TemporaryDirectory fails to cleanup read-only files (Windows, py<3.8)

On python < 3.8, TemporaryDirectory fails when cleaning up dirs
containing read-only files on Windows.

lektor/compat.py

@@ -0,0 +1,53 @@
+import os
+import stat
+import sys
+import tempfile
+from functools import partial
+from itertools import chain
+
+
+def _ensure_tree_writeable(path: str) -> None:
+    """Attempt to ensure that all files in the tree rooted at path are writeable."""
+    dirscans = []
+
+    def fix_mode(path, statfunc):
+        try:
+            # paranoia regarding symlink attacks
+            current_mode = statfunc(follow_symlinks=False).st_mode
+            if not stat.S_ISLNK(current_mode):
+                isdir = stat.S_ISDIR(current_mode)
+                fixed_mode = current_mode | (0o700 if isdir else 0o200)
+                if current_mode != fixed_mode:
+                    os.chmod(path, fixed_mode)
+                if isdir:
+                    dirscans.append(os.scandir(path))
+        except FileNotFoundError:
+            pass
+
+    fix_mode(path, partial(os.stat, path))
+    for entry in chain.from_iterable(dirscans):
+        fix_mode(entry.path, entry.stat)
+
+
+class FixedTemporaryDirectory(tempfile.TemporaryDirectory):
+    """A version of tempfile.TemporaryDirectory that works if dir contains read-only files.
+
+    On python < 3.8 under Windows, if any read-only files are created
+    in a TemporaryDirectory, TemporaryDirectory will throw an
+    exception when it tries to remove them on cleanup. See
+    https://bugs.python.org/issue26660
+
+    This can create issues, e.g., with temporary git repositories since
+    git creates read-only files in its object store.
+
+    """
+
+    def cleanup(self) -> None:
+        _ensure_tree_writeable(self.name)
+        super().cleanup()
+
+
+if sys.version_info >= (3, 8):
+    TemporaryDirectory = tempfile.TemporaryDirectory
+else:
+    TemporaryDirectory = FixedTemporaryDirectory

lektor/publisher.py

@@ -14,7 +14,6 @@
 from subprocess import DEVNULL
 from subprocess import PIPE
 from subprocess import STDOUT
-from tempfile import TemporaryDirectory
 from typing import Any
 from typing import Callable
 from typing import ContextManager
@@ -31,6 +30,7 @@
 
 from werkzeug import urls
 
+from lektor.compat import TemporaryDirectory
 from lektor.exception import LektorException
 from lektor.utils import locate_executable
 from lektor.utils import portable_popen

tests/test_compat.py

@@ -0,0 +1,32 @@
+import os
+from pathlib import Path
+
+import pytest
+
+from lektor.compat import _ensure_tree_writeable
+from lektor.compat import FixedTemporaryDirectory
+from lektor.compat import TemporaryDirectory
+
+
+def test_ensure_tree_writeable(tmp_path):
+    topdir = tmp_path / "topdir"
+    subdir = topdir / "subdir"
+    regfile = subdir / "regfile"
+    subdir.mkdir(parents=True)
+    regfile.touch(mode=0)
+    subdir.chmod(0)
+    topdir.chmod(0)
+
+    _ensure_tree_writeable(topdir)
+
+    for p in topdir, subdir, regfile:
+        assert os.access(p, os.W_OK)
+
+
+@pytest.mark.parametrize("tmpdir_class", [FixedTemporaryDirectory, TemporaryDirectory])
+def test_TemporaryDirectory(tmpdir_class):
+    with tmpdir_class() as tmpdir:
+        file = Path(tmpdir, "test-file")
+        file.touch(mode=0)
+        os.chmod(tmpdir, 0)
+    assert not os.path.exists(tmpdir)