gh-100809: Fix handling of drive-relative paths in pathlib.Path.absolute()

Lib/pathlib.py

@@ -19,6 +19,10 @@
 from operator import attrgetter
 from stat import S_ISDIR, S_ISLNK, S_ISREG, S_ISSOCK, S_ISBLK, S_ISCHR, S_ISFIFO
 from urllib.parse import quote_from_bytes as urlquote_from_bytes
+try:
+    from nt import _getfullpathname
+except ImportError:
+    _getfullpathname = None
 
 
 __all__ = [
@@ -827,7 +831,14 @@ def absolute(self):
         """
         if self.is_absolute():
             return self
-        return self._from_parts([os.getcwd()] + self._parts)
+        elif self._drv and _getfullpathname:
+            try:
+                cwd = _getfullpathname(self._drv)
+            except (ValueError, OSError):
+                cwd = os.getcwd()
+        else:
+            cwd = os.getcwd()
+        return self._from_parts([cwd] + self._parts)
 
     def resolve(self, strict=False):
         """

Lib/test/test_pathlib.py

@@ -3002,6 +3002,16 @@ def test_absolute(self):
             self.assertEqual(str(P('a', 'b', 'c').absolute()),
                              os.path.join(share, 'a', 'b', 'c'))
 
+        drive = os.path.splitdrive(BASE)[0]
+        with os_helper.change_cwd(BASE):
+            # Relative path with drive
+            self.assertEqual(str(P(drive).absolute()), BASE)
+            self.assertEqual(str(P(drive + 'foo').absolute()), os.path.join(BASE, 'foo'))
+
+            # Relative path with root
+            self.assertEqual(str(P('\\').absolute()), drive + '\\')
+            self.assertEqual(str(P('\\foo').absolute()), drive + '\\foo')
+
 
     def test_glob(self):
         P = self.cls

Misc/NEWS.d/next/Library/2023-01-06-21-14-41.gh-issue-100809.I697UT.rst

@@ -0,0 +1,3 @@
+Fix handling of drive-relative paths (like 'C:' and 'C:foo') in
+:meth:`pathlib.Path.absolute`. This method now calls
+``nt._getfullpathname()`` on Windows.