From: Jakub Narebski <jnareb@gmail•com>
To: Miklos Vajna <vmiklos@frugalware•org>
Cc: "SZEDER Gábor" <szeder@ira•uka.de>,
git@vger•kernel.org, "Shawn O. Pearce" <spearce@spearce•org>,
Johannes.Schindelin@gmx•de
Subject: Re: [PATCH] builtin-commit: avoid using reduce_heads()
Date: Fri, 26 Sep 2008 09:17:39 -0700 (PDT) [thread overview]
Message-ID: <m37i8y3mqt.fsf@localhost.localdomain> (raw)
In-Reply-To: <20080926151517.GV23137@genesis.frugalware.org>
Miklos Vajna <vmiklos@frugalware•org> writes:
> OK, here is the scenario.
>
> The basic problemis that if it's git-commit that creates the merge
> commit and not git-merge, then git-commit does not "know" that git-merge
> was invoked using --no-ff.
>
> --no-ff means that if reduce_heads() removes a parent, that will be a
> problem, since the resulting commit will no longer be a merge commit.
>
> I think we can't avoid storing this info in a MERGE_MODE file, because
> we have to add HEAD to the list of parents in case --no-ff is used, but
> we should not do so in case it's reachable from existing heads and
> --no-ff is not used.
>
> I'll send a patch that does this in a bit.
The following is summary of short dicussion about this issue on #git
see: http://colabti.org/irclogger/irclogger_log/git?date=2008-09-26,Fri#l1176
The problem is that sometimes git-commit finishes doing the merge, be
it use of --no-commit option, or a conflict occurred; depending on
whether git-merge was invoked with or without --no-ff (--ff=never)
option it should recurd reduced or non-reduced heads.
The problem for example occurs in the following situation:
.---.---.---. <--- a <--- HEAD
|\
| \-1---2 <--- b
\
\--x---y <--- c
$ git merge b c
/------------- b
v
.---.---.---.---1---2---M <--- a <--- HEAD
\ /
\--x---y-/ <--- c
$ git merge --no-ff b c
.---.---.---.---------M <--- a <--- HEAD
|\ /|
| \-1---2 | <--- b
\ /
\--x---y/ <--- c
We can select one of the following solutions:
1. As proposed above save git-merge options, for example in MERGE_MODE
or MERGE_OPTS file, so git-commit knows what options to use if it
was invoked to finish a merge.
2. git-merge saves _reduced_ heads in MERGE_HEAD, and git-commit
reduces only HEAD, unless it is in MERGE_HEAD. This means that
git-commit uses the following pseudo-code
if (resolve_ref(HEAD) == MERGE_HEAD[0]) {
/* non fast-forward case */
merge HEAD + MERGE_HEAD
} else {
reduce_HEAD_maybe()
merge [HEAD] + MERGE_HEAD
}
This has the advantage that it doesn't change MERGE_HEAD semantic
for simple merge which did not began as octopus
3. Remove reduce_heads() from git-commit entirely, and record in
MERGE_HEAD (or rather now MERGE_HEADS) _all_ _reduced_ heads.
_All_ means that HEAD is included in MERGE_HEAD if it is not
reduced, _reduced_ means that only non-dependent heads are in
MERGE_HEAD. This for example means that for simple non-octopus
merge case MERGE_HEAD/MERGE_HEADS now contain _all_ parents,
and not only other side of merge.
This solution has the advantage of being clear solution, clarifying
semantic of MERGE_HEAD (currently HEAD is used both as target, i.e.
where merge is to be recorded, and as one of heads to merge/to
consider), and making it possible to separate layers: git-merge
is about merging, git-commit doesn't need to know anything about
merging.
The disadvantage is that it changes format (well, semantic) of
MERGE_HEAD, possibly breaking users' scripts; perhaps some of
git commands like "git log --merge" or "git diff --merge" should
be updated on such change.
--
Jakub Narebski
Poland
ShadeHawk on #git
next prev parent reply other threads:[~2008-09-26 16:18 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-09-25 23:50 [BUG] merge --no-ff --no-commit && commit SZEDER Gábor
2008-09-26 0:35 ` [PATCH] builtin-commit: avoid using reduce_heads() Miklos Vajna
2008-09-26 1:03 ` SZEDER Gábor
2008-09-26 6:24 ` Miklos Vajna
2008-09-26 15:15 ` Miklos Vajna
2008-09-26 15:20 ` [PATCH] builtin-commit: avoid always " Miklos Vajna
2008-09-26 15:52 ` Shawn O. Pearce
2008-09-26 19:37 ` Miklos Vajna
2008-10-03 2:35 ` Shawn O. Pearce
2008-10-03 12:04 ` Miklos Vajna
2008-10-03 14:59 ` Shawn O. Pearce
2008-10-05 19:51 ` Miklos Vajna
2008-10-06 14:19 ` Shawn O. Pearce
2008-10-03 15:09 ` [PATCH] builtin-commit: use reduce_heads() only when appropriate SZEDER Gábor
2008-10-05 19:43 ` Miklos Vajna
2008-09-26 16:17 ` Jakub Narebski [this message]
2008-09-26 19:31 ` [PATCH] builtin-commit: avoid using reduce_heads() Miklos Vajna
2008-09-26 23:51 ` Jakub Narebski
2008-09-29 15:07 ` Miklos Vajna
2008-09-29 18:18 ` Miklos Vajna
2008-09-29 18:44 ` Jakub Narebski
2008-09-27 0:16 ` SZEDER Gábor
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