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Re: [Gnu-arch-users] Type-specific diff & patch

From: Stefan Monnier
Subject: Re: [Gnu-arch-users] Type-specific diff & patch
Date: Tue, 02 May 2006 15:30:40 -0400
User-agent: Gnus/5.11 (Gnus v5.11) Emacs/22.0.50 (gnu/linux)

>> Agreed.  Also it's crucial that the patch and diff used to build up the
>> internal deltas used to store patches in the archive be perfect inverses
>> of each other.
>> E.g. using "diff -b" is not an option, even for files for which changes
>> in whitespace is not significant.
>> In other words, the compression of patches (based on diff) should
>> be lossless.

> That's critical for Arch-1 style storage and for a lot of other things but
> maybe there's more to the story, too.

I think it's critical for sanity's sake.

> A common use for patching is to do merging.   Maybe it is a mistake to
> insist that the way precise diffs are computed, inverted, composed, and
> applied is the only way merges get done.

And sanity says that if you want funny merge tools, you should separate the
notion of an internal patch (only used internally by applying it to the
original base file, in order to recreate a specific revision), from the
notion of an external patch (potentially applied by cherry picking, or
something like that).  An external patch can always be generated from the
internal one.


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