Nicolas Pitre <nico@xxxxxxx> writes:
> On Fri, 18 Aug 2006, A Large Angry SCM wrote:
>
>> Historic fact. Between Thu May 19 08:56:22 2005 and Thu Feb 9 21:06:38
>> 2006 bit 6 of the first byte of a delta hunk was interpreted to mean
>> that the source of the copy was the result buffer. From Thu May 19
>> 08:56:22 2005 on, the code to decode delta hunks in type 2 packs was
>> available to everyone and anyone interested could make a pack encoder
>> that would create packs that the core Git code would correctly read. The
>> commit of Thu Feb 9 21:06:38 2006, d60fc, actually introduced a bug
>> that would treat valid type 2 packs as invalid.
It is more like the said commit made the pack format extensible
by declaring the bit reserved for the future use, by declaring
retroactively that a type 2 pack that used that bit invalid.
And it was deemed a reasonable and safe decision because no
official git ever produced a type 2 pack that used that bit,
Yes, that was a backward incompatible change, strictly speaking,
and probably I should have made an announcement that looked
similar to this by Linus:
From: Linus Torvalds <torvalds@xxxxxxxx>
Subject: CAREFUL! No more delta object support!
Date: Mon, 27 Jun 2005 18:14:40 -0700 (PDT)
Message-ID: <Pine.LNX.4.58.0506271755140.19755@xxxxxxxxxxxxxxx>
To: Git Mailing List <git@xxxxxxxxxxxxxxx>
So you could argue I was incompetent not to make a big fuss
about this backward incompatibility back then, if you like.
I did not think it was worth it back then, and I do not think it
is worth it now, either. But if it makes you feel better, I
could retroactively make such an announcement about the
unofficial bit 6.
The announcement would have read like this:
The current git code does not support type #2 packs that
uses delta with bit 6 to mean "copy inside destination
buffer". Although the code that interpreted delta data
supported bit 6 that way for a brief period of time, no
official git ever released produced delta that used the
bit that way.
In other words, if you have created packs with your own,
modified git, that took advantage of "copy inside
destination buffer" feature in the delta interpretation
code, such packs are not usable by the official git, so
you need to unpack them using your own version of git
and then repack with the official version of git.
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