Fungible and fungibles adapters should allow account death like burns and mints

[franciscoaguirre]

The fungible and fungibles adapters set the preservation of the burn operation to Expendable: here and here.
This allows accounts to transfer all their funds (and getting reaped because of it) out of their account.
However, this only works if they're using the WithdrawAsset and DepositAsset instructions, which correspond to burn_from and mint_into.
If TransferAsset is used, as is the case with limited_reserve_assets_transfer, then the transfer function will be called with Preserve.

This distinction is arbitrary and we should change the way TransferAsset is handled to also allow transferring all the funds of an account. It results in confusing errors for users.
If needed, we could add a Hint for changing the default of ALL operations from Expendable to Preserve.

[antonkhvorov]

Very much needed

[dhirajs0]

I would like to work on this one.

[franciscoaguirre]

@dhirajs0 Thank you for wanting to work on this! Let me know if everything is understood or if you have any questions. I'm here to help.

[dhirajs0]

@franciscoaguirre

This distinction is arbitrary and we should change the way TransferAsset is handled to also allow transferring all the funds of an account. It results in confusing errors for users.

We can change the Preservation of transfer function from Preserve to Expendable so that the behavior will be consistent with the WithdrawAsset function, as in fungible and fungibles adapter.

If needed, we could add a Hint for changing the default of ALL operations from Expendable to Preserve.

If we add PreservationType { preservation: Preservation } to the Hint and import use frame_support::traits::tokens::Preservation; in the same file(mod.rs), and then while building xcm instruction the set_hints(vec![PreservationType { preservation: Preserve}]) method is called, is this good enough to change the default of ALL operations from Expendable to Preserve or do we need to make more changes for the PreservationType hint to works?

[franciscoaguirre]

We can change the Preservation of transfer function from Preserve to Expendable so that the behavior will be consistent with the WithdrawAsset function, as in fungible and fungibles adapter.

Yes, we should do exactly this.

If we add PreservationType { preservation: Preservation } to the Hint and import use frame_support::traits::tokens::Preservation; in the same file(mod.rs), and then while building xcm instruction the set_hints(vec![PreservationType { preservation: Preserve}]) method is called, is this good enough to change the default of ALL operations from Expendable to Preserve or do we need to make more changes for the PreservationType hint to works?

We can't add a new Hint now because XCMv5 is already frozen, released in stable2412. But for XCMv6 for example, we can add a hint PreserveAccounts: bool that just lets you specify whether you want to make sure to preserve accounts. I think it's much simpler if it's just a bool.
But for now, don't worry about the hint, we can add it later.

[dhirajs0]

Hi @franciscoaguirre,

Thanks for the clarification!

I’ve raised a PR to address this issue. Would greatly appreciate it if you could review it and share your feedback when you have a moment.