This repo contains code to combine multiple git repos into a single monolithic repo (a.k.a. a monorepo) while preserving full history, branches, and tags.

The contents of each sub-repo are incorporated with their original history (i.e. every commit to the original repo will exist in the new repo with the same SHA) and all branches and tags will be added, renamed to be prefixed by the name of the repo being added. So if the subrepo is foo.git and it contains a branch whatever, in the monorepo the SHA pointed to by the branch whatever in the original repo will now be pointed to by a branch named foo/whatever.

Additionally the contents of main branch from each sub-repo will be added in a subdirectory named for the sub-repo and merged to the monorepo’s main branch. (Or you can specify a different default branch as the second argument to the build script.)

To create a monorepo.

Make a file containing the git URLs of the repos you want to combine. These can be paths to bare repos (ideally created with git clone --mirror) or git@github.com: URLs. This file should be named something.repos where something is the name of the new monorepo you want to create.

Run ./build something.repos. It will create a directory named something and incorporate all the repos listed in the something.repos file.

After the monorepo is built, look for empty-repo.txt and no-branch.txt files in the subdirectories. These are created if the repo incorporated had either no changes (empty-repo.txt) or no main branch. In the latter case the no-branch.txt file will contain a list of the refs from the repo. If there’s an appropriate branch (say the repo used prod instead of main) you can fix things up with the pushdown script. In the monorepo remove the no-branch.txt and then run ./pushdown foo/prod to put the contents of the foo/prod branch into the foo subdirectory and merge them to main.

Pushing to GitHub

After you’ve built your monorepo, you’ll probably want to push it to GitHub. In the normal case you can probably just create a repo on GitHub and then do the normal:

git remote add origin git@github.com:<whatever>

Then to push everything:

git push --all origin
git push --tags origin

However, if you made a really big repo, you might get an error about pack files or something when you try to push. This probably means your repo is too big to push in one go. To get around that just push specific branches one at a time. Because your repo was built from smaller repos one good thing to try is pushing the original main branch from each sub repo. For example within the repo you could make a list of all the main branches (except the top-level main which would drag in almost everything at once) with this command.

git branch | grep main | cut -c 3- | egrep -v '^main$' > mains.txt

Then use the slow_push script to push one branch at a time:

cat mains.txt | ./slow_push

This might not push everything (if there were branches in the sub repos that never got merged to main) but it should get most things so that you can then do a:

git push --all origin

to push all the objects and branches.

If the git push --tags origin fails, you may need to push fewer tags at a time. Here’s a way to do that assuming you don’t already have files named tags.txt or starting with tags- in the root directory of you repo (which you shouldn`t if you just built it).

git tag --list > tags.txt
split -l 100 tags.txt tags-
for f in tags-*; do git push origin $(cat $f); done
rm tags-*
rm tags.txt