Allows to customize how calls are dispatched from XCM

runtime/kusama/src/xcm_config.rs

@@ -161,6 +161,7 @@ impl xcm_executor::Config for XcmConfig {
 	// No bridges yet...
 	type MessageExporter = ();
 	type UniversalAliases = Nothing;
+	type CallDispatcher = Call;
 }
 
 parameter_types! {

runtime/polkadot/src/xcm_config.rs

@@ -158,6 +158,7 @@ impl xcm_executor::Config for XcmConfig {
 	// No bridges yet...
 	type MessageExporter = ();
 	type UniversalAliases = Nothing;
+	type CallDispatcher = Call;
 }
 
 parameter_types! {

runtime/rococo/src/xcm_config.rs

@@ -144,6 +144,7 @@ impl xcm_executor::Config for XcmConfig {
 	type FeeManager = ();
 	type MessageExporter = ();
 	type UniversalAliases = Nothing;
+	type CallDispatcher = Call;
 }
 
 parameter_types! {

runtime/test-runtime/src/xcm_config.rs

@@ -103,4 +103,5 @@ impl xcm_executor::Config for XcmConfig {
 	type FeeManager = ();
 	type MessageExporter = ();
 	type UniversalAliases = Nothing;
+	type CallDispatcher = Call;
 }

runtime/westend/src/xcm_config.rs

@@ -123,6 +123,7 @@ impl xcm_executor::Config for XcmConfig {
 	type FeeManager = ();
 	type MessageExporter = ();
 	type UniversalAliases = Nothing;
+	type CallDispatcher = Call;
 }
 
 /// Type to convert an `Origin` type value into a `MultiLocation` value which represents an interior location

xcm/xcm-executor/src/config.rs

@@ -15,8 +15,9 @@
 // along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.
 
 use crate::traits::{
-	AssetExchange, AssetLock, ClaimAssets, ConvertOrigin, DropAssets, ExportXcm, FeeManager,
-	OnResponse, ShouldExecute, TransactAsset, VersionChangeNotifier, WeightBounds, WeightTrader,
+	AssetExchange, AssetLock, CallDispatcher, ClaimAssets, ConvertOrigin, DropAssets, ExportXcm,
+	FeeManager, OnResponse, ShouldExecute, TransactAsset, VersionChangeNotifier, WeightBounds,
+	WeightTrader,
 };
 use frame_support::{
 	dispatch::{Dispatchable, Parameter},
@@ -94,4 +95,10 @@ pub trait Config {
 	/// The origin locations and specific universal junctions to which they are allowed to elevate
 	/// themselves.
 	type UniversalAliases: Contains<(MultiLocation, Junction)>;
+
+	/// The call dispatcher used by XCM.
+	///
+	/// XCM will use this to dispatch any calls. When no special call dispatcher is required,
+	/// this can be set to the same type as `Self::Call`.
+	type CallDispatcher: CallDispatcher<Self::Call>;
 }

xcm/xcm-executor/src/lib.rs

@@ -17,7 +17,7 @@
 #![cfg_attr(not(feature = "std"), no_std)]
 
 use frame_support::{
-	dispatch::{Dispatchable, Weight},
+	dispatch::Weight,
 	ensure,
 	traits::{Contains, ContainsPair, Get, PalletsInfoAccess},
 	weights::GetDispatchInfo,
@@ -30,8 +30,8 @@ use xcm::latest::prelude::*;
 
 pub mod traits;
 use traits::{
-	validate_export, AssetExchange, AssetLock, ClaimAssets, ConvertOrigin, DropAssets, Enact,
-	ExportXcm, FeeManager, FeeReason, OnResponse, ShouldExecute, TransactAsset,
+	validate_export, AssetExchange, AssetLock, CallDispatcher, ClaimAssets, ConvertOrigin,
+	DropAssets, Enact, ExportXcm, FeeManager, FeeReason, OnResponse, ShouldExecute, TransactAsset,
 	VersionChangeNotifier, WeightBounds, WeightTrader,
 };
 
@@ -512,16 +512,17 @@ impl<Config: config::Config> XcmExecutor<Config> {
 					.map_err(|_| XcmError::BadOrigin)?;
 				let weight = message_call.get_dispatch_info().weight;
 				ensure!(weight <= require_weight_at_most, XcmError::MaxWeightInvalid);
-				let maybe_actual_weight = match message_call.dispatch(dispatch_origin) {
-					Ok(post_info) => {
-						self.transact_status = MaybeErrorCode::Success;
-						post_info.actual_weight
-					},
-					Err(error_and_info) => {
-						self.transact_status = error_and_info.error.encode().into();
-						error_and_info.post_info.actual_weight
-					},
-				};
+				let maybe_actual_weight =
+					match Config::CallDispatcher::dispatch(message_call, dispatch_origin) {
+						Ok(post_info) => {
+							self.transact_status = MaybeErrorCode::Success;
+							post_info.actual_weight
+						},
+						Err(error_and_info) => {
+							self.transact_status = error_and_info.error.encode().into();
+							error_and_info.post_info.actual_weight
+						},
+					};
 				let actual_weight = maybe_actual_weight.unwrap_or(weight);
 				let surplus = weight.saturating_sub(actual_weight);
 				// We assume that the `Config::Weigher` will counts the `require_weight_at_most`

xcm/xcm-executor/src/traits/conversion.rs

@@ -15,6 +15,7 @@
 // along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.
 
 use parity_scale_codec::{Decode, Encode};
+use sp_runtime::{traits::Dispatchable, DispatchErrorWithPostInfo};
 use sp_std::{borrow::Borrow, prelude::*, result::Result};
 use xcm::latest::prelude::*;
 
@@ -203,3 +204,24 @@ impl<O> ConvertOrigin<O> for Tuple {
 		Err(origin)
 	}
 }
+
+/// Defines how a call is dispatched with given origin.
+/// Allows to customize call dispatch, such as adapting the origin based on the call
+/// or modifying the call.
+pub trait CallDispatcher<Call: Dispatchable> {
+	fn dispatch(
+		call: Call,
+		origin: Call::Origin,
+	) -> Result<Call::PostInfo, DispatchErrorWithPostInfo<Call::PostInfo>>;
+}
+
+// We implement it for every calls so they can dispatch themselves
+// (without any change).
+impl<Call: Dispatchable> CallDispatcher<Call> for Call {
+	fn dispatch(
+		call: Call,
+		origin: Call::Origin,
+	) -> Result<Call::PostInfo, DispatchErrorWithPostInfo<Call::PostInfo>> {
+		call.dispatch(origin)
+	}
+}

xcm/xcm-executor/src/traits/mod.rs

@@ -17,7 +17,7 @@
 //! Various traits used in configuring the executor.
 
 mod conversion;
-pub use conversion::{Convert, ConvertOrigin, Decoded, Encoded, Identity, JustTry};
+pub use conversion::{CallDispatcher, Convert, ConvertOrigin, Decoded, Encoded, Identity, JustTry};
 mod drop_assets;
 pub use drop_assets::{ClaimAssets, DropAssets};
 mod asset_lock;