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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 12:45:08 -0500
User-agent: Mutt/1.5.21 (2010-09-15)

Eli Zaretskii <address@hidden>:
> > In other VCSes it would be difficult to even attempt this.
> ??? It's known as "reverse cherry-picking", and is AFAIK possible in
> Git, bzr, and hg.
> Or maybe I don't understand what ttn was alluding to.

You don't, not quite.  Reverse cherry pick doesn't actually do the git
equivalent of removing a delta; the history is not altered.  Reverse
cherry pic only requires forward composition of a reversed patch onto
the current branch tip - a much, *much* more tractable problem.

The git equivalent of actually removing a delta would be *really hard*.  
You'd have to apply a reverse patch (in effect) against the blob, then
against all of its successors, dealing with conflicts in some way.  
All the downstream hashes would be invalidated.  A mess.

This is why git only lets you remove tip deltas.
                <a href="http://www.catb.org/~esr/";>Eric S. Raymond</a>

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