.NET Core + Mono Side-by-Side: 'Microsoft.NET.Sdk' specified could not be found.

I’m running into the common The SDK 'Microsoft.NET.Sdk' specified could not be found error on Arch Linux (Manjaro) - the same error apparently as #3287, #3160, #2356, #2937, and others.

I suspect my case is different. I worked on a .NET Core game for a while, then installed godot-mono, which includes Mono; when I came back to .NET Core, I get this error.

I suspect that VS Code finds the Mono runtime/SDK first, and then says “whelp there’s no .NET Core SDK installed for that” and fails hard. I hesitate to uninstall Godot and verify that this works, because I really do need both working side-by-side.

Is this an impossible/unsupported configuration?

OmniSharp log

OmniSharp server started with Mono 6.0.0.
    Path: /home/nightblade/.vscode/extensions/ms-vscode.csharp-1.21.3/.omnisharp/1.34.3/omnisharp/OmniSharp.exe
    PID: 8134

[info]: OmniSharp.Stdio.Host
        Starting OmniSharp on manjaro 0.0 (x64)
[info]: OmniSharp.Services.DotNetCliService
        DotNetPath set to dotnet
[warn]: OmniSharp.MSBuild.Discovery.Providers.MonoInstanceProvider
        It looks like you have Mono 5.2.0 or greater installed but MSBuild could not be found.
Try installing MSBuild into Mono (e.g. 'sudo apt-get install msbuild') to enable better MSBuild support.
[info]: OmniSharp.MSBuild.Discovery.MSBuildLocator
        Located 1 MSBuild instance(s)
            1: StandAlone 16.0 - "/home/nightblade/.vscode/extensions/ms-vscode.csharp-1.21.3/.omnisharp/1.34.3/omnisharp/.msbuild/Current/Bin"
[info]: OmniSharp.MSBuild.Discovery.MSBuildLocator
        MSBUILD_EXE_PATH environment variable set to '/home/nightblade/.vscode/extensions/ms-vscode.csharp-1.21.3/.omnisharp/1.34.3/omnisharp/.msbuild/Current/Bin/MSBuild.dll'
[info]: OmniSharp.MSBuild.Discovery.MSBuildLocator
        Registered MSBuild instance: StandAlone 16.0 - "/home/nightblade/.vscode/extensions/ms-vscode.csharp-1.21.3/.omnisharp/1.34.3/omnisharp/.msbuild/Current/Bin"
            CscToolExe = csc.exe
            TargetFrameworkRootPath = /usr/lib/mono/xbuild-frameworks
            MSBuildToolsPath = /home/nightblade/.vscode/extensions/ms-vscode.csharp-1.21.3/.omnisharp/1.34.3/omnisharp/.msbuild/Current/Bin
            CscToolPath = /home/nightblade/.vscode/extensions/ms-vscode.csharp-1.21.3/.omnisharp/1.34.3/omnisharp/.msbuild/Current/Bin/Roslyn
            BypassFrameworkInstallChecks = true
            MSBuildExtensionsPath = /usr/lib/mono/xbuild
[info]: OmniSharp.Cake.CakeProjectSystem
        Detecting Cake files in '/home/nightblade/code/ali-the-android'.
[info]: OmniSharp.Cake.CakeProjectSystem
        Could not find any Cake files
[info]: OmniSharp.MSBuild.ProjectSystem
        Detecting projects in '/home/nightblade/code/ali-the-android/AliTheAndroid.sln'.
[info]: OmniSharp.MSBuild.ProjectManager
        Queue project update for '/home/nightblade/code/ali-the-android/AliTheAndroid/AliTheAndroid.csproj'
[info]: OmniSharp.MSBuild.ProjectManager
        Queue project update for '/home/nightblade/code/ali-the-android/AliTheAndroid.Tests/AliTheAndroid.Tests.csproj'
[info]: OmniSharp.Script.ScriptProjectSystem
        Detecting CSX files in '/home/nightblade/code/ali-the-android'.
[info]: OmniSharp.Script.ScriptProjectSystem
        Could not find any CSX files
[info]: OmniSharp.WorkspaceInitializer
        Invoking Workspace Options Provider: OmniSharp.Roslyn.CSharp.Services.CSharpFormattingWorkspaceOptionsProvider, Order: 0
[info]: OmniSharp.MSBuild.ProjectManager
        Loading project: /home/nightblade/code/ali-the-android/AliTheAndroid/AliTheAndroid.csproj
[info]: OmniSharp.WorkspaceInitializer
        Invoking Workspace Options Provider: OmniSharp.Roslyn.CSharp.Services.RenameWorkspaceOptionsProvider, Order: 100
[info]: OmniSharp.WorkspaceInitializer
        Invoking Workspace Options Provider: OmniSharp.Roslyn.CSharp.Services.EditorConfigWorkspaceOptionsProvider, Order: 200
[info]: OmniSharp.WorkspaceInitializer
        Configuration finished.
[info]: OmniSharp.Stdio.Host
        Omnisharp server running using Stdio at location '/home/nightblade/code/ali-the-android' on host 8000.
[warn]: OmniSharp.MSBuild.ProjectManager
        Failed to load project file '/home/nightblade/code/ali-the-android/AliTheAndroid/AliTheAndroid.csproj'.
/home/nightblade/code/ali-the-android/AliTheAndroid/AliTheAndroid.csproj(1,1)
Microsoft.Build.Exceptions.InvalidProjectFileException: The SDK 'Microsoft.NET.Sdk' specified could not be found.  /home/nightblade/code/ali-the-android/AliTheAndroid/AliTheAndroid.csproj

Environment information

VSCode version: 1.38.1 C# Extension: 1.21.3

Mono Information

OmniSharp using global mono :6.0.0

Dotnet Information

.NET Core SDK (reflecting any global.json): Version: 2.2.108 Commit: 33ed5b90ce

Runtime Environment: OS Name: manjaro OS Version:
OS Platform: Linux RID: arch-x64 Base Path: /opt/dotnet/sdk/2.2.108/

Host (useful for support): Version: 2.2.6 Commit: 7dac9b1b51

.NET Core SDKs installed: 2.2.108 [/opt/dotnet/sdk]

.NET Core runtimes installed: Microsoft.NETCore.App 2.2.6 [/opt/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-vscode	1.21.3
godot-tools	geequlim	0.3.7
mono-debug	ms-vscode	0.15.8
python	ms-python	2019.9.34911
vscode-nxunit-test-adapter	wghats	0.1.2
vscode-test-explorer	hbenl	2.14.6

[kinglionsz]

Microsoft.Build.Exceptions.InvalidProjectFileException: The SDK ‘Microsoft.NET.Sdk’ specified could not be found. /home/nightblade/code/ali-the-android/AliTheAndroid/AliTheAndroid.csproj

PLS ADD THE FILE:

omnisharp.json :

{ “MSBuild”: { “UseLegacySdkResolver”: true } }

https://github.com/OmniSharp/omnisharp-vscode/issues/3287#issuecomment-536180721

[Baltasarq]

I’ve run into this issue with Manjaro Linux fully updated (Arch based). I’ve MonoDevelop installed, working fine with Mono. I wanted to try dotnet core, so I downloaded & installed & created the expected symbols in .bashrc. These are the last two lines.

export DOTNET_ROOT=$HOME/bin/dotnet
export PATH=$PATH:$HOME/bin/dotnet

…which seem to work fine:

$ echo $DOTNET_ROOT
/home/baltasarq/bin/dotnet
$ echo $PATH
/home/baltasarq/bin/google-cloud-sdk/bin:/home/baltasarq/.local/bin:/home/baltasarq/.local/bin:/usr/local/sbin:/usr/local/bin:/usr/bin:/home/baltasarq/.local/share/flatpak/exports/bin:/usr/lib/jvm/default/bin:/usr/bin/site_perl:/usr/bin/vendor_perl:/usr/bin/core_perl:/home/baltasarq/.local/share/flatpak/exports/bin:/usr/lib/jvm/default/bin:/usr/bin/site_perl:/usr/bin/vendor_perl:/usr/bin/core_perl:/home/baltasarq/bin/node/bin:/home/baltasarq/bin/dotnet:/home/baltasarq/bin/node/bin:/home/baltasarq/bin/dotnet

$ dotnet --info
.NET Core SDK (reflecting any global.json):
 Version:   3.0.100
 Commit:    04339c3a26

Runtime Environment:
 OS Name:     manjaro
 OS Version:  
 OS Platform: Linux
 RID:         linux-x64
 Base Path:   /home/baltasarq/bin/dotnet/sdk/3.0.100/

Host (useful for support):
  Version: 3.0.0
  Commit:  7d57652f33

.NET Core SDKs installed:
  3.0.100 [/home/baltasarq/bin/dotnet/sdk]

.NET Core runtimes installed:
  Microsoft.AspNetCore.App 3.0.0 [/home/baltasarq/bin/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 3.0.0 [/home/baltasarq/bin/dotnet/shared/Microsoft.NETCore.App]

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

I can create a hello world dotnet application with:

$ dotnet new console --name HelloApp
$ cd HelloApp
$ dotnet run
Hello World!

Since I wanted to try Visual Studio Code and .NET Core, I installed Visual Studio Code: $ yay -S visual-studio-code-bin … which worked flawlessly. The problem is when I try to open the folder of the app HelloApp created before, then OmniSharp steps in and fails.

OmniSharp server started with Mono 6.0.0.
    Path: /home/baltasarq/.vscode/extensions/ms-vscode.csharp-1.21.3/.omnisharp/1.34.3/omnisharp/OmniSharp.exe
    PID: 26562

[warn]: OmniSharp.MSBuild.Discovery.Providers.MonoInstanceProvider
        It looks like you have Mono 5.2.0 or greater installed but MSBuild could not be found.
Try installing MSBuild into Mono (e.g. 'sudo apt-get install msbuild') to enable better MSBuild support.
[info]: OmniSharp.MSBuild.Discovery.MSBuildLocator
        Located 1 MSBuild instance(s)
            1: StandAlone 16.0 - "/home/baltasarq/.vscode/extensions/ms-vscode.csharp-1.21.3/.omnisharp/1.34.3/omnisharp/.msbuild/Current/Bin"
[info]: OmniSharp.MSBuild.Discovery.MSBuildLocator
        Registered MSBuild instance: StandAlone 16.0 - "/home/baltasarq/.vscode/extensions/ms-vscode.csharp-1.21.3/.omnisharp/1.34.3/omnisharp/.msbuild/Current/Bin"
            CscToolExe = csc.exe
            TargetFrameworkRootPath = /usr/lib/mono/xbuild-frameworks
            MSBuildToolsPath = /home/baltasarq/.vscode/extensions/ms-vscode.csharp-1.21.3/.omnisharp/1.34.3/omnisharp/.msbuild/Current/Bin
            CscToolPath = /home/baltasarq/.vscode/extensions/ms-vscode.csharp-1.21.3/.omnisharp/1.34.3/omnisharp/.msbuild/Current/Bin/Roslyn
            BypassFrameworkInstallChecks = true
            MSBuildExtensionsPath = /usr/lib/mono/xbuild
Microsoft.Build.Exceptions.InvalidProjectFileException: The SDK 'Microsoft.NET.Sdk' specified could not be found.  /home/baltasarq/tmp/HelloApp/HelloApp.csproj
[fail]: OmniSharp.MSBuild.ProjectManager
        Attempted to update project that is not loaded: /home/baltasarq/tmp/HelloApp/HelloApp.csproj

I’ve looked for a solution in the form of a framework selector or “PATH to dotnet” or similar configuration, unfortunately to no avail. Since OmniSharp’s output suggest to install msbuild for Linux, I also tried that, uninstalled the extension and installed it back again. Unofrtunately, that did not solve anything.