Null suppression doesn't work when the body has a null suppression

[RenderMichael]

A null suppression throws the null warning suppression out of whack.

One might say why is str not getting checked for null. The following is a minimal repro, the actual scenarios I've ran into are less trivial. Suffice it to say, the existence of the null-suppression operator should be evidence enough that it needs to be used sometimes.

internal static string GetString(HasString str)
{
    Assert.That(str.Inner, Is.Not.Null);
    return str.Inner; // works great
}

internal static string GetStringSuppress(HasString? str) // argument is nullable
{
    Assert.That(str!.Inner, Is.Not.Null);
    return str.Inner; // warning: possible null reference return
}

public record HasString(string? Inner);

[manfred-brands]

In this case Assert.That(str?.Inner, Is.Not.Null); would have been a safer statement as it asserts both str and str.Inner.

But as you said, your real code is more complicated.

The null-suppression-operator indicates that the writer knows more about the code than the compiler can deduct.
I created a PR to ignore '!' when matching diagnostics with expressions tested with Is.Not.Null