Remove redundant XCMs from dry run's forwarded xcms

bridges/modules/xcm-bridge-hub-router/src/lib.rs

@@ -99,7 +99,7 @@ pub mod pallet {
 		type DestinationVersion: GetVersion;
 
 		/// Actual message sender (`HRMP` or `DMP`) to the sibling bridge hub location.
-		type ToBridgeHubSender: SendXcm + InspectMessageQueues;
+		type ToBridgeHubSender: SendXcm;
 		/// Local XCM channel manager.
 		type LocalXcmChannelManager: XcmChannelStatusProvider;
 
@@ -408,12 +408,12 @@ impl<T: Config<I>, I: 'static> SendXcm for Pallet<T, I> {
 }
 
 impl<T: Config<I>, I: 'static> InspectMessageQueues for Pallet<T, I> {
-	fn clear_messages() {
-		ViaBridgeHubExporter::<T, I>::clear_messages()
-	}
+	fn clear_messages() {}
 
+	/// This router needs to implement `InspectMessageQueues` but doesn't have to
+	/// return any messages, since it just reuses the `XcmpQueue` router.
 	fn get_messages() -> Vec<(VersionedLocation, Vec<VersionedXcm<()>>)> {
-		ViaBridgeHubExporter::<T, I>::get_messages()
+		Vec::new()
 	}
 }
 

cumulus/pallets/parachain-system/src/lib.rs

@@ -1627,7 +1627,11 @@ impl<T: Config> InspectMessageQueues for Pallet<T> {
 			.map(|encoded_message| VersionedXcm::<()>::decode(&mut &encoded_message[..]).unwrap())
 			.collect();
 
-		vec![(VersionedLocation::V4(Parent.into()), messages)]
+		if messages.is_empty() {
+			vec![]
+		} else {
+			vec![(VersionedLocation::from(Location::parent()), messages)]
+		}
 	}
 }
 

cumulus/parachains/integration-tests/emulated/common/src/macros.rs

@@ -403,3 +403,51 @@ macro_rules! test_chain_can_claim_assets {
 		}
 	};
 }
+
+#[macro_export]
+macro_rules! test_dry_run_transfer_across_pk_bridge {
+	( $sender_asset_hub:ty, $sender_bridge_hub:ty, $destination:expr ) => {
+		$crate::macros::paste::paste! {
+			use frame_support::{dispatch::RawOrigin, traits::fungible};
+			use sp_runtime::AccountId32;
+			use xcm::prelude::*;
+			use xcm_runtime_apis::dry_run::runtime_decl_for_dry_run_api::DryRunApiV1;
+
+			let who = AccountId32::new([1u8; 32]);
+			let transfer_amount = 10_000_000_000_000u128;
+			let initial_balance = transfer_amount * 10;
+
+			// Bridge setup.
+			$sender_asset_hub::force_xcm_version($destination, XCM_VERSION);
+			open_bridge_between_asset_hub_rococo_and_asset_hub_westend();
+
+			<$sender_asset_hub as TestExt>::execute_with(|| {
+				type Runtime = <$sender_asset_hub as Chain>::Runtime;
+				type RuntimeCall = <$sender_asset_hub as Chain>::RuntimeCall;
+				type OriginCaller = <$sender_asset_hub as Chain>::OriginCaller;
+				type Balances = <$sender_asset_hub as [<$sender_asset_hub Pallet>]>::Balances;
+
+				// Give some initial funds.
+				<Balances as fungible::Mutate<_>>::set_balance(&who, initial_balance);
+
+				let call = RuntimeCall::PolkadotXcm(pallet_xcm::Call::transfer_assets {
+					dest: Box::new(VersionedLocation::from($destination)),
+					beneficiary: Box::new(VersionedLocation::from(Junction::AccountId32 {
+						id: who.clone().into(),
+						network: None,
+					})),
+					assets: Box::new(VersionedAssets::from(vec![
+						(Parent, transfer_amount).into(),
+					])),
+					fee_asset_item: 0,
+					weight_limit: Unlimited,
+				});
+				let result = Runtime::dry_run_call(OriginCaller::system(RawOrigin::Signed(who)), call).unwrap();
+				// We assert the dry run succeeds and sends only one message to the local bridge hub.
+				assert!(result.execution_result.is_ok());
+				assert_eq!(result.forwarded_xcms.len(), 1);
+				assert_eq!(result.forwarded_xcms[0].0, VersionedLocation::from(Location::new(1, [Parachain($sender_bridge_hub::para_id().into())])));
+			});
+		}
+	};
+}

cumulus/parachains/integration-tests/emulated/tests/bridges/bridge-hub-rococo/Cargo.toml

@@ -28,6 +28,7 @@ sp-runtime = { workspace = true }
 xcm = { workspace = true }
 pallet-xcm = { workspace = true }
 xcm-executor = { workspace = true }
+xcm-runtime-apis = { workspace = true }
 
 # Bridges
 pallet-bridge-messages = { workspace = true }

cumulus/parachains/integration-tests/emulated/tests/bridges/bridge-hub-rococo/src/lib.rs

@@ -33,8 +33,8 @@ mod imports {
 	pub use emulated_integration_tests_common::{
 		accounts::ALICE,
 		impls::Inspect,
-		test_parachain_is_trusted_teleporter, test_parachain_is_trusted_teleporter_for_relay,
-		test_relay_is_trusted_teleporter,
+		test_dry_run_transfer_across_pk_bridge, test_parachain_is_trusted_teleporter,
+		test_parachain_is_trusted_teleporter_for_relay, test_relay_is_trusted_teleporter,
 		xcm_emulator::{
 			assert_expected_events, bx, Chain, Parachain as Para, RelayChain as Relay, TestExt,
 		},

cumulus/parachains/integration-tests/emulated/tests/bridges/bridge-hub-rococo/src/tests/asset_transfers.rs

@@ -534,3 +534,12 @@ fn send_back_wnds_from_penpal_rococo_through_asset_hub_rococo_to_asset_hub_weste
 	assert!(receiver_wnds_after > receiver_wnds_before);
 	assert!(receiver_wnds_after <= receiver_wnds_before + amount);
 }
+
+#[test]
+fn dry_run_transfer_to_westend_sends_xcm_to_bridge_hub() {
+	test_dry_run_transfer_across_pk_bridge!(
+		AssetHubRococo,
+		BridgeHubRococo,
+		asset_hub_westend_location()
+	);
+}

cumulus/parachains/integration-tests/emulated/tests/bridges/bridge-hub-westend/Cargo.toml

@@ -29,6 +29,7 @@ sp-runtime = { workspace = true }
 xcm = { workspace = true }
 pallet-xcm = { workspace = true }
 xcm-executor = { workspace = true }
+xcm-runtime-apis = { workspace = true }
 
 # Bridges
 pallet-bridge-messages = { workspace = true }

cumulus/parachains/integration-tests/emulated/tests/bridges/bridge-hub-westend/src/lib.rs

@@ -32,8 +32,8 @@ mod imports {
 	pub use emulated_integration_tests_common::{
 		accounts::ALICE,
 		impls::Inspect,
-		test_parachain_is_trusted_teleporter, test_parachain_is_trusted_teleporter_for_relay,
-		test_relay_is_trusted_teleporter,
+		test_dry_run_transfer_across_pk_bridge, test_parachain_is_trusted_teleporter,
+		test_parachain_is_trusted_teleporter_for_relay, test_relay_is_trusted_teleporter,
 		xcm_emulator::{
 			assert_expected_events, bx, Chain, Parachain as Para, RelayChain as Relay, TestExt,
 		},

cumulus/parachains/integration-tests/emulated/tests/bridges/bridge-hub-westend/src/tests/asset_transfers.rs

@@ -554,3 +554,12 @@ fn send_back_rocs_from_penpal_westend_through_asset_hub_westend_to_asset_hub_roc
 	assert!(receiver_rocs_after > receiver_rocs_before);
 	assert!(receiver_rocs_after <= receiver_rocs_before + amount);
 }
+
+#[test]
+fn dry_run_transfer_to_rococo_sends_xcm_to_bridge_hub() {
+	test_dry_run_transfer_across_pk_bridge!(
+		AssetHubWestend,
+		BridgeHubWestend,
+		asset_hub_rococo_location()
+	);
+}

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

@@ -337,15 +337,15 @@ impl<Bridges: ExporterFor, Router: SendXcm, UniversalLocation: Get<InteriorLocat
 	}
 }
 
-impl<Bridges, Router: InspectMessageQueues, UniversalLocation> InspectMessageQueues
+impl<Bridges, Router, UniversalLocation> InspectMessageQueues
 	for SovereignPaidRemoteExporter<Bridges, Router, UniversalLocation>
 {
-	fn clear_messages() {
-		Router::clear_messages()
-	}
+	fn clear_messages() {}
 
+	/// This router needs to implement `InspectMessageQueues` but doesn't have to
+	/// return any messages, since it just reuses the `XcmpQueue` router.
 	fn get_messages() -> Vec<(VersionedLocation, Vec<VersionedXcm<()>>)> {
-		Router::get_messages()
+		Vec::new()
 	}
 }
 

prdoc/pr_5913.prdoc

@@ -0,0 +1,20 @@
+# Schema: Polkadot SDK PRDoc Schema (prdoc) v1.0.0
+# See doc at https://raw.githubusercontent.com/paritytech/polkadot-sdk/master/prdoc/schema_user.json
+
+title: Remove redundant XCMs from dry run's forwarded xcms
+
+doc:
+  - audience: Runtime User
+    description: |
+      The DryRunApi was returning the same message repeated multiple times in the
+      `forwarded_xcms` field. This is no longer the case.
+
+crates:
+  - name: pallet-xcm-bridge-hub-router
+    bump: patch
+  - name: cumulus-pallet-parachain-system
+    bump: patch
+  - name: staging-xcm-builder
+    bump: patch
+  - name: emulated-integration-tests-common
+    bump: minor