conflict-notifier.yml

name: Merge Conflict Notifier

on:
  schedule:
    - cron: '*/30 * * * *' # Hourly/half-hourly fallback
  push:
    branches:
      - main
  pull_request_target:
    types: [synchronize, reopened, edited]
  workflow_dispatch:

permissions:
  issues: write
  pull-requests: write

jobs:
  check-conflicts:
    runs-on: ubuntu-latest
    steps:
      - name: Check open PRs for merge conflicts
        uses: actions/github-script@v7
        with:
          script: |
            const label = 'needs-rebase';

            // Ensure the label exists in the repo
            try {
              await github.rest.issues.getLabel({
                owner: context.repo.owner,
                repo: context.repo.repo,
                name: label,
              });
            } catch {
              await github.rest.issues.createLabel({
                owner: context.repo.owner,
                repo: context.repo.repo,
                name: label,
                color: 'e11d48',
                description: 'This PR has merge conflicts and needs a rebase.',
              });
            }

            // Fetch all open PRs
            const { data: openPRs } = await github.rest.pulls.list({
              owner: context.repo.owner,
              repo: context.repo.repo,
              state: 'open',
              per_page: 100,
            });

            for (const pr of openPRs) {
              // GitHub computes `mergeable` lazily — fetch each PR individually with retries to trigger and wait for computation
              let fullPR = null;
              for (let attempt = 1; attempt <= 3; attempt++) {
                const { data } = await github.rest.pulls.get({
                  owner: context.repo.owner,
                  repo: context.repo.repo,
                  pull_number: pr.number,
                });
                fullPR = data;
                if (fullPR.mergeable !== null) {
                  break;
                }
                core.info(`PR #${pr.number}: mergeable is null, waiting 5 seconds (attempt ${attempt}/3)...`);
                await new Promise(resolve => setTimeout(resolve, 5000));
              }

              const isConflicting = fullPR.mergeable === false;
              const currentLabels = fullPR.labels.map(l => l.name);
              const alreadyLabeled = currentLabels.includes(label);

              if (isConflicting) {
                // Apply label if not already applied
                if (!alreadyLabeled) {
                  await github.rest.issues.addLabels({
                    owner: context.repo.owner,
                    repo: context.repo.repo,
                    issue_number: pr.number,
                    labels: [label],
                  });

                  // Post notification comment ONLY ONCE (when the label is first applied)
                  await github.rest.issues.createComment({
                    owner: context.repo.owner,
                    repo: context.repo.repo,
                    issue_number: pr.number,
                    body: `⚠️ Hey @${fullPR.user.login}, this PR has merge conflicts with the \`main\` branch.

            Please pull the latest changes and resolve the conflicts so we can review it!

            \`\`\`bash
            git fetch origin
            git rebase origin/main
            # resolve any conflicts, then:
            git push --force-with-lease
            \`\`\`

            Once resolved, the \`needs-rebase\` label will be removed automatically on the next check. 🙌`,
                  });
                }
              } else if (!isConflicting && alreadyLabeled) {
                // PR is no longer conflicting — remove the stale label
                await github.rest.issues.removeLabel({
                  owner: context.repo.owner,
                  repo: context.repo.repo,
                  issue_number: pr.number,
                  name: label,
                });
              }
            }