back-merge-main-to-develop.yaml

name: Back-merge main into develop

# back-merge-main-to-develop.yaml
#
# Purpose: After CI release-chore commits land on main (sync-packaging-version,
# readme stats, metainfo/debian regeneration, Crowdin), automatically merge
# main back into develop so the two branches never drift apart again.
#
# Trigger model:
#   - workflow_run: catches the chore workflows that push via GITHUB_TOKEN.
#     GitHub's "on: push" is NOT retriggered for GITHUB_TOKEN-authored pushes,
#     so we watch for those workflow runs completing instead.
#   - schedule (hourly): catch-all safety net for any drift source not enumerated
#     above (e.g. direct pushes from tools or future CI jobs not listed here).
#   - push: branches: [main]: covers human pushes promptly; harmless for
#     GITHUB_TOKEN-authored pushes (those are silently skipped by GitHub).
#   - workflow_dispatch: allows a manual run at any time.
#
# Loop safety: GITHUB_TOKEN-authored pushes do NOT retrigger workflow runs, so
# this job pushing to develop will never kick off another instance of itself.

on:
  workflow_run:
    workflows:
      - "Sync packaging version"
      - "Update README stats"
      - "Create GitHub Release"
      - "Crowdin Sync"
    types:
      - completed

  # Catch-all safety net: runs hourly to catch any drift source not covered
  # by the workflow_run triggers above (offset to avoid top-of-hour rush).
  schedule:
    - cron: '17 * * * *'

  workflow_dispatch:

  push:
    branches:
      - main

# Queue runs rather than cancel them, so back-merges land in order.
concurrency:
  group: back-merge-develop
  cancel-in-progress: false

permissions:
  contents: write

jobs:
  back-merge:
    runs-on: ubuntu-latest

    steps:
      - name: Checkout develop
        uses: actions/checkout@v4
        with:
          ref: develop
          fetch-depth: 0
          # Default GITHUB_TOKEN is fine; its pushes do not retrigger workflows.

      - name: Configure git identity
        run: |
          git config user.name  "github-actions[bot]"
          git config user.email "github-actions[bot]@users.noreply.github.com"

      - name: Merge main into develop and push
        run: |
          git fetch origin main

          if git merge --no-edit --no-ff origin/main; then
            # Merge succeeded — check whether there is actually anything new to push.
            if git diff --quiet origin/develop..HEAD; then
              echo "develop already up to date with main — nothing to push."
            else
              git push origin develop
            fi
          else
            echo "::error::Automatic back-merge of main into develop hit a conflict — resolve manually."
            git merge --abort || true
            exit 1
          fi