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

On Fri, 2012-11-09 at 11:16:47 -0500, Jeff King wrote:

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

quoted

Ulrich Spörlein [off-list ref] writes:

quoted

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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).

Yeah, thanks, looks like I have some more work to do. I don't quite get
how it could come up with a different order, seeing that it is using svn
as the base.

Will run some more experiments, thanks for the info so far.

Cheers,
Uli