From 6702e25e5330e8b4271e40a4a1c15bb23af59ea6 Mon Sep 17 00:00:00 2001
From: David Wengier <david.wengier@microsoft.com>
Date: Fri, 25 Oct 2024 14:53:08 +1100
Subject: [PATCH] Invalidate project engine when UseRoslynTokenizer changes

---
 .../ProjectSystem/ProjectState.cs                 | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/ProjectSystem/ProjectState.cs b/src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/ProjectSystem/ProjectState.cs
index 1e1e738399..bbb5418aaf 100644
--- a/src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/ProjectSystem/ProjectState.cs
+++ b/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 != older.CSharpLanguageVersion)
-        {
-            // C# language version changed. This impacts the ProjectEngine, reset it.
-            _projectEngine = null;
-            ConfigurationVersion = Version;
+            // CSharpLanguageVersion and UseRoslynTokenizer are part of the ProjectWorkspaceState, but they affect the project engine
+            // so we check for those specifically changing, and clear that.
+            if (CSharpLanguageVersion != older.CSharpLanguageVersion ||
+                ProjectWorkspaceState.UseRoslynTokenizer != older.ProjectWorkspaceState.UseRoslynTokenizer)
+            {
+                _projectEngine = null;
+                ConfigurationVersion = Version;
+            }
         }
     }