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More aggressive rollback for error CS0165 #3548

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More aggressive rollback for error CS0165 #3548

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7 changes: 6 additions & 1 deletion src/Stryker.Core/Stryker.Core/Compiling/CSharpRollbackProcess.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -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)
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Copilot AI Apr 14, 2026

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The comment describing CS0165 as “usage of uninitialized variables” is inaccurate/misleading (CS0165 is “use of unassigned local variable”). Updating this comment to the correct wording will make it clearer why this diagnostic needs recursive rollback.

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// errors that must trigger a deep removal of mutations
// usage of uninitialized variables (165)
// Errors that must trigger a deep removal of mutations.
// CS0165: use of unassigned local variable.

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private static readonly HashSet<string> ErrorsRequiringRecursiveRemoval = ["CS0165"];
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The PR description says this should fix #3542, but that issue’s concrete example is CS0161 (“not all code paths return a value”) from removing a trailing throw. This change only adds special handling for CS0165; please either (a) clarify in the PR description how CS0165 relates to #3542, or (b) include CS0161 (and any other intended diagnostics) in the set of errors that trigger recursive removal.

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private Collection<SyntaxNode> IdentifyMutationsAndFlagForRollback(IEnumerable<Diagnostic> diagnosticInfo,
SyntaxNode rollbackRoot, out Diagnostic[] diagnostics)
{
Expand All @@ -326,7 +331,7 @@ private Collection<SyntaxNode> IdentifyMutationsAndFlagForRollback(IEnumerable<D
continue;
}

if (MutantPlacer.RequiresRemovingChildMutations(mutationIf))
if (MutantPlacer.RequiresRemovingChildMutations(mutationIf) || ErrorsRequiringRecursiveRemoval.Contains(diagnostic.Id))
{
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The new CS0165-specific branch changes rollback behavior (it will recursively remove child mutations instead of only the enclosing mutation). This is a functional change in compile-error recovery logic but there’s no unit test exercising the CS0165 scenario; please add coverage in Stryker.Core.UnitTest/Compiling/CSharpRollbackProcessTests validating that on a CS0165 diagnostic, the rollback process removes child mutations as intended (i.e., multiple mutant ids are rolled back in one pass, and the follow-up compilation succeeds).

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FlagChildrenMutationsForRollback(mutationIf, brokenMutations);
}
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4 changes: 2 additions & 2 deletions ...ryker.TestRunner.MicrosoftTestPlatform.UnitTest/SingleMicrosoftTestPlatformRunnerTests.cs
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Expand Up @@ -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);
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