GH-73991: Disallow copying directory into itself via pathlib.Path.copy()

Lib/pathlib/_abc.py

@@ -583,6 +583,11 @@ def _ensure_distinct_path(self, other_path):
         """
         Raise OSError(EINVAL) if the other path is within this path.
         """
+        # Note: there is no straightforward, foolproof algorithm to determine
+        # if one directory is within another. A particularly perverse example:
+        # consider a single network share mounted in one location via NFS, and
+        # in another location via CIFS. This method simply checks whether the
+        # other_path is lexically equal to, or within, this path.
         if self == other_path:
             err = OSError(EINVAL, "Source and target are the same path")
         elif self in other_path.parents: