Always prefer causes when backtracking

src/resolvelib/providers.py

@@ -9,14 +9,7 @@ def identify(self, requirement_or_candidate):
         """
         raise NotImplementedError
 
-    def get_preference(
-        self,
-        identifier,
-        resolutions,
-        candidates,
-        information,
-        backtrack_causes,
-    ):
+    def get_preference(self, identifier, resolutions, candidates, information):
         """Produce a sort key for given requirement based on preference.
 
         The preference is defined as "I think this requirement should be
@@ -32,8 +25,6 @@ def get_preference(
             Each value is an iterator of candidates.
         :param information: Mapping of requirement information of each package.
             Each value is an iterator of *requirement information*.
-        :param backtrack_causes: Sequence of requirement information that were
-            the requirements that caused the resolver to most recently backtrack.
 
         A *requirement information* instance is a named tuple with two members:
 

src/resolvelib/providers.pyi

@@ -24,7 +24,6 @@ class AbstractProvider(Generic[RT, CT, KT]):
         resolutions: Mapping[KT, CT],
         candidates: Mapping[KT, Iterator[CT]],
         information: Mapping[KT, Iterator[RequirementInformation[RT, CT]]],
-        backtrack_causes: Sequence[RequirementInformation[RT, CT]],
     ) -> Preference: ...
     def find_matches(
         self,

src/resolvelib/reporters.py

@@ -41,3 +41,12 @@ def rejecting_candidate(self, criterion, candidate):
 
     def pinning(self, candidate):
         """Called when adding a candidate to the potential solution."""
+
+    def backtracking_on(self, names, unsatisfied_names):
+        """Called when resolver identifies specific projects causing backtracking.
+
+        :param causes: The names of projects causing the backtracking.
+        :param causes: The names of projects and their parents that are
+            currently unsatisfied by the resolver.
+
+        """

src/resolvelib/reporters.pyi

@@ -9,3 +9,6 @@ class BaseReporter:
     def rejecting_candidate(self, criterion: Any, candidate: Any) -> Any: ...
     def resolving_conflicts(self, causes: Any) -> Any: ...
     def pinning(self, candidate: Any) -> Any: ...
+    def backtracking_on(
+        self, names: set[str], unsatisfied_names: set[str]
+    ) -> Any: ...

src/resolvelib/resolvers.py

@@ -211,7 +211,6 @@ def _get_preference(self, name):
                 self.state.criteria,
                 operator.attrgetter("information"),
             ),
-            backtrack_causes=self.state.backtrack_causes,
         )
 
     def _is_current_pin_satisfying(self, name, criterion):
@@ -418,10 +417,29 @@ def resolve(self, requirements, max_rounds):
                 return self.state
 
             # keep track of satisfied names to calculate diff after pinning
-            satisfied_names = set(self.state.criteria.keys()) - set(
-                unsatisfied_names
+            unsatisfied_names_set = set(unsatisfied_names)
+            satisfied_names = (
+                set(self.state.criteria.keys()) - unsatisfied_names_set
             )
 
+            # If backtrack causes prefer them and their parents first
+            if self.state.backtrack_causes:
+                backtrack_cause_names = set()
+                for backtrack_cause in self.state.backtrack_causes:
+                    backtrack_cause_names.add(backtrack_cause.requirement.name)
+                    if backtrack_cause.parent:
+                        backtrack_cause_names.add(backtrack_cause.parent.name)
+
+                unsatisfied_causes_names = unsatisfied_names_set & (
+                    backtrack_cause_names
+                )
+                if unsatisfied_causes_names:
+                    unsatisfied_names = list(unsatisfied_causes_names)
+
+                self._r.backtracking_on(
+                    backtrack_cause_names, unsatisfied_causes_names
+                )
+
             # Choose the most preferred unpinned criterion to try.
             name = min(unsatisfied_names, key=self._get_preference)
             failure_causes = self._attempt_to_pin_criterion(name)

tests/functional/cocoapods/test_resolvers_cocoapods.py

@@ -174,14 +174,7 @@ def __init__(self, filename):
     def identify(self, requirement_or_candidate):
         return requirement_or_candidate.name
 
-    def get_preference(
-        self,
-        identifier,
-        resolutions,
-        candidates,
-        information,
-        backtrack_causes,
-    ):
+    def get_preference(self, identifier, resolutions, candidates, information):
         return sum(1 for _ in candidates[identifier])
 
     def _iter_matches(self, name, requirements, incompatibilities):

tests/functional/python/test_resolvers_python.py

@@ -71,14 +71,7 @@ def identify(self, requirement_or_candidate):
             return "{}[{}]".format(name, extras_str)
         return name
 
-    def get_preference(
-        self,
-        identifier,
-        resolutions,
-        candidates,
-        information,
-        backtrack_causes,
-    ):
+    def get_preference(self, identifier, resolutions, candidates, information):
         transitive = all(p is not None for _, p in information[identifier])
         return (transitive, identifier)
 

tests/functional/swift-package-manager/test_resolvers_swift.py

@@ -78,14 +78,7 @@ def __init__(self, filename):
     def identify(self, requirement_or_candidate):
         return requirement_or_candidate.container["identifier"]
 
-    def get_preference(
-        self,
-        identifier,
-        resolutions,
-        candidates,
-        information,
-        backtrack_causes,
-    ):
+    def get_preference(self, identifier, resolutions, candidates, information):
         return sum(1 for _ in candidates[identifier])
 
     def _iter_matches(self, identifier, requirements, incompatibilities):