[Bug 2009885] Re: Timeshift 21.09.1-1 broken after Rsync upgrade to 3.2.7-0ubuntu0.22.04.2

[Dave Jones]

Patch looks mostly good. Needed a couple of trivial changes (run update-
maintainer to deal with maintainer address in d/control, and add bug-ref
in d/changelog), but I've sponsored with those changes, thanks!

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Title:
  Timeshift 21.09.1-1 broken after Rsync upgrade  to
  3.2.7-0ubuntu0.22.04.2

Status in timeshift package in Ubuntu:
  Fix Released
Status in timeshift source package in Jammy:
  In Progress

Bug description:
  [ Impact ]

  Timeshift is broken after upgrade to 21.09.1-1. This is because of
  a change in behaviour by rsync; rsync 3.2.4 changed how the locale's
  worked out. From https://download.samba.org/pub/rsync/NEWS#3.2.4

  "A long-standing bug was preventing rsync from figuring out the
  current locale's decimal point character, which made rsync always
  output numbers using the "C" locale. Since this is now fixed in 3.2.4,
  a script that parses rsync's decimal numbers (e.g. from the verbose
  footer) may want to setup the environment in a way that the output
  continues to be in the C locale. For instance, one of the following
  should work fine:

      export LC_ALL=C.UTF-8
  "

  This broke timeshift and the workaround mentioned in rsync release
  notes needed to be applied to fix the locale.

   * justification for backporting the fix to the stable release.

  While the behaviour change is external to timeshift (it's in rsync),
  for anyone using newer rsync it broke timeshift completely and worse,
  users aren't even aware that their existing snapshots and backups are no longer
  working.

  The said workaround has been applied in upstream timeshift
  https://github.com/teejee2008/timeshift/pull/904

  But we haven't got this fix in Jammy.

  [ Test Plan ]

  It's readily reproducible on Jammy:
  1. Install Ubuntu 22.04 LTS
  2. Install the latest Timeshift
  3. Change locale to any language with a (,) decimal seperator (e.g. German)
  4. (a) Launch Timeshift, start rsync-backup, log message said that rsync failed to create backup.
     (b) Can use CLI too with `sudo timeshift --create` and see it fail.
  5. Then use the timshift package from PPA https://launchpad.net/~pponnuvel/+archive/ubuntu/jammy-timeshift
     which contains the fix and `sudo timeshift --create` will succeed.

  [ Where problems could occur ]

  This changes the locale to "C.UTF-8". If anyone relies existing broken behaviour
  that won't work anymore. Similarly, if rsync doesn't changes behaviour again based
  on locale, timeshift might start failing again.

  [ Other Info ]

  I've looked into Focal, Jammy, Mantic, and Noble for this issue.

  Focal is using older rsync (before the locale change [0]), so it's unaffected.
  Both Mantic, and Noble have the upstream fix [1] incorporated (fixed through new releases).
  So they don't have this issue either.

  Thus this is a Jammy-only backport of the fix [1].

  [0] https://download.samba.org/pub/rsync/NEWS#3.2.4
  [1] https://github.com/teejee2008/timeshift/pull/904

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