Add XCM Origin and converter (#2896)

* Add XCM Origin and converter

* IsMajority filter can be location-prefixed

* Update xcm/pallet-xcm/src/lib.rs

Co-authored-by: Alexander Popiak <alexander.popiak@parity.io>

* Update xcm/src/v0/multi_location.rs

Co-authored-by: Alexander Popiak <alexander.popiak@parity.io>

* Introduce UsingComponents to allow reuse of fee payment in XCM

* Use Drop rather than finalize

* Add errors for weight.

* Apply suggestions from code review

Co-authored-by: Alexander Popiak <alexander.popiak@parity.io>

* Fixes

* Update xcm/xcm-builder/src/weight.rs

Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com>

* Various XCM fixes and improvements

* Fixes

* Update xcm/xcm-builder/src/weight.rs

Co-authored-by: Alexander Popiak <alexander.popiak@parity.io>

* Update xcm/xcm-builder/src/weight.rs

Co-authored-by: Alexander Popiak <alexander.popiak@parity.io>

* Update xcm/xcm-builder/src/weight.rs

Co-authored-by: Alexander Popiak <alexander.popiak@parity.io>

* Fixes

Co-authored-by: Alexander Popiak <alexander.popiak@parity.io>
Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com>

polkadot/runtime/rococo/src/lib.rs

@@ -92,7 +92,7 @@ use xcm_builder::{
 	AccountId32Aliases, ChildParachainConvertsVia, SovereignSignedViaLocation,
 	CurrencyAdapter as XcmCurrencyAdapter, ChildParachainAsNative, SignedAccountId32AsNative,
 	ChildSystemParachainAsSuperuser, LocationInverter, IsConcrete, FixedWeightBounds,
-	FixedRateOfConcreteFungible, BackingToPlurality, SignedToAccountId32
+	BackingToPlurality, SignedToAccountId32, UsingComponents,
 };
 use constants::{time::*, currency::*, fee::*, size::*};
 use frame_support::traits::InstanceFilter;
@@ -110,7 +110,7 @@ pub const VERSION: RuntimeVersion = RuntimeVersion {
 	spec_name: create_runtime_str!("rococo"),
 	impl_name: create_runtime_str!("parity-rococo-v1.5"),
 	authoring_version: 0,
-	spec_version: 231,
+	spec_version: 232,
 	impl_version: 0,
 	#[cfg(not(feature = "disable-runtime-api"))]
 	apis: RUNTIME_API_VERSIONS,
@@ -646,7 +646,7 @@ impl xcm_executor::Config for XcmConfig {
 	type LocationInverter = LocationInverter<Ancestry>;
 	type Barrier = Barrier;
 	type Weigher = FixedWeightBounds<BaseXcmWeight, Call>;
-	type Trader = FixedRateOfConcreteFungible<RocFee>;
+	type Trader = UsingComponents<WeightToFee, RocLocation, AccountId, Balances, ToAuthor<Runtime>>;
 	type ResponseHandler = ();
 }
 
@@ -657,7 +657,8 @@ parameter_types! {
 /// Type to convert an `Origin` type value into a `MultiLocation` value which represents an interior location
 /// of this chain.
 pub type LocalOriginToLocation = (
-	// We allow an origin from the Collective pallet to be used in XCM as a corresponding Plurality
+	// We allow an origin from the Collective pallet to be used in XCM as a corresponding Plurality of the
+	// `Unit` body.
 	BackingToPlurality<Origin, pallet_collective::Origin<Runtime>, CollectiveBodyId>,
 	// And a usual Signed origin to be used in XCM as a corresponding AccountId32
 	SignedToAccountId32<Origin, AccountId, RococoNetwork>,
@@ -881,8 +882,8 @@ impl pallet_collective::Config for Runtime {
 	type Event = Event;
 	type MotionDuration = MotionDuration;
 	type MaxProposals = MaxProposals;
-	type MaxMembers = MaxMembers;
 	type DefaultVote = pallet_collective::PrimeDefaultVote;
+	type MaxMembers = MaxMembers;
 	type WeightInfo = ();
 }
 

polkadot/xcm/pallet-xcm/Cargo.toml

@@ -14,6 +14,7 @@ frame-support = { git = "https://github.com/paritytech/substrate", default-featu
 frame-system = { git = "https://github.com/paritytech/substrate", default-features = false, branch = "master" }
 
 xcm = { path = "..", default-features = false }
+xcm-executor = { path = "../xcm-executor", default-features = false }
 
 [features]
 default = ["std"]

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

@@ -20,7 +20,8 @@
 
 use sp_std::{marker::PhantomData, convert::TryInto, boxed::Box};
 use codec::{Encode, Decode};
-use xcm::v0::{BodyId, MultiLocation::{self, X1}, Junction::Plurality};
+use xcm::v0::{BodyId, OriginKind, MultiLocation, Junction::Plurality};
+use xcm_executor::traits::ConvertOrigin;
 use sp_runtime::{RuntimeDebug, traits::BadOrigin};
 use frame_support::traits::{EnsureOrigin, OriginTrait, Filter, Get};
 
@@ -62,6 +63,7 @@ pub mod pallet {
 	#[pallet::generate_deposit(pub(super) fn deposit_event)]
 	pub enum Event<T: Config> {
 		Attempted(xcm::v0::Outcome),
+		Sent(MultiLocation, MultiLocation, Xcm<()>),
 	}
 
 	#[pallet::error]
@@ -78,11 +80,12 @@ pub mod pallet {
 		#[pallet::weight(1_000)]
 		fn send(origin: OriginFor<T>, dest: MultiLocation, message: Xcm<()>) -> DispatchResult {
 			let origin_location = T::SendXcmOrigin::ensure_origin(origin)?;
-			Self::send_xcm(origin_location, dest, message)
+			Self::send_xcm(origin_location.clone(), dest.clone(), message.clone())
 				.map_err(|e| match e {
 					XcmError::CannotReachDestination(..) => Error::<T>::Unreachable,
 					_ => Error::<T>::SendFailure,
 				})?;
+			Self::deposit_event(Event::Sent(origin_location, dest, message));
 			Ok(())
 		}
 
@@ -149,10 +152,11 @@ pub fn ensure_xcm<OuterOrigin>(o: OuterOrigin) -> Result<MultiLocation, BadOrigi
 /// plurality.
 ///
 /// May reasonably be used with `EnsureXcm`.
-pub struct IsMajorityOfBody<Body>(PhantomData<Body>);
-impl<Body: Get<BodyId>> Filter<MultiLocation> for IsMajorityOfBody<Body> {
+pub struct IsMajorityOfBody<Prefix, Body>(PhantomData<(Prefix, Body)>);
+impl<Prefix: Get<MultiLocation>, Body: Get<BodyId>> Filter<MultiLocation> for IsMajorityOfBody<Prefix, Body> {
 	fn filter(l: &MultiLocation) -> bool {
-		matches!(l, X1(Plurality { id, part }) if id == &Body::get() && part.is_majority())
+		let maybe_suffix = l.match_and_split(&Prefix::get());
+		matches!(maybe_suffix, Some(Plurality { id, part }) if id == &Body::get() && part.is_majority())
 	}
 }
 
@@ -180,3 +184,17 @@ impl<O: OriginTrait + From<Origin>, F: Filter<MultiLocation>> EnsureOrigin<O> fo
 		O::from(Origin::Xcm(MultiLocation::Null))
 	}
 }
+
+/// A simple passthrough where we reuse the `MultiLocation`-typed XCM origin as the inner value of
+/// this crate's `Origin::Xcm` value.
+pub struct XcmPassthrough<Origin>(PhantomData<Origin>);
+impl<
+	Origin: From<crate::Origin>,
+> ConvertOrigin<Origin> for XcmPassthrough<Origin> {
+	fn convert_origin(origin: MultiLocation, kind: OriginKind) -> Result<Origin, MultiLocation> {
+		match (kind, origin) {
+			(OriginKind::Xcm, l) => Ok(crate::Origin::Xcm(l).into()),
+			(_, origin) => Err(origin),
+		}
+	}
+}

polkadot/xcm/src/v0/mod.rs

@@ -39,8 +39,10 @@ pub use traits::{Error, Result, SendXcm, ExecuteXcm, Outcome};
 /// Basically just the XCM (more general) version of `ParachainDispatchOrigin`.
 #[derive(Copy, Clone, Eq, PartialEq, Encode, Decode, Debug)]
 pub enum OriginKind {
-	/// Origin should just be the native origin for the sender. For Cumulus/Frame chains this is
-	/// the `Parachain` origin.
+	/// Origin should just be the native dispatch origin representation for the sender in the
+	/// local runtime framework. For Cumulus/Frame chains this is the `Parachain` or `Relay` origin
+	/// if coming from a chain, though there may be others if the `MultiLocation` XCM origin has a
+	/// primary/native dispatch origin form.
 	Native,
 
 	/// Origin should just be the standard account-based origin with the sovereign account of
@@ -50,6 +52,11 @@ pub enum OriginKind {
 	/// Origin should be the super-user. For Cumulus/Frame chains, this is the `Root` origin.
 	/// This will not usually be an available option.
 	Superuser,
+
+	/// Origin should be interpreted as an XCM native origin and the `MultiLocation` should be
+	/// encoded directly in the dispatch origin unchanged. For Cumulus/Frame chains, this will be
+	/// the `pallet_xcm::Origin::Xcm` type.
+	Xcm,
 }
 
 /// Response data to a query.

polkadot/xcm/src/v0/multi_location.rs

@@ -442,6 +442,20 @@ impl MultiLocation {
 		MultiLocationReverseIterator(self)
 	}
 
+	/// Ensures that self begins with `prefix` and that it has a single `Junction` item following. If
+	/// so, returns a reference to this `Junction` item.
+	pub fn match_and_split(&self, prefix: &MultiLocation) -> Option<&Junction> {
+		if prefix.len() + 1 != self.len() {
+			return None
+		}
+		for i in 0..prefix.len() {
+			if prefix.at(i) != self.at(i) {
+				return None
+			}
+		}
+		return self.at(prefix.len())
+	}
+
 	/// Mutates `self`, suffixing it with `new`. Returns `Err` in case of overflow.
 	pub fn push(&mut self, new: Junction) -> result::Result<(), ()> {
 		let mut n = MultiLocation::Null;

polkadot/xcm/src/v0/traits.rs

@@ -72,6 +72,8 @@ pub enum Error {
 	NotWithdrawable,
 	/// Indicates that the consensus system cannot deposit an asset under the ownership of a particular location.
 	LocationCannotHold,
+	/// The assets given to purchase weight is are insufficient for the weight desired.
+	TooExpensive,
 }
 
 impl From<()> for Error {

polkadot/xcm/xcm-builder/Cargo.toml

@@ -16,6 +16,7 @@ sp-io = { git = "https://github.com/paritytech/substrate", branch = "master", de
 sp-runtime = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 frame-support = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 frame-system = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
+pallet-transaction-payment = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 
 # Polkadot dependencies
 polkadot-parachain = { path = "../../parachain", default-features = false }
@@ -33,4 +34,5 @@ std = [
 	"sp-runtime/std",
 	"frame-support/std",
 	"polkadot-parachain/std",
+	"pallet-transaction-payment/std",
 ]

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

@@ -46,7 +46,7 @@ mod fungibles_adapter;
 pub use fungibles_adapter::FungiblesAdapter;
 
 mod weight;
-pub use weight::{FixedRateOfConcreteFungible, FixedWeightBounds};
+pub use weight::{FixedRateOfConcreteFungible, FixedWeightBounds, UsingComponents};
 
 mod matches_fungible;
 pub use matches_fungible::{IsAbstract, IsConcrete};

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

@@ -272,6 +272,6 @@ impl Config for TestConfig {
 	type LocationInverter = LocationInverter<TestAncestry>;
 	type Barrier = TestBarrier;
 	type Weigher = FixedWeightBounds<UnitWeightCost, TestCall>;
-	type Trader = FixedRateOfConcreteFungible<WeightPrice>;
+	type Trader = FixedRateOfConcreteFungible<WeightPrice, ()>;
 	type ResponseHandler = TestResponseHandler;
 }

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

@@ -14,19 +14,22 @@
 // You should have received a copy of the GNU General Public License
 // along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.
 
-use sp_std::{result::Result, marker::PhantomData};
+use sp_std::{result::Result, marker::PhantomData, convert::TryInto};
 use parity_scale_codec::Decode;
-use xcm::v0::{Xcm, Order, MultiAsset, MultiLocation};
-use frame_support::{traits::Get, weights::{Weight, GetDispatchInfo}};
+use xcm::v0::{Xcm, Order, MultiAsset, MultiLocation, Error};
+use sp_runtime::traits::{Zero, Saturating, SaturatedConversion};
+use frame_support::traits::{Get, OnUnbalanced as OnUnbalancedT, tokens::currency::Currency as CurrencyT};
+use frame_support::weights::{Weight, GetDispatchInfo, WeightToFeePolynomial};
 use xcm_executor::{Assets, traits::{WeightBounds, WeightTrader}};
 
 pub struct FixedWeightBounds<T, C>(PhantomData<(T, C)>);
 impl<T: Get<Weight>, C: Decode + GetDispatchInfo> WeightBounds<C> for FixedWeightBounds<T, C> {
 	fn shallow(message: &mut Xcm<C>) -> Result<Weight, ()> {
-		let min = match message {
+		Ok(match message {
 			Xcm::Transact { call, .. } => {
 				call.ensure_decoded()?.get_dispatch_info().weight + T::get()
 			}
+			Xcm::RelayedFrom { ref mut message, .. } => T::get() + Self::shallow(message.as_mut())?,
 			Xcm::WithdrawAsset { effects, .. }
 			| Xcm::ReserveAssetDeposit { effects, .. }
 			| Xcm::TeleportAsset { effects, .. } => {
@@ -45,16 +48,16 @@ impl<T: Get<Weight>, C: Decode + GetDispatchInfo> WeightBounds<C> for FixedWeigh
 				T::get() + inner
 			}
 			_ => T::get(),
-		};
-		Ok(min)
+		})
 	}
 	fn deep(message: &mut Xcm<C>) -> Result<Weight, ()> {
-		let mut extra = 0;
-		match message {
-			Xcm::Transact { .. } => {}
+		Ok(match message {
+			Xcm::RelayedFrom { ref mut message, .. } => Self::deep(message.as_mut())?,
 			Xcm::WithdrawAsset { effects, .. }
 			| Xcm::ReserveAssetDeposit { effects, .. }
-			| Xcm::TeleportAsset { effects, .. } => {
+			| Xcm::TeleportAsset { effects, .. }
+			=> {
+				let mut extra = 0;
 				for effect in effects.iter_mut() {
 					match effect {
 						Order::BuyExecution { xcm, .. } => {
@@ -65,34 +68,116 @@ impl<T: Get<Weight>, C: Decode + GetDispatchInfo> WeightBounds<C> for FixedWeigh
 						_ => {}
 					}
 				}
-			}
-			_ => {}
-		};
-		Ok(extra)
+				extra
+			},
+			_ => 0,
+		})
 	}
 }
 
+/// Function trait for handling some revenue. Similar to a negative imbalance (credit) handler, but for a
+/// `MultiAsset`. Sensible implementations will deposit the asset in some known treasury or block-author account.
+pub trait TakeRevenue {
+	/// Do something with the given `revenue`, which is a single non-wildcard `MultiAsset`.
+	fn take_revenue(revenue: MultiAsset);
+}
+
+/// Null implementation just burns the revenue.
+impl TakeRevenue for () {
+	fn take_revenue(_revenue: MultiAsset) {}
+}
+
 /// Simple fee calculator that requires payment in a single concrete fungible at a fixed rate.
 ///
 /// The constant `Get` type parameter should be the concrete fungible ID and the amount of it required for
 /// one second of weight.
-pub struct FixedRateOfConcreteFungible<T>(Weight, PhantomData<T>);
-impl<T: Get<(MultiLocation, u128)>> WeightTrader for FixedRateOfConcreteFungible<T> {
-	fn new() -> Self { Self(0, PhantomData) }
-	fn buy_weight(&mut self, weight: Weight, payment: Assets) -> Result<Assets, ()> {
+pub struct FixedRateOfConcreteFungible<
+	T: Get<(MultiLocation, u128)>,
+	R: TakeRevenue,
+>(Weight, u128, PhantomData<(T, R)>);
+impl<T: Get<(MultiLocation, u128)>, R: TakeRevenue> WeightTrader for FixedRateOfConcreteFungible<T, R> {
+	fn new() -> Self { Self(0, 0, PhantomData) }
+
+	fn buy_weight(&mut self, weight: Weight, payment: Assets) -> Result<Assets, Error> {
 		let (id, units_per_second) = T::get();
-		let amount = units_per_second * (weight as u128) / 1_000_000_000_000u128;
+		use frame_support::weights::constants::WEIGHT_PER_SECOND;
+		let amount = units_per_second * (weight as u128) / (WEIGHT_PER_SECOND as u128);
 		let required = MultiAsset::ConcreteFungible { amount, id };
-		let (used, _) = payment.less(required).map_err(|_| ())?;
+		let (unused, _) = payment.less(required).map_err(|_| Error::TooExpensive)?;
 		self.0 = self.0.saturating_add(weight);
-		Ok(used)
+		self.1 = self.1.saturating_add(amount);
+		Ok(unused)
 	}
+
 	fn refund_weight(&mut self, weight: Weight) -> MultiAsset {
-		let weight = weight.min(self.0);
-		self.0 -= weight;
 		let (id, units_per_second) = T::get();
+		let weight = weight.min(self.0);
 		let amount = units_per_second * (weight as u128) / 1_000_000_000_000u128;
+		self.0 -= weight;
+		self.1 = self.1.saturating_sub(amount);
 		let result = MultiAsset::ConcreteFungible { amount, id };
 		result
 	}
 }
+
+impl<T: Get<(MultiLocation, u128)>, R: TakeRevenue> Drop for FixedRateOfConcreteFungible<T, R> {
+	fn drop(&mut self) {
+		let revenue = MultiAsset::ConcreteFungible { amount: self.1, id: T::get().0 };
+		R::take_revenue(revenue);
+	}
+}
+
+/// Weight trader which uses the TransactionPayment pallet to set the right price for weight and then
+/// places any weight bought into the right account.
+pub struct UsingComponents<
+	WeightToFee: WeightToFeePolynomial<Balance=Currency::Balance>,
+	AssetId: Get<MultiLocation>,
+	AccountId,
+	Currency: CurrencyT<AccountId>,
+	OnUnbalanced: OnUnbalancedT<Currency::NegativeImbalance>,
+>(Weight, Currency::Balance, PhantomData<(WeightToFee, AssetId, AccountId, Currency, OnUnbalanced)>);
+impl<
+	WeightToFee: WeightToFeePolynomial<Balance=Currency::Balance>,
+	AssetId: Get<MultiLocation>,
+	AccountId,
+	Currency: CurrencyT<AccountId>,
+	OnUnbalanced: OnUnbalancedT<Currency::NegativeImbalance>,
+> WeightTrader for UsingComponents<WeightToFee, AssetId, AccountId, Currency, OnUnbalanced> {
+	fn new() -> Self { Self(0, Zero::zero(), PhantomData) }
+
+	fn buy_weight(&mut self, weight: Weight, payment: Assets) -> Result<Assets, Error> {
+		let amount = WeightToFee::calc(&weight);
+		let required = MultiAsset::ConcreteFungible {
+			amount: amount.try_into().map_err(|_| Error::Overflow)?,
+			id: AssetId::get(),
+		};
+		let (unused, _) = payment.less(required).map_err(|_| Error::TooExpensive)?;
+		self.0 = self.0.saturating_add(weight);
+		self.1 = self.1.saturating_add(amount);
+		Ok(unused)
+	}
+
+	fn refund_weight(&mut self, weight: Weight) -> MultiAsset {
+		let weight = weight.min(self.0);
+		let amount = WeightToFee::calc(&weight);
+		self.0 -= weight;
+		self.1 = self.1.saturating_sub(amount);
+		let result = MultiAsset::ConcreteFungible {
+			amount: amount.saturated_into(),
+			id: AssetId::get(),
+		};
+		result
+	}
+
+}
+impl<
+	WeightToFee: WeightToFeePolynomial<Balance=Currency::Balance>,
+	AssetId: Get<MultiLocation>,
+	AccountId,
+	Currency: CurrencyT<AccountId>,
+	OnUnbalanced: OnUnbalancedT<Currency::NegativeImbalance>,
+> Drop for UsingComponents<WeightToFee, AssetId, AccountId, Currency, OnUnbalanced> {
+	fn drop(&mut self) {
+		OnUnbalanced::on_unbalanced(Currency::issue(self.1));
+	}
+}

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

@@ -60,7 +60,9 @@ impl<Config: config::Config> ExecuteXcm<Config::Call> for XcmExecutor<Config> {
 			return Outcome::Error(XcmError::WeightLimitReached);
 		}
 		let mut trader = Config::Trader::new();
-		match Self::do_execute_xcm(origin, true, message, &mut 0, Some(shallow_weight), &mut trader) {
+		let result = Self::do_execute_xcm(origin, true, message, &mut 0, Some(shallow_weight), &mut trader);
+		drop(trader);
+		match result {
 			Ok(surplus) => Outcome::Complete(maximum_weight.saturating_sub(surplus)),
 			// TODO: #2841 #REALWEIGHT We can do better than returning `maximum_weight` here, and we should otherwise
 			//  we'll needlessly be disregarding block execution time.
@@ -76,7 +78,9 @@ impl<Config: config::Config> XcmExecutor<Config> {
 		assets.into_assets_iter().collect::<Vec<_>>()
 	}
 
-	/// Execute the XCM and return any unexpected and unknowable surplus weight.
+	/// Execute the XCM and return the portion of weight of `shallow_weight + deep_weight` that `message` did not use.
+	///
+	/// NOTE: The amount returned must be less than `shallow_weight + deep_weight` of `message`.
 	fn do_execute_xcm(
 		origin: MultiLocation,
 		top_level: bool,
@@ -95,8 +99,8 @@ impl<Config: config::Config> XcmExecutor<Config> {
 			.map_err(|()| XcmError::Barrier)?;
 
 		// The surplus weight, defined as the amount by which `shallow_weight` plus all nested
-		// `shallow_weight` values (ensuring no double-counting) is an overestimate of the actual weight
-		// consumed.
+		// `shallow_weight` values (ensuring no double-counting and also known as `deep_weight`) is an
+		// over-estimate of the actual weight consumed.
 		let mut total_surplus: Weight = 0;
 
 		let maybe_holding_effects = match (origin.clone(), message) {

polkadot/xcm/xcm-executor/src/traits/weight.rs

@@ -15,7 +15,7 @@
 // along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.
 
 use sp_std::result::Result;
-use xcm::v0::{Xcm, MultiAsset};
+use xcm::v0::{Xcm, MultiAsset, Error};
 use frame_support::weights::Weight;
 use crate::Assets;
 
@@ -46,14 +46,14 @@ pub trait WeightBounds<Call> {
 }
 
 /// Charge for weight in order to execute XCM.
-pub trait WeightTrader {
+pub trait WeightTrader: Sized {
 	/// Create a new trader instance.
 	fn new() -> Self;
 
 	/// Purchase execution weight credit in return for up to a given `fee`. If less of the fee is required
 	/// then the surplus is returned. If the `fee` cannot be used to pay for the `weight`, then an error is
 	/// returned.
-	fn buy_weight(&mut self, weight: Weight, payment: Assets) -> Result<Assets, ()>;
+	fn buy_weight(&mut self, weight: Weight, payment: Assets) -> Result<Assets, Error>;
 
 	/// Attempt a refund of `weight` into some asset. The caller does not guarantee that the weight was
 	/// purchased using `buy_weight`.