Enhance interoperability for pallet-assets

[bkontur]

Relates to old comment: #1130 (comment)
Relates to: #4826 (new XCMv5)

Potential problem

Let's imagine a simple scenario where a sibling parachain of AssetHub wants to create/register an asset on AssetHub's foreign assets instance, which uses xcm::v3::Location as the AssetId:

impl pallet_assets::Config<ForeignAssetsInstance> for Runtime {
	type AssetId = xcm::v3::Location;
	type AssetIdParameter = xcm::v3::Location;

This means that the sibling needs to construct an XCM Transact with an encoded call that uses xcm::v3::Location:

Xcm([Transact {
	origin_kind: ...,
	require_weight_at_most: ...,
	call: pallet_assets::Call::create {
		id: xcm::v3::Location::new(1, Parachain(...), ...),    // <- XCMv3     
		admin: ...,
		min_balance: ...,
	}.encode()                                                     // <- encoded
}]),

Now, let's imagine we upgrade AssetHub to use xcm::v4::Location. At this point, the sibling parachain could encounter problems if it doesn't upgrade at the same time as AssetHub. And also upgrading at the "same" time is not 100%, because there could be some (e.g. HRMP) messages on the way. The real issue could arise if the new XCM version used by AssetHub has encoding/decoding that is incompatible with the older version. Essentially, AssetHub would be unable to decode the Transact's encoded call and would discard the messages.

Solution

I suggest changing pallet_assets:

- type AssetIdParameter: Parameter + From<Self::AssetId> + Into<Self::AssetId>
+ type AssetIdParameter: Parameter + TryFrom<Self::AssetId> + TryInto<Self::AssetId>

This could escalate to enable setting up the runtime like this:

impl pallet_assets::Config<ForeignAssetsInstance> for Runtime {
   ...
	type AssetId = xcm::v3::Location;
	type AssetIdParameter = VersionedLocation;
   ...

AssetIdParameter is used for extrinsic parameters. Therefore, if it were VersionedLocation, external users, such as wallets or sibling parachains, wouldn’t need to make any changes when a new XCM version is released.
Additionally, there is an unwritten consensus that we should use VersionedLocation for extrinsic parameters.

Yes, this solution is a kind of 'best-effort' approach and assumes that we can convert/decode older XCM Location versions to the new one.

[xlc]

there is an unwritten consensus that we should use VersionedLocation for extrinsic parameters

someone please make this a written requirement

[acatangiu]

there is an unwritten consensus that we should use VersionedLocation for extrinsic parameters

someone please make this a written requirement

yes, @bkontur please create an "epic" along the lines of "Use versioned parameters across all FRAME pallets"

this issue concerning only pallet-assets would fall under that