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>

cumulus/parachains/runtimes/bridge-hubs/test-utils/src/test_cases/from_grandpa_chain.rs

@@ -336,9 +336,9 @@ where
 				(),
 			>(
 				LaneId::default(),
-				vec![xcm::v3::Instruction::<()>::ClearOrigin; 1_024].into(),
+				vec![Instruction::<()>::ClearOrigin; 1_024].into(),
 				1,
-				X2(GlobalConsensus(Polkadot), Parachain(1_000)),
+				[GlobalConsensus(Polkadot), Parachain(1_000)].into(),
 				1u32.into(),
 			);
 

cumulus/parachains/runtimes/bridge-hubs/test-utils/src/test_cases/from_parachain.rs

@@ -418,9 +418,9 @@ where
 			(),
 		>(
 			LaneId::default(),
-			vec![xcm::v3::Instruction::<()>::ClearOrigin; 1_024].into(),
+			vec![Instruction::<()>::ClearOrigin; 1_024].into(),
 			1,
-			X2(GlobalConsensus(Polkadot), Parachain(1_000)),
+			[GlobalConsensus(Polkadot), Parachain(1_000)].into(),
 			1,
 			5,
 			1_000,

cumulus/parachains/runtimes/bridge-hubs/test-utils/src/test_cases/helpers.rs

@@ -230,7 +230,7 @@ pub fn relayed_incoming_message_works<Runtime, AllPalletsWithoutSystem, MPI>(
 	prepare_message_proof_import: impl FnOnce(
 		Runtime::AccountId,
 		Runtime::InboundRelayer,
-		InteriorMultiLocation,
+		InteriorLocation,
 		MessageNonce,
 		Xcm<()>,
 	) -> CallsAndVerifiers<Runtime>,
@@ -276,21 +276,21 @@ pub fn relayed_incoming_message_works<Runtime, AllPalletsWithoutSystem, MPI>(
 
 			// set up relayer details and proofs
 
-			let message_destination =
-				X2(GlobalConsensus(local_relay_chain_id), Parachain(sibling_parachain_id));
+			let message_destination: InteriorLocation =
+				[GlobalConsensus(local_relay_chain_id), Parachain(sibling_parachain_id)].into();
 			// some random numbers (checked by test)
 			let message_nonce = 1;
 
-			let xcm = vec![xcm::v3::Instruction::<()>::ClearOrigin; 42];
+			let xcm = vec![Instruction::<()>::ClearOrigin; 42];
 			let expected_dispatch = xcm::latest::Xcm::<()>({
 				let mut expected_instructions = xcm.clone();
 				// dispatch prepends bridge pallet instance
 				expected_instructions.insert(
 					0,
-					DescendOrigin(X1(PalletInstance(
+					DescendOrigin([PalletInstance(
 						<pallet_bridge_messages::Pallet<Runtime, MPI> as PalletInfoAccess>::index()
 							as u8,
-					))),
+					)].into()),
 				);
 				expected_instructions
 			});

cumulus/parachains/runtimes/bridge-hubs/test-utils/src/test_cases/mod.rs

@@ -319,8 +319,8 @@ pub fn handle_export_message_from_system_parachain_to_outbound_queue_works<
 	>,
 	export_message_instruction: fn() -> Instruction<XcmConfig::RuntimeCall>,
 	expected_lane_id: LaneId,
-	existential_deposit: Option<MultiAsset>,
-	maybe_paid_export_message: Option<MultiAsset>,
+	existential_deposit: Option<Asset>,
+	maybe_paid_export_message: Option<Asset>,
 	prepare_configuration: impl Fn(),
 ) where
 	Runtime: BasicParachainRuntime + BridgeMessagesConfig<MessagesPalletInstance>,
@@ -328,7 +328,7 @@ pub fn handle_export_message_from_system_parachain_to_outbound_queue_works<
 	MessagesPalletInstance: 'static,
 {
 	assert_ne!(runtime_para_id, sibling_parachain_id);
-	let sibling_parachain_location = MultiLocation::new(1, Parachain(sibling_parachain_id));
+	let sibling_parachain_location = Location::new(1, [Parachain(sibling_parachain_id)]);
 
 	run_test::<Runtime, _>(collator_session_key, runtime_para_id, vec![], || {
 		prepare_configuration();
@@ -361,7 +361,7 @@ pub fn handle_export_message_from_system_parachain_to_outbound_queue_works<
 			.expect("deposited fee");
 
 			Xcm(vec![
-				WithdrawAsset(MultiAssets::from(vec![fee.clone()])),
+				WithdrawAsset(Assets::from(vec![fee.clone()])),
 				BuyExecution { fees: fee, weight_limit: Unlimited },
 				export_message_instruction(),
 			])
@@ -373,12 +373,13 @@ pub fn handle_export_message_from_system_parachain_to_outbound_queue_works<
 		};
 
 		// execute XCM
-		let hash = xcm.using_encoded(sp_io::hashing::blake2_256);
-		assert_ok!(XcmExecutor::<XcmConfig>::execute_xcm(
+		let mut hash = xcm.using_encoded(sp_io::hashing::blake2_256);
+		assert_ok!(XcmExecutor::<XcmConfig>::prepare_and_execute(
 			sibling_parachain_location,
 			xcm,
-			hash,
+			&mut hash,
 			RuntimeHelper::<Runtime>::xcm_max_weight(XcmReceivedFrom::Sibling),
+			Weight::zero(),
 		)
 		.ensure_complete());
 
@@ -446,9 +447,9 @@ pub fn message_dispatch_routing_works<
 	NetworkDistanceAsParentCount: Get<u8>,
 {
 	struct NetworkWithParentCount<N, C>(core::marker::PhantomData<(N, C)>);
-	impl<N: Get<NetworkId>, C: Get<u8>> Get<MultiLocation> for NetworkWithParentCount<N, C> {
-		fn get() -> MultiLocation {
-			MultiLocation { parents: C::get(), interior: X1(GlobalConsensus(N::get())) }
+	impl<N: Get<NetworkId>, C: Get<u8>> Get<Location> for NetworkWithParentCount<N, C> {
+		fn get() -> Location {
+			Location::new(C::get(), [GlobalConsensus(N::get())])
 		}
 	}
 
@@ -495,7 +496,7 @@ pub fn message_dispatch_routing_works<
 			BridgedNetwork,
 			NetworkWithParentCount<RuntimeNetwork, NetworkDistanceAsParentCount>,
 			AlwaysLatest,
-		>((RuntimeNetwork::get(), X1(Parachain(sibling_parachain_id))));
+		>((RuntimeNetwork::get(), [Parachain(sibling_parachain_id)].into()));
 
 		// 2.1. WITHOUT opened hrmp channel -> RoutingError
 		let result =
@@ -565,52 +566,43 @@ where
 {
 	// data here are not relevant for weighing
 	let mut xcm = Xcm(vec![
-		WithdrawAsset(MultiAssets::from(vec![MultiAsset {
-			id: Concrete(MultiLocation { parents: 1, interior: Here }),
+		WithdrawAsset(Assets::from(vec![Asset {
+			id: AssetId(Location::new(1, [])),
 			fun: Fungible(34333299),
 		}])),
 		BuyExecution {
-			fees: MultiAsset {
-				id: Concrete(MultiLocation { parents: 1, interior: Here }),
-				fun: Fungible(34333299),
-			},
+			fees: Asset { id: AssetId(Location::new(1, [])), fun: Fungible(34333299) },
 			weight_limit: Unlimited,
 		},
 		ExportMessage {
 			network: Polkadot,
-			destination: X1(Parachain(1000)),
+			destination: [Parachain(1000)].into(),
 			xcm: Xcm(vec![
-				ReserveAssetDeposited(MultiAssets::from(vec![MultiAsset {
-					id: Concrete(MultiLocation {
-						parents: 2,
-						interior: X1(GlobalConsensus(Kusama)),
-					}),
+				ReserveAssetDeposited(Assets::from(vec![Asset {
+					id: AssetId(Location::new(2, [GlobalConsensus(Kusama)])),
 					fun: Fungible(1000000000000),
 				}])),
 				ClearOrigin,
 				BuyExecution {
-					fees: MultiAsset {
-						id: Concrete(MultiLocation {
-							parents: 2,
-							interior: X1(GlobalConsensus(Kusama)),
-						}),
+					fees: Asset {
+						id: AssetId(Location::new(2, [GlobalConsensus(Kusama)])),
 						fun: Fungible(1000000000000),
 					},
 					weight_limit: Unlimited,
 				},
 				DepositAsset {
 					assets: Wild(AllCounted(1)),
-					beneficiary: MultiLocation {
-						parents: 0,
-						interior: X1(xcm::latest::prelude::AccountId32 {
+					beneficiary: Location::new(
+						0,
+						[xcm::latest::prelude::AccountId32 {
 							network: None,
 							id: [
 								212, 53, 147, 199, 21, 253, 211, 28, 97, 20, 26, 189, 4, 169, 159,
 								214, 130, 44, 133, 88, 133, 76, 205, 227, 154, 86, 132, 231, 165,
 								109, 162, 125,
 							],
-						}),
-					},
+						}],
+					),
 				},
 				SetTopic([
 					116, 82, 194, 132, 171, 114, 217, 165, 23, 37, 161, 177, 165, 179, 247, 114,
@@ -618,10 +610,7 @@ where
 				]),
 			]),
 		},
-		DepositAsset {
-			assets: Wild(All),
-			beneficiary: MultiLocation { parents: 1, interior: X1(Parachain(1000)) },
-		},
+		DepositAsset { assets: Wild(All), beneficiary: Location::new(1, [Parachain(1000)]) },
 		SetTopic([
 			36, 224, 250, 165, 82, 195, 67, 110, 160, 170, 140, 87, 217, 62, 201, 164, 42, 98, 219,
 			157, 124, 105, 248, 25, 131, 218, 199, 36, 109, 173, 100, 122,

cumulus/parachains/runtimes/bridge-hubs/test-utils/src/test_data/mod.rs

@@ -37,10 +37,10 @@ use xcm_executor::traits::{validate_export, ExportXcm};
 
 pub fn prepare_inbound_xcm<InnerXcmRuntimeCall>(
 	xcm_message: Xcm<InnerXcmRuntimeCall>,
-	destination: InteriorMultiLocation,
+	destination: InteriorLocation,
 ) -> Vec<u8> {
-	let location = xcm::VersionedInteriorMultiLocation::V3(destination);
-	let xcm = xcm::VersionedXcm::<InnerXcmRuntimeCall>::V3(xcm_message);
+	let location = xcm::VersionedInteriorLocation::V4(destination);
+	let xcm = xcm::VersionedXcm::<InnerXcmRuntimeCall>::V4(xcm_message);
 	// this is the `BridgeMessage` from polkadot xcm builder, but it has no constructor
 	// or public fields, so just tuple
 	// (double encoding, because `.encode()` is called on original Xcm BLOB when it is pushed
@@ -101,7 +101,7 @@ macro_rules! grab_haul_blob (
 /// which are transferred over bridge.
 pub(crate) fn simulate_message_exporter_on_bridged_chain<
 	SourceNetwork: Get<NetworkId>,
-	DestinationNetwork: Get<MultiLocation>,
+	DestinationNetwork: Get<Location>,
 	DestinationVersion: GetVersion,
 >(
 	(destination_network, destination_junctions): (NetworkId, Junctions),
@@ -109,8 +109,8 @@ pub(crate) fn simulate_message_exporter_on_bridged_chain<
 	grab_haul_blob!(GrabbingHaulBlob, GRABBED_HAUL_BLOB_PAYLOAD);
 
 	// lets pretend that some parachain on bridged chain exported the message
-	let universal_source_on_bridged_chain =
-		X2(GlobalConsensus(SourceNetwork::get()), Parachain(5678));
+	let universal_source_on_bridged_chain: Junctions =
+		[GlobalConsensus(SourceNetwork::get()), Parachain(5678)].into();
 	let channel = 1_u32;
 
 	// simulate XCM message export