Subject: Re[2]: Merge two different repositories (v2.4 + v2.5) into the one (v2.4 -> v2.5). Possible?

From: Алексей Шумкин <[email-masked]>
Date: Tue, 11 Jan 2011 17:49:07 +0300

Hello, Jakub.

Thank you very much. Your method works great and it suits for me well

>> 1.5 years ago I had sources of a project in a SVN repository (actually it does not
>> matter what SCM was used before). And I had two branches: v2.4 and v2.5.
>> They differed enough at that moment and (as usual for SVN branches)
>> laid in two different folders.
>> Then I had known of Git and I decided to try to use this powerful DVCS.
>> But as I was a newbie I created two git-repositories: one per each
>> branch. So v2.4 has its own git-repo. v2.5 (and above) has another one.
>> 
>> Now I'd like to merge them as v2.5 was a continuos branch from v2.4,
>> but without a rebasing (i.e. without a global changing of v2.5
>> repository, which already has another branches)
>> It must look like LAST commit of v2.4 should be a PARENT of FIRST commit of v2.5
>> 
>> Now there's a question: Is it possible to do so (no rebasing!), and If
>> "yes" then how to?

JN> As Andreas Ericsson wrote, you can do this using grafts (and you can
JN> make history with grafts permanent using "git filter-branch").

JN> Better solution might be to use more modern replace mechanism, see
JN> e.g. "git replace" manpage.  Below there is untested step-by-step
JN> instruction.

JN> First, you have put history of v2.4 and of v2.5 in a single repository
JN> (e.g. using "git remote add").  Then you need to find FIRST commit of
JN> v2.5 among

JN>   $ git rev-list master --parents | grep -v ' '

JN> The above finds all parent-less commits in 'master' branch; replace it
JN> with branch holding v2.5 history.  Then you need to find LAST commit
JN> of v2.4 and its SHA-1, e.g. via

JN>   $ git rev-parse v2.4

JN> Save current state of FIRST commit of v2.5 to a file

JN>   $ git cat-file -p FIRST > tmp

JN> Edit this file, adding 'parent' line between 'tree' and 'author'
JN> headers, so the header of this file looks like the following:

JN>   tree 13d050266e05f7c66000240814199fcf3b559d43
JN>   parent ada9983c4256f5a7bac1f7f0e29d52011741d6aa
JN>   author Jakub Narebski <[email-masked]> 1294231771 +0100

JN> (trailing space added for better readibility).

JN> Then you need to add newly created object to repository:

JN>   $ git hash-object -t commit -w tmp

JN> and then use it as replacement

JN>   $ git replace <SHA-1 of FIRST> <SHA-1 returned by hash-object>

JN> Finally check that replacement works, e.g.:

JN>   $ git show FIRST
JN>   $ git log --graph --oneline -3 FIRST

JN> The anyone who would fetch refs/replace/ would get joined history, and
JN> who doesn't would see it not connected.

JN> P.S. This probably should made it into Documentation/howto