Incorrect discount amount when applying multiple 'Fixed amount discount for whole cart' rules

[nghia-34th]

Preconditions and environment

• Magento version: 2.4.7 and above

Steps to reproduce

1. Create at least three cart rules with the 'Fixed amount discount for whole cart' action.
2. Add product to cart.
3. Make sure the cart condition matches the three rules created in step 1.

Expected result

The Discount amount in the cart summary section should be correct.

Actual result

Incorrect Discount amount shown.

Additional information

Rule 1:

Rule 2:

Rule 3:

Expected discount amount should be 15,00 US$. The actual amount shown is 15,30 US$.

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 @nghia-34th. Thank you for your report.
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[nghia-34th]

The issue is due to this class Magento\SalesRule\Model\Quote\Discount, line 209. $totalDiscount should be the sum of each rule's base discount applied to the current item.
Adding the item's base discount amount would re-add all the base discount amounts of previous rules to $totalDiscount, leading to incorrect discount amount calculation.

[m2-assistant]

Hi @engcom-Bravo. Thank you for working on this issue.
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[engcom-Bravo]

Hi @nghia-34th,

Thanks for your reporting and collaboration.

We have tried to reproduce the issue in Latest 2.4-develop instance and the issue is not reproducible.Kindly refer the screenshots.

The Discount amount in the cart summary section was correctly applied.

Kindly recheck the issue in Latest 2.4-develop instance and elaborate the steps to reproduce if the issue is still reproducible.

Thanks.

[nghia-34th]

@magento give me 2.4-develop instance

[nghia-34th]

@engcom-Bravo I'm unable to request a 2.4-develop instance on this issue, do you have any advice?
This is reproducible on a fresh 2.4.7 installation btw.