Determines which classifiers have to be imported into given module.

def imported_classifiers(p: ecore.EPackage):
        """Determines which classifiers have to be imported into given module."""
        classes = {c for c in p.eClassifiers if isinstance(c, ecore.EClass)}

        supertypes = itertools.chain(*(c.eAllSuperTypes() for c in classes))
        imported = {c for c in supertypes if c.ePackage is not p}

        attributes = itertools.chain(*(c.eAttributes for c in classes))
        attributes_types = (a.eType for a in attributes)
        imported |= {t for t in attributes_types if t.ePackage not in {p, ecore.eClass, None}}

        imported_dict = {}
        for classifier in imported:
            imported_dict.setdefault(classifier.ePackage, set()).add(classifier)

        return imported_dict