Omnisharp crashes while opening folder

[mkorsukov]

Environment data

Env	Version
OS	Ubuntu 26.04
.NET	10.0.11
VS Code	1.134.0
C# extension	2.160.4

C# logs

OmniSharp server started with .NET 10.0.111
.
    Path: /home/max/.vscode/extensions/ms-dotnettools.csharp-2.160.4-linux-x64/.omnisharp/1.39.14-net6.0/OmniSharp.dll
    PID: 4323

[STDERR] System.ArgumentException: OmniSharp only supports being launched with a directory path or a path to a solution (.sln, .slnf) file. (Parameter 'path')
   at OmniSharp.Services.OmniSharpEnvironment..ctor(String path, Int32 hostPid, LogLevel logLevel, String[
[STDERR] ] additionalArguments) in /home/vsts/work/1/s/src/OmniSharp.Host/Services/OmniSharpEnvironment.cs:line 38
   at OmniSharp.CommandLineApplicationExtensions.CreateEnvironment(CommandLineApplication application) in /home/vsts/work/1/s/src/OmniSharp.Host/CommandLineApplicationExtensions.cs:line 12
   at OmniSharp.Stdio.Driver.Program.<>c__DisplayClass0_1.<Main>b__1() in /home/vsts/work/1/s/src/OmniSharp.Stdio.Driver/Program.cs:line 49
   at OmniSharp.CommandLineApplication.<>c__DisplayClass13_0.<OnExecute>b__0() in /home/vsts/work/1/s/src/OmniSharp.Host/CommandLineApplication.cs:line 98
   at McMaster.Extensions.CommandLineUtils.CommandLineApplication.<>c__DisplayClass143_0.<OnExecute>b__0(CancellationToken _)
   at McMaster.Extensions.CommandLineUtils.CommandLineApplication.ExecuteAsync(String[] args, CancellationToken cancellationToken)
   at McMaster.Extensions.CommandLineUtils.CommandLineApplication.Execute(String[] args)
   at OmniSharp.CommandLineApplication.Execute(String[] args) in /home/vsts/work/1/s/src/OmniSharp.Host/CommandLineApplication.cs:line 68
   at OmniSharp.Stdio.Driver.Program.<>c__DisplayClass0_0.<Main>b__0() in /home/vsts/work/1/s/src/OmniSharp.Stdio.Driver/Program.cs:line 84
   at OmniSharp.HostHelpers.Start(Func`1 action) in /home/vsts/work/1/s/src/OmniSharp.Host/HostHelpers.cs:line 30

Steps to reproduce

1. Open a folder with solution file (slnx) and projects)
2. See output tab in VS Code

Expected behavior

Solution discovered and projects loaded as before.

[JoeRobich]

OmniSharp does not support .slnx files in 1.39.x. Do you have the dotnet.defaultSolution setting set?

[jasonmalinowski]

@mkorsukov And just to check, is there a missing gap that forced you to enable Omnisharp? Because the easy workaround here would be to switch off of that, but if that's going to break you in a different way, that's not good. 😄

[mkorsukov]

OmniSharp does not support .slnx files in 1.39.x. Do you have the dotnet.defaultSolution setting set?

@JoeRobich @jasonmalinowski Please see my current C# settings. Any weird combinations here?

"omnisharp.loggingLevel": "error",
"omnisharp.sdkIncludePrereleases": false,
"dotnet.server.useOmnisharp": true,
"dotnet.defaultSolution": "disable",
"dotnet.codeLens.enableReferencesCodeLens": false,
"dotnet.codeLens.enableTestsCodeLens": false,
"dotnetAcquisitionExtension.enableTelemetry": false

A couple weeks ago I worked on the same code base (using previous C# extension version) and there was no issues. I have C# extension installed only, there is no C# DevKit on machine.

[jasonmalinowski]

@mkorsukov Try removing the omnisharp line and the "dotnet.server.useOmnisharp" line and see if that helps. That said if defaultSolution was set to "disable" then I'm quite confused what was causing the solution load unless you were picking it manually.

[mkorsukov]

@jasonmalinowski I appreciate your response! So I removed / commented the settings:

// "omnisharp.loggingLevel": "error",
// "omnisharp.sdkIncludePrereleases": false,
// "dotnet.server.useOmnisharp": true,

Then opened the folder with code as usual. There were no errors / warnings in the VS Code output, just [info] lines from the Microsoft.CodeAnalysis.LanguageServer. However, I noticed the code highlighting is not properly working. Then I run the .NET: Open solution by F1 command (I never used that command before), and code syntax + navigation restored! 👍🏻

So, is C# extension working now on top of Microsoft.CodeAnalysis.LanguageServer vs OmniSharp internals?

[jasonmalinowski]

@mkorsukov -- it defaults to Microsoft.CodeAnalysis.LanguageServer unless set it to use Omnisharp explicitly.

Your setting for dotnet.defaultSolution is why the solution had to be specified explicitly; either remove that (if you have just one solution) or point it to your solution for the automatic load.

[mkorsukov]

@jasonmalinowski Before I close the issue, let me ask if I'm using VS Code + C# extension in some unusual or deprecated way? Yes, "dotnet.defaultSolution" is disabled to not point to specific one. So, Microsoft.CodeAnalysis.LanguageServer doesn't pick the only solution (in a folder) by default?

[jasonmalinowski]

"disabled" means "don't load anything, I'll tell you what to open". Unless maybe this is why you were using Omnisharp, which has some more logic to load things as you open source files?

[jasonmalinowski]

And maybe to answer your question differently: we know lots of folks might have turned on Omnisharp mode at some point, and then forgot they did that. It's not getting the same investment as the main language server so I'm starting to ask folks if they remember why they had changed.

[mkorsukov]

@jasonmalinowski @JoeRobich I appreciate your support and feedback! The issue is resolved with proper configuration and C# extension works fine now.