Omnisharp not working in VS Code online (code spaces) for standard dotnet web api application.

Issue Description

In VS Code online (codespaces), Omnisharp seems to not work anymore. It doesn’t find any of the system libraries, etc:

Lot’s of error messages like:

The type or namespace name 'System' could not be found (are you missing a using directive or an assembly reference?) [TestApi, TestApi]

Steps to Reproduce

1. Create a new VS code online (codespaces) instance with the standard image.
2. Create a new web api with dotnet new webapi
3. Install C# extensions
4. Open .cs file and look at the highlighting and errors.

Expected Behavior

Omnisharp and C# extensions should work out of the box.

Actual Behavior

As described above. Highlighting and intellisense does not appear to work.

Logs

OmniSharp log

Starting OmniSharp server at 7/15/2020, 4:14:17 PM Target: /home/codespace/workspace

OmniSharp server started. Path: /home/codespace/.vscode-remote/extensions/ms-dotnettools.csharp-1.22.1/.omnisharp/1.35.3/run PID: 1885

    Starting OmniSharp on debian 9.0 (x64)

    DotNetPath set to dotnet

    Located 1 MSBuild instance(s)
        1: StandAlone 16.4 - "/home/codespace/.vscode-remote/extensions/ms-dotnettools.csharp-1.22.1/.omnisharp/1.35.3/omnisharp/.msbuild/Current/Bin"

    MSBUILD_EXE_PATH environment variable set to '/home/codespace/.vscode-remote/extensions/ms-dotnettools.csharp-1.22.1/.omnisharp/1.35.3/omnisharp/.msbuild/Current/Bin/MSBuild.dll'

    Registered MSBuild instance: StandAlone 16.4 - "/home/codespace/.vscode-remote/extensions/ms-dotnettools.csharp-1.22.1/.omnisharp/1.35.3/omnisharp/.msbuild/Current/Bin"
        CscToolExe = csc.exe
        MSBuildToolsPath = /home/codespace/.vscode-remote/extensions/ms-dotnettools.csharp-1.22.1/.omnisharp/1.35.3/omnisharp/.msbuild/Current/Bin
        CscToolPath = /home/codespace/.vscode-remote/extensions/ms-dotnettools.csharp-1.22.1/.omnisharp/1.35.3/omnisharp/.msbuild/Current/Bin/Roslyn
        BypassFrameworkInstallChecks = true
        MSBuildExtensionsPath = /home/codespace/.vscode-remote/extensions/ms-dotnettools.csharp-1.22.1/.omnisharp/1.35.3/omnisharp/.msbuild

    Detecting Cake files in '/home/codespace/workspace'.

    Could not find any Cake files

    No solution files found in '/home/codespace/workspace'

    Queue project update for '/home/codespace/workspace/TestApi/TestApi.csproj'

    Detecting CSX files in '/home/codespace/workspace'.

    Could not find any CSX files

    Invoking Workspace Options Provider: OmniSharp.Roslyn.CSharp.Services.CSharpFormattingWorkspaceOptionsProvider, Order: 0

    Loading project: /home/codespace/workspace/TestApi/TestApi.csproj

    Invoking Workspace Options Provider: OmniSharp.Roslyn.CSharp.Services.RenameWorkspaceOptionsProvider, Order: 100

    Invoking Workspace Options Provider: OmniSharp.Roslyn.CSharp.Services.ImplementTypeWorkspaceOptionsProvider, Order: 110

    Invoking Workspace Options Provider: OmniSharp.Roslyn.CSharp.Services.BlockStructureWorkspaceOptionsProvider, Order: 140

    Configuration finished.

    Omnisharp server running using Stdio at location '/home/codespace/workspace' on host 1783.

    Successfully loaded project file '/home/codespace/workspace/TestApi/TestApi.csproj'.

    Adding project '/home/codespace/workspace/TestApi/TestApi.csproj'

    Update project: TestApi

C# log

It is empty

Environment information

VSCode version: 1.45.1 C# Extension: 1.22.1

Mono Information

OmniSharp using built-in mono

Dotnet Information

.NET Core SDK (reflecting any global.json): Version: 3.1.202 Commit: 6ea70c8dca

Runtime Environment: OS Name: debian OS Version: 9 OS Platform: Linux RID: debian.9-x64 Base Path: /opt/dotnet/sdks/3.1.202/sdk/3.1.202/

Host (useful for support): Version: 3.1.4 Commit: 0c2e69caa6

.NET Core SDKs installed: 1.1.14 [/home/codespace/.dotnet/sdk] 2.1.806 [/home/codespace/.dotnet/sdk] 2.2.402 [/home/codespace/.dotnet/sdk] 3.0.103 [/home/codespace/.dotnet/sdk] 3.1.202 [/home/codespace/.dotnet/sdk]

.NET Core runtimes installed: Microsoft.AspNetCore.All 2.2.7 [/home/codespace/.dotnet/shared/Microsoft.AspNetCore.All] Microsoft.AspNetCore.App 2.2.7 [/home/codespace/.dotnet/shared/Microsoft.AspNetCore.App] Microsoft.AspNetCore.App 3.0.3 [/home/codespace/.dotnet/shared/Microsoft.AspNetCore.App] Microsoft.AspNetCore.App 3.1.4 [/home/codespace/.dotnet/shared/Microsoft.AspNetCore.App] Microsoft.NETCore.App 1.1.13 [/home/codespace/.dotnet/shared/Microsoft.NETCore.App] Microsoft.NETCore.App 2.2.7 [/home/codespace/.dotnet/shared/Microsoft.NETCore.App] Microsoft.NETCore.App 3.0.3 [/home/codespace/.dotnet/shared/Microsoft.NETCore.App] Microsoft.NETCore.App 3.1.4 [/home/codespace/.dotnet/shared/Microsoft.NETCore.App]

To install additional .NET Core runtimes or SDKs: https://aka.ms/dotnet-download

Visual Studio Code Extensions

Extension	Author	Version
csharp	ms-dotnettools	1.22.1
vscode-pull-request-github	GitHub	0.16.0
vsonline	ms-vsonline	1.0.2471

[JoeRobich]

@hansenms Thanks for reporting this issue. I was able to reproduce it.

From the command line the project restores and builds fine. The design time build seems to be fine because the project loads and errors are reported. But it seems the sdk reference assemblies are not being added properly to the workspace. Will need some additional investigation to determine where the issue lies.

[JoeRobich]

Closing this issue. Codespaces has updated to a newer version of the .dev-container used in the default codespaces environment with properly installed .net core SDK.

You will need to either delete and recreate your codespaces environment or follow the workaround in https://github.com/OmniSharp/omnisharp-vscode/issues/3913#issuecomment-663749636 to install a working SDK.