Re: Automatic merge failed, fix up by hand

From: Linus Torvalds <torvalds@osdl.org>
Date: Aug 24, 2005, 00:48 UTC
Message-ID: <Pine.LNX.4.58.0508231733500.3317@g5.osdl.org>
In-Reply-To: <1124831571.13042.27.camel@firebird.lenb.worldpath.net>

On Tue, 23 Aug 2005, Len Brown wrote:

Show 6 quoted lines

>
> I'm having trouble using git for merging kernel trees.
> 
> git seems to manufacture conflicts in files that
> I never touched, and on some files it completely
> throws up its arms, see "Not handling case" below.

Cool.

You've found a case where git-merge-base finds what appears to be two equally good merge candidates, but they really aren't.

The merge candidates are 30e332f3307e9f7718490a706e5ce99f0d3a7b26 and 3edea4833a1efcd43e1dff082bc8001fdfe74b34.

To see this graphically, do:

	echo 30e332f3307e9f7718490a706e5ce99f0d3a7b26 > .git/refs/tags/selected-merge-base
	echo 3edea4833a1efcd43e1dff082bc8001fdfe74b34 > .git/refs/tags/other-merge-base

	echo 81065e2f415af6c028eac13f481fb9e60a0b487b > .git/refs/tags/linus-head
	echo 702c7e7626deeabb057b6f529167b65ec2eefbdb > .git/refs/tags/lenb-head

	gitk --all

and notice how the not-selected one is:

	Author: Antonino A. Daplas <adaplas@gmail.com>  2005-08-15 06:29:11
	Committer: Linus Torvalds <torvalds@g5.osdl.org>  2005-08-15 09:59:39
	Tags: not-selected

while the selected on is:

	Author: Luming Yu <luming.yu@intel.com>  2005-08-11 21:31:00
	Committer: Len Brown <len.brown@intel.com>  2005-08-15 12:46:58
	Tags: selected

and the reason we chose that one is that it's three hours later than the other one, and we don't know any better.

> Not clear how I got into this state -- probably
> something to do with adding commits on branches
> and them git-pull-branch'ing them into the master;
> combined with updating the master from-linus.

No, it's git.

Well, it's git, together with your propensity to merge old work, which causes this kind of confusion where there are two "equally good" points to choose from as the merge base, and git chose the wrong one because it _looked_ newer and there was a recent merge to an old version of my tree.

Cross-merges cause this, but I'm sure there's a good algorithm for selecting _which_ of the two interesting commits to pick.

Give me a moment to think about this.

		Linus