Expense - System message is shown incorrectly when distance split amount is edited

[jponikarchuk]

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Version Number: V9.3.26-4
Reproducible in staging?: Yes
Reproducible in production?: Yes
If this was caught during regression testing, add the test name, ID and link from BrowserStack: https://test-management.browserstack.com/projects/2219752/test-runs/TR-6480/folder/18717689/49855697/1213507913
Email or phone of affected tester (no customers): Applausetester+oao@applause.expensifail.com
Issue reported by: Applause Internal Team
Bug source: Exploratory - Significant User Experience Deterioration
Device used: Redminote 10S Android 13
App Component: Money Requests

Action Performed:

1. Launch app
2. Open workspace chat
3. Create a manual distance expense
4. Open the expense
5. Tap more - split the expense
6. Open the second split expense
7. Tap date and change the dateand save
8. Note correct system message is shown
9. Tap amount and change the amount & save
10. Open the expense

Expected Result:

System message must show changed the amount to ₹12.00 (previously ₹120.71), which updated the distance to 16.55 mi @ ₹0.725 / mi (previously 166.50 mi @ ₹0.725 / mi)."

Actual Result:

System message shows "changed the distance to 16.55 mi @ ₹0.725 / mi (previously 166.50 mi @ ₹0.725 / mi), which updated the amount to ₹12.00 (previously ₹120.71)" incorrectly.

Workaround:

Unknown

Platforms:

• Android: App
• Android: mWeb Chrome
• iOS: App
• iOS: mWeb Safari
• iOS: mWeb Chrome
• Windows: Chrome
• MacOS: Chrome / Safari

Screenshots/Videos

1.mp4

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[imadirtydog]

Proposal

Please re-state the problem that we are trying to solve in this issue.

When editing the amount on a split distance expense, the system message incorrectly shows:

"changed the distance to 16.55 mi @ ₹0.725 / mi (previously 166.50 mi @ ₹0.725 / mi), which updated the amount to ₹12.00 (previously ₹120.71)"

Expected message:

"changed the amount to ₹12.00 (previously ₹120.71), which updated the distance to 16.55 mi @ ₹0.725 / mi (previously 166.50 mi @ ₹0.725 / mi)"

What is the root cause of that problem?

This is a backend + frontend issue.

The backend (ModifiedExpense::getNewDotComment in Web-Expensify) does not include information about which field was the primary edit. The originalMessage in the report action only contains:

{
  merchant: "2.07 mi @ Kč0.725 / mi",
  oldMerchant: "20.00 mi @ Kč0.725 / mi",
  amount: 150,
  oldAmount: 1450,
  currency: "CZK",
  oldCurrency: "CZK"
}

The frontend getForDistanceRequest function in src/libs/ModifiedExpenseMessage.ts has no way to distinguish between:

1. User changed distance → amount was recalculated
2. User changed amount → distance was recalculated

Both scenarios produce identical data (different distance + different amount + same rate), so the frontend defaults to "distance changed".

https://github.com/Expensify/App/blob/5e00a65a0aa/src/libs/ModifiedExpenseMessage.ts#L133-L161

function getForDistanceRequest(...) {
    let changedField: 'distance' | 'rate' = 'distance';

    // Only detects rate change, defaults to distance otherwise
    if (oldDistance === newDistance && oldRate !== newRate) {
        changedField = 'rate';
    }
    // Missing: detection for when amount was the primary change
}

What changes do you think we should make in order to solve the problem?

Backend Changes (Web-Expensify)

Add a changedField property to the originalMessage when creating MODIFIEDEXPENSE report actions for distance expenses. This field should indicate which field the user actually edited.

In ModifiedExpense::getNewDotComment (or equivalent), when the modification involves a distance expense with both amount and merchant changes:

// When user edits amount on distance expense
$originalMessage['changedField'] = 'amount';

// When user edits distance on distance expense
$originalMessage['changedField'] = 'distance';

// When user edits rate on distance expense
$originalMessage['changedField'] = 'rate';

Frontend Changes (App)

1. Update OriginalMessageModifiedExpense type:

https://github.com/Expensify/App/blob/5e00a65a0aa/src/types/onyx/OriginalMessage.ts#L738

type OriginalMessageModifiedExpense = {
    // ... existing fields ...

    /** The field that was primarily changed by the user (for distance expenses) */
    changedField?: 'distance' | 'rate' | 'amount';
};

2. Update getForDistanceRequest to use the new field:

https://github.com/Expensify/App/blob/5e00a65a0aa/src/libs/ModifiedExpenseMessage.ts#L133

function getForDistanceRequest(
    translate: LocalizedTranslate,
    newMerchant: string,
    oldMerchant: string,
    newAmount: string,
    oldAmount: string,
    changedField?: 'distance' | 'rate' | 'amount'
): string {
    let field: 'distance' | 'rate' | 'amount' = changedField ?? 'distance';

    // Fallback logic if changedField not provided (for older actions)
    if (!changedField && CONST.REGEX.DISTANCE_MERCHANT.test(newMerchant) && CONST.REGEX.DISTANCE_MERCHANT.test(oldMerchant)) {
        const oldValues = oldMerchant.split('@');
        const newValues = newMerchant.split('@');
        const oldDistance = oldValues.at(0)?.trim() ?? '';
        const oldRate = oldValues.at(1)?.trim() ?? '';
        const newDistance = newValues.at(0)?.trim() ?? '';
        const newRate = newValues.at(1)?.trim() ?? '';

        if (oldDistance === newDistance && oldRate !== newRate) {
            field = 'rate';
        }
    }

    if (field === 'amount') {
        return translate('iou.updatedTheDistanceAmount', {
            newAmountToDisplay: newAmount,
            oldAmountToDisplay: oldAmount,
            newMerchant,
            oldMerchant,
        });
    }

    const translatedChangedField = translate(`common.${field}`).toLowerCase();
    if (!oldMerchant.length) {
        return translate('iou.setTheDistanceMerchant', translatedChangedField, newMerchant, newAmount);
    }
    return translate('iou.updatedTheDistanceMerchant', {
        translatedChangedField,
        newMerchant,
        oldMerchant,
        newAmountToDisplay: newAmount,
        oldAmountToDisplay: oldAmount,
    });
}

3. Add new translation string:

https://github.com/Expensify/App/blob/5e00a65a0aa/src/languages/en.ts#L1321

updatedTheDistanceAmount: ({newAmountToDisplay, oldAmountToDisplay, newMerchant, oldMerchant}: UpdatedTheDistanceAmountParams) =>
    `changed the amount to ${newAmountToDisplay} (previously ${oldAmountToDisplay}), which updated the distance to ${newMerchant} (previously ${oldMerchant})`,

4. Update call site to pass changedField:

https://github.com/Expensify/App/blob/5e00a65a0aa/src/libs/ModifiedExpenseMessage.ts#L309

if (hasModifiedMerchant && (reportActionOriginalMessage?.merchant ?? '').includes('@')) {
    return getForDistanceRequest(
        translateLocal,
        reportActionOriginalMessage?.merchant ?? '',
        reportActionOriginalMessage?.oldMerchant ?? '',
        amount,
        oldAmount,
        reportActionOriginalMessage?.changedField
    );
}