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>

bridges/snowbridge/parachain/pallets/inbound-queue/src/lib.rs

@@ -54,8 +54,8 @@ use scale_info::TypeInfo;
 use sp_core::{H160, H256};
 use sp_std::{convert::TryFrom, vec};
 use xcm::prelude::{
-	send_xcm, Instruction::SetTopic, Junction::*, Junctions::*, MultiLocation,
-	SendError as XcmpSendError, SendXcm, Xcm, XcmContext, XcmHash,
+	send_xcm, Instruction::SetTopic, Junction::*, Location, SendError as XcmpSendError, SendXcm,
+	Xcm, XcmContext, XcmHash,
 };
 use xcm_executor::traits::TransactAsset;
 
@@ -324,7 +324,7 @@ pub mod pallet {
 		}
 
 		pub fn send_xcm(xcm: Xcm<()>, dest: ParaId) -> Result<XcmHash, Error<T>> {
-			let dest = MultiLocation { parents: 1, interior: X1(Parachain(dest.into())) };
+			let dest = Location::new(1, [Parachain(dest.into())]);
 			let (xcm_hash, _) = send_xcm::<T::XcmSender>(dest, xcm).map_err(Error::<T>::from)?;
 			Ok(xcm_hash)
 		}
@@ -341,8 +341,8 @@ pub mod pallet {
 		pub fn burn_fees(para_id: ParaId, fee: BalanceOf<T>) -> DispatchResult {
 			let dummy_context =
 				XcmContext { origin: None, message_id: Default::default(), topic: None };
-			let dest = MultiLocation { parents: 1, interior: X1(Parachain(para_id.into())) };
-			let fees = (MultiLocation::parent(), fee.saturated_into::<u128>()).into();
+			let dest = Location::new(1, [Parachain(para_id.into())]);
+			let fees = (Location::parent(), fee.saturated_into::<u128>()).into();
 			T::AssetTransactor::can_check_out(&dest, &fees, &dummy_context).map_err(|error| {
 				log::error!(
 					target: LOG_TARGET,

bridges/snowbridge/parachain/pallets/inbound-queue/src/mock.rs

@@ -21,8 +21,8 @@ use sp_runtime::{
 	BuildStorage, FixedU128, MultiSignature,
 };
 use sp_std::convert::From;
-use xcm::v3::{prelude::*, MultiAssets, SendXcm};
-use xcm_executor::Assets;
+use xcm::v4::{prelude::*, SendXcm};
+use xcm_executor::AssetsInHolding;
 
 use crate::{self as inbound_queue};
 
@@ -155,17 +155,16 @@ impl SendXcm for MockXcmSender {
 	type Ticket = Xcm<()>;
 
 	fn validate(
-		dest: &mut Option<MultiLocation>,
-		xcm: &mut Option<xcm::v3::Xcm<()>>,
+		dest: &mut Option<Location>,
+		xcm: &mut Option<Xcm<()>>,
 	) -> SendResult<Self::Ticket> {
-		match dest {
-			Some(MultiLocation { interior, .. }) => {
-				if let X1(Parachain(1001)) = interior {
-					return Err(XcmpSendError::NotApplicable)
-				}
-				Ok((xcm.clone().unwrap(), MultiAssets::default()))
-			},
-			_ => Ok((xcm.clone().unwrap(), MultiAssets::default())),
+		if let Some(location) = dest {
+			match location.unpack() {
+				(_, [Parachain(1001)]) => return Err(XcmpSendError::NotApplicable),
+				_ => Ok((xcm.clone().unwrap(), Assets::default())),
+			}
+		} else {
+			Ok((xcm.clone().unwrap(), Assets::default()))
 		}
 	}
 
@@ -203,45 +202,33 @@ impl StaticLookup for MockChannelLookup {
 
 pub struct SuccessfulTransactor;
 impl TransactAsset for SuccessfulTransactor {
-	fn can_check_in(
-		_origin: &MultiLocation,
-		_what: &MultiAsset,
-		_context: &XcmContext,
-	) -> XcmResult {
+	fn can_check_in(_origin: &Location, _what: &Asset, _context: &XcmContext) -> XcmResult {
 		Ok(())
 	}
 
-	fn can_check_out(
-		_dest: &MultiLocation,
-		_what: &MultiAsset,
-		_context: &XcmContext,
-	) -> XcmResult {
+	fn can_check_out(_dest: &Location, _what: &Asset, _context: &XcmContext) -> XcmResult {
 		Ok(())
 	}
 
-	fn deposit_asset(
-		_what: &MultiAsset,
-		_who: &MultiLocation,
-		_context: Option<&XcmContext>,
-	) -> XcmResult {
+	fn deposit_asset(_what: &Asset, _who: &Location, _context: Option<&XcmContext>) -> XcmResult {
 		Ok(())
 	}
 
 	fn withdraw_asset(
-		_what: &MultiAsset,
-		_who: &MultiLocation,
+		_what: &Asset,
+		_who: &Location,
 		_context: Option<&XcmContext>,
-	) -> Result<Assets, XcmError> {
-		Ok(Assets::default())
+	) -> Result<AssetsInHolding, XcmError> {
+		Ok(AssetsInHolding::default())
 	}
 
 	fn internal_transfer_asset(
-		_what: &MultiAsset,
-		_from: &MultiLocation,
-		_to: &MultiLocation,
+		_what: &Asset,
+		_from: &Location,
+		_to: &Location,
 		_context: &XcmContext,
-	) -> Result<Assets, XcmError> {
-		Ok(Assets::default())
+	) -> Result<AssetsInHolding, XcmError> {
+		Ok(AssetsInHolding::default())
 	}
 }
 

bridges/snowbridge/parachain/pallets/inbound-queue/src/test.rs

@@ -41,8 +41,8 @@ fn test_submit_happy_path() {
 				.into(),
 			nonce: 1,
 			message_id: [
-				27, 217, 88, 127, 46, 143, 199, 70, 236, 66, 212, 244, 85, 221, 153, 104, 175, 37,
-				224, 20, 140, 95, 140, 7, 27, 74, 182, 199, 77, 12, 194, 236,
+				57, 61, 232, 3, 66, 61, 25, 190, 234, 188, 193, 174, 13, 186, 1, 64, 237, 94, 73,
+				83, 14, 18, 209, 213, 78, 121, 43, 108, 251, 245, 107, 67,
 			],
 			fee_burned: 110000000000,
 		}