pythongh-100809: Fix handling of drive-relative paths in pathlib.Path…

….absolute()

If it's available, use `nt._getfullpathname()` to retrieve an absolute
path. This allows paths such as 'X:' to be made absolute even when
`os.getcwd()` returns a path on another drive. It follows the behaviour of
`os.path.abspath()`, except that no path normalisation is performed.

Lib/pathlib.py

@@ -19,6 +19,17 @@
 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:
+    def _absolute_parts(path):
+        return [os.getcwd()] + path._parts
+else:
+    def _absolute_parts(path):
+        try:
+            return [_getfullpathname(path)]
+        except (OSError, ValueError):
+            return [os.getcwd()] + path._parts
 
 
 __all__ = [
@@ -827,7 +838,7 @@ def absolute(self):
         """
         if self.is_absolute():
             return self
-        return self._from_parts([os.getcwd()] + self._parts)
+        return self._from_parts(_absolute_parts(self))
 
     def resolve(self, strict=False):
         """

Lib/test/test_pathlib.py

@@ -1554,8 +1554,7 @@ def test_cwd(self):
     def test_absolute_common(self):
         P = self.cls
 
-        with mock.patch("os.getcwd") as getcwd:
-            getcwd.return_value = BASE
+        with os_helper.change_cwd(BASE):
 
             # Simple relative paths.
             self.assertEqual(str(P().absolute()), BASE)
@@ -2993,15 +2992,26 @@ def test_absolute(self):
         self.assertEqual(str(P(share + 'a\\b').absolute()), share + 'a\\b')
 
         # UNC relative paths.
-        with mock.patch("os.getcwd") as getcwd:
-            getcwd.return_value = share
+        def getfullpathname(path):
+            return os.path.join(share, path)
 
+        with mock.patch("nt._getfullpathname", getfullpathname):
             self.assertEqual(str(P().absolute()), share)
             self.assertEqual(str(P('.').absolute()), share)
             self.assertEqual(str(P('a').absolute()), os.path.join(share, 'a'))
             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.