[XNFT PoC] xtokens non-fungible multiassets support (#966)

* feat: xtokens non-fungible multiassets support PoC

* test: nft/fee related tests for multiasset transfer

* fix: do_transfer_multiassets zero fee issue

Author: mrshiposha

xtokens/src/lib.rs

@@ -520,20 +520,31 @@ pub mod module {
 				T::MultiLocationsFilter::contains(&dest),
 				Error::<T>::NotSupportedMultiLocation
 			);
+
+			// Fee payment can only be made by using the non-zero amount of fungibles
+			ensure!(
+				matches!(fee.fun, Fungibility::Fungible(x) if !x.is_zero()),
+				Error::<T>::InvalidAsset
+			);
+
 			let origin_location = T::AccountIdToMultiLocation::convert(who.clone());
 
 			let mut non_fee_reserve: Option<MultiLocation> = None;
 			let asset_len = assets.len();
 			for i in 0..asset_len {
 				let asset = assets.get(i).ok_or(Error::<T>::AssetIndexNonExistent)?;
-				ensure!(
-					matches!(asset.fun, Fungibility::Fungible(x) if !x.is_zero()),
-					Error::<T>::InvalidAsset
-				);
+
+				match asset.fun {
+					Fungibility::Fungible(x) => ensure!(!x.is_zero(), Error::<T>::InvalidAsset),
+					Fungibility::NonFungible(AssetInstance::Undefined) => return Err(Error::<T>::InvalidAsset.into()),
+					_ => {}
+				}
+
 				// `assets` includes fee, the reserve location is decided by non fee asset
-				if (fee != *asset && non_fee_reserve.is_none()) || asset_len == 1 {
+				if non_fee_reserve.is_none() && asset.id != fee.id {
 					non_fee_reserve = T::ReserveProvider::reserve(asset);
 				}
+
 				// make sure all non fee assets share the same reserve
 				if non_fee_reserve.is_some() {
 					ensure!(
@@ -544,7 +555,7 @@ pub mod module {
 			}
 
 			let fee_reserve = T::ReserveProvider::reserve(&fee);
-			if fee_reserve != non_fee_reserve {
+			if asset_len > 1 && fee_reserve != non_fee_reserve {
 				// Current only support `ToReserve` with relay-chain asset as fee. other case
 				// like `NonReserve` or `SelfReserve` with relay-chain fee is not support.
 				ensure!(non_fee_reserve == dest.chain_part(), Error::<T>::InvalidAsset);
@@ -610,7 +621,7 @@ pub mod module {
 					origin_location,
 					assets.clone(),
 					fee.clone(),
-					non_fee_reserve,
+					fee_reserve,
 					&dest,
 					None,
 					dest_weight_limit,

xtokens/src/tests.rs

@@ -1721,3 +1721,100 @@ fn send_with_insufficient_weight_limit() {
 		assert_eq!(ParaTokens::free_balance(CurrencyId::A, &BOB), 0);
 	});
 }
+
+#[test]
+fn send_multiasset_with_zero_fee_should_yield_an_error() {
+	TestNet::reset();
+
+	let asset_id: AssetId = X1(Junction::from(BoundedVec::try_from(b"A".to_vec()).unwrap())).into();
+	ParaA::execute_with(|| {
+		assert_noop!(
+			ParaXTokens::transfer_multiasset_with_fee(
+				Some(ALICE).into(),
+				Box::new((asset_id, 100).into()),
+				Box::new((asset_id, Fungibility::Fungible(0)).into()),
+				Box::new(
+					MultiLocation::new(
+						1,
+						X2(
+							Parachain(2),
+							Junction::AccountId32 {
+								network: None,
+								id: BOB.into()
+							},
+						)
+					)
+					.into()
+				),
+				WeightLimit::Unlimited,
+			),
+			Error::<para::Runtime>::InvalidAsset
+		);
+	});
+}
+
+#[test]
+fn send_undefined_nft_should_yield_an_error() {
+	TestNet::reset();
+
+	let fee_id: AssetId = X1(Junction::from(BoundedVec::try_from(b"A".to_vec()).unwrap())).into();
+	let nft_id: AssetId = X1(Junction::GeneralIndex(42)).into();
+
+	ParaA::execute_with(|| {
+		assert_noop!(
+			ParaXTokens::transfer_multiasset_with_fee(
+				Some(ALICE).into(),
+				Box::new((nft_id, Undefined).into()),
+				Box::new((fee_id, 100).into()),
+				Box::new(
+					MultiLocation::new(
+						1,
+						X2(
+							Parachain(2),
+							Junction::AccountId32 {
+								network: None,
+								id: BOB.into()
+							},
+						)
+					)
+					.into()
+				),
+				WeightLimit::Unlimited,
+			),
+			Error::<para::Runtime>::InvalidAsset
+		);
+	});
+}
+
+#[test]
+fn nfts_cannot_be_fee_assets() {
+	TestNet::reset();
+
+	let asset_id: AssetId = X1(Junction::from(BoundedVec::try_from(b"A".to_vec()).unwrap())).into();
+	let nft_id: AssetId = X1(Junction::GeneralIndex(42)).into();
+
+	ParaA::execute_with(|| {
+		assert_noop!(
+			ParaXTokens::transfer_multiasset_with_fee(
+				Some(ALICE).into(),
+				Box::new((asset_id, 100).into()),
+				Box::new((nft_id, Index(1)).into()),
+				Box::new(
+					MultiLocation::new(
+						1,
+						X2(
+							Parachain(2),
+							Junction::AccountId32 {
+								network: None,
+								id: BOB.into()
+							},
+						)
+					)
+					.into()
+				),
+				WeightLimit::Unlimited,
+			),
+			Error::<para::Runtime>::InvalidAsset
+		);
+	});
+}