feat: rmtree() test helper

This is no more than a wrapper around `shutil.rmtree()`, but with an
error handler that tries to set write permissions on error.

This is a common-enough fix needed on the windows platform that it
seems worth providing a helper for.

Legacy DataLad also has one, but it's implementation seems to be very
much stuck in Python 2 times.

datalad_core/repo/tests/test_repo.py

@@ -1,7 +1,7 @@
-from shutil import rmtree
-
 import pytest
 
+from datalad_core.tests import rmtree
+
 from ..repo import Repo
 
 

datalad_core/tests/__init__.py

@@ -1,5 +1,9 @@
 __all__ = [
     'call_git_addcommit',
+    'rmtree',
 ]
 
-from .utils import call_git_addcommit
+from .utils import (
+    call_git_addcommit,
+    rmtree,
+)

datalad_core/tests/utils.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import os
 from typing import TYPE_CHECKING
 
 if TYPE_CHECKING:
@@ -8,7 +9,7 @@
         PurePath,
     )
 
-from shutil import rmtree
+from shutil import rmtree as shutil_rmtree
 
 from datalad_core.repo import Worktree
 from datalad_core.runners import (
@@ -149,3 +150,31 @@ def modify_dataset(path: Path) -> str:
     file_am_obj.write_text('modified')
 
     return modify_dataset_promise
+
+
+def _rmtree_onerror(func, path, exc_info):  # noqa: ARG001
+    """
+    Error handler for ``shutil.rmtree``.
+
+    If the error is due to an access error (read only file)
+    it attempts to add write permission and then retries.
+
+    If the error is for another reason it re-raises the error.
+    """
+    import stat
+
+    # Is the error an access error?
+    if not os.access(path, os.W_OK):
+        os.chmod(path, stat.S_IWUSR)
+        func(path)
+    else:
+        raise
+
+
+def rmtree(path: Path) -> None:
+    """``shutil.rmtree()`` with an error handler that sets write permissions"""
+    shutil_rmtree(
+        path,
+        # deprecated with PY3.12 -> onexc=
+        onerror=_rmtree_onerror,
+    )