Merge a subdirectory of another repository with git
Here is me, doing yet another write-up of: merging a single directory of files from a remote repository into your current repository without loosing the history of commits on those files (otherwise a
git checkout would be enough).
Set up a test environment
Let's start with a simple test directory to allow us to play around:
rm -rf /tmp/merge mkdir /tmp/merge cd /tmp/merge git clone https://github.com/bneijt/autotrash.git git clone https://github.com/bneijt/ccbuild.git
Doing the merge
Now let's merge
ccbuild/src directory into the
First, let git know the other repo exists and what to name it:
cd /tmp/merge/autotrash git remote add ccbuild ../ccbuild
Note that we use the local file system as the remote, because we already have the files here, which makes everything faster.
Now fetch the information of our remote into the local .git directory
git fetch ccbuild
Set up a merge point between the two repositories, but don't perform the commit. Git will simulate the merge failed, meaning that we can then use the next command to copy only the right commits onto the merge we started:
git merge -s ours --no-commit ccbuild/master
Now read the commits about
ccbuild/master and place the files resulting from them under
git read-tree --prefix=ccbuildsrc -u ccbuild/master:src
Your working tree should now have a
ccbuildsrc directory. But the merge commit has not been done yet, the changes have only been read onto the current tree. Now we have to finalize with a merge commit:
The default commit message should mention "Merge remote-tracking...". If it does not, you probably forgot to mention you started a commit using the
git merge command above.
All seems well, but if you look in your git history, you will see the full commit log of the remote files and you will be able to see unrelated commits in the history. This should not really be a problem, but as the other history can be quite large, let's see how
git will allow use to solve this. Even though rewriting of history is almost always an optimization, it may a nice thing to do here.
Filter before merging
I've tried getting the
sub-tree, which should make this all look much nicer, but even
sudo apt-add-repository ppa:git-core/ppa sudo apt-get update sudo apt-get install git
Did not include the
subtree command because it's still in
contrib and not the main git reference. So here is the old approach. If you want to use the new approach, create a branch with git subtree and use that branch instead of master in the above example.
If you are not sure what you did earlier and don't know how to reset it all, create a new test environment as above.
We start by destroying the master branch on the
ccbuild project, by removing everything but the files in the subdirectory and creating a new history:
cd /tmp/merge/ccbuild git filter-branch --prune-empty --subdirectory-filter src --
Now all the files from the
src directory are in the top level directory of the
ccbuild repository. This means we no longer want to pull in the subdirectory, but the root into the prefix
cd /tmp/merge/autotrash git remote add ccbuild ../ccbuild git fetch ccbuild git merge -s ours --no-commit ccbuild/master git read-tree --prefix=ccbuildsrc -u ccbuild/master git commit
That's it. Then share your glory with a
Please note: never ever should you have to
--force anywhere in this process.