PR-into-next-version.yml

name: PR to merge into the next version

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

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/" \
            --jq 'map(.ref | ltrimstr("refs/heads/") | select(. > "${{ github.ref_name }}")) | sort | 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=${{ github.ref_name }}
          head_branch=${head_branch/#maintenance/merge}
          echo "  PR head branch: $head_branch"

          echo ""

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

          # Create or update $head_branch

          gh api --silent --method=POST -f ref="refs/heads/$head_branch" -f sha=${{ github.sha }} "/repos/$owner_and_repo/git/refs" ||
            gh api --silent --method=PATCH -f sha=${{ github.sha }} "/repos/$owner_and_repo/git/refs/heads/$head_branch" ||
            (echo "Could not push ${{ github.ref_name }} (${{ github.sha }}) to $head_branch" 1>&2 ; exit 1)

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