S3220 — Method calls should not resolve ambiguously to overloads with "params"

Why is this an issue?

The rules for method resolution are complex and perhaps not properly understood by all coders. The params keyword can make method declarations overlap in non-obvious ways, so that slight changes in the argument types of an invocation can resolve to different methods.

This rule raises an issue when an invocation resolves to a method declaration with params, but could also resolve to another non-params method too.

Noncompliant code example

public class MyClass
{
    private void Format(string a, params object[] b) { }

    private void Format(object a, object b, object c) { }
}

// ...
MyClass myClass = new MyClass();

myClass.Format("", null, null); // Noncompliant, resolves to the first Format with params, but was that intended?