Take responsibility to remove incompatibilities

src/pip/_internal/resolution/resolvelib/factory.py

@@ -7,6 +7,7 @@
     Iterable,
     Iterator,
     List,
+    Mapping,
     Optional,
     Sequence,
     Set,
@@ -104,6 +105,9 @@ def __init__(
         self._installed_candidate_cache = (
             {}
         )  # type: Dict[str, AlreadyInstalledCandidate]
+        self._extras_candidate_cache = (
+            {}
+        )  # type: Dict[Tuple[int, FrozenSet[str]], ExtrasCandidate]
 
         if not ignore_installed:
             self._installed_dists = {
@@ -118,6 +122,16 @@ def force_reinstall(self):
         # type: () -> bool
         return self._force_reinstall
 
+    def _make_extras_candidate(self, base, extras):
+        # type: (BaseCandidate, FrozenSet[str]) -> ExtrasCandidate
+        cache_key = (id(base), extras)
+        try:
+            candidate = self._extras_candidate_cache[cache_key]
+        except KeyError:
+            candidate = ExtrasCandidate(base, extras)
+            self._extras_candidate_cache[cache_key] = candidate
+        return candidate
+
     def _make_candidate_from_dist(
         self,
         dist,  # type: Distribution
@@ -130,9 +144,9 @@ def _make_candidate_from_dist(
         except KeyError:
             base = AlreadyInstalledCandidate(dist, template, factory=self)
             self._installed_candidate_cache[dist.key] = base
-        if extras:
-            return ExtrasCandidate(base, extras)
-        return base
+        if not extras:
+            return base
+        return self._make_extras_candidate(base, extras)
 
     def _make_candidate_from_link(
         self,
@@ -182,18 +196,18 @@ def _make_candidate_from_link(
                     return None
             base = self._link_candidate_cache[link]
 
-        if extras:
-            return ExtrasCandidate(base, extras)
-        return base
+        if not extras:
+            return base
+        return self._make_extras_candidate(base, extras)
 
     def _iter_found_candidates(
         self,
-        ireqs,  # type: Sequence[InstallRequirement]
-        specifier,  # type: SpecifierSet
-        hashes,  # type: Hashes
-        prefers_installed,  # type: bool
-    ):
-        # type: (...) -> Iterable[Candidate]
+        ireqs: Sequence[InstallRequirement],
+        specifier: SpecifierSet,
+        hashes: Hashes,
+        prefers_installed: bool,
+        incompatible_ids: Set[int],
+    ) -> Iterable[Candidate]:
         if not ireqs:
             return ()
 
@@ -257,20 +271,27 @@ def iter_index_candidate_infos():
             iter_index_candidate_infos,
             installed_candidate,
             prefers_installed,
+            incompatible_ids,
         )
 
     def find_candidates(
         self,
-        requirements,  # type: Sequence[Requirement]
-        constraint,  # type: Constraint
-        prefers_installed,  # type: bool
-    ):
-        # type: (...) -> Iterable[Candidate]
+        identifier: str,
+        requirements: Mapping[str, Iterator[Requirement]],
+        incompatibilities: Mapping[str, Iterator[Candidate]],
+        constraint: Constraint,
+        prefers_installed: bool,
+    ) -> Iterable[Candidate]:
+
+        # Since we cache all the candidates, incompatibility identification
+        # can be made quicker by comparing only the id() values.
+        incompat_ids = {id(c) for c in incompatibilities.get(identifier, ())}
+
         explicit_candidates = set()  # type: Set[Candidate]
         ireqs = []  # type: List[InstallRequirement]
-        for req in requirements:
+        for req in requirements[identifier]:
             cand, ireq = req.get_candidate_lookup()
-            if cand is not None:
+            if cand is not None and id(cand) not in incompat_ids:
                 explicit_candidates.add(cand)
             if ireq is not None:
                 ireqs.append(ireq)
@@ -283,13 +304,14 @@ def find_candidates(
                 constraint.specifier,
                 constraint.hashes,
                 prefers_installed,
+                incompat_ids,
             )
 
         return (
             c
             for c in explicit_candidates
             if constraint.is_satisfied_by(c)
-            and all(req.is_satisfied_by(c) for req in requirements)
+            and all(req.is_satisfied_by(c) for req in requirements[identifier])
         )
 
     def make_requirement_from_install_req(self, ireq, requested_extras):

src/pip/_internal/resolution/resolvelib/found_candidates.py

@@ -100,13 +100,15 @@ class FoundCandidates(collections_abc.Sequence):
 
     def __init__(
         self,
-        get_infos,  # type: Callable[[], Iterator[IndexCandidateInfo]]
-        installed,  # type: Optional[Candidate]
-        prefers_installed,  # type: bool
+        get_infos: Callable[[], Iterator[IndexCandidateInfo]],
+        installed: Optional[Candidate],
+        prefers_installed: bool,
+        incompatible_ids: Set[int],
     ):
         self._get_infos = get_infos
         self._installed = installed
         self._prefers_installed = prefers_installed
+        self._incompatible_ids = incompatible_ids
 
     def __getitem__(self, index):
         # type: (int) -> Candidate
@@ -119,10 +121,12 @@ def __iter__(self):
         # type: () -> Iterator[Candidate]
         infos = self._get_infos()
         if not self._installed:
-            return _iter_built(infos)
-        if self._prefers_installed:
-            return _iter_built_with_prepended(self._installed, infos)
-        return _iter_built_with_inserted(self._installed, infos)
+            iterator = _iter_built(infos)
+        elif self._prefers_installed:
+            iterator = _iter_built_with_prepended(self._installed, infos)
+        else:
+            iterator = _iter_built_with_inserted(self._installed, infos)
+        return (c for c in iterator if id(c) not in self._incompatible_ids)
 
     def __len__(self):
         # type: () -> int

src/pip/_internal/resolution/resolvelib/provider.py

@@ -149,11 +149,6 @@ def find_matches(
         requirements: Mapping[str, Iterator[Requirement]],
         incompatibilities: Mapping[str, Iterator[Candidate]],
     ) -> Iterable[Candidate]:
-        try:
-            current_requirements = requirements[identifier]
-        except KeyError:
-            return []
-
         def _eligible_for_upgrade(name):
             # type: (str) -> bool
             """Are upgrades allowed for this project?
@@ -173,9 +168,11 @@ def _eligible_for_upgrade(name):
             return False
 
         return self._factory.find_candidates(
-            list(current_requirements),
+            identifier=identifier,
+            requirements=requirements,
             constraint=self._constraints.get(identifier, Constraint.empty()),
             prefers_installed=(not _eligible_for_upgrade(identifier)),
+            incompatibilities=incompatibilities,
         )
 
     def is_satisfied_by(self, requirement, candidate):