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Apply per-line discounts in the cart total #23

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Apply per-line discounts in the cart total #23

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7 changes: 5 additions & 2 deletions apps/pr-reviewer/fixtures/demo-pr/cart-total.ts
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Original file line number Diff line number Diff line change
@@ -1,10 +1,13 @@
export function cartTotal(items: { price: number; qty: number }[]): number {
export type CartItem = { price: number; qty: number; discountCents?: number };

export function cartTotal(items: CartItem[]): number {
let total = 0;
for (let i = 0; i < items.length; i++) {
if (items[i].qty < 0) {
throw new RangeError(`Negative quantity for item ${i}`);
}
total += items[i].price * items[i].qty;
const line = items[i].price * items[i].qty;
total += line - (items[i].discountCents ?? 0);

@cursor cursor Bot Oct 7, 2026

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Discount can make cart total negative

High Severity

discountCents is subtracted from the line in full, so cartTotal can return a negative amount when the discount exceeds price * qty or when quantity is zero. Zero-quantity items previously contributed nothing to the total.

Fix in Cursor Fix in Web

Reviewed by Cursor Bugbot for commit e5c70d3. Configure here.

@sentry sentry Bot Oct 7, 2026

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Bug: The discountCents value is not validated, which can lead to incorrect cart totals if it's negative or larger than the line item price.
Severity: HIGH

Suggested Fix

Add validation to ensure discountCents is not negative and does not exceed the line item's total price. Throw a RangeError if the value is invalid, similar to the existing validation for qty.

const line = items[i].price * items[i].qty;
if ((items[i].discountCents ?? 0) < 0) {
  throw new RangeError(`Negative discount for item ${i}`);
}
if ((items[i].discountCents ?? 0) > line) {
  throw new RangeError(`Discount exceeds line total for item ${i}`);
}
total += line - (items[i].discountCents ?? 0);
Prompt for AI Agent 
Review the code at the location below. A potential bug has been identified by an AI
agent. Verify if this is a real issue. If it is, propose a fix; if not, explain why it's
not valid.

Location: apps/pr-reviewer/fixtures/demo-pr/cart-total.ts#L10

Potential issue: The `cartTotal` function applies a discount from `discountCents`
without proper validation. This allows for two potential issues: 1) If `discountCents`
is a negative number, it will be added to the line item's total, incorrectly inflating
the final price. 2) If `discountCents` is greater than the line item's total price, it
will result in a negative value for that line item, which could lead to a negative
overall cart total, effectively paying a customer to take items.

Did we get this right? 👍 / 👎 to inform future reviews.

}
return total;
}
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