Fix path pollution again

src/pyproject_hooks/_in_process/_in_process.py

@@ -348,6 +348,13 @@ def main():
     control_dir = sys.argv[2]
     if hook_name not in HOOK_NAMES:
         sys.exit("Unknown hook: %s" % hook_name)
+
+    # Remove the parent directory from sys.path to avoid polluting the backend
+    # import namespace with this directory.
+    here = os.path.dirname(__file__)
+    if here in sys.path:
+        sys.path.remove(here)
+
     hook = globals()[hook_name]
 
     hook_input = read_json(pjoin(control_dir, "input.json"))

tests/samples/path-pollution/setup.py

@@ -1,12 +1,12 @@
 import json
 import sys
-from os import environ, listdir, path
+from os import environ, path
 
 from setuptools import setup
 
-children = listdir(sys.path[0])
+captured_sys_path = sys.path
 out = path.join(environ["TEST_POLLUTION_OUTDIR"], "out.json")
 with open(out, "w") as f:
-    json.dump(children, f)
+    json.dump(captured_sys_path, f)
 
 setup()

tests/test_call_hooks.py

@@ -16,6 +16,7 @@
     UnsupportedOperation,
     default_subprocess_runner,
 )
+from pyproject_hooks._in_process import _in_proc_script_path as in_proc_script_path
 from tests.compat import tomllib
 
 SAMPLES_DIR = pjoin(dirname(abspath(__file__)), "samples")
@@ -196,14 +197,11 @@ def test_path_pollution():
         ):
             hooks.get_requires_for_build_wheel({})
         with open(pjoin(outdir, "out.json")) as f:
-            children = json.load(f)
-    assert set(children) <= {
-        "__init__.py",
-        "__init__.pyc",
-        "_in_process.py",
-        "_in_process.pyc",
-        "__pycache__",
-    }
+            captured_sys_path = json.load(f)
+
+    with in_proc_script_path() as path:
+        assert os.path.dirname(path) not in captured_sys_path
+    assert captured_sys_path[0] == BUILDSYS_PKGS
 
 
 def test_setup_py():