Invalidate project engine when UseRoslynTokenizer changes

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/ProjectSystem/ProjectState.cs

@@ -151,14 +151,15 @@ internal class ProjectState
         else
         {
             ProjectWorkspaceStateVersion = Version;
-        }
 
-        if ((difference & ClearProjectWorkspaceStateVersionMask) != 0 &&
+            // CSharpLanguageVersion and UseRoslynTokenizer are part of the ProjectWorkspaceState, but they affect the project engine
-            CSharpLanguageVersion != older.CSharpLanguageVersion)
+            // so we check for those specifically changing, and clear that.
-        {
+            if (CSharpLanguageVersion != older.CSharpLanguageVersion ||
-            // C# language version changed. This impacts the ProjectEngine, reset it.
+                ProjectWorkspaceState.UseRoslynTokenizer != older.ProjectWorkspaceState.UseRoslynTokenizer)
-            _projectEngine = null;
+            {
-            ConfigurationVersion = Version;
+                _projectEngine = null;
+                ConfigurationVersion = Version;
+            }
         }
     }