Cart price rules - Incorrect discount amount when using fixed discount amount for whole cart

[vandersonramoslybe]

Preconditions and environment

• Magento version: 2.3., 2.4.

Steps to reproduce

Create a Cart price rule:

1 - Marketing -> Promotions -> Cart Price Rules

Conditions:

2 - Actions:

It is important to be: Fixed amount discount for whole cart

3 - Create a plugin afterGetPrice for the class Magento\Quote\Model\Quote\Item. method getPrice()

<type name="Magento\Quote\Model\Quote\Item">
    <plugin name="my_plugin_name" type="Vendor\Module\Plugin\GetPriceFromQuoteItemPlugin" />
</type>

EXAMPLE:

`<?php

declare(strict_types=1);

namespace Vendor\Module\Plugin;

use Magento\Quote\Model\Quote\Item as QuoteItem;

class GetPriceFromQuoteItemPlugin
{

public function afterGetPrice(QuoteItem $subject, $result): float
{
    // ADD THE CHANGES HERE....
    
    $result = 1070.0;

    return $result;
}

}`

Choose a configurable product, and add it to the cart. The price will be changed to the new one, after that, apply the coupon code:

Check the discount value.

Expected result

It should be 500.00, not 250.00

Actual result

It is 250.00

Additional information

No response

Release note

No response

Triage and priority

• Severity: S0 - Affects critical data or functionality and leaves users without workaround.
• Severity: S1 - Affects critical data or functionality and forces users to employ a workaround.
• Severity: S2 - Affects non-critical data or functionality and forces users to employ a workaround.
• Severity: S3 - Affects non-critical data or functionality and does not force users to employ a workaround.
• Severity: S4 - Affects aesthetics, professional look and feel, “quality” or “usability”.

[m2-assistant]

Hi @vandersonramoslybe. Thank you for your report.
To speed up processing of this issue, make sure that the issue is reproducible on the vanilla Magento instance following Steps to reproduce. To deploy vanilla Magento instance on our environment, Add a comment to the issue:

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[Chris-Kiddier]

Hi,

I've recently experience this problem after upgrading to 2.4.5. It only happens when I try and apply a Fixed amount discount coupon to a quote with a configurable product in it.
For example, a £5 discount will amount to a £2.50 discount when applied to the configurable product.

Considering it's exactly half, my first thought was that the discount is somehow applying to both the Parent and Child product, however, as only 1 of those is taken into account when calculating row totals, it only takes into account half the discount.

More evidence for that is from a self developed module that applies loyalty points to products. Only since 2.4.5 has it started applying double the amount to configurable products, as if there were two products in 1 row.

Maybe that will help, but I'll be keeping an eye on this issue as well!

[vandersonramoslybe]

Hi,

I've recently experience this problem after upgrading to 2.4.5. It only happens when I try and apply a Fixed amount discount coupon to a quote with a configurable product in it. For example, a £5 discount will amount to a £2.50 discount when applied to the configurable product.

Considering it's exactly half, my first thought was that the discount is somehow applying to both the Parent and Child product, however, as only 1 of those is taken into account when calculating row totals, it only takes into account half the discount.

More evidence for that is from a self developed module that applies loyalty points to products. Only since 2.4.5 has it started applying double the amount to configurable products, as if there were two products in 1 row.

Maybe that will help, but I'll be keeping an eye on this issue as well!

I tested on Magento 2.3.7 as well, same behavior.

This is the class used when we have a cart rule as a Whole cart: https://github.com/magento/magento2/blob/2.4.6/app/code/Magento/SalesRule/Model/Rule/Action/Discount/CartFixed.php

The value on line 82 $baseRuleTotals = $ruleTotals['base_items_price'] ?? 0.0; contains the price for 2 items instead of only one as expected. For some reason, the method isChildrenCalculated from https://github.com/magento/magento2/blob/2.4.5-p2/app/code/Magento/SalesRule/Model/Validator.php is interfering with the calculation

[chernenm]

@magento give me 2.4-develop instance

[magento-deployment-service]

Hi @chernenm. Thank you for your request. I'm working on Magento instance for you.

[magento-deployment-service]

Hi @chernenm, here is your Magento Instance: https://301ee372ee8c8fa8afd70181c0924925.instances-prod.magento-community.engineering
Admin access: https://301ee372ee8c8fa8afd70181c0924925.instances-prod.magento-community.engineering/admin_f0c5
Login: 52511410
Password: dd4be1f6c765

[m2-assistant]

Hi @engcom-Dash. Thank you for working on this issue.
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[Chris-Kiddier]

I had a nosey through Validator.php. I'm not sure what constitutes a child item as 'calculated' and considering how often that method is referenced I was hesitant to change anything.

However, I added an extra line to the if statement on line 464 of the Validator class (function initTotals()) and it seems to have fixed the issue for me, calculating the fixed amount discount correctly when I go to checkout.

if (!$this->isValidItemForRule($item, $rule)
    || ($item->getChildren() && $item->isChildrenCalculated())
    || $item->getNoDiscount()
    || ($item->getProductType() == "simple" && $item->getParentItemId() != null) // New line added
) {
    continue;
}

I figured, as the statement seems to be including Simple products that are also children, they should be omitted from the calculation.
This is not elegant by any means (and involves editing core), but it has provided some functionality back to my dev site.

I'll await any further info, currently this is staying safely away from production

[abdul0231]

I had proposed a simple fix through Validator.php. I am also interrupting this above if statement but I'm excluding a check

$item->isChildrenCalculated()

The updated code is below

foreach ($items as $item) { if (!$this->isValidItemForRule($item, $rule) || ($item->getChildren()) || $item->getNoDiscount() ) { continue; }

I have seen that parent and child were getting calculated and amount was getting double the accurate price and then the ratio calculated 0.5 causing discount to get half.

I'm not very 100 percent sure this will be optimal solution but I have tested all the scenarios with loggedin and non logged in customers and every possible test case. Everything works fine.

[m2-assistant]

Hi @engcom-Hotel. Thank you for working on this issue.
In order to make sure that issue has enough information and ready for development, please read and check the following instruction: 👇

• 1. Verify that issue has all the required information. (Preconditions, Steps to reproduce, Expected result, Actual result).
• 2. Verify that issue has a meaningful description and provides enough information to reproduce the issue.
• 3. Add Area: XXXXX label to the ticket, indicating the functional areas it may be related to.
• 4. Verify that the issue is reproducible on 2.4-develop branch
  Details

  - Add the comment @magento give me 2.4-develop instance to deploy test instance on Magento infrastructure.
  - If the issue is reproducible on 2.4-develop branch, please, add the label Reproduced on 2.4.x.
  - If the issue is not reproducible, add your comment that issue is not reproducible and close the issue and stop verification process here!
• 5. Add label Issue: Confirmed once verification is complete.
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[engcom-Hotel]

Hello @vandersonramoslybe,

Thanks for the report and collaboration!

We have tried to reproduce the issue with the mentioned steps in the main description. We have used the 2.4-develop branch in order to reproduce the issue. But for us, the discount amount is showing $500. Please have a look to the below screenshot for reference:

Please review the steps and let us know if we need to do any additional steps in order to reproduce the issue.

Thanks

[vandersonramoslybe]

Hi @engcom-Hotel

Do you have a plugin as explained in the description? Step 3

3 - Create a plugin afterGetPrice for the class Magento\Quote\Model\Quote\Item. method getPrice()

[engcom-Hotel]

Yes @vandersonramoslybe,

Let me attach the same here for reference:

Magz.zip

Please let me know if we missed anything.

Thanks

[vandersonramoslybe]

Hi @engcom-Hotel

Thanks, I installed your plugin. I am running a vanilla Magento 2.4.6. The issue is reproducible with Configurable products.

[engcom-Hotel]

Hello @vandersonramoslybe,

Thanks for the response!

Now we are able to reproduce the issue. Please refer to the below screenshot for reference:

Hence confirming the issue.

Thanks

[github-jira-sync-bot]

✅ Jira issue https://jira.corp.adobe.com/browse/AC-8853 is successfully created for this GitHub issue.

[m2-assistant]

✅ Confirmed by @engcom-Hotel. Thank you for verifying the issue.
Issue Available: @engcom-Hotel, You will be automatically unassigned. Contributors/Maintainers can claim this issue to continue. To reclaim and continue work, reassign the ticket to yourself.

[aasim110]

@magento I'm working on this