gh-59616: Support os.chmod(follow_symlinks=True) and os.lchmod() on Windows (GH-113049)

Author: serhiy-storchaka

Doc/library/os.rst

@@ -2062,6 +2062,7 @@ features:
       Although Windows supports :func:`chmod`, you can only set the file's
       read-only flag with it (via the ``stat.S_IWRITE`` and ``stat.S_IREAD``
       constants or a corresponding integer value).  All other bits are ignored.
+      The default value of *follow_symlinks* is ``False`` on Windows.
 
       The function is limited on Emscripten and WASI, see
       :ref:`wasm-availability` for more information.
@@ -2075,6 +2076,9 @@ features:
    .. versionchanged:: 3.6
       Accepts a :term:`path-like object`.
 
+   .. versionchanged:: 3.13
+      Added support for the *follow_symlinks* argument on Windows.
+
 
 .. function:: chown(path, uid, gid, *, dir_fd=None, follow_symlinks=True)
 
@@ -2165,11 +2169,14 @@ features:
 
    .. audit-event:: os.chmod path,mode,dir_fd os.lchmod
 
-   .. availability:: Unix, not Linux, FreeBSD >= 1.3, NetBSD >= 1.3, not OpenBSD
+   .. availability:: Unix, Windows, not Linux, FreeBSD >= 1.3, NetBSD >= 1.3, not OpenBSD
 
    .. versionchanged:: 3.6
       Accepts a :term:`path-like object`.
 
+   .. versionchanged:: 3.13
+      Added support on Windows.
+
 .. function:: lchown(path, uid, gid)
 
    Change the owner and group id of *path* to the numeric *uid* and *gid*.  This

Doc/whatsnew/3.13.rst

@@ -261,6 +261,12 @@ os
   CPU resources of a container system without having to modify the container (application code).
   (Contributed by Donghee Na in :gh:`109595`)
 
+* Add support of :func:`os.lchmod` and the *follow_symlinks* argument
+  in :func:`os.chmod` on Windows.
+  Note that the default value of *follow_symlinks* in :func:`!os.lchmod` is
+  ``False`` on Windows.
+  (Contributed by Serhiy Storchaka in :gh:`59616`)
+
 pathlib
 -------
 

Lib/os.py

@@ -171,6 +171,7 @@ def _add(str, fn):
     _add("HAVE_FSTATAT",    "stat")
     _add("HAVE_LCHFLAGS",   "chflags")
     _add("HAVE_LCHMOD",     "chmod")
+    _add("MS_WINDOWS",      "chmod")
     if _exists("lchown"): # mac os x10.3
         _add("HAVE_LCHOWN", "chown")
     _add("HAVE_LINKAT",     "link")

Lib/tempfile.py

@@ -273,7 +273,7 @@ def _dont_follow_symlinks(func, path, *args):
     # Pass follow_symlinks=False, unless not supported on this platform.
     if func in _os.supports_follow_symlinks:
         func(path, *args, follow_symlinks=False)
-    elif _os.name == 'nt' or not _os.path.islink(path):
+    elif not _os.path.islink(path):
         func(path, *args)
 
 def _resetperms(path):

Lib/test/test_posix.py

@@ -1019,7 +1019,7 @@ def test_chmod_file_symlink(self):
             self.check_lchmod_link(posix.chmod, target, link)
         else:
             self.check_chmod_link(posix.chmod, target, link)
-            self.check_chmod_link(posix.chmod, target, link, follow_symlinks=True)
+        self.check_chmod_link(posix.chmod, target, link, follow_symlinks=True)
 
     @os_helper.skip_unless_symlink
     def test_chmod_dir_symlink(self):
@@ -1031,7 +1031,7 @@ def test_chmod_dir_symlink(self):
             self.check_lchmod_link(posix.chmod, target, link)
         else:
             self.check_chmod_link(posix.chmod, target, link)
-            self.check_chmod_link(posix.chmod, target, link, follow_symlinks=True)
+        self.check_chmod_link(posix.chmod, target, link, follow_symlinks=True)
 
     @unittest.skipUnless(hasattr(posix, 'lchmod'), 'test needs os.lchmod()')
     @os_helper.skip_unless_symlink

Misc/NEWS.d/next/Library/2023-12-13-17-08-21.gh-issue-59616.JNlWSs.rst

@@ -0,0 +1,3 @@
+Add support of :func:`os.lchmod` and the *follow_symlinks* argument in
+:func:`os.chmod` on Windows. Note that the default value of *follow_symlinks*
+in :func:`!os.lchmod` is ``False`` on Windows.

Modules/clinic/posixmodule.c.h

@@ -3309,6 +3309,29 @@ os_fchdir_impl(PyObject *module, int fd)
 }
 #endif /* HAVE_FCHDIR */
 
+#ifdef MS_WINDOWS
+# define CHMOD_DEFAULT_FOLLOW_SYMLINKS 0
+#else
+# define CHMOD_DEFAULT_FOLLOW_SYMLINKS 1
+#endif
+
+#ifdef MS_WINDOWS
+static int
+win32_lchmod(LPCWSTR path, int mode)
+{
+    DWORD attr = GetFileAttributesW(path);
+    if (attr == INVALID_FILE_ATTRIBUTES) {
+        return 0;
+    }
+    if (mode & _S_IWRITE) {
+        attr &= ~FILE_ATTRIBUTE_READONLY;
+    }
+    else {
+        attr |= FILE_ATTRIBUTE_READONLY;
+    }
+    return SetFileAttributesW(path, attr);
+}
+#endif
 
 /*[clinic input]
 os.chmod
@@ -3331,7 +3354,8 @@ os.chmod
         and path should be relative; path will then be relative to that
         directory.
 
-    follow_symlinks: bool = True
+    follow_symlinks: bool(c_default="CHMOD_DEFAULT_FOLLOW_SYMLINKS", \
+                          py_default="(os.name != 'nt')") = CHMOD_DEFAULT_FOLLOW_SYMLINKS
         If False, and the last element of the path is a symbolic link,
         chmod will modify the symbolic link itself instead of the file
         the link points to.
@@ -3348,20 +3372,16 @@ dir_fd and follow_symlinks may not be implemented on your platform.
 static PyObject *
 os_chmod_impl(PyObject *module, path_t *path, int mode, int dir_fd,
               int follow_symlinks)
-/*[clinic end generated code: output=5cf6a94915cc7bff input=674a14bc998de09d]*/
+/*[clinic end generated code: output=5cf6a94915cc7bff input=fcf115d174b9f3d8]*/
 {
     int result;
 
-#ifdef MS_WINDOWS
-    DWORD attr;
-#endif
-
 #ifdef HAVE_FCHMODAT
     int fchmodat_nofollow_unsupported = 0;
     int fchmodat_unsupported = 0;
 #endif
 
-#if !(defined(HAVE_FCHMODAT) || defined(HAVE_LCHMOD))
+#if !(defined(HAVE_FCHMODAT) || defined(HAVE_LCHMOD) || defined(MS_WINDOWS))
     if (follow_symlinks_specified("chmod", follow_symlinks))
         return NULL;
 #endif
@@ -3372,19 +3392,36 @@ os_chmod_impl(PyObject *module, path_t *path, int mode, int dir_fd,
     }
 
 #ifdef MS_WINDOWS
+    result = 0;
     Py_BEGIN_ALLOW_THREADS
-    attr = GetFileAttributesW(path->wide);
-    if (attr == INVALID_FILE_ATTRIBUTES)
-        result = 0;
+    if (follow_symlinks) {
+        HANDLE hfile;
+        FILE_BASIC_INFO info;
+
+        hfile = CreateFileW(path->wide,
+                            FILE_READ_ATTRIBUTES|FILE_WRITE_ATTRIBUTES,
+                            0, NULL,
+                            OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS, NULL);
+        if (hfile != INVALID_HANDLE_VALUE) {
+            if (GetFileInformationByHandleEx(hfile, FileBasicInfo,
+                                             &info, sizeof(info)))
+            {
+                if (mode & _S_IWRITE) {
+                    info.FileAttributes &= ~FILE_ATTRIBUTE_READONLY;
+                }
+                else {
+                    info.FileAttributes |= FILE_ATTRIBUTE_READONLY;
+                }
+                result = SetFileInformationByHandle(hfile, FileBasicInfo,
+                                                    &info, sizeof(info));
+            }
+            (void)CloseHandle(hfile);
+        }
+    }
     else {
-        if (mode & _S_IWRITE)
-            attr &= ~FILE_ATTRIBUTE_READONLY;
-        else
-            attr |= FILE_ATTRIBUTE_READONLY;
-        result = SetFileAttributesW(path->wide, attr);
+        result = win32_lchmod(path->wide, mode);
     }
     Py_END_ALLOW_THREADS
-
     if (!result) {
         return path_error(path);
     }
@@ -3514,7 +3551,7 @@ os_fchmod_impl(PyObject *module, int fd, int mode)
 #endif /* HAVE_FCHMOD */
 
 
-#ifdef HAVE_LCHMOD
+#if defined(HAVE_LCHMOD) || defined(MS_WINDOWS)
 /*[clinic input]
 os.lchmod
 
@@ -3535,16 +3572,26 @@ os_lchmod_impl(PyObject *module, path_t *path, int mode)
     if (PySys_Audit("os.chmod", "Oii", path->object, mode, -1) < 0) {
         return NULL;
     }
+#ifdef MS_WINDOWS
+    Py_BEGIN_ALLOW_THREADS
+    res = win32_lchmod(path->wide, mode);
+    Py_END_ALLOW_THREADS
+    if (!res) {
+        path_error(path);
+        return NULL;
+    }
+#else /* MS_WINDOWS */
     Py_BEGIN_ALLOW_THREADS
     res = lchmod(path->narrow, mode);
     Py_END_ALLOW_THREADS
     if (res < 0) {
         path_error(path);
         return NULL;
     }
+#endif /* MS_WINDOWS */
     Py_RETURN_NONE;
 }
-#endif /* HAVE_LCHMOD */
+#endif /* HAVE_LCHMOD || MS_WINDOWS */
 
 
 #ifdef HAVE_CHFLAGS

Modules/posixmodule.c

@@ -3737,7 +3737,7 @@ def converter_init(self, *, accept: TypeSet = {object}) -> None:
             self.format_unit = 'i'
         elif accept != {object}:
             fail(f"bool_converter: illegal 'accept' argument {accept!r}")
-        if self.default is not unspecified:
+        if self.default is not unspecified and self.default is not unknown:
             self.default = bool(self.default)
             self.c_default = str(int(self.default))