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/src/exporter.rs

@@ -52,10 +52,10 @@ where
 	fn validate(
 		network: NetworkId,
 		channel: u32,
-		universal_source: &mut Option<InteriorMultiLocation>,
-		destination: &mut Option<InteriorMultiLocation>,
+		universal_source: &mut Option<InteriorLocation>,
+		destination: &mut Option<InteriorLocation>,
 		message: &mut Option<Xcm<()>>,
-	) -> Result<(Self::Ticket, MultiAssets), SendError> {
+	) -> Result<(Self::Ticket, Assets), SendError> {
 		// Find supported lane_id.
 		let sender_and_lane = Self::lane_for(
 			universal_source.as_ref().ok_or(SendError::MissingArgument)?,
@@ -137,11 +137,11 @@ mod tests {
 	use frame_support::assert_ok;
 	use xcm_executor::traits::export_xcm;
 
-	fn universal_source() -> InteriorMultiLocation {
-		X2(GlobalConsensus(RelayNetwork::get()), Parachain(SIBLING_ASSET_HUB_ID))
+	fn universal_source() -> InteriorLocation {
+		[GlobalConsensus(RelayNetwork::get()), Parachain(SIBLING_ASSET_HUB_ID)].into()
 	}
 
-	fn universal_destination() -> InteriorMultiLocation {
+	fn universal_destination() -> InteriorLocation {
 		BridgedDestination::get()
 	}
 

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

@@ -45,25 +45,25 @@ pub mod pallet {
 		BridgeMessagesConfig<Self::BridgeMessagesPalletInstance>
 	{
 		/// Runtime's universal location.
-		type UniversalLocation: Get<InteriorMultiLocation>;
+		type UniversalLocation: Get<InteriorLocation>;
 		// TODO: https://github.com/paritytech/parity-bridges-common/issues/1666 remove `ChainId` and
 		// replace it with the `NetworkId` - then we'll be able to use
 		// `T as pallet_bridge_messages::Config<T::BridgeMessagesPalletInstance>::BridgedChain::NetworkId`
 		/// Bridged network as relative location of bridged `GlobalConsensus`.
 		#[pallet::constant]
-		type BridgedNetwork: Get<MultiLocation>;
+		type BridgedNetwork: Get<Location>;
 		/// Associated messages pallet instance that bridges us with the
 		/// `BridgedNetworkId` consensus.
 		type BridgeMessagesPalletInstance: 'static;
 
 		/// Price of single message export to the bridged consensus (`Self::BridgedNetworkId`).
-		type MessageExportPrice: Get<MultiAssets>;
+		type MessageExportPrice: Get<Assets>;
 		/// Checks the XCM version for the destination.
 		type DestinationVersion: GetVersion;
 
 		/// Get point-to-point links with bridged consensus (`Self::BridgedNetworkId`).
 		/// (this will be replaced with dynamic on-chain bridges - `Bridges V2`)
-		type Lanes: Get<sp_std::vec::Vec<(SenderAndLane, (NetworkId, InteriorMultiLocation))>>;
+		type Lanes: Get<sp_std::vec::Vec<(SenderAndLane, (NetworkId, InteriorLocation))>>;
 		/// Support for point-to-point links
 		/// (this will be replaced with dynamic on-chain bridges - `Bridges V2`)
 		type LanesSupport: XcmBlobHauler;
@@ -86,10 +86,10 @@ pub mod pallet {
 	impl<T: Config<I>, I: 'static> Pallet<T, I> {
 		/// Returns dedicated/configured lane identifier.
 		pub(crate) fn lane_for(
-			source: &InteriorMultiLocation,
-			dest: (&NetworkId, &InteriorMultiLocation),
+			source: &InteriorLocation,
+			dest: (&NetworkId, &InteriorLocation),
 		) -> Option<SenderAndLane> {
-			let source = source.relative_to(&T::UniversalLocation::get());
+			let source = source.clone().relative_to(&T::UniversalLocation::get());
 
 			// Check that we have configured a point-to-point lane for 'source' and `dest`.
 			T::Lanes::get()

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

@@ -170,16 +170,13 @@ impl pallet_bridge_messages::WeightInfoExt for TestMessagesWeights {
 parameter_types! {
 	pub const RelayNetwork: NetworkId = NetworkId::Kusama;
 	pub const BridgedRelayNetwork: NetworkId = NetworkId::Polkadot;
-	pub const BridgedRelayNetworkLocation: MultiLocation = MultiLocation {
-		parents: 1,
-		interior: X1(GlobalConsensus(BridgedRelayNetwork::get()))
-	};
+	pub BridgedRelayNetworkLocation: Location = (Parent, GlobalConsensus(BridgedRelayNetwork::get())).into();
 	pub const NonBridgedRelayNetwork: NetworkId = NetworkId::Rococo;
 	pub const BridgeReserve: Balance = 100_000;
-	pub UniversalLocation: InteriorMultiLocation = X2(
+	pub UniversalLocation: InteriorLocation = [
 		GlobalConsensus(RelayNetwork::get()),
 		Parachain(THIS_BRIDGE_HUB_ID),
-	);
+	].into();
 	pub const Penalty: Balance = 1_000;
 }
 
@@ -197,13 +194,13 @@ impl pallet_xcm_bridge_hub::Config for TestRuntime {
 
 parameter_types! {
 	pub TestSenderAndLane: SenderAndLane = SenderAndLane {
-		location: MultiLocation::new(1, X1(Parachain(SIBLING_ASSET_HUB_ID))),
+		location: Location::new(1, [Parachain(SIBLING_ASSET_HUB_ID)]),
 		lane: TEST_LANE_ID,
 	};
-	pub const BridgedDestination: InteriorMultiLocation = X1(
+	pub BridgedDestination: InteriorLocation = [
 		Parachain(BRIDGED_ASSET_HUB_ID)
-	);
-	pub TestLanes: sp_std::vec::Vec<(SenderAndLane, (NetworkId, InteriorMultiLocation))> = sp_std::vec![
+	].into();
+	pub TestLanes: sp_std::vec::Vec<(SenderAndLane, (NetworkId, InteriorLocation))> = sp_std::vec![
 		(TestSenderAndLane::get(), (BridgedRelayNetwork::get(), BridgedDestination::get()))
 	];
 }