autocomplete: Introduce a field for sorted users

This field will be used to maintain a list of sorted users based on the
most relevant autocomplete criteria in the upcoming commits.

This commit also removes the retry logic for an in-progress query
computation as there is no longer the cause that would necessitate such
a retry.

Author: sm-sayedi

lib/model/autocomplete.dart

@@ -164,17 +164,29 @@ class AutocompleteViewManager {
 ///  * When the object will no longer be used, call [dispose] to free
 ///    resources on the [PerAccountStore].
 class MentionAutocompleteView extends ChangeNotifier {
-  MentionAutocompleteView._({required this.store, required this.narrow});
+  MentionAutocompleteView._({
+    required this.store,
+    required this.narrow,
+    required this.sortedUsers,
+  });
 
   factory MentionAutocompleteView.init({
     required PerAccountStore store,
     required Narrow narrow,
   }) {
-    final view = MentionAutocompleteView._(store: store, narrow: narrow);
+    final view = MentionAutocompleteView._(
+      store: store,
+      narrow: narrow,
+      sortedUsers: _usersByRelevance(store: store),
+    );
     store.autocompleteViewManager.registerMentionAutocomplete(view);
     return view;
   }
 
+  static List<User> _usersByRelevance({required PerAccountStore store}) {
+    return store.users.values.toList(); // TODO(#228): sort for most relevant first
+  }
+
   @override
   void dispose() {
     store.autocompleteViewManager.unregisterMentionAutocomplete(this);
@@ -186,6 +198,7 @@ class MentionAutocompleteView extends ChangeNotifier {
 
   final PerAccountStore store;
   final Narrow narrow;
+  final List<User> sortedUsers;
 
   MentionAutocompleteQuery? get query => _query;
   MentionAutocompleteQuery? _query;
@@ -209,18 +222,7 @@ class MentionAutocompleteView extends ChangeNotifier {
   List<MentionAutocompleteResult> _results = [];
 
   Future<void> _startSearch(MentionAutocompleteQuery query) async {
-    List<MentionAutocompleteResult>? newResults;
-
-    while (true) {
-      try {
-        newResults = await _computeResults(query);
-        break;
-      } on ConcurrentModificationError {
-        // Retry
-        // TODO backoff?
-      }
-    }
-
+    final newResults = await _computeResults(query);
     if (newResults == null) {
       // Query was old; new search is in progress. Or, no listeners to notify.
       return;
@@ -232,9 +234,7 @@ class MentionAutocompleteView extends ChangeNotifier {
 
   Future<List<MentionAutocompleteResult>?> _computeResults(MentionAutocompleteQuery query) async {
     final List<MentionAutocompleteResult> results = [];
-    final Iterable<User> users = store.users.values;
-
-    final iterator = users.iterator;
+    final iterator = sortedUsers.iterator;
     bool isDone = false;
     while (!isDone) {
       // CPU perf: End this task; enqueue a new one for resuming this work
@@ -245,7 +245,7 @@ class MentionAutocompleteView extends ChangeNotifier {
       }
 
       for (int i = 0; i < 1000; i++) {
-        if (!iterator.moveNext()) { // Can throw ConcurrentModificationError
+        if (!iterator.moveNext()) {
           isDone = true;
           break;
         }
@@ -256,7 +256,7 @@ class MentionAutocompleteView extends ChangeNotifier {
         }
       }
     }
-    return results; // TODO(#228) sort for most relevant first
+    return results;
   }
 }
 

test/model/autocomplete_test.dart

@@ -274,37 +274,35 @@ void main() {
     }
   });
 
-  test('MentionAutocompleteView mutating store.users while in progress causes retry', () async {
+  test('MentionAutocompleteView mutating store.users while in progress does not '
+      'interrupt the current query results', () async {
     const narrow = CombinedFeedNarrow();
     final store = eg.store();
-    for (int i = 0; i < 1500; i++) {
+    for (int i = 0; i < 2500; i++) {
       await store.addUser(eg.user(userId: i, email: 'user$i@example.com', fullName: 'User $i'));
     }
     final view = MentionAutocompleteView.init(store: store, narrow: narrow);
 
     bool done = false;
     view.addListener(() { done = true; });
-    view.query = MentionAutocompleteQuery('User 10000');
+    view.query = MentionAutocompleteQuery('User 110');
 
     await Future(() {});
     check(done).isFalse();
-    await store.addUser(eg.user(userId: 10000, email: '[email protected]', fullName: 'User 10000'));
-    await Future(() {});
-    check(done).isFalse();
+    await store.addUser(eg.user(userId: 11000, email: '[email protected]', fullName: 'User 11000'));
     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
+    while (!done) {
       await Future(() {});
-      check(view.results).single
-        .isA<UserMentionAutocompleteResult>()
-        .userId.equals(10000);
     }
+    check(done).isTrue();
+    final results = view.results
+      .map((e) => (e as UserMentionAutocompleteResult).userId);
+    check(results)
+      ..contains(110)
+      ..contains(1100)
+      // Does not include the newly-added user as we finish the query with stale users.
+      ..not((results) => results.contains(11000));
   });
 
   group('MentionAutocompleteQuery.testUser', () {