create-lts-pr.yml

name: Create LTS Promotion PR

on:
  push:
    branches: [main]
  workflow_dispatch:

concurrency:
  group: create-lts-pr
  cancel-in-progress: true

permissions:
  contents: read
  pull-requests: write

jobs:
  create-pr:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout main
        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6
        with:
          ref: main
          fetch-depth: 0

      - name: Fetch lts
        run: git fetch origin lts

      - name: Check content diff
        id: diff
        run: |
          if git diff --quiet origin/lts origin/main; then
            echo "No content difference between lts and main. Nothing to promote."
            echo "has_diff=false" >> "$GITHUB_OUTPUT"
          elif [ -z "$(git log origin/lts..origin/main --oneline)" ]; then
            echo "lts is ahead of or diverged from main with no commits to promote. Nothing to promote."
            echo "has_diff=false" >> "$GITHUB_OUTPUT"
          else
            echo "has_diff=true" >> "$GITHUB_OUTPUT"
          fi

      - name: Build commit list
        if: steps.diff.outputs.has_diff == 'true'
        id: commits
        run: |
          # Find the most-recent commit on main whose tree hash matches the current lts tree.
          # This is the anchor point from which we show only genuinely new commits, even after
          # squash-merge promotions (which lose individual commit provenance in lts history).
          LTS_TREE=$(git rev-parse origin/lts^{tree})
          ANCHOR=$(git log origin/main --format="%H %T" --max-count=500 \
            | awk -v t="$LTS_TREE" '$2==t{print $1; exit}')

          if [ -n "$ANCHOR" ]; then
            LIST=$(git log "${ANCHOR}..origin/main" --oneline)
          else
            # Fallback when the tree match isn't in recent history (e.g., first ever promotion).
            LIST=$(git diff --name-status origin/lts origin/main)
          fi

          {
            echo "list<<EOF"
            echo "$LIST"
            echo "EOF"
          } >> "$GITHUB_OUTPUT"

      - name: Create or update promote PR
        if: steps.diff.outputs.has_diff == 'true'
        env:
          GH_TOKEN: ${{ github.token }}
          COMMIT_LIST: ${{ steps.commits.outputs.list }}
        run: |
          # Build body with printf so commit messages containing quotes are safe
          BODY=$(printf '## Commits pending promotion to `lts`\n\n%s\n\n---\n_Squash-merge this PR to promote. The PR body updates automatically as `main` advances._\n' "${COMMIT_LIST}")

          EXISTING=$(gh pr list \
            --base lts \
            --head main \
            --state open \
            --json number \
            --jq '.[0].number' \
            2>/dev/null || echo "")

          if [ -n "$EXISTING" ]; then
            echo "Updating existing promote PR #${EXISTING}"
            printf '%s\n' "${BODY}" | gh pr edit "$EXISTING" --body-file -
          else
            echo "Creating new draft promote PR"
            printf '%s\n' "${BODY}" | gh pr create \
              --draft \
              --base lts \
              --head main \
              --title "promote: main → lts" \
              --body-file -
          fi