Is relationship of attributes for null-state static analysis to nullable value type questionable?

[deep-outcome]

Let discuss null-state static analysis attributes:

• AllowNullAttribute Class
• DisallowNullAttribute Class
• MaybeNullAttribute Class
• NotNullAttribute Class
• MaybeNullWhenAttribute Class
• NotNullWhenAttribute Class
• NotNullIfNotNullAttribute Class
• MemberNotNullAttribute Class
• MemberNotNullWhenAttribute Class

1. Some of them works fine with nullable value type, i.e: DisallowNullAttribute, NotNullAttribute, NotNullWhenAttribute NotNullIfNotNullAttribute.

static void Nullable ( [NotNull] ref int? i )
{
} // Warning CS8777  Parameter 'i' must have a non-null value when exiting.

static void Nullable2 ( ref int? i )
{
}

static void NullableTest ()
{
  int? i = null;
  Nullable (ref i);

  Console.WriteLine (i.Value); // No issue here.

  Nullable2 (ref i);
  Console.WriteLine (i.Value); // Warning  CS8629 Nullable value type may be null.
}

2. On the other hand they (that 4 ones) does not declares facts just right.

Value type is never null. Even when it is declared as nullable via ? suffix, it is just shorthand for generic constructed closed value type, Nullable<X>, where X is corresponding value type. Thus to state out that null is fine value for instance of Nullable<int> variable is not true at all. (Correct is to use default.)

◼ Why these ones are not named using default keyword? E.g. DisallowDefaultAttribute or NotDefaultWhenAttribute.

It is well known that for nullable value type null assignation is equal to assignation of default (default(Nullable<X>). (Drolly reference type has it just opposite.)

Polemic can be that Nullable<> should never be named like that a instead it would have been named Empty<>. Nowadays it will be beneficial for countermeasure of tendency to state that Nullable<> variable has / has not null value. Precisely Nullable<> has or has not value.

> int? i;
> i.Value
System.InvalidOperationException: Nullable object must have a value.
  + System.ThrowHelper.ThrowInvalidOperationException(System.ExceptionResource)
  + Nullable<T>.get_Value()

◼ If these ones (that 4 ones) uses null keyword why are they allowed for Nullable<>?

[deep-outcome]

No, it is not. See #4964.