Display only products on wordpress search results page

search_results_only_products.php

add_filter( 'pre_get_posts','mz_search_posts_per_page' );

// Alter search posts per page
function mz_search_posts_per_page($query) {
	if ( $query->is_search ) {
		$query->set( 'posts_per_page', '-1' );
		$query->set( 'post_type', 'product' );
	}
	return $query;
}