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/testing/rococo-parachain/src/lib.rs

@@ -42,10 +42,10 @@ pub use frame_support::{
 	construct_runtime, derive_impl,
 	dispatch::DispatchClass,
 	genesis_builder_helper::{build_config, create_default_config},
-	match_types, parameter_types,
+	parameter_types,
 	traits::{
-		AsEnsureOriginWithArg, ConstBool, ConstU32, ConstU64, ConstU8, EitherOfDiverse, Everything,
-		IsInVec, Nothing, Randomness,
+		AsEnsureOriginWithArg, ConstBool, ConstU32, ConstU64, ConstU8, Contains, EitherOfDiverse,
+		Everything, IsInVec, Nothing, Randomness,
 	},
 	weights::{
 		constants::{
@@ -330,14 +330,14 @@ impl pallet_message_queue::Config for Runtime {
 impl cumulus_pallet_aura_ext::Config for Runtime {}
 
 parameter_types! {
-	pub const RocLocation: MultiLocation = MultiLocation::parent();
+	pub const RocLocation: Location = Location::parent();
 	pub const RococoNetwork: Option<NetworkId> = Some(NetworkId::Rococo);
 	pub RelayChainOrigin: RuntimeOrigin = cumulus_pallet_xcm::Origin::Relay.into();
-	pub UniversalLocation: InteriorMultiLocation = X1(Parachain(ParachainInfo::parachain_id().into()));
+	pub UniversalLocation: InteriorLocation = [Parachain(ParachainInfo::parachain_id().into())].into();
 	pub CheckingAccount: AccountId = PolkadotXcm::check_account();
 }
 
-/// Type for specifying how a `MultiLocation` can be converted into an `AccountId`. This is used
+/// Type for specifying how a `Location` can be converted into an `AccountId`. This is used
 /// when determining ownership of accounts for asset transacting and when attempting to use XCM
 /// `Transact` in order to determine the dispatch Origin.
 pub type LocationToAccountId = (
@@ -356,7 +356,7 @@ pub type CurrencyTransactor = CurrencyAdapter<
 	Balances,
 	// Use this currency when it is a fungible asset matching the given location or name:
 	IsConcrete<RocLocation>,
-	// Do a simple punn to convert an AccountId32 MultiLocation into a native chain account ID:
+	// Do a simple punn to convert an AccountId32 Location into a native chain account ID:
 	LocationToAccountId,
 	// Our chain's account ID type (we can't get away without mentioning it explicitly):
 	AccountId,
@@ -379,7 +379,7 @@ pub type FungiblesTransactor = FungiblesAdapter<
 		>,
 		JustTry,
 	>,
-	// Convert an XCM MultiLocation into a local account id:
+	// Convert an XCM Location into a local account id:
 	LocationToAccountId,
 	// Our chain's account ID type (we can't get away without mentioning it explicitly):
 	AccountId,
@@ -420,20 +420,22 @@ parameter_types! {
 	// One XCM operation is 1_000_000_000 weight - almost certainly a conservative estimate.
 	pub UnitWeightCost: Weight = Weight::from_parts(1_000_000_000, 64 * 1024);
 	// One ROC buys 1 second of weight.
-	pub const WeightPrice: (MultiLocation, u128) = (MultiLocation::parent(), ROC);
+	pub const WeightPrice: (Location, u128) = (Location::parent(), ROC);
 	pub const MaxInstructions: u32 = 100;
 }
 
-match_types! {
-	// The parent or the parent's unit plurality.
-	pub type ParentOrParentsUnitPlurality: impl Contains<MultiLocation> = {
-		MultiLocation { parents: 1, interior: Here } |
-		MultiLocation { parents: 1, interior: X1(Plurality { id: BodyId::Unit, .. }) }
-	};
-	// The location recognized as the Relay network's Asset Hub.
-	pub type AssetHub: impl Contains<MultiLocation> = {
-		MultiLocation { parents: 1, interior: X1(Parachain(1000)) }
-	};
+pub struct ParentOrParentsUnitPlurality;
+impl Contains<Location> for ParentOrParentsUnitPlurality {
+	fn contains(location: &Location) -> bool {
+		matches!(location.unpack(), (1, []) | (1, [Plurality { id: BodyId::Unit, .. }]))
+	}
+}
+
+pub struct AssetHub;
+impl Contains<Location> for AssetHub {
+	fn contains(location: &Location) -> bool {
+		matches!(location.unpack(), (1, [Parachain(1000)]))
+	}
 }
 
 pub type Barrier = TrailingSetTopicAsId<(
@@ -451,11 +453,11 @@ pub type Barrier = TrailingSetTopicAsId<(
 
 parameter_types! {
 	pub MaxAssetsIntoHolding: u32 = 64;
-	pub SystemAssetHubLocation: MultiLocation = MultiLocation::new(1, X1(Parachain(1000)));
+	pub SystemAssetHubLocation: Location = Location::new(1, [Parachain(1000)]);
 	// ALWAYS ensure that the index in PalletInstance stays up-to-date with
 	// the Relay Chain's Asset Hub's Assets pallet index
-	pub SystemAssetHubAssetsPalletLocation: MultiLocation =
-		MultiLocation::new(1, X2(Parachain(1000), PalletInstance(50)));
+	pub SystemAssetHubAssetsPalletLocation: Location =
+		Location::new(1, [Parachain(1000), PalletInstance(50)]);
 }
 
 pub type Reserves = (NativeAsset, AssetsFrom<SystemAssetHubLocation>);