterprise\MSBuild\15.0\Bin"
            2: Visual Studio Enterprise 2022 17.0.31324.12 - "C:\Program Files\Microsoft Visual Studio\2022\Preview\MSBuild\Current\Bin"
            3: Visual Studio Enterprise 2019 16.11.31320.298 - "C:\Program Files (x86)\Microsoft Visual Studio\2019\Preview\MSBuild\Current\Bin"
            4: Visual Studio Enterprise 2019 16.9.31313.79 - "C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\MSBuild\Current\Bin"
            5: StandAlone 16.9.0 - "c:\Users\raines\.vscode\extensions\ms-dotnettools.csharp-1.23.11\.omnisharp\1.37.8\.msbuild\Current\Bin"
[info]: OmniSharp.MSBuild.Discovery.MSBuildLocator
        Registered MSBuild instance: Visual Studio Enterprise 2022 17.0.31324.12 - "C:\Program Files\Microsoft Visual Studio\2022\Preview\MSBuild\Current\Bin"

Are you seeing otherwise? That might be an unrelated O# issue.

[snickler]

The more I think about it, the more I believe this issue is something likely to occur with Win Arm64 devices and Linux/macOS.

On Win Arm64 VSCode, it fails to resolve MSBuild instances except for the Standalone (even though the OmniSharp executable and OmniSharp.MSBuild.dll are .NET 4.7.2 and I have the latest VS 2019 Enterprise Preview installed).

[richlander]

@rainersigwald -- I thought it wasn't working on my Windows machine, but it looks good now. Must be my macOS machine only. I updated VS during this same experience, so it's possible that new bits came down that improved the situation after I tried O#.

[info]: OmniSharp.MSBuild.Discovery.MSBuildLocator
        Located 2 MSBuild instance(s)
            1: Visual Studio Community 2019 16.10.31313.381 - "C:\Program Files (x86)\Microsoft Visual Studio\2019\Preview\MSBuild\Current\Bin"
            2: StandAlone 16.9.0 - "c:\Users\rich\.vscode\extensions\ms-dotnettools.csharp-1.23.11\.omnisharp\1.37.8\.msbuild\Current\Bin"
[info]: OmniSharp.MSBuild.Discovery.MSBuildLocator
        Registered MSBuild instance: Visual Studio Community 2019 16.10.31313.381 - "C:\Program Files (x86)\Microsoft Visual Studio\2019\Preview\MSBuild\Current\Bin"

I think you are right that this is an O# issue and it's msbuild is too old.

/cc @JoeRobich @cartermp

[marcpopMSFT]

Closing as this is tracked in this issue: dotnet/core#6278