gh-119826: Improved fallback for ntpath.abspath() on Windows (GH-119938)

Lib/ntpath.py

@@ -553,13 +553,13 @@ except ImportError:
         return prefix + sep.join(comps)
 
 
-def _abspath_fallback(path):
-    """Return the absolute version of a path as a fallback function in case
-    `nt._getfullpathname` is not available or raises OSError. See bpo-31047 for
-    more.
-
-    """
+# Return an absolute path.
+try:
+    from nt import _getfullpathname
 
+except ImportError: # not running on Windows - mock up something sensible
+    def abspath(path):
+        """Return the absolute version of a path."""
         path = os.fspath(path)
         if not isabs(path):
             if isinstance(path, bytes):
@@ -569,20 +569,33 @@ def _abspath_fallback(path):
             path = join(cwd, path)
         return normpath(path)
 
-# Return an absolute path.
-try:
-    from nt import _getfullpathname
-
-except ImportError: # not running on Windows - mock up something sensible
-    abspath = _abspath_fallback
-
 else:  # use native Windows method on Windows
     def abspath(path):
         """Return the absolute version of a path."""
         try:
             return _getfullpathname(normpath(path))
         except (OSError, ValueError):
-            return _abspath_fallback(path)
+            # See gh-75230, handle outside for cleaner traceback
+            pass
+        path = os.fspath(path)
+        if not isabs(path):
+            if isinstance(path, bytes):
+                sep = b'\\'
+                getcwd = os.getcwdb
+            else:
+                sep = '\\'
+                getcwd = os.getcwd
+            drive, root, path = splitroot(path)
+            # Either drive or root can be nonempty, but not both.
+            if drive or root:
+                try:
+                    path = join(_getfullpathname(drive + root), path)
+                except (OSError, ValueError):
+                    # Drive "\0:" cannot exist; use the root directory.
+                    path = drive + sep + path
+            else:
+                path = join(getcwd(), path)
+        return normpath(path)
 
 try:
     from nt import _findfirstfile, _getfinalpathname, readlink as _nt_readlink

Lib/test/test_ntpath.py

@@ -806,6 +806,9 @@ class TestNtpath(NtpathTestCase):
         tester('ntpath.abspath("C:\\spam. . .")', "C:\\spam")
         tester('ntpath.abspath("C:/nul")',  "\\\\.\\nul")
         tester('ntpath.abspath("C:\\nul")', "\\\\.\\nul")
+        self.assertTrue(ntpath.isabs(ntpath.abspath("C:spam")))
+        self.assertEqual(ntpath.abspath("C:\x00"), ntpath.join(ntpath.abspath("C:"), "\x00"))
+        self.assertEqual(ntpath.abspath("\x00:spam"), "\x00:\\spam")
         tester('ntpath.abspath("//..")',           "\\\\")
         tester('ntpath.abspath("//../")',          "\\\\..\\")
         tester('ntpath.abspath("//../..")',        "\\\\..\\")

Misc/NEWS.d/next/Library/2024-06-02-11-48-19.gh-issue-119826.N1obGa.rst

@@ -0,0 +1 @@
+Always return an absolute path for :func:`os.path.abspath` on Windows.