XCMv4 (paritytech#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>

substrate/frame/assets/src/lib.rs

@@ -259,11 +259,7 @@ pub mod pallet {
 		/// This type includes the `From<Self::AssetId>` bound, since tightly coupled pallets may
 		/// want to convert an `AssetId` into a parameter for calling dispatchable functions
 		/// directly.
-		type AssetIdParameter: Parameter
-			+ Copy
-			+ From<Self::AssetId>
-			+ Into<Self::AssetId>
-			+ MaxEncodedLen;
+		type AssetIdParameter: Parameter + From<Self::AssetId> + Into<Self::AssetId> + MaxEncodedLen;
 
 		/// The currency mechanism.
 		type Currency: ReservableCurrency<Self::AccountId>;

substrate/frame/contracts/mock-network/src/lib.rs

@@ -24,7 +24,7 @@ mod tests;
 
 use crate::primitives::{AccountId, UNITS};
 use sp_runtime::BuildStorage;
-use xcm::latest::{prelude::*, MultiLocation};
+use xcm::latest::prelude::*;
 use xcm_executor::traits::ConvertLocation;
 use xcm_simulator::{decl_test_network, decl_test_parachain, decl_test_relay_chain, TestExt};
 
@@ -67,20 +67,20 @@ decl_test_network! {
 }
 
 pub fn relay_sovereign_account_id() -> AccountId {
-	let location: MultiLocation = (Parent,).into();
+	let location: Location = (Parent,).into();
 	parachain::SovereignAccountOf::convert_location(&location).unwrap()
 }
 
 pub fn parachain_sovereign_account_id(para: u32) -> AccountId {
-	let location: MultiLocation = (Parachain(para),).into();
+	let location: Location = (Parachain(para),).into();
 	relay_chain::SovereignAccountOf::convert_location(&location).unwrap()
 }
 
 pub fn parachain_account_sovereign_account_id(
 	para: u32,
 	who: sp_runtime::AccountId32,
 ) -> AccountId {
-	let location: MultiLocation = (
+	let location: Location = (
 		Parachain(para),
 		AccountId32 { network: Some(relay_chain::RelayNetwork::get()), id: who.into() },
 	)

substrate/frame/contracts/mock-network/src/mocks/msg_queue.rs

@@ -96,16 +96,23 @@ pub mod pallet {
 			max_weight: Weight,
 		) -> Result<Weight, XcmError> {
 			let hash = Encode::using_encoded(&xcm, T::Hashing::hash);
-			let message_hash = Encode::using_encoded(&xcm, sp_io::hashing::blake2_256);
+			let mut message_hash = Encode::using_encoded(&xcm, sp_io::hashing::blake2_256);
 			let (result, event) = match Xcm::<T::RuntimeCall>::try_from(xcm) {
 				Ok(xcm) => {
 					let location = (Parent, Parachain(sender.into()));
-					match T::XcmExecutor::execute_xcm(location, xcm, message_hash, max_weight) {
-						Outcome::Error(e) => (Err(e), Event::Fail(Some(hash), e)),
-						Outcome::Complete(w) => (Ok(w), Event::Success(Some(hash))),
+					match T::XcmExecutor::prepare_and_execute(
+						location,
+						xcm,
+						&mut message_hash,
+						max_weight,
+						Weight::zero(),
+					) {
+						Outcome::Error { error } => (Err(error), Event::Fail(Some(hash), error)),
+						Outcome::Complete { used } => (Ok(used), Event::Success(Some(hash))),
 						// As far as the caller is concerned, this was dispatched without error, so
 						// we just report the weight used.
-						Outcome::Incomplete(w, e) => (Ok(w), Event::Fail(Some(hash), e)),
+						Outcome::Incomplete { used, error } =>
+							(Ok(used), Event::Fail(Some(hash), error)),
 					}
 				},
 				Err(()) => (Err(XcmError::UnhandledXcmVersion), Event::BadVersion(Some(hash))),
@@ -146,7 +153,7 @@ pub mod pallet {
 			limit: Weight,
 		) -> Weight {
 			for (_i, (_sent_at, data)) in iter.enumerate() {
-				let id = sp_io::hashing::blake2_256(&data[..]);
+				let mut id = sp_io::hashing::blake2_256(&data[..]);
 				let maybe_versioned = VersionedXcm::<T::RuntimeCall>::decode(&mut &data[..]);
 				match maybe_versioned {
 					Err(_) => {
@@ -155,7 +162,13 @@ pub mod pallet {
 					Ok(versioned) => match Xcm::try_from(versioned) {
 						Err(()) => Self::deposit_event(Event::UnsupportedVersion(id)),
 						Ok(x) => {
-							let outcome = T::XcmExecutor::execute_xcm(Parent, x.clone(), id, limit);
+							let outcome = T::XcmExecutor::prepare_and_execute(
+								Parent,
+								x.clone(),
+								&mut id,
+								limit,
+								Weight::zero(),
+							);
 							<ReceivedDmp<T>>::append(x);
 							Self::deposit_event(Event::ExecutedDownward(id, outcome));
 						},

substrate/frame/contracts/mock-network/src/parachain.rs

@@ -143,10 +143,10 @@ parameter_types! {
 }
 
 parameter_types! {
-	pub const KsmLocation: MultiLocation = MultiLocation::parent();
-	pub const TokenLocation: MultiLocation = Here.into_location();
+	pub const KsmLocation: Location = Location::parent();
+	pub const TokenLocation: Location = Here.into_location();
 	pub const RelayNetwork: NetworkId = ByGenesis([0; 32]);
-	pub UniversalLocation: InteriorMultiLocation = Parachain(MsgQueue::parachain_id().into()).into();
+	pub UniversalLocation: InteriorLocation = Parachain(MsgQueue::parachain_id().into()).into();
 }
 
 pub type XcmOriginToCallOrigin = (
@@ -158,13 +158,13 @@ pub type XcmOriginToCallOrigin = (
 
 parameter_types! {
 	pub const XcmInstructionWeight: Weight = Weight::from_parts(1_000, 1_000);
-	pub TokensPerSecondPerMegabyte: (AssetId, u128, u128) = (Concrete(Parent.into()), 1_000_000_000_000, 1024 * 1024);
+	pub TokensPerSecondPerMegabyte: (AssetId, u128, u128) = (AssetId(Parent.into()), 1_000_000_000_000, 1024 * 1024);
 	pub const MaxInstructions: u32 = 100;
 	pub const MaxAssetsIntoHolding: u32 = 64;
-	pub ForeignPrefix: MultiLocation = (Parent,).into();
+	pub ForeignPrefix: Location = (Parent,).into();
 	pub CheckingAccount: AccountId = PolkadotXcm::check_account();
-	pub TrustedLockPairs: (MultiLocation, MultiAssetFilter) =
-	(Parent.into(), Wild(AllOf { id: Concrete(Parent.into()), fun: WildFungible }));
+	pub TrustedLockPairs: (Location, AssetFilter) =
+	(Parent.into(), Wild(AllOf { id: AssetId(Parent.into()), fun: WildFungible }));
 }
 
 pub fn estimate_message_fee(number_of_instructions: u64) -> u128 {
@@ -188,20 +188,19 @@ pub fn estimate_fee_for_weight(weight: Weight) -> u128 {
 pub type LocalBalancesTransactor =
 	XcmCurrencyAdapter<Balances, IsConcrete<TokenLocation>, SovereignAccountOf, AccountId, ()>;
 
-pub struct FromMultiLocationToAsset<MultiLocation, AssetId>(PhantomData<(MultiLocation, AssetId)>);
-impl MaybeEquivalence<MultiLocation, AssetIdForAssets>
-	for FromMultiLocationToAsset<MultiLocation, AssetIdForAssets>
+pub struct FromLocationToAsset<Location, AssetId>(PhantomData<(Location, AssetId)>);
+impl MaybeEquivalence<Location, AssetIdForAssets>
+	for FromLocationToAsset<Location, AssetIdForAssets>
 {
-	fn convert(value: &MultiLocation) -> Option<AssetIdForAssets> {
-		match *value {
-			MultiLocation { parents: 1, interior: Here } => Some(0 as AssetIdForAssets),
-			MultiLocation { parents: 1, interior: X1(Parachain(para_id)) } =>
-				Some(para_id as AssetIdForAssets),
+	fn convert(value: &Location) -> Option<AssetIdForAssets> {
+		match value.unpack() {
+			(1, []) => Some(0 as AssetIdForAssets),
+			(1, [Parachain(para_id)]) => Some(*para_id as AssetIdForAssets),
 			_ => None,
 		}
 	}
 
-	fn convert_back(_id: &AssetIdForAssets) -> Option<MultiLocation> {
+	fn convert_back(_id: &AssetIdForAssets) -> Option<Location> {
 		None
 	}
 }
@@ -211,7 +210,7 @@ pub type ForeignAssetsTransactor = FungiblesAdapter<
 	ConvertedConcreteId<
 		AssetIdForAssets,
 		Balance,
-		FromMultiLocationToAsset<MultiLocation, AssetIdForAssets>,
+		FromLocationToAsset<Location, AssetIdForAssets>,
 		JustTry,
 	>,
 	SovereignAccountOf,
@@ -224,18 +223,15 @@ pub type ForeignAssetsTransactor = FungiblesAdapter<
 pub type AssetTransactors = (LocalBalancesTransactor, ForeignAssetsTransactor);
 
 pub struct ParentRelay;
-impl Contains<MultiLocation> for ParentRelay {
-	fn contains(location: &MultiLocation) -> bool {
+impl Contains<Location> for ParentRelay {
+	fn contains(location: &Location) -> bool {
 		location.contains_parents_only(1)
 	}
 }
 pub struct ThisParachain;
-impl Contains<MultiLocation> for ThisParachain {
-	fn contains(location: &MultiLocation) -> bool {
-		matches!(
-			location,
-			MultiLocation { parents: 0, interior: Junctions::X1(Junction::AccountId32 { .. }) }
-		)
+impl Contains<Location> for ThisParachain {
+	fn contains(location: &Location) -> bool {
+		matches!(location.unpack(), (0, [Junction::AccountId32 { .. }]))
 	}
 }
 
@@ -251,12 +247,12 @@ pub type Barrier = (
 );
 
 parameter_types! {
-	pub NftCollectionOne: MultiAssetFilter
-		= Wild(AllOf { fun: WildNonFungible, id: Concrete((Parent, GeneralIndex(1)).into()) });
-	pub NftCollectionOneForRelay: (MultiAssetFilter, MultiLocation)
+	pub NftCollectionOne: AssetFilter
+		= Wild(AllOf { fun: WildNonFungible, id: AssetId((Parent, GeneralIndex(1)).into()) });
+	pub NftCollectionOneForRelay: (AssetFilter, Location)
 		= (NftCollectionOne::get(), Parent.into());
-	pub RelayNativeAsset: MultiAssetFilter = Wild(AllOf { fun: WildFungible, id: Concrete((Parent, Here).into()) });
-	pub RelayNativeAssetForRelay: (MultiAssetFilter, MultiLocation) = (RelayNativeAsset::get(), Parent.into());
+	pub RelayNativeAsset: AssetFilter = Wild(AllOf { fun: WildFungible, id: AssetId((Parent, Here).into()) });
+	pub RelayNativeAssetForRelay: (AssetFilter, Location) = (RelayNativeAsset::get(), Parent.into());
 }
 pub type TrustedTeleporters =
 	(xcm_builder::Case<NftCollectionOneForRelay>, xcm_builder::Case<RelayNativeAssetForRelay>);
@@ -298,10 +294,8 @@ impl mock_msg_queue::Config for Runtime {
 pub type LocalOriginToLocation = SignedToAccountId32<RuntimeOrigin, AccountId, RelayNetwork>;
 
 pub struct TrustedLockerCase<T>(PhantomData<T>);
-impl<T: Get<(MultiLocation, MultiAssetFilter)>> ContainsPair<MultiLocation, MultiAsset>
-	for TrustedLockerCase<T>
-{
-	fn contains(origin: &MultiLocation, asset: &MultiAsset) -> bool {
+impl<T: Get<(Location, AssetFilter)>> ContainsPair<Location, Asset> for TrustedLockerCase<T> {
+	fn contains(origin: &Location, asset: &Asset) -> bool {
 		let (o, a) = T::get();
 		a.matches(asset) && &o == origin
 	}

substrate/frame/contracts/mock-network/src/relay_chain.rs

@@ -107,8 +107,8 @@ impl configuration::Config for Runtime {
 
 parameter_types! {
 	pub RelayNetwork: NetworkId = ByGenesis([0; 32]);
-	pub const TokenLocation: MultiLocation = Here.into_location();
-	pub UniversalLocation: InteriorMultiLocation = Here;
+	pub const TokenLocation: Location = Here.into_location();
+	pub UniversalLocation: InteriorLocation = Here;
 	pub UnitWeightCost: u64 = 1_000;
 }
 
@@ -134,15 +134,15 @@ type LocalOriginConverter = (
 parameter_types! {
 	pub const XcmInstructionWeight: Weight = Weight::from_parts(1_000, 1_000);
 	pub TokensPerSecondPerMegabyte: (AssetId, u128, u128) =
-		(Concrete(TokenLocation::get()), 1_000_000_000_000, 1024 * 1024);
+		(AssetId(TokenLocation::get()), 1_000_000_000_000, 1024 * 1024);
 	pub const MaxInstructions: u32 = 100;
 	pub const MaxAssetsIntoHolding: u32 = 64;
 }
 
 pub struct ChildrenParachains;
-impl Contains<MultiLocation> for ChildrenParachains {
-	fn contains(location: &MultiLocation) -> bool {
-		matches!(location, MultiLocation { parents: 0, interior: X1(Parachain(_)) })
+impl Contains<Location> for ChildrenParachains {
+	fn contains(location: &Location) -> bool {
+		matches!(location.unpack(), (0, [Parachain(_)]))
 	}
 }
 

substrate/frame/contracts/mock-network/src/tests.rs

@@ -31,7 +31,7 @@ use frame_support::{
 use pallet_balances::{BalanceLock, Reasons};
 use pallet_contracts::{Code, CollectEvents, DebugInfo, Determinism};
 use pallet_contracts_fixtures::compile_module;
-use xcm::{v3::prelude::*, VersionedMultiLocation, VersionedXcm};
+use xcm::{v4::prelude::*, VersionedLocation, VersionedXcm};
 use xcm_simulator::TestExt;
 
 type ParachainContracts = pallet_contracts::Pallet<parachain::Runtime>;
@@ -82,7 +82,7 @@ fn test_xcm_execute() {
 		let amount: u128 = 10 * CENTS;
 
 		// The XCM used to transfer funds to Bob.
-		let message: xcm_simulator::Xcm<()> = Xcm(vec![
+		let message: Xcm<()> = Xcm(vec![
 			WithdrawAsset(vec![(Here, amount).into()].into()),
 			DepositAsset {
 				assets: All.into(),
@@ -96,7 +96,7 @@ fn test_xcm_execute() {
 			0,
 			Weight::MAX,
 			None,
-			VersionedXcm::V3(message).encode(),
+			VersionedXcm::V4(message).encode(),
 			DebugInfo::UnsafeDebug,
 			CollectEvents::UnsafeCollect,
 			Determinism::Enforced,
@@ -106,7 +106,7 @@ fn test_xcm_execute() {
 
 		let mut data = &result.data[..];
 		let outcome = Outcome::decode(&mut data).expect("Failed to decode xcm_execute Outcome");
-		assert_matches!(outcome, Outcome::Complete(_));
+		assert_matches!(outcome, Outcome::Complete { .. });
 
 		// Check if the funds are subtracted from the account of Alice and added to the account of
 		// Bob.
@@ -137,7 +137,7 @@ fn test_xcm_execute_filtered_call() {
 			0,
 			Weight::MAX,
 			None,
-			VersionedXcm::V3(message).encode(),
+			VersionedXcm::V4(message).encode(),
 			DebugInfo::UnsafeDebug,
 			CollectEvents::UnsafeCollect,
 			Determinism::Enforced,
@@ -178,7 +178,7 @@ fn test_xcm_execute_reentrant_call() {
 			0,
 			Weight::MAX,
 			None,
-			VersionedXcm::V3(message).encode(),
+			VersionedXcm::V4(message).encode(),
 			DebugInfo::UnsafeDebug,
 			CollectEvents::UnsafeCollect,
 			Determinism::Enforced,
@@ -188,7 +188,10 @@ fn test_xcm_execute_reentrant_call() {
 
 		let mut data = &result.data[..];
 		let outcome = Outcome::decode(&mut data).expect("Failed to decode xcm_execute Outcome");
-		assert_matches!(outcome, Outcome::Incomplete(_, XcmError::ExpectationFalse));
+		assert_matches!(
+			outcome,
+			Outcome::Incomplete { used: _, error: XcmError::ExpectationFalse }
+		);
 
 		// Funds should not change hands as the XCM transact failed.
 		assert_eq!(ParachainBalances::free_balance(BOB), INITIAL_BALANCE);
@@ -203,15 +206,15 @@ fn test_xcm_send() {
 
 	// Send XCM instructions through the contract, to lock some funds on the relay chain.
 	ParaA::execute_with(|| {
-		let dest = MultiLocation::from(Parent);
-		let dest = VersionedMultiLocation::V3(dest);
+		let dest = Location::from(Parent);
+		let dest = VersionedLocation::V4(dest);
 
-		let message: xcm_simulator::Xcm<()> = Xcm(vec![
+		let message: Xcm<()> = Xcm(vec![
 			WithdrawAsset((Here, fee).into()),
 			BuyExecution { fees: (Here, fee).into(), weight_limit: WeightLimit::Unlimited },
 			LockAsset { asset: (Here, 5 * CENTS).into(), unlocker: (Parachain(1)).into() },
 		]);
-		let message = VersionedXcm::V3(message);
+		let message = VersionedXcm::V4(message);
 		let exec = ParachainContracts::bare_call(
 			ALICE,
 			contract_addr.clone(),

substrate/frame/contracts/src/wasm/runtime.rs

@@ -2169,11 +2169,11 @@ pub mod env {
 		msg_len: u32,
 		output_ptr: u32,
 	) -> Result<ReturnErrorCode, TrapReason> {
-		use xcm::{VersionedMultiLocation, VersionedXcm};
+		use xcm::{VersionedLocation, VersionedXcm};
 		use xcm_builder::{SendController, SendControllerWeightInfo};
 
 		ctx.charge_gas(RuntimeCosts::CopyFromContract(msg_len))?;
-		let dest: VersionedMultiLocation = ctx.read_sandbox_memory_as(memory, dest_ptr)?;
+		let dest: VersionedLocation = ctx.read_sandbox_memory_as(memory, dest_ptr)?;
 
 		let message: VersionedXcm<()> =
 			ctx.read_sandbox_memory_as_unbounded(memory, msg_ptr, msg_len)?;

substrate/frame/support/src/traits/tokens/pay.rs

@@ -26,7 +26,7 @@ use sp_std::fmt::Debug;
 use super::{fungible, fungibles, Balance, Preservation::Expendable};
 
 /// Can be implemented by `PayFromAccount` using a `fungible` impl, but can also be implemented with
-/// XCM/MultiAsset and made generic over assets.
+/// XCM/Asset and made generic over assets.
 pub trait Pay {
 	/// The type by which we measure units of the currency in which we make payments.
 	type Balance: Balance;