Identify method to C#8 as a nullable checker? [duplicate]

Question

I often use extension methods to check method arguments

void MyMethod(string? test)
{
    Require.NotNull(test, nameof(test));
    // Same as
    // if (test == null) throw new ArgumentNullExeception(nameof(test))

    ...
}

When enabling C# 8's nullables however, the compiler does not think I've checked the argument for null when using the extension method.

Is there a way to identify the extension method Require.NotNull as a nullable checker?

Answer 1

There is ongoing work in roslyn#36039 to eventually allow authors to annotate their methods in a way that gives back nullable information to the compiler. There are some features currently in preview but I don’t know the exact state.

However, I would question your approach here: If the first thing you do in your method is to check against null and effectively throw an exception, then passing a null value to your method is not a valid input. So your method should not be annotated in a way that it would accept null.

You rather want to mark it so that it does not accept null, so the compiler will properly tell you where you are calling the method with a potential null value.