Added updating of username based mentions on username change

store/sql_user_store.go

@@ -5,6 +5,7 @@ package store
 
 import (
 	"fmt"
+	"strings"
 	"github.com/mattermost/platform/model"
 	"github.com/mattermost/platform/utils"
 )
@@ -163,6 +164,17 @@ func (us SqlUserStore) Update(user *model.User, allowActiveUpdate bool) StoreCha
 				user.EmailVerified = false
 			}
 
+			if user.Username != oldUser.Username {
+				nonUsernameKeys := []string{}
+				splitKeys := strings.Split(user.NotifyProps["mention_keys"], ",")
+				for _, key := range splitKeys {
+					if key != oldUser.Username && key != "@" + oldUser.Username {
+						nonUsernameKeys = append(nonUsernameKeys, key)
+					}
+				}
+				user.NotifyProps["mention_keys"] = strings.Join(nonUsernameKeys, ",") + user.Username + ",@" + user.Username
+			}
+
 			if count, err := us.GetMaster().Update(user); err != nil {
 				if IsUniqueConstraintError(err.Error(), "Email", "users_email_teamid_key") {
 					result.Err = model.NewAppError("SqlUserStore.Update", "This email is already taken. Please choose another", "user_id="+user.Id+", "+err.Error())