.NET 6 Winforms Designer / Argument Exception: Illegal characters in path

[thomasmiko]

.NET 6
VS2022 17.2 Preview 1 (Same Problem with 17.1)

Problem description:
When I edit a .NET 6 WinForms project and want to open the Designer for a UserControl / Form there, the following exception appears

Output from Winforms Designer logging (Verbose)

[11:06:01.0283033] Creating VSCodeDomDesignerLoader
[11:06:01.0543468] Processed 'System.Design' in 00:00:00.0998389
[11:06:01.0638662] Added 'System.Design'
[11:06:01.0648675] Loaded System.Drawing.Design in 00:00:00.0000189 [thread 35]
[11:06:01.0648675] Processed 'System.Drawing.Design' in 00:00:00.0001717
[11:06:01.0648675] Added 'System.Drawing.Design'
[11:06:01.2783607] [Thread 1] Creating design-time ITypeResolutionService.
[11:06:01.3429998] Current VS Version = 17.0
[11:06:01.3439981] Start processing enqueued assemblies
[11:06:01.3449974] Loaded Microsoft.WinForms.DesignTools.Protocol in 00:00:00.0000081 [thread 31]
[11:06:01.3599982] Processed 'Microsoft.WinForms.DesignTools.Protocol' in 00:00:00.0149551
[11:06:01.3619986] Added 'Microsoft.WinForms.DesignTools.Protocol'
[11:06:01.3619986] Loaded Microsoft.WinForms.DesignTools.Client in 00:00:00.0000074 [thread 31]
[11:06:01.3849983] Processed 'Microsoft.WinForms.DesignTools.Client' in 00:00:00.0224528
[11:06:01.3859974] Added 'Microsoft.WinForms.DesignTools.Client'
[11:06:01.5205867] [Thread 68] Launching server...
[11:06:03.3003038] System.ArgumentException: Illegal characters in path.
at System.Security.Permissions.FileIOPermission.EmulateFileIOPermissionChecks(String fullPath)
at System.IO.Directory.InternalCreateDirectoryHelper(String path, Boolean checkHost)
at Microsoft.WinForms.Utilities.Shared.ShadowCacheFolder..ctor(Boolean isNetCoreProject)
at Microsoft.DotNet.DesignTools.Client.Host.ServerLayout.d__8.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.DotNet.DesignTools.Client.Host.ServerProcess.d__21.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.DotNet.DesignTools.Client.Host.ServerHostFactory.d__7.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.DotNet.DesignTools.Client.DesignToolsClientLoader.d__28.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at Microsoft.VisualStudio.Telemetry.WindowsErrorReporting.WatsonReport.GetClrWatsonExceptionInfo(Exception exceptionObject)
[11:06:04.1210052] Cannot update selection in server process as Session is not connected.

I've tried it with several .NET 6 Projects, allways the same error.

Expected behavior:

Designer should open without any exception

[RussKie]

Duplicate of #6826