NET-2219 Fix S1128 FP: Deconstruct method C#

[relrafie]

Description

'S1128' Remove this unnecessary 'using'' is raised when ref. is needed for a deconstructed method.

Reproducer

using CSharpFunctionalExtensions;

    private void SomeMethod()
    {
        var (_, _, _) = GetResult();
    }

    private CSharpFunctionalExtensions.Result GetResult()
    {
        return CSharpFunctionalExtensions.Result.Success();
    }

Removing the using statement will result in an error, adding it will result in a sonar smell.

Expected behavior
S1128 shouldn't be detected as there is no error there

Actual behavior
A code smell is detected

Product and Version

SonarQube Server: 2025.1.1.104738; csharpenterprise: "10.4.1 (build 110446)"

[pavel-mikula-sonarsource]

Hi @relrafie,

I tried to reproduce this case, but I couldn't get into the scenario with an error, or S1128 raising. Can you try to write both files as a snippets? I tried

using CSharpFunctionalExtensions;   // IDE0005 raised
using System.Globalization;         // IDE0005 and S1128 raised

public class Sample
{
    private void SomeMethod()
    {
        var (_, _, _) = GetResult();
    }

    private CSharpFunctionalExtensions.Result GetResult() => null;
}

and

namespace CSharpFunctionalExtensions;

public class Result
{
    public void Deconstruct(out int a, out int b, out int c)
    {
        a = 42;
        b = 42;
        c = 42;
    }
}

[relrafie]

Hi @pavel-mikula-sonarsource,
Thank you for attempting to reproduce and I apologize for the incomplete solution. I looked into CSharpFunctionalExtensions and it appears that the deconstruct method is actually a static extension method.
So please try the following:

using Namespace.Should.Need; // IDE0005 and S1128 raised

public class Sample
{
    private void SomeMethod()
    {
        var (_, _, _) = Namespace.SonarResult.SonarResult.Success();
    }
}

namespace Namespace.SonarResult;

public readonly struct SonarResult
{
    public SonarResult(bool b, string c)
    {
        B = b;
        C = c;
    }

    public bool A => !B;
    public bool B { get; } = true;
    public string C { get; } = string.Empty;

    public static SonarResult Success()
    {
        return new SonarResult(false, null!);
    }
}

where the deconstruct is some extension method for SonarResult here:

namespace Namespace.Should.Need;

public static class SonarResultExtensions
{
    public static void Deconstruct(this SonarResult.SonarResult result, out bool a, out bool b,
        out string c)
    {
        a = result.A;
        b = result.B;
        c = result.B ? result.C : default;
    }
}

Let me know if you need any more information.

[pavel-mikula-sonarsource]

Hi @relrafie,

Thank you for the reproducer. The static extension method was indeed the root cause of the problem that was missing.

I confirm this as a False Positive

[github-actions]

Internal ticket NET-2219