conflict-check.yaml

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#
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name: PR Merge Conflict Check

on:
  push:
    branches:
      - main
  workflow_dispatch: {}

permissions:
  contents: read

concurrency:
  group: ${{ github.workflow }}

jobs:

  conflicts:
    name: Check Open PRs for Conflicts
    runs-on: ubuntu-latest
    permissions:
      contents: read
      pull-requests: write
    timeout-minutes: 10
    steps:
      - name: Check Mergeable State
        uses: actions/github-script@ed597411d8f924073f98dfc5c65a23a2325f34cd  # v8.0.0
        with:
          script: |
            const label = 'needs-rebase';
            const { data: prs } = await github.rest.pulls.list({
              owner: context.repo.owner,
              repo: context.repo.repo,
              state: 'open',
              per_page: 100,
            });

            for (const pr of prs) {
              // Fetch full PR to get mergeable state
              const { data: full } = await github.rest.pulls.get({
                owner: context.repo.owner,
                repo: context.repo.repo,
                pull_number: pr.number,
              });

              const hasLabel = full.labels.some(l => l.name === label);

              if (full.mergeable === false) {
                if (!hasLabel) {
                  await github.rest.issues.addLabels({
                    owner: context.repo.owner,
                    repo: context.repo.repo,
                    issue_number: pr.number,
                    labels: [label],
                  });
                  await github.rest.issues.createComment({
                    owner: context.repo.owner,
                    repo: context.repo.repo,
                    issue_number: pr.number,
                    body: `@${pr.user.login} this PR now has merge conflicts with \`main\`. Please rebase to resolve them.`,
                  });
                }
              } else if (full.mergeable === true && hasLabel) {
                await github.rest.issues.removeLabel({
                  owner: context.repo.owner,
                  repo: context.repo.repo,
                  issue_number: pr.number,
                  name: label,
                });
              }
            }