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/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));