Re: [1/5] Parsing code in revision.h

From: Daniel Barkalow <barkalow@iabervon.org>
Date: Apr 17, 2005, 20:22 UTC
Message-ID: <Pine.LNX.4.21.0504171608070.30848-100000@iabervon.org>
In-Reply-To: <Pine.LNX.4.58.0504171254500.7211@ppc970.osdl.org>

On Sun, 17 Apr 2005, Linus Torvalds wrote:

Show 36 quoted lines

> On Sun, 17 Apr 2005, Linus Torvalds wrote:
> > 
> > Yes. I'm not opposed to yours, I was just opposed to some of the things 
> > around it you did, so I wrote mine as a kind of place-holder. I'll happily 
> > take patches to turn it from a rally simple and stupid one into a more 
> > polished version.
> 
> Btw, before I forget - I did have another reason. I actually think that
> the date is potentially a lot more important than "how many parents deep".
> 
> In particular, it's entirely possible that the top of my head might be a
> veru recent merge that merges with a small fix relative to a very old
> parent (making that old parent be just two hops away from the head), while
> the thing I want to merge might also have that old parent (for similar
> reasons) as a relatively "close" parent from a pure link-counting
> standpoint.
> 
> The reason I bring this up is that quite often people end up basing their
> work on a specific release version, so a merge (especially in specialized
> areas) may thus bring such an old parent pretty close to the head, and it
> can actually be quite possible (indeed probable) that such a parent ends
> up being a common parent.
> 
> However, it can easily be a very _bad_ parent.
> 
> In ascii barfic:
> 
> 	        ----------------------- patch ---------
> 	       /                                        \
> 	      /                                          \
> 	- old release -- ... lots of development .. -----HEAD
> 	     \  \                 /
> 	      \  \               /
> 	       \  --------------/------patch-- MERGE-HEAD      
> 	        \              /              /
> 		  .. lots of development ..  /

(I added a merge line so there's another commit to discuss in the picture)

Show 9 quoted lines

> it looks like "old release" is pretty close to both HEAD and MERGE-HEAD, 
> right?
> 
> But that's just an artifact of the fact that they both had a trivial merge
> against some older code, and if the two "lots of development" things have
> ever done an earlier merge, there's quite possibly a _much_ better common
> parent there somewhere.
> 
> I dunno.

I think you're going to want multiple common ancestors being used in the merge when this thing starts to happen; otherwise, you're going to have to fix up conflicts for "patch" for all the trees you pull. (Also, you're only going to see a parent for patch (that is, the old revision as an ancestor of the application of patch) if the trees are merging it in via git, in which case you'll also see a commit for patch, which will have a recent date. So you'd see "just yesterday, we both merged a tiny change; so that tree, which is very much like an ancient one, is more recent that last weeks major merge".

I dunno either, but I hope we'll have 2+n-way-merge before there's a lot of complex history to deal with.

	-Daniel
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