presto-main/src/main/java/io/prestosql/metadata/SignatureBinder.java/SolverReturnStatusMerger/add
class SolverReturnStatusMerger:        public void add(SolverReturnStatus newStatus)
        {
            switch (newStatus) {
                case UNCHANGED_SATISFIED:
                    break;
                case UNCHANGED_NOT_SATISFIED:
                    if (current == SolverReturnStatus.UNCHANGED_SATISFIED) {
                        current = SolverReturnStatus.UNCHANGED_NOT_SATISFIED;
                    }
                    break;
                case CHANGED:
                    if (current == SolverReturnStatus.UNCHANGED_SATISFIED || current == SolverReturnStatus.UNCHANGED_NOT_SATISFIED) {
                        current = SolverReturnStatus.CHANGED;
                    }
                    break;
                case UNSOLVABLE:
                    current = SolverReturnStatus.UNSOLVABLE;
                    break;
            }
        }