Re: [PATCH] A new merge stragety 'subtree'.

From: Shawn O. Pearce <spearce@spearce.org>
Date: Feb 17, 2007, 07:14 UTC
Message-ID: <20070217071425.GD27864@spearce.org>
In-Reply-To: <7vfy95y2n9.fsf@assigned-by-dhcp.cox.net>

Junio C Hamano <junkio@cox.net> wrote:

Show 15 quoted lines

> For normal merge strategies, if you are on branch A and merge
> branch B into it, what you will get is exactly the same as what
> you would get by merging branch A while being on branch A
> (modulo the direction of conflict markers).  With the subtree
> merge, it is not the case anymore.  If I pull from git-gui.git,
> the resulting tree look like git.git with Shawn's updates.  If
> Shawn pulls from git.git, even after I did some changes on my
> own to git-gui subdirectory, bypassing his tree, he will get a
> merged result pertaining to git-gui.git repository
> (i.e. git-gui/ subdirectory of what I have).  This way, we can
> continue merging from each other.
> 
> Although I do not plan to commit anything in git-gui/ part of my
> tree myself, bypassing Shawn, it is nice to know that it will
> not introduce problems down the road.

This does actually cause a problem if you merge a git.git commit into git-gui.git (by stripping the git-gui/ part off). The problem is the entire git.git history would then become the second parent of the git-gui.git merge commit, and suddenly the git-gui.git repository increases by >11 MiB in size... ;-)

With regards to maintaining git-gui: I'll apply all patches to my tree and do testing there, then ask Junio to merge a tagged release over to git.git for inclusion in the next git release.

To avoid pulling the entire git.git history into git-gui, I'd ask that anyone bypassing me (e.g. if I'm being horribly unresponsive one week) checkout the git-gui branch from git.git, apply the change(s) there, then merge that branch into git.git using the subtree strategy. This way I can later fast-forward git-gui.git to the fixed commit, without sucking in more than I bargained for.

For example:

	git log -n1 -- git-gui
	# copy the second parent...
	git checkout -b fixgg <secondparent>
	# do fixes...
	git checkout master
	git merge -s subtree fixgg

Then I can later obtain `fixgg` from the merge commit in git.git and update git-gui.git, without sucking in git.git's objects.

-- 
Shawn.