msglist [nfc]: s/VisibilityEffect/UserTopicVisibilityEffect/

This is awkwardly verbose, but we're about to add another kind of
visibility effect, and I think the code will end up clearer if we
make a separate enum for it.

Greg points out that an upcoming Dart feature "dot shorthands"
should help with this verbosity:
  zulip#1561 (comment)

Author: chrisbobbe

lib/model/channel.dart

@@ -69,10 +69,10 @@ mixin ChannelStore {
 
   /// Whether the given event will change the result of [isTopicVisibleInStream]
   /// for its stream and topic, compared to the current state.
-  VisibilityEffect willChangeIfTopicVisibleInStream(UserTopicEvent event) {
+  UserTopicVisibilityEffect willChangeIfTopicVisibleInStream(UserTopicEvent event) {
     final streamId = event.streamId;
     final topic = event.topicName;
-    return VisibilityEffect._fromBeforeAfter(
+    return UserTopicVisibilityEffect._fromBeforeAfter(
       _isTopicVisibleInStream(topicVisibilityPolicy(streamId, topic)),
       _isTopicVisibleInStream(event.visibilityPolicy));
   }
@@ -106,10 +106,10 @@ mixin ChannelStore {
 
   /// Whether the given event will change the result of [isTopicVisible]
   /// for its stream and topic, compared to the current state.
-  VisibilityEffect willChangeIfTopicVisible(UserTopicEvent event) {
+  UserTopicVisibilityEffect willChangeIfTopicVisible(UserTopicEvent event) {
     final streamId = event.streamId;
     final topic = event.topicName;
-    return VisibilityEffect._fromBeforeAfter(
+    return UserTopicVisibilityEffect._fromBeforeAfter(
       _isTopicVisible(streamId, topicVisibilityPolicy(streamId, topic)),
       _isTopicVisible(streamId, event.visibilityPolicy));
   }
@@ -137,7 +137,7 @@ mixin ChannelStore {
 /// Whether and how a given [UserTopicEvent] will affect the results
 /// that [ChannelStore.isTopicVisible] or [ChannelStore.isTopicVisibleInStream]
 /// would give for some messages.
-enum VisibilityEffect {
+enum UserTopicVisibilityEffect {
   /// The event will have no effect on the visibility results.
   none,
 
@@ -147,11 +147,11 @@ enum VisibilityEffect {
   /// The event will change some visibility results from false to true.
   unmuted;
 
-  factory VisibilityEffect._fromBeforeAfter(bool before, bool after) {
+  factory UserTopicVisibilityEffect._fromBeforeAfter(bool before, bool after) {
     return switch ((before, after)) {
-      (false, true) => VisibilityEffect.unmuted,
-      (true, false) => VisibilityEffect.muted,
-      _             => VisibilityEffect.none,
+      (false, true) => UserTopicVisibilityEffect.unmuted,
+      (true, false) => UserTopicVisibilityEffect.muted,
+      _             => UserTopicVisibilityEffect.none,
     };
   }
 }

lib/model/message_list.dart

@@ -661,20 +661,20 @@ class MessageListView with ChangeNotifier, _MessageSequence {
 
   /// Whether this event could affect the result that [_messageVisible]
   /// would ever have returned for any possible message in this message list.
-  VisibilityEffect _canAffectVisibility(UserTopicEvent event) {
+  UserTopicVisibilityEffect _userTopicEventCanAffectVisibility(UserTopicEvent event) {
     switch (narrow) {
       case CombinedFeedNarrow():
         return store.willChangeIfTopicVisible(event);
 
       case ChannelNarrow(:final streamId):
-        if (event.streamId != streamId) return VisibilityEffect.none;
+        if (event.streamId != streamId) return UserTopicVisibilityEffect.none;
         return store.willChangeIfTopicVisibleInStream(event);
 
       case TopicNarrow():
       case DmNarrow():
       case MentionsNarrow():
       case StarredMessagesNarrow():
-        return VisibilityEffect.none;
+        return UserTopicVisibilityEffect.none;
     }
   }
 
@@ -950,11 +950,11 @@ class MessageListView with ChangeNotifier, _MessageSequence {
   }
 
   void handleUserTopicEvent(UserTopicEvent event) {
-    switch (_canAffectVisibility(event)) {
-      case VisibilityEffect.none:
+    switch (_userTopicEventCanAffectVisibility(event)) {
+      case UserTopicVisibilityEffect.none:
         return;
 
-      case VisibilityEffect.muted:
+      case UserTopicVisibilityEffect.muted:
         bool removed = _removeMessagesWhere((message) =>
           message is StreamMessage
             && message.streamId == event.streamId
@@ -969,7 +969,7 @@ class MessageListView with ChangeNotifier, _MessageSequence {
           notifyListeners();
         }
 
-      case VisibilityEffect.unmuted:
+      case UserTopicVisibilityEffect.unmuted:
         // TODO get the newly-unmuted messages from the message store
         // For now, we simplify the task by just refetching this message list
         // from scratch.

test/model/channel_test.dart

@@ -223,7 +223,8 @@ void main() {
 
       void checkChanges(PerAccountStore store,
           UserTopicVisibilityPolicy newPolicy,
-          VisibilityEffect expectedInStream, VisibilityEffect expectedOverall) {
+          UserTopicVisibilityEffect expectedInStream,
+          UserTopicVisibilityEffect expectedOverall) {
         final event = mkEvent(newPolicy);
         check(store.willChangeIfTopicVisibleInStream(event)).equals(expectedInStream);
         check(store.willChangeIfTopicVisible        (event)).equals(expectedOverall);
@@ -234,31 +235,31 @@ void main() {
         await store.addStream(stream1);
         await store.addSubscription(eg.subscription(stream1));
         checkChanges(store, UserTopicVisibilityPolicy.followed,
-          VisibilityEffect.none, VisibilityEffect.none);
+          UserTopicVisibilityEffect.none, UserTopicVisibilityEffect.none);
       });
 
       test('stream not muted, policy none -> muted, means muted', () async {
         final store = eg.store();
         await store.addStream(stream1);
         await store.addSubscription(eg.subscription(stream1));
         checkChanges(store, UserTopicVisibilityPolicy.muted,
-          VisibilityEffect.muted, VisibilityEffect.muted);
+          UserTopicVisibilityEffect.muted, UserTopicVisibilityEffect.muted);
       });
 
       test('stream muted, policy none -> followed, means none/unmuted', () async {
         final store = eg.store();
         await store.addStream(stream1);
         await store.addSubscription(eg.subscription(stream1, isMuted: true));
         checkChanges(store, UserTopicVisibilityPolicy.followed,
-          VisibilityEffect.none, VisibilityEffect.unmuted);
+          UserTopicVisibilityEffect.none, UserTopicVisibilityEffect.unmuted);
       });
 
       test('stream muted, policy none -> muted, means muted/none', () async {
         final store = eg.store();
         await store.addStream(stream1);
         await store.addSubscription(eg.subscription(stream1, isMuted: true));
         checkChanges(store, UserTopicVisibilityPolicy.muted,
-          VisibilityEffect.muted, VisibilityEffect.none);
+          UserTopicVisibilityEffect.muted, UserTopicVisibilityEffect.none);
       });
 
       final policies = [
@@ -293,10 +294,10 @@ void main() {
               final newVisibleInStream = store.isTopicVisibleInStream(stream1.streamId, eg.t('topic'));
               final newVisible         = store.isTopicVisible(stream1.streamId, eg.t('topic'));
 
-              VisibilityEffect fromOldNew(bool oldVisible, bool newVisible) {
-                if (newVisible == oldVisible) return VisibilityEffect.none;
-                if (newVisible) return VisibilityEffect.unmuted;
-                return VisibilityEffect.muted;
+              UserTopicVisibilityEffect fromOldNew(bool oldVisible, bool newVisible) {
+                if (newVisible == oldVisible) return UserTopicVisibilityEffect.none;
+                if (newVisible) return UserTopicVisibilityEffect.unmuted;
+                return UserTopicVisibilityEffect.muted;
               }
               check(willChangeInStream)
                 .equals(fromOldNew(oldVisibleInStream, newVisibleInStream));