Subject: Re: Grafting mis-aligned trees.

From: "Boyd Stephen Smith Jr." <[email-masked]>
Date: Tue, 2 Dec 2008 11:19:46 -0600

On Tuesday 02 December 2008, Michael J Gruber <[email-masked]> 
wrote about 'Re: Grafting mis-aligned trees.':
>Boyd Stephen Smith Jr. venit, vidit, dixit 29.11.2008 00:01:
>> On Tuesday 2008 November 18 03:24, Michael J Gruber wrote:
>>> Boyd Stephen Smith Jr. venit, vidit, dixit 17.11.2008 23:45:
>>>> Trees look something like this right now.
>>>>
>>>> <some history> -> FT
>>>>
>>>> TI -> <non-linear history> -> A -> <non-linear history> -> C
>>>>    \                            \                           \
>>>>     -> PI ------------------------> B ------------------------> D
>>>>
>>>> I'd like to have it look something like:
>>>>
>>>> <some history> -> FT -> <non-linear history> -> A' -> <non-linear
>>>> history> -> C' \                            \                        
>>>>   \ -> PI' ----------------------> B' -----------------------> D'
>>>>
>>>> A', B', C', and D' are different commits, but the diff (and history)
>>>> between FT and A' is the same as the diff (and history) between TI
>>>> and A.
>>>
>>> So, your base directory for TI and FT is different, right? I.e.: In
>>> the TI repo, your project sits at the root, whereas in the FT repo it
>>> sits in project/web?
>>
>> Yes.
>>
>>> Has FT advanced since you took the initial subdir
>>> snapshot for TI?
>>
>> No.
>
>OK, here's a possibly primitive solution, but it works with my little
>toy model of your layout:

That sounds like it will work fine.  Thank you very much.

It does feel a bit "hacky", I was hoping git would have better support 
this, through the subtree merge or something else.  It seems like 
something that might happen to others, perhaps as a side-effect of a 
failed attempt at using submodules.

I can't help thinking that rebase -ip might have helped.  I wasn't aware 
of -p when I was initially working on this problem.  (It doesn't help that 
I generally use Debian stable, and git 1.4 did not have -p.)

>- filter-branch your TI branches so that they are in the proper subdir
>(you did that already)

If I need to "undo" this, it's really easy.

>- take a snapshot (say ftstuff.tar) of everything in FT's head (assuming
>this is where TI branched off, or else take that point) *but exclude
>project/web*
>
>- using filter-branch again, rewrite your TI branches to contain those
>missing FT files:
>git filter-branch --tree-filter 'tar -xf /tmp/ftstuff.tar && git add .'
>-f -- ti/master ti/whatever

I probably don't need the -f.  If there are files that should be ignored 
(and thus shouldn't be in the repo), I'll filter-branch to cut them out of 
the history at some point.

Now is as good a time as any.

>Now your TI branches produce the same diffs as before, but are based on
>the full tree. You can happily graft FT's head onto TI's root as a
> parent. In fact those two should produce no diff in between them, so you
> might as well get rid of one of them.

Makes sense.

>[cleaning out refs/original and repack -adf might be in order afterwards]

I generally do these after a successful filter-branch.

>The tree-filter part feels hacky but does the job (probably with -f). I
>don't think a subtree merge can do what you want.

What *exactly* is the subtree merge.  The documentation I've read sounds 
like this case, sort of, but it's rather unclear to me.
-- 
Boyd Stephen Smith Jr.                     ,= ,-_-. =. 
[email-masked]                      ((_/)o o(\_))
ICQ: 514984 YM/AIM: DaTwinkDaddy           `-'(. .)`-' 
http://iguanasuicide.org/                      \_/