MM-35123 - CRT: Replying to a post with mention causes two mention badges to appear (#17506)

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

app/notification.go

@@ -172,11 +172,12 @@ func (a *App) SendNotifications(post *model.Post, team *model.Team, channel *mod
 	mentionAutofollowChans := []chan *model.AppError{}
 	threadParticipants := map[string]bool{post.UserId: true}
 	if *a.Config().ServiceSettings.ThreadAutoFollow && post.RootId != "" {
+		var rootMentions *ExplicitMentions
 		if parentPostList != nil {
 			threadParticipants[parentPostList.Posts[parentPostList.Order[0]].UserId] = true
 			if channel.Type != model.CHANNEL_DIRECT {
 				rootPost := parentPostList.Posts[parentPostList.Order[0]]
-				rootMentions := getExplicitMentions(rootPost, keywords, groups)
+				rootMentions = getExplicitMentions(rootPost, keywords, groups)
 				for id := range rootMentions.Mentions {
 					threadParticipants[id] = true
 				}
@@ -190,6 +191,10 @@ func (a *App) SendNotifications(post *model.Post, team *model.Team, channel *mod
 			mac := make(chan *model.AppError, 1)
 			go func(userID string) {
 				defer close(mac)
+				isRootMention := false
+				if rootMentions != nil {
+					_, isRootMention = rootMentions.Mentions[userID]
+				}
 				_, incrementMentions := mentions.Mentions[userID]
 				// if the user was not explicitly mentioned, check if they explicitly unfollowed the thread
 				if !incrementMentions {
@@ -205,7 +210,7 @@ func (a *App) SendNotifications(post *model.Post, team *model.Team, channel *mod
 						return
 					}
 				}
-				_, err := a.Srv().Store.Thread().MaintainMembership(userID, post.RootId, true, incrementMentions, *a.Config().ServiceSettings.ThreadAutoFollow, userID == post.UserId, userID == post.UserId)
+				_, err := a.Srv().Store.Thread().MaintainMembership(userID, post.RootId, true, !isRootMention && incrementMentions, *a.Config().ServiceSettings.ThreadAutoFollow, userID == post.UserId, userID == post.UserId)
 				if err != nil {
 					mac <- model.NewAppError("SendNotifications", "app.channel.autofollow.app_error", nil, err.Error(), http.StatusInternalServerError)
 					return