WordPress: Mandatory Excerpt

gistfile1.aw

<?

function mandatory_excerpt($data) {
  $excerpt = $data['post_excerpt'];

  if (empty($excerpt)) {
    if ($data['post_status'] === 'publish') {
      add_filter('redirect_post_location', 'excerpt_error_message_redirect', '99');
    }

    $data['post_status'] = 'draft';
  }

  return $data;
}

add_filter('wp_insert_post_data', 'mandatory_excerpt');

function excerpt_error_message_redirect($location) {
  remove_filter('redirect_post_location', __FILTER__, '99');
  return add_query_arg('excerpt_required', 1, $location);
}

function excerpt_admin_notice() {
  if (!isset($_GET['excerpt_required'])) return;

  switch (absint($_GET['excerpt_required'])) {
    case 1:
      $message = 'Excerpt is required to publish a post.';
      break;
    default:
      $message = 'Unexpected error';
  }

  echo '<div id="notice" class="error"><p>' . $message . '</p></div>';
}

add_action('admin_notices', 'excerpt_admin_notice');

If you want to only have this happen on a specific post type you can use some logic:

if (empty($data['post_excerpt']) && $data['post_type']=='post') {

changing 'post' to whatever post type you wish.

I do really love you guys. I know closely none PHP and I needed this for a freelance project!!
I owe you'all one!

The code works as expected on posts, but there is an issue with menu. Somehow, after updating a menu, the menu items get marked as pending. Removing your code fixed the issue.