0.6.06 can't restore backup made with 0.4.x

[az]

this is a forward/copy of debian bug #572102 which lives over there: http://bugs.debian.org/572102

a debian user has reported that his duplicity restoration attempts die with an assertion traceback
on the very first file to restore. the backup was made with 0.4.11, the restoration attempt used 0.6.06.

the assertion error:
---
  File "/usr/lib/python2.5/site-packages/duplicity/patchdir.py", line 492, in integrate_patch_iters
    final_ropath = patch_seq2ropath(normalize_ps(patch_seq))
  File "/usr/lib/python2.5/site-packages/duplicity/patchdir.py", line 459, in patch_seq2ropath
    assert first.difftype != "diff", patch_seq
AssertionError: [(('bin', 'gunzip') reg)]
---
the debian bug system includes an appropriate -v9 dump at the url above, so i'm not including any further
details in this report.

i (az) can't find anything specific in the changelogs that indicates that 0.6 can't read 0.4 backups,
but i'm obviously not the upstream author - whom i'm asking hereby.

regards
az

[Kenneth Loafman (kenneth-loafman)]

The 0.4 series is out of date by years. While I can't find anything in the docs that indicate it should not be restorable by the 0.6 series, I suspect enough changes have been made regarding error checks that older versions may be violating something that the new code requires. You can still download the old version from:

http://download.savannah.gnu.org/releases-noredirect/duplicity/OLD/

[Jamus Jegier (jamus+launchpad)]

I think this bug shows the need to have some kind of backwards compatibility documentation and runtime checks. Version 0.6.x is more than happy to continue backing up to a set created by 0.4.x. If I didn't need to restore a file, I could have gone years before realizing that I may have problems restoring my data. Furthermore, what happens if the next version introduces something that version 0.4.x can't handle, and I continue with the backup set created by 0.4.x? Then both versions won't be able to read the backup set.