From 6ad53f433e0353b1462b943cdd1985fb4db9123c Mon Sep 17 00:00:00 2001
From: Cyrille DUPUYDAUBY <dupdob@gmail.com>
Date: Tue, 14 Apr 2026 17:47:01 +0200
Subject: [PATCH] feat: improve rollback logic for error CS0165

---
 .../Stryker.Core/Compiling/CSharpRollbackProcess.cs        | 7 ++++++-
 .../SingleMicrosoftTestPlatformRunnerTests.cs              | 4 ++--
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/src/Stryker.Core/Stryker.Core/Compiling/CSharpRollbackProcess.cs b/src/Stryker.Core/Stryker.Core/Compiling/CSharpRollbackProcess.cs
index 7da7852bad..c2b31948dc 100644
--- a/src/Stryker.Core/Stryker.Core/Compiling/CSharpRollbackProcess.cs
+++ b/src/Stryker.Core/Stryker.Core/Compiling/CSharpRollbackProcess.cs
@@ -312,6 +312,11 @@ private string DisplayName(SyntaxNode initNode) =>
             not null => initNode.Parent == null ? "whole file" : "the current node",
         };
 
+
+    // errors that must trigger a deep removal of mutations
+    // usage of uninitialized variables (165)
+    private static readonly HashSet<string> ErrorsRequiringRecursiveRemoval = ["CS0165"];
+
     private Collection<SyntaxNode> IdentifyMutationsAndFlagForRollback(IEnumerable<Diagnostic> diagnosticInfo,
         SyntaxNode rollbackRoot, out Diagnostic[] diagnostics)
     {
@@ -326,7 +331,7 @@ private Collection<SyntaxNode> IdentifyMutationsAndFlagForRollback(IEnumerable<D
                 continue;
             }
 
-            if (MutantPlacer.RequiresRemovingChildMutations(mutationIf))
+            if (MutantPlacer.RequiresRemovingChildMutations(mutationIf) || ErrorsRequiringRecursiveRemoval.Contains(diagnostic.Id))
             {
                 FlagChildrenMutationsForRollback(mutationIf, brokenMutations);
             }
diff --git a/src/Stryker.TestRunner.MicrosoftTestPlatform.UnitTest/SingleMicrosoftTestPlatformRunnerTests.cs b/src/Stryker.TestRunner.MicrosoftTestPlatform.UnitTest/SingleMicrosoftTestPlatformRunnerTests.cs
index 7ac478aa6a..c8bccff20a 100644
--- a/src/Stryker.TestRunner.MicrosoftTestPlatform.UnitTest/SingleMicrosoftTestPlatformRunnerTests.cs
+++ b/src/Stryker.TestRunner.MicrosoftTestPlatform.UnitTest/SingleMicrosoftTestPlatformRunnerTests.cs
@@ -1154,9 +1154,9 @@ public TestableRunner(
 
         public override void Dispose(bool disposing)
         {
-            var disposedField = typeof(SingleMicrosoftTestPlatformRunner).GetField("_disposed", 
+            var disposedField = typeof(SingleMicrosoftTestPlatformRunner).GetField("_disposed",
                 System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance);
-            
+
             var wasDisposedBefore = (bool)disposedField!.GetValue(this)!;
 
             base.Dispose(disposing);