$form->getWidgetSchema()->setFormFormatterName('list');

The question is, “where do you put this to alter sfGuard’s login form?”

In the case of sfGuard you just need to create a new folder under apps/frontend/modules/ (replace frontend with your app name) called sfGuardAuth, in this you create a folder called actions, and within this again a file called actions.class.php.

apps/
-frontend/
--modules/
---sfGuardAuth/
----actions/
-----actions.class.php

Inside the actions.class.php file you put this:

<?php
    require_once sfConfig::get('sf_plugins_dir').
    '/sfGuardDoctrinePlugin/modules/sfGuardAuth/lib/BasesfGuardAuthActions.class.php';

/**
* Extend to use list schema formatter
*/
class sfGuardAuthActions extends BasesfGuardAuthActions
{
    public function executeSignin($request)
    {
        parent::executeSignin($request);
        $this->form->getWidgetSchema()->setFormFormatterName('List');
    }
}
?>

We manually include BasesfGuardAuthActions.class.php because symfony’s black magic autoloader doesn’t pick this up. Voila. Nice and easy!

If you wanna make your completely own sfWidgetFormSchemaFormatter you can read about it over at notjosh’s blog.