seal: Refactor ext_gas_price (#6478)

* seal: Refactor ext_gas_price

* Remove seals dependency on pallet_transaction_payment
* Add weight as an argument to ext_gas_price

* Fixed documentation nits from review

* Do not use unchecked math even in test code

substrate/frame/contracts/src/exec.rs

@@ -21,10 +21,11 @@ use crate::rent;
 use crate::storage;
 
 use sp_std::prelude::*;
-use sp_runtime::traits::{Bounded, Zero};
+use sp_runtime::traits::{Bounded, Zero, Convert};
 use frame_support::{
 	storage::unhashed, dispatch::DispatchError,
 	traits::{ExistenceRequirement, Currency, Time, Randomness},
+	weights::Weight,
 };
 
 pub type AccountIdOf<T> = <T as frame_system::Trait>::AccountId;
@@ -216,8 +217,8 @@ pub trait Ext {
 	/// Returns `None` if the value doesn't exist.
 	fn get_runtime_storage(&self, key: &[u8]) -> Option<Vec<u8>>;
 
-	/// Returns the price of one weight unit.
-	fn get_weight_price(&self) -> BalanceOf<Self::T>;
+	/// Returns the price for the specified amount of weight.
+	fn get_weight_price(&self, weight: Weight) -> BalanceOf<Self::T>;
 }
 
 /// Loader is a companion of the `Vm` trait. It loads an appropriate abstract
@@ -874,11 +875,8 @@ where
 		unhashed::get_raw(&key)
 	}
 
-	fn get_weight_price(&self) -> BalanceOf<Self::T> {
-		use pallet_transaction_payment::Module as Payment;
-		use sp_runtime::SaturatedConversion;
-		let price = Payment::<T>::weight_to_fee_with_adjustment::<u128>(1);
-		price.saturated_into()
+	fn get_weight_price(&self, weight: Weight) -> BalanceOf<Self::T> {
+		T::WeightPrice::convert(weight)
 	}
 }
 

substrate/frame/contracts/src/lib.rs

@@ -102,7 +102,7 @@ use sp_std::{prelude::*, marker::PhantomData, fmt::Debug};
 use codec::{Codec, Encode, Decode};
 use sp_runtime::{
 	traits::{
-		Hash, StaticLookup, Zero, MaybeSerializeDeserialize, Member,
+		Hash, StaticLookup, Zero, MaybeSerializeDeserialize, Member, Convert,
 	},
 	RuntimeDebug,
 };
@@ -117,6 +117,7 @@ use frame_support::traits::{OnUnbalanced, Currency, Get, Time, Randomness};
 use frame_support::weights::GetDispatchInfo;
 use frame_system::{self as system, ensure_signed, RawOrigin, ensure_root};
 use pallet_contracts_primitives::{RentProjection, ContractAccessError};
+use frame_support::weights::Weight;
 
 pub type CodeHash<T> = <T as frame_system::Trait>::Hash;
 pub type TrieId = Vec<u8>;
@@ -289,9 +290,10 @@ where
 	}
 }
 
-pub type BalanceOf<T> = <<T as pallet_transaction_payment::Trait>::Currency as Currency<<T as frame_system::Trait>::AccountId>>::Balance;
+pub type BalanceOf<T> =
+	<<T as Trait>::Currency as Currency<<T as frame_system::Trait>::AccountId>>::Balance;
 pub type NegativeImbalanceOf<T> =
-	<<T as pallet_transaction_payment::Trait>::Currency as Currency<<T as frame_system::Trait>::AccountId>>::NegativeImbalance;
+	<<T as Trait>::Currency as Currency<<T as frame_system::Trait>::AccountId>>::NegativeImbalance;
 
 parameter_types! {
 	/// A reasonable default value for [`Trait::SignedClaimedHandicap`].
@@ -312,10 +314,13 @@ parameter_types! {
 	pub const DefaultMaxValueSize: u32 = 16_384;
 }
 
-pub trait Trait: frame_system::Trait + pallet_transaction_payment::Trait {
+pub trait Trait: frame_system::Trait {
 	type Time: Time;
 	type Randomness: Randomness<Self::Hash>;
 
+	/// The currency in which fees are paid and contract balances are held.
+	type Currency: Currency<Self::AccountId>;
+
 	/// The outer call dispatch type.
 	type Call:
 		Parameter +
@@ -371,6 +376,10 @@ pub trait Trait: frame_system::Trait + pallet_transaction_payment::Trait {
 
 	/// The maximum size of a storage value in bytes.
 	type MaxValueSize: Get<u32>;
+
+	/// Used to answer contracts's queries regarding the current weight price. This is **not**
+	/// used to calculate the actual fee and is only for informational purposes.
+	type WeightPrice: Convert<Weight, BalanceOf<Self>>;
 }
 
 /// Simple contract address determiner.

substrate/frame/contracts/src/tests.rs

@@ -30,7 +30,7 @@ use frame_support::{
 	assert_ok, assert_err_ignore_postinfo, impl_outer_dispatch, impl_outer_event,
 	impl_outer_origin, parameter_types, StorageMap, StorageValue,
 	traits::{Currency, Get},
-	weights::{Weight, PostDispatchInfo, IdentityFee},
+	weights::{Weight, PostDispatchInfo},
 };
 use std::cell::RefCell;
 use frame_system::{self as system, EventRecord, Phase};
@@ -169,17 +169,10 @@ impl Convert<Weight, BalanceOf<Self>> for Test {
 	}
 }
 
-impl pallet_transaction_payment::Trait for Test {
-	type Currency = Balances;
-	type OnTransactionPayment = ();
-	type TransactionByteFee = TransactionByteFee;
-	type WeightToFee = IdentityFee<BalanceOf<Self>>;
-	type FeeMultiplierUpdate = ();
-}
-
 impl Trait for Test {
 	type Time = Timestamp;
 	type Randomness = Randomness;
+	type Currency = Balances;
 	type Call = Call;
 	type DetermineContractAddress = DummyContractAddressFor;
 	type Event = MetaEvent;
@@ -193,6 +186,7 @@ impl Trait for Test {
 	type SurchargeReward = SurchargeReward;
 	type MaxDepth = MaxDepth;
 	type MaxValueSize = MaxValueSize;
+	type WeightPrice = Self;
 }
 
 type Balances = pallet_balances::Module<Test>;

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

@@ -162,6 +162,7 @@ mod tests {
 	use hex_literal::hex;
 	use assert_matches::assert_matches;
 	use sp_runtime::DispatchError;
+	use frame_support::weights::Weight;
 
 	const GAS_LIMIT: Gas = 10_000_000_000;
 
@@ -373,8 +374,8 @@ mod tests {
 				)
 			)
 		}
-		fn get_weight_price(&self) -> BalanceOf<Self::T> {
-			1312_u32.into()
+		fn get_weight_price(&self, weight: Weight) -> BalanceOf<Self::T> {
+			BalanceOf::<Self::T>::from(1312_u32).saturating_mul(weight.into())
 		}
 	}
 
@@ -479,8 +480,8 @@ mod tests {
 		fn get_runtime_storage(&self, key: &[u8]) -> Option<Vec<u8>> {
 			(**self).get_runtime_storage(key)
 		}
-		fn get_weight_price(&self) -> BalanceOf<Self::T> {
-			(**self).get_weight_price()
+		fn get_weight_price(&self, weight: Weight) -> BalanceOf<Self::T> {
+			(**self).get_weight_price(weight)
 		}
 	}
 
@@ -1056,7 +1057,7 @@ mod tests {
 
 	const CODE_GAS_PRICE: &str = r#"
 (module
-	(import "env" "ext_gas_price" (func $ext_gas_price))
+	(import "env" "ext_gas_price" (func $ext_gas_price (param i64)))
 	(import "env" "ext_scratch_size" (func $ext_scratch_size (result i32)))
 	(import "env" "ext_scratch_read" (func $ext_scratch_read (param i32 i32 i32)))
 	(import "env" "memory" (memory 1 1))
@@ -1072,7 +1073,7 @@ mod tests {
 
 	(func (export "call")
 		;; This stores the gas price in the scratch buffer
-		(call $ext_gas_price)
+		(call $ext_gas_price (i64.const 1))
 
 		;; assert $ext_scratch_size == 8
 		(call $assert

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

@@ -696,12 +696,14 @@ define_env!(Env, <E: Ext>,
 		Ok(())
 	},
 
-	// Stores the gas price for the current transaction into the scratch buffer.
+	// Stores the price for the specified amount of gas in scratch buffer.
 	//
 	// The data is encoded as T::Balance. The current contents of the scratch buffer are overwritten.
-	ext_gas_price(ctx) => {
+	// It is recommended to avoid specifying very small values for `gas` as the prices for a single
+	// gas can be smaller than one.
+	ext_gas_price(ctx, gas: u64) => {
 		ctx.scratch_buf.clear();
-		ctx.ext.get_weight_price().encode_to(&mut ctx.scratch_buf);
+		ctx.ext.get_weight_price(gas).encode_to(&mut ctx.scratch_buf);
 		Ok(())
 	},