pythongh-113188: Fix shutil.copymode() and shutil.copystat() on Windows

Previously it worked differenly if dst is a symbolic link:
it modified the permission bits of dst itself rather than the file
it points to if follow_symlinks is true or src is not a symbolic link,
and did nothing if follow_symlinks is false and src is a symbolic link.

Lib/shutil.py

@@ -302,11 +302,15 @@ def copymode(src, dst, *, follow_symlinks=True):
     sys.audit("shutil.copymode", src, dst)
 
     if not follow_symlinks and _islink(src) and os.path.islink(dst):
-        if hasattr(os, 'lchmod'):
+        if os.name == 'nt':
+            stat_func, chmod_func = os.lstat, os.chmod
+        elif hasattr(os, 'lchmod'):
             stat_func, chmod_func = os.lstat, os.lchmod
         else:
             return
     else:
+        if os.name == 'nt' and os.path.islink(dst):
+            dst = os.realpath(dst, strict=True)
         stat_func, chmod_func = _stat, os.chmod
 
     st = stat_func(src)
@@ -382,8 +386,16 @@ def lookup(name):
     # We must copy extended attributes before the file is (potentially)
     # chmod()'ed read-only, otherwise setxattr() will error with -EACCES.
     _copyxattr(src, dst, follow_symlinks=follow)
+    _chmod = lookup("chmod")
+    if os.name == 'nt':
+        if follow:
+            if os.path.islink(dst):
+                dst = os.path.realpath(dst, strict=True)
+        else:
+            def _chmod(*args, **kwargs):
+                os.chmod(*args)
     try:
-        lookup("chmod")(dst, mode, follow_symlinks=follow)
+        _chmod(dst, mode, follow_symlinks=follow)
     except NotImplementedError:
         # if we got a NotImplementedError, it's because
         #   * follow_symlinks=False,

Lib/test/test_shutil.py

@@ -1046,19 +1046,18 @@ def test_copymode_follow_symlinks(self):
         shutil.copymode(src, dst)
         self.assertEqual(os.stat(src).st_mode, os.stat(dst).st_mode)
         # On Windows, os.chmod does not follow symlinks (issue #15411)
-        if os.name != 'nt':
-            # follow src link
-            os.chmod(dst, stat.S_IRWXO)
-            shutil.copymode(src_link, dst)
-            self.assertEqual(os.stat(src).st_mode, os.stat(dst).st_mode)
-            # follow dst link
-            os.chmod(dst, stat.S_IRWXO)
-            shutil.copymode(src, dst_link)
-            self.assertEqual(os.stat(src).st_mode, os.stat(dst).st_mode)
-            # follow both links
-            os.chmod(dst, stat.S_IRWXO)
-            shutil.copymode(src_link, dst_link)
-            self.assertEqual(os.stat(src).st_mode, os.stat(dst).st_mode)
+        # follow src link
+        os.chmod(dst, stat.S_IRWXO)
+        shutil.copymode(src_link, dst)
+        self.assertEqual(os.stat(src).st_mode, os.stat(dst).st_mode)
+        # follow dst link
+        os.chmod(dst, stat.S_IRWXO)
+        shutil.copymode(src, dst_link)
+        self.assertEqual(os.stat(src).st_mode, os.stat(dst).st_mode)
+        # follow both links
+        os.chmod(dst, stat.S_IRWXO)
+        shutil.copymode(src_link, dst_link)
+        self.assertEqual(os.stat(src).st_mode, os.stat(dst).st_mode)
 
     @unittest.skipUnless(hasattr(os, 'lchmod'), 'requires os.lchmod')
     @os_helper.skip_unless_symlink

Misc/NEWS.d/next/Library/2023-12-15-20-29-49.gh-issue-113188.AvoraB.rst

@@ -0,0 +1,5 @@
+Fix :func:`shutil.copymode` on Windows. Previously it worked differenly if
+*dst* is a symbolic link: it modified the permission bits of *dst* itself
+rather than the file it points to if *follow_symlinks* is true or *src* is
+not a symbolic link, and did not modify the permission bits if
+*follow_symlinks* is false and *src* is a symbolic link.