PLT-6217-bis Fixes system message posted to Town Square when a user joins a team #7863 (#7864)

* Adds new string post message when a user has joined a team (#6483)

* Simplifies long if statement in post.go (#6483)

app/channel.go

@@ -64,7 +64,7 @@ func (a *App) JoinDefaultChannels(teamId string, user *model.User, channelRole s
 		}
 
 		if requestor == nil {
-			if err := a.postJoinChannelMessage(user, townSquare); err != nil {
+			if err := a.postJoinTeamMessage(user, townSquare); err != nil {
 				l4g.Error(utils.T("api.channel.post_user_add_remove_message_and_forget.error"), err)
 			}
 		} else {
@@ -965,6 +965,24 @@ func (a *App) postJoinChannelMessage(user *model.User, channel *model.Channel) *
 	return nil
 }
 
+func (a *App) postJoinTeamMessage(user *model.User, channel *model.Channel) *model.AppError {
+	post := &model.Post{
+		ChannelId: channel.Id,
+		Message:   fmt.Sprintf(utils.T("api.team.join_team.post_and_forget"), user.Username),
+		Type:      model.POST_JOIN_TEAM,
+		UserId:    user.Id,
+		Props: model.StringInterface{
+			"username": user.Username,
+		},
+	}
+
+	if _, err := a.CreatePost(post, channel, false); err != nil {
+		return model.NewAppError("postJoinTeamMessage", "api.channel.post_user_add_remove_message_and_forget.error", nil, err.Error(), http.StatusInternalServerError)
+	}
+
+	return nil
+}
+
 func (a *App) LeaveChannel(channelId string, userId string) *model.AppError {
 	sc := a.Srv.Store.Channel().Get(channelId, true)
 	uc := a.Srv.Store.User().Get(userId)