From: "Jan D." <jan.h.d@swipnet.se>
To: "Eric S. Raymond" <esr@snark.se>
Cc: emacs-devel@gnu.org
Subject: Re: My plans for VC mode
Date: Sat, 22 Nov 2014 15:17:02 +0100 [thread overview]
Message-ID: <593E5C6A-D8AF-4D15-9A0E-79E43784ACAA@swipnet.se> (raw)
In-Reply-To: <20141122133351.46279382C23@snark.thyrsus.com>
Hi.
Do you have any plans for async checkin/commit from vc?
Jan D.
> 22 nov 2014 kl. 14:33 skrev Eric S. Raymond <esr@snark.se>:
>
> I have noted in previous mail that the VC code lacks a clean set of
> primitives to deal with branching. My goal is to fix that.
>
> In the way is the fact that the VC backend API is still something of
> a mess. Everyone who has previously modified it (including me in 2007
> when I did the fileset rewrite) has tried to preserve backward
> compatibility to the year zero. As a result, the upper-level code
> has never gotten completely divorced from the file-oriented back ends.
>
> The merge command is a particular trouble spot where the back-end model
> pokes upward into what should be VCS-independent - as is revealed
> by the ";; FIXME: This is CVS/RCS/SCCS specific." in vc/vc.el.
> Because of the code that calls out, SVN merge in particular plain
> doesn't work right - it assumes RCS behavior in SVN revision numbers.
>
> A related effect of trying to preserve backward compatibility is that
> the backend API has more entry points than it should and is harder to
> understand than it should be. I had my nose rubbed in this writing the
> support for SRC. Given the advantages of having written both VC mode
> and SRC and the freedom to modify SRC to make VC-mode happy, it was
> *way* more difficult than it should have been.
>
> Accordingly, I have concluded that it is time to chuck backward
> compatibility and rewrite tha back-end API, simplifying as radically
> as I can and enforcing much stricter separation between the VC upper
> layer and the back ends.
>
> This is going to break out-of-tree back ends - not in any way that is
> fundamentally difficult to fix, but it will break them. I've already had
> one polite complaint about that in email, but explained that we can't
> be stuck with the cruft and the previous design mistakes forever.
>
> I'm explaining this, while "make bootstrap" runs to test a build,
> because it may cause some minor disruptions. I'm a little worried
> about breaking CVS support; that back end is both the worst hairball
> in the file-oriented group (SCCS/RCS/CVS/SRC) and the one I'm least
> able to test well. I could use some help with this if there is
> anyone on the list using vc-cvs regularly.
>
> While I do branching I'm also going to look at removing the elaborate
> caching the older back ends use to avoid disk traffic as much as
> possible. That made sense when I first wrote it twenty-odd years
> ago, but it's been a chronic source of TOCTOU bugs and other
> coherency problems ever since. Disks are much faster now; it's
> probably time for the state-heuristic stuff to die.
> --
> <a href="http://www.catb.org/~esr/">Eric S. Raymond</a>
>
> The saddest life is that of a political aspirant under democracy. His
> failure is ignominious and his success is disgraceful.
> -- H.L. Mencken
next prev parent reply other threads:[~2014-11-22 14:17 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-11-22 13:33 My plans for VC mode Unknown
2014-11-22 14:17 ` Jan D. [this message]
2014-11-22 16:29 ` Eric S. Raymond
2014-11-22 16:44 ` Jan D.
2014-11-22 14:33 ` Dmitry Gutov
2014-11-22 16:37 ` Eric S. Raymond
2014-11-22 17:46 ` Dmitry Gutov
2014-11-22 18:08 ` Eric S. Raymond
2014-11-23 1:27 ` Dmitry Gutov
2014-11-22 22:32 ` Stefan Monnier
2014-11-23 1:01 ` Dmitry Gutov
2014-11-23 6:25 ` Eric S. Raymond
2014-11-22 23:17 ` Steinar Bang
2014-11-23 20:02 ` Eric S. Raymond
2014-11-23 20:11 ` Eli Zaretskii
2014-11-22 16:11 ` Stefan Monnier
2014-11-22 16:41 ` Eric S. Raymond
2014-11-22 16:59 ` Dieter Deyke
2014-11-22 22:34 ` Stefan Monnier
2014-11-23 19:58 ` Eric S. Raymond
2014-11-24 6:40 ` Dieter Deyke
2014-11-24 7:50 ` Eric S. Raymond
2014-11-24 7:55 ` Kan-Ru Chen (陳侃如)
2014-11-24 8:07 ` Eric S. Raymond
2014-11-24 14:33 ` Stefan Monnier
2014-11-24 17:57 ` Eric S. Raymond
2014-11-23 19:27 ` Ivan Shmakov
2014-11-23 20:10 ` Eric S. Raymond
2014-11-22 19:02 ` Michael Albinus
2014-11-23 6:26 ` Eric S. Raymond
2014-11-23 8:23 ` Michael Albinus
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