S2589 FP and FN: Conditional access and pattern matching

[jjolidon]

Description

S2589 triggers a false positive for a null check after a first test with pattern matching.

Repro steps

private void Test(Exception ex)
{
    if (ex?.Data["FOO"] is string myString)
    {
        // intentionally empty for the reproducer
    }
    else
    {
        if (ex != null) // This test triggers S2589
        {
            // intentionally empty for the reproducer
        }
    }
}

Expected behavior

The above code should not trigger S2589

Actual behavior

The above code triggers S2589

Known workarounds

No known workaround

Related information

• SonarAnalyzer.CSharp version: 8.13.0.25740
• Visual Studio version: 16.8.3
• MSBuild / dotnet version: 16.8.2.56705 / 5.0.101
• SonarScanner for .NET version (if used)
• Operating System: Win 10

[pavel-mikula-sonarsource]

Hi @jjolidon ,

Thank you for reporting this case. I can confirm it as False Positive.

[andrei-epure-sonarsource]

other conditional access FPs: #3416 , #2528, #2704

[mary-georgiou-sonarsource]

Fixed by #7750