Fetch several branches locally in GitHub actions

Edited

Working on Open Terms Archive, I recently needed to fetch both the main branch and my current branch locally in order to make a programmatic git diff on a file.

Unfortunately, GitHub Actions only allows the local fetch of one branch at a time, and even though such a syntax:

- uses: actions/checkout@v2
  with:
    fetch-depth: 0 # fetch all history for all branches and tags
  fetchLocal: ["main"]

would have been great, it does not exist.

NOTE: fetch-depth: 0 will fetch all the branches and will make them available on remotes/origin/<branch> but my script used the local branch main so I had to map it locally

So here is how fetching 2 branches locally can be done:

Solution

Thanks to Matti

- uses: actions/checkout@v2
  with:
    fetch-depth: 0 # fetch all history for all branches and tags
- run: git branch main remotes/origin/main

Other workaround

I keep it here as it shows how to retrieve the current branch name on both push and pull_request events (which I did not see anywhere).
But you should definitely use the above solution

- name: Get branch name
  run: |
    if [ -z $GITHUB_HEAD_REF ]; then BRANCH=$GITHUB_REF_NAME; else BRANCH=$GITHUB_HEAD_REF; fi
    echo "BRANCH=$BRANCH" >> $GITHUB_ENV
- uses: actions/checkout@v2
  with:
    ref: main
    fetch-depth: 0 # fetch all history for all branches and tags
- run: git checkout --force -B $BRANCH refs/remotes/origin/$BRANCH

Conclusion

This way, both branches are available locally for the diff.

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