Using git to merge two directories with common parent (but different SHA1)

Question

In our project somebody took a copy of the code. They started a new git repository in their directory and continued their work there. Meanwhile the work on our main project

Answer 1

First, I'm going to redraw your diagram.

A --- B --- C --- D  master

         E --- F --- G  copy

Let's first put both of these in the same repo. There are no special steps to this, you just git fetch both into the same repository.

Then you create a graft. Edit .git/info/grafts...

<E-sha1> <B-sha1>

Then run git filter-branch to make it permanent.

git filter-branch --tag-name-filter cat -- --all

This will create a new history, the "correct" history:

A --- B --- C --- D  master
        \
         E --- F --- G  copy

After that, you can just merge.

Demo in action

I created two repositories which matched the diagram, copying from commit B to make commit E.

• E has SHA-1 3aa6b69127d20ac42746c39be3c273a9d80fb706
• B has SHA-1 95b0fc836dbea7eaa0d043390df841d184af7cd5

$ git init
$ git remote add master ../gittest
$ git remote add copy ../gittest2
$ git fetch master
remote: Counting objects: 12, done.
remote: Compressing objects: 100% (7/7), done.
remote: Total 12 (delta 2), reused 0 (delta 0)
Unpacking objects: 100% (12/12), done.
From ../gittest
 * [new branch]      master     -> master/master
$ git checkout -b master master/master
Branch master set up to track remote branch master from master.
Already on 'master'
$ git fetch copy
warning: no common commits
remote: Counting objects: 9, done.
remote: Compressing objects: 100% (6/6), done.
remote: Total 9 (delta 0), reused 0 (delta 0)
Unpacking objects: 100% (9/9), done.
From ../gittest2
 * [new branch]      master     -> copy/master
$ git log --format=oneline copy/master | tail -n 1
3aa6b69127d20ac42746c39be3c273a9d80fb706 E
$ git log --format=oneline master/master
1532332fe705931babe9db04c8d84051867b52c9 D
90903c0ac8dc26649b875ee00ea39bfd7571b1fb C
95b0fc836dbea7eaa0d043390df841d184af7cd5 B
e9de90c82a32041cff3a19f8e40d4358bc4ec2ca Commit A
$ git log --format=oneline master/master
bec0e7af9374e4c57cb87f3fd5b2fb2b6a3f431b G
a61e01d096e81c36bcc450afd98ca94cff909622 F
3aa6b69127d20ac42746c39be3c273a9d80fb706 E

What happens if you merge now?

I got merge conflicts that I'd rather auto-resolve.

$ git merge copy/master
Auto-merging test.txt
CONFLICT (add/add): Merge conflict in test.txt
Automatic merge failed; fix conflicts and then commit the result.

Grafts in action

$ echo 3aa6b69127d20ac42746c39be3c273a9d80fb706 \
    95b0fc836dbea7eaa0d043390df841d184af7cd5 > .git/info/grafts
$ git filter-branch --tag-name-filter cat -- --all
Rewrite bec0e7af9374e4c57cb87f3fd5b2fb2b6a3f431b (7/7)
WARNING: Ref 'refs/heads/master' is unchanged
Ref 'refs/remotes/copy/master' was rewritten
WARNING: Ref 'refs/remotes/master/master' is unchanged
$ git merge copy/master
Auto-merging test.txt
Merge made by the 'recursive' strategy.
 test.txt |    5 +++++
 1 file changed, 5 insertions(+)

The final result

$ git log --graph --oneline | cat
*   4dadb0a Merge remote-tracking branch 'copy/master'
|\  
| * bb2fc85 G
| * be88bc5 F
| * 0816baf E
* | 1532332 D
* | 90903c0 C
|/  
* 95b0fc8 B
* e9de90c Commit A

Answer 2

Assume you are now in the repo include A---B---C---D.

You need first to add the other repo into this repo use the command.

$git remote add another_repo <git repo path>
$git fetch another_repo

Then you can merge, use

$git merge another_repo/master