In some cases, we want to share just one folder of a private project with external collaborators.

The constraints are as follows:

• external collaborators should be able to access modifications to the subdirectory in real-time (as soon as the files are modified in the main project repository)
• we don’t want to add extra work for the primary project maintainers (i.e., no additional commands to push to another repo)
• we don’t want external collaborators to access the rest of the project

To give context to the tutorial, let’s suppose we want to share the tests folder of our project while keeping the rest private.

Git Submodules ❌

To adhere to the second constraint, we won’t use Git Submodules, for example. That would involve creating a repository that contains the tests folder, then configuring Git in our main repository to say “this tests folder, get it from this repository” using the command git submodule add <URL-of-the-tests-repository> tests.

Problem: it requires using git pull --recurse-submodules and ensuring you’re well within the submodule folder to commit and push. In short, a hassle we want to avoid.

GitHub Actions ✅

To solve this problem, we will use GitHub Actions and two repositories, one for the main (private) project and one for sharing the tests (shared with external collaborators).

Step 1: Create a P.A.T

We will need to create a Personal Access Token for our GitHub Actions.

Note for organizations: if you work with repositories in an organization, you need to go to Organization Settings then Personal Access Tokens then Settings, and check Allow access via fine-grained personal access tokens. When creating the P.A.T you need to set the Resource Owner as the organization.

Select Repository > Contents > Read and Write as permissions.

In both repositories, you’ll need to add the P.A.T as Secrets for the Actions (named PAT).

Step 2: Create the Action on the Tests Repository

On the tests repository, we will create an action with the following functionality:

• when I receive a web request,
• clone the main repository
• clone the tests repository
• copy the tests folder from the main repository into the tests repository
• commit and push

Here’s what the code looks like:

name: Sync Specific Folder

on: 
  repository_dispatch:
    types:
      - webhook

jobs:
  sync-folder:
    runs-on: ubuntu-latest
    steps:

      - name: Checkout Test Repository
        uses: actions/checkout@v3
        with:
          path: 'shared-tests'
    
      - name: Checkout Main Repository
        uses: actions/checkout@v3
        with:
          repository: 'Androz2091/main-project'
          token: ${{ secrets.PAT }}
          path: 'main-project'

      - name: Configure Git
        run: |
          git config --global user.email "bot@androz2091.fr"
          git config --global user.name "Syncer"

      - name: Sync Changes to Specific Folder
        run: |
          cd shared-tests
          cp -R ../main-project/tests/* .
          git add .
          git commit -m "Add tests"
          git push https://androz2091:${{ secrets.PAT }}@github.com/Androz2091/shared-tests.git HEAD:master

• The main repo’s URL is Androz2091/main-project
• The tests one is Androz2091/shared-tests

Step 3: Create the Action on the Main Repository

The action on the main repository is very simple:

• when I push,
• make a web request to the action on the tests repo

name: Trigger Tests Synchronization

on: [push]

jobs:
  http_request_job:
    runs-on: ubuntu-latest
    steps:
    - name: Checkout code
      uses: actions/checkout@v2
      
    - name: Send webhook
      run: |
        curl -X POST -H "Authorization: Bearer ${{ secrets.PAT }}" -H "Content-Type: application/json" -d '{"event_type":"webhook"}' https://api.github.com/repos/Androz2091/shared-tests/dispatches

And there you go! On GitLab, the procedure is similar. They’ve even written a tutorial for migrating your GitHub Actions to GitLab.