S2699 Reproducer for AssertionMethodAttribute is ignored when assertion method is inherited

[martin-strecker-sonarsource]

Test for #6525

[sonarqubecloud]

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[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

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[cristian-ambrosini-sonarsource]

Based on the result of the following snippet it seems to me that this is not a FP.
The following will print 'false' both with this implementation and with the base.MyMethod(); call inside Child MyMethod().
It seems to me that once overriden the attributes are lost. For this reason I think the CustomAssertionMethod() within this test case is not decorated by [AssertionMethod] attribute anymore, hence raising the issue. WDYT?

[AttributeUsage(AttributeTargets.Method)]
public class MyAttribute : Attribute { }

public class Parent
{
    [My]
    public virtual void MyMethod() { }
}

public class Child : Parent
{
    public override void MyMethod() { }
}

public class MainClass
{
    public static void Main() =>
        Console.WriteLine(typeof(Child).GetMember("MyMethod")
                                       .SelectMany(m => m.CustomAttributes)
                                       .Any());
}

[martin-strecker-sonarsource]

The code will print true when you do these variations to the code:

• AttributeUsage.Inherited = true (Note: Inherited = true is the default)
• m.GetCustomAttributes(inherit: true)

using System;
using System.Linq;

[AttributeUsage(AttributeTargets.Method, Inherited = true)]
public class MyAttribute : Attribute { }

public class Parent
{
    [My]
    public virtual void MyMethod() { }
}

public class Child : Parent
{
    public override void MyMethod() { }
}

public class MainClass
{
    public static void Main() =>
        Console.WriteLine(typeof(Child).GetMember("MyMethod")
                                       .SelectMany(m => m.GetCustomAttributes(inherit: true))
                                       .OfType<MyAttribute>()
                                       .Any());
}

So we should check if there is an AssertionMethodAttribute in the compilation and if it is marked with AttributeUsage.Inherited = true. If so we should look at the original definition (in case of generic parameters as in the OPs request) and the override chain if the attribute was applied somewhere before. There might be some helper method in Roslyn that helps with this, but I couldn't find anything at first glance.