Ghost variables are not correctly initialized in interfaces

[rodrigomilisse]

Ghost variable initialization is dependent on declaring the constructor for the type the that the refinements are for. This declaration implicitly initializes int variables in a way equivalent to @StateRefinement(to = "var(this) == 0")
It is not possible to declare constructors for interface types as these don't have constructors. This prohibits the correct initialization of both Ghost variables and States for interfaces

@ExternalRefinementsFor("java.util.List")
@Ghost("int size2")
public interface ListRefinements<E> {

	@StateRefinement(to = "size2(this) == (size2(old(this)) + 1)")
	public boolean add(E elem);

	@StateRefinement(from = "size2(this) > 0", to = "size2(this) == (size2(old(this)) - 1)")
	public void remove(@Refinement("index >= 0") int index);
}

	public static void main(String[] args) {
		List<Integer> l = new ArrayList<>();

		l.add(0);

		int a = l.remove(0);
	}

The error provided is Failed to check state transitions when calling l.remove(0)

This error messages is identical to the error message that would appear when attempting the same operation on a concrete class without a declared constructor in the Refinement definitions

[CatarinaGamboa]

This issue is actually bigger than just not having the constructor; we don't really support polymorphism very well yet, especially for external refinements.
When a class implements an interface or extends another class, we verify the refinements hierarchy (there's a subsection about it in here ), but we didn't use states or add this information to the external refinements.
I think Jonathan has a paper on this that we can check