From 9a62bcde36aaa4863576ac9adaf418d96e0598d9 Mon Sep 17 00:00:00 2001
From: Arun Babu Neelicattu <arun.neelicattu@gmail.com>
Date: Sun, 5 Jan 2025 17:28:40 +0100
Subject: [PATCH] fix(env): ensure all system site paths are used

With this change, when using newer Python versions (>=3.12), Poetry
correctly detects and considers read-only system site packages when
an environment is loaded.

Resolves: #9878
---
 src/poetry/utils/env/base_env.py       | 13 ++++++++-----
 src/poetry/utils/env/script_strings.py |  5 +++++
 tests/utils/env/test_env.py            |  2 +-
 3 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/src/poetry/utils/env/base_env.py b/src/poetry/utils/env/base_env.py
index f57fb9cc2ae..3c0da4ffa20 100644
--- a/src/poetry/utils/env/base_env.py
+++ b/src/poetry/utils/env/base_env.py
@@ -175,13 +175,10 @@ def os(self) -> str:
     @property
     def site_packages(self) -> SitePackages:
         if self._site_packages is None:
-            # we disable write checks if no user site exist
-            fallbacks = [self.usersite] if self.usersite else []
             self._site_packages = SitePackages(
                 self.purelib,
                 self.platlib,
-                fallbacks,
-                skip_write_checks=not fallbacks,
+                self.fallbacks,
             )
         return self._site_packages
 
@@ -214,8 +211,14 @@ def platlib(self) -> Path:
 
         return self._platlib
 
+    @cached_property
+    def fallbacks(self) -> list[Path]:
+        paths = [Path(path) for path in self.paths.get("fallbacks", [])]
+        paths += [self.usersite] if self.usersite else []
+        return paths
+
     def _get_lib_dirs(self) -> list[Path]:
-        return [self.purelib, self.platlib]
+        return [self.purelib, self.platlib, *self.fallbacks]
 
     def is_path_relative_to_lib(self, path: Path) -> bool:
         for lib_path in self._get_lib_dirs():
diff --git a/src/poetry/utils/env/script_strings.py b/src/poetry/utils/env/script_strings.py
index f95663fbc94..a2935b566e9 100644
--- a/src/poetry/utils/env/script_strings.py
+++ b/src/poetry/utils/env/script_strings.py
@@ -97,6 +97,11 @@ def _version_nodot(version):
 
 paths = sysconfig.get_paths().copy()
 
+paths["fallbacks"] = [
+    p for p in site.getsitepackages()
+    if p and p not in {paths.get("purelib"), paths.get("platlib")}
+]
+
 if site.check_enableusersite():
     paths["usersite"] = site.getusersitepackages()
     paths["userbase"] = site.getuserbase()
diff --git a/tests/utils/env/test_env.py b/tests/utils/env/test_env.py
index b3f63a7339d..97eda471416 100644
--- a/tests/utils/env/test_env.py
+++ b/tests/utils/env/test_env.py
@@ -309,7 +309,7 @@ def test_env_system_packages_are_relative_to_lib(
 
     # These are the virtual environments' base env packages,
     # in this case the system site packages.
-    for dist in metadata.distributions(path=[str(env.parent_env.site_packages.path)]):
+    for dist in env.parent_env.site_packages.distributions():
         assert (
             env.is_path_relative_to_lib(
                 Path(str(dist._path))  # type: ignore[attr-defined]