Parse Smarty template without triggering calls to user plugins - symfony

Question

I'm writing a (Symfony2) SmartyBundle extension to support Assetic.
To support the stylesheets feature I've registered a block plugin called stylesheets:
{stylesheets
assets='#SmartyBundle/Resources/public/css/*'
debug=true}
{$asset_url}
{/stylesheets}
This plugin gets called properly and everything work as expected when the Symfony/assetic cache is created.
The problem arises When the Symfony cache is empty and Assetic loads every template file resource and asks the template engine to retrieve a PHP array with the tokens found in the stylesheets tag. The class called to retrieve the array is SmartyFormulaLoader.
<?php
class SmartyFormulaLoader implements \Assetic\Factory\Loader\FormulaLoaderInterface
{
public function load(ResourceInterface $resource)
{
// raw template content
$content = $resource->getContent();
// a FileLoaderImportCircularReferenceException is throw here
$smartyParsed = $this->smarty->fetch('string: '.$content);
// build an array with tokens extracted from the block function
$formulae = $this->extractStylesheetsTokens($smartyParsed);
return $formulae;
}
When $smarty->fetch() is called in the load() method an exception is thrown: Symfony\Component\Config\Exception\FileLoaderImportCircularReferenceException: Circular reference detected in "." ("." > ".").
This is caused by the Smarty template being parsed/compiled and the stylesheets plugin being called again.
So I'm asking if Smarty provides a template parser that extracts the block function tokens (without calling the stylesheets plugin) so I can feed Assetic. Or any other solution that I may be missing to solve this.
Thanks.

Answer 1

After a little chat with Smarty dev #rodneyrehm we came to the conclusion that:
Should parse raw template source instead of compiling the template and parsing it
Should write my own parser (instead of using some Smarty internal helper)
So, for this particular case we came up with this implementation:
<?php
class SmartyFormulaLoader
{
public function load(ResourceInterface $resource)
{
// template source
$templateSource = $resource->getContent();
// ask Smarty which delimiters to use
$ldelim = $smarty->left_delimiter;
$rdelim = $smarty->right_delimiter;
$_ldelim = preg_quote($ldelim);
$_rdelim = preg_quote($rdelim);
// template block tags to look for
$tags = implode('|', array('stylesheets', 'javascripts', 'image));
// match every assetic tag
if (preg_match_all('#'.$_ldelim.'(?<type>'.$tags.').*?'.$_rdelim.'#s', $templateSource, $matches, PREG_SET_ORDER)) {
foreach ($matches as $match) {
// extract block attributes
if (preg_match_all('#(?<key>[a-zA-Z0-9_]+)\s*=\s*(["\']?)(?<value>[^\2]*?)\2(\s|'.$_rdelim.')#s', $match[0], $_matches, PREG_SET_ORDER)) {
$t = array(
'type' => $match['type'],
'attributes' => array(),
);
foreach ($_matches as $_match) {
if (empty($_match[2])) {
// make eval a little bit safer
preg_match('#[^\w|^\.]#', $_match['value'], $evalMatches);
$_match['value'] = ($evalMatches) ? null : eval(sprintf('return %s;', $_match['value']));
}
$t['attributes'][$_match['key']] = $_match['value'];
}
// call some Assetic methods with the extracted attributes
$formulae += $this->buildFormula($match['type'], $t['attributes']);
}
}
}
return $formulae;
}
}
Full implementation is available here: https://github.com/noiselabs/SmartyBundle/blob/master/Assetic/SmartyFormulaLoader.php