fix #3928 line item sale price calculation and discount “stop processing”

Author: nfourtythree

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Release Notes for Craft Commerce
 
+## Unreleased
+
+- Fixed a bug where a line item’s sale price could be incorrectly calculated. ([#3928](https://github.com/craftcms/commerce/issues/3928))
+
 ## 4.8.1.2 - 2025-02-10
 
 - Fixed a bug where carts’ adjustment totals could be calculated incorrectly. ([#3888](https://github.com/craftcms/commerce/issues/3888))

src/models/LineItem.php

@@ -610,10 +610,16 @@ public function populateFromPurchasable(PurchasableInterface $purchasable): void
         $ignoreSales = false;
         foreach (Plugin::getInstance()->getDiscounts()->getAllActiveDiscounts($this->getOrder()) as $discount) {
             if (Plugin::getInstance()->getDiscounts()->matchLineItem($this, $discount, true)) {
+                // Break if matched discount is set to ignore sales.
                 $ignoreSales = $discount->ignoreSales;
                 if ($ignoreSales) {
                     break;
                 }
+
+                // Break if matched discount is set to not apply any subsequent discounts.
+                if ($discount->stopProcessing) {
+                    break;
+                }
             }
         }