Merge pull request #9994 from uranusjr/requires-python-before-other-deps

Check Requires-Python before other dependencies

news/9925.feature.rst

@@ -0,0 +1,3 @@
+New resolver: A distribution's ``Requires-Python`` metadata is now checked
+before its Python dependencies. This makes the resolver fail quicker when
+there's an interpreter version conflict.

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

@@ -32,6 +32,9 @@
  "LinkCandidate",
 ]
 
+# Avoid conflicting with the PyPI package "Python".
+REQUIRES_PYTHON_IDENTIFIER = cast(NormalizedName, "<Python from Requires-Python>")
+
 
 def as_base_candidate(candidate: Candidate) -> Optional[BaseCandidate]:
  """The runtime version of BaseCandidate."""
@@ -578,13 +581,12 @@ def __str__(self):
  @property
  def project_name(self):
  # type: () -> NormalizedName
- # Avoid conflicting with the PyPI package "Python".
- return cast(NormalizedName, "<Python from Requires-Python>")
+ return REQUIRES_PYTHON_IDENTIFIER
 
  @property
  def name(self):
  # type: () -> str
- return self.project_name
+ return REQUIRES_PYTHON_IDENTIFIER
 
  @property
  def version(self):

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

@@ -3,6 +3,7 @@
 from pip._vendor.resolvelib.providers import AbstractProvider
 
 from .base import Candidate, Constraint, Requirement
+from .candidates import REQUIRES_PYTHON_IDENTIFIER
 from .factory import Factory
 
 if TYPE_CHECKING:
@@ -121,6 +122,10 @@ def _get_restrictive_rating(requirements):
  rating = _get_restrictive_rating(r for r, _ in information[identifier])
  order = self._user_requested.get(identifier, float("inf"))
 
+ # Requires-Python has only one candidate and the check is basically
+ # free, so we always do it first to avoid needless work if it fails.
+ requires_python = identifier == REQUIRES_PYTHON_IDENTIFIER
+
  # HACK: Setuptools have a very long and solid backward compatibility
  # track record, and extremely few projects would request a narrow,
  # non-recent version range of it since that would break a lot things.
@@ -131,7 +136,7 @@ def _get_restrictive_rating(requirements):
  # while we work on "proper" branch pruning techniques.
  delay_this = identifier == "setuptools"
 
- return (delay_this, rating, order, identifier)
+ return (not requires_python, delay_this, rating, order, identifier)
 
  def find_matches(
  self,

tests/functional/test_new_resolver_errors.py

@@ -1,3 +1,4 @@
+import pathlib
 import sys
 
 from tests.lib import create_basic_wheel_for_package, create_test_package_with_setup
@@ -73,3 +74,34 @@ def test_new_resolver_requires_python_error(script):
  # conflict, not the compatible one.
  assert incompatible_python in result.stderr, str(result)
  assert compatible_python not in result.stderr, str(result)
+
+
+def test_new_resolver_checks_requires_python_before_dependencies(script):
+ incompatible_python = "<{0.major}.{0.minor}".format(sys.version_info)
+
+ pkg_dep = create_basic_wheel_for_package(
+ script,
+ name="pkg-dep",
+ version="1",
+ )
+ create_basic_wheel_for_package(
+ script,
+ name="pkg-root",
+ version="1",
+ # Refer the dependency by URL to prioritise it as much as possible,
+ # to test that Requires-Python is *still* inspected first.
+ depends=[f"pkg-dep@{pathlib.Path(pkg_dep).as_uri()}"],
+ requires_python=incompatible_python,
+ )
+
+ result = script.pip(
+ "install", "--no-cache-dir",
+ "--no-index", "--find-links", script.scratch_path,
+ "pkg-root",
+ expect_error=True,
+ )
+
+ # Resolution should fail because of pkg-a's Requires-Python.
+ # This check should be done before pkg-b, so pkg-b should never be pulled.
+ assert incompatible_python in result.stderr, str(result)
+ assert "pkg-b" not in result.stderr, str(result)