Re: git merge commits are non-deterministic? what changed?

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On Fri, Nov 09, 2012 at 04:52:48PM +0100, Matthieu Moy wrote:

> Ulrich Spörlein <uqs@xxxxxxxxxxxxx> writes:
> 
> >> > 2. Why the hell is the commit hash dependent on the ordering of the
> >> > parent commits? IMHO it should sort the set of parents before
> >> > calculating the hash ...
> >> 
> >> What would be the sort key?
> >
> > Trivially, the hash of the parents itself. So you'd always get
> >
> > ...
> > parent 0000
> > parent 1111
> > parent aaaa
> > parent ffff
> 
> That would change the behavior of --first-parent. Or you'd need to
> compute the sha1 of the sorted list, but keep the unsorted one in the
> commit. Possible, but weird ;-).

Right. The reason that merge parents are stored in the order given on
the command line is not random or because it was not considered. It
encodes a valuable piece of information: did the user merge "foo" into
"bar", or did they merge "bar" into "foo"?

So I think this discussion is going in the wrong direction; git should
never sort the parents, because the order is meaningful. The original
complaint was that a run of svn2git produced different results on two
different git versions. The important question to me is: did svn2git
feed the parents to git in the same order?

If it did, and git produced different results, then that is a serious
bug.

If it did not, then the issue needs to be resolved in svn2git (which
_may_ want to sort the parents that it feeds to git, but it would depend
on whether the order it is currently presenting is meaningful).

-Peff
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