Potential fix for 4279

Author: lukeholder

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## Unreleased
 
+- Fixed a bug where `forgetCart()` was ineffective when `getCart()` was called later in the same request. ([#4279](https://github.com/craftcms/commerce/issues/4279))
 - Fixed a bug where variants weren’t being saved for product types with a Variant SKU Format that could cause duplicate SKUs. ([#4249](https://github.com/craftcms/commerce/issues/4249))
 - Fixed a PHP error that occurred when marking an inventory transfer as pending. ([#4267](https://github.com/craftcms/commerce/issues/4267))
 - Improved the performance of migrations when upgrading to 5.x. ([#4277](https://github.com/craftcms/commerce/issues/4277))

src/services/Carts.php

@@ -505,6 +505,11 @@ protected function loadCookie(): void
             $this->cartCookie['name'] = md5(sprintf('Craft.%s.%s.%s', self::class, Craft::$app->id, $currentStore->handle)) . '_commerce_cart';
         }
 
+        // Don't restore from cookie if the cart was explicitly forgotten this request.
+        if ($this->_cartNumber === false) {
+            return;
+        }
+
         $request = Craft::$app->getRequest();
         if (!$request->getIsConsoleRequest()) {
             $this->cartCookie = Craft::cookieConfig($this->cartCookie);