The filter doesn't generate id

Here my implementation. I use http://simplehtmldom.sourceforge.net/ instead of a regex. So you have to download it rename it "simple_html_dom.inc" and add in the module folder.

If you like this approach I can provide a patch.

/**
 * Implementation of hook_filter_info().
 */
function tableofcontents_filter_info() {
  module_load_include('admin.inc', 'tableofcontents');
  $filters['filter_toc'] = array(
    'title' => t('Table of contents'),
    'description' => t('Inserts a table of contents in place of [toc ...] tags.'),
    'process callback' => '_tableofcontents_process',
    'prepare callback' => '_tableofcontents_prepare',
    'settings callback' => '_tableofcontents_settings',
    'cache' => TRUE,
    'tips callback' => 'tableofcontents_filter_tips',
    );
  $filters['filter_toc_id'] = array(
    'title' => t('Assign an ID to each anchors'),
    'description' => t('Add an ID to all the anchors on the page. May be necessary in case the table of contents block is used.'),
    'process callback' => 'tableofcontents_filter_toc_id_process',
    //'settings callback' => '_tableofcontents_settings',
    'cache' => TRUE,
    'tips callback' => 'tableofcontents_filter_tips',
  );
  return $filters;
  }
/**
 * Filter toc_id
 * 
 * This is not really a hook. 
 * The function name is manually specified via 'process callback' in filter_info
 * 
 * Assign an ID to each anchors
 * 
 * @see tableofcontents_filter_info
 * 
 */
function tableofcontents_filter_toc_id_process($text, $filter, $format, $langcode, $cache, $cache_id) {
  if (empty($text)) {
    return '';
  }
  module_load_include('inc', 'tableofcontents', 'simple_html_dom');

  $html = str_get_html($text);

  $tags = array('h2', 'h3','h4'); //TODO make a settings
  
  foreach ($tags as $tag) {
    $matchs = $html->find($tag);
    foreach ($matchs as $match) {
      if (!$match->hasAttribute("id"))
        $match->id = drupal_html_id($match->innertext);
    }
  }

  return $html->save();
}

AlexisWilke I tried first to move the definition in the .module and make in include but the function fail in other part... I was faster for me to rewrite the filter instead of trying to debug the code. I move all in module because it was short and I want to avoid to load an other file (I use the other .inc but only for the toc block, and I forced the block to be cache by page)

I'm note sure is really useful to save the list of header because filter result are cached anyway. But we can store the result in a static variable so if the filter is called two time with the same text we return the static variable.

The big issue is than, we can't auto number the header like that and we can't create a multi level TOC. Perhaps with something like that to create a nested array of all the header and send this array to a theme function:

$headersLevel = array('h1'=>1,'h2'=>2,'h3'=>3);
foreach($html->find('h1, h2,h3,h4') as $header){
  if($headersLevel[$lastHeader->tag] == $headersLevel[$header->tag]){
  }else if($headersLevel[$lastHeader->tag] > $headersLevel[$header-tag]){
  }else{
 }
 $lastHeader = $header;
}

I have to think about that.