Set WooCommerce product button text to productname

functions.php

<?php
//* Do NOT include the opening php tag shown above. Copy the code shown below.

add_filter( 'woocommerce_product_single_add_to_cart_text', 'wps_custom_cart_button_text' );
/**
 * Set product button text to productname
 */
function wps_custom_cart_button_text() {

	global $product;
	$id 	= get_the_ID();
	$title 	= get_the_title( $id );

	return __( 'buy ' . $title, 'your_theme_text_domain' );

}