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Fix S3459 FP: Backing field with ref property #9383

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Merged
martin-strecker-sonarsource merged 4 commits into from
Jun 4, 2024
Merged

Fix S3459 FP: Backing field with ref property #9383

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d1d9ac8
Fix RefExpressionSyntax handling
martin-strecker-sonarsource Jun 4, 2024
fbb3aad
Fix UT
martin-strecker-sonarsource Jun 4, 2024
c92e764
Reivew 1
martin-strecker-sonarsource Jun 4, 2024
6490502
Remove duplicate snippet
martin-strecker-sonarsource Jun 4, 2024
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3 changes: 2 additions & 1 deletion analyzers/src/SonarAnalyzer.CSharp/Rules/NotAssignedPrivateMember.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -184,7 +184,8 @@ private static ISet<ISymbol> GetAssignedMemberSymbols(IList<MemberUsage> memberU

if (PreOrPostfixOpSyntaxKinds.Contains(parentNode.Kind())
|| (parentNode is AssignmentExpressionSyntax assignment && assignment.Left == node)
|| (parentNode is ArgumentSyntax argument && (!argument.RefOrOutKeyword.IsKind(SyntaxKind.None) || TupleExpressionSyntaxWrapper.IsInstance(argument.Parent))))
|| (parentNode is ArgumentSyntax argument && (!argument.RefOrOutKeyword.IsKind(SyntaxKind.None) || TupleExpressionSyntaxWrapper.IsInstance(argument.Parent)))
|| RefExpressionSyntaxWrapper.IsInstance(parentNode))
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@Tim-Pohlmann Tim-Pohlmann Jun 4, 2024 •
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This is too simple and introduces an FN (run with C# 9):

    private int _foo; // FN
    public int Foo => _foo;
    void Method()
    {
        _ = ref _foo;
    }

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@martin-strecker-sonarsource martin-strecker-sonarsource Jun 4, 2024

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This is not a FN. If you get a reference to the field, you have write access to it and that write can happen anywhere. This is like calling SomeMethod(ref field) where you do not know what happens inside SomeMethod. We would need to do symbolic execution on the assigned variable to properly detect all scenarios.

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@Tim-Pohlmann Tim-Pohlmann Jun 4, 2024

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But you have access to the method where the ref was used. I accept that this is out of the scope of this ticket, but at least add a reproducer to document the limitation.

{
assignedMembers.Add(memberSymbol);
assignedMembers.Add(memberSymbol.OriginalDefinition);
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2 changes: 1 addition & 1 deletion analyzers/tests/SonarAnalyzer.Test/TestCases/NotAssignedPrivateMember.cs
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Expand Up @@ -205,7 +205,7 @@ public void Print()
// Reproducer: https://github.com/SonarSource/sonar-dotnet/issues/9106
public class Repro_9106
{
private int _foo; // Noncompliant FP
private int _foo; // Compliant

public ref int Foo => ref _foo;
}