C8602 nullability warning after comparing not null member to null

[joshudson]

Reduced sample code:

class Login {
	private static SortedDictionary<string, Login> logins = null!;

	public static bool TryGetLogin(string email, [NotNullWhen(true)] out Login? login)
	{
		if (logins is null) InitLogins();
		return logins.TryGetValue(email, out login);
		// CS8602 'logins' may be null here. 
	}

	/// InitLogins() omitted for brevity. It's statically verifiable that after calling it, logins can't be null.
}

So the gist of this code is really simple. The property starts off null, but after InitLogins() it won't be null, and nothing ever assigns null to it again.

There's reasons why I'm not just exposing the member as a property but even if I did it doesn't seem to help.

Rewriting this to logins ??= InitLogins(); doesn't work due to thread race issues at the point of the assignment. The assignment needs to happen inside InitLogins().

So basically, the nullability warning is getting in the way here.

Since it's a static class variable not a local variable I'm kind of expecting it to throw out what it can infer between statements and just use the class level declaration every time. In the alternate hypothesis, different code can still get a null into it without a ! or a warning anywhere due to thread race issues.

[jnm2]

You can do this by applying [MemberNotNull(nameof(logins))] to the InitLogins method. Then the compiler will not warn in your sample, and it will check that logins is indeed not null for each return point within InitLogins.

[joshudson]

I hope my title's clear enough so the next person who hits this finds this discussion.