Scheduled-Dependabot-PRs-Auto-Merge.yml

# ------------------------------------------------------------------------------
# Scheduled Dependabot PRs Auto-Merge Workflow
#
# Purpose:
#   - Automatically detect, rebase (if needed), and merge Dependabot PRs targeting
#     the `dependabotchanges` branch, supporting different merge strategies.
#
# Features:
#   ✅ Filters PRs authored by Dependabot and targets the specific base branch
#   ✅ Rebases PRs with conflicts and auto-resolves using "prefer-theirs" strategy
#   ✅ Attempts all three merge strategies: merge, squash, rebase (first success wins)
#   ✅ Handles errors gracefully, logs clearly
#
# Triggers:
#   - Scheduled daily run (midnight UTC)
#   - Manual trigger (via GitHub UI)
#
# Required Permissions:
#   - contents: write
#   - pull-requests: write
# ------------------------------------------------------------------------------

name: Scheduled Dependabot PRs Auto-Merge

on:
  schedule:
    - cron: '0 0 * * *'  # Runs once a day at midnight UTC
  workflow_dispatch:

permissions:
  contents: write
  pull-requests: write

jobs:
  merge-dependabot:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout repository
        uses: actions/checkout@v4

      - name: Install GitHub CLI
        run: |
          sudo apt update
          sudo apt install -y gh
      - name: Fetch & Filter Dependabot PRs
        env:
          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
        run: |
          echo "🔍 Fetching all Dependabot PRs targeting 'dependabotchanges'..."
          > matched_prs.txt
          pr_batch=$(gh pr list --state open --json number,title,author,baseRefName,url \
            --jq '.[] | "\(.number)|\(.title)|\(.author.login)|\(.baseRefName)|\(.url)"')
          while IFS='|' read -r number title author base url; do
            author=$(echo "$author" | xargs)
            base=$(echo "$base" | xargs)
            if [[ "$author" == "app/dependabot" && "$base" == "dependabotchanges" ]]; then
              echo "$url" >> matched_prs.txt
              echo "✅ Matched PR #$number - $title"
            else
              echo "❌ Skipped PR #$number - $title (Author: $author, Base: $base)"
            fi
          done <<< "$pr_batch"
          echo "👉 Matched PRs:"
          cat matched_prs.txt || echo "None"
      - name: Rebase PR if Conflicts Exist
        if: success()
        env:
          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
        run: |
          if [[ ! -s matched_prs.txt ]]; then
            echo "⚠️ No matching PRs to process."
            exit 0
          fi
          while IFS= read -r pr_url; do
            pr_number=$(basename "$pr_url")
            echo "🔁 Checking PR #$pr_number for conflicts..."
            mergeable=$(gh pr view "$pr_number" --json mergeable --jq '.mergeable')
            if [[ "$mergeable" == "CONFLICTING" ]]; then
              echo "⚠️ Merge conflicts detected. Performing manual rebase for PR #$pr_number..."
              head_branch=$(gh pr view "$pr_number" --json headRefName --jq '.headRefName')
              base_branch=$(gh pr view "$pr_number" --json baseRefName --jq '.baseRefName')
              git fetch origin "$base_branch":"$base_branch"
              git fetch origin "$head_branch":"$head_branch"
              git checkout "$head_branch"
              git config user.name "github-actions"
              git config user.email "action@github.com"
              # Attempt rebase with 'theirs' strategy
              if git rebase --strategy=recursive -X theirs "$base_branch"; then
                echo "✅ Rebase successful. Pushing..."
                git push origin "$head_branch" --force
              else
                echo "❌ Rebase failed. Aborting..."
                git rebase --abort || true
              fi
            else
              echo "✅ PR #$pr_number is mergeable. Skipping rebase."
            fi
          done < matched_prs.txt
          
      - name: Auto-Merge PRs using available strategy
        if: success()
        env:
          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
        run: |
          if [[ ! -s matched_prs.txt ]]; then
            echo "⚠️ No matching PRs to process."
            exit 0
          fi
          while IFS= read -r pr_url; do
            pr_number=$(basename "$pr_url")
            echo "🔍 Checking mergeability for PR #$pr_number"
            attempt=0
            max_attempts=8
            mergeable=""
            sleep 5  # Let GitHub calculate mergeable status
            while [[ $attempt -lt $max_attempts ]]; do
              mergeable=$(gh pr view "$pr_number" --json mergeable --jq '.mergeable' 2>/dev/null || echo "UNKNOWN")
              echo "🔁 Attempt $((attempt+1))/$max_attempts: mergeable=$mergeable"
              if [[ "$mergeable" == "MERGEABLE" ]]; then
                success=0
                for strategy in rebase squash merge; do
                  echo "🚀 Trying to auto-merge PR #$pr_number using '$strategy' strategy..."
                  set -x
                  merge_output=$(gh pr merge --auto --"$strategy" "$pr_url" 2>&1)
                  merge_status=$?
                  set +x
                  echo "$merge_output"
                  if [[ $merge_status -eq 0 ]]; then
                    echo "✅ Auto-merge succeeded using '$strategy'."
                    success=1
                    break
                  else
                    echo "❌ Auto-merge failed using '$strategy'. Trying next strategy..."
                  fi
                done
                if [[ $success -eq 0 ]]; then
                  echo "❌ All merge strategies failed for PR #$pr_number"
                fi
                break
              elif [[ "$mergeable" == "CONFLICTING" ]]; then
                echo "❌ Cannot merge due to conflicts. Skipping PR #$pr_number"
                break
              else
                echo "🕒 Waiting for GitHub to determine mergeable status..."
                sleep 15
              fi
              ((attempt++))
            done
            if [[ "$mergeable" != "MERGEABLE" && "$mergeable" != "CONFLICTING" ]]; then
              echo "❌ Mergeability undetermined after $max_attempts attempts. Skipping PR #$pr_number"
            fi
          done < matched_prs.txt || echo "⚠️ Completed loop with some errors, but continuing gracefully."