check-merge-conflicts.yml

name: Check Merge Conflicts

on:
  pull_request:
    types: [opened, synchronize, reopened]

jobs:
  check-merge-conflicts:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout code
        uses: actions/checkout@v4
        with:
          fetch-depth: 0

      - name: Check if PR is against main branch
        id: check-target-branch
        run: |
          TARGET_BRANCH="${{ github.base_ref }}"
          if [[ "$TARGET_BRANCH" == "main" ]]; then
            echo "PR is against main branch, no need to check for conflicts"
            echo "is_main=true" >> $GITHUB_OUTPUT
          else
            echo "PR is not against main branch, will check for conflicts"
            echo "is_main=false" >> $GITHUB_OUTPUT
          fi

      - name: Check for merge conflicts with main
        if: steps.check-target-branch.outputs.is_main == 'false'
        id: check-conflicts
        run: |

          # Set Git identity for the merge operation
          git config --global user.email "github-actions@github.com"
          git config --global user.name "GitHub Actions"

          # Fetch main branch
          git fetch origin main:main

          # Try to merge main into the current branch
          MERGE_EXIT_CODE=0
          git merge main --no-commit --no-ff || MERGE_EXIT_CODE=$?

          if [ $MERGE_EXIT_CODE -eq 0 ]; then
            echo "No merge conflicts detected"
            # Abort the merge since we're just checking
            git merge --abort || true  # Don't fail if there's nothing to abort
          else
            echo "Merge conflicts detected!"
            # Abort the merge
            git merge --abort || true  # Don't fail if there's nothing to abort
            echo "::error::This branch has merge conflicts with main. Please pull from main and rebase your branch before creating a PR."
            exit 1
          fi

      - name: Success message
        if: success()
        run: echo "No merge conflicts detected or PR is against main branch"