[OPENJPA-2961] Include subclasses of the treated class in the TREAT discriminator filter

[rzo1]

The TREAT discriminator filter only matched the exact treated class (disc = value), so TREAT(x AS Middle) dropped instances of Middle's subclasses. It now reuses the discriminator's class conditions, like InstanceofExpression, which emit IN (...) over the treated class and its subclasses. Note that for LEFT JOIN TREAT(...) rows without a related entity are now kept (disc IS NULL OR ...); TestTreatSubclassDiscriminator covers a three-level single-table hierarchy.

[cristof]

@rzo1 , could you add, in your tests, a revision number for both software and game, and a genre for game, and add the following tests? It seems to fail when using WHERE TREAT:

   public void testTreatInWhereExclusiveProperty() {
        try (EntityManager em = emf.createEntityManager()){
            List<String> results = em.createQuery(
                "SELECT p.name FROM TProduct p WHERE TREAT(p AS TGameProduct).genre = 'FPS'",
                String.class).getResultList();
            assertEquals(List.of("Game"), results);
        } 
    }

    public void testTreatInWhereCommonProperty() {
        try (EntityManager em = emf.createEntityManager()){
            List<String> results = em.createQuery(
                "SELECT p.name FROM TProduct p WHERE TREAT(p AS TGameProduct).revisionNumber = 2.0",
                String.class).getResultList();
            assertEquals(List.of("Game"), results);
        } 
    }

[rzo1]

Thanks, good catch. The exclusive-property case only passed because genre is null on the other rows; the common-property one returned [Software, Game]. A TREAT path in WHERE didn't restrict the type at all. A predicate over TREAT(x AS Type) is now false when x isn't a Type or one of its subclasses (spec 4.4.9). The restriction is applied to that predicate only, so other OR branches still match. I added both of your tests, plus one for an OR condition and one for TREAT on a join variable.

[cristof]

@solomax, as I've added some code, could you please review and merge?