refactor: use weightToFee for xcm Trader (paritytech#752)

* refactor: use weightToFee for xcm Trader

* fix format

parachain/runtime/common/Cargo.toml

@@ -7,6 +7,7 @@ edition = "2021"
 repository = "https://github.com/Snowfork/snowbridge"
 
 [dependencies]
+smallvec = "1.8.0"
 frame-support = { git = "https://github.com/paritytech/substrate.git", branch = "polkadot-v0.9.30", default-features = false }
 frame-system = { git = "https://github.com/paritytech/substrate.git", branch = "polkadot-v0.9.30", default-features = false }
 sp-core = { git = "https://github.com/paritytech/substrate.git", branch = "polkadot-v0.9.30", default-features = false }
@@ -16,6 +17,8 @@ sp-runtime = { git = "https://github.com/paritytech/substrate.git", branch = "po
 snowbridge-core = { path = "../../primitives/core", package = "snowbridge-core", default-features = false }
 basic-channel = { path = "../../pallets/basic-channel", package = "snowbridge-basic-channel", default-features = false }
 incentivized-channel = { path = "../../pallets/incentivized-channel", package = "snowbridge-incentivized-channel", default-features = false }
+runtime-primitives = { path = "../../primitives/runtime", default-features = false, package = "snowbridge-runtime-primitives" }
+
 
 [features]
 default = [ "std" ]
@@ -27,5 +30,6 @@ std = [
     "sp-runtime/std",
     "snowbridge-core/std",
     "basic-channel/std",
-    "incentivized-channel/std"
+    "incentivized-channel/std",
+    "runtime-primitives/std"
 ]

parachain/runtime/common/src/lib.rs

@@ -35,3 +35,70 @@ parameter_types! {
 	pub const TreasuryPalletId: PalletId = PalletId(*b"s/treasy");
 	pub const DotPalletId: PalletId = PalletId(*b"s/dotapp");
 }
+
+/// Money matters.
+pub mod currency {
+	use runtime_primitives::Balance;
+
+	pub const UNITS: Balance = 1_000_000_000_000;
+	pub const CENTS: Balance = UNITS / 100;
+	pub const MILLICENTS: Balance = CENTS / 1_000;
+}
+
+/// Fee-related.
+pub mod fee {
+	use frame_support::weights::{
+		constants::ExtrinsicBaseWeight, WeightToFeeCoefficient, WeightToFeeCoefficients,
+		WeightToFeePolynomial,
+	};
+	use runtime_primitives::Balance;
+	use smallvec::smallvec;
+	pub use sp_runtime::Perbill;
+
+	/// Handles converting a weight scalar to a fee value, based on the scale and granularity of the
+	/// node's balance type.
+	///
+	/// This should typically create a mapping between the following ranges:
+	///   - [0, MAXIMUM_BLOCK_WEIGHT]
+	///   - [Balance::min, Balance::max]
+	///
+	/// Yet, it can be used for any other sort of change to weight-fee. Some examples being:
+	///   - Setting it to `0` will essentially disable the weight fee.
+	///   - Setting it to `1` will cause the literal `#[weight = x]` values to be charged.
+	pub struct WeightToFee;
+	impl WeightToFeePolynomial for WeightToFee {
+		type Balance = Balance;
+		fn polynomial() -> WeightToFeeCoefficients<Self::Balance> {
+			// extrinsic base weight map to 1/100 CENT
+			let p = super::currency::CENTS;
+			let q = 100 * Balance::from(ExtrinsicBaseWeight::get().ref_time());
+			smallvec![WeightToFeeCoefficient {
+				degree: 1,
+				negative: false,
+				coeff_frac: Perbill::from_rational(p % q, q),
+				coeff_integer: p / q,
+			}]
+		}
+	}
+}
+
+#[cfg(test)]
+mod tests {
+	use super::{
+		currency::{CENTS, MILLICENTS},
+		fee::WeightToFee,
+	};
+	use frame_support::weights::{constants::ExtrinsicBaseWeight, WeightToFee as WeightToFeeT};
+
+	#[test]
+	// This function tests that the fee for `ExtrinsicBaseWeight` of weight is correct
+	fn extrinsic_base_fee_is_correct() {
+		// `ExtrinsicBaseWeight` should cost 1/100 of a CENT
+		println!("Base Weight: {}", ExtrinsicBaseWeight::get());
+		let x = WeightToFee::weight_to_fee(&ExtrinsicBaseWeight::get());
+		println!("Base Fee: {}", x);
+		let y = CENTS / 100;
+		println!("CENTS: {}", y);
+		assert!(x.max(y) - x.min(y) < MILLICENTS);
+	}
+}

parachain/runtime/snowbase/src/lib.rs

@@ -68,7 +68,8 @@ use xcm_builder::{
 use xcm_executor::{traits::JustTry, Config, XcmExecutor};
 
 use runtime_common::{
-	DotPalletId, MaxMessagePayloadSize, MaxMessagesPerCommit, OutboundRouter, TreasuryPalletId,
+	fee::WeightToFee, DotPalletId, MaxMessagePayloadSize, MaxMessagesPerCommit, OutboundRouter,
+	TreasuryPalletId,
 };
 
 pub use runtime_primitives::{AccountId, Address, Balance, BlockNumber, Hash, Index, Signature};
@@ -366,7 +367,7 @@ impl Config for XcmConfig {
 	type LocationInverter = LocationInverter<Ancestry>;
 	type Barrier = Barrier;
 	type Weigher = FixedWeightBounds<UnitWeightCost, RuntimeCall, MaxInstructions>;
-	type Trader = UsingComponents<IdentityFee<Balance>, RococoLocation, AccountId, Balances, ()>;
+	type Trader = UsingComponents<WeightToFee, RococoLocation, AccountId, Balances, ()>;
 	type ResponseHandler = (); // Don't handle responses for now.
 	type SubscriptionService = PolkadotXcm;
 	type AssetTrap = (); // Don't handle asset trap.

parachain/runtime/snowblink/src/lib.rs

@@ -66,7 +66,8 @@ use xcm_builder::{
 use xcm_executor::{traits::JustTry, Config, XcmExecutor};
 
 use runtime_common::{
-	DotPalletId, MaxMessagePayloadSize, MaxMessagesPerCommit, OutboundRouter, TreasuryPalletId,
+	fee::WeightToFee, DotPalletId, MaxMessagePayloadSize, MaxMessagesPerCommit, OutboundRouter,
+	TreasuryPalletId,
 };
 
 pub use runtime_primitives::{AccountId, Address, Balance, BlockNumber, Hash, Index, Signature};
@@ -364,7 +365,7 @@ impl Config for XcmConfig {
 	type LocationInverter = LocationInverter<Ancestry>;
 	type Barrier = Barrier;
 	type Weigher = FixedWeightBounds<UnitWeightCost, RuntimeCall, MaxInstructions>;
-	type Trader = UsingComponents<IdentityFee<Balance>, RococoLocation, AccountId, Balances, ()>;
+	type Trader = UsingComponents<WeightToFee, RococoLocation, AccountId, Balances, ()>;
 	type ResponseHandler = (); // Don't handle responses for now.
 	type SubscriptionService = PolkadotXcm;
 	type AssetTrap = (); // Don't handle asset trap.

parachain/runtime/snowbridge/src/lib.rs

@@ -66,7 +66,8 @@ use xcm_builder::{
 use xcm_executor::{traits::JustTry, Config, XcmExecutor};
 
 use runtime_common::{
-	DotPalletId, MaxMessagePayloadSize, MaxMessagesPerCommit, OutboundRouter, TreasuryPalletId,
+	fee::WeightToFee, DotPalletId, MaxMessagePayloadSize, MaxMessagesPerCommit, OutboundRouter,
+	TreasuryPalletId,
 };
 
 pub use runtime_primitives::{AccountId, Address, Balance, BlockNumber, Hash, Index, Signature};
@@ -364,7 +365,7 @@ impl Config for XcmConfig {
 	type LocationInverter = LocationInverter<Ancestry>;
 	type Barrier = Barrier;
 	type Weigher = FixedWeightBounds<UnitWeightCost, RuntimeCall, MaxInstructions>;
-	type Trader = UsingComponents<IdentityFee<Balance>, RococoLocation, AccountId, Balances, ()>;
+	type Trader = UsingComponents<WeightToFee, RococoLocation, AccountId, Balances, ()>;
 	type ResponseHandler = (); // Don't handle responses for now.
 	type SubscriptionService = PolkadotXcm;
 	type AssetTrap = (); // Don't handle asset trap.