[pallet_assets] How to destroy an asset with potentially `u32::MAX` accounts?

[Chralt98]

Hey valuable Substrate maintainers,

I found out, that the witness limits the number of deletions here, but when there are too many accounts for one asset, then a sufficiently high number for the accounts in the witness param would lead to a weight which exceeds the maximum block limit. What could be done, if there are u32::MAX accounts with non-zero balances? Then, we couldn't destroy the asset right? Or is the consumed weight with u32::MAX below the maximum block limit? I don't think so.

What can I do to destroy a portion of all accounts? For example one could call an extrinsic multiple times with a small witness to destroy all u32::MAX accounts.

u32::MAX should only be an example to get a better understanding of this problem

[kianenigma]

cc @jsidorenko

[jsidorenko]

cc @tonyalaribe

[jsidorenko]

What if we change the assets deletion process a bit:

1. we mark an asset as soft-deleted and thus prevent any transfers
2. we create a method to wipe user balances for such a token by passing either the addresses or the number of accounts to wipe. This would allow calling the same method multiple times
3. and finally, completely delete the token

[ggwpez]

1. we mark an asset as soft-deleted and thus prevent any transfers

freeze_asset could be enough for that.

[joepetrowski]

It's a bit of an edge case, but freeze_asset should really be used in advance of deleting an asset anyway in order to provide the correct witness data. Otherwise, a simple transfer getting between your transaction construction and inclusion will invalidate the destroy call.

[tonyalaribe]

So an alternate solution would be to destroy the maximum number of accounts, and then emit a PartiallyDestroyed event to encourage reexecuting the action to complete destroying the asset. Like the refund and dissolve pattern in crowdloans

[Joe edit: changed master to commit to save in the future]

[jsidorenko]

yeah, that could work as well

[tonyalaribe]

I'll create a PR for this.