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/modules/xcm-bridge-hub-router/src/benchmarking.rs

@@ -37,10 +37,10 @@ pub trait Config<I: 'static>: crate::Config<I> {
 	/// Returns destination which is valid for this router instance.
 	/// (Needs to pass `T::Bridges`)
 	/// Make sure that `SendXcm` will pass.
-	fn ensure_bridged_target_destination() -> Result<MultiLocation, BenchmarkError> {
-		Ok(MultiLocation::new(
+	fn ensure_bridged_target_destination() -> Result<Location, BenchmarkError> {
+		Ok(Location::new(
 			Self::UniversalLocation::get().len() as u8,
-			X1(GlobalConsensus(Self::BridgedNetworkId::get().unwrap())),
+			[GlobalConsensus(Self::BridgedNetworkId::get().unwrap())],
 		))
 	}
 }

bridges/modules/xcm-bridge-hub-router/src/lib.rs

@@ -80,7 +80,7 @@ pub mod pallet {
 		type WeightInfo: WeightInfo;
 
 		/// Universal location of this runtime.
-		type UniversalLocation: Get<InteriorMultiLocation>;
+		type UniversalLocation: Get<InteriorLocation>;
 		/// The bridged network that this config is for if specified.
 		/// Also used for filtering `Bridges` by `BridgedNetworkId`.
 		/// If not specified, allows all networks pass through.
@@ -235,9 +235,9 @@ type ViaBridgeHubExporter<T, I> = SovereignPaidRemoteExporter<
 impl<T: Config<I>, I: 'static> ExporterFor for Pallet<T, I> {
 	fn exporter_for(
 		network: &NetworkId,
-		remote_location: &InteriorMultiLocation,
+		remote_location: &InteriorLocation,
 		message: &Xcm<()>,
-	) -> Option<(MultiLocation, Option<MultiAsset>)> {
+	) -> Option<(Location, Option<Asset>)> {
 		// ensure that the message is sent to the expected bridged network (if specified).
 		if let Some(bridged_network) = T::BridgedNetworkId::get() {
 			if *network != bridged_network {
@@ -268,7 +268,7 @@ impl<T: Config<I>, I: 'static> ExporterFor for Pallet<T, I> {
 		// take `base_fee` from `T::Brides`, but it has to be the same `T::FeeAsset`
 		let base_fee = match maybe_payment {
 			Some(payment) => match payment {
-				MultiAsset { fun: Fungible(amount), id } if id.eq(&T::FeeAsset::get()) => amount,
+				Asset { fun: Fungible(amount), id } if id.eq(&T::FeeAsset::get()) => amount,
 				invalid_asset => {
 					log::error!(
 						target: LOG_TARGET,
@@ -318,7 +318,7 @@ impl<T: Config<I>, I: 'static> SendXcm for Pallet<T, I> {
 	type Ticket = (u32, <T::ToBridgeHubSender as SendXcm>::Ticket);
 
 	fn validate(
-		dest: &mut Option<MultiLocation>,
+		dest: &mut Option<Location>,
 		xcm: &mut Option<Xcm<()>>,
 	) -> SendResult<Self::Ticket> {
 		// `dest` and `xcm` are required here
@@ -446,7 +446,7 @@ mod tests {
 		run_test(|| {
 			assert_eq!(
 				send_xcm::<XcmBridgeHubRouter>(
-					MultiLocation::new(2, X2(GlobalConsensus(Rococo), Parachain(1000))),
+					Location::new(2, [GlobalConsensus(Rococo), Parachain(1000)]),
 					vec![].into(),
 				),
 				Err(SendError::NotApplicable),
@@ -459,7 +459,7 @@ mod tests {
 		run_test(|| {
 			assert_eq!(
 				send_xcm::<XcmBridgeHubRouter>(
-					MultiLocation::new(2, X2(GlobalConsensus(Rococo), Parachain(1000))),
+					Location::new(2, [GlobalConsensus(Rococo), Parachain(1000)]),
 					vec![ClearOrigin; HARD_MESSAGE_SIZE_LIMIT as usize].into(),
 				),
 				Err(SendError::ExceedsMaxMessageSize),
@@ -483,14 +483,14 @@ mod tests {
 	#[test]
 	fn returns_proper_delivery_price() {
 		run_test(|| {
-			let dest = MultiLocation::new(2, X1(GlobalConsensus(BridgedNetworkId::get())));
+			let dest = Location::new(2, [GlobalConsensus(BridgedNetworkId::get())]);
 			let xcm: Xcm<()> = vec![ClearOrigin].into();
 			let msg_size = xcm.encoded_size();
 
 			// initially the base fee is used: `BASE_FEE + BYTE_FEE * msg_size + HRMP_FEE`
 			let expected_fee = BASE_FEE + BYTE_FEE * (msg_size as u128) + HRMP_FEE;
 			assert_eq!(
-				XcmBridgeHubRouter::validate(&mut Some(dest), &mut Some(xcm.clone()))
+				XcmBridgeHubRouter::validate(&mut Some(dest.clone()), &mut Some(xcm.clone()))
 					.unwrap()
 					.1
 					.get(0),
@@ -518,10 +518,7 @@ mod tests {
 		run_test(|| {
 			let old_bridge = XcmBridgeHubRouter::bridge();
 			assert_ok!(send_xcm::<XcmBridgeHubRouter>(
-				MultiLocation::new(
-					2,
-					X2(GlobalConsensus(BridgedNetworkId::get()), Parachain(1000))
-				),
+				Location::new(2, [GlobalConsensus(BridgedNetworkId::get()), Parachain(1000)]),
 				vec![ClearOrigin].into(),
 			)
 			.map(drop));
@@ -538,10 +535,7 @@ mod tests {
 
 			let old_bridge = XcmBridgeHubRouter::bridge();
 			assert_ok!(send_xcm::<XcmBridgeHubRouter>(
-				MultiLocation::new(
-					2,
-					X2(GlobalConsensus(BridgedNetworkId::get()), Parachain(1000))
-				),
+				Location::new(2, [GlobalConsensus(BridgedNetworkId::get()), Parachain(1000)]),
 				vec![ClearOrigin].into(),
 			)
 			.map(drop));
@@ -560,10 +554,7 @@ mod tests {
 
 			let old_bridge = XcmBridgeHubRouter::bridge();
 			assert_ok!(send_xcm::<XcmBridgeHubRouter>(
-				MultiLocation::new(
-					2,
-					X2(GlobalConsensus(BridgedNetworkId::get()), Parachain(1000))
-				),
+				Location::new(2, [GlobalConsensus(BridgedNetworkId::get()), Parachain(1000)]),
 				vec![ClearOrigin].into(),
 			)
 			.map(drop));

bridges/modules/xcm-bridge-hub-router/src/mock.rs

@@ -49,9 +49,9 @@ construct_runtime! {
 parameter_types! {
 	pub ThisNetworkId: NetworkId = Polkadot;
 	pub BridgedNetworkId: NetworkId = Kusama;
-	pub UniversalLocation: InteriorMultiLocation = X2(GlobalConsensus(ThisNetworkId::get()), Parachain(1000));
-	pub SiblingBridgeHubLocation: MultiLocation = ParentThen(X1(Parachain(1002))).into();
-	pub BridgeFeeAsset: AssetId = MultiLocation::parent().into();
+	pub UniversalLocation: InteriorLocation = [GlobalConsensus(ThisNetworkId::get()), Parachain(1000)].into();
+	pub SiblingBridgeHubLocation: Location = ParentThen([Parachain(1002)].into()).into();
+	pub BridgeFeeAsset: AssetId = Location::parent().into();
 	pub BridgeTable: Vec<NetworkExportTableItem>
 		= vec![
 			NetworkExportTableItem::new(
@@ -61,7 +61,7 @@ parameter_types! {
 				Some((BridgeFeeAsset::get(), BASE_FEE).into())
 			)
 		];
-	pub UnknownXcmVersionLocation: MultiLocation = MultiLocation::new(2, X2(GlobalConsensus(BridgedNetworkId::get()), Parachain(9999)));
+	pub UnknownXcmVersionLocation: Location = Location::new(2, [GlobalConsensus(BridgedNetworkId::get()), Parachain(9999)]);
 }
 
 #[derive_impl(frame_system::config_preludes::TestDefaultConfig as frame_system::DefaultConfig)]
@@ -87,11 +87,11 @@ impl pallet_xcm_bridge_hub_router::Config<()> for TestRuntime {
 }
 
 pub struct LatestOrNoneForLocationVersionChecker<Location>(sp_std::marker::PhantomData<Location>);
-impl<Location: Contains<MultiLocation>> GetVersion
-	for LatestOrNoneForLocationVersionChecker<Location>
+impl<LocationValue: Contains<Location>> GetVersion
+	for LatestOrNoneForLocationVersionChecker<LocationValue>
 {
-	fn get_version_for(dest: &MultiLocation) -> Option<XcmVersion> {
-		if Location::contains(dest) {
+	fn get_version_for(dest: &Location) -> Option<XcmVersion> {
+		if LocationValue::contains(dest) {
 			return None
 		}
 		Some(XCM_VERSION)
@@ -110,7 +110,7 @@ impl SendXcm for TestToBridgeHubSender {
 	type Ticket = ();
 
 	fn validate(
-		_destination: &mut Option<MultiLocation>,
+		_destination: &mut Option<Location>,
 		_message: &mut Option<Xcm<()>>,
 	) -> SendResult<Self::Ticket> {
 		Ok(((), (BridgeFeeAsset::get(), HRMP_FEE).into()))