Re: not null constraints, again

I did some refactoring on transformColumnDefinition
since transformColumnDefinition only deals with a single ColumnDef.
and serial/primary/identity cannot allow not-null no inherit.
We can preliminary iterate through ColumnDef->constraints to check
that ColumnDef can allow not-null no inherit or not.
if not allowed, then error out at CONSTR_NOTNULL.
please check attached.


in MergeConstraintsIntoExisting
we can

        while (HeapTupleIsValid(child_tuple = systable_getnext(child_scan)))
        {
            Form_pg_constraint child_con = (Form_pg_constraint)
GETSTRUCT(child_tuple);
            HeapTuple    child_copy;
            if (child_con->contype != parent_con->contype)
                continue;
            if (child_con->connoinherit)
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
                         errmsg("constraint \"%s\" conflicts with
non-inherited constraint on child table \"%s\"",
                                NameStr(child_con->conname),
RelationGetRelationName(child_rel))));
            if (parent_con->convalidated && !child_con->convalidated)
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
                         errmsg("constraint \"%s\" conflicts with NOT
VALID constraint on child table \"%s\"",
                                NameStr(child_con->conname),
RelationGetRelationName(child_rel))));
}
error out earlier, save some cache search cycle.


MergeConstraintsIntoExisting comment says
" * XXX See MergeWithExistingConstraint too if you change this code."
we actually did change the MergeConstraintsIntoExisting, not change
MergeWithExistingConstraint
but it seems MergeWithExistingConstraint does not deal with CONSTRAINT_NOTNULL.
So I guess  the comments are fine.


previously, we mentioned adding some domain tests at [1].
but it seems v8, we don't have domain related regression tests.


[1] https://www.postgresql.org/message-id/202409252014.74iepgsyuyws%40alvherre.pgsql