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/assets/asset-hub-westend/src/weights/xcm/mod.rs

@@ -23,14 +23,14 @@ use pallet_xcm_benchmarks_generic::WeightInfo as XcmGeneric;
 use sp_std::prelude::*;
 use xcm::{latest::prelude::*, DoubleEncoded};
 
-trait WeighMultiAssets {
-	fn weigh_multi_assets(&self, weight: Weight) -> Weight;
+trait WeighAssets {
+	fn weigh_assets(&self, weight: Weight) -> Weight;
 }
 
 const MAX_ASSETS: u64 = 100;
 
-impl WeighMultiAssets for MultiAssetFilter {
-	fn weigh_multi_assets(&self, weight: Weight) -> Weight {
+impl WeighAssets for AssetFilter {
+	fn weigh_assets(&self, weight: Weight) -> Weight {
 		match self {
 			Self::Definite(assets) => weight.saturating_mul(assets.inner().iter().count() as u64),
 			Self::Wild(asset) => match asset {
@@ -49,40 +49,36 @@ impl WeighMultiAssets for MultiAssetFilter {
 	}
 }
 
-impl WeighMultiAssets for MultiAssets {
-	fn weigh_multi_assets(&self, weight: Weight) -> Weight {
+impl WeighAssets for Assets {
+	fn weigh_assets(&self, weight: Weight) -> Weight {
 		weight.saturating_mul(self.inner().iter().count() as u64)
 	}
 }
 
 pub struct AssetHubWestendXcmWeight<Call>(core::marker::PhantomData<Call>);
 impl<Call> XcmWeightInfo<Call> for AssetHubWestendXcmWeight<Call> {
-	fn withdraw_asset(assets: &MultiAssets) -> Weight {
-		assets.weigh_multi_assets(XcmFungibleWeight::<Runtime>::withdraw_asset())
+	fn withdraw_asset(assets: &Assets) -> Weight {
+		assets.weigh_assets(XcmFungibleWeight::<Runtime>::withdraw_asset())
 	}
-	fn reserve_asset_deposited(assets: &MultiAssets) -> Weight {
-		assets.weigh_multi_assets(XcmFungibleWeight::<Runtime>::reserve_asset_deposited())
+	fn reserve_asset_deposited(assets: &Assets) -> Weight {
+		assets.weigh_assets(XcmFungibleWeight::<Runtime>::reserve_asset_deposited())
 	}
-	fn receive_teleported_asset(assets: &MultiAssets) -> Weight {
-		assets.weigh_multi_assets(XcmFungibleWeight::<Runtime>::receive_teleported_asset())
+	fn receive_teleported_asset(assets: &Assets) -> Weight {
+		assets.weigh_assets(XcmFungibleWeight::<Runtime>::receive_teleported_asset())
 	}
 	fn query_response(
 		_query_id: &u64,
 		_response: &Response,
 		_max_weight: &Weight,
-		_querier: &Option<MultiLocation>,
+		_querier: &Option<Location>,
 	) -> Weight {
 		XcmGeneric::<Runtime>::query_response()
 	}
-	fn transfer_asset(assets: &MultiAssets, _dest: &MultiLocation) -> Weight {
-		assets.weigh_multi_assets(XcmFungibleWeight::<Runtime>::transfer_asset())
+	fn transfer_asset(assets: &Assets, _dest: &Location) -> Weight {
+		assets.weigh_assets(XcmFungibleWeight::<Runtime>::transfer_asset())
 	}
-	fn transfer_reserve_asset(
-		assets: &MultiAssets,
-		_dest: &MultiLocation,
-		_xcm: &Xcm<()>,
-	) -> Weight {
-		assets.weigh_multi_assets(XcmFungibleWeight::<Runtime>::transfer_reserve_asset())
+	fn transfer_reserve_asset(assets: &Assets, _dest: &Location, _xcm: &Xcm<()>) -> Weight {
+		assets.weigh_assets(XcmFungibleWeight::<Runtime>::transfer_reserve_asset())
 	}
 	fn transact(
 		_origin_type: &OriginKind,
@@ -110,44 +106,36 @@ impl<Call> XcmWeightInfo<Call> for AssetHubWestendXcmWeight<Call> {
 	fn clear_origin() -> Weight {
 		XcmGeneric::<Runtime>::clear_origin()
 	}
-	fn descend_origin(_who: &InteriorMultiLocation) -> Weight {
+	fn descend_origin(_who: &InteriorLocation) -> Weight {
 		XcmGeneric::<Runtime>::descend_origin()
 	}
 	fn report_error(_query_response_info: &QueryResponseInfo) -> Weight {
 		XcmGeneric::<Runtime>::report_error()
 	}
 
-	fn deposit_asset(assets: &MultiAssetFilter, _dest: &MultiLocation) -> Weight {
-		assets.weigh_multi_assets(XcmFungibleWeight::<Runtime>::deposit_asset())
+	fn deposit_asset(assets: &AssetFilter, _dest: &Location) -> Weight {
+		assets.weigh_assets(XcmFungibleWeight::<Runtime>::deposit_asset())
 	}
-	fn deposit_reserve_asset(
-		assets: &MultiAssetFilter,
-		_dest: &MultiLocation,
-		_xcm: &Xcm<()>,
-	) -> Weight {
-		assets.weigh_multi_assets(XcmFungibleWeight::<Runtime>::deposit_reserve_asset())
+	fn deposit_reserve_asset(assets: &AssetFilter, _dest: &Location, _xcm: &Xcm<()>) -> Weight {
+		assets.weigh_assets(XcmFungibleWeight::<Runtime>::deposit_reserve_asset())
 	}
-	fn exchange_asset(_give: &MultiAssetFilter, _receive: &MultiAssets, _maximal: &bool) -> Weight {
+	fn exchange_asset(_give: &AssetFilter, _receive: &Assets, _maximal: &bool) -> Weight {
 		Weight::MAX
 	}
 	fn initiate_reserve_withdraw(
-		assets: &MultiAssetFilter,
-		_reserve: &MultiLocation,
+		assets: &AssetFilter,
+		_reserve: &Location,
 		_xcm: &Xcm<()>,
 	) -> Weight {
-		assets.weigh_multi_assets(XcmFungibleWeight::<Runtime>::initiate_reserve_withdraw())
+		assets.weigh_assets(XcmFungibleWeight::<Runtime>::initiate_reserve_withdraw())
 	}
-	fn initiate_teleport(
-		assets: &MultiAssetFilter,
-		_dest: &MultiLocation,
-		_xcm: &Xcm<()>,
-	) -> Weight {
-		assets.weigh_multi_assets(XcmFungibleWeight::<Runtime>::initiate_teleport())
+	fn initiate_teleport(assets: &AssetFilter, _dest: &Location, _xcm: &Xcm<()>) -> Weight {
+		assets.weigh_assets(XcmFungibleWeight::<Runtime>::initiate_teleport())
 	}
-	fn report_holding(_response_info: &QueryResponseInfo, _assets: &MultiAssetFilter) -> Weight {
+	fn report_holding(_response_info: &QueryResponseInfo, _assets: &AssetFilter) -> Weight {
 		XcmGeneric::<Runtime>::report_holding()
 	}
-	fn buy_execution(_fees: &MultiAsset, _weight_limit: &WeightLimit) -> Weight {
+	fn buy_execution(_fees: &Asset, _weight_limit: &WeightLimit) -> Weight {
 		XcmGeneric::<Runtime>::buy_execution()
 	}
 	fn refund_surplus() -> Weight {
@@ -162,7 +150,7 @@ impl<Call> XcmWeightInfo<Call> for AssetHubWestendXcmWeight<Call> {
 	fn clear_error() -> Weight {
 		XcmGeneric::<Runtime>::clear_error()
 	}
-	fn claim_asset(_assets: &MultiAssets, _ticket: &MultiLocation) -> Weight {
+	fn claim_asset(_assets: &Assets, _ticket: &Location) -> Weight {
 		XcmGeneric::<Runtime>::claim_asset()
 	}
 	fn trap(_code: &u64) -> Weight {
@@ -174,13 +162,13 @@ impl<Call> XcmWeightInfo<Call> for AssetHubWestendXcmWeight<Call> {
 	fn unsubscribe_version() -> Weight {
 		XcmGeneric::<Runtime>::unsubscribe_version()
 	}
-	fn burn_asset(assets: &MultiAssets) -> Weight {
-		assets.weigh_multi_assets(XcmGeneric::<Runtime>::burn_asset())
+	fn burn_asset(assets: &Assets) -> Weight {
+		assets.weigh_assets(XcmGeneric::<Runtime>::burn_asset())
 	}
-	fn expect_asset(assets: &MultiAssets) -> Weight {
-		assets.weigh_multi_assets(XcmGeneric::<Runtime>::expect_asset())
+	fn expect_asset(assets: &Assets) -> Weight {
+		assets.weigh_assets(XcmGeneric::<Runtime>::expect_asset())
 	}
-	fn expect_origin(_origin: &Option<MultiLocation>) -> Weight {
+	fn expect_origin(_origin: &Option<Location>) -> Weight {
 		XcmGeneric::<Runtime>::expect_origin()
 	}
 	fn expect_error(_error: &Option<(u32, XcmError)>) -> Weight {
@@ -213,16 +201,16 @@ impl<Call> XcmWeightInfo<Call> for AssetHubWestendXcmWeight<Call> {
 	fn export_message(_: &NetworkId, _: &Junctions, _: &Xcm<()>) -> Weight {
 		Weight::MAX
 	}
-	fn lock_asset(_: &MultiAsset, _: &MultiLocation) -> Weight {
+	fn lock_asset(_: &Asset, _: &Location) -> Weight {
 		Weight::MAX
 	}
-	fn unlock_asset(_: &MultiAsset, _: &MultiLocation) -> Weight {
+	fn unlock_asset(_: &Asset, _: &Location) -> Weight {
 		Weight::MAX
 	}
-	fn note_unlockable(_: &MultiAsset, _: &MultiLocation) -> Weight {
+	fn note_unlockable(_: &Asset, _: &Location) -> Weight {
 		Weight::MAX
 	}
-	fn request_unlock(_: &MultiAsset, _: &MultiLocation) -> Weight {
+	fn request_unlock(_: &Asset, _: &Location) -> Weight {
 		Weight::MAX
 	}
 	fn set_fees_mode(_: &bool) -> Weight {
@@ -234,11 +222,11 @@ impl<Call> XcmWeightInfo<Call> for AssetHubWestendXcmWeight<Call> {
 	fn clear_topic() -> Weight {
 		XcmGeneric::<Runtime>::clear_topic()
 	}
-	fn alias_origin(_: &MultiLocation) -> Weight {
+	fn alias_origin(_: &Location) -> Weight {
 		// XCM Executor does not currently support alias origin operations
 		Weight::MAX
 	}
-	fn unpaid_execution(_: &WeightLimit, _: &Option<MultiLocation>) -> Weight {
+	fn unpaid_execution(_: &WeightLimit, _: &Option<Location>) -> Weight {
 		XcmGeneric::<Runtime>::unpaid_execution()
 	}
 }