Receiving multiple notifications about the same reply

Contribute Feature
6

Above all, I do not want to receive another notification if nothing has changed in the post that would cause a notification. Correcting a typo should not notify me if I have already been notified just because 2 notifications about the same topic were collapsed before. And I never noticed that for years until it happened in December.

I asked ChatGPT to write a summary of what it told me about this issue, when I tried to find repro steps based on the code

Summary: Why duplicate notifications are normally prevented, and why it fails here AI

Core issue

Duplicate-prevention relies on finding a reply notification that is still scoped to the edited post, but reply notifications are collapsed, destroyed, or re-attached to a different post.
As a result, edit-time suppression cannot reliably detect that the user was already notified about the reply.

Duplicate notifications are prevented in PostAlerter by:

  1. Tracking users already notified during post creation
notified = []
  1. Suppressing secondary triggers if a reply notification exists
if [:quoted, :linked, :mentioned, :chat_quoted].include?(type)
  return if existing_notifications.find { |n|
    n.notification_type == Notification.types[:replied]
  }
end

This is meant to avoid notifying a user twice about the same post.

  1. Collapsing reply notifications
    Reply notifications (:replied) are collapsed per topic:
destroy_notifications(user, COLLAPSED_NOTIFICATION_TYPES, topic)

The surviving notification is re-attached to:

post = first_unread_post(user, topic)

so the notification no longer represents the post that originally triggered it. As a result, suppression logic that relies on matching post_number cannot reliably detect prior notifications for edited posts.

Why this fails in the repro case

In the repro:

  • The user is notified about the reply initially
  • When multiple replies exist, reply notifications are collapsed
  • The collapsed notification:
    • may no longer exist for the edited post, or
    • exists with a different post_number
  • On edit:
    • reply logic does not run (new_record == false)
    • suppression checks only for a post-scoped :replied notification
    • none is found → suppression fails
  • Quote/link detection runs again and creates new notifications

From the user’s perspective:

“I was already notified about this reply.”

From the code’s perspective:

“There is no existing notification for this post.”

Both are true.