Contracts: xcm host fn fixes (paritytech#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
paritytech#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 <>

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

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

@@ -21,7 +21,6 @@ use crate::{
 	exec::{ExecError, ExecResult, Ext, Key, TopicOf},
 	gas::{ChargedAmount, Token},
 	primitives::ExecReturnValue,
-	schedule::HostFnWeights,
 	BalanceOf, CodeHash, Config, DebugBufferVec, Error, SENTINEL,
 };
 use codec::{Decode, DecodeLimit, Encode, MaxEncodedLen};
@@ -235,6 +234,8 @@ pub enum RuntimeCosts {
 	ChainExtension(Weight),
 	/// Weight charged for calling into the runtime.
 	CallRuntime(Weight),
+	/// Weight charged for calling xcm_execute.
+	CallXcmExecute(Weight),
 	/// Weight of calling `seal_set_code_hash`
 	SetCodeHash,
 	/// Weight of calling `ecdsa_to_eth_address`
@@ -251,10 +252,18 @@ pub enum RuntimeCosts {
 	RemoveDelegateDependency,
 }
 
-impl RuntimeCosts {
-	fn token<T: Config>(&self, s: &HostFnWeights<T>) -> RuntimeToken {
+impl<T: Config> Token<T> for RuntimeCosts {
+	fn influence_lowest_gas_limit(&self) -> bool {
+		match self {
+			&Self::CallXcmExecute(_) => false,
+			_ => true,
+		}
+	}
+
+	fn weight(&self) -> Weight {
+		let s = T::Schedule::get().host_fn_weights;
 		use self::RuntimeCosts::*;
-		let weight = match *self {
+		match *self {
 			CopyFromContract(len) => s.return_per_byte.saturating_mul(len.into()),
 			CopyToContract(len) => s.input_per_byte.saturating_mul(len.into()),
 			Caller => s.caller,
@@ -323,20 +332,14 @@ impl RuntimeCosts {
 			Sr25519Verify(len) => s
 				.sr25519_verify
 				.saturating_add(s.sr25519_verify_per_byte.saturating_mul(len.into())),
-			ChainExtension(weight) => weight,
-			CallRuntime(weight) => weight,
+			ChainExtension(weight) | CallRuntime(weight) | CallXcmExecute(weight) => weight,
 			SetCodeHash => s.set_code_hash,
 			EcdsaToEthAddress => s.ecdsa_to_eth_address,
 			ReentrantCount => s.reentrance_count,
 			AccountEntranceCount => s.account_reentrance_count,
 			InstantationNonce => s.instantiation_nonce,
 			AddDelegateDependency => s.add_delegate_dependency,
 			RemoveDelegateDependency => s.remove_delegate_dependency,
-		};
-		RuntimeToken {
-			#[cfg(test)]
-			_created_from: *self,
-			weight,
 		}
 	}
 }
@@ -347,25 +350,10 @@ impl RuntimeCosts {
 /// a function won't work out.
 macro_rules! charge_gas {
 	($runtime:expr, $costs:expr) => {{
-		let token = $costs.token(&$runtime.ext.schedule().host_fn_weights);
-		$runtime.ext.gas_meter_mut().charge(token)
+		$runtime.ext.gas_meter_mut().charge($costs)
 	}};
 }
 
-#[cfg_attr(test, derive(Debug, PartialEq, Eq))]
-#[derive(Copy, Clone)]
-struct RuntimeToken {
-	#[cfg(test)]
-	_created_from: RuntimeCosts,
-	weight: Weight,
-}
-
-impl<T: Config> Token<T> for RuntimeToken {
-	fn weight(&self) -> Weight {
-		self.weight
-	}
-}
-
 /// The kind of call that should be performed.
 enum CallType {
 	/// Execute another instantiated contract
@@ -506,28 +494,25 @@ impl<'a, E: Ext + 'a> Runtime<'a, E> {
 	/// 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(&mut self, charged: ChargedAmount, actual_costs: RuntimeCosts) {
-		let token = actual_costs.token(&self.ext.schedule().host_fn_weights);
-		self.ext.gas_meter_mut().adjust_gas(charged, token);
+		self.ext.gas_meter_mut().adjust_gas(charged, actual_costs);
 	}
 
 	/// Charge, Run and adjust gas, for executing the given dispatchable.
-	fn call_dispatchable<
-		ErrorReturnCode: Get<ReturnErrorCode>,
-		F: FnOnce(&mut Self) -> DispatchResultWithPostInfo,
-	>(
+	fn call_dispatchable<ErrorReturnCode: Get<ReturnErrorCode>>(
 		&mut self,
 		dispatch_info: DispatchInfo,
-		run: F,
+		runtime_cost: impl Fn(Weight) -> RuntimeCosts,
+		run: impl FnOnce(&mut Self) -> DispatchResultWithPostInfo,
 	) -> Result<ReturnErrorCode, TrapReason> {
 		use frame_support::dispatch::extract_actual_weight;
-		let charged = self.charge_gas(RuntimeCosts::CallRuntime(dispatch_info.weight))?;
+		let charged = self.charge_gas(runtime_cost(dispatch_info.weight))?;
 		let result = run(self);
 		let actual_weight = extract_actual_weight(&result, &dispatch_info);
-		self.adjust_gas(charged, RuntimeCosts::CallRuntime(actual_weight));
+		self.adjust_gas(charged, runtime_cost(actual_weight));
 		match result {
 			Ok(_) => Ok(ReturnErrorCode::Success),
 			Err(e) => {
-				if self.ext.append_debug_buffer("") {
+				if self.ext.debug_buffer_enabled() {
 					self.ext.append_debug_buffer("call failed with: ");
 					self.ext.append_debug_buffer(e.into());
 				};
@@ -2113,9 +2098,11 @@ pub mod env {
 		ctx.charge_gas(RuntimeCosts::CopyFromContract(call_len))?;
 		let call: <E::T as Config>::RuntimeCall =
 			ctx.read_sandbox_memory_as_unbounded(memory, call_ptr, call_len)?;
-		ctx.call_dispatchable::<CallRuntimeFailed, _>(call.get_dispatch_info(), |ctx| {
-			ctx.ext.call_runtime(call)
-		})
+		ctx.call_dispatchable::<CallRuntimeFailed>(
+			call.get_dispatch_info(),
+			RuntimeCosts::CallRuntime,
+			|ctx| ctx.ext.call_runtime(call),
+		)
 	}
 
 	/// Execute an XCM program locally, using the contract's address as the origin.
@@ -2126,7 +2113,6 @@ pub mod env {
 		memory: _,
 		msg_ptr: u32,
 		msg_len: u32,
-		output_ptr: u32,
 	) -> Result<ReturnErrorCode, TrapReason> {
 		use frame_support::dispatch::DispatchInfo;
 		use xcm::VersionedXcm;
@@ -2135,26 +2121,27 @@ pub mod env {
 		ctx.charge_gas(RuntimeCosts::CopyFromContract(msg_len))?;
 		let message: VersionedXcm<CallOf<E::T>> =
 			ctx.read_sandbox_memory_as_unbounded(memory, msg_ptr, msg_len)?;
+		ensure_executable::<E::T>(&message)?;
 
 		let execute_weight =
 			<<E::T as Config>::Xcm as ExecuteController<_, _>>::WeightInfo::execute();
 		let weight = ctx.ext.gas_meter().gas_left().max(execute_weight);
 		let dispatch_info = DispatchInfo { weight, ..Default::default() };
 
-		ensure_executable::<E::T>(&message)?;
-		ctx.call_dispatchable::<XcmExecutionFailed, _>(dispatch_info, |ctx| {
-			let origin = crate::RawOrigin::Signed(ctx.ext.address().clone()).into();
-			let outcome = <<E::T as Config>::Xcm>::execute(
-				origin,
-				Box::new(message),
-				weight.saturating_sub(execute_weight),
-			)?;
+		ctx.call_dispatchable::<XcmExecutionFailed>(
+			dispatch_info,
+			RuntimeCosts::CallXcmExecute,
+			|ctx| {
+				let origin = crate::RawOrigin::Signed(ctx.ext.address().clone()).into();
+				let weight_used = <<E::T as Config>::Xcm>::execute(
+					origin,
+					Box::new(message),
+					weight.saturating_sub(execute_weight),
+				)?;
 
-			ctx.write_sandbox_memory(memory, output_ptr, &outcome.encode())?;
-			let pre_dispatch_weight =
-				<<E::T as Config>::Xcm as ExecuteController<_, _>>::WeightInfo::execute();
-			Ok(Some(outcome.weight_used().saturating_add(pre_dispatch_weight)).into())
-		})
+				Ok(Some(weight_used.saturating_add(execute_weight)).into())
+			},
+		)
 	}
 
 	/// Send an XCM program from the contract to the specified destination.

substrate/frame/contracts/uapi/src/host.rs

@@ -792,7 +792,7 @@ pub trait HostFn {
 	#[deprecated(
 		note = "Unstable function. Behaviour can change without further notice. Use only for testing."
 	)]
-	fn xcm_execute(msg: &[u8], output: &mut &mut [u8]) -> Result;
+	fn xcm_execute(msg: &[u8]) -> Result;
 
 	/// Send an XCM program from the contract to the specified destination.
 	/// This is equivalent to dispatching `pallet_xcm::send` through `call_runtime`, except that
@@ -804,7 +804,6 @@ pub trait HostFn {
 	///   traps otherwise.
 	/// - `msg`: The message, should be decodable as a [VersionedXcm](https://paritytech.github.io/polkadot-sdk/master/staging_xcm/enum.VersionedXcm.html),
 	///   traps otherwise.
-	/// - `output`: A reference to the output data buffer to write the [XcmHash](https://paritytech.github.io/polkadot-sdk/master/staging_xcm/v3/type.XcmHash.html)
 	///
 	/// # Return
 	///