Fix deadlock in shutil.copytree

- support recursive entry into patch functions
- happened if using shutil's own function as
  copy_function argument

Author: mrbean-bremen

CHANGES.md

@@ -17,6 +17,10 @@ The released versions correspond to PyPI releases.
 * changed the default for `FakeFilesystem.shuffle_listdir_results` to `True` to reflect
   the real filesystem behavior
 
+### Fixes
+* fixed a deadlock in `shutil.copytree` if copying using an `shutil` function as
+  `copy_function` argument (see [#1235](../../issues/1235))
+
 ## [Version 5.10.0](https://pypi.python.org/pypi/pyfakefs/5.10.0) (2025-10-11)
 Adds official support for Python 3.14. Last minor version before the 6.0 release.
 

pyfakefs/fake_filesystem_shutil.py

@@ -32,7 +32,7 @@
 import os
 import shutil
 import sys
-from threading import Lock
+from threading import RLock
 from collections.abc import Callable
 
 
@@ -44,7 +44,7 @@ class FakeShutilModule:
     the `fs` fixture, the `patchfs` decorator, or directly the `Patcher`.
     """
 
-    module_lock = Lock()
+    module_lock = RLock()
 
     use_copy_file_range = (
         hasattr(shutil, "_USE_CP_COPY_FILE_RANGE") and shutil._USE_CP_COPY_FILE_RANGE  # type: ignore[attr-defined]
@@ -71,9 +71,12 @@ def __init__(self, filesystem):
         """
         self.filesystem = filesystem
         self.shutil_module = shutil
-        self._in_get_attribute = False
+        self._patch_level = 0
 
     def _start_patching_global_vars(self):
+        self._patch_level += 1
+        if self._patch_level > 1:
+            return  # nested call - already patched
         if self.has_fcopy_file:
             self.shutil_module._HAS_FCOPYFILE = False
         if self.use_copy_file_range:
@@ -89,6 +92,9 @@ def _start_patching_global_vars(self):
                 self.shutil_module._use_fd_functions = False
 
     def _stop_patching_global_vars(self):
+        self._patch_level -= 1
+        if self._patch_level > 0:
+            return  # nested call - remains patched
         if self.has_fcopy_file:
             self.shutil_module._HAS_FCOPYFILE = True
         if self.use_copy_file_range:

pyfakefs/tests/fake_filesystem_shutil_test.py

@@ -212,6 +212,18 @@ def test_copy(self):
         self.assertTrue(os.path.exists(dst_file))
         self.assertEqual(os.stat(src_file).st_mode, os.stat(dst_file).st_mode)
 
+    def test_copytree_with_copy_function(self):
+        # regression test for #1235 (deadlock)
+        source_dir = Path(self.make_path("source_dir"))
+        target_dir = Path(self.make_path("target_dir"))
+        test_contents = "Test contents"
+        source_file = source_dir / "test.txt"
+        target_file = target_dir / "test.txt"
+        self.create_file(source_file, contents=test_contents)
+
+        shutil.copytree(source_dir, target_dir, copy_function=shutil.copy2)
+        assert target_file.read_text() == test_contents
+
     def test_permission_error_message(self):
         self.check_posix_only()
         dst_dir = Path(self.make_path("home1"))