Merge pull request #8924 from uranusjr/new-resolver-try-user-requeste…

…d-combinations-first

news/8924.feature

@@ -0,0 +1,2 @@
+New resolver: Tweak resolution logic to improve user experience when
+user-supplied requirements conflict.

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

@@ -43,7 +43,7 @@ def __init__(
  self._constraints = constraints
  self._ignore_dependencies = ignore_dependencies
  self._upgrade_strategy = upgrade_strategy
- self.user_requested = user_requested
+ self._user_requested = user_requested
 
  def _sort_matches(self, matches):
  # type: (Iterable[Candidate]) -> Sequence[Candidate]
@@ -84,7 +84,7 @@ def _eligible_for_upgrade(name):
  if self._upgrade_strategy == "eager":
  return True
  elif self._upgrade_strategy == "only-if-needed":
- return (name in self.user_requested)
+ return (name in self._user_requested)
  return False
 
  def sort_key(c):
@@ -115,11 +115,18 @@ def get_preference(
  self,
  resolution, # type: Optional[Candidate]
  candidates, # type: Sequence[Candidate]
- information # type: Sequence[Tuple[Requirement, Candidate]]
+ information # type: Sequence[Tuple[Requirement, Optional[Candidate]]]
  ):
  # type: (...) -> Any
- # Use the "usual" value for now
- return len(candidates)
+ """Return a sort key to determine what dependency to look next.
+
+ A smaller value makes a dependency higher priority. We put direct
+ (user-requested) dependencies first since they may contain useful
+ user-specified version ranges. Users tend to expect us to catch
+ problems in them early as well.
+ """
+ transitive = all(parent is not None for _, parent in information)
+ return (transitive, len(candidates))
 
  def find_matches(self, requirements):
  # type: (Sequence[Requirement]) -> Iterable[Candidate]