MSBuildWorkspace compilation errors for netcoreapp31/net5.0 'The type or namespace name 'System' could not be found'

[Rora]

Version Used:
3.9.0

Steps to Reproduce:

1. Use MSBuildLocator.RegisterDefaults
2. Create a MSBuildWorkspace
3. Load a solution
4. Compile a net5.0 or netcoreapp3.1 project
5. Validate the compilation diagnostics

Expected Behavior:
No errors

Actual Behavior:
The following errors occur:

1. error CS0246: The type or namespace name 'System' could not be found (are you missing a using directive or an assembly reference?)
2. error CS0518: Predefined type 'System.Object' is not defined or imported
3. error CS1729: 'object' does not contain a constructor that takes 0 arguments

I've also tried to scan a netstandard2.1 project and that seems to work fine. I created a solution which reproduces this issue: https://github.com/Rora/msbuild-workspace-dotnetcoreapp-repro

[koenbeuk]

I'm experiencing the same issue, is there a known workaround?

[JoeRobich]

@Rora So looking at the contents of workspace.Diagnostics after loading the solution, there are several errors of the form:

Msbuild failed when processing the file '/Users/joeyrobichaud/Source/msbuild-workspace-dotnetcoreapp-repro/RoslynScanner/RoslynScanner/RoslynScanner.csproj' with message: /usr/local/share/dotnet/sdk/5.0.203/Sdks/Microsoft.NET.Sdk/targets/Microsoft.NET.Sdk.FrameworkReferenceResolution.targets: (63, 5): The \"ProcessFrameworkReferences\" task failed unexpectedly.
System.MissingMethodException: Method not found: 'System.String NuGet.Frameworks.NuGetFramework.get_Platform()'.
   at Microsoft.NET.Build.Tasks.ProcessFrameworkReferences.KnownFrameworkReferenceAppliesToTargetFramework(NuGetFramework knownFrameworkReferenceTargetFramework)
   at Microsoft.NET.Build.Tasks.ProcessFrameworkReferences.<ExecuteCore>b__105_1(KnownFrameworkReference kfr)
   at System.Linq.Enumerable.WhereEnumerableIterator`1.ToList()
   at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
   at Microsoft.NET.Build.Tasks.ProcessFrameworkReferences.ExecuteCore()
   at Microsoft.NET.Build.Tasks.TaskBase.Execute()
   at Microsoft.Build.BackEnd.TaskExecutionHost.Microsoft.Build.BackEnd.ITaskExecutionHost.Execute()
   at Microsoft.Build.BackEnd.TaskBuilder.ExecuteInstantiatedTask(ITaskExecutionHost taskExecutionHost, TaskLoggingContext taskLoggingContext, TaskHost taskHost, ItemBucket bucket, TaskExecutionMode howToExecuteTask)

This is an issue where Microsoft.NET.Test.Sdk depends on Microsoft.TestPlatform.TestHost which depends on Microsoft.TestPlatform.ObjectModel which depends on and older version of NuGet.Frameworks. To fix this in your tests you can add a PackageReference to "NuGet.Frameworks" version 5.9.0+.

[koenbeuk]

I can confirm that adding NuGet.Frameworks as a package reference as suggest by @JoeRobich solves this issue.

There are a triage of other issues when having .net core 6 preview installed. After uninstalling .net core 6 preview, things finally started working. I suspect that those other issues are unrelated to this issue though, will open new issues if I see the need.

[JoeRobich]

Closing this issue as a duplicate of #52954