Add an option to delete mentioning messages also

[erkinalp]

In MESSAGE_DELETE, MESSAGE_BULK_DELETE and GUILD_BAN_ADD (sorry I referred to them by gateway event names but it actually applies to REST counterparts), also add an option to remove messages that mention that user/message.
For the sake of performance, deletion of such messages may happen asynchronously with the exception of last 100 or so messages mentioning the banned user/removed message(s).

[MichailiK]

This could be abused by mentioning someone & deleting the message with this feature. The user gets a notification sound, but will likely have no idea from where it is coming from.

I've misinterpreted this idea as marking pings, which the banned user has caused, as read.

[erkinalp]

Ghost pings cannot be prevented, hence I tend to ignore them. This could be abused to rewrite history? Yes, but there are use cases you want to pretend that user never joined in the first place.

[jhgg]

This isn't feasible with the way we store messages. A message is only singly linked to its reply. So we can't go from message -> the messages that replied to it easily, only message -> the message that was replied to.

[erkinalp]

@jhgg I think that could be solved by adding double links in the backend while still serving single-links in the API side to prevent abuse by non mods. And migration to double links could be performed lazily, with forward links initially populated as null and filled in as reply messages with back links are fetched.

[erkinalp]

And yes, this feature request has been a response to a real abuse scenario I have experienced while moderating a real Discord guild. I had to manually go and delete 2k+ messages of the offending user or mentioning the offending user. It took more than seven hours to manually identify and delete all them one by one, as no existing bots had that functionality and making and testing a new bot with that functionality would have taken something like a week.