[MM-41993]: fixed counting thread mentions in unread root post (#19874)

* removed appending the root post to the posts list

also changed `UpdateAt` to `CreateAt` in thread_store.go in accordance with kyriakos

* fixed failing test after latest change

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

api4/user_test.go

@@ -6522,8 +6522,8 @@ func TestMarkThreadUnreadMentionCount(t *testing.T) {
 	require.Nil(t, appErr)
 
 	rpost, _ := postAndCheck(t, client, &model.Post{ChannelId: th.BasicChannel.Id, Message: "testMsg @" + th.BasicUser2.Username})
-	reply, _ := postAndCheck(t, client, &model.Post{ChannelId: th.BasicChannel.Id, Message: "testReply1", RootId: rpost.Id})
-	postAndCheck(t, client, &model.Post{ChannelId: th.BasicChannel.Id, Message: "testReply2", RootId: rpost.Id})
+	reply1, _ := postAndCheck(t, client, &model.Post{ChannelId: th.BasicChannel.Id, Message: "testReply1 @" + th.BasicUser2.Username, RootId: rpost.Id})
+	reply2, _ := postAndCheck(t, client, &model.Post{ChannelId: th.BasicChannel.Id, Message: "testReply2", RootId: rpost.Id})
 
 	th.SystemAdminClient.UpdateThreadReadForUser(th.BasicUser2.Id, th.BasicTeam.Id, rpost.Id, model.GetMillis())
 
@@ -6535,7 +6535,12 @@ func TestMarkThreadUnreadMentionCount(t *testing.T) {
 	u, _, _ = th.SystemAdminClient.GetUserThreads(th.BasicUser2.Id, th.BasicTeam.Id, model.GetUserThreadsOpts{})
 	require.EqualValues(t, 1, u.TotalUnreadMentions)
 
-	th.SystemAdminClient.UpdateThreadReadForUser(th.BasicUser2.Id, th.BasicTeam.Id, rpost.Id, reply.CreateAt)
+	th.SystemAdminClient.UpdateThreadReadForUser(th.BasicUser2.Id, th.BasicTeam.Id, rpost.Id, reply1.CreateAt)
+
+	u, _, _ = th.SystemAdminClient.GetUserThreads(th.BasicUser2.Id, th.BasicTeam.Id, model.GetUserThreadsOpts{})
+	require.EqualValues(t, 1, u.TotalUnreadMentions)
+
+	th.SystemAdminClient.UpdateThreadReadForUser(th.BasicUser2.Id, th.BasicTeam.Id, rpost.Id, reply2.CreateAt)
 
 	u, _, _ = th.SystemAdminClient.GetUserThreads(th.BasicUser2.Id, th.BasicTeam.Id, model.GetUserThreadsOpts{})
 	require.EqualValues(t, 0, u.TotalUnreadMentions)

app/post.go

@@ -1502,7 +1502,6 @@ func (a *App) countThreadMentions(user *model.User, post *model.Post, teamID str
 	if nErr != nil {
 		return 0, model.NewAppError("countMentionsFromPost", "app.channel.count_posts_since.app_error", nil, nErr.Error(), http.StatusInternalServerError)
 	}
-	posts = append(posts, post)
 
 	for _, p := range posts {
 		if p.CreateAt >= timestamp {

store/sqlstore/thread_store.go

@@ -890,7 +890,7 @@ func (s *SqlThreadStore) GetPosts(threadId string, since int64) ([]*model.Post,
 		From("Posts").
 		Where(sq.Eq{"RootId": threadId}).
 		Where(sq.Eq{"DeleteAt": 0}).
-		Where(sq.GtOrEq{"UpdateAt": since}).ToSql()
+		Where(sq.GtOrEq{"CreateAt": since}).ToSql()
 	if err != nil {
 		return nil, errors.Wrap(err, "failed to build query to fetch thread posts")
 	}