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Re: git diff: add option for omitting the contents of deletes

From
Jeff King <peff@peff.net>
Date
Feb 28, 2011, 12:17 UTC
Message-ID
<20110228121726.GA5197@sigill.intra.peff.net>
In-Reply-To
<4D6B4F6B.1040209@drmicha.warpmail.net>
On Mon, Feb 28, 2011 at 08:31:55AM +0100, Michael J Gruber wrote:
Show 17 quoted lines
> > Junio C Hamano <gitster@pobox.com> writes:
> >>
> >> There is a big difference: -M and -C lets your recipient reproduce the
> >> state using the change you are trying to convey with the diff output in
> >> either direction (iow, "apply -R" works), but your "-D" would not have
> >> that property.
>
> [...]
>
> Yes, it is purely intended as "for viewing by humans". Even in the
> forward direction saying "delete that path" is different from saying
> "delete that content from that path", i.e. "diff -D" output may apply
> without conflicts in cases where "diff" output does not.
> 
> That aspect is similar to -M and -C, though - unless we check the sha1
> of the blobs before applying the patch (which would be possible for -D
> also) - do we?

Yes, I think we do check the sha1s for a "-M" patch. And we should do so for a "-D" patch, too. Which would make it just as likely to conflict as a version with the actual patch content, _except_ that it relies on the recipient having that sha1.

I don't see how "-D" is any less reversible than -M or -C, though. If I get your -D patch, I use the index line to see that the blob went from 1234abcd to 0000000, check that we are at 1234abcd, and then delete the file. To reverse it, I reinstate 1234abcd from nothing (and conflict if the file exists). _Neither_ case works without the sha1.

So I think the problem is not about "this cannot be reversed" but about "the recipient must have your sha1 to make sense of it, in either direction". Which is the same case as with "-M" and "-C", and why we have long cautioned about their use on mailing lists. But the right rule is not "do not use on mailing lists" but rather "do not use on mailing lists for projects where the recipients will not be using git to apply".

> Reminds me of my failed attempt to make the diff output for symlinks
> more human-friendly. The latter can be solved with textconv, though.

I am still carrying around my "symlinks as a special class of diff" patches if you are interested:

  https://github.com/peff/git/tree/jk/userdiff-symlinks
-Peff
Previous: Michael J GruberNext: Jeff King
Message 10 of 32 in “git diff: add option for omitting the contents of deletes”
  1. Mart SõmermaaFeb 26, 2011
  2. Junio C HamanoFeb 26, 2011
  3. Michael J GruberFeb 27, 2011
  4. Mart SõmermaaFeb 27, 2011
  5. Michael J GruberFeb 28, 2011
  6. Mart SõmermaaFeb 28, 2011
  7. Junio C HamanoFeb 27, 2011
  8. Junio C HamanoFeb 27, 2011
  9. Michael J GruberFeb 28, 2011
  10. Jeff KingFeb 28, 2011
  11. Jeff KingFeb 28, 2011
  12. Michael J GruberFeb 28, 2011
  13. Jeff KingFeb 28, 2011
  14. Michael J GruberFeb 28, 2011
  15. Jeff KingFeb 28, 2011
  16. Junio C HamanoFeb 28, 2011
  17. Jeff KingFeb 28, 2011
  18. Junio C HamanoFeb 28, 2011
  19. Junio C HamanoMar 1, 2011
  20. Mart SõmermaaMar 7, 2011
  21. Michael J GruberMar 8, 2011
  22. Junio C HamanoMar 8, 2011
  23. Mart SõmermaaMar 8, 2011
  24. Jeff KingMar 8, 2011
  25. symling diff driver (Was: Re: git diff: add option for omitting the contents of deletes)Michael J Gruber, Feb 28, 2011
  26. Jeff KingFeb 28, 2011
  27. attr: make attributes depend on file typeMichael J Gruber, Feb 28, 2011
  28. Jeff KingFeb 28, 2011
  29. Junio C HamanoFeb 28, 2011
  30. Michael J GruberMar 1, 2011
  31. Mart SõmermaaFeb 28, 2011
  32. Michael J GruberFeb 28, 2011

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