XCM native fee reduction (#1092)

* Solution suggestion

* Apply to to other runtimes

runtime/astar/src/lib.rs

@@ -668,6 +668,18 @@ impl WeightToFeePolynomial for WeightToFee {
     }
 }
 
+/// Handles coverting weight consumed by XCM into native currency fee.
+///
+/// Similar to standard `WeightToFee` handler, but force uses the minimum multiplier.
+pub struct XcmWeightToFee;
+impl frame_support::weights::WeightToFee for XcmWeightToFee {
+    type Balance = Balance;
+
+    fn weight_to_fee(n: &Weight) -> Self::Balance {
+        MinimumMultiplier::get().saturating_mul_int(WeightToFee::weight_to_fee(&n))
+    }
+}
+
 pub struct DealWithFees;
 impl OnUnbalanced<NegativeImbalance> for DealWithFees {
     fn on_unbalanceds<B>(mut fees_then_tips: impl Iterator<Item = NegativeImbalance>) {

runtime/astar/src/xcm_config.rs

@@ -19,7 +19,7 @@
 use super::{
     AccountId, AllPalletsWithSystem, AssetId, Assets, AstarAssetLocationIdConverter, Balance,
     Balances, DealWithFees, ParachainInfo, ParachainSystem, PolkadotXcm, Runtime, RuntimeCall,
-    RuntimeEvent, RuntimeOrigin, TreasuryAccountId, WeightToFee, XcAssetConfig, XcmpQueue,
+    RuntimeEvent, RuntimeOrigin, TreasuryAccountId, XcAssetConfig, XcmWeightToFee, XcmpQueue,
 };
 use crate::weights;
 use frame_support::{
@@ -251,7 +251,7 @@ impl xcm_executor::Config for XcmConfig {
     type Barrier = XcmBarrier;
     type Weigher = Weigher;
     type Trader = (
-        UsingComponents<WeightToFee, AstarLocation, AccountId, Balances, DealWithFees>,
+        UsingComponents<XcmWeightToFee, AstarLocation, AccountId, Balances, DealWithFees>,
         FixedRateOfForeignAsset<XcAssetConfig, AstarXcmFungibleFeeHandler>,
     );
     type ResponseHandler = PolkadotXcm;

runtime/shibuya/src/lib.rs

@@ -715,6 +715,18 @@ impl WeightToFeePolynomial for WeightToFee {
     }
 }
 
+/// Handles coverting weight consumed by XCM into native currency fee.
+///
+/// Similar to standard `WeightToFee` handler, but force uses the minimum multiplier.
+pub struct XcmWeightToFee;
+impl frame_support::weights::WeightToFee for XcmWeightToFee {
+    type Balance = Balance;
+
+    fn weight_to_fee(n: &Weight) -> Self::Balance {
+        MinimumMultiplier::get().saturating_mul_int(WeightToFee::weight_to_fee(&n))
+    }
+}
+
 pub struct DealWithFees;
 impl OnUnbalanced<NegativeImbalance> for DealWithFees {
     fn on_unbalanceds<B>(mut fees_then_tips: impl Iterator<Item = NegativeImbalance>) {

runtime/shibuya/src/xcm_config.rs

@@ -19,7 +19,7 @@
 use super::{
     AccountId, AllPalletsWithSystem, AssetId, Assets, Balance, Balances, DealWithFees,
     ParachainInfo, ParachainSystem, PolkadotXcm, Runtime, RuntimeCall, RuntimeEvent, RuntimeOrigin,
-    ShibuyaAssetLocationIdConverter, TreasuryAccountId, WeightToFee, XcAssetConfig, XcmpQueue,
+    ShibuyaAssetLocationIdConverter, TreasuryAccountId, XcAssetConfig, XcmWeightToFee, XcmpQueue,
 };
 use crate::weights;
 use frame_support::{
@@ -185,7 +185,7 @@ impl xcm_executor::Config for XcmConfig {
     type Barrier = XcmBarrier;
     type Weigher = Weigher;
     type Trader = (
-        UsingComponents<WeightToFee, ShibuyaLocation, AccountId, Balances, DealWithFees>,
+        UsingComponents<XcmWeightToFee, ShibuyaLocation, AccountId, Balances, DealWithFees>,
         FixedRateOfForeignAsset<XcAssetConfig, ShibuyaXcmFungibleFeeHandler>,
     );
     type ResponseHandler = PolkadotXcm;

runtime/shiden/src/lib.rs

@@ -660,8 +660,20 @@ impl WeightToFeePolynomial for WeightToFee {
     }
 }
 
-pub struct BurnFees;
-impl OnUnbalanced<NegativeImbalance> for BurnFees {
+/// Handles coverting weight consumed by XCM into native currency fee.
+///
+/// Similar to standard `WeightToFee` handler, but force uses the minimum multiplier.
+pub struct XcmWeightToFee;
+impl frame_support::weights::WeightToFee for XcmWeightToFee {
+    type Balance = Balance;
+
+    fn weight_to_fee(n: &Weight) -> Self::Balance {
+        MinimumMultiplier::get().saturating_mul_int(WeightToFee::weight_to_fee(&n))
+    }
+}
+
+pub struct DealWithFees;
+impl OnUnbalanced<NegativeImbalance> for DealWithFees {
     /// Payout tips but burn all the fees
     fn on_unbalanceds<B>(mut fees_then_tips: impl Iterator<Item = NegativeImbalance>) {
         if let Some(fees) = fees_then_tips.next() {
@@ -682,7 +694,7 @@ impl OnUnbalanced<NegativeImbalance> for BurnFees {
 
 impl pallet_transaction_payment::Config for Runtime {
     type RuntimeEvent = RuntimeEvent;
-    type OnChargeTransaction = pallet_transaction_payment::CurrencyAdapter<Balances, BurnFees>;
+    type OnChargeTransaction = pallet_transaction_payment::CurrencyAdapter<Balances, DealWithFees>;
     type WeightToFee = WeightToFee;
     type OperationalFeeMultiplier = OperationalFeeMultiplier;
     type FeeMultiplierUpdate = TargetedFeeAdjustment<

runtime/shiden/src/xcm_config.rs

@@ -17,9 +17,9 @@
 // along with Astar. If not, see <http://www.gnu.org/licenses/>.
 
 use super::{
-    AccountId, AllPalletsWithSystem, AssetId, Assets, Balance, Balances, BurnFees, ParachainInfo,
-    ParachainSystem, PolkadotXcm, Runtime, RuntimeCall, RuntimeEvent, RuntimeOrigin,
-    ShidenAssetLocationIdConverter, TreasuryAccountId, WeightToFee, XcAssetConfig, XcmpQueue,
+    AccountId, AllPalletsWithSystem, AssetId, Assets, Balance, Balances, DealWithFees,
+    ParachainInfo, ParachainSystem, PolkadotXcm, Runtime, RuntimeCall, RuntimeEvent, RuntimeOrigin,
+    ShidenAssetLocationIdConverter, TreasuryAccountId, XcAssetConfig, XcmWeightToFee, XcmpQueue,
 };
 use crate::weights;
 use frame_support::{
@@ -255,7 +255,7 @@ impl xcm_executor::Config for XcmConfig {
     type Barrier = XcmBarrier;
     type Weigher = Weigher;
     type Trader = (
-        UsingComponents<WeightToFee, ShidenLocation, AccountId, Balances, BurnFees>,
+        UsingComponents<XcmWeightToFee, ShidenLocation, AccountId, Balances, DealWithFees>,
         FixedRateOfForeignAsset<XcAssetConfig, ShidenXcmFungibleFeeHandler>,
     );
     type ResponseHandler = PolkadotXcm;