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/contracts/contracts-rococo/src/lib.rs

@@ -704,28 +704,28 @@ impl_runtime_apis! {
 			use xcm::latest::prelude::*;
 			use pallet_xcm::benchmarking::Pallet as PalletXcmExtrinsicsBenchmark;
 			impl pallet_xcm::benchmarking::Config for Runtime {
-				fn reachable_dest() -> Option<MultiLocation> {
+				fn reachable_dest() -> Option<Location> {
 					Some(Parent.into())
 				}
 
-				fn teleportable_asset_and_dest() -> Option<(MultiAsset, MultiLocation)> {
+				fn teleportable_asset_and_dest() -> Option<(Asset, Location)> {
 					// Relay/native token can be teleported between Contracts-System-Para and Relay.
 					Some((
-						MultiAsset {
+						Asset {
 							fun: Fungible(EXISTENTIAL_DEPOSIT),
-							id: Concrete(Parent.into())
+							id: AssetId(Parent.into())
 						},
 						Parent.into(),
 					))
 				}
 
-				fn reserve_transferable_asset_and_dest() -> Option<(MultiAsset, MultiLocation)> {
+				fn reserve_transferable_asset_and_dest() -> Option<(Asset, Location)> {
 					// Reserve transfers are disabled on Contracts-System-Para.
 					None
 				}
 
 				fn set_up_complex_asset_transfer(
-				) -> Option<(MultiAssets, u32, MultiLocation, Box<dyn FnOnce()>)> {
+				) -> Option<(Assets, u32, Location, Box<dyn FnOnce()>)> {
 					// Contracts-System-Para only supports teleports to system parachain.
 					// Relay/native token can be teleported between Contracts-System-Para and Relay.
 					let native_location = Parent.into();

cumulus/parachains/runtimes/contracts/contracts-rococo/src/xcm_config.rs

@@ -20,8 +20,8 @@ use super::{
 use crate::common::rococo::currency::CENTS;
 use cumulus_primitives_core::AggregateMessageOrigin;
 use frame_support::{
-	match_types, parameter_types,
-	traits::{ConstU32, EitherOfDiverse, Equals, Everything, Nothing},
+	parameter_types,
+	traits::{ConstU32, Contains, EitherOfDiverse, Equals, Everything, Nothing},
 	weights::Weight,
 };
 use frame_system::EnsureRoot;
@@ -51,13 +51,13 @@ use xcm_builder::{
 use xcm_executor::XcmExecutor;
 
 parameter_types! {
-	pub const RelayLocation: MultiLocation = MultiLocation::parent();
+	pub const RelayLocation: Location = Location::parent();
 	pub const RelayNetwork: Option<NetworkId> = None;
 	pub RelayChainOrigin: RuntimeOrigin = cumulus_pallet_xcm::Origin::Relay.into();
-	pub UniversalLocation: InteriorMultiLocation = Parachain(ParachainInfo::parachain_id().into()).into();
+	pub UniversalLocation: InteriorLocation = Parachain(ParachainInfo::parachain_id().into()).into();
 	pub const ExecutiveBody: BodyId = BodyId::Executive;
 	pub TreasuryAccount: AccountId = TREASURY_PALLET_ID.into_account_truncating();
-	pub RelayTreasuryLocation: MultiLocation = (Parent, PalletInstance(rococo_runtime_constants::TREASURY_PALLET_ID)).into();
+	pub RelayTreasuryLocation: Location = (Parent, PalletInstance(rococo_runtime_constants::TREASURY_PALLET_ID)).into();
 }
 
 /// We allow root and the Relay Chain council to execute privileged collator selection operations.
@@ -66,7 +66,7 @@ pub type CollatorSelectionUpdateOrigin = EitherOfDiverse<
 	EnsureXcm<IsMajorityOfBody<RelayLocation, ExecutiveBody>>,
 >;
 
-/// 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 = (
@@ -85,7 +85,7 @@ pub type CurrencyTransactor = CurrencyAdapter<
 	Balances,
 	// Use this currency when it is a fungible asset matching the given location or name:
 	IsConcrete<RelayLocation>,
-	// 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,
@@ -123,11 +123,11 @@ parameter_types! {
 	pub const MaxInstructions: u32 = 100;
 }
 
-match_types! {
-	pub type ParentOrParentsPlurality: impl Contains<MultiLocation> = {
-		MultiLocation { parents: 1, interior: Here } |
-		MultiLocation { parents: 1, interior: X1(Plurality { .. }) }
-	};
+pub struct ParentOrParentsPlurality;
+impl Contains<Location> for ParentOrParentsPlurality {
+	fn contains(location: &Location) -> bool {
+		matches!(location.unpack(), (1, []) | (1, [Plurality { .. }]))
+	}
 }
 
 pub type Barrier = TrailingSetTopicAsId<
@@ -200,7 +200,7 @@ impl xcm_executor::Config for XcmConfig {
 	type Aliasers = Nothing;
 }
 
-/// Converts a local signed origin into an XCM multilocation.
+/// Converts a local signed origin into an XCM location.
 /// Forms the basis for local origins sending/executing XCMs.
 pub type LocalOriginToLocation = SignedToAccountId32<RuntimeOrigin, AccountId, RelayNetwork>;
 
@@ -254,7 +254,7 @@ impl cumulus_pallet_xcm::Config for Runtime {
 
 parameter_types! {
 	/// The asset ID for the asset that we use to pay for message delivery fees.
-	pub FeeAssetId: AssetId = Concrete(RelayLocation::get());
+	pub FeeAssetId: AssetId = AssetId(RelayLocation::get());
 	/// The base fee for the message delivery fees.
 	pub const BaseDeliveryFee: u128 = CENTS.saturating_mul(3);
 }