N4JS allows private abstract methods and forces overriding them in sub classes

[yoosiba]

N4JS allows private abstract methods and forces overriding them in sub classes

export public abstract class Abstract {
    // XPECT error ---> "abstract not allowed on private methods"
    private abstract m();
}

export public class Concrete extends Abstract {
    //XPECT error ---> "cannot override private method"
    @Override
    private m(){};
}

see error when private abstract is not overridden

[kduske-n4]

Interestingly, making virtual (i.e. overridable) methods private is a recommended practice for C++: https://stackoverflow.com/questions/2170688/private-virtual-method-in-c

Not saying N4JS should have this, since it doesn't really make sense in a language that follows Java's footsteps. Just a point of interest.

Furthermore, whoever fixes this should check why the access control test suite didn't catch this. It's possible that it's missing the case of overriding an abstract method.

[jpilgrim]

Remark: added new constraint in spec (Req IDE-46).

Did not remove consequential error in subtype overriding the "private abstract" method -- if you get that error, that means you have ignored the error in the super type.

[jpilgrim]

Since we allow access to private members from within the module, it is possible to implement an abstract method in a class defined in the same module. Therefor it is ok to not add an error.

I created #1221 for redefining private member access. But even in this case it would be possible to override a private abstract method from a nested class (defined by means of class expressions).

[jpilgrim]

I think the quickfix does not make much sense, that's true. Again I think we should fix that in the context of #1221.