Expense - System message changes from "changed the attendees to.." to "set the attendees to.."

src/libs/ModifiedExpenseMessage.ts

@@ -525,8 +525,8 @@ function getForReportAction({
 
     const hasModifiedAttendees = isReportActionOriginalMessageAnObject && 'oldAttendees' in reportActionOriginalMessage && 'newAttendees' in reportActionOriginalMessage;
     if (hasModifiedAttendees) {
-        const [oldAttendees, attendees] = getFormattedAttendees(reportActionOriginalMessage.newAttendees, reportActionOriginalMessage.oldAttendees);
-        buildMessageFragmentForValue(translate, oldAttendees, attendees, translate('iou.attendees'), false, setFragments, removalFragments, changeFragments);
+        const [oldAttendees, newAttendees] = getFormattedAttendees(reportActionOriginalMessage.oldAttendees, reportActionOriginalMessage.newAttendees);
+        buildMessageFragmentForValue(translate, newAttendees, oldAttendees, translate('iou.attendees'), false, setFragments, removalFragments, changeFragments);
     }
 
     const hasPersonalRulesModifiedFields = isReportActionOriginalMessageAnObject && 'personalRulesModifiedFields' in reportActionOriginalMessage;

src/libs/ReportUtils.ts

@@ -120,7 +120,7 @@ import {openUnreportedExpense} from './actions/Report';
 import {isAnonymousUser as isAnonymousUserSession} from './actions/Session';
 import {removeDraftTransactionsByIDs} from './actions/TransactionEdit';
 import {getOnboardingMessages} from './actions/Welcome/OnboardingFlow';
-import {convertAttendeesToArray} from './AttendeeUtils';
+import {convertAttendeesToArray, normalizeAttendees} from './AttendeeUtils';
 import {getCategoryGLCode} from './CategoryUtils';
 import {convertToDisplayStringEnLocale} from './CurrencyUtils';
 import DateUtils from './DateUtils';
@@ -6271,7 +6271,12 @@ function getModifiedExpenseOriginalMessage(
         originalMessage.merchant = transactionChanges?.merchant;
     }
     if ('attendees' in transactionChanges) {
-        originalMessage.oldAttendees = getAttendees(oldTransaction);
+        // Only `modifiedAttendees` counts as a previous edit, so we deliberately ignore `comment.attendees` (the default
+        // attendee the app adds when the expense is created). Otherwise the optimistic message would read
+        // "changed the attendees from <self> to X" while the server returns "set the attendees to X", causing a flicker.
+        // Note: this must stay an empty array rather than being omitted, because ModifiedExpenseMessage checks
+        // `'oldAttendees' in originalMessage` to decide whether to build the attendees fragment at all.
+        originalMessage.oldAttendees = normalizeAttendees(convertAttendeesToArray(oldTransaction?.modifiedAttendees));
         originalMessage.newAttendees = transactionChanges?.attendees;
     }
 

tests/actions/ReportTest.ts

@@ -37,6 +37,7 @@ import type * as SearchQueryUtilsType from '@src/libs/SearchQueryUtils';
 import ONYXKEYS from '@src/ONYXKEYS';
 import ROUTES from '@src/ROUTES';
 import type * as OnyxTypes from '@src/types/onyx';
+import type {Attendee} from '@src/types/onyx/IOU';
 
 import type {OnyxCollection, OnyxEntry, OnyxUpdate} from 'react-native-onyx';
 
@@ -9642,6 +9643,33 @@ describe('actions/Report', () => {
         });
     });
 
+    describe('buildOptimisticModifiedExpenseReportAction attendees', () => {
+        const TRANSACTION_ID = '888';
+        const ownerAttendee: Attendee = {email: 'owner@example.com', displayName: 'Owner', avatarUrl: ''};
+        const otherAttendee: Attendee = {email: 'other@example.com', displayName: 'Other', avatarUrl: ''};
+
+        const getAttendeesOriginalMessage = (oldTransaction: OnyxTypes.Transaction, newAttendees: Attendee[]) => {
+            const result = ReportUtils.buildOptimisticModifiedExpenseReportAction(undefined, oldTransaction, {attendees: newAttendees}, false, undefined, undefined);
+            return getOriginalMessage(result as OnyxTypes.ReportAction<typeof CONST.REPORT.ACTIONS.TYPE.MODIFIED_EXPENSE>);
+        };
+
+        it('treats oldAttendees as empty (set message) on the first edit, when attendees have never been modified', () => {
+            // Only the auto-added default attendee is present (comment.attendees), with no modifiedAttendees history.
+            const oldTransaction = createMock<OnyxTypes.Transaction>({transactionID: TRANSACTION_ID, comment: {attendees: [ownerAttendee]}});
+            const originalMessage = getAttendeesOriginalMessage(oldTransaction, [otherAttendee]);
+            expect(originalMessage?.oldAttendees).toEqual([]);
+            expect(originalMessage?.newAttendees).toEqual([otherAttendee]);
+        });
+
+        it('keeps oldAttendees (changed message) on subsequent edits, even when the previous value is just the owner', () => {
+            // After previous edits, modifiedAttendees holds the last value - here it happens to be only the owner.
+            const oldTransaction = createMock<OnyxTypes.Transaction>({transactionID: TRANSACTION_ID, modifiedAttendees: [ownerAttendee], comment: {attendees: [ownerAttendee]}});
+            const originalMessage = getAttendeesOriginalMessage(oldTransaction, [ownerAttendee, otherAttendee]);
+            expect(originalMessage?.oldAttendees).toEqual([ownerAttendee]);
+            expect(originalMessage?.newAttendees).toEqual([ownerAttendee, otherAttendee]);
+        });
+    });
+
     describe('buildOptimisticModifiedExpenseReportAction distance currency', () => {
         it('keeps the expense currency when a route switch leaves modifiedCurrency unset', () => {
             const oldTransaction = createMock<OnyxTypes.Transaction>({

tests/unit/ModifiedExpenseMessageTest.ts

@@ -2278,6 +2278,77 @@ describe('ModifiedExpenseMessage', () => {
             });
         });
 
+        describe('when attendees are changed', () => {
+            it('returns the correct message with old and new attendees in the right order', () => {
+                const reportAction = {
+                    ...createRandomReportAction(1),
+                    actionName: CONST.REPORT.ACTIONS.TYPE.MODIFIED_EXPENSE,
+                    originalMessage: {
+                        oldAttendees: [{email: 'alice@example.com', displayName: 'Alice', avatarUrl: ''}],
+                        newAttendees: [
+                            {email: 'alice@example.com', displayName: 'Alice', avatarUrl: ''},
+                            {email: 'bob@example.com', displayName: 'Bob', avatarUrl: ''},
+                        ],
+                    },
+                };
+
+                const result = getForReportAction({
+                    convertToDisplayString,
+                    translate: translateLocal,
+                    reportAction,
+                    policy: undefined,
+                    policyTags: undefined,
+                    currentUserLogin: 'test@example.com',
+                });
+
+                expect(result).toEqual('changed the attendees to Alice, Bob (previously Alice)');
+            });
+
+            it('returns "set" message when attendees are added from empty', () => {
+                const reportAction = {
+                    ...createRandomReportAction(1),
+                    actionName: CONST.REPORT.ACTIONS.TYPE.MODIFIED_EXPENSE,
+                    originalMessage: {
+                        oldAttendees: [],
+                        newAttendees: [{email: 'alice@example.com', displayName: 'Alice', avatarUrl: ''}],
+                    },
+                };
+
+                const result = getForReportAction({
+                    convertToDisplayString,
+                    translate: translateLocal,
+                    reportAction,
+                    policy: undefined,
+                    policyTags: undefined,
+                    currentUserLogin: 'test@example.com',
+                });
+
+                expect(result).toEqual('set the attendees to Alice');
+            });
+
+            it('returns "removed" message when attendees are cleared', () => {
+                const reportAction = {
+                    ...createRandomReportAction(1),
+                    actionName: CONST.REPORT.ACTIONS.TYPE.MODIFIED_EXPENSE,
+                    originalMessage: {
+                        oldAttendees: [{email: 'alice@example.com', displayName: 'Alice', avatarUrl: ''}],
+                        newAttendees: [],
+                    },
+                };
+
+                const result = getForReportAction({
+                    convertToDisplayString,
+                    translate: translateLocal,
+                    reportAction,
+                    policy: undefined,
+                    policyTags: undefined,
+                    currentUserLogin: 'test@example.com',
+                });
+
+                expect(result).toEqual('removed the attendees (previously Alice)');
+            });
+        });
+
         describe('vendor changes', () => {
             // QBO policy with two named vendors used by the resolver. No `config` block — the resolver
             // must look up vendors regardless of the workspace's current export mode so historical