feat: add workflow that automatically pulls upstream

.github/workflows/pull-upstream.yml

@@ -0,0 +1,91 @@
+on:
+  schedule:
+    - cron: "10 10 * * *" # This gives mirror sync, which runs at 9:57, some time to complete.
+  workflow_dispatch: {}
+
+permissions:
+  contents: write
+  pull-requests: write
+
+env:
+  upstream: "https://github.com/mage-os/mirror-magento2.git"
+
+jobs:
+  pull-upstream:
+    name: "Pull Upstream"
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        # We might support other branches in the future.
+        branch: [ '2.4-develop' ]
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+        with:
+          ref: ${{ matrix.branch }}
+          fetch-depth: 0
+
+      # If there is already a 2.x-develop-upstream branch, we're in the process of handling a conflict.
+      # Skip any subsequent steps.
+      - name: Check if we're already resolving conflicts
+        run: "! git ls-remote --exit-code origin ${{ matrix.branch }}-upstream"
+
+      # Add the upstream remote, in normal circumstances this will be mirror-magento2.
+      - name: Set upstream
+        run: git remote add upstream ${{ env.upstream }}
+
+      # These settings are required for the merge commit.
+      - name: Configure git
+        run: |
+          git config user.email info@mage-os.org
+          git config user.name "Mage-OS"
+
+      # Instead of doing a git pull, we do a fetch followed by a merge.
+      # This is functionally equivalent, but allows us to capture the output of the merge specifically.
+      - name: Attempt merge
+        id: merge
+        run: |
+          git fetch upstream ${{ matrix.branch }}
+          git merge --no-edit FETCH_HEAD 2>&1 | tee merge.log
+          result_code=${PIPESTATUS[0]}
+          echo "::set-output name=merge::$(cat merge.log)"
+          exit $result_code
+
+      # When merge succeeds, simply push to the original branch.
+      # If an upstream branch exists, we'll delete it.
+      - name: Push
+        run: |
+          git push origin ${{ matrix.branch }}
+          git push --delete origin ${{ matrix.branch }}-upstream || true
+
+      # If the merge failed, checkout the upstream branch and push it to our repo.
+      - name: Create Upstream Branch
+        id: create_branch
+        if: failure() && steps.merge.outcome == 'failure'
+        run: |
+          git merge --abort
+          git checkout -b ${{ matrix.branch }}-upstream FETCH_HEAD
+          git push --set-upstream --force origin ${{ matrix.branch }}-upstream
+          git remote remove upstream
+
+      # If the merge failed, and we successfully created an upstream branch, create a pull request.
+      - name: Create Pull Request
+        id: create_pr
+        if: failure() && steps.merge.outcome == 'failure' && steps.create_branch.outcome == 'success'
+        uses: devops-infra/action-pull-request@v0.5.0
+        with:
+          draft: true
+          title: "Upstream Merge Conflict (${{ matrix.branch }})"
+          body: "This PR was automatically generated: a human is required.\n\n${{ steps.merge.outputs.merge }}"
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          source_branch: ${{ matrix.branch }}-upstream
+          target_branch: ${{ matrix.branch }}
+
+      # If the merge failed, and we successfully created a PR, send a message to discord.
+      - name: Notify Discord
+        if: failure() && steps.merge.outcome == 'failure' && steps.create_pr.outcome == 'success'
+        uses: Ilshidur/action-discord@master
+        env:
+          DISCORD_WEBHOOK: ${{ secrets.DISCORD_WEBHOOK }}
+          DISCORD_USERNAME: "Mage-OS"
+          DISCORD_EMBEDS: '[{"title": "Upstream Merge Conflict", "description": "Pull Request: ${{ steps.create_pr.outputs.url }}\nAction: ${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }}\n\nConflicts:\n ${{ steps.merge.outputs.merge }}"}]'