autocomplete: Terminate the already-running search when there is a new one

Author: sm-sayedi

lib/model/autocomplete.dart

@@ -235,14 +235,11 @@ class MentionAutocompleteView extends ChangeNotifier {
   _startSearch(MentionAutocompleteQuery query) async {
     List<MentionAutocompleteResult>? newResults;
 
-    while (true) {
-      try {
-        newResults = await _computeResults(query);
-        break;
-      } on ConcurrentModificationError {
-        // Retry
-        // TODO backoff?
-      }
+    try {
+      newResults = await _computeResults(query);
+    } on ConcurrentModificationError {
+      // Terminate this search as there is a new search going on
+      return;
     }
 
     if (newResults == null) {

lib/model/store.dart

@@ -448,6 +448,16 @@ class PerAccountStore extends ChangeNotifier with StreamStore {
           user.profileData = null;
         }
       }
+      // The following two lines will eventually not change [users], but are here to
+      // trigger a modification to the collection as only changing the properties
+      // of [user] does not signal a modification of [users] where needed.
+      //
+      // One example of this is [MentionAutocompleteView._computeResults] which
+      // throws a `ConcurrentModificationError` when there is a modification done
+      // to [users].
+      users[-1] = user;
+      users.remove(-1);
+
       autocompleteViewManager.handleRealmUserUpdateEvent(event);
       notifyListeners();
     } else if (event is StreamEvent) {

test/model/autocomplete_test.dart

@@ -8,6 +8,7 @@ import 'package:test/scaffolding.dart';
 import 'package:zulip/api/model/model.dart';
 import 'package:zulip/model/autocomplete.dart';
 import 'package:zulip/model/narrow.dart';
+import 'package:zulip/model/store.dart';
 import 'package:zulip/widgets/compose_box.dart';
 
 import '../example_data.dart' as eg;
@@ -274,35 +275,111 @@ void main() {
     }
   });
 
-  test('MentionAutocompleteView mutating store.users while in progress causes retry', () async {
-    const narrow = CombinedFeedNarrow();
-    final store = eg.store();
-    for (int i = 0; i < 1500; i++) {
-      await store.addUser(eg.user(userId: i, email: 'user$i@example.com', fullName: 'User $i'));
-    }
-    final view = MentionAutocompleteView.init(store: store, narrow: narrow);
+  group('MentionAutocompleteView recomputes results', () {
+    Future<void> doCheck({
+      required List<User> users,
+      required String rawQuery,
+      required Future<void> Function(PerAccountStore store) act,
+      required void Function(Iterable<MentionAutocompleteResult>) expect,
+    }) async {
+      const narrow = CombinedFeedNarrow();
+      final store = eg.store();
+      await store.addUsers(users);
+      final view = MentionAutocompleteView.init(store: store, narrow: narrow);
 
-    bool done = false;
-    view.addListener(() { done = true; });
-    view.query = MentionAutocompleteQuery('User 10000');
+      bool done = false;
+      view.addListener(() { done = true; });
+      view.query = MentionAutocompleteQuery(rawQuery);
 
-    await Future(() {});
-    check(done).isFalse();
-    await store.addUser(eg.user(userId: 10000, email: '[email protected]', fullName: 'User 10000'));
-    await Future(() {});
-    check(done).isFalse();
-    await Future(() {});
-    check(done).isTrue();
-    check(view.results).single
-      .isA<UserMentionAutocompleteResult>()
-      .userId.equals(10000);
-    // new result sticks; no "zombie" result from `store.users` pre-mutation
-    for (int i = 0; i < 10; i++) { // for good measure
       await Future(() {});
-      check(view.results).single
+      check(done).isFalse();
+
+      await act(store);
+
+      await Future(() {});
+      check(done).isFalse();
+      await Future(() {});
+      check(done).isTrue();
+      expect(view.results);
+      // new result sticks; no "zombie" result
+      for (int i = 0; i < 10; i++) { // for good measure
+        await Future(() {});
+        expect(view.results);
+      }
+    }
+
+    List<User> generateUsers({required int count}) {
+      return List.generate(
+        count,
+        (i) => eg.user(
+          userId: i,
+          email: 'user$i@example.com',
+          fullName: 'User $i'));
+    }
+
+    test('RealmUserAddEvent', () async {
+      final users = generateUsers(count: 1500);
+
+      Future<void> act(PerAccountStore store) async {
+        await store.addUser(eg.user(
+          userId: 10000,
+          email: '[email protected]',
+          fullName: 'User 10000'));
+      }
+
+      void expect(Iterable<MentionAutocompleteResult> results) {
+        check(results).single
         .isA<UserMentionAutocompleteResult>()
         .userId.equals(10000);
-    }
+      }
+
+      await doCheck(
+        users: users,
+        rawQuery: 'User 10000',
+        act: act,
+        expect: expect,
+      );
+    });
+
+    test('RealmUserRemoveEvent', () async {
+      final users = generateUsers(count: 1500);
+
+      Future<void> act(PerAccountStore store) async {
+        await store.removeUser(1495);
+      }
+
+      void expect(Iterable<MentionAutocompleteResult> results) {
+        check(results).isEmpty();
+      }
+
+      await doCheck(
+        users: users,
+        rawQuery: 'User 1495',
+        act: act,
+        expect: expect,
+      );
+    });
+
+    test('RealmUserUpdateEvent', () async {
+      final users = generateUsers(count: 1500);
+
+      Future<void> act(PerAccountStore store) async {
+        await store.updateUser(1, fullName: 'Updated User 1');
+      }
+
+      void expect(Iterable<MentionAutocompleteResult> results) {
+        check(results).single
+        .isA<UserMentionAutocompleteResult>()
+        .userId.equals(1);
+      }
+
+      await doCheck(
+        users: users,
+        rawQuery: 'Updated User 1',
+        act: act,
+        expect: expect,
+      );
+    });
   });
 
   group('MentionAutocompleteQuery.testUser', () {