Fix resolution to respect --python-version when checking Requires-Python

news/12216.bugfix.rst

@@ -0,0 +1 @@
+Fix resolution to respect ``--python-version`` when checking ``Requires-Python``.

src/pip/_internal/commands/install.py

@@ -370,6 +370,7 @@ def run(self, options: Values, args: List[str]) -> int:
                 force_reinstall=options.force_reinstall,
                 upgrade_strategy=upgrade_strategy,
                 use_pep517=options.use_pep517,
+                py_version_info=options.python_version,
             )
 
             self.trace_basic_info(finder)

tests/conftest.py

@@ -379,7 +379,10 @@ def _common_wheel_editable_install(
     tmpdir_factory: pytest.TempPathFactory, common_wheels: Path, package: str
 ) -> Path:
     wheel_candidates = list(common_wheels.glob(f"{package}-*.whl"))
-    assert len(wheel_candidates) == 1, wheel_candidates
+    assert len(wheel_candidates) == 1, (
+        f"Missing wheels in {common_wheels}, expected 1 got '{wheel_candidates}'."
+        " Are you running the tests via nox? See https://pip.pypa.io/en/latest/development/getting-started/#running-tests"
+    )
     install_dir = tmpdir_factory.mktemp(package) / "install"
     lib_install_dir = install_dir / "lib"
     bin_install_dir = install_dir / "bin"

tests/functional/test_new_resolver.py

@@ -414,6 +414,30 @@ def test_new_resolver_requires_python_error(script: PipTestEnvironment) -> None:
     assert message in result.stderr, str(result)
 
 
+def test_new_resolver_requires_python_ok_with_python_version_flag(
+    script: PipTestEnvironment,
+) -> None:
+    create_basic_wheel_for_package(
+        script,
+        "base",
+        "0.1.0",
+        requires_python="<3",
+    )
+    result = script.pip(
+        "install",
+        "--no-cache-dir",
+        "--no-index",
+        "--find-links",
+        script.scratch_path,
+        "--dry-run",
+        "--python-version=2",
+        "--only-binary=:all:",
+        "base",
+    )
+
+    assert not result.stderr, str(result)
+
+
 def test_new_resolver_installed(script: PipTestEnvironment) -> None:
     create_basic_wheel_for_package(
         script,