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Flag Assert.AreEqual(x, x) / AreSame(x, x) / AreNotEqual(x, x) / AreNotSame(x, x) (#9087) #9088

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Flag Assert.AreEqual(x, x) / AreSame(x, x) / AreNotEqual(x, x) / AreNotSame(x, x) (#9087) #9088

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f0195a9
Flag Assert.AreEqual/AreSame (and AreNotEqual/AreNotSame) with identi…
Evangelink Jun 12, 2026
e6f5d0d
Address review: don't unwrap user-defined conversions
Evangelink Jun 12, 2026
b220434
Address self-review on #9088: exclude indexers from IsEquivalentRefer…
Jun 12, 2026
7ff443b
Address review on #9088: add AreNotSame-with-message and property cov…
Jun 12, 2026
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12 changes: 11 additions & 1 deletion src/Analyzers/MSTest.Analyzers/PreferAssertFailOverAlwaysFalseConditionsAnalyzer.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -92,12 +92,22 @@ private static bool IsAlwaysFalse(IInvocationOperation operation)
"IsTrue" => GetConditionArgument(operation) is { ConstantValue: { HasValue: true, Value: false } },
"IsFalse" => GetConditionArgument(operation) is { ConstantValue: { HasValue: true, Value: true } },
"AreEqual" => GetEqualityStatus(operation, ExpectedParameterName) == EqualityStatus.NotEqual,
"AreNotEqual" => GetEqualityStatus(operation, NotExpectedParameterName) == EqualityStatus.Equal,
"AreNotEqual" => GetEqualityStatus(operation, NotExpectedParameterName) == EqualityStatus.Equal
|| HasIdenticalExpectedAndActual(operation, NotExpectedParameterName),
"AreNotSame" => HasIdenticalExpectedAndActual(operation, NotExpectedParameterName),
"IsNotNull" => GetValueArgument(operation) is { ConstantValue: { HasValue: true, Value: null } },
"IsNull" => GetValueArgument(operation) is { } valueArgumentOperation && IsNotNullableType(valueArgumentOperation),
_ => false,
};

private static bool HasIdenticalExpectedAndActual(IInvocationOperation operation, string expectedOrNotExpectedParameterName)
=> GetRawArgumentValueWithName(operation, expectedOrNotExpectedParameterName) is { } expectedArgument
&& GetRawArgumentValueWithName(operation, ActualParameterName) is { } actualArgument
&& expectedArgument.IsEquivalentReferenceTo(actualArgument);

private static IOperation? GetRawArgumentValueWithName(IInvocationOperation operation, string name)
=> operation.Arguments.FirstOrDefault(arg => arg.Parameter?.Name == name)?.Value;

private static bool IsNotNullableType(IOperation valueArgumentOperation)
{
ITypeSymbol? valueArgType = valueArgumentOperation.GetReferencedMemberOrLocalOrParameter().GetReferencedMemberOrLocalOrParameter();
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12 changes: 11 additions & 1 deletion src/Analyzers/MSTest.Analyzers/ReviewAlwaysTrueAssertConditionAnalyzer.cs
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Expand Up @@ -81,13 +81,23 @@ private static bool IsAlwaysTrue(IInvocationOperation operation)
{
"IsTrue" => GetConditionArgument(operation) is { ConstantValue: { HasValue: true, Value: true } },
"IsFalse" => GetConditionArgument(operation) is { ConstantValue: { HasValue: true, Value: false } },
"AreEqual" => GetEqualityStatus(operation, ExpectedParameterName) == EqualityStatus.Equal,
"AreEqual" => GetEqualityStatus(operation, ExpectedParameterName) == EqualityStatus.Equal
|| HasIdenticalExpectedAndActual(operation, ExpectedParameterName),
"AreNotEqual" => GetEqualityStatus(operation, NotExpectedParameterName) == EqualityStatus.NotEqual,
"AreSame" => HasIdenticalExpectedAndActual(operation, ExpectedParameterName),
"IsNull" => GetValueArgument(operation) is { ConstantValue: { HasValue: true, Value: null } },
"IsNotNull" => GetValueArgument(operation) is { } valueArgumentOperation && IsNotNullableType(valueArgumentOperation),
_ => false,
};

private static bool HasIdenticalExpectedAndActual(IInvocationOperation operation, string expectedOrNotExpectedParameterName)
=> GetRawArgumentValueWithName(operation, expectedOrNotExpectedParameterName) is { } expectedArgument
&& GetRawArgumentValueWithName(operation, ActualParameterName) is { } actualArgument
&& expectedArgument.IsEquivalentReferenceTo(actualArgument);

private static IOperation? GetRawArgumentValueWithName(IInvocationOperation operation, string name)
=> operation.Arguments.FirstOrDefault(arg => arg.Parameter?.Name == name)?.Value;

private static bool IsNotNullableType(IOperation valueArgumentOperation)
{
ITypeSymbol? valueArgType = valueArgumentOperation.GetReferencedMemberOrLocalOrParameter().GetReferencedMemberOrLocalOrParameter();
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65 changes: 65 additions & 0 deletions src/Analyzers/MSTest.Analyzers/RoslynAnalyzerHelpers/IOperationExtensions.cs
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Expand Up @@ -56,4 +56,69 @@ public static IOperation WalkDownBuiltInConversion(this IOperation operation)

return operation;
}

/// <summary>
/// Returns <see langword="true"/> when the two operations are structurally equivalent
/// side-effect-free references to the same local, parameter, field, property, or <c>this</c>.
/// </summary>
/// <remarks>
/// This intentionally excludes method invocations and indexer accesses, since those may
/// have side effects or return different values on repeated evaluation. Parenthesized
/// expressions and <em>built-in</em> conversions are skipped transparently, but
/// user-defined conversions are treated as opaque because their operators may execute
/// arbitrary code with side effects.
/// </remarks>
public static bool IsEquivalentReferenceTo(this IOperation? left, IOperation? right)
{
if (left is null || right is null)
{
return false;
}

left = Unwrap(left);
right = Unwrap(right);

return (left, right) switch
{
(ILocalReferenceOperation la, ILocalReferenceOperation lb) =>
SymbolEqualityComparer.Default.Equals(la.Local, lb.Local),

(IParameterReferenceOperation pa, IParameterReferenceOperation pb) =>
SymbolEqualityComparer.Default.Equals(pa.Parameter, pb.Parameter),

(IFieldReferenceOperation fa, IFieldReferenceOperation fb) =>
SymbolEqualityComparer.Default.Equals(fa.Field, fb.Field) &&
AreInstancesEquivalent(fa.Instance, fb.Instance),

(IPropertyReferenceOperation pra, IPropertyReferenceOperation prb) =>
!pra.Property.IsIndexer &&
SymbolEqualityComparer.Default.Equals(pra.Property, prb.Property) &&
AreInstancesEquivalent(pra.Instance, prb.Instance),

Comment on lines +95 to +97

@Evangelink Evangelink Jun 12, 2026

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[MAJOR] Algorithmic Correctness / Analyzer Quality — false positive on custom indexers

The IPropertyReferenceOperation arm does not exclude custom indexers (Property.IsIndexer == true). In Roslyn, list[0] on any type that has a C# indexer (List<T>, Dictionary<K,V>, ImmutableArray<T>, any user-defined this[...] accessor) produces an IPropertyReferenceOperation whose Property.IsIndexer == true. The current code checks only that the property symbol and the receiver instance are equivalent — it does not compare the index arguments.

Concrete false-positive scenario:

var list = new List<string> { "a", "b" };
// list[0] == "a", list[1] == "b" — clearly not always equal, but
Assert.AreEqual(list[0], list[1]);   // ← MSTEST0032 fires incorrectly
Assert.AreSame(list[0], list[1]);    // ← same false-positive path

Both operands produce IPropertyReferenceOperation with the same Item property symbol and the same list local as instance. The switch arm returns true, causing a spurious diagnostic.

Note: plain array access (arr[i]) produces IArrayElementReferenceOperation, not IPropertyReferenceOperation, so that case is already excluded by the _ => false default. Only C#-defined indexers hit this arm.

The <remarks> doc comment already states the correct intent — "This intentionally excludes method invocations and indexer accesses" — but the code doesn't enforce it for IPropertyReferenceOperation.

Recommended fix — add !pra.Property.IsIndexer as the first guard:

(IPropertyReferenceOperation pra, IPropertyReferenceOperation prb) =>
    !pra.Property.IsIndexer &&
    SymbolEqualityComparer.Default.Equals(pra.Property, prb.Property) &&
    AreInstancesEquivalent(pra.Instance, prb.Instance),

A matching no-diagnostic test is also needed, e.g.:

var list = new List<object>();
Assert.AreEqual(list[0], list[1]);  // different indices → no diagnostic
Assert.AreEqual(list[i], list[i]);  // same-variable index, still no diagnostic (side-effect risk)

@Evangelink Evangelink Jun 12, 2026

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Good catch -- fixed in b220434. Added !pra.Property.IsIndexer as the first guard on the IPropertyReferenceOperation arm so list[0] / dict[k] / any user-defined indexer access falls through to _ => false. The xmldoc remark already documented this intent (This intentionally excludes method invocations and indexer accesses); the code now enforces it. Added WhenAssertAreEqualIsPassedIndexerAccess_NoDiagnostic exercising list[0] vs list[1], list[0] vs list[0], and the AreSame variant. Review reply handled.

(IInstanceReferenceOperation, IInstanceReferenceOperation) => true,

_ => false,
};

static IOperation Unwrap(IOperation operation)
{
while (true)
{
switch (operation)
{
case IParenthesizedOperation parenthesized:
operation = parenthesized.Operand;
break;
case IConversionOperation conversion when !conversion.Conversion.IsUserDefined:
operation = conversion.Operand;
break;
default:
return operation;
}
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}
}

static bool AreInstancesEquivalent(IOperation? a, IOperation? b)
=> (a is null && b is null) || IsEquivalentReferenceTo(a, b);
}
}
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