v0.9.10

Added

• Path._same_filesystem(other), an override hook answering whether two
  paths of one type resolve their segments in the same place. Path equality
  ignores that, and copy(), move() and PathSyncer now ask it before
  calling two paths the same file, nested, or overlapping. A path type whose
  instances can front different hosts or stores should override it; the
  default keeps the previous behaviour. pathlib_next.testing.PathContract
  gains two tests: a file copied onto a separately built spelling of itself
  is refused with its content intact, and paths under one root share a
  filesystem.

Changed

• The built-in Base*Backend classes (s3, gs, az, ftp, sftp,
  github/gitlab) are weakly referenceable, which is how a UriPath
  tells a backend it derived for itself from one it was given. A custom
  backend class using __slots__ without "__weakref__" still works; it is
  simply always read as supplied.

Fixed

• A path type that fronts several hosts can transfer between them again.
  Since 0.9.4, copy()/move() raised OSError(EINVAL) "Source and target
  are the same file" and PathSyncer raised "source and target overlap" for
  /app.conf on one host onto /app.conf on another, whenever the type kept
  its connection under any attribute other than the private _backend the
  guards looked for. Such a type now overrides _same_filesystem().
• Two separately built URIs to the same URL are recognised as the same
  file. Each derived its own backend on first use, which the guards read as
  two hosts: UriPath(url).copy(UriPath(url), overwrite=True) was not
  refused on any scheme without st_dev/st_ino (S3 and WebDAV among
  them), and neither was a sync of a URL onto itself. Only two backends the
  caller supplied now tell equal URIs apart. One consequence: a path given a
  backend and a bare path to the same URL are now the same file for
  copy()/move(), as they already were for PathSyncer.
• copy(recursive=True)'s "into itself" check now honours two supplied
  backends, like the other two guards; it refused a copy between two hosts
  whose URIs nested.

Full Changelog: v0.9.9...v0.9.10