schema.base.Element.validate malfunction

[ThomasWaldmann]

there is a commented/disabled doctest in validation.containers.SetWithKnownFields now (introduced by c3d08d3 ):

from flatland import Dict, Integer
from flatland.validation import SetWithKnownFields
schema = Dict.of(Integer.named('x'), Integer.named('y')).validated_by(SetWithKnownFields())
schema.policy = None
element = schema()
element.set({'x': 123})
assert element.validate()  # assertion error, issue #25, FIXME!    (1)
element.set({'x': 123, 'z': 789})
assert not element.validate()  # no assertion error, but maybe due to #25 also.    (2)

I did a bit of debugging, but I am not familiar enough with the code to fix it, so here is what I found out:

There's a problem in validate():

valid might get set to False early (when encountering the y == None value) and thus validate() will not be able to return True after that. This is why assertion (1) fails although the SetWithKnownFields validator returns True.

    def validate(self, state=None, recurse=True):
        if not recurse:
            down = self._validate(state, True)
            if down is Unevaluated:
                self.valid = down
            else:
                self.valid = bool(down)

            up = self._validate(state, False)
            # an Unevaluated ascent validator does not override the results
            # of descent validation
            if up is not Unevaluated:
                self.valid = bool(up)
            return self.valid

        valid = True
        elements, seen, queue = [], set(), collections.deque([self])

        # descend breadth first, skipping any branches that return All*
        while queue:
            element = queue.popleft()
            if id(element) in seen:
                continue
            seen.add(id(element))
            elements.append(element)
            validated = element._validate(state, True)

            if validated is Unevaluated:
                element.valid = validated
            else:
                element.valid = bool(validated)
                if valid:
                    valid &= validated  # <<<<<<<<<<<<<<<<<< getting False here due to y == None
            if validated is SkipAll or validated is SkipAllFalse:
                continue
            queue.extend(element.children)

        # back up, visiting only the elements that weren't skipped above
        for element in reversed(elements):
            validated = element._validate(state, False)  # <<< SetWithKnownFields gets called, validated = True

            # an Unevaluated ascent validator does not override the results
            # of descent validation
            if validated is Unevaluated:
                pass
            elif element.valid:
                element.valid = bool(validated)
                if valid:  # <<<<<<< as valid is already False, it stays False
                    valid &= validated
        return bool(valid)