GH-113528: Deoptimise `pathlib._abc.PurePathBase.relative_to()` (#113529)

Replace use of `_from_parsed_parts()` with `with_segments()` in
`PurePathBase.relative_to()`, and move the assignment of `_drv`, `_root`
and `_tail_cached` slots into `PurePath.relative_to()`.

2 files changed, 5 insertions, 2 deletions

diff --git a/Lib/pathlib/__init__.py b/Lib/pathlib/__init__.py
index d83f292..a432d45 100644
--- a/Lib/pathlib/__init__.py
+++ b/Lib/pathlib/__init__.py
@@ -245,7 +245,10 @@ class PurePath(_abc.PurePathBase):
                    "scheduled for removal in Python 3.14")
             warnings.warn(msg, DeprecationWarning, stacklevel=2)
             other = self.with_segments(other, *_deprecated)
-        return _abc.PurePathBase.relative_to(self, other, walk_up=walk_up)
+        path = _abc.PurePathBase.relative_to(self, other, walk_up=walk_up)
+        path._drv = path._root = ''
+        path._tail_cached = path._raw_paths.copy()
+        return path
 
     def is_relative_to(self, other, /, *_deprecated):
         """Return True if the path is relative to another path or False.
diff --git a/Lib/pathlib/_abc.py b/Lib/pathlib/_abc.py
index aca2bd5..97663b9 100644
--- a/Lib/pathlib/_abc.py
+++ b/Lib/pathlib/_abc.py
@@ -371,7 +371,7 @@ class PurePathBase:
         else:
             raise ValueError(f"{str(self)!r} and {str(other)!r} have different anchors")
         parts = ['..'] * step + self._tail[len(path._tail):]
-        return self._from_parsed_parts('', '', parts)
+        return self.with_segments(*parts)
 
     def is_relative_to(self, other):
         """Return True if the path is relative to another path or False.