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Created September 25, 2017 13:26
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Forking a single package in a monorepo
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README.md

Forking a single package in a monorepo

The trend of using monorepos makes a lot of things easier to manage. However, when you want to fork a single package inside a monorepo, you'll have to chose one of two options:

  • Fork the entire monorepo (meaning you get all those extra boilerplate you don't really care about)
  • Manually copying the package files into a new git repo (meaning you'll loose all git history and have a lot of work to do when there's a new version of your base package)

The good news: There's a solution for this! And it's actually built in to git.

git subtree

One of the lesser-known (and vaguely documented) features of git is subtree. It's intended for this purpose, working as a great alternative to the criticized submodules. There are very few resources about using this in practice, so here's a guide for this specific use case.

Set up

In this example we want to fork react-scripts out of the create-react-app monorepo.

Setting up the monorepo

  1. Start out by cloning the repo: git clone git@github.com:facebookincubator/create-react-app.git.
  2. cd create-react-app
  3. Check out the branch/version tag you want to fork from: git checkout v1.0.13
  4. Create a new branch representing just the package we want (react-scripts): git subtree split -P packages/react-scripts -b react-scripts-v1.0.13

Add to your repo

  1. Change into your repository: cd my-repo
  2. Add the monorepo fork as a new remote: git remote add react-scripts-source ../create-react-app
  3. Add react-scripts to your project (in the directory you specify): git subtree add -P path/to/react-scripts/in/your/repo react-scripts-source react-scripts-v1.0.13 --squash

Updating the package

  1. Create a new branch representing the new version (see step 4 of Setting up the monorepo), e.g. git checkout master && git subtree split -P packages/react-scripts -b react-scripts-master.
  2. In your own repo, use git subtree pull to merge the changes: git subtree pull -P path/to/react-scripts/in/your/repo react-scripts-source react-scripts-master --squash

Using --squash or not?

When we add --squash to the command (as suggested), it means that all the commits done to the original package will be squashed into a single commit when merging into your own repo. This means that your git log will only show whatever commits you've made in the repo, a squash commit showing what commits where squashed into one + a merge commit whenever you merge.

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