Contracts: xcm host fn fixes (#3086)

## Xcm changes:
- Fix `pallet_xcm::execute`, move the logic into The `ExecuteController`
so it can be shared with anything that implement that trait.
- Make `ExecuteController::execute` retursn `DispatchErrorWithPostInfo`
instead of `DispatchError`, so that we don't charge the full
`max_weight` provided if the execution is incomplete (useful for
force_batch or contracts calls)
- Fix docstring for `pallet_xcm::execute`, to reflect the changes from
#2405
- Update the signature for `ExecuteController::execute`, we don't need
to return the `Outcome` anymore since we only care about
`Outcome::Complete`

## Contracts changes:

- Update host fn `xcm_exexute`, we don't need to write the `Outcome` to
the sandbox memory anymore. This was also not charged as well before so
it if fixes this too.
- One of the issue was that the dry_run of a contract that call
`xcm_execute` would exhaust the `gas_limit`.

This is because `XcmExecuteController::execute` takes a `max_weight`
argument, and since we don't want the user to specify it manually we
were passing everything left by pre-charghing
`ctx.ext.gas_meter().gas_left()`

- To fix it I added a `fn influence_lowest_limit` on the `Token` trait
and make it return false for `RuntimeCost::XcmExecute`.
- Got rid of the `RuntimeToken` indirection, we can just use
`RuntimeCost` directly.

---------

Co-authored-by: command-bot <>

polkadot/xcm/pallet-xcm/src/lib.rs

@@ -29,7 +29,7 @@ pub mod migration;
 
 use codec::{Decode, Encode, EncodeLike, MaxEncodedLen};
 use frame_support::{
-	dispatch::GetDispatchInfo,
+	dispatch::{DispatchErrorWithPostInfo, GetDispatchInfo, WithPostDispatchInfo},
 	pallet_prelude::*,
 	traits::{
 		Contains, ContainsPair, Currency, Defensive, EnsureOrigin, Get, LockableCurrency,
@@ -291,22 +291,38 @@ pub mod pallet {
 			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 mut 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::prepare_and_execute(
-				origin_location,
-				message,
-				&mut hash,
-				max_weight,
-				max_weight,
-			);
+		) -> Result<Weight, DispatchErrorWithPostInfo> {
+			log::trace!(target: "xcm::pallet_xcm::execute", "message {:?}, max_weight {:?}", message, max_weight);
+			let outcome = (|| {
+				let origin_location = T::ExecuteXcmOrigin::ensure_origin(origin)?;
+				let mut 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;
+				Ok(T::XcmExecutor::prepare_and_execute(
+					origin_location,
+					message,
+					&mut hash,
+					max_weight,
+					max_weight,
+				))
+			})()
+			.map_err(|e: DispatchError| {
+				e.with_weight(<Self::WeightInfo as ExecuteControllerWeightInfo>::execute())
+			})?;
+
 			Self::deposit_event(Event::Attempted { outcome: outcome.clone() });
-			Ok(outcome)
+			let weight_used = outcome.weight_used();
+			outcome.ensure_complete().map_err(|error| {
+				log::error!(target: "xcm::pallet_xcm::execute", "XCM execution failed with error {:?}", error);
+				Error::<T>::LocalExecutionIncomplete.with_weight(
+					weight_used.saturating_add(
+						<Self::WeightInfo as ExecuteControllerWeightInfo>::execute(),
+					),
+				)
+			})?;
+			Ok(weight_used)
 		}
 	}
 
@@ -1009,23 +1025,15 @@ pub mod pallet {
 		/// No more than `max_weight` will be used in its attempted execution. If this is less than
 		/// the maximum amount of weight that the message could take to be executed, then no
 		/// execution attempt will be made.
-		///
-		/// NOTE: A successful return to this does *not* imply that the `msg` 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 {
-			log::trace!(target: "xcm::pallet_xcm::execute", "message {:?}, max_weight {:?}", message, max_weight);
-			let outcome = <Self as ExecuteController<_, _>>::execute(origin, message, max_weight)?;
-			let weight_used = outcome.weight_used();
-			outcome.ensure_complete().map_err(|error| {
-				log::error!(target: "xcm::pallet_xcm::execute", "XCM execution failed with error {:?}", error);
-				Error::<T>::LocalExecutionIncomplete
-			})?;
+			let weight_used =
+				<Self as ExecuteController<_, _>>::execute(origin, message, max_weight)?;
 			Ok(Some(weight_used.saturating_add(T::WeightInfo::execute())).into())
 		}
 

polkadot/xcm/pallet-xcm/src/tests/mod.rs

@@ -20,11 +20,12 @@ pub(crate) mod assets_transfer;
 
 use crate::{
 	mock::*, pallet::SupportedVersion, AssetTraps, Config, CurrentMigration, Error,
-	LatestVersionedLocation, Pallet, Queries, QueryStatus, VersionDiscoveryQueue,
-	VersionMigrationStage, VersionNotifiers, VersionNotifyTargets, WeightInfo,
+	ExecuteControllerWeightInfo, LatestVersionedLocation, Pallet, Queries, QueryStatus,
+	VersionDiscoveryQueue, VersionMigrationStage, VersionNotifiers, VersionNotifyTargets,
+	WeightInfo,
 };
 use frame_support::{
-	assert_noop, assert_ok,
+	assert_err_ignore_postinfo, assert_noop, assert_ok,
 	traits::{Currency, Hooks},
 	weights::Weight,
 };
@@ -450,19 +451,19 @@ fn trapped_assets_can_be_claimed() {
 		assert_eq!(Balances::total_balance(&BOB), INITIAL_BALANCE + SEND_AMOUNT);
 		assert_eq!(AssetTraps::<Test>::iter().collect::<Vec<_>>(), vec![]);
 
-		let weight = BaseXcmWeight::get() * 3;
-		assert_ok!(<XcmPallet as xcm_builder::ExecuteController<_, _>>::execute(
-			RuntimeOrigin::signed(ALICE),
-			Box::new(VersionedXcm::from(Xcm(vec![
-				ClaimAsset { assets: (Here, SEND_AMOUNT).into(), ticket: Here.into() },
-				buy_execution((Here, SEND_AMOUNT)),
-				DepositAsset { assets: AllCounted(1).into(), beneficiary: dest },
-			]))),
-			weight
-		));
-		let outcome =
-			Outcome::Incomplete { used: BaseXcmWeight::get(), error: XcmError::UnknownClaim };
-		assert_eq!(last_event(), RuntimeEvent::XcmPallet(crate::Event::Attempted { outcome }));
+		// Can't claim twice.
+		assert_err_ignore_postinfo!(
+			XcmPallet::execute(
+				RuntimeOrigin::signed(ALICE),
+				Box::new(VersionedXcm::from(Xcm(vec![
+					ClaimAsset { assets: (Here, SEND_AMOUNT).into(), ticket: Here.into() },
+					buy_execution((Here, SEND_AMOUNT)),
+					DepositAsset { assets: AllCounted(1).into(), beneficiary: dest },
+				]))),
+				weight
+			),
+			Error::<Test>::LocalExecutionIncomplete
+		);
 	});
 }
 
@@ -495,11 +496,14 @@ fn incomplete_execute_reverts_side_effects() {
 		// all effects are reverted and balances unchanged for either sender or receiver
 		assert_eq!(Balances::total_balance(&ALICE), INITIAL_BALANCE);
 		assert_eq!(Balances::total_balance(&BOB), INITIAL_BALANCE);
+
 		assert_eq!(
 			result,
 			Err(sp_runtime::DispatchErrorWithPostInfo {
 				post_info: frame_support::dispatch::PostDispatchInfo {
-					actual_weight: None,
+					actual_weight: Some(
+						<Pallet<Test> as ExecuteControllerWeightInfo>::execute() + weight
+					),
 					pays_fee: frame_support::dispatch::Pays::Yes,
 				},
 				error: sp_runtime::DispatchError::Module(sp_runtime::ModuleError {

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

@@ -18,7 +18,10 @@
 //! Controller traits defined in this module are high-level traits that will rely on other traits
 //! from `xcm-executor` to perform their tasks.
 
-use frame_support::pallet_prelude::DispatchError;
+use frame_support::{
+	dispatch::{DispatchErrorWithPostInfo, WithPostDispatchInfo},
+	pallet_prelude::DispatchError,
+};
 use sp_std::boxed::Box;
 use xcm::prelude::*;
 pub use xcm_executor::traits::QueryHandler;
@@ -52,7 +55,8 @@ pub trait ExecuteController<Origin, RuntimeCall> {
 	/// Weight information for ExecuteController functions.
 	type WeightInfo: ExecuteControllerWeightInfo;
 
-	/// Attempt to execute an XCM locally, and return the outcome.
+	/// Attempt to execute an XCM locally, returns Ok with the weight consumed if the execution
+	/// complete successfully, Err otherwise.
 	///
 	/// # Parameters
 	///
@@ -63,7 +67,7 @@ pub trait ExecuteController<Origin, RuntimeCall> {
 		origin: Origin,
 		message: Box<VersionedXcm<RuntimeCall>>,
 		max_weight: Weight,
-	) -> Result<Outcome, DispatchError>;
+	) -> Result<Weight, DispatchErrorWithPostInfo>;
 }
 
 /// Weight functions needed for [`SendController`].
@@ -137,8 +141,9 @@ impl<Origin, RuntimeCall> ExecuteController<Origin, RuntimeCall> for () {
 		_origin: Origin,
 		_message: Box<VersionedXcm<RuntimeCall>>,
 		_max_weight: Weight,
-	) -> Result<Outcome, DispatchError> {
-		Ok(Outcome::Error { error: XcmError::Unimplemented })
+	) -> Result<Weight, DispatchErrorWithPostInfo> {
+		Err(DispatchError::Other("ExecuteController::execute not implemented")
+			.with_weight(Weight::zero()))
 	}
 }
 

substrate/frame/contracts/fixtures/contracts/xcm_execute.rs

@@ -30,10 +30,11 @@ pub extern "C" fn deploy() {}
 pub extern "C" fn call() {
 	input!(512, msg: [u8],);
 
-	let mut outcome = [0u8; 512];
-	let outcome = &mut &mut outcome[..];
-
 	#[allow(deprecated)]
-	api::xcm_execute(msg, outcome).unwrap();
-	api::return_value(uapi::ReturnFlags::empty(), outcome);
+	let err_code = match api::xcm_execute(msg) {
+		Ok(_) => 0u32,
+		Err(code) => code as u32,
+	};
+
+	api::return_value(uapi::ReturnFlags::empty(), &err_code.to_le_bytes());
 }

substrate/frame/contracts/mock-network/src/lib.rs

@@ -26,7 +26,8 @@ use crate::primitives::{AccountId, UNITS};
 use sp_runtime::BuildStorage;
 use xcm::latest::prelude::*;
 use xcm_executor::traits::ConvertLocation;
-use xcm_simulator::{decl_test_network, decl_test_parachain, decl_test_relay_chain, TestExt};
+pub use xcm_simulator::TestExt;
+use xcm_simulator::{decl_test_network, decl_test_parachain, decl_test_relay_chain};
 
 // Accounts
 pub const ADMIN: sp_runtime::AccountId32 = sp_runtime::AccountId32::new([0u8; 32]);

substrate/frame/contracts/mock-network/src/tests.rs

@@ -21,7 +21,6 @@ use crate::{
 	primitives::{AccountId, CENTS},
 	relay_chain, MockNet, ParaA, ParachainBalances, Relay, ALICE, BOB, INITIAL_BALANCE,
 };
-use assert_matches::assert_matches;
 use codec::{Decode, Encode};
 use frame_support::{
 	assert_err,
@@ -31,11 +30,18 @@ use frame_support::{
 use pallet_balances::{BalanceLock, Reasons};
 use pallet_contracts::{Code, CollectEvents, DebugInfo, Determinism};
 use pallet_contracts_fixtures::compile_module;
+use pallet_contracts_uapi::ReturnErrorCode;
 use xcm::{v4::prelude::*, VersionedLocation, VersionedXcm};
 use xcm_simulator::TestExt;
 
 type ParachainContracts = pallet_contracts::Pallet<parachain::Runtime>;
 
+macro_rules! assert_return_code {
+	( $x:expr , $y:expr $(,)? ) => {{
+		assert_eq!(u32::from_le_bytes($x.data[..].try_into().unwrap()), $y as u32);
+	}};
+}
+
 /// Instantiate the tests contract, and fund it with some balance and assets.
 fn instantiate_test_contract(name: &str) -> AccountId {
 	let (wasm, _) = compile_module::<Runtime>(name).unwrap();
@@ -100,19 +106,57 @@ fn test_xcm_execute() {
 			DebugInfo::UnsafeDebug,
 			CollectEvents::UnsafeCollect,
 			Determinism::Enforced,
-		)
-		.result
-		.unwrap();
+		);
 
-		let mut data = &result.data[..];
-		let outcome = Outcome::decode(&mut data).expect("Failed to decode xcm_execute Outcome");
-		assert_matches!(outcome, Outcome::Complete { .. });
+		assert_eq!(result.gas_consumed, result.gas_required);
+		assert_return_code!(&result.result.unwrap(), ReturnErrorCode::Success);
 
 		// Check if the funds are subtracted from the account of Alice and added to the account of
 		// Bob.
 		let initial = INITIAL_BALANCE;
-		assert_eq!(parachain::Assets::balance(0, contract_addr), initial);
 		assert_eq!(ParachainBalances::free_balance(BOB), initial + amount);
+		assert_eq!(ParachainBalances::free_balance(&contract_addr), initial - amount);
+	});
+}
+
+#[test]
+fn test_xcm_execute_incomplete() {
+	MockNet::reset();
+
+	let contract_addr = instantiate_test_contract("xcm_execute");
+	let amount = 10 * CENTS;
+
+	// Execute XCM instructions through the contract.
+	ParaA::execute_with(|| {
+		// The XCM used to transfer funds to Bob.
+		let message: Xcm<()> = Xcm(vec![
+			WithdrawAsset(vec![(Here, amount).into()].into()),
+			// This will fail as the contract does not have enough balance to complete both
+			// withdrawals.
+			WithdrawAsset(vec![(Here, INITIAL_BALANCE).into()].into()),
+			DepositAsset {
+				assets: All.into(),
+				beneficiary: AccountId32 { network: None, id: BOB.clone().into() }.into(),
+			},
+		]);
+
+		let result = ParachainContracts::bare_call(
+			ALICE,
+			contract_addr.clone(),
+			0,
+			Weight::MAX,
+			None,
+			VersionedXcm::V4(message).encode(),
+			DebugInfo::UnsafeDebug,
+			CollectEvents::UnsafeCollect,
+			Determinism::Enforced,
+		);
+
+		assert_eq!(result.gas_consumed, result.gas_required);
+		assert_return_code!(&result.result.unwrap(), ReturnErrorCode::XcmExecutionFailed);
+
+		assert_eq!(ParachainBalances::free_balance(BOB), INITIAL_BALANCE);
+		assert_eq!(ParachainBalances::free_balance(&contract_addr), INITIAL_BALANCE - amount);
 	});
 }
 
@@ -182,17 +226,10 @@ fn test_xcm_execute_reentrant_call() {
 			DebugInfo::UnsafeDebug,
 			CollectEvents::UnsafeCollect,
 			Determinism::Enforced,
-		)
-		.result
-		.unwrap();
-
-		let mut data = &result.data[..];
-		let outcome = Outcome::decode(&mut data).expect("Failed to decode xcm_execute Outcome");
-		assert_matches!(
-			outcome,
-			Outcome::Incomplete { used: _, error: XcmError::ExpectationFalse }
 		);
 
+		assert_return_code!(&result.result.unwrap(), ReturnErrorCode::XcmExecutionFailed);
+
 		// Funds should not change hands as the XCM transact failed.
 		assert_eq!(ParachainBalances::free_balance(BOB), INITIAL_BALANCE);
 	});

substrate/frame/contracts/src/exec.rs

@@ -287,6 +287,9 @@ pub trait Ext: sealing::Sealed {
 	/// Returns `true` if debug message recording is enabled. Otherwise `false` is returned.
 	fn append_debug_buffer(&mut self, msg: &str) -> bool;
 
+	/// Returns `true` if debug message recording is enabled. Otherwise `false` is returned.
+	fn debug_buffer_enabled(&self) -> bool;
+
 	/// Call some dispatchable and return the result.
 	fn call_runtime(&self, call: <Self::T as Config>::RuntimeCall) -> DispatchResultWithPostInfo;
 
@@ -1429,6 +1432,10 @@ where
 		self.top_frame_mut().nested_storage.charge(diff)
 	}
 
+	fn debug_buffer_enabled(&self) -> bool {
+		self.debug_message.is_some()
+	}
+
 	fn append_debug_buffer(&mut self, msg: &str) -> bool {
 		if let Some(buffer) = &mut self.debug_message {
 			buffer

substrate/frame/contracts/src/gas.rs

@@ -63,6 +63,11 @@ pub trait Token<T: Config>: Copy + Clone + TestAuxiliaries {
 	/// while calculating the amount. In this case it is ok to use saturating operations
 	/// since on overflow they will return `max_value` which should consume all gas.
 	fn weight(&self) -> Weight;
+
+	/// Returns true if this token is expected to influence the lowest gas limit.
+	fn influence_lowest_gas_limit(&self) -> bool {
+		true
+	}
 }
 
 /// A wrapper around a type-erased trait object of what used to be a `Token`.
@@ -160,7 +165,9 @@ impl<T: Config> GasMeter<T> {
 	/// This is when a maximum a priori amount was charged and then should be partially
 	/// refunded to match the actual amount.
 	pub fn adjust_gas<Tok: Token<T>>(&mut self, charged_amount: ChargedAmount, token: Tok) {
-		self.gas_left_lowest = self.gas_left_lowest();
+		if token.influence_lowest_gas_limit() {
+			self.gas_left_lowest = self.gas_left_lowest();
+		}
 		let adjustment = charged_amount.0.saturating_sub(token.weight());
 		self.gas_left = self.gas_left.saturating_add(adjustment).min(self.gas_limit);
 	}

substrate/frame/contracts/src/wasm/mod.rs

@@ -687,6 +687,10 @@ mod tests {
 			&mut self.gas_meter
 		}
 		fn charge_storage(&mut self, _diff: &crate::storage::meter::Diff) {}
+
+		fn debug_buffer_enabled(&self) -> bool {
+			true
+		}
 		fn append_debug_buffer(&mut self, msg: &str) -> bool {
 			self.debug_buffer.extend(msg.as_bytes());
 			true