GitHub Workflow to Sync Branches

Problem

I have a GitHub repository using main as the default branch, but I am trying to integrate a third party tool (loading JSFiddle contents from GitHub) that has master hardcoded as the default branch.

There is an issue in the tool, but stale bot has killed it.

Requirements

• Every push to main will also be applied to master.
• Both branches will share the same refs and tags.
• No workflows will execute on pushes to the master branch.
• No manual interaction is required (no pull requests).
• A maximum delay of only a few minutes.

Implementation

Below is a simple GitHub workflow that pushes main to master. The key option to be aware of is the fetch-depth for actions/checkout, which fetches all branches and tags for the repository. The default is to only get the current branch.

Only a single commit is fetched by default, for the ref/SHA that triggered the workflow. Set fetch-depth: 0 to fetch all history for all branches and tags. Refer here to learn which commit $GITHUB_SHA points to for different events.

# .github/workflows/push-to-master.yml
name: Push to Master
on:
  push:
    branches:
      - main
jobs:
  push:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
        with:
          fetch-depth: 0
      - name: Update master branch from main
        run: |
          git config --global user.name 'Justin Poehnelt'
          git config --global user.email 'jpoehnelt@users.noreply.github.com'
          git checkout master
          git reset --hard origin/main
          git push origin master

Depending on how you use GitHub workflows, you may also want to ignore the master branch. The following workflow will trigger on every branch except master using branches-ignore.

on:
  push:
    branches-ignore:
      - master