Add back support for zero gas price validated transactions

frame/ethereum/src/tests/eip1559.rs

@@ -18,8 +18,9 @@
 //! Consensus extension module tests for BABE consensus.
 
 use super::*;
+use fp_ethereum::ValidatedTransaction;
 use frame_support::{traits::Get, weights::DispatchClass};
-use pallet_evm::GasWeightMapping;
+use pallet_evm::{AddressMapping, GasWeightMapping};
 
 fn eip1559_erc20_creation_unsigned_transaction() -> EIP1559UnsignedTransaction {
 	EIP1559UnsignedTransaction {
@@ -453,3 +454,35 @@ fn self_contained_transaction_with_extra_gas_should_adjust_weight_with_post_disp
 		);
 	});
 }
+
+#[test]
+fn validated_transaction_apply_zero_gas_price_works() {
+	let (pairs, mut ext) = new_test_ext_with_initial_balance(2, 1_000);
+	let alice = &pairs[0];
+	let bob = &pairs[1];
+	let substrate_alice =
+		<Test as pallet_evm::Config>::AddressMapping::into_account_id(alice.address);
+	let substrate_bob = <Test as pallet_evm::Config>::AddressMapping::into_account_id(bob.address);
+
+	ext.execute_with(|| {
+		let transaction = EIP1559UnsignedTransaction {
+			nonce: U256::zero(),
+			max_priority_fee_per_gas: U256::zero(),
+			max_fee_per_gas: U256::zero(),
+			gas_limit: U256::from(21_000),
+			action: ethereum::TransactionAction::Call(bob.address),
+			value: U256::from(100),
+			input: Default::default(),
+		}
+		.sign(&alice.private_key, None);
+
+		assert_ok!(crate::ValidatedTransaction::<Test>::apply(
+			alice.address,
+			transaction
+		));
+		// Alice didn't pay fees, transfer 100 to Bob.
+		assert_eq!(Balances::free_balance(&substrate_alice), 900);
+		// Bob received 100 from Alice.
+		assert_eq!(Balances::free_balance(&substrate_bob), 1_100);
+	});
+}

frame/ethereum/src/tests/eip2930.rs

@@ -18,6 +18,8 @@
 //! Consensus extension module tests for BABE consensus.
 
 use super::*;
+use fp_ethereum::ValidatedTransaction;
+use pallet_evm::AddressMapping;
 
 fn eip2930_erc20_creation_unsigned_transaction() -> EIP2930UnsignedTransaction {
 	EIP2930UnsignedTransaction {
@@ -374,3 +376,34 @@ fn self_contained_transaction_with_extra_gas_should_adjust_weight_with_post_disp
 		);
 	});
 }
+
+#[test]
+fn validated_transaction_apply_zero_gas_price_works() {
+	let (pairs, mut ext) = new_test_ext_with_initial_balance(2, 1_000);
+	let alice = &pairs[0];
+	let bob = &pairs[1];
+	let substrate_alice =
+		<Test as pallet_evm::Config>::AddressMapping::into_account_id(alice.address);
+	let substrate_bob = <Test as pallet_evm::Config>::AddressMapping::into_account_id(bob.address);
+
+	ext.execute_with(|| {
+		let transaction = EIP2930UnsignedTransaction {
+			nonce: U256::zero(),
+			gas_price: U256::zero(),
+			gas_limit: U256::from(21_000),
+			action: ethereum::TransactionAction::Call(bob.address),
+			value: U256::from(100),
+			input: Default::default(),
+		}
+		.sign(&alice.private_key, None);
+
+		assert_ok!(crate::ValidatedTransaction::<Test>::apply(
+			alice.address,
+			transaction
+		));
+		// Alice didn't pay fees, transfer 100 to Bob.
+		assert_eq!(Balances::free_balance(&substrate_alice), 900);
+		// Bob received 100 from Alice.
+		assert_eq!(Balances::free_balance(&substrate_bob), 1_100);
+	});
+}

frame/ethereum/src/tests/legacy.rs

@@ -18,6 +18,8 @@
 //! Consensus extension module tests for BABE consensus.
 
 use super::*;
+use fp_ethereum::ValidatedTransaction;
+use pallet_evm::AddressMapping;
 
 fn legacy_erc20_creation_unsigned_transaction() -> LegacyUnsignedTransaction {
 	LegacyUnsignedTransaction {
@@ -374,3 +376,34 @@ fn self_contained_transaction_with_extra_gas_should_adjust_weight_with_post_disp
 		);
 	});
 }
+
+#[test]
+fn validated_transaction_apply_zero_gas_price_works() {
+	let (pairs, mut ext) = new_test_ext_with_initial_balance(2, 1_000);
+	let alice = &pairs[0];
+	let bob = &pairs[1];
+	let substrate_alice =
+		<Test as pallet_evm::Config>::AddressMapping::into_account_id(alice.address);
+	let substrate_bob = <Test as pallet_evm::Config>::AddressMapping::into_account_id(bob.address);
+
+	ext.execute_with(|| {
+		let transaction = LegacyUnsignedTransaction {
+			nonce: U256::zero(),
+			gas_price: U256::zero(),
+			gas_limit: U256::from(21_000),
+			action: ethereum::TransactionAction::Call(bob.address),
+			value: U256::from(100),
+			input: Default::default(),
+		}
+		.sign(&alice.private_key);
+
+		assert_ok!(crate::ValidatedTransaction::<Test>::apply(
+			alice.address,
+			transaction
+		));
+		// Alice didn't pay fees, transfer 100 to Bob.
+		assert_eq!(Balances::free_balance(&substrate_alice), 900);
+		// Bob received 100 from Alice.
+		assert_eq!(Balances::free_balance(&substrate_bob), 1_100);
+	});
+}

frame/evm/src/runner/stack.rs

@@ -132,6 +132,9 @@ where
 	{
 		let (total_fee_per_gas, _actual_priority_fee_per_gas) =
 			match (max_fee_per_gas, max_priority_fee_per_gas, is_transactional) {
+				// Zero max_fee_per_gas for validated transactional calls exist in XCM -> EVM
+				// because fees are already withdrawn in the xcm-executor.
+				(Some(max_fee), _, true) if max_fee.is_zero() => (U256::zero(), U256::zero()),
 				// With no tip, we pay exactly the base_fee
 				(Some(_), None, _) => (base_fee, U256::zero()),
 				// With tip, we include as much of the tip on top of base_fee that we can, never