autocomplete: Add "alphabetical order" criterion

In @-mention autocomplete, users are suggested based on:
  1. Recent activity in the current topic/stream.
  2. Recent DM conversations.
  3. Human vs. Bot users (human users come first).
  4. Alphabetical order.

Fixes: #228

Author: sm-sayedi

lib/model/autocomplete.dart

@@ -249,7 +249,12 @@ class MentionAutocompleteView extends ChangeNotifier {
     } else if (userA.isBot && !userB.isBot) {
       return 1;
     }
-    return 0;
+
+    final userAName = store.autocompleteViewManager.autocompleteDataCache
+      .normalizedNameForUser(userA);
+    final userBName = store.autocompleteViewManager.autocompleteDataCache
+      .normalizedNameForUser(userB);
+    return userAName.compareTo(userBName);
   }
 
   /// Determines which of the two users has more recent activity (messages sent

test/model/autocomplete_test.dart

@@ -508,15 +508,17 @@ void main() {
       }
 
       test('TopicNarrow: topic recency > stream recency > DM recency '
-          '> human vs. bot user', () async {
+          '> human vs. bot user > alphabetical order', () async {
         final users = [
-          eg.user(),
+          eg.user(fullName: 'Z'),
           eg.user(),
           eg.user(isBot: true),
           eg.user(),
           eg.user(),
           eg.user(),
           eg.user(isBot: true),
+          eg.user(fullName: 'ab'),
+          eg.user(fullName: 'bc'),
         ];
         final stream = eg.stream();
         final narrow = TopicNarrow(stream.streamId, 'this');
@@ -533,16 +535,20 @@ void main() {
         checkPrecedes(narrow, users[2], users.skip(3));
         checkRankEqual(narrow, [users[3], users[4]]);
         checkPrecedes(narrow, users[5], users.skip(6));
+        checkPrecedes(narrow, users[7], users.skip(8));
       });
 
-      test('ChannelNarrow: stream recency > DM recency > human vs. bot user', () async {
+      test('ChannelNarrow: stream recency > DM recency > human vs. bot user '
+          '> alphabetical order', () async {
         final users = [
-          eg.user(isBot: true),
+          eg.user(isBot: true, fullName: 'Z'),
           eg.user(),
           eg.user(),
           eg.user(),
           eg.user(),
           eg.user(isBot: true),
+          eg.user(fullName: 'ab', isBot: true),
+          eg.user(fullName: 'bc', isBot: true),
         ];
         final stream = eg.stream();
         final narrow = ChannelNarrow(stream.streamId);
@@ -557,17 +563,20 @@ void main() {
         checkPrecedes(narrow, users[1], users.skip(2));
         checkRankEqual(narrow, [users[2], users[3]]);
         checkPrecedes(narrow, users[4], users.skip(5));
+        checkPrecedes(narrow, users[6], users.skip(7));
       });
 
       test('DmNarrow: DM recency > this-conversation recency or stream recency '
-          'or human vs. bot user', () async {
+          'or human vs. bot user or alphabetical order', () async {
         final users = [
-          eg.user(isBot: true),
+          eg.user(isBot: true, fullName: 'Z'),
           eg.user(),
           eg.user(),
           eg.user(),
           eg.user(),
           eg.user(isBot: true),
+          eg.user(fullName: 'ab'),
+          eg.user(fullName: 'bc'),
         ];
         await prepare(users: users, messages: [
           eg.dmMessage(from: users[3], to: [eg.selfUser]),
@@ -588,6 +597,7 @@ void main() {
           checkPrecedes(narrow, users[1], users.skip(3));
           checkPrecedes(narrow, users[2], users.skip(3));
           checkPrecedes(narrow, users[4], users.skip(5));
+          checkPrecedes(narrow, users[6], users.skip(7));
         }
       });
 
@@ -626,6 +636,8 @@ void main() {
         eg.user(userId: 5, fullName: 'User Five'),
         eg.user(userId: 6, fullName: 'User Six', isBot: true),
         eg.user(userId: 7, fullName: 'User Seven'),
+        eg.user(userId: 8, fullName: 'User Xy', isBot: true),
+        eg.user(userId: 9, fullName: 'User Xz', isBot: true),
       ];
 
       await prepare(users: users, messages: [
@@ -642,8 +654,9 @@ void main() {
       // 1. Users most recent in the current topic/stream.
       // 2. Users most recent in the DM conversations.
       // 3. Human vs. Bot users (human users come first).
+      // 4. Alphabetical order.
       check(await getResults(topicNarrow, MentionAutocompleteQuery('')))
-        .deepEquals([1, 5, 4, 2, 3, 7, 6]);
+        .deepEquals([1, 5, 4, 2, 7, 3, 6, 8, 9]);
 
       // Check the ranking applies also to results filtered by a query.
       check(await getResults(topicNarrow, MentionAutocompleteQuery('t')))
@@ -652,6 +665,8 @@ void main() {
         .deepEquals([5, 4]);
       check(await getResults(topicNarrow, MentionAutocompleteQuery('s')))
         .deepEquals([7, 6]);
+      check(await getResults(topicNarrow, MentionAutocompleteQuery('user x')))
+        .deepEquals([8, 9]);
     });
   });
 }