PR-into-next-version.yml

name: PR to merge into the next version

on:
  push:
    branches:
      - 'maintenance/mps*'

jobs:
  create-pr:
    runs-on: ubuntu-latest
    steps:
      - shell: bash
        env:
          GH_TOKEN: ${{ github.token }}
          owner_and_repo: ${{ github.repository }}
        run: |
          echo "Calculating PR branches:"

          # Next branch matching refs/heads/maintenance/* pattern, or empty if we're on the last one
          next_maintenance_branch=$(gh api "/repos/$owner_and_repo/git/matching-refs/heads/maintenance/mps" \
            --jq 'map(.ref | ltrimstr("refs/heads/") | select(. > "${{ github.ref_name }}" and . < "maintenance/mps3")) | min')
          echo "  Next maintenance branch: ${next_maintenance_branch:-(none)}"

          # Substitute the default branch if empty
          default_branch=${{ github.event.repository.default_branch }}
          base_branch=${next_maintenance_branch:-$default_branch}
          echo "  PR base branch: $base_branch"

          # Calculate PR head branch name (the branch to merge) by substituting 'maintenance' for 'merge'
          head_branch=${{ github.ref_name }}
          merge_branch=${head_branch/#maintenance/merge}
          echo "  Merge branch (will be used as PR head): $merge_branch"

          echo ""

          echo "Pushing ${{ github.ref_name }} to $merge_branch"

          # Create or update $merge_branch
          if gh api repos/$owner_and_repo/git/ref/heads/$merge_branch --silent
          then
            # Branch exists, merge $head_branch into it
            gh api repos/$owner_and_repo/merges --silent --method=POST -f base=$merge_branch -f head=$head_branch ||
              (echo "Merging $head_branch to existing $merge_branch failed, aborting." ; exit 1)
          else
            # Branch does not exist, create it from $head_branch
            gh api repos/$owner_and_repo/git/refs --silent --method=POST -f ref="refs/heads/$merge_branch" -f sha=${{ github.sha }} ||
              (echo "Could not create merge branch $merge_branch" ; exit 1)
          fi

          # Merge $base_branch -> $merge_branch, in order for $merge_branch to be up to date, as required by the branch
          # protection rules.

          # The head and base arguments are intentionally reversed because this is a reverse merge.
          gh api repos/$owner_and_repo/merges --silent --method=POST -f base=$merge_branch -f head=$base_branch ||
            echo "Updating $merge_branch from $base_branch failed, please do it manually."

          # Create PR if it does not exist yet
          existing_pr_url=$(gh pr list --repo $owner_and_repo --head $merge_branch --base $base_branch --json url --jq 'map(.url[]).[]')
          if [[ $existing_pr_url ]]
          then
            echo "Pull request $merge_branch -> $base_branch already exists at $existing_pr_url"
          else
            echo "Creating a new pull request $merge_branch -> $base_branch"
            gh pr create --repo $owner_and_repo --head $merge_branch --base $base_branch \
              --title "Merge ${{ github.ref_name }} into $base_branch" \
              --body "An automatic PR to merge changes from \`${{ github.ref_name }}\` to \`$base_branch\`." \
              --assignee '${{ github.actor }}' \
              --reviewer '${{ github.actor }}'
          fi