VSCode on Linux not loading .csproj file, outputs error : Some projects have trouble loading. Please review the output for more details

Question

Mono is installed, everything is installed, but it can't load the .csproj file from Unity. Outputs an error:

Starting OmniSharp server at 26/2/2022, 8:26:37 am
    Target: /E/projects/My project/My project.sln

OmniSharp server started with Mono 6.12.0.
    Path: /home/mistreaper/.vscode/extensions/ms-dotnettools.csharp-1.24.0/.omnisharp/1.38.1-beta.72/omnisharp/OmniSharp.exe
    PID: 30651

[info]: OmniSharp.Stdio.Host
        Starting OmniSharp on arch 0.0 (x64)
[info]: OmniSharp.Services.DotNetCliService
        Checking the 'DOTNET_ROOT' environment variable to find a .NET SDK
[info]: OmniSharp.Services.DotNetCliService
        DotNetPath set to /usr/share/dotnet/dotnet
[warn]: OmniSharp.MSBuild.Discovery.Providers.MonoInstanceProvider
        It looks like you have Mono 6.4.0 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, or upgrade to latest Mono: https://www.mono-project.com/download/stable/.
[info]: OmniSharp.MSBuild.Discovery.MSBuildLocator
        Located 1 MSBuild instance(s)
            1: StandAlone 17.1.0 - "/home/mistreaper/.vscode/extensions/ms-dotnettools.csharp-1.24.0/.omnisharp/1.38.1-beta.72/omnisharp/.msbuild/Current/Bin"
[info]: OmniSharp.MSBuild.Discovery.MSBuildLocator
        MSBUILD_EXE_PATH environment variable set to '/home/mistreaper/.vscode/extensions/ms-dotnettools.csharp-1.24.0/.omnisharp/1.38.1-beta.72/omnisharp/.msbuild/Current/Bin/MSBuild.exe'
[info]: OmniSharp.MSBuild.Discovery.MSBuildLocator
        Registered MSBuild instance: StandAlone 17.1.0 - "/home/mistreaper/.vscode/extensions/ms-dotnettools.csharp-1.24.0/.omnisharp/1.38.1-beta.72/omnisharp/.msbuild/Current/Bin"
            CscToolExe = csc.exe
            MSBuildToolsPath = /home/mistreaper/.vscode/extensions/ms-dotnettools.csharp-1.24.0/.omnisharp/1.38.1-beta.72/omnisharp/.msbuild/Current/Bin
            CscToolPath = /home/mistreaper/.vscode/extensions/ms-dotnettools.csharp-1.24.0/.omnisharp/1.38.1-beta.72/omnisharp/.msbuild/Current/Bin/Roslyn
            BypassFrameworkInstallChecks = true
            MSBuildExtensionsPath = /home/mistreaper/.vscode/extensions/ms-dotnettools.csharp-1.24.0/.omnisharp/1.38.1-beta.72/omnisharp/.msbuild
[info]: OmniSharp.WorkspaceInitializer
        Invoking Workspace Options Provider: OmniSharp.Roslyn.CSharp.Services.CSharpFormattingWorkspaceOptionsProvider, Order: 0
[info]: OmniSharp.WorkspaceInitializer
        Invoking Workspace Options Provider: OmniSharp.Roslyn.CSharp.Services.ImplementTypeWorkspaceOptionsProvider, Order: 110
[info]: OmniSharp.Cake.CakeProjectSystem
        Detecting Cake files in '/E/projects/My project'.
[info]: OmniSharp.Cake.CakeProjectSystem
        Did not find any Cake files
[info]: OmniSharp.MSBuild.ProjectSystem
        Detecting projects in '/E/projects/My project/My project.sln'.
[info]: OmniSharp.MSBuild.ProjectManager
        Queue project update for '/E/projects/My project/Assembly-CSharp.csproj'
[info]: OmniSharp.Script.ScriptProjectSystem
        Detecting CSX files in '/E/projects/My project'.
[info]: OmniSharp.Script.ScriptProjectSystem
        Did not find any CSX files
[info]: OmniSharp.WorkspaceInitializer
        Configuration finished.
[info]: OmniSharp.Stdio.Host
        Omnisharp server running using Stdio at location '/E/projects/My project' on host 30408.
[info]: OmniSharp.MSBuild.ProjectManager
        Loading project: /E/projects/My project/Assembly-CSharp.csproj
Can't find custom attr constructor image: /E/projects/My project/Library/ScriptAssemblies/Unity.Rider.Editor.dll mtoken: 0x0a000007 due to: Could not find method '.ctor' due to a type load error: Could not set up parent class, due to: Could not set up parent class, due to:  assembly:/home/mistreaper/Unity/Hub/Editor/2020.3.30f1/Editor/Data/NetStandard/ref/2.0.0/netstandard.dll type:Object member:(null) assembly:/home/mistreaper/Unity/Hub/Editor/2020.3.30f1/Editor/Data/NetStandard/ref/2.0.0/netstandard.dll type:Attribute member:(null) assembly:/E/projects/My project/Library/ScriptAssemblies/UnityEngine.TestRunner.dll type:TestRunCallbackAttribute member:(null) assembly:/E/projects/My project/Library/ScriptAssemblies/UnityEngine.TestRunner.dll type:TestRunCallbackAttribute member:(null)
[fail]: OmniSharp.MSBuild.ProjectLoader
        The "ResolveAssemblyReference" task failed unexpectedly.
System.TypeLoadException: Could not find method '.ctor' due to a type load error: Could not set up parent class, due to: Could not set up parent class, due to:  assembly:/home/mistreaper/Unity/Hub/Editor/2020.3.30f1/Editor/Data/NetStandard/ref/2.0.0/netstandard.dll type:Object member:(null) assembly:/home/mistreaper/Unity/Hub/Editor/2020.3.30f1/Editor/Data/NetStandard/ref/2.0.0/netstandard.dll type:Attribute member:(null) assembly:/E/projects/My project/Library/ScriptAssemblies/UnityEngine.TestRunner.dll type:TestRunCallbackAttribute member:(null)
  at (wrapper managed-to-native) System.MonoCustomAttrs.GetCustomAttributesDataInternal(System.Reflection.ICustomAttributeProvider)
  at System.MonoCustomAttrs.GetCustomAttributesDataBase (System.Reflection.ICustomAttributeProvider obj, System.Type attributeType, System.Boolean inheritedOnly) [0x00010] in <62b430b945fa49a19a75382ef03e7bed>:0 
  at System.MonoCustomAttrs.GetCustomAttributesData (System.Reflection.ICustomAttributeProvider obj, System.Boolean inherit) [0x00011] in <62b430b945fa49a19a75382ef03e7bed>:0 
  at System.Reflection.CustomAttributeData.GetCustomAttributes (System.Reflection.Assembly target) [0x00000] in <62b430b945fa49a19a75382ef03e7bed>:0 
  at System.Reflection.RuntimeAssembly.GetCustomAttributesData () [0x00000] in <62b430b945fa49a19a75382ef03e7bed>:0 
  at Microsoft.Build.Tasks.AssemblyInformation.GetFrameworkName () [0x00025] in <20c026c297134c06b9590841bcdf5d79>:0 
  at Microsoft.Build.Tasks.AssemblyInformation.get_FrameworkNameAttribute () [0x00028] in <20c026c297134c06b9590841bcdf5d79>:0 
  at Microsoft.Build.Tasks.AssemblyDependency.AssemblyMetadata..ctor (System.String path) [0x00019] in <20c026c297134c06b9590841bcdf5d79>:0 
  at Microsoft.Build.Tasks.AssemblyInformation+<>c.<GetAssemblyMetadata>b__21_0 (System.String p) [0x00000] in <20c026c297134c06b9590841bcdf5d79>:0 
  at System.Collections.Concurrent.ConcurrentDictionary`2[TKey,TValue].GetOrAdd (TKey key, System.Func`2[T,TResult] valueFactory) [0x00034] in <62b430b945fa49a19a75382ef03e7bed>:0 
  at Microsoft.Build.Tasks.AssemblyInformation.GetAssemblyMetadata (System.String path, System.Collections.Concurrent.ConcurrentDictionary`2[TKey,TValue] assemblyMetadataCache, Microsoft.Build.Shared.AssemblyNameExtension[]& dependencies, System.String[]& scatterFiles, System.Runtime.Versioning.FrameworkName& frameworkName) [0x00006] in <20c026c297134c06b9590841bcdf5d79>:0 
  at Microsoft.Build.Tasks.ResolveAssemblyReference+<>c.<Execute>b__255_4 (System.String path, System.Collections.Concurrent.ConcurrentDictionary`2[TKey,TValue] assemblyMetadataCache, Microsoft.Build.Shared.AssemblyNameExtension[]& dependencies, System.String[]& scatterFiles, System.Runtime.Versioning.FrameworkName& frameworkName) [0x00000] in <20c026c297134c06b9590841bcdf5d79>:0 
  at Microsoft.Build.Tasks.SystemState.GetAssemblyMetadata (System.String path, System.Collections.Concurrent.ConcurrentDictionary`2[TKey,TValue] assemblyMetadataCache, Microsoft.Build.Shared.AssemblyNameExtension[]& dependencies, System.String[]& scatterFiles, System.Runtime.Versioning.FrameworkName& frameworkName) [0x00010] in <20c026c297134c06b9590841bcdf5d79>:0 
  at Microsoft.Build.Tasks.ReferenceTable.GetUnifiedAssemblyMetadata (Microsoft.Build.Tasks.Reference reference, System.Collections.Generic.IEnumerable`1[Microsoft.Build.Tasks.UnifiedAssemblyName]& unifiedDependencies, System.String[]& scatterFiles) [0x00023] in <20c026c297134c06b9590841bcdf5d79>:0 
  at Microsoft.Build.Tasks.ReferenceTable.FindDependenciesAndScatterFiles (Microsoft.Build.Tasks.Reference reference, System.Collections.Generic.List`1[T] newEntries) [0x0003a] in <20c026c297134c06b9590841bcdf5d79>:0 
  at Microsoft.Build.Tasks.ReferenceTable.FindAssociatedFiles () [0x000ea] in <20c026c297134c06b9590841bcdf5d79>:0 
  at Microsoft.Build.Tasks.ReferenceTable.ComputeClosure () [0x0000a] in <20c026c297134c06b9590841bcdf5d79>:0 
  at Microsoft.Build.Tasks.ReferenceTable.ComputeClosure (System.Collections.Generic.IEnumerable`1[T] remappedAssembliesValue, Microsoft.Build.Framework.ITaskItem[] referenceAssemblyFiles, Microsoft.Build.Framework.ITaskItem[] referenceAssemblyNames, System.Collections.Generic.List`1[T] exceptions) [0x00038] in <20c026c297134c06b9590841bcdf5d79>:0 
  at Microsoft.Build.Tasks.ResolveAssemblyReference.Execute (Microsoft.Build.Shared.FileExists fileExists, Microsoft.Build.Shared.DirectoryExists directoryExists, Microsoft.Build.Tasks.GetDirectories getDirectories, Microsoft.Build.Tasks.GetAssemblyName getAssemblyName, Microsoft.Build.Tasks.GetAssemblyMetadata getAssemblyMetadata, Microsoft.Build.Shared.GetRegistrySubKeyNames getRegistrySubKeyNames, Microsoft.Build.Shared.GetRegistrySubKeyDefaultValue getRegistrySubKeyDefaultValue, Microsoft.Build.Tasks.GetLastWriteTime getLastWriteTime, Microsoft.Build.Tasks.GetAssemblyRuntimeVersion getRuntimeVersion, Microsoft.Build.Shared.OpenBaseKey openBaseKey, Microsoft.Build.Tasks.GetAssemblyPathInGac getAssemblyPathInGac, Microsoft.Build.Tasks.IsWinMDFile isWinMDFile, Microsoft.Build.Tasks.ReadMachineTypeFromPEHeader readMachineTypeFromPEHeader) [0x00515] in <20c026c297134c06b9590841bcdf5d79>:0 
  at Microsoft.Build.Tasks.ResolveAssemblyReference.Execute () [0x00000] in <20c026c297134c06b9590841bcdf5d79>:0 
  at Microsoft.Build.BackEnd.TaskExecutionHost.Microsoft.Build.BackEnd.ITaskExecutionHost.Execute () [0x00029] in <29047405fcfe41bbb744a55b7d0f20fa>:0 
  at Microsoft.Build.BackEnd.TaskBuilder.ExecuteInstantiatedTask (Microsoft.Build.BackEnd.ITaskExecutionHost taskExecutionHost, Microsoft.Build.BackEnd.Logging.TaskLoggingContext taskLoggingContext, Microsoft.Build.BackEnd.TaskHost taskHost, Microsoft.Build.BackEnd.ItemBucket bucket, Microsoft.Build.BackEnd.TaskExecutionMode howToExecuteTask) [0x002fb] in <29047405fcfe41bbb744a55b7d0f20fa>:0 
[warn]: OmniSharp.MSBuild.ProjectManager
        Failed to load project file '/E/projects/My project/Assembly-CSharp.csproj'.
/E/projects/My project/Assembly-CSharp.csproj
/home/mistreaper/.vscode/extensions/ms-dotnettools.csharp-1.24.0/.omnisharp/1.38.1-beta.72/omnisharp/.msbuild/Current/Bin/Microsoft.Common.CurrentVersion.targets(2301,5): Error: The "ResolveAssemblyReference" task failed unexpectedly.
System.TypeLoadException: Could not find method '.ctor' due to a type load error: Could not set up parent class, due to: Could not set up parent class, due to:  assembly:/home/mistreaper/Unity/Hub/Editor/2020.3.30f1/Editor/Data/NetStandard/ref/2.0.0/netstandard.dll type:Object member:(null) assembly:/home/mistreaper/Unity/Hub/Editor/2020.3.30f1/Editor/Data/NetStandard/ref/2.0.0/netstandard.dll type:Attribute member:(null) assembly:/E/projects/My project/Library/ScriptAssemblies/UnityEngine.TestRunner.dll type:TestRunCallbackAttribute member:(null)
  at (wrapper managed-to-native) System.MonoCustomAttrs.GetCustomAttributesDataInternal(System.Reflection.ICustomAttributeProvider)
  at System.MonoCustomAttrs.GetCustomAttributesDataBase (System.Reflection.ICustomAttributeProvider obj, System.Type attributeType, System.Boolean inheritedOnly) [0x00010] in <62b430b945fa49a19a75382ef03e7bed>:0 
  at System.MonoCustomAttrs.GetCustomAttributesData (System.Reflection.ICustomAttributeProvider obj, System.Boolean inherit) [0x00011] in <62b430b945fa49a19a75382ef03e7bed>:0 
  at System.Reflection.CustomAttributeData.GetCustomAttributes (System.Reflection.Assembly target) [0x00000] in <62b430b945fa49a19a75382ef03e7bed>:0 
  at System.Reflection.RuntimeAssembly.GetCustomAttributesData () [0x00000] in <62b430b945fa49a19a75382ef03e7bed>:0 
  at Microsoft.Build.Tasks.AssemblyInformation.GetFrameworkName () [0x00025] in <20c026c297134c06b9590841bcdf5d79>:0 
  at Microsoft.Build.Tasks.AssemblyInformation.get_FrameworkNameAttribute () [0x00028] in <20c026c297134c06b9590841bcdf5d79>:0 
  at Microsoft.Build.Tasks.AssemblyDependency.AssemblyMetadata..ctor (System.String path) [0x00019] in <20c026c297134c06b9590841bcdf5d79>:0 
  at Microsoft.Build.Tasks.AssemblyInformation+<>c.<GetAssemblyMetadata>b__21_0 (System.String p) [0x00000] in <20c026c297134c06b9590841bcdf5d79>:0 
  at System.Collections.Concurrent.ConcurrentDictionary`2[TKey,TValue].GetOrAdd (TKey key, System.Func`2[T,TResult] valueFactory) [0x00034] in <62b430b945fa49a19a75382ef03e7bed>:0 
  at Microsoft.Build.Tasks.AssemblyInformation.GetAssemblyMetadata (System.String path, System.Collections.Concurrent.ConcurrentDictionary`2[TKey,TValue] assemblyMetadataCache, Microsoft.Build.Shared.AssemblyNameExtension[]& dependencies, System.String[]& scatterFiles, System.Runtime.Versioning.FrameworkName& frameworkName) [0x00006] in <20c026c297134c06b9590841bcdf5d79>:0 
  at Microsoft.Build.Tasks.ResolveAssemblyReference+<>c.<Execute>b__255_4 (System.String path, System.Collections.Concurrent.ConcurrentDictionary`2[TKey,TValue] assemblyMetadataCache, Microsoft.Build.Shared.AssemblyNameExtension[]& dependencies, System.String[]& scatterFiles, System.Runtime.Versioning.FrameworkName& frameworkName) [0x00000] in <20c026c297134c06b9590841bcdf5d79>:0 
  at Microsoft.Build.Tasks.SystemState.GetAssemblyMetadata (System.String path, System.Collections.Concurrent.ConcurrentDictionary`2[TKey,TValue] assemblyMetadataCache, Microsoft.Build.Shared.AssemblyNameExtension[]& dependencies, System.String[]& scatterFiles, System.Runtime.Versioning.FrameworkName& frameworkName) [0x00010] in <20c026c297134c06b9590841bcdf5d79>:0 
  at Microsoft.Build.Tasks.ReferenceTable.GetUnifiedAssemblyMetadata (Microsoft.Build.Tasks.Reference reference, System.Collections.Generic.IEnumerable`1[Microsoft.Build.Tasks.UnifiedAssemblyName]& unifiedDependencies, System.String[]& scatterFiles) [0x00023] in <20c026c297134c06b9590841bcdf5d79>:0 
  at Microsoft.Build.Tasks.ReferenceTable.FindDependenciesAndScatterFiles (Microsoft.Build.Tasks.Reference reference, System.Collections.Generic.List`1[T] newEntries) [0x0003a] in <20c026c297134c06b9590841bcdf5d79>:0 
  at Microsoft.Build.Tasks.ReferenceTable.FindAssociatedFiles () [0x000ea] in <20c026c297134c06b9590841bcdf5d79>:0 
  at Microsoft.Build.Tasks.ReferenceTable.ComputeClosure () [0x0000a] in <20c026c297134c06b9590841bcdf5d79>:0 
  at Microsoft.Build.Tasks.ReferenceTable.ComputeClosure (System.Collections.Generic.IEnumerable`1[T] remappedAssembliesValue, Microsoft.Build.Framework.ITaskItem[] referenceAssemblyFiles, Microsoft.Build.Framework.ITaskItem[] referenceAssemblyNames, System.Collections.Generic.List`1[T] exceptions) [0x00038] in <20c026c297134c06b9590841bcdf5d79>:0 
  at Microsoft.Build.Tasks.ResolveAssemblyReference.Execute (Microsoft.Build.Shared.FileExists fileExists, Microsoft.Build.Shared.DirectoryExists directoryExists, Microsoft.Build.Tasks.GetDirectories getDirectories, Microsoft.Build.Tasks.GetAssemblyName getAssemblyName, Microsoft.Build.Tasks.GetAssemblyMetadata getAssemblyMetadata, Microsoft.Build.Shared.GetRegistrySubKeyNames getRegistrySubKeyNames, Microsoft.Build.Shared.GetRegistrySubKeyDefaultValue getRegistrySubKeyDefaultValue, Microsoft.Build.Tasks.GetLastWriteTime getLastWriteTime, Microsoft.Build.Tasks.GetAssemblyRuntimeVersion getRuntimeVersion, Microsoft.Build.Shared.OpenBaseKey openBaseKey, Microsoft.Build.Tasks.GetAssemblyPathInGac getAssemblyPathInGac, Microsoft.Build.Tasks.IsWinMDFile isWinMDFile, Microsoft.Build.Tasks.ReadMachineTypeFromPEHeader readMachineTypeFromPEHeader) [0x00515] in <20c026c297134c06b9590841bcdf5d79>:0 
  at Microsoft.Build.Tasks.ResolveAssemblyReference.Execute () [0x00000] in <20c026c297134c06b9590841bcdf5d79>:0 
  at Microsoft.Build.BackEnd.TaskExecutionHost.Microsoft.Build.BackEnd.ITaskExecutionHost.Execute () [0x00029] in <29047405fcfe41bbb744a55b7d0f20fa>:0 
  at Microsoft.Build.BackEnd.TaskBuilder.ExecuteInstantiatedTask (Microsoft.Build.BackEnd.ITaskExecutionHost taskExecutionHost, Microsoft.Build.BackEnd.Logging.TaskLoggingContext taskLoggingContext, Microsoft.Build.BackEnd.TaskHost taskHost, Microsoft.Build.BackEnd.ItemBucket bucket, Microsoft.Build.BackEnd.TaskExecutionMode howToExecuteTask) [0x002fb] in <29047405fcfe41bbb744a55b7d0f20fa>:0 

[fail]: OmniSharp.MSBuild.ProjectManager
        Attempted to update project that is not loaded: /E/projects/My project/Assembly-CSharp.csproj

Am I missing anything? C# extensions are installed along with Unity extensions. Mono is also installed. I'm using Arch Linux, latest version and installed visual-studio-code-bin. Unity > External Tools > Generate .csproj files for Local packages.

Answer 1

This workaround on github comment fixed it for me. Set the VS Code omnisharp setting "Use Modern Net" to true.
(This also entails installing dotnet sdk 6.x, and from what I see uses that version to build the projects, not sure if that breaks stuff for people using previous versions.)

Here's a screenshot of the extension settings: