Fix S1144 FP: Erroneously flagged Add() method used in Collection Initializer

[markusschaber]

Description

When a custom Add(...) Method is only used in a collection initializer, SonarQube regards it as unused, although it's called in the initialization code.

Reproducer

using Xunit;

public class Class1
{
    private static readonly SettingsDict TheoryData = new()
    {
        new MySettings(1, 2), new MySettings(3, 4)
    };

    // Theory data in xUnit is restricted to serializable values, so we need to
    // pack our data into a dictionary, and use the keys as theory data.
    public static readonly TheoryData<string> Settings = new(TheoryData.Keys);

    [Theory]
    [MemberData(nameof(Settings))]
    public void SomeTest(string key)
    {
        var (alpha, beta) = TheoryData[key];
        // some fake test
        Assert.NotEqual(alpha, beta);
    }

    private class SettingsDict : Dictionary<string, MySettings >
    {
        // This "Add" method triggers csharpsquid:S1144
        // Remove the unused private method Add.
        internal void Add(MySettings settings)
        {
            Add($"{settings.Alpha}/{settings.Beta}", settings);
        }
    }

    // Some arbitrary data type which we (have to) use as (part of) our theory data.
    private record MySettings(int Alpha, int Beta);
}

Product and Version

SonarQube for IDE 11.6.0.83783 (in JetBrains Rider)

[jilles-sg]

This seems like a valid FP. It does not seem Roslyn's fault, since Find All References on the Add method in Visual Studio Code ms-dotnettools.csharp version 2.110.4 correctly shows two uses in the collection initializer.

However, this dictionary can be created in fewer lines of code, also avoiding the FP:

    private static readonly Dictionary<string, MySettings> TheoryData = new MySettings[] {
        new(1, 2), new(3, 4)
    }.ToDictionary(settings => $"{settings.Alpha}/{settings.Beta}");