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/test-utils/src/lib.rs

@@ -37,11 +37,11 @@ use sp_consensus_aura::{SlotDuration, AURA_ENGINE_ID};
 use sp_core::Encode;
 use sp_runtime::{traits::Header, BuildStorage, Digest, DigestItem};
 use xcm::{
-	latest::{MultiAsset, MultiLocation, XcmContext, XcmHash},
+	latest::{Asset, Location, XcmContext, XcmHash},
 	prelude::*,
 	VersionedXcm, MAX_XCM_DECODE_DEPTH,
 };
-use xcm_executor::{traits::TransactAsset, Assets};
+use xcm_executor::{traits::TransactAsset, AssetsInHolding};
 
 pub mod test_cases;
 
@@ -307,12 +307,12 @@ impl<XcmConfig: xcm_executor::Config, AllPalletsWithoutSystem>
 	RuntimeHelper<XcmConfig, AllPalletsWithoutSystem>
 {
 	pub fn do_transfer(
-		from: MultiLocation,
-		to: MultiLocation,
-		(asset, amount): (MultiLocation, u128),
-	) -> Result<Assets, XcmError> {
+		from: Location,
+		to: Location,
+		(asset, amount): (Location, u128),
+	) -> Result<AssetsInHolding, XcmError> {
 		<XcmConfig::AssetTransactor as TransactAsset>::transfer_asset(
-			&MultiAsset { id: Concrete(asset), fun: Fungible(amount) },
+			&Asset { id: AssetId(asset), fun: Fungible(amount) },
 			&from,
 			&to,
 			// We aren't able to track the XCM that initiated the fee deposit, so we create a
@@ -329,9 +329,9 @@ impl<
 {
 	pub fn do_teleport_assets<HrmpChannelOpener>(
 		origin: <Runtime as frame_system::Config>::RuntimeOrigin,
-		dest: MultiLocation,
-		beneficiary: MultiLocation,
-		(asset, amount): (MultiLocation, u128),
+		dest: Location,
+		beneficiary: Location,
+		(asset, amount): (Location, u128),
 		open_hrmp_channel: Option<(u32, u32)>,
 		included_head: HeaderFor<Runtime>,
 		slot_digest: &[u8],
@@ -356,7 +356,7 @@ impl<
 			origin,
 			Box::new(dest.into()),
 			Box::new(beneficiary.into()),
-			Box::new((Concrete(asset), amount).into()),
+			Box::new((AssetId(asset), amount).into()),
 			0,
 		)
 	}
@@ -379,12 +379,13 @@ impl<
 		]);
 
 		// execute xcm as parent origin
-		let hash = xcm.using_encoded(sp_io::hashing::blake2_256);
-		<<Runtime as pallet_xcm::Config>::XcmExecutor>::execute_xcm(
-			MultiLocation::parent(),
+		let mut hash = xcm.using_encoded(sp_io::hashing::blake2_256);
+		<<Runtime as pallet_xcm::Config>::XcmExecutor>::prepare_and_execute(
+			Location::parent(),
 			xcm,
-			hash,
+			&mut hash,
 			Self::xcm_max_weight(XcmReceivedFrom::Parent),
+			Weight::zero(),
 		)
 	}
 }
@@ -451,7 +452,7 @@ impl<
 }
 
 pub fn assert_metadata<Fungibles, AccountId>(
-	asset_id: impl Into<Fungibles::AssetId> + Copy,
+	asset_id: impl Into<Fungibles::AssetId> + Clone,
 	expected_name: &str,
 	expected_symbol: &str,
 	expected_decimals: u8,
@@ -459,20 +460,20 @@ pub fn assert_metadata<Fungibles, AccountId>(
 	Fungibles: frame_support::traits::fungibles::metadata::Inspect<AccountId>
 		+ frame_support::traits::fungibles::Inspect<AccountId>,
 {
-	assert_eq!(Fungibles::name(asset_id.into()), Vec::from(expected_name),);
-	assert_eq!(Fungibles::symbol(asset_id.into()), Vec::from(expected_symbol),);
+	assert_eq!(Fungibles::name(asset_id.clone().into()), Vec::from(expected_name),);
+	assert_eq!(Fungibles::symbol(asset_id.clone().into()), Vec::from(expected_symbol),);
 	assert_eq!(Fungibles::decimals(asset_id.into()), expected_decimals);
 }
 
 pub fn assert_total<Fungibles, AccountId>(
-	asset_id: impl Into<Fungibles::AssetId> + Copy,
+	asset_id: impl Into<Fungibles::AssetId> + Clone,
 	expected_total_issuance: impl Into<Fungibles::Balance>,
 	expected_active_issuance: impl Into<Fungibles::Balance>,
 ) where
 	Fungibles: frame_support::traits::fungibles::metadata::Inspect<AccountId>
 		+ frame_support::traits::fungibles::Inspect<AccountId>,
 {
-	assert_eq!(Fungibles::total_issuance(asset_id.into()), expected_total_issuance.into());
+	assert_eq!(Fungibles::total_issuance(asset_id.clone().into()), expected_total_issuance.into());
 	assert_eq!(Fungibles::active_issuance(asset_id.into()), expected_active_issuance.into());
 }