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[efficiency-improver] perf: eliminate LINQ iterator allocations in MSTest Analyzer DerivesFrom interface check #9466

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Evangelink merged 1 commit into from
Jun 28, 2026
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[efficiency-improver] perf: eliminate LINQ iterator allocations in MSTest Analyzer DerivesFrom interface check #9466

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21 changes: 12 additions & 9 deletions src/Analyzers/MSTest.Analyzers/RoslynAnalyzerHelpers/ITypeSymbolExtensions.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -48,16 +48,19 @@ public static bool DerivesFrom([NotNullWhen(returnValue: true)] this ITypeSymbol

if (!baseTypesOnly && candidateBaseType.TypeKind == TypeKind.Interface)
{
IEnumerable<ITypeSymbol> allInterfaces = symbol.AllInterfaces.OfType<ITypeSymbol>();
if (SymbolEqualityComparer.Default.Equals(candidateBaseType.OriginalDefinition, candidateBaseType))
// Avoid OfType<ITypeSymbol>() + optional Select() + Contains() chain — each creates a heap-allocated
// LINQ iterator state machine. AllInterfaces is ImmutableArray<INamedTypeSymbol>; iterating it
// directly uses the struct enumerator (zero heap allocation).
bool useOriginalDefinition = SymbolEqualityComparer.Default.Equals(candidateBaseType.OriginalDefinition, candidateBaseType);
foreach (INamedTypeSymbol iface in symbol.AllInterfaces)
{
// Candidate base type is not a constructed generic type, so use original definition for interfaces.
allInterfaces = allInterfaces.Select(i => i.OriginalDefinition);
}

if (allInterfaces.Contains(candidateBaseType, SymbolEqualityComparer.Default))
{
return true;
// When the candidate is not a constructed generic type, compare via OriginalDefinition
// (mirrors the original Select(i => i.OriginalDefinition) projection).
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ITypeSymbol candidate = useOriginalDefinition ? iface.OriginalDefinition : iface;
if (SymbolEqualityComparer.Default.Equals(candidate, candidateBaseType))
{
return true;
}
}
}

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