Reply notifications not being sent out to users

[SychO9]

Bug Report

Current Behavior
When someone replies to a discussion you follow, you do not receive a notification.

Steps to Reproduce

1. Follow a discussion you have read.
2. Reply with a different user
3. No notification is sent out.

Expected Behavior
A notification should be sent out.

Environment

• Flarum version: Introduced in 1.3.0

Possible Solution
Context: If the actor has read the post number 6 which at the time was the last, and someone replies, the subscriptions extension sends out notifications to those following who have last read post number 6. It doesn't send notifications to all those who have last read less than post number 7 (newest reply) to avoid repetitive notifications.

Additional Context
It does this by listening to the Posted event and using the $event->post->discussion->last_post_number (should be 6), it expects to run before DiscussionMetadataUpdater subscriber (updates last_post_number to 7), however in 1.3 this PR (#3373) changes the behavior and leads to extension listeners to run after all core listeners. So what's happening now is that the last_post_number used in the subscriptions listener has already been updated to 7 in this example.

v1.2	v1.3

Potential Solutions

• We could introduce a listener priority system to make sure the listener runs before the discussion metadata updater listener.
• We could go for a last_post_number - 1 change in the subscriptions listener. This wouldn't be a solution if we were still using post_number_index, but since we now count new post numbers based on previous existing post number, it might be fine to do.

[luceos]

As the post has already been saved when the listener is dispatched, why don't we use $post->number -1 instead? Relying on a relationship inside that listener seems unnecessary and the number should already have been updated.

[SychO9]

Yes I believe we could just do that, I would just like to make sure that is the case first, I'll investigate further sometime later today.

[matteocontrini]

Is there a chance for this fix to be released as a patch? I would personally skip 1.3.0 altogether otherwise...

[luceos]

@matteocontrini yes we'll do a patch release for this soon.