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

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 @@ if _exists("_have_functions"):
     _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):

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

@@ -493,7 +493,8 @@ exit:
 #endif /* defined(HAVE_FCHDIR) */
 
 PyDoc_STRVAR(os_chmod__doc__,
-"chmod($module, /, path, mode, *, dir_fd=None, follow_symlinks=True)\n"
+"chmod($module, /, path, mode, *, dir_fd=None,\n"
+"      follow_symlinks=(os.name != \'nt\'))\n"
 "--\n"
 "\n"
 "Change the access permissions of a file.\n"
@@ -562,7 +563,7 @@ os_chmod(PyObject *module, PyObject *const *args, Py_ssize_t nargs, PyObject *kw
     path_t path = PATH_T_INITIALIZE("chmod", "path", 0, PATH_HAVE_FCHMOD);
     int mode;
     int dir_fd = DEFAULT_DIR_FD;
-    int follow_symlinks = 1;
+    int follow_symlinks = CHMOD_DEFAULT_FOLLOW_SYMLINKS;
 
     args = _PyArg_UnpackKeywords(args, nargs, NULL, kwnames, &_parser, 2, 2, 0, argsbuf);
     if (!args) {
@@ -677,7 +678,7 @@ exit:
 
 #endif /* defined(HAVE_FCHMOD) */
 
-#if defined(HAVE_LCHMOD)
+#if (defined(HAVE_LCHMOD) || defined(MS_WINDOWS))
 
 PyDoc_STRVAR(os_lchmod__doc__,
 "lchmod($module, /, path, mode)\n"
@@ -747,7 +748,7 @@ exit:
     return return_value;
 }
 
-#endif /* defined(HAVE_LCHMOD) */
+#endif /* (defined(HAVE_LCHMOD) || defined(MS_WINDOWS)) */
 
 #if defined(HAVE_CHFLAGS)
 
@@ -12421,4 +12422,4 @@ os__supports_virtual_terminal(PyObject *module, PyObject *Py_UNUSED(ignored))
 #ifndef OS__SUPPORTS_VIRTUAL_TERMINAL_METHODDEF
     #define OS__SUPPORTS_VIRTUAL_TERMINAL_METHODDEF
 #endif /* !defined(OS__SUPPORTS_VIRTUAL_TERMINAL_METHODDEF) */
-/*[clinic end generated code: output=ff0ec3371de19904 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=1be15e60a553b40d input=a9049054013a1b77]*/

Modules/posixmodule.c

@@ -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
-    Py_BEGIN_ALLOW_THREADS
-    attr = GetFileAttributesW(path->wide);
-    if (attr == INVALID_FILE_ATTRIBUTES)
     result = 0;
+    Py_BEGIN_ALLOW_THREADS
+    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 {
-        if (mode & _S_IWRITE)
-            attr &= ~FILE_ATTRIBUTE_READONLY;
-        else
-            attr |= FILE_ATTRIBUTE_READONLY;
-        result = SetFileAttributesW(path->wide, attr);
+                    info.FileAttributes |= FILE_ATTRIBUTE_READONLY;
+                }
+                result = SetFileInformationByHandle(hfile, FileBasicInfo,
+                                                    &info, sizeof(info));
+            }
+            (void)CloseHandle(hfile);
+        }
+    }
+    else {
+        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
 
@@ -3535,6 +3572,15 @@ 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
@@ -3542,9 +3588,10 @@ os_lchmod_impl(PyObject *module, path_t *path, int mode)
         path_error(path);
         return NULL;
     }
+#endif /* MS_WINDOWS */
     Py_RETURN_NONE;
 }
-#endif /* HAVE_LCHMOD */
+#endif /* HAVE_LCHMOD || MS_WINDOWS */
 
 
 #ifdef HAVE_CHFLAGS

Tools/clinic/clinic.py

@@ -3737,7 +3737,7 @@ class bool_converter(CConverter):
             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))