| import collections |
| |
| from .compat import collections_abc |
| from .providers import AbstractResolver |
| from .structs import DirectedGraph |
| |
| |
| RequirementInformation = collections.namedtuple( |
| "RequirementInformation", ["requirement", "parent"] |
| ) |
| |
| |
| class ResolverException(Exception): |
| """A base class for all exceptions raised by this module. |
| |
| Exceptions derived by this class should all be handled in this module. Any |
| bubbling pass the resolver should be treated as a bug. |
| """ |
| |
| |
| class RequirementsConflicted(ResolverException): |
| def __init__(self, criterion): |
| super(RequirementsConflicted, self).__init__(criterion) |
| self.criterion = criterion |
| |
| def __str__(self): |
| return "Requirements conflict: {}".format( |
| ", ".join(repr(r) for r in self.criterion.iter_requirement()), |
| ) |
| |
| |
| class InconsistentCandidate(ResolverException): |
| def __init__(self, candidate, criterion): |
| super(InconsistentCandidate, self).__init__(candidate, criterion) |
| self.candidate = candidate |
| self.criterion = criterion |
| |
| def __str__(self): |
| return "Provided candidate {!r} does not satisfy {}".format( |
| self.candidate, |
| ", ".join(repr(r) for r in self.criterion.iter_requirement()), |
| ) |
| |
| |
| class Criterion(object): |
| """Representation of possible resolution results of a package. |
| |
| This holds three attributes: |
| |
| * `information` is a collection of `RequirementInformation` pairs. |
| Each pair is a requirement contributing to this criterion, and the |
| candidate that provides the requirement. |
| * `incompatibilities` is a collection of all known not-to-work candidates |
| to exclude from consideration. |
| * `candidates` is a collection containing all possible candidates deducted |
| from the union of contributing requirements and known incompatibilities. |
| It should never be empty, except when the criterion is an attribute of a |
| raised `RequirementsConflicted` (in which case it is always empty). |
| |
| .. note:: |
| This class is intended to be externally immutable. **Do not** mutate |
| any of its attribute containers. |
| """ |
| |
| def __init__(self, candidates, information, incompatibilities): |
| self.candidates = candidates |
| self.information = information |
| self.incompatibilities = incompatibilities |
| |
| def __repr__(self): |
| requirements = ", ".join( |
| "({!r}, via={!r})".format(req, parent) |
| for req, parent in self.information |
| ) |
| return "Criterion({})".format(requirements) |
| |
| @classmethod |
| def from_requirement(cls, provider, requirement, parent): |
| """Build an instance from a requirement. |
| """ |
| candidates = provider.find_matches([requirement]) |
| if not isinstance(candidates, collections_abc.Sequence): |
| candidates = list(candidates) |
| criterion = cls( |
| candidates=candidates, |
| information=[RequirementInformation(requirement, parent)], |
| incompatibilities=[], |
| ) |
| if not candidates: |
| raise RequirementsConflicted(criterion) |
| return criterion |
| |
| def iter_requirement(self): |
| return (i.requirement for i in self.information) |
| |
| def iter_parent(self): |
| return (i.parent for i in self.information) |
| |
| def merged_with(self, provider, requirement, parent): |
| """Build a new instance from this and a new requirement. |
| """ |
| infos = list(self.information) |
| infos.append(RequirementInformation(requirement, parent)) |
| candidates = provider.find_matches([r for r, _ in infos]) |
| if not isinstance(candidates, collections_abc.Sequence): |
| candidates = list(candidates) |
| criterion = type(self)(candidates, infos, list(self.incompatibilities)) |
| if not candidates: |
| raise RequirementsConflicted(criterion) |
| return criterion |
| |
| def excluded_of(self, candidate): |
| """Build a new instance from this, but excluding specified candidate. |
| |
| Returns the new instance, or None if we still have no valid candidates. |
| """ |
| incompats = list(self.incompatibilities) |
| incompats.append(candidate) |
| candidates = [c for c in self.candidates if c != candidate] |
| if not candidates: |
| return None |
| criterion = type(self)(candidates, list(self.information), incompats) |
| return criterion |
| |
| |
| class ResolutionError(ResolverException): |
| pass |
| |
| |
| class ResolutionImpossible(ResolutionError): |
| def __init__(self, causes): |
| super(ResolutionImpossible, self).__init__(causes) |
| # causes is a list of RequirementInformation objects |
| self.causes = causes |
| |
| |
| class ResolutionTooDeep(ResolutionError): |
| def __init__(self, round_count): |
| super(ResolutionTooDeep, self).__init__(round_count) |
| self.round_count = round_count |
| |
| |
| # Resolution state in a round. |
| State = collections.namedtuple("State", "mapping criteria") |
| |
| |
| class Resolution(object): |
| """Stateful resolution object. |
| |
| This is designed as a one-off object that holds information to kick start |
| the resolution process, and holds the results afterwards. |
| """ |
| |
| def __init__(self, provider, reporter): |
| self._p = provider |
| self._r = reporter |
| self._states = [] |
| |
| @property |
| def state(self): |
| try: |
| return self._states[-1] |
| except IndexError: |
| raise AttributeError("state") |
| |
| def _push_new_state(self): |
| """Push a new state into history. |
| |
| This new state will be used to hold resolution results of the next |
| coming round. |
| """ |
| try: |
| base = self._states[-1] |
| except IndexError: |
| state = State(mapping=collections.OrderedDict(), criteria={}) |
| else: |
| state = State( |
| mapping=base.mapping.copy(), criteria=base.criteria.copy(), |
| ) |
| self._states.append(state) |
| |
| def _merge_into_criterion(self, requirement, parent): |
| self._r.adding_requirement(requirement, parent) |
| name = self._p.identify(requirement) |
| try: |
| crit = self.state.criteria[name] |
| except KeyError: |
| crit = Criterion.from_requirement(self._p, requirement, parent) |
| else: |
| crit = crit.merged_with(self._p, requirement, parent) |
| return name, crit |
| |
| def _get_criterion_item_preference(self, item): |
| name, criterion = item |
| try: |
| pinned = self.state.mapping[name] |
| except KeyError: |
| pinned = None |
| return self._p.get_preference( |
| pinned, criterion.candidates, criterion.information, |
| ) |
| |
| def _is_current_pin_satisfying(self, name, criterion): |
| try: |
| current_pin = self.state.mapping[name] |
| except KeyError: |
| return False |
| return all( |
| self._p.is_satisfied_by(r, current_pin) |
| for r in criterion.iter_requirement() |
| ) |
| |
| def _get_criteria_to_update(self, candidate): |
| criteria = {} |
| for r in self._p.get_dependencies(candidate): |
| name, crit = self._merge_into_criterion(r, parent=candidate) |
| criteria[name] = crit |
| return criteria |
| |
| def _attempt_to_pin_criterion(self, name, criterion): |
| causes = [] |
| for candidate in criterion.candidates: |
| try: |
| criteria = self._get_criteria_to_update(candidate) |
| except RequirementsConflicted as e: |
| causes.append(e.criterion) |
| continue |
| |
| # Check the newly-pinned candidate actually works. This should |
| # always pass under normal circumstances, but in the case of a |
| # faulty provider, we will raise an error to notify the implementer |
| # to fix find_matches() and/or is_satisfied_by(). |
| satisfied = all( |
| self._p.is_satisfied_by(r, candidate) |
| for r in criterion.iter_requirement() |
| ) |
| if not satisfied: |
| raise InconsistentCandidate(candidate, criterion) |
| |
| # Put newly-pinned candidate at the end. This is essential because |
| # backtracking looks at this mapping to get the last pin. |
| self._r.pinning(candidate) |
| self.state.mapping.pop(name, None) |
| self.state.mapping[name] = candidate |
| self.state.criteria.update(criteria) |
| |
| return [] |
| |
| # All candidates tried, nothing works. This criterion is a dead |
| # end, signal for backtracking. |
| return causes |
| |
| def _backtrack(self): |
| # Drop the current state, it's known not to work. |
| del self._states[-1] |
| |
| # We need at least 2 states here: |
| # (a) One to backtrack to. |
| # (b) One to restore state (a) to its state prior to candidate-pinning, |
| # so we can pin another one instead. |
| |
| while len(self._states) >= 2: |
| # Retract the last candidate pin. |
| prev_state = self._states.pop() |
| try: |
| name, candidate = prev_state.mapping.popitem() |
| except KeyError: |
| continue |
| self._r.backtracking(candidate) |
| |
| # Create a new state to work on, with the newly known not-working |
| # candidate excluded. |
| self._push_new_state() |
| |
| # Mark the retracted candidate as incompatible. |
| criterion = self.state.criteria[name].excluded_of(candidate) |
| if criterion is None: |
| # This state still does not work. Try the still previous state. |
| del self._states[-1] |
| continue |
| self.state.criteria[name] = criterion |
| |
| return True |
| |
| return False |
| |
| def resolve(self, requirements, max_rounds): |
| if self._states: |
| raise RuntimeError("already resolved") |
| |
| self._push_new_state() |
| for r in requirements: |
| try: |
| name, crit = self._merge_into_criterion(r, parent=None) |
| except RequirementsConflicted as e: |
| raise ResolutionImpossible(e.criterion.information) |
| self.state.criteria[name] = crit |
| |
| self._r.starting() |
| |
| for round_index in range(max_rounds): |
| self._r.starting_round(round_index) |
| |
| self._push_new_state() |
| curr = self.state |
| |
| unsatisfied_criterion_items = [ |
| item |
| for item in self.state.criteria.items() |
| if not self._is_current_pin_satisfying(*item) |
| ] |
| |
| # All criteria are accounted for. Nothing more to pin, we are done! |
| if not unsatisfied_criterion_items: |
| del self._states[-1] |
| self._r.ending(curr) |
| return self.state |
| |
| # Choose the most preferred unpinned criterion to try. |
| name, criterion = min( |
| unsatisfied_criterion_items, |
| key=self._get_criterion_item_preference, |
| ) |
| failure_causes = self._attempt_to_pin_criterion(name, criterion) |
| |
| # Backtrack if pinning fails. |
| if failure_causes: |
| result = self._backtrack() |
| if not result: |
| causes = [ |
| i for crit in failure_causes for i in crit.information |
| ] |
| raise ResolutionImpossible(causes) |
| |
| self._r.ending_round(round_index, curr) |
| |
| raise ResolutionTooDeep(max_rounds) |
| |
| |
| def _has_route_to_root(criteria, key, all_keys, connected): |
| if key in connected: |
| return True |
| if key not in criteria: |
| return False |
| for p in criteria[key].iter_parent(): |
| try: |
| pkey = all_keys[id(p)] |
| except KeyError: |
| continue |
| if pkey in connected: |
| connected.add(key) |
| return True |
| if _has_route_to_root(criteria, pkey, all_keys, connected): |
| connected.add(key) |
| return True |
| return False |
| |
| |
| Result = collections.namedtuple("Result", "mapping graph criteria") |
| |
| |
| def _build_result(state): |
| mapping = state.mapping |
| all_keys = {id(v): k for k, v in mapping.items()} |
| all_keys[id(None)] = None |
| |
| graph = DirectedGraph() |
| graph.add(None) # Sentinel as root dependencies' parent. |
| |
| connected = {None} |
| for key, criterion in state.criteria.items(): |
| if not _has_route_to_root(state.criteria, key, all_keys, connected): |
| continue |
| if key not in graph: |
| graph.add(key) |
| for p in criterion.iter_parent(): |
| try: |
| pkey = all_keys[id(p)] |
| except KeyError: |
| continue |
| if pkey not in graph: |
| graph.add(pkey) |
| graph.connect(pkey, key) |
| |
| return Result( |
| mapping={k: v for k, v in mapping.items() if k in connected}, |
| graph=graph, |
| criteria=state.criteria, |
| ) |
| |
| |
| class Resolver(AbstractResolver): |
| """The thing that performs the actual resolution work. |
| """ |
| |
| base_exception = ResolverException |
| |
| def resolve(self, requirements, max_rounds=100): |
| """Take a collection of constraints, spit out the resolution result. |
| |
| The return value is a representation to the final resolution result. It |
| is a tuple subclass with three public members: |
| |
| * `mapping`: A dict of resolved candidates. Each key is an identifier |
| of a requirement (as returned by the provider's `identify` method), |
| and the value is the resolved candidate. |
| * `graph`: A `DirectedGraph` instance representing the dependency tree. |
| The vertices are keys of `mapping`, and each edge represents *why* |
| a particular package is included. A special vertex `None` is |
| included to represent parents of user-supplied requirements. |
| * `criteria`: A dict of "criteria" that hold detailed information on |
| how edges in the graph are derived. Each key is an identifier of a |
| requirement, and the value is a `Criterion` instance. |
| |
| The following exceptions may be raised if a resolution cannot be found: |
| |
| * `ResolutionImpossible`: A resolution cannot be found for the given |
| combination of requirements. The `causes` attribute of the |
| exception is a list of (requirement, parent), giving the |
| requirements that could not be satisfied. |
| * `ResolutionTooDeep`: The dependency tree is too deeply nested and |
| the resolver gave up. This is usually caused by a circular |
| dependency, but you can try to resolve this by increasing the |
| `max_rounds` argument. |
| """ |
| resolution = Resolution(self.provider, self.reporter) |
| state = resolution.resolve(requirements, max_rounds=max_rounds) |
| return _build_result(state) |
