Re: I have end-of-lifed cvsps

From: Eric S. Raymond <esr@thyrsus.com>
Date: Dec 13, 2013, 03:38 UTC
Message-ID: <20131213033833.GB20850@thyrsus.com>
In-Reply-To: <CACPiFCLJfefNaPYtCXd21fO-ztmaaX6xdz1TtcMdYc0y19t56g@mail.gmail.com>

Martin Langhoff <martin.langhoff@gmail.com>:

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> On Thu, Dec 12, 2013 at 6:04 PM, Eric S. Raymond <esr@thyrsus.com> wrote:
> > I'm not sure what counts as a nonsensical branching point. I do know that
> > Keith left this rather cryptic note in a REAME:
> 
> Keith names exactly what we are talking about.

Oh, yeah, I figured that much out. What I wasn't clear on was (a) whether that's a complete description of "nonsensical branching point" or whether there are other pathologies fundamentally *different* from that one.

I'm also not sure I have the end state of what cvs-fast-export does in that case visualized correctly. When he says: "an entirely disjoint history will be created containing the branch revisions and all parents back to the root", I'm visualizing something like this:

  a----b----c----d----e----f----g----h
                  \
                   +----1----2----3---4

Suppose the root is a our pathological branch point is at d, then it sounds like he's saying cvs-fast-export will produce a changeset DAG that looks like this:

  a----b'---c'---d'---e----f----g----h
   \
    +----b''---c''---d''----1----2----3----4

What I'm not clear on here is how b is related to b' and b'', c to c' and c'', and d to d' and d''. Which file changes go to which commit? I shall have to craft some broken RCS files to find out.

Have I explained that I'm building a test suite? I intend to know exactly what the tool does in these cases and document it.

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> Between my earlier explanation and Keith's notes it should be clear to
> you. It is absolutely trivial in CVS to have an "inconsistent"
> checkout (for example, if you switch branch with the -l parameter
> disabling recursion, or if you accidentally switch branch in a
> subdirectory).

That last one sounds easy to fall into and nasty.

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> On that inconsistent checkout, nothing prevents you from tagging it,
> nor from creating a new branch.
> 
> An importer with a 'consistent tree mentality' will look at the
> files/revs involved in that tag (or branching point) and find no tree
> to match.
> 
> CVS repos with that crap exist. x11/xorg did (Jim Gettys challenged me
> to try importing it at an LCA, after the Bazaar NG folks passed on
> it). Mozilla did as well.
> 
> 
> IMHO it is a valid path to skip importing the tag/branch. As long as
> main dev work was in HEAD, things end up ok (which goes back to my
> flying fish notes).

The other way to handle it would be to translate the history as though every branch of a file subset had been an attempt to branch eveything.

-- 
		<a href="http://www.catb.org/~esr/">Eric S. Raymond</a>