OmniSharp fails to load projects due to Microsoft.CodeAnalysis.CSharp.CodeStyle analyzer reference

[alexrp]

• OmniSharp: 1.37.10
• .NET: 6.0.100-preview.4.21255.9

Loading one of my larger solutions results in the OmniSharp log being flooded with the following:

[fail]: OmniSharp.MSBuild.ProjectManager
        Failure while loading the analyzer reference 'Microsoft.CodeAnalysis.CSharp.CodeStyle': Could not load file or assembly 'Microsoft.CodeAnalysis, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The system cannot find the file specified.

Unfortunately, it's going to be very hard to reduce this solution to a reasonable repro that I can post here so I'm hoping the error might ring a bell to someone.

[filipw]

OmniSharp does not support Microsoft.CodeAnalysis 4.x.x because it ships with its own 3.11.0-1.21262.10 this will converge in the future but for now it is too early for us to move to 4.

[alexrp]

I'm not referencing that version of Microsoft.CodeAnalysis anywhere though. I have an analyzer project referencing 3.9.0 only.

[alexrp]

I also have a project in the solution that uses RoslynCodeTaskFactory FWIW.

But what's weird is that if I disable the use of RoslynCodeTaskFactory and remove all analyzer references, I still get these errors.

I'm really not sure where the 4.x reference could be coming from.

[alexrp]

Good news. I have a relatively simple project that repros the issue: https://github.com/alexrp/system-terminal

Just clone the master branch and open the folder in VS Code with the latest OmniSharp and .NET 6 Preview 4 installed. I assume this is happening (somehow) because this project uses Microsoft.CodeAnalysis.BannedApiAnalyzers. Projects that don't use external analyzers from NuGet have no issues.

[alexrp]

Narrowed it down: EnforceCodeStyleInBuild=true seems to cause it.

I guess these analyzers are compiled against a newer Roslyn version. I've worked around this for now by doing:

        <EnforceCodeStyleInBuild Condition="'$(DesignTimeBuild)' != 'true'">true</EnforceCodeStyleInBuild>

[filipw]

Resolved by #2175