XCM: Utility struct for AccountId conversion (#7321)

* XCM: Utility struct for AccountId conversion

* Update conversion.rs

polkadot/xcm/xcm-builder/src/location_conversion.rs

@@ -237,18 +237,11 @@ impl<Network: Get<Option<NetworkId>>, AccountId: From<[u8; 32]> + Into<[u8; 32]>
 /// network (provided by `Network`) and the `AccountId`'s `[u8; 32]` datum for the `id`.
 pub struct AliasesIntoAccountId32<Network, AccountId>(PhantomData<(Network, AccountId)>);
 impl<'a, Network: Get<Option<NetworkId>>, AccountId: Clone + Into<[u8; 32]> + Clone>
-	Convert<&'a AccountId, MultiLocation> for AliasesIntoAccountId32<Network, AccountId>
+	sp_runtime::traits::Convert<&'a AccountId, MultiLocation>
+	for AliasesIntoAccountId32<Network, AccountId>
 {
-	fn convert(who: &AccountId) -> Result<MultiLocation, &'a AccountId> {
-		Ok(AccountId32 { network: Network::get(), id: who.clone().into() }.into())
-	}
-}
-
-impl<Network: Get<Option<NetworkId>>, AccountId: Into<[u8; 32]> + Clone>
-	Convert<AccountId, MultiLocation> for AliasesIntoAccountId32<Network, AccountId>
-{
-	fn convert(who: AccountId) -> Result<MultiLocation, AccountId> {
-		Ok(AccountId32 { network: Network::get(), id: who.into() }.into())
+	fn convert(who: &AccountId) -> MultiLocation {
+		AccountId32 { network: Network::get(), id: who.clone().into() }.into()
 	}
 }
 
@@ -313,7 +306,8 @@ impl<UniversalLocation: Get<InteriorMultiLocation>, AccountId: From<[u8; 32]> +
 	}
 
 	fn reverse_ref(_: impl Borrow<AccountId>) -> Result<MultiLocation, ()> {
-		// if this will be needed, we could implement some kind of guessing, if we have configuration for supported networkId+paraId
+		// if this is ever be needed, we could implement some kind of guessing, if we have
+		// configuration for supported networkId+paraId
 		Err(())
 	}
 }

polkadot/xcm/xcm-builder/src/pay.rs

@@ -28,8 +28,11 @@ use xcm_executor::traits::{QueryHandler, QueryResponseStatus};
 /// Implementation of the `frame_support::traits::tokens::Pay` trait, to allow
 /// for XCM-based payments of a given `Balance` of some asset ID existing on some chain under
 /// ownership of some `Interior` location of the local chain to a particular `Beneficiary`. The
-/// `AssetKind` value can be converted into both the XCM `AssetId` (via and `Into` bound) and the
-/// the destination chain's location, via the `AssetKindToLocatableAsset` type parameter.
+/// `AssetKind` value is not itself bounded (to avoid the issue of needing to wrap some preexisting
+/// datatype), however a converter type `AssetKindToLocatableAsset` must be provided in order to
+/// translate it into a `LocatableAsset`, which comprises both an XCM `MultiLocation` describing
+/// the XCM endpoint on which the asset to be paid resides and an XCM `AssetId` to identify the
+/// specific asset at that endpoint.
 ///
 /// This relies on the XCM `TransferAsset` instruction. A trait `BeneficiaryRefToLocation` must be
 /// provided in order to convert the `Beneficiary` reference into a location usable by
@@ -200,6 +203,3 @@ impl<Location: Get<MultiLocation>, AssetKind: Into<AssetId>> Convert<AssetKind,
 		LocatableAssetId { asset_id: value.into(), location: Location::get() }
 	}
 }
-
-#[test]
-fn it_builds() {}