Contracts: Add XCM traits to interface with contracts (#2086)

We are introducing a new set of `XcmController` traits (final name yet
to be determined).
These traits are implemented by `pallet-xcm` and allows other pallets,
such as `pallet_contracts`, to rely on these traits instead of tight
coupling them to `pallet-xcm`.

Using only the existing Xcm traits would mean duplicating the logic from
`pallet-xcm` in these other pallets, which we aim to avoid. Our
objective is to ensure that when these APIs are called from
`pallet-contracts`, they produce the exact same outcomes as if called
directly from `pallet-xcm`.

The other benefits is that we can also expose return values to
`pallet-contracts` instead of just calling `pallet-xcm` dispatchable and
getting a `DispatchResult` back.

See traits integration in this PR
paritytech/polkadot-sdk#1248, where the traits
are used as follow to define and implement `pallet-contracts` Config.
```rs
// Contracts config:
pub trait Config: frame_system::Config {
  // ...

  /// A type that exposes XCM APIs, allowing contracts to interact with other parachains, and
  /// execute XCM programs.
  type Xcm: xcm_executor::traits::Controller<
	  OriginFor<Self>,
	  <Self as frame_system::Config>::RuntimeCall,
	  BlockNumberFor<Self>,
  >;
}

// implementation
impl pallet_contracts::Config for Runtime {
        // ...

	type Xcm = pallet_xcm::Pallet<Self>;
}
```

---------

Co-authored-by: Alexander Theißen <alex.theissen@me.com>
Co-authored-by: command-bot <>

pallet-xcm/Cargo.toml

@@ -23,12 +23,12 @@ sp-std = { path = "../../../substrate/primitives/std", default-features = false}
 
 xcm = { package = "staging-xcm", path = "..", default-features = false }
 xcm-executor = { package = "staging-xcm-executor", path = "../xcm-executor", default-features = false }
+xcm-builder = { package = "staging-xcm-builder", path = "../xcm-builder", default-features = false }
 
 [dev-dependencies]
 pallet-balances = { path = "../../../substrate/frame/balances" }
 polkadot-runtime-parachains = { path = "../../runtime/parachains" }
 polkadot-parachain-primitives = { path = "../../parachain" }
-xcm-builder = { package = "staging-xcm-builder", path = "../xcm-builder" }
 
 [features]
 default = [ "std" ]
@@ -45,6 +45,7 @@ std = [
 	"sp-io/std",
 	"sp-runtime/std",
 	"sp-std/std",
+	"xcm-builder/std",
 	"xcm-executor/std",
 	"xcm/std",
 ]

pallet-xcm/src/benchmarking.rs

@@ -190,6 +190,33 @@ benchmarks! {
 		Pallet::<T>::check_xcm_version_change(VersionMigrationStage::MigrateAndNotifyOldTargets, Weight::zero());
 	}
 
+	new_query {
+		let responder = MultiLocation::from(Parent);
+		let timeout = 1u32.into();
+		let match_querier = MultiLocation::from(Here);
+	}: {
+		Pallet::<T>::new_query(responder, timeout, match_querier);
+	}
+
+	take_response {
+		let responder = MultiLocation::from(Parent);
+		let timeout = 1u32.into();
+		let match_querier = MultiLocation::from(Here);
+		let query_id = Pallet::<T>::new_query(responder, timeout, match_querier);
+		let infos = (0 .. xcm::v3::MaxPalletsInfo::get()).map(|_| PalletInfo::new(
+			u32::MAX,
+			(0..xcm::v3::MaxPalletNameLen::get()).map(|_| 97u8).collect::<Vec<_>>().try_into().unwrap(),
+			(0..xcm::v3::MaxPalletNameLen::get()).map(|_| 97u8).collect::<Vec<_>>().try_into().unwrap(),
+			u32::MAX,
+			u32::MAX,
+			u32::MAX,
+		).unwrap()).collect::<Vec<_>>();
+		Pallet::<T>::expect_response(query_id, Response::PalletsInfo(infos.try_into().unwrap()));
+
+	}: {
+		<Pallet::<T> as QueryHandler>::take_response(query_id);
+	}
+
 	impl_benchmark_test_suite!(
 		Pallet,
 		crate::mock::new_test_ext_with_balances(Vec::new()),

pallet-xcm/src/lib.rs

@@ -28,9 +28,17 @@ mod tests;
 pub mod migration;
 
 use codec::{Decode, Encode, EncodeLike, MaxEncodedLen};
-use frame_support::traits::{
-	Contains, ContainsPair, Currency, Defensive, EnsureOrigin, Get, LockableCurrency, OriginTrait,
+use frame_support::{
+	dispatch::GetDispatchInfo,
+	pallet_prelude::*,
+	traits::{
+		Contains, ContainsPair, Currency, Defensive, EnsureOrigin, Get, LockableCurrency,
+		OriginTrait, WithdrawReasons,
+	},
+	PalletId,
 };
+use frame_system::pallet_prelude::{BlockNumberFor, *};
+pub use pallet::*;
 use scale_info::TypeInfo;
 use sp_runtime::{
 	traits::{
@@ -41,17 +49,15 @@ use sp_runtime::{
 };
 use sp_std::{boxed::Box, marker::PhantomData, prelude::*, result::Result, vec};
 use xcm::{latest::QueryResponseInfo, prelude::*};
-use xcm_executor::traits::{ConvertOrigin, Properties};
-
-use frame_support::{
-	dispatch::GetDispatchInfo, pallet_prelude::*, traits::WithdrawReasons, PalletId,
+use xcm_builder::{
+	ExecuteController, ExecuteControllerWeightInfo, QueryController, QueryControllerWeightInfo,
+	SendController, SendControllerWeightInfo,
 };
-use frame_system::pallet_prelude::*;
-pub use pallet::*;
 use xcm_executor::{
 	traits::{
-		CheckSuspension, ClaimAssets, ConvertLocation, DropAssets, MatchesFungible, OnResponse,
-		QueryHandler, QueryResponseStatus, VersionChangeNotifier, WeightBounds,
+		CheckSuspension, ClaimAssets, ConvertLocation, ConvertOrigin, DropAssets, MatchesFungible,
+		OnResponse, Properties, QueryHandler, QueryResponseStatus, VersionChangeNotifier,
+		WeightBounds,
 	},
 	Assets,
 };
@@ -73,6 +79,8 @@ pub trait WeightInfo {
 	fn notify_target_migration_fail() -> Weight;
 	fn migrate_version_notify_targets() -> Weight;
 	fn migrate_and_notify_old_targets() -> Weight;
+	fn new_query() -> Weight;
+	fn take_response() -> Weight;
 }
 
 /// fallback implementation
@@ -141,6 +149,14 @@ impl WeightInfo for TestWeightInfo {
 	fn migrate_and_notify_old_targets() -> Weight {
 		Weight::from_parts(100_000_000, 0)
 	}
+
+	fn new_query() -> Weight {
+		Weight::from_parts(100_000_000, 0)
+	}
+
+	fn take_response() -> Weight {
+		Weight::from_parts(100_000_000, 0)
+	}
 }
 
 #[frame_support::pallet]
@@ -267,6 +283,93 @@ pub mod pallet {
 		type ReachableDest: Get<Option<MultiLocation>>;
 	}
 
+	impl<T: Config> ExecuteControllerWeightInfo for Pallet<T> {
+		fn execute() -> Weight {
+			T::WeightInfo::execute()
+		}
+	}
+
+	impl<T: Config> ExecuteController<OriginFor<T>, <T as Config>::RuntimeCall> for Pallet<T> {
+		type WeightInfo = Self;
+		fn execute(
+			origin: OriginFor<T>,
+			message: Box<VersionedXcm<<T as Config>::RuntimeCall>>,
+			max_weight: Weight,
+		) -> Result<Outcome, DispatchError> {
+			let origin_location = T::ExecuteXcmOrigin::ensure_origin(origin)?;
+			let hash = message.using_encoded(sp_io::hashing::blake2_256);
+			let message = (*message).try_into().map_err(|()| Error::<T>::BadVersion)?;
+			let value = (origin_location, message);
+			ensure!(T::XcmExecuteFilter::contains(&value), Error::<T>::Filtered);
+			let (origin_location, message) = value;
+			let outcome = T::XcmExecutor::execute_xcm_in_credit(
+				origin_location,
+				message,
+				hash,
+				max_weight,
+				max_weight,
+			);
+			Self::deposit_event(Event::Attempted { outcome: outcome.clone() });
+			Ok(outcome)
+		}
+	}
+
+	impl<T: Config> SendControllerWeightInfo for Pallet<T> {
+		fn send() -> Weight {
+			T::WeightInfo::send()
+		}
+	}
+
+	impl<T: Config> SendController<OriginFor<T>> for Pallet<T> {
+		type WeightInfo = Self;
+		fn send(
+			origin: OriginFor<T>,
+			dest: Box<VersionedMultiLocation>,
+			message: Box<VersionedXcm<()>>,
+		) -> Result<XcmHash, DispatchError> {
+			let origin_location = T::SendXcmOrigin::ensure_origin(origin)?;
+			let interior: Junctions =
+				origin_location.try_into().map_err(|_| Error::<T>::InvalidOrigin)?;
+			let dest = MultiLocation::try_from(*dest).map_err(|()| Error::<T>::BadVersion)?;
+			let message: Xcm<()> = (*message).try_into().map_err(|()| Error::<T>::BadVersion)?;
+
+			let message_id =
+				Self::send_xcm(interior, dest, message.clone()).map_err(Error::<T>::from)?;
+			let e = Event::Sent { origin: origin_location, destination: dest, message, message_id };
+			Self::deposit_event(e);
+			Ok(message_id)
+		}
+	}
+
+	impl<T: Config> QueryControllerWeightInfo for Pallet<T> {
+		fn query() -> Weight {
+			T::WeightInfo::new_query()
+		}
+		fn take_response() -> Weight {
+			T::WeightInfo::take_response()
+		}
+	}
+
+	impl<T: Config> QueryController<OriginFor<T>, BlockNumberFor<T>> for Pallet<T> {
+		type WeightInfo = Self;
+
+		fn query(
+			origin: OriginFor<T>,
+			timeout: BlockNumberFor<T>,
+			match_querier: VersionedMultiLocation,
+		) -> Result<Self::QueryId, DispatchError> {
+			let responder = <T as Config>::ExecuteXcmOrigin::ensure_origin(origin)?;
+			let query_id = <Self as QueryHandler>::new_query(
+				responder,
+				timeout,
+				MultiLocation::try_from(match_querier)
+					.map_err(|_| Into::<DispatchError>::into(Error::<T>::BadVersion))?,
+			);
+
+			Ok(query_id)
+		}
+	}
+
 	#[pallet::event]
 	#[pallet::generate_deposit(pub(super) fn deposit_event)]
 	pub enum Event<T: Config> {
@@ -771,16 +874,7 @@ pub mod pallet {
 			dest: Box<VersionedMultiLocation>,
 			message: Box<VersionedXcm<()>>,
 		) -> DispatchResult {
-			let origin_location = T::SendXcmOrigin::ensure_origin(origin)?;
-			let interior: Junctions =
-				origin_location.try_into().map_err(|_| Error::<T>::InvalidOrigin)?;
-			let dest = MultiLocation::try_from(*dest).map_err(|()| Error::<T>::BadVersion)?;
-			let message: Xcm<()> = (*message).try_into().map_err(|()| Error::<T>::BadVersion)?;
-
-			let message_id =
-				Self::send_xcm(interior, dest, message.clone()).map_err(Error::<T>::from)?;
-			let e = Event::Sent { origin: origin_location, destination: dest, message, message_id };
-			Self::deposit_event(e);
+			<Self as SendController<_>>::send(origin, dest, message)?;
 			Ok(())
 		}
 
@@ -896,31 +990,16 @@ pub mod pallet {
 		/// execution attempt will be made.
 		///
 		/// NOTE: A successful return to this does *not* imply that the `msg` was executed
-		/// successfully to completion; only that *some* of it was executed.
+		/// successfully to completion; only that it was attempted.
 		#[pallet::call_index(3)]
 		#[pallet::weight(max_weight.saturating_add(T::WeightInfo::execute()))]
 		pub fn execute(
 			origin: OriginFor<T>,
 			message: Box<VersionedXcm<<T as Config>::RuntimeCall>>,
 			max_weight: Weight,
 		) -> DispatchResultWithPostInfo {
-			let origin_location = T::ExecuteXcmOrigin::ensure_origin(origin)?;
-			let hash = message.using_encoded(sp_io::hashing::blake2_256);
-			let message = (*message).try_into().map_err(|()| Error::<T>::BadVersion)?;
-			let value = (origin_location, message);
-			ensure!(T::XcmExecuteFilter::contains(&value), Error::<T>::Filtered);
-			let (origin_location, message) = value;
-			let outcome = T::XcmExecutor::execute_xcm_in_credit(
-				origin_location,
-				message,
-				hash,
-				max_weight,
-				max_weight,
-			);
-			let result =
-				Ok(Some(outcome.weight_used().saturating_add(T::WeightInfo::execute())).into());
-			Self::deposit_event(Event::Attempted { outcome });
-			result
+			let outcome = <Self as ExecuteController<_, _>>::execute(origin, message, max_weight)?;
+			Ok(Some(outcome.weight_used().saturating_add(T::WeightInfo::execute())).into())
 		}
 
 		/// Extoll that a particular destination can be communicated with through a particular
@@ -1145,7 +1224,7 @@ impl<T: Config> QueryHandler for Pallet<T> {
 		timeout: BlockNumberFor<T>,
 		match_querier: impl Into<MultiLocation>,
 	) -> Self::QueryId {
-		Self::do_new_query(responder, None, timeout, match_querier).into()
+		Self::do_new_query(responder, None, timeout, match_querier)
 	}
 
 	/// To check the status of the query, use `fn query()` passing the resultant `QueryId`