On Wed, Oct 10, 2007 at 08:48:31AM -0700, David Brown <git@davidb.org> wrote:
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> On Wed, Oct 10, 2007 at 08:25:15AM -0700, Linus Torvalds wrote:

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> >Yes, *some* SCM's have tried to do that. In particular, the ones that are "patch-based" tend to think that patches are "identical" regardless of where they are, and while re-ordering of them is a special event, it's not somethign that changes the fundamental 'ID' of the patch.

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> >For example, I think the darcs "patch algebra" works that way.

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> >It's a really horrible model. Not only doesn't it scale, but it leads to various very strange linkages between patches, and it fails the most important part: it means that merges get different results just because people are doing the same changes two different ways.

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> Actually, specifically darcs, different merges _always_ result in the same
> data.  It's a fundamental part of is patch algebra.  No matter what order
> you apply a given set of patches, even with conflicts and reordering, you
> always get the same result, or no result.  Conflicts are "resolved" by
> inserting conflict markers in the file, ordered by the patch ID.  It
> doesn't matter which order you apply them in, you get the same markers.
> Then there will be a merge patch which fixes the markers that someone could
> apply, no matter what order the applied the previous patches.

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> Darcs breaks down in a few places, though.

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>   - The no result.  Sometimes, it just can't figure out how to reorder
>     patches.  Even worse, occasionally, the implementation will fail to
>     terminate try to figure this out.  There isn't much to do at this
>     point, except manually apply the patch, hence generating a new patch
>     ID.

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>   - It doesn't scale well.

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> The strange linkages between patches could be thought of as a feature,
> since it is basically constraining the order that the patches can be
> applied in.

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> There is a darcs-git project that tries to do the darcs things on top of
> git.

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> Dave
> -
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thanks,
- VMiklos