Search from paged page should reset to first page

[helgatheviking]

Ex: if you are on /directory/page/2 and you run a search, you should be sent back to /directory. The easiest way to do this is to make the form action equal to the permalink. This is what is used to be, but it was removed (I think to support custom $_GET params and maybe use as a widget). How to achieve this without changing the action?

Would want to redirect to page 1 when form is submitted, but not in cases where search results may legit span multiple pages.

Form $_POST ? pre_get_posts?

Sadly, this did not work:

function search_filter( $query ) {
  if ( isset( $_POST['as'] ) ) {
        $query->set( 'paged', 0 );
  }
}
add_action( 'pre_get_posts', 'search_filter' );