Correctly revoke AlsoPosted notification on comment deletion

pkg/controller/forum/new_post.go

@@ -392,7 +392,7 @@ func NewPost() http.HandlerFunc {
 								TableName: "threads",
 								TableID:   thread.ID,
 								Message:   message,
-								Link:      fmt.Sprintf("/forum/thread/%d%s#p%d", thread.ID, queryString, reply.ID),
+								Link:      fmt.Sprintf("/go/comment?id=%d", reply.ID),
 							}
 							if err := models.CreateNotification(notif); err != nil {
 								log.Error("Couldn't create thread reply notification for subscriber %d: %s", userID, err)

pkg/models/notification.go

@@ -2,6 +2,7 @@ package models
 
 import (
 	"errors"
+	"fmt"
 	"strings"
 	"time"
 
@@ -100,6 +101,33 @@ func RemoveNotification(tableName string, tableID uint64) error {
 	return result.Error
 }
 
+// RemoveAlsoPostedNotification removes a 'has also posted' notification if the comment is later deleted.
+//
+// This is specialized for deleting replies to forum threads where subscribers were notified that the
+// user has AlsoPosted on that thread. If the user deletes their comment, this specific notification
+// needs to be revoked from people who received it before, so the head of their original comment is not
+// leaked on their notifications page.
+//
+// These notifications have a Type=also_posted TableName=threads TableID=threads.ID with the only hard
+// link to the specific comment on that thread being the hyperlink URL that goes to their comment.
+func RemoveAlsoPostedNotification(thread *Thread, commentID uint64) error {
+	// Match the specific notification by its link URL.
+	var (
+		// Modern link URL ('/go/comment?id=1234' which finds the right page to see the comment)
+		newLink = fmt.Sprintf("/go/comment?id=%d", commentID)
+
+		// Legacy link URL ('/forum/thread/123?page=4#p456') which embeds the thread ID, an
+		// optional query string (page number) and the comment ID anchor.
+		legacyLink = fmt.Sprintf("/forum/thread/%d%%#p%d", thread.ID, commentID)
+	)
+
+	result := DB.Where(
+		"type = ? AND table_name = 'threads' AND table_id = ? AND (link = ? OR link LIKE ?)",
+		NotificationAlsoPosted, thread.ID, newLink, legacyLink,
+	).Delete(&Notification{})
+	return result.Error
+}
+
 // RemoveNotificationBulk about several table IDs, e.g. when bulk removing private photo upload
 // notifications for everybody on the site.
 func RemoveNotificationBulk(tableName string, tableIDs []uint64) error {

pkg/models/thread.go

@@ -184,6 +184,11 @@ func (t *Thread) DeleteReply(comment *Comment) error {
 		return errors.New("that comment doesn't belong to this thread")
 	}
 
+	// Revoke any notifications sent to subscribers when this reply was first created.
+	if err := RemoveAlsoPostedNotification(t, comment.ID); err != nil {
+		log.Error("Thread.DeleteReply: RemoveAlsoPostedNotification: %s", err)
+	}
+
 	// Is this the primary comment that started the thread? If so, delete the whole thread.
 	if comment.ID == t.CommentID {
 		log.Error("DeleteReply(%d): this is the parent comment of a thread (%d '%s'), remove the whole thread", comment.ID, t.ID, t.Title)