MM-3543/MM-35436: fix thread being marked unread when updating reply post (#17645)

Summary
Threads should not be returned as unread if a reply post has been edited or reacted to since the time the thread was last viewed

Ticket Link
https://mattermost.atlassian.net/browse/MM-35436
https://mattermost.atlassian.net/browse/MM-35437

store/sqlstore/thread_store.go

@@ -121,7 +121,7 @@ func (s *SqlThreadStore) GetThreadsForUser(userId, teamId string, opts model.Get
 		model.Post
 	}
 
-	unreadRepliesQuery := "SELECT COUNT(Posts.Id) From Posts Where Posts.RootId=ThreadMemberships.PostId AND Posts.UpdateAt >= ThreadMemberships.LastViewed"
+	unreadRepliesQuery := "SELECT COUNT(Posts.Id) From Posts Where Posts.RootId=ThreadMemberships.PostId AND Posts.CreateAt >= ThreadMemberships.LastViewed"
 	fetchConditions := sq.And{
 		sq.Or{sq.Eq{"Channels.TeamId": teamId}, sq.Eq{"Channels.TeamId": ""}},
 		sq.Eq{"ThreadMemberships.UserId": userId},
@@ -147,7 +147,7 @@ func (s *SqlThreadStore) GetThreadsForUser(userId, teamId string, opts model.Get
 			LeftJoin("ThreadMemberships ON Posts.RootId = ThreadMemberships.PostId").
 			LeftJoin("Channels ON Posts.ChannelId = Channels.Id").
 			Where(fetchConditions).
-			Where("Posts.UpdateAt >= ThreadMemberships.LastViewed").ToSql()
+			Where("Posts.CreateAt >= ThreadMemberships.LastViewed").ToSql()
 
 		totalUnreadThreads, err := s.GetMaster().SelectInt(repliesQuery, repliesQueryArgs...)
 		totalUnreadThreadsChan <- store.StoreResult{Data: totalUnreadThreads, NErr: errors.Wrapf(err, "failed to get count unread on threads for user id=%s", userId)}
@@ -334,7 +334,7 @@ func (s *SqlThreadStore) GetThreadForUser(userId, teamId, threadId string, exten
 		model.Post
 	}
 
-	unreadRepliesQuery := "SELECT COUNT(Posts.Id) From Posts Where Posts.RootId=ThreadMemberships.PostId AND Posts.UpdateAt >= ThreadMemberships.LastViewed AND Posts.DeleteAt=0"
+	unreadRepliesQuery := "SELECT COUNT(Posts.Id) From Posts Where Posts.RootId=ThreadMemberships.PostId AND Posts.CreateAt >= ThreadMemberships.LastViewed AND Posts.DeleteAt=0"
 	fetchConditions := sq.And{
 		sq.Or{sq.Eq{"Channels.TeamId": teamId}, sq.Eq{"Channels.TeamId": ""}},
 		sq.Eq{"ThreadMemberships.UserId": userId},

store/storetest/thread_store.go

@@ -329,4 +329,29 @@ func testThreadStorePopulation(t *testing.T, ss store.Store) {
 			return m2.LastUpdated < m.LastUpdated
 		}, time.Second, 10*time.Millisecond)
 	})
+
+	t.Run("Updating post does not make thread unread", func(t *testing.T) {
+		newPosts := makeSomePosts()
+		m, err := ss.Thread().MaintainMembership(newPosts[0].UserId, newPosts[0].Id, true, false, true, true, false)
+		require.NoError(t, err)
+		th, err := ss.Thread().GetThreadForUser(newPosts[0].UserId, "", newPosts[0].Id, false)
+		require.NoError(t, err)
+		require.Equal(t, int64(2), th.UnreadReplies)
+
+		m.LastViewed = newPosts[2].UpdateAt + 1
+		_, err = ss.Thread().UpdateMembership(m)
+		require.NoError(t, err)
+		th, err = ss.Thread().GetThreadForUser(newPosts[0].UserId, "", newPosts[0].Id, false)
+		require.NoError(t, err)
+		require.Equal(t, int64(0), th.UnreadReplies)
+
+		editedPost := newPosts[2].Clone()
+		editedPost.Message = "This is an edited post"
+		_, err = ss.Post().Update(editedPost, newPosts[2])
+		require.NoError(t, err)
+
+		th, err = ss.Thread().GetThreadForUser(newPosts[0].UserId, "", newPosts[0].Id, false)
+		require.NoError(t, err)
+		require.Equal(t, int64(0), th.UnreadReplies)
+	})
 }