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Re: Removing rollback from VC mode - request for comment

From: Eric S. Raymond
Subject: Re: Removing rollback from VC mode - request for comment
Date: Thu, 11 Dec 2014 07:51:45 -0500
User-agent: Mutt/1.5.21 (2010-09-15)

Thien-Thi Nguyen <address@hidden>:
> So, i think "rollback" as a concept is actually not far
> enough.  Being able to select arbitrary commits to drop (like
> ā€˜dā€™ and ā€˜xā€™ in Dired) is what i'd like to see, in its stead.

RCCS and SCCS can do this, in theory.  But I've never trusted that
feature.  The obvious problem is that if you delete an earlier delta
you may well change the preconditions for a later one, so it will have
unexpected effects.  

I know how RCS's delta representation works; it is *not* smart enough
to fully compensate.  And no wonder. General patch composition is a
hard enough problem that it scuttled Darcs thirty years later!

In other VCSes it would be difficult to even attempt this.  In view
of the known problems, I recommend staying way the hell away from
it unless and until David Roundy successfully proves a correct
composition algorithm and we integrate it into Emacs somehow.
                <a href="http://www.catb.org/~esr/";>Eric S. Raymond</a>

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