Implement constraints

Author: pfmoore

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

@@ -21,7 +21,7 @@
 )
 
 if MYPY_CHECK_RUNNING:
-    from typing import Dict, Iterator, Optional, Set, Tuple, TypeVar
+    from typing import Dict, Iterator, List, Optional, Set, Tuple, TypeVar
 
     from pip._vendor.packaging.specifiers import SpecifierSet
     from pip._vendor.packaging.version import _BaseVersion
@@ -71,6 +71,8 @@ def __init__(
         else:
             self._installed_dists = {}
 
+        self._constraints = {}  # type: Dict[str,List[SpecifierSet]]
+
     def _make_candidate_from_dist(
         self,
         dist,  # type: Distribution
@@ -154,7 +156,7 @@ def make_requirement_from_install_req(self, ireq):
             cand = self._make_candidate_from_link(
                 ireq.link, extras=set(), parent=ireq,
             )
-            return ExplicitRequirement(cand)
+            return ExplicitRequirement(cand, factory=self)
         return SpecifierRequirement(ireq, factory=self)
 
     def make_requirement_from_spec(self, specifier, comes_from):

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

@@ -1,5 +1,6 @@
 from pip._vendor.packaging.utils import canonicalize_name
 
+from pip._internal.exceptions import InstallationError
 from pip._internal.utils.typing import MYPY_CHECK_RUNNING
 
 from .base import Requirement, format_name
@@ -16,9 +17,10 @@
 
 
 class ExplicitRequirement(Requirement):
-    def __init__(self, candidate):
-        # type: (Candidate) -> None
+    def __init__(self, candidate, factory):
+        # type: (Candidate, Factory) -> None
         self.candidate = candidate
+        self._factory = factory
 
     def __repr__(self):
         # type: () -> str
@@ -35,6 +37,12 @@ def name(self):
 
     def find_matches(self):
         # type: () -> Sequence[Candidate]
+        if self.name in self._factory._constraints:
+            raise InstallationError(
+                "Could not satisfy constraints for '{}': "
+                "installation from path or url cannot be "
+                "constrained to a version".format(self.name)
+            )
         return [self.candidate]
 
     def is_satisfied_by(self, candidate):
@@ -70,7 +78,11 @@ def name(self):
     def find_matches(self):
         # type: () -> Sequence[Candidate]
         it = self._factory.iter_found_candidates(self._ireq, self.extras)
-        return list(it)
+        constraints = self._factory._constraints.get(self.name, [])
+        lit = [c for c in it if all(
+            s.contains(c.version, prereleases=True) for s in constraints
+        )]
+        return lit
 
     def is_satisfied_by(self, candidate):
         # type: (Candidate) -> bool

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

@@ -1,5 +1,6 @@
 import functools
 import logging
+from collections import defaultdict
 
 from pip._vendor import six
 from pip._vendor.packaging.utils import canonicalize_name
@@ -17,6 +18,7 @@
 if MYPY_CHECK_RUNNING:
     from typing import Dict, List, Optional, Tuple
 
+    from pip._vendor.packaging.specifiers import SpecifierSet
     from pip._vendor.resolvelib.resolvers import Result
 
     from pip._internal.cache import WheelCache
@@ -60,9 +62,21 @@ def __init__(
     def resolve(self, root_reqs, check_supported_wheels):
         # type: (List[InstallRequirement], bool) -> RequirementSet
 
-        # FIXME: Implement constraints.
-        if any(r.constraint for r in root_reqs):
-            raise InstallationError("Constraints are not yet supported.")
+        constraints = defaultdict(list)  # type: Dict[str,List[SpecifierSet]]
+        requirements = []
+        for req in root_reqs:
+            if req.constraint:
+                assert req.name
+                assert req.specifier
+                name = canonicalize_name(req.name)
+                constraints[name].append(req.specifier)
+            else:
+                requirements.append(
+                    self.factory.make_requirement_from_install_req(req)
+                )
+
+        # TODO: Refactor this, it's just for proof of concept
+        self.factory._constraints = constraints
 
         provider = PipProvider(
             factory=self.factory,
@@ -71,11 +85,6 @@ def resolve(self, root_reqs, check_supported_wheels):
         reporter = BaseReporter()
         resolver = RLResolver(provider, reporter)
 
-        requirements = [
-            self.factory.make_requirement_from_install_req(r)
-            for r in root_reqs
-        ]
-
         try:
             self._result = resolver.resolve(requirements)