msglist: In "Starred messages", show DMs even if all recipients muted

See reasoning in added dartdoc and implementation comments in
_messageVisible.

Author: chrisbobbe

lib/model/message_list.dart

@@ -668,7 +668,10 @@ class MessageListView with ChangeNotifier, _MessageSequence {
   /// This depends in particular on whether the message is muted in
   /// one way or another.
   ///
-  /// See also [_allMessagesVisible].
+  /// See also:
+  ///   - [_allMessagesVisible], message-fetch optimization related to this
+  ///   - Message-list UI that mitigates spam/harrassment
+  ///     by obscuring messages from muted senders, with a "reveal" button
   bool _messageVisible(MessageBase message) {
     switch (narrow) {
       case CombinedFeedNarrow():
@@ -694,7 +697,23 @@ class MessageListView with ChangeNotifier, _MessageSequence {
         // If changing this, consider whether [Unreads.countInMentionsNarrow]
         // should be changed correspondingly, so the message-list view matches
         // the unread-count badge.
+        if (message.conversation case DmConversation(:final allRecipientIds)) {
+          return !store.shouldMuteDmConversation(DmNarrow(
+            allRecipientIds: allRecipientIds, selfUserId: store.selfUserId));
+        }
+        return true;
+
       case StarredMessagesNarrow():
+        // Include messages even if muted in some way.
+        // Other users can't spam the starred-messages view by starring;
+        // the starred state is read/write by the self-user only.
+        //
+        // If we want to change this, consider that we need to compute a
+        // starred-message count without relying on fetched message data:
+        //   https://zulip.com/help/star-a-message#view-your-starred-messages
+        // ([MessageStore.starredMessages] is just a list of message IDs.)
+        return true;
+
       case KeywordSearchNarrow():
         if (message.conversation case DmConversation(:final allRecipientIds)) {
           return !store.shouldMuteDmConversation(DmNarrow(
@@ -718,7 +737,11 @@ class MessageListView with ChangeNotifier, _MessageSequence {
         return true;
 
       case MentionsNarrow():
+        return false;
+
       case StarredMessagesNarrow():
+        return true;
+
       case KeywordSearchNarrow():
         return false;
     }
@@ -757,7 +780,11 @@ class MessageListView with ChangeNotifier, _MessageSequence {
         return MutedUsersVisibilityEffect.none;
 
       case MentionsNarrow():
+        return store.mightChangeShouldMuteDmConversation(event);
+
       case StarredMessagesNarrow():
+        return MutedUsersVisibilityEffect.none;
+
       case KeywordSearchNarrow():
         return store.mightChangeShouldMuteDmConversation(event);
     }

test/model/message_list_test.dart

@@ -1253,8 +1253,8 @@ void main() {
       checkHasMessageIds([1, 2, 3]);
 
       await store.setMutedUsers([user1.userId]);
-      checkNotifiedOnce();
-      checkHasMessageIds([2, 3]);
+      checkNotNotified();
+      checkHasMessageIds([1, 2, 3]);
     });
 
     test('ChannelNarrow -> do nothing', () async {
@@ -3261,12 +3261,12 @@ void checkInvariants(MessageListView model) {
       switch (model.narrow) {
         case CombinedFeedNarrow():
         case MentionsNarrow():
-        case StarredMessagesNarrow():
         case KeywordSearchNarrow():
           check(model.store.shouldMuteDmConversation(narrow)).isFalse();
         case ChannelNarrow():
         case TopicNarrow():
         case DmNarrow():
+        case StarredMessagesNarrow():
       }
     }
   }