ValidatedNotNull bug for R# nullability analysis

[ndrwrbgs]

Steps:

• Mark parameter as [CanBeNull]
• Use EnsureArg.IsNotNull(parameter) - which is documented with [ValidatedNotNull]
• After that call, do something like var _ = parameter.ToString();

Expectation:

• parameter is known to not be null at the .ToString() call

Reality:

• R# does not seem to recognize that (in 2018.2 at least).

I think I mistakenly believed R# would acknowledge ValidatedNotNull (or it used to), either way we can work around it if we are willing to add a ContractAnnotation
[ContractAnnotation("=> parameter:notnull")] Which says if the method returns, parameter will be non-null.