`relative_to` on `GCSPath`s does not return a relative path

[xjmdale]

Observed behavior:

>>> p1 = upath.UPath("gs://bucket/foo/bar")
>>> p2 = upath.UPath("gs://bucket/foo/bar/baz/quux.txt")
>>> p2.relative_to(p1)
GCSPath('gs://bucket/baz/quux.txt')

The result is not a relative path; it is an absolute path to an alternative GCS object which may or may not exist.

My expectation is that this call would return a fully-relative path to baz/quux.txt. I suppose there is uncertainty is around which path subtype should be returned. baz/quux.txt is not a valid GCS path; but upath.UPath('baz/quux.txt') returns a PosixUPath which also seems wrong.

Python version: 3.11.7
upath version: 0.1.4

[ap--]

Thank you for reporting!

We need to revisit the implementation of relative_to(). The problem is that relative paths should probably be returned as a custom filesystem independent PurePathBase subclass once we switch to pathlib_abc.

Would you be interested in creating a PR with a test case for your issue?

Cheers,
Andreas