CS8602 should look deeper ("Dereference possibly null reference")

[JVimes]

Brief description:

CS8602 seems to have a lot of false positives. Suggest making it look deeper to see if value could actually be null.

Languages applicable:

C#
Not sure on VB.

Code example that the analyzer should [not] report:

var text = "foo";
var notNull = text != null;
if (notNull)
{
    var length = text.Length;
}

Additional information:

I vaguely recall that the analzyers used to look deeper to see if a reference could actually be null. Didn't that used to be the case?

Documentation requirements:

N/A

[huoyaoyuan]

This is by design. All the nullable features only take account for expressions directly inside the if statement. Boolean variables are never propagated. See also #27011 #66807 .

Also note that nullable analysis isn't "analyzer". It is a part of core compiler/language and uses CSxxxx id.

[JVimes]

@Hyleon-Ou Thank you. Are requests for design changes accepted, or not really?

[huoyaoyuan]

It's unlikely to be changed, because more deep analysis may have unconstrained overhead.