XCMv4 (#1230)

# Note for reviewer

Most changes are just syntax changes necessary for the new version.
Most important files should be the ones under the `xcm` folder.

# Description 

Added XCMv4.

## Removed `Multi` prefix
The following types have been renamed:
- MultiLocation -> Location
- MultiAsset -> Asset
- MultiAssets -> Assets
- InteriorMultiLocation -> InteriorLocation
- MultiAssetFilter -> AssetFilter
- VersionedMultiAsset -> VersionedAsset
- WildMultiAsset -> WildAsset
- VersionedMultiLocation -> VersionedLocation

In order to fix a name conflict, the `Assets` in `xcm-executor` were
renamed to `HoldingAssets`, as they represent assets in holding.

## Removed `Abstract` asset id

It was not being used anywhere and this simplifies the code.

Now assets are just constructed as follows:

```rust
let asset: Asset = (AssetId(Location::new(1, Here)), 100u128).into();
```

No need for specifying `Concrete` anymore.

## Outcome is now a named fields struct

Instead of

```rust
pub enum Outcome {
  Complete(Weight),
  Incomplete(Weight, Error),
  Error(Error),
}
```

we now have

```rust
pub enum Outcome {
  Complete { used: Weight },
  Incomplete { used: Weight, error: Error },
  Error { error: Error },
}
```

## Added Reanchorable trait

Now both locations and assets implement this trait, making it easier to
reanchor both.

## New syntax for building locations and junctions

Now junctions are built using the following methods:

```rust
let location = Location {
    parents: 1,
    interior: [Parachain(1000), PalletInstance(50), GeneralIndex(1984)].into()
};
```

or

```rust
let location = Location::new(1, [Parachain(1000), PalletInstance(50), GeneralIndex(1984)]);
```

And they are matched like so:

```rust
match location.unpack() {
  (1, [Parachain(id)]) => ...
  (0, Here) => ...,
  (1, [_]) => ...,
}
```

This syntax is mandatory in v4, and has been also implemented for v2 and
v3 for easier migration.

This was needed to make all sizes smaller.

# TODO
- [x] Scaffold v4
- [x] Port github.com/paritytech/polkadot/pull/7236
- [x] Remove `Multi` prefix
- [x] Remove `Abstract` asset id

---------

Co-authored-by: command-bot <>
Co-authored-by: Keith Yeung <kungfukeith11@gmail.com>

bridges/snowbridge/parachain/runtime/runtime-common/src/lib.rs

@@ -46,43 +46,38 @@ impl<Balance, AccountId, FeeAssetLocation, EthereumNetwork, AssetTransactor, Fee
 	> where
 	Balance: BaseArithmetic + Unsigned + Copy + From<u128> + Into<u128>,
 	AccountId: Clone + Into<[u8; 32]> + From<[u8; 32]>,
-	FeeAssetLocation: Get<MultiLocation>,
+	FeeAssetLocation: Get<Location>,
 	EthereumNetwork: Get<NetworkId>,
 	AssetTransactor: TransactAsset,
 	FeeProvider: SendMessageFeeProvider<Balance = Balance>,
 {
-	fn handle_fee(
-		fees: MultiAssets,
-		context: Option<&XcmContext>,
-		reason: FeeReason,
-	) -> MultiAssets {
+	fn handle_fee(fees: Assets, context: Option<&XcmContext>, reason: FeeReason) -> Assets {
 		let token_location = FeeAssetLocation::get();
 
 		// Check the reason to see if this export is for snowbridge.
 		if !matches!(
 			reason,
-			FeeReason::Export { network: bridged_network, destination }
-				if bridged_network == EthereumNetwork::get() && destination == Here
+			FeeReason::Export { network: bridged_network, ref destination }
+				if bridged_network == EthereumNetwork::get() && destination == &Here
 		) {
 			return fees
 		}
 
 		// Get the parachain sovereign from the `context`.
-		let para_sovereign = if let Some(XcmContext {
-			origin: Some(MultiLocation { parents: 1, interior }),
-			..
-		}) = context
-		{
-			if let Some(Parachain(sibling_para_id)) = interior.first() {
-				let account: AccountId =
-					sibling_sovereign_account_raw((*sibling_para_id).into()).into();
-				account
+		let para_sovereign =
+			if let Some(XcmContext { origin: Some(Location { parents: 1, interior }), .. }) =
+				context
+			{
+				if let Some(Parachain(sibling_para_id)) = interior.first() {
+					let account: AccountId =
+						sibling_sovereign_account_raw((*sibling_para_id).into()).into();
+					account
+				} else {
+					return fees
+				}
 			} else {
 				return fees
-			}
-		} else {
-			return fees
-		};
+			};
 
 		// Get the total fee offered by export message.
 		let maybe_total_supplied_fee: Option<(usize, Balance)> = fees
@@ -90,8 +85,8 @@ impl<Balance, AccountId, FeeAssetLocation, EthereumNetwork, AssetTransactor, Fee
 			.iter()
 			.enumerate()
 			.filter_map(|(index, asset)| {
-				if let MultiAsset { id: Concrete(location), fun: Fungible(amount) } = asset {
-					if *location == token_location {
+				if let Asset { id: location, fun: Fungible(amount) } = asset {
+					if location.0 == token_location {
 						return Some((index, (*amount).into()))
 					}
 				}
@@ -104,7 +99,7 @@ impl<Balance, AccountId, FeeAssetLocation, EthereumNetwork, AssetTransactor, Fee
 			if remote_fee > (0u128).into() {
 				// Refund remote component of fee to physical origin
 				deposit_or_burn_fee::<AssetTransactor, _>(
-					MultiAsset { id: Concrete(token_location), fun: Fungible(remote_fee.into()) }
+					Asset { id: AssetId(token_location.clone()), fun: Fungible(remote_fee.into()) }
 						.into(),
 					context,
 					para_sovereign,
@@ -112,8 +107,8 @@ impl<Balance, AccountId, FeeAssetLocation, EthereumNetwork, AssetTransactor, Fee
 				// Return remaining fee to the next fee handler in the chain.
 				let mut modified_fees = fees.inner().clone();
 				modified_fees.remove(fee_index);
-				modified_fees.push(MultiAsset {
-					id: Concrete(token_location),
+				modified_fees.push(Asset {
+					id: AssetId(token_location),
 					fun: Fungible((total_fee - remote_fee).into()),
 				});
 				return modified_fees.into()

bridges/snowbridge/parachain/runtime/test-common/src/lib.rs

@@ -49,38 +49,36 @@ where
 		+ snowbridge_pallet_outbound_queue::Config,
 	XcmConfig: xcm_executor::Config,
 {
-	let assethub_parachain_location = MultiLocation::new(1, Parachain(assethub_parachain_id));
-	let asset = MultiAsset {
-		id: Concrete(MultiLocation {
-			parents: 0,
-			interior: X1(AccountKey20 { network: None, key: weth_contract_address.into() }),
-		}),
+	let assethub_parachain_location = Location::new(1, Parachain(assethub_parachain_id));
+	let asset = Asset {
+		id: AssetId(Location::new(
+			0,
+			[AccountKey20 { network: None, key: weth_contract_address.into() }],
+		)),
 		fun: Fungible(1000000000),
 	};
 	let assets = vec![asset.clone()];
 
 	let inner_xcm = Xcm(vec![
-		WithdrawAsset(MultiAssets::from(assets.clone())),
+		WithdrawAsset(Assets::from(assets.clone())),
 		ClearOrigin,
 		BuyExecution { fees: asset, weight_limit: Unlimited },
 		DepositAsset {
 			assets: Wild(All),
-			beneficiary: MultiLocation {
-				parents: 0,
-				interior: X1(AccountKey20 { network: None, key: destination_address.into() }),
-			},
+			beneficiary: Location::new(
+				0,
+				[AccountKey20 { network: None, key: destination_address.into() }],
+			),
 		},
 		SetTopic([0; 32]),
 	]);
 
-	let fee = MultiAsset {
-		id: Concrete(MultiLocation { parents: 1, interior: Here }),
-		fun: Fungible(fee_amount),
-	};
+	let fee =
+		Asset { id: AssetId(Location { parents: 1, interior: Here }), fun: Fungible(fee_amount) };
 
 	// prepare transfer token message
 	let xcm = Xcm(vec![
-		WithdrawAsset(MultiAssets::from(vec![fee.clone()])),
+		WithdrawAsset(Assets::from(vec![fee.clone()])),
 		BuyExecution { fees: fee, weight_limit: Unlimited },
 		ExportMessage {
 			network: Ethereum { chain_id: 11155111 },
@@ -90,12 +88,13 @@ where
 	]);
 
 	// execute XCM
-	let hash = xcm.using_encoded(sp_io::hashing::blake2_256);
-	XcmExecutor::<XcmConfig>::execute_xcm(
+	let mut hash = xcm.using_encoded(sp_io::hashing::blake2_256);
+	XcmExecutor::<XcmConfig>::prepare_and_execute(
 		assethub_parachain_location,
 		xcm,
-		hash,
+		&mut hash,
 		RuntimeHelper::<Runtime>::xcm_max_weight(XcmReceivedFrom::Sibling),
+		Weight::zero(),
 	)
 }
 
@@ -176,7 +175,7 @@ pub fn send_unpaid_transfer_token_message<Runtime, XcmConfig>(
 	XcmConfig: xcm_executor::Config,
 	ValidatorIdOf<Runtime>: From<AccountIdOf<Runtime>>,
 {
-	let assethub_parachain_location = MultiLocation::new(1, Parachain(assethub_parachain_id));
+	let assethub_parachain_location = Location::new(1, Parachain(assethub_parachain_id));
 
 	ExtBuilder::<Runtime>::default()
 		.with_collators(collator_session_key.collators())
@@ -194,28 +193,25 @@ pub fn send_unpaid_transfer_token_message<Runtime, XcmConfig>(
 			)
 			.unwrap();
 
-			let asset = MultiAsset {
-				id: Concrete(MultiLocation {
-					parents: 0,
-					interior: X1(AccountKey20 { network: None, key: weth_contract_address.into() }),
-				}),
+			let asset = Asset {
+				id: AssetId(Location::new(
+					0,
+					[AccountKey20 { network: None, key: weth_contract_address.into() }],
+				)),
 				fun: Fungible(1000000000),
 			};
 			let assets = vec![asset.clone()];
 
 			let inner_xcm = Xcm(vec![
-				WithdrawAsset(MultiAssets::from(assets.clone())),
+				WithdrawAsset(Assets::from(assets.clone())),
 				ClearOrigin,
 				BuyExecution { fees: asset, weight_limit: Unlimited },
 				DepositAsset {
 					assets: Wild(AllCounted(1)),
-					beneficiary: MultiLocation {
-						parents: 0,
-						interior: X1(AccountKey20 {
-							network: None,
-							key: destination_contract.into(),
-						}),
-					},
+					beneficiary: Location::new(
+						0,
+						[AccountKey20 { network: None, key: destination_contract.into() }],
+					),
 				},
 				SetTopic([0; 32]),
 			]);
@@ -231,12 +227,13 @@ pub fn send_unpaid_transfer_token_message<Runtime, XcmConfig>(
 			]);
 
 			// execute XCM
-			let hash = xcm.using_encoded(sp_io::hashing::blake2_256);
-			let outcome = XcmExecutor::<XcmConfig>::execute_xcm(
+			let mut hash = xcm.using_encoded(sp_io::hashing::blake2_256);
+			let outcome = XcmExecutor::<XcmConfig>::prepare_and_execute(
 				assethub_parachain_location,
 				xcm,
-				hash,
+				&mut hash,
 				RuntimeHelper::<Runtime>::xcm_max_weight(XcmReceivedFrom::Sibling),
+				Weight::zero(),
 			);
 			// check error is barrier
 			assert_err!(outcome.ensure_complete(), Barrier);