New 'view' option in taxonomy hook to add to display

Similar to the 'view' option in the _nodeapi hook, the attached small patch adds a 'view' option to the _taxonomy hook, enabling modules to add to the display when a taxonomy is being viewed.

While the existing _taxonomy hook responds to insert, update, and delete actions, it has no way to interact with taxonomy display. This is a significant limitation, as there are numerous cases in which responding to a taxonomy display might be needed.

Specifically, the current term display is limited to nodes, being composed of the following call:

      $output = taxonomy_render_nodes(taxonomy_select_nodes($tids, $operator, $depth, TRUE));

This patch simply puts a hook call before the node call, allowing insertion of prior content:

      $output = implode('', module_invoke_all('taxonomy', 'view', 'term', $tids));
      $output .= taxonomy_render_nodes(taxonomy_select_nodes($tids, $operator, $depth, TRUE));

An example of the patch in action:

function test_taxonomy  ($op, $type, $object) {
  switch($op) {
    case 'view':
      if (($type == 'term') && is_array($object) && (count($object) == 1)) {
        $count = taxonomy_term_count_nodes($object[0]);
        switch ($count) {
          case 0:
            $message = t('Sorry, there are no postings yet in this category.');
            break;
          case 1:
            $message = t('There is one posting in this category.');
            break;
          default:
            $message = t('There are %count postings in this category.', array('%count' => $count));
            break;
        }
        return '<p>' . $message . '</p>';
      }
      break;
  }
}

function test_node_name() {
  return("test");
}

When enabled with the proposed patch applied, this test.module will add text displayed between the page title and the node display of a taxonomy term. Only if there is a single term being viewed (count($object) == 1), the hook tests the number of nodes in the term and displays different messages for none, one, or more than one. Incidentally, I've taken this example from an identified need for messaging on empty terms, see issue at http://drupal.org/node/view/10279.

One current need for this functionality is the taxonomy_context module, which presents the description for a term being viewed and for its child terms. For lack of an available hook, in the 4.4 version this module used drupal_set_message() to render content between the page title and the node listings for a taxonomy. This approach led to problems, e.g., theme-specific ways of presenting messages. Having a hook available would be a much better solution. Taxonomy_context provides significant functionality and has a significant user base; this small addition to the taxonomy.module would enable seamless display in Drupal 4.5.

Other contexts in which adding to term information would be desirable include:

• Presenting additional information about the taxonomy, e.g., number of nodes.
• Presenting external information linked to a taxonomy. For example, I'm working on a module that will make statistical calculations on data linked to terms (specifically, for agricultural products, the average import distance). A 'view' option in the taxonomy hook would allow me to look up and present information from these other sources on the term being viewed.