Merge pull request pypa#9369 from uranusjr/resolvelib-054

news/9180.bugfix.rst

@@ -0,0 +1 @@
+Fix error when an existing incompatibility is unable to be applied to a backtracked state.

news/resolvelib.vendor.rst

@@ -0,0 +1 @@
+Upgrade resolvelib to 0.5.4.

src/pip/_vendor/resolvelib/__init__.py

@@ -11,7 +11,7 @@
     "ResolutionTooDeep",
 ]
 
-__version__ = "0.5.3"
+__version__ = "0.5.4"
 
 
 from .providers import AbstractProvider, AbstractResolver

src/pip/_vendor/resolvelib/resolvers.py

@@ -257,7 +257,7 @@ def _backtrack(self):
             information from Y to Y'.
         4a. If this causes Y' to conflict, we need to backtrack again. Make Y'
             the new Z and go back to step 2.
-        4b. If the incompatibilites apply cleanly, end backtracking.
+        4b. If the incompatibilities apply cleanly, end backtracking.
         """
         while len(self._states) >= 3:
             # Remove the state that triggered backtracking.
@@ -271,28 +271,36 @@ def _backtrack(self):
                 for k, v in broken_state.criteria.items()
             ]
 
+            # Also mark the newly known incompatibility.
+            incompatibilities_from_broken.append((name, [candidate]))
+
             self._r.backtracking(candidate)
 
             # Create a new state from the last known-to-work one, and apply
             # the previously gathered incompatibility information.
-            self._push_new_state()
-            for k, incompatibilities in incompatibilities_from_broken:
-                try:
-                    crit = self.state.criteria[k]
-                except KeyError:
-                    continue
-                self.state.criteria[k] = crit.excluded_of(incompatibilities)
+            def _patch_criteria():
+                for k, incompatibilities in incompatibilities_from_broken:
+                    if not incompatibilities:
+                        continue
+                    try:
+                        criterion = self.state.criteria[k]
+                    except KeyError:
+                        continue
+                    criterion = criterion.excluded_of(incompatibilities)
+                    if criterion is None:
+                        return False
+                    self.state.criteria[k] = criterion
+                return True
 
-            # Mark the newly known incompatibility.
-            criterion = self.state.criteria[name].excluded_of([candidate])
+            self._push_new_state()
+            success = _patch_criteria()
 
             # It works! Let's work on this new state.
-            if criterion:
-                self.state.criteria[name] = criterion
+            if success:
                 return True
 
-            # State does not work after adding the new incompatibility
-            # information. Try the still previous state.
+            # State does not work after applying known incompatibilities.
+            # Try the still previous state.
 
         # No way to backtrack anymore.
         return False

src/pip/_vendor/vendor.txt

@@ -16,7 +16,7 @@ requests==2.25.0
     chardet==3.0.4
     idna==2.10
     urllib3==1.26.2
-resolvelib==0.5.3
+resolvelib==0.5.4
 retrying==1.3.3
 setuptools==44.0.0
 six==1.15.0