Fixed object subtotal retrieved in Discounts class for orders when prices include tax

plugins/woocommerce/includes/abstracts/abstract-wc-order.php

@@ -445,6 +445,16 @@ abstract class WC_Abstract_Order extends WC_Abstract_Legacy_Order {
 		return apply_filters( 'woocommerce_order_get_subtotal', (float) $subtotal, $this );
 	}
 
+	/**
+	 * Gets order subtotal tax.
+	 *
+	 * @return float
+	 */
+	public function get_subtotal_tax() {
+		$subtotal = NumberUtil::round( $this->get_cart_subtotal_tax_for_order(), wc_get_price_decimals() );
+		return apply_filters( 'woocommerce_order_get_subtotal_tax', (float) $subtotal, $this );
+	}
+
 	/**
 	 * Get taxes, merged by code, formatted ready for output.
 	 *
@@ -1695,6 +1705,19 @@ abstract class WC_Abstract_Order extends WC_Abstract_Legacy_Order {
 			)
 		);
 	}
+	/**
+	 * Helper function.
+	 * If you add all items in this order in cart again, this would be the cart subtotal tax (assuming all other settings are same).
+	 *
+	 * @return float Cart subtotal tax.
+	 */
+	protected function get_cart_subtotal_tax_for_order() {
+		return wc_remove_number_precision(
+			$this->get_rounded_items_total(
+				$this->get_values_for_total( 'subtotal_tax' )
+			)
+		);
+	}
 
 	/**
 	 * Helper function.

plugins/woocommerce/includes/class-wc-discounts.php

@@ -948,7 +948,7 @@ class WC_Discounts {
 
 			if ( $this->object->get_prices_include_tax() ) {
 				// Add tax to tax-exclusive subtotal.
-				$subtotal = $subtotal + wc_add_number_precision( NumberUtil::round( $this->object->get_total_tax(), wc_get_price_decimals() ) );
+				$subtotal = $subtotal + wc_add_number_precision( NumberUtil::round( $this->object->get_subtotal_tax(), wc_get_price_decimals() ) );
 			}
 
 			return $subtotal;