Re: [RFC/PATCH 1/2] commit: add parse_commit_repl() to replace commits at parsing time

[Christian Couder <chriscool@tuxfamily.org>]

On Wednesday 18 August 2010 16:50:24 Junio C Hamano wrote:
> Christian Couder <chriscool@tuxfamily.org> writes:
> > On Wednesday 18 August 2010 05:17:52 Nguyen Thai Ngoc Duy wrote:
> >> On Wed, Aug 18, 2010 at 7:18 AM, Junio C Hamano <gitster@pobox.com> 
wrote:
> >> > Christian Couder <chriscool@tuxfamily.org> writes:
> >> >> The function parse_commit() is not safe regarding replaced commits
> >> >> because it uses the buffer of the replacement commit but the object
> >> >> part of the commit struct stay the same. Especially the sha1 is not
> >> >> changed so it doesn't match the content of the commit.
> >> > 
> >> > This all sounds backwards to me, if I am reading the discussion
> >> > correctly.
> >> > 
> >> > If a replace record says commit 0123 is replaced by commit 4567 (iow,
> >> > 0123 was a mistake, and pretend that its content is what is recorded
> >> > in 4567), and when we are honoring the replace records (iow, we are
> >> > not fsck), shouldn't read_sha1("0123") give us a piece of memory that
> >> > stores what is recorded in 4567, parse_object("0123") return a struct
> >> > commit whose buffer points at a block of memory that has what is
> >> > recorded in 4567 _while_ its object.sha1[] say "0 123"?
> >> 
> >> 1. parse_object() as it is now would return object.sha1[] = "4567".
> >> 2. lookup_commit(), then parse_commit() would return object.sha1[] =
> >> "0123".
> >> 
> >> > What problem are you trying to solve?
> >> 
> >> Inconsistency in replacing objects. I have no comments whether #1 or
> >> #2 is expected behavior. But at least it should stick to one behavior
> >> only.
> > 
> > We discussed this inconsistency in this thread:
> > 
> > http://thread.gmane.org/gmane.comp.version-control.git/152321/
> > 
> > So we can resolve the inconsistency with Duy's patch to make
> > parse_object() return object.sha1[] = "0123".
> > 
> > It's simpler and probably safer. The downside is that the sha1 will not
> > be consistent with the content anymore and that it will be more
> > difficult to realize that an object has been replaced as there will be
> > no sha1 change to be seen.
> 
> I do not see it as a downside at all.
> 
> If the user wants to take replaced objects, they should be shown just like
> an ordinary objects at the machinery level.
> 
> Of course, the user is free to add comments on the commit log to note the
> fact that a new commit is replacing some other commit and for what
> purpose.  Also if somebody really wants to, cat-file piped to hash-object
> can be used to see the difference.

Ok so please apply Duy's patch perhaps with an improved commit message.

Thanks,
Christian.