[3.12] gh-105002: [pathlib] Fix relative_to with walk_up=True using ".." (GH-107014) (#107315)

gh-105002: [pathlib] Fix relative_to with walk_up=True using ".." (GH-107014)

It makes sense to raise an Error because ".." can not
be resolved and the current working directory is unknown.
(cherry picked from commit e7e6e4b035f51ab4a962b45a957254859f264f4f)

Co-authored-by: János Kukovecz <kukoveczjanos@gmail.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/Lib/pathlib.py b/Lib/pathlib.py
index b99bf6e..65631b7 100644
--- a/Lib/pathlib.py
+++ b/Lib/pathlib.py
@@ -679,10 +679,12 @@ class PurePath(object):
         for step, path in enumerate([other] + list(other.parents)):
             if self.is_relative_to(path):
                 break
+            elif not walk_up:
+                raise ValueError(f"{str(self)!r} is not in the subpath of {str(other)!r}")
+            elif path.name == '..':
+                raise ValueError(f"'..' segment in {str(other)!r} cannot be walked")
         else:
             raise ValueError(f"{str(self)!r} and {str(other)!r} have different anchors")
-        if step and not walk_up:
-            raise ValueError(f"{str(self)!r} is not in the subpath of {str(other)!r}")
         parts = ['..'] * step + self._tail[len(path._tail):]
         return self.with_segments(*parts)