XCMv4

[franciscoaguirre]

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:

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

pub enum Outcome {
  Complete(Weight),
  Incomplete(Weight, Error),
  Error(Error),
}

we now have

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:

let location = Location {
    parents: 1,
    interior: [Parachain(1000), PalletInstance(50), GeneralIndex(1984)].into()
};

or

let location = Location::new(1, [Parachain(1000), PalletInstance(50), GeneralIndex(1984)]);

And they are matched like so:

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

• Scaffold v4
• Port github.com/Make AssetId and MultiLocation non-Copy; make Instruction 92% smaller polkadot#7236
• Remove Multi prefix
• Remove Abstract asset id

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