Consider system packages as installed if the venv includes them

This changesets adds a getter to `env.virtual_env.VirtualEnv` to check
whether it has access to system packages, and overrides the
`is_path_relative_to_lib` method to take it into account.

This will prevent Poetry from reinstalling system packages in the venv
when they are already installed with a compatible version.

Fixes: #6035

Signed-off-by: Aurélien Bompard <[email protected]>

src/poetry/utils/env/virtual_env.py

@@ -3,6 +3,7 @@
 import json
 import os
 import re
+import sys
 
 from contextlib import contextmanager
 from copy import deepcopy
@@ -20,6 +21,7 @@
 from poetry.utils.env.script_strings import GET_PYTHON_VERSION
 from poetry.utils.env.script_strings import GET_SYS_PATH
 from poetry.utils.env.script_strings import GET_SYS_TAGS
+from poetry.utils.env.system_env import SystemEnv
 
 
 if TYPE_CHECKING:
@@ -133,3 +135,14 @@ def temp_environ(self) -> Iterator[None]:
 
     def _updated_path(self) -> str:
         return os.pathsep.join([str(self._bin_dir), os.environ.get("PATH", "")])
+
+    def includes_system_site_packages(self) -> bool:
+        pyvenv_cfg = self._path / "pyvenv.cfg"
+        return "include-system-site-packages = true" in pyvenv_cfg.read_text()
+
+    def is_path_relative_to_lib(self, path: Path) -> bool:
+        system_env = SystemEnv(Path(sys.prefix))
+        return (
+            self.includes_system_site_packages()
+            and system_env.is_path_relative_to_lib(path)
+        ) or super().is_path_relative_to_lib(path)

tests/utils/test_env.py

@@ -18,6 +18,7 @@
 from poetry.repositories.installed_repository import InstalledRepository
 from poetry.toml.file import TOMLFile
 from poetry.utils._compat import WINDOWS
+from poetry.utils._compat import metadata
 from poetry.utils.env import GET_BASE_PREFIX
 from poetry.utils.env import GET_PYTHON_VERSION_ONELINER
 from poetry.utils.env import EnvCommandError
@@ -1462,8 +1463,20 @@ def test_env_system_packages(tmp_path: Path, poetry: Poetry) -> None:
     pyvenv_cfg = venv_path / "pyvenv.cfg"
 
     EnvManager(poetry).build_venv(path=venv_path, flags={"system-site-packages": True})
+    env = VirtualEnv(venv_path)
 
     assert "include-system-site-packages = true" in pyvenv_cfg.read_text()
+    assert env.includes_system_site_packages()
+
+
+def test_env_system_packages_are_relative_to_lib(
+    tmp_path: Path, poetry: Poetry
+) -> None:
+    venv_path = tmp_path / "venv"
+    EnvManager(poetry).build_venv(path=venv_path, flags={"system-site-packages": True})
+    env = VirtualEnv(venv_path)
+    pytest_dist = metadata.distribution("pytest")
+    assert env.is_path_relative_to_lib(pytest_dist._path)  # type: ignore[attr-defined]
 
 
 @pytest.mark.parametrize(