omnisharp is using bits not available in a 5.0 source-built sdk

[tmds]

Steps

1. Use a source-built SDK, like the 5.0-preview8 sdk on Fedora.
2. Create a dotnet new console project.
3. Add an omnisharp.json file:

{
    "RoslynExtensionsOptions": {
        "enableAnalyzersSupport": true
    },
    "FormattingOptions": {
        "enableEditorConfigSupport": true
    }
}

4. Open vscode with csharp 1.23.2 installed.

Result

The project fails to load with this message in the log:

fail]: OmniSharp.MSBuild.ProjectLoader
        The "CheckForDuplicateFrameworkReferences" task could not be loaded from the assembly /usr/lib64/dotnet/sdk/5.0.100-preview.8.20417.9/Sdks/Microsoft.NET.Sdk/targets/../tools/net472/Microsoft.NET.Build.Tasks.dll. Invalid Image Confirm that the <UsingTask> declaration is correct, that the assembly and all its dependencies are available, and that the task contains a public class that implements Microsoft.Build.Framework.ITask.
[warn]: OmniSharp.MSBuild.ProjectManager
        Failed to load project file '/tmp/console/console.csproj'.
/tmp/console/console.csproj
/usr/lib64/dotnet/sdk/5.0.100-preview.8.20417.9/Sdks/Microsoft.NET.Sdk/targets/Microsoft.NET.Sdk.FrameworkReferenceResolution.targets(39,5): Error: The "CheckForDuplicateFrameworkReferences" task could not be loaded from the assembly /usr/lib64/dotnet/sdk/5.0.100-preview.8.20417.9/Sdks/Microsoft.NET.Sdk/targets/../tools/net472/Microsoft.NET.Build.Tasks.dll. Invalid Image Confirm that the <UsingTask> declaration is correct, that the assembly and all its dependencies are available, and that the task contains a public class that implements Microsoft.Build.Framework.ITask.

The net472 folder OmniSharp is trying to use does not exist on a source-built sdk:

$ ls /usr/lib64/dotnet/sdk/5.0.100-preview.8.20417.9/Sdks/Microsoft.NET.Sdk/targets/../tools
net5.0

cc @crummel @dagood @omajid

[tmds]

We ran into a similar issue with .NET Core 2.0: dotnet/vscode-csharp#1744, dotnet/source-build#125.

[dagood]

dotnet/source-build#1650 is open on the source-build side to build for net* target frameworks properly. Some .NET Framework removal patches got added for 5.0 that are causing this the same way as last time. /cc @dseefeld

[filipw]

yes indeed, I am not sure it is really OmniSharp problem. As a Mono based tool it will also try to load .NET Framework build tasks

[tmds]

@filipw as .NET Core and mono are sharing more code, I wonder what is still missing for mono to use the netstandard/netcoreapp assemblies? Do you know?

[tmds]

We were not able to resolve this for 5.0.0 release of source-build.

as .NET Core and mono are sharing more code, I wonder what is still missing for mono to use the netstandard/netcoreapp assemblies? Do you know?

@filipw your thoughts? something we could look into for .NET 6 perhaps? It would be really nice if we could get rid of the net4* assemblies all together.

[omajid]

I was speaking about this to @leecow and @dleeapho earlier today too.

[leecow]

OmniSharp is aware of the difficulties and while there is a general desire to move to .NET Core/.NET 5, technical dependencies will keep them on .NET Framework for the foreseeable future.

@dseefeld, can you add your current plan here that you mentioned this morning?

[dseefeld]

OmniSharp is aware of the difficulties and while there is a general desire to move to .NET Core/.NET 5, technical dependencies will keep them on .NET Framework for the foreseeable future.

@dseefeld Dan Seefeldt FTE, can you add your current plan here that you mentioned this morning?

The current plan for source-build is to build the necessary assemblies for net4x in source-build. PR is here: dotnet/source-build#1928

[tmds]

OmniSharp is aware of the difficulties and while there is a general desire to move to .NET Core/.NET 5

I was assuming mono would support net6.0, making this problem disappear. But I'm not sure what ithe plan with mono actually is with .NET 5+. I've raised the question here: dotnet/standard#1785.

[tmds]

I've raised the question here: dotnet/standard#1785.

I got some interesting answers on that issue, though I don't know what it means in practice for a mono-user like omnishiarp.

The current plan for source-build is to build the necessary assemblies for net4x in source-build. PR is here: dotnet/source-build#1928

🎉 @dagood completed this, so I'm closing this issue.