Fix S2589 FP: Unsigned number doubling by adding with itself inside while loop

[MineCake147E]

Description

S2589 is being reported when using unsigned x += x.

Repro steps

public static void UIntPtrS2589FalsePositive()
{
    nuint u = 1;
    while (u > 0)   // noncompliant FP
    {
        u += u;     // this addition could overflow to 0
    }
}

public static void UInt64S2589FalsePositive()
{
    ulong u = 1;
    while (u > 0)   // noncompliant FP
    {
        u += u;     // this addition could overflow to 0
    }
}

public static void UInt32S2589FalsePositive()
{
    uint u = 1;
    while (u > 0)   // noncompliant FP
    {
        u += u;     // this addition could overflow to 0
    }
}

Expected behavior

No issue should be found.

Actual behavior

u > 0 gets S2589

Known workarounds

Use either u *= 2; or u <<= 1; instead of u += u;.

Related information

• SonarLint for Visual Studio 2022 7.8.0.88494
• Microsoft Visual Studio Community 2022 (64-bit) - Preview Version 17.10.0 Preview 4.0
• dotnet 8.0.300-preview.24203.14
• Operating System: Windows 11 Home 22H2 22621.3447

[martin-strecker-sonarsource]

Hello @MineCake147E, thank you for bringing this issue to our attention. Upon investigation, I can confirm that it is a false positive. I have added a reproducer in #9192 to document this. S2589 is designed not to consider overflows intentionally (otherwise, we would miss a lot of true positives).

However, we should respect unchecked statements/expressions. By adding unchecked in your examples, the code becomes clearer and more intentional.

Unfortunately, we are not taking unchecked into account yet, but I have added this issue to our backlog for future implementation.