From: Kevin Ballard <kevin@sb.org>
To: Junio C Hamano <gitster@pobox.com>
Cc: git@vger.kernel.org,
Johannes Schindelin <Johannes.Schindelin@gmx.de>,
Petr Baudis <pasky@suse.cz>
Subject: Re: [PATCH] Documentation/git-filter-branch.txt: Fix description of --commit-filter
Date: Sat, 31 May 2008 16:50:00 -0700 [thread overview]
Message-ID: <CEA5A26A-9109-4D22-9D3F-8FFF8305DBEE@sb.org> (raw)
In-Reply-To: <7vskvydrys.fsf@gitster.siamese.dyndns.org>
On May 31, 2008, at 3:33 PM, Junio C Hamano wrote:
> Junio C Hamano <gitster@pobox.com> writes:
>
>> Kevin Ballard <kevin@sb.org> writes:
>>
>>> You're still talking about the parent-filter here. I think you're
>>> quite confused.
>>
>> Blush. I should go to bed.
>
> Now after following the codepath, your original
>
> diff --git a/Documentation/git-filter-branch.txt b/Documentation/
> git-filter-branch.txt
> index 506c37a..541bf23 100644
> --- a/Documentation/git-filter-branch.txt
> +++ b/Documentation/git-filter-branch.txt
> @@ -113,8 +113,8 @@ OPTIONS
> stdin. The commit id is expected on stdout.
> +
> As a special extension, the commit filter may emit multiple
> -commit ids; in that case, ancestors of the original commit will
> -have all of them as parents.
> +commit ids; in that case, the rewritten children of the original
> commit will
> +have all of them as parents. You probably don't want to do this.
> +
> You can use the 'map' convenience function in this filter, and
> other
> convenience functions, too. For example, calling 'skip_commit
> "$@"'
>
> does make sense to me. Except for "You probably don't want to do
> this."
> part. It is just "the utility of this feature is unknown to us" ;-)
>
> I dug the code with "git blame" and the basic logic has been the same
> since its introduction to git with 6f6826c (Add git-filter-branch,
> 2007-06-03). The commit-filter itself appeared first in Cogito as
> d690516
> (cg-admin-rewritehist --commit-filter for omitting commits,
> 2006-03-26),
> and the commit log message claims that it was primarily meant to
> _omit_
> unwanted commits from the history, but at the same time it
> advertises the
> multiple commits case as a "feature" without telling why somebody
> wants to
> do so.
>
> Except for this gem, which may have been lost in our copy:
>
> # ... Note that this handles merges properly! In case Darl
> # committed a merge between P1 and P2, it will be propagated
> properly
> # and all children of the merge will become merge commits with
> P1,P2
> # as their parents instead of the merge commit.
>
> IOW, to rewrite this history:
>
> ---A---C---D---E
> /
> B
>
> to pretend C never happened, you would give A' and B' back when you
> rewrite C, to end up with this history:
>
> ---A'--D'--E'
> /
> B'
>
> I'd agree with "You probably don't want to do this", but perhaps it
> needs
> a bit of clarification as to _why_ you would not:
>
> - If the history is being rewritten for the whole tree, this will
> make D' an evil merge that contains difference between C to D.
>
> - If the filtering of the history is done to ignore parts of the tree
> that is touched between C and D (iow, history simplification would
> leave trees C and D the same), you would want to simplify away D'
> not
> C'. IOW, you would want the resulting history to look like:
>
> ---A'--C'--E'
> /
> B'
>
> and for that you do not need to use this "feature".
Yeah, this utility of omitting commits occurred to me last night after
I went to bed. It does seem pretty limited in use, but I guess someone
might want to do it. For example, if C resolved merge conflicts
incorrectly and D fixed it, and then later somebody said "why do I
have two commits when I should just have one?" and wanted to omit C
and leave D behind as the merge.
I'll submit a new patch later that has better wording and perhaps a
diagram or two.
-Kevin Ballard
--
Kevin Ballard
http://kevin.sb.org
kevin@sb.org
http://www.tildesoft.com
prev parent reply other threads:[~2008-05-31 23:50 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-05-30 21:43 [PATCH] Documentation/git-filter-branch.txt: Fix description of --commit-filter Kevin Ballard
2008-05-30 22:52 ` Junio C Hamano
2008-05-30 23:07 ` Kevin Ballard
2008-05-30 23:41 ` Junio C Hamano
2008-05-31 0:33 ` Kevin Ballard
2008-05-31 1:48 ` Junio C Hamano
2008-05-31 22:33 ` Junio C Hamano
2008-05-31 23:50 ` Kevin Ballard [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
List information: http://vger.kernel.org/majordomo-info.html
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CEA5A26A-9109-4D22-9D3F-8FFF8305DBEE@sb.org \
--to=kevin@sb.org \
--cc=Johannes.Schindelin@gmx.de \
--cc=git@vger.kernel.org \
--cc=gitster@pobox.com \
--cc=pasky@suse.cz \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
Code repositories for project(s) associated with this public inbox
https://80x24.org/mirrors/git.git
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).