gh-84419: Fix the execute permissions in os.stat() on Windows

Windows strips trailing dots and spaces from the last component of the path,
so os.stat('spam.bat ') opened the same file as os.stat('spam.bat'), but did
not set the execute permissions in st_mode, because the extension did not
match.  They are now ignored, unless the \\?\ prefix disables the path
normalization.

Author: serhiy-storchaka

Lib/test/test_os/test_windows.py

@@ -608,5 +608,43 @@ def cleanup():
         self.assertGreaterEqual(stat1.st_atime, stat2.st_atime)
 
 
+class Win32StatExecutableTests(unittest.TestCase):
+    # gh-84419: Windows strips trailing dots and spaces from the last
+    # component of the path, so they should be ignored when guessing
+    # the execute permissions from the file extension.
+
+    SUFFIXES = ['', ' ', '   ', '.', '..', ' . .']
+
+    def check(self, ext, mask):
+        filename = os_helper.TESTFN + ext
+        create_file(filename)
+        try:
+            for suffix in self.SUFFIXES:
+                with self.subTest(suffix=suffix):
+                    mode = os.stat(filename + suffix).st_mode
+                    self.assertEqual(mode & 0o111, mask)
+        finally:
+            os_helper.unlink(filename)
+
+    def test_executable_extension(self):
+        for ext in '.exe', '.bat', '.cmd', '.com', '.EXE', '.Bat':
+            with self.subTest(ext=ext):
+                self.check(ext, 0o111)
+
+    def test_not_executable_extension(self):
+        for ext in '.txt', '.py', '.exe.txt', '':
+            with self.subTest(ext=ext):
+                self.check(ext, 0)
+
+    def test_extended_path(self):
+        # The \\?\ prefix disables normalization: trailing spaces and dots
+        # are part of the file name.
+        filename = os.path.abspath(os_helper.TESTFN + '.exe')
+        create_file(filename)
+        self.addCleanup(os_helper.unlink, filename)
+        self.assertEqual(os.stat('\\\\?\\' + filename).st_mode & 0o111, 0o111)
+        self.assertRaises(OSError, os.stat, '\\\\?\\' + filename + ' ')
+
+
 if __name__ == "__main__":
     unittest.main()

Misc/NEWS.d/next/Library/2026-08-08-21-40-00.gh-issue-84419.statexe.rst

@@ -0,0 +1,3 @@
+Fix :func:`os.stat` on Windows: trailing dots and spaces, which are ignored
+by the operating system, are no longer taken into account when the execute
+permissions are guessed from the file extension.

Modules/posixmodule.c

@@ -2108,12 +2108,20 @@ update_st_mode_from_path(const wchar_t *path, DWORD attr,
            GetSecurityInfo, OpenThreadToken/OpenProcessToken, and
            AccessCheck to check for generic read, write, and execute
            access. */
-        const wchar_t *fileExtension = wcsrchr(path, '.');
-        if (fileExtension) {
-            if (_wcsicmp(fileExtension, L".exe") == 0 ||
-                _wcsicmp(fileExtension, L".bat") == 0 ||
-                _wcsicmp(fileExtension, L".cmd") == 0 ||
-                _wcsicmp(fileExtension, L".com") == 0) {
+        size_t len = wcslen(path);
+        if (wcsncmp(path, L"\\\\?\\", 4) != 0) {
+            /* Trailing dots and spaces are stripped from the last component
+               of the path, unless the \\?\ prefix disables normalization. */
+            while (len > 0 && (path[len - 1] == L'.' || path[len - 1] == L' ')) {
+                len--;
+            }
+        }
+        if (len >= 4) {
+            const wchar_t *fileExtension = path + len - 4;
+            if (_wcsnicmp(fileExtension, L".exe", 4) == 0 ||
+                _wcsnicmp(fileExtension, L".bat", 4) == 0 ||
+                _wcsnicmp(fileExtension, L".cmd", 4) == 0 ||
+                _wcsnicmp(fileExtension, L".com", 4) == 0) {
                 result->st_mode |= 0111;
             }
         }