Backport of 1318 (#1348)

* recognise no reserves

* adjust should_execute

* docs and pass should_execute

* typo

parachain-template/runtime/src/xcm_config.rs

@@ -137,13 +137,14 @@ impl ShouldExecute for DenyReserveTransferToRelayChain {
 			return Err(()) // Deny
 		}
 
-		// allow reserve transfers to arrive from relay chain
+		// An unexpected reserve transfer has arrived from the Relay Chain. Generally, `IsReserve`
+		// should not allow this, but we just log it here.
 		if matches!(origin, MultiLocation { parents: 1, interior: Here }) &&
 			message.0.iter().any(|inst| matches!(inst, ReserveAssetDeposited { .. }))
 		{
 			log::warn!(
 				target: "xcm::barriers",
-				"Unexpected ReserveAssetDeposited from the relay chain",
+				"Unexpected ReserveAssetDeposited from the Relay Chain",
 			);
 		}
 		// Permit everything else

parachains/common/src/xcm_config.rs

@@ -52,13 +52,14 @@ impl ShouldExecute for DenyReserveTransferToRelayChain {
 			return Err(()) // Deny
 		}
 
-		// allow reserve transfers to arrive from relay chain
+		// An unexpected reserve transfer has arrived from the Relay Chain. Generally, `IsReserve`
+		// should not allow this, but we just log it here.
 		if matches!(origin, MultiLocation { parents: 1, interior: Here }) &&
 			message.0.iter().any(|inst| matches!(inst, ReserveAssetDeposited { .. }))
 		{
 			log::warn!(
 				target: "xcm::barrier",
-				"Unexpected ReserveAssetDeposited from the relay chain",
+				"Unexpected ReserveAssetDeposited from the Relay Chain",
 			);
 		}
 		// Permit everything else

parachains/runtimes/assets/statemine/src/xcm_config.rs

@@ -162,7 +162,10 @@ impl xcm_executor::Config for XcmConfig {
 	type XcmSender = XcmRouter;
 	type AssetTransactor = AssetTransactors;
 	type OriginConverter = XcmOriginToTransactDispatchOrigin;
-	type IsReserve = NativeAsset;
+	// Statemine does not recognize a reserve location for any asset. This does not prevent
+	// Statemine acting _as_ a reserve location for KSM and assets created under `pallet-assets`.
+	// For KSM, users must use teleport where allowed (e.g. with the Relay Chain).
+	type IsReserve = ();
 	type IsTeleporter = NativeAsset; // <- should be enough to allow teleportation of KSM
 	type LocationInverter = LocationInverter<Ancestry>;
 	type Barrier = Barrier;

parachains/runtimes/assets/statemint/src/xcm_config.rs

@@ -162,7 +162,10 @@ impl xcm_executor::Config for XcmConfig {
 	type XcmSender = XcmRouter;
 	type AssetTransactor = AssetTransactors;
 	type OriginConverter = XcmOriginToTransactDispatchOrigin;
-	type IsReserve = NativeAsset;
+	// Statemint does not recognize a reserve location for any asset. This does not prevent
+	// Statemint acting _as_ a reserve location for DOT and assets created under `pallet-assets`.
+	// For DOT, users must use teleport where allowed (e.g. with the Relay Chain).
+	type IsReserve = ();
 	type IsTeleporter = NativeAsset; // <- should be enough to allow teleportation of DOT
 	type LocationInverter = LocationInverter<Ancestry>;
 	type Barrier = Barrier;

parachains/runtimes/assets/westmint/src/xcm_config.rs

@@ -158,7 +158,10 @@ impl xcm_executor::Config for XcmConfig {
 	type XcmSender = XcmRouter;
 	type AssetTransactor = AssetTransactors;
 	type OriginConverter = XcmOriginToTransactDispatchOrigin;
-	type IsReserve = NativeAsset;
+	// Westmint does not recognize a reserve location for any asset. This does not prevent
+	// Westmint acting _as_ a reserve location for WND and assets created under `pallet-assets`.
+	// For WND, users must use teleport where allowed (e.g. with the Relay Chain).
+	type IsReserve = ();
 	type IsTeleporter = NativeAsset; // <- should be enough to allow teleportation of WND
 	type LocationInverter = LocationInverter<Ancestry>;
 	type Barrier = Barrier;