Ignore PermissionError during import from cwd

moreati · moreati · commit f2f5e1cb9018 · 2024-05-13T09:55:21.000+01:00
On macOS `getcwd(3)` can return EACCES if a path component isn't readable,
resulting in PermissionError. `PathFinder.find_spec()` now catches these and
ignores them - the same treatment as a missing/deleted cwd.
diff --git a/Doc/reference/import.rst b/Doc/reference/import.rst
@@ -871,10 +871,10 @@ module.
 
 The current working directory -- denoted by an empty string -- is handled
 slightly differently from other entries on :data:`sys.path`. First, if the
-current working directory is found to not exist, no value is stored in
-:data:`sys.path_importer_cache`. Second, the value for the current working
-directory is looked up fresh for each module lookup. Third, the path used for
-:data:`sys.path_importer_cache` and returned by
+current working directory cannot be determined or is found to not exist, no
+value is stored in :data:`sys.path_importer_cache`. Second, the value for the
+current working directory is looked up fresh for each module lookup. Third,
+the path used for :data:`sys.path_importer_cache` and returned by
 :meth:`importlib.machinery.PathFinder.find_spec` will be the actual current
 working directory and not the empty string.
 
diff --git a/Lib/importlib/_bootstrap_external.py b/Lib/importlib/_bootstrap_external.py
@@ -1503,7 +1503,7 @@ def _path_importer_cache(cls, path):
         if path == '':
             try:
                 path = _os.getcwd()
-            except FileNotFoundError:
+            except (FileNotFoundError, PermissionError):
                 # Don't cache the failure as the cwd can easily change to
                 # a valid directory later on.
                 return None
diff --git a/Lib/test/test_importlib/import_/test_path.py b/Lib/test/test_importlib/import_/test_path.py
@@ -1,3 +1,5 @@
+from test.support import os_helper
+from test.test_importlib import fixtures
 from test.test_importlib import util
 
 importlib = util.import_importlib('importlib')
@@ -153,6 +155,25 @@ def test_deleted_cwd(self):
             # Do not want FileNotFoundError raised.
             self.assertIsNone(self.machinery.PathFinder.find_spec('whatever'))
 
+    @os_helper.skip_unless_working_chmod
+    def test_permission_error_cwd(self):
+        # gh-115911
+        with (
+            fixtures.tempdir() as new_dir,
+            fixtures.save_mode(new_dir),
+            fixtures.save_cwd(),
+            util.import_state(path=['']),
+        ):
+            os.chdir(new_dir)
+            try:
+                os.chmod(new_dir, 0o000)
+            except OSError:
+                self.skipTest("platform does not allow "
+                              "changing mode of the cwd")
+
+            # Do not want PermissionError raised.
+            self.assertIsNone(self.machinery.PathFinder.find_spec('whatever'))
+
     def test_invalidate_caches_finders(self):
         # Finders with an invalidate_caches() method have it called.
         class FakeFinder:
diff --git a/Lib/test/test_importlib/metadata/fixtures.py b/Lib/test/test_importlib/metadata/fixtures.py
@@ -44,6 +44,16 @@ def save_cwd():
         os.chdir(orig)
 
 
+@contextlib.contextmanager
+def save_mode(path, *, follow_symlinks=True):
+    path = pathlib.Path(path)
+    orig = path.stat(follow_symlinks=follow_symlinks)
+    try:
+        yield
+    finally:
+        path.chmod(orig.st_mode, follow_symlinks=follow_symlinks)
+
+
 @contextlib.contextmanager
 def tempdir_as_cwd():
     with tempdir() as tmp:
diff --git a/Misc/NEWS.d/next/Core and Builtins/2024-02-29-16-55-52.gh-issue-115911.Vnkue_.rst b/Misc/NEWS.d/next/Core and Builtins/2024-02-29-16-55-52.gh-issue-115911.Vnkue_.rst
@@ -0,0 +1,3 @@
+If the current working directory cannot be determined due to permissions,
+then import will no longer raise :exc:`PermissionError`. Patch by Alex
+Willmer.

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,3 @@`
	`1`	`+If the current working directory cannot be determined due to permissions,`
	`2`	+then import will no longer raise :exc:`PermissionError`. Patch by Alex
	`3`	`+Willmer.`