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>

polkadot/xcm/xcm-builder/src/tests/querying.rs

@@ -18,7 +18,7 @@ use super::*;
 
 #[test]
 fn pallet_query_should_work() {
-	AllowUnpaidFrom::set(vec![X1(Parachain(1)).into()]);
+	AllowUnpaidFrom::set(vec![[Parachain(1)].into()]);
 	// They want to transfer 100 of our native asset from sovereign account of parachain #1 into #2
 	// and let them know to hand it to account #3.
 	let message = Xcm(vec![QueryPallet {
@@ -29,14 +29,15 @@ fn pallet_query_should_work() {
 			max_weight: Weight::from_parts(50, 50),
 		},
 	}]);
-	let hash = fake_message_hash(&message);
-	let r = XcmExecutor::<TestConfig>::execute_xcm(
+	let mut hash = fake_message_hash(&message);
+	let r = XcmExecutor::<TestConfig>::prepare_and_execute(
 		Parachain(1),
 		message,
-		hash,
+		&mut hash,
 		Weight::from_parts(50, 50),
+		Weight::zero(),
 	);
-	assert_eq!(r, Outcome::Complete(Weight::from_parts(10, 10)));
+	assert_eq!(r, Outcome::Complete { used: Weight::from_parts(10, 10) });
 
 	let expected_msg = Xcm::<()>(vec![QueryResponse {
 		query_id: 1,
@@ -50,7 +51,7 @@ fn pallet_query_should_work() {
 
 #[test]
 fn pallet_query_with_results_should_work() {
-	AllowUnpaidFrom::set(vec![X1(Parachain(1)).into()]);
+	AllowUnpaidFrom::set(vec![[Parachain(1)].into()]);
 	// They want to transfer 100 of our native asset from sovereign account of parachain #1 into #2
 	// and let them know to hand it to account #3.
 	let message = Xcm(vec![QueryPallet {
@@ -61,14 +62,15 @@ fn pallet_query_with_results_should_work() {
 			max_weight: Weight::from_parts(50, 50),
 		},
 	}]);
-	let hash = fake_message_hash(&message);
-	let r = XcmExecutor::<TestConfig>::execute_xcm(
+	let mut hash = fake_message_hash(&message);
+	let r = XcmExecutor::<TestConfig>::prepare_and_execute(
 		Parachain(1),
 		message,
-		hash,
+		&mut hash,
 		Weight::from_parts(50, 50),
+		Weight::zero(),
 	);
-	assert_eq!(r, Outcome::Complete(Weight::from_parts(10, 10)));
+	assert_eq!(r, Outcome::Complete { used: Weight::from_parts(10, 10) });
 
 	let expected_msg = Xcm::<()>(vec![QueryResponse {
 		query_id: 1,
@@ -106,15 +108,27 @@ fn prepaid_result_of_query_should_get_free_execution() {
 		max_weight: Weight::from_parts(10, 10),
 		querier: Some(Here.into()),
 	}]);
-	let hash = fake_message_hash(&message);
+	let mut hash = fake_message_hash(&message);
 	let weight_limit = Weight::from_parts(10, 10);
 
 	// First time the response gets through since we're expecting it...
-	let r = XcmExecutor::<TestConfig>::execute_xcm(Parent, message.clone(), hash, weight_limit);
-	assert_eq!(r, Outcome::Complete(Weight::from_parts(10, 10)));
+	let r = XcmExecutor::<TestConfig>::prepare_and_execute(
+		Parent,
+		message.clone(),
+		&mut hash,
+		weight_limit,
+		Weight::zero(),
+	);
+	assert_eq!(r, Outcome::Complete { used: Weight::from_parts(10, 10) });
 	assert_eq!(response(query_id).unwrap(), the_response);
 
 	// Second time it doesn't, since we're not.
-	let r = XcmExecutor::<TestConfig>::execute_xcm(Parent, message.clone(), hash, weight_limit);
-	assert_eq!(r, Outcome::Error(XcmError::Barrier));
+	let r = XcmExecutor::<TestConfig>::prepare_and_execute(
+		Parent,
+		message.clone(),
+		&mut hash,
+		weight_limit,
+		Weight::zero(),
+	);
+	assert_eq!(r, Outcome::Error { error: XcmError::Barrier });
 }