Re: The coolest merge EVER!

From: Linus Torvalds <torvalds@osdl.org>
Date: Jun 24, 2005, 19:22 UTC
Message-ID: <Pine.LNX.4.58.0506241211100.11175@ppc970.osdl.org>
In-Reply-To: <pan.2005.06.24.11.54.51.598627@smurf.noris.de>

On Fri, 24 Jun 2005, Matthias Urlichs wrote:

Show 8 quoted lines

> Hi, Junio C Hamano wrote:
> 
> > I suspect there
> > would be a massive additional support needed if you want to make it easy
> > for Paul to pull changes made to gitk in your tree.
> 
> I don't think that's possible; after all, the trees are now merged, so any
> pull would fetch all of Linus' tree.

No no.

A merge is a one-way thing. I merged Paul's tree, but Paul didn't merge mine. His is still independent, and you can still pull his tree without getting the rest of git, and Paul can still continue to work on his tree as if I never merged it at all.

Now, merging back isn't as easy: if any gitk changes get done in my "union" tree, Paul can't just pull those, becasue they now end up being linked to the history of the unified thing, so when pulling, he'd now end up getting all of the regular git stuff too.

Which is probably acceptable, but Junio's point was that this is not a symmetric setup: git is like a black hole that never lets any information escape, and once you've been sucked into a git archive, you end up not being able to separate it.

Or rather, you _can_ separate out pieces of it, but now it's a matter of cherry-picking, not automatic merges. Of course, people want to be able to do that anyway, and normally that will also merge back perfectly, so there's no huge downside, except that we should make it fairly easy.

		Linus