gh-140774: Fix pathlib.Path.chmod handling of Windows Archive bit

Lib/pathlib/__init__.py

@@ -1222,7 +1222,8 @@ def chmod(self, mode, *, follow_symlinks=True):
         """
         Change the permissions of the path, like os.chmod().
         """
-        os.chmod(self, mode, follow_symlinks=follow_symlinks)
+        # GH-127380: Force string path to ensure Windows archive bit handling works
+        os.chmod(str(self), mode, follow_symlinks=follow_symlinks)
 
     def lchmod(self, mode):
         """

Lib/test/test_pathlib/test_pathlib.py

@@ -12,6 +12,7 @@
 import stat
 import tempfile
 import unittest
+import subprocess
 from unittest import mock
 from urllib.request import pathname2url
 
@@ -3622,11 +3623,51 @@ def test_walk_symlink_location(self):
 class PosixPathTest(PathTest, PurePosixPathTest):
     cls = pathlib.PosixPath
 
-
 @unittest.skipIf(os.name != 'nt', 'test requires a Windows-compatible system')
 class WindowsPathTest(PathTest, PureWindowsPathTest):
     cls = pathlib.WindowsPath
 
+    def test_chmod_archive_bit_behavior(self):
+
+        # gh-140774: Fix chmod failing to clear Read-Only if Archive bit is cleared.
+        base = self.cls(self.base)
+        filename = base / 'test_chmod_archive.txt'
+        filename.touch()
+
+        # Robust cleanup: Force write permission before deleting
+        def force_remove():
+            try:
+                os.chmod(filename, stat.S_IWRITE)
+            except OSError:
+                pass
+            try:
+                filename.unlink(missing_ok=True)
+            except OSError:
+                pass
+
+        self.addCleanup(force_remove)
+
+        def is_read_only(p):
+            try:
+                return (p.stat().st_file_attributes & stat.FILE_ATTRIBUTE_READONLY) > 0
+            except AttributeError:
+                return False
+
+        try:
+            # Case 1: Archive bit CLEARED, Read-Only SET
+            # We use the Windows 'attrib' command to manipulate the Archive bit directly
+            subprocess.run(['attrib', '-a', '+r', str(filename)], check=True, shell=True)
+
+            # Try to make it Writable (clearing the Read-Only flag)
+            filename.chmod(stat.S_IWRITE | stat.S_IREAD)
+
+            self.assertFalse(is_read_only(filename),
+                             "chmod failed to clear Read-Only when Archive bit was cleared")
+
+        except subprocess.CalledProcessError:
+            self.skipTest("attrib command failed")
+        except FileNotFoundError:
+            self.skipTest("attrib command not found")
 
 class PathSubclassTest(PathTest):
     class cls(pathlib.Path):

Modules/posixmodule.c

@@ -3986,6 +3986,11 @@
     }
     if (mode & _S_IWRITE) {
         attr &= ~FILE_ATTRIBUTE_READONLY;
+
+    if (attr == 0) {
+        /* gh-140774: If all attributes are cleared, set to NORMAL
+           to avoid failing to clear the Read-Only bit. */
+        attr = FILE_ATTRIBUTE_NORMAL;
     }
     else {
         attr |= FILE_ATTRIBUTE_READONLY;
@@ -3995,9 +4000,9 @@
 
 static int
 win32_hchmod(HANDLE hfile, int mode)
 {
     FILE_BASIC_INFO info;
     if (!GetFileInformationByHandleEx(hfile, FileBasicInfo,
                                       &info, sizeof(info)))
     {
         return 0;
@@ -4008,14 +4013,14 @@
     else {
         info.FileAttributes |= FILE_ATTRIBUTE_READONLY;
     }
     return SetFileInformationByHandle(hfile, FileBasicInfo,
                                       &info, sizeof(info));
 }
 
 static int
 win32_fchmod(int fd, int mode)
 {
     HANDLE hfile = _Py_get_osfhandle_noraise(fd);
     if (hfile == INVALID_HANDLE_VALUE) {
         SetLastError(ERROR_INVALID_HANDLE);
         return 0;
@@ -4065,7 +4070,7 @@
 os_chmod_impl(PyObject *module, path_t *path, int mode, int dir_fd,
               int follow_symlinks)
 /*[clinic end generated code: output=5cf6a94915cc7bff input=fcf115d174b9f3d8]*/
 {
     int result;
 
 #ifdef HAVE_FCHMODAT
@@ -4078,22 +4083,22 @@
         return NULL;
 #endif
 
     if (PySys_Audit("os.chmod", "Oii", path->object, mode,
                     dir_fd == DEFAULT_DIR_FD ? -1 : dir_fd) < 0) {
         return NULL;
     }
 
 #ifdef MS_WINDOWS
     result = 0;
     Py_BEGIN_ALLOW_THREADS
     if (path->fd != -1) {
         result = win32_fchmod(path->fd, mode);
     }
     else if (follow_symlinks) {
         HANDLE hfile = CreateFileW(path->wide,
                                    FILE_READ_ATTRIBUTES|FILE_WRITE_ATTRIBUTES,
                                    0, NULL,
                                    OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS, NULL);
         if (hfile != INVALID_HANDLE_VALUE) {
             result = win32_hchmod(hfile, mode);
             (void)CloseHandle(hfile);