discount.php

 <?php
 
        craft()->on('commerce_discounts.onBeforeMatchLineItem', function ($event)
        {
            /** @var Commerce_LineItemModel $currentLineItem */
            $currentLineItem = $event['lineItem'];

            /** @var Purchasable $currentPurchasable */
            $currentPurchasable = $currentLineItem->getPurchasable();

            if ($currentPurchasable instanceof Commerce_VariantModel)
            {
                $order = $currentLineItem->getOrder();

                $otherPurchasablesIdsOrder = [];

                /** @var Commerce_LineItemModel $lineItem */
                foreach ($order->lineItems as $lineItem)
                {
                    $otherPurchasablesIdsOrder[] = $lineItem->purchasableId();
                }

                $relatedProducts = $currentPurchasable->relatedProductForBundle->find();

                foreach ($relatedProducts as $product)
                {
                    $relatedProductDefaultPurchasableIds[] = $product->defaultVariantId;
                }

                if (!empty($relatedProductDefaultPurchasableIds))
                {
                    $allOtherProductsAreInCart = count(array_intersect($relatedProductDefaultPurchasableIds, $otherPurchasablesIdsOrder)) == count($relatedProductDefaultPurchasableIds);

                    if (!$allOtherProductsAreInCart)
                    {
                        $event->performAction = false;
                    }
                }

            }
        });