add_action( 'woocommerce_before_add_to_cart_form', 'before_variation_form_hook', 10 );
add_action( 'woocommerce_product_meta_start', 'single_product_summary', 10 );

//untuk product instock
public function before_variation_form_hook(){
	$this->show_variation_form();
}

//untuk product outofstock
public function single_product_summary(){
	global $product;
	
	if ( ! $product->is_in_stock() ) {
		$this->show_variation_form();
	}
}