pallet-evm: add support for tuple-based precompile declarations (#6681)

* pallet-evm: add support for tuple-based precompile declarations

* Add missing license header

* Switch to use impl_for_tuples

* Remove unnecessary impl for ()

Cargo.toml

@@ -26,6 +26,7 @@ primitive-types = { version = "0.7.0", default-features = false, features = ["rl
 rlp = { version = "0.4", default-features = false }
 evm = { version = "0.17", default-features = false }
 sha3 = { version = "0.8", default-features = false }
+impl-trait-for-tuples = "0.1"
 
 [features]
 default = ["std"]

src/lib.rs

@@ -21,8 +21,10 @@
 #![cfg_attr(not(feature = "std"), no_std)]
 
 mod backend;
+mod precompiles;
 mod tests;
 
+pub use crate::precompiles::{Precompile, Precompiles};
 pub use crate::backend::{Account, Log, Vicinity, Backend};
 
 use sp_std::vec::Vec;
@@ -175,30 +177,6 @@ impl<H: Hasher<Out=H256>> AddressMapping<AccountId32> for HashedAddressMapping<H
 	}
 }
 
-/// Custom precompiles to be used by EVM engine.
-pub trait Precompiles {
-	/// Try to execute the code address as precompile. If the code address is not
-	/// a precompile or the precompile is not yet available, return `None`.
-	/// Otherwise, calculate the amount of gas needed with given `input` and
-	/// `target_gas`. Return `Some(Ok(status, output, gas_used))` if the execution
-	/// is successful. Otherwise return `Some(Err(_))`.
-	fn execute(
-		address: H160,
-		input: &[u8],
-		target_gas: Option<usize>
-	) -> Option<core::result::Result<(ExitSucceed, Vec<u8>, usize), ExitError>>;
-}
-
-impl Precompiles for () {
-	fn execute(
-		_address: H160,
-		_input: &[u8],
-		_target_gas: Option<usize>
-	) -> Option<core::result::Result<(ExitSucceed, Vec<u8>, usize), ExitError>> {
-		None
-	}
-}
-
 /// Substrate system chain ID.
 pub struct SystemChainId;
 

src/precompiles.rs

@@ -0,0 +1,69 @@
+// This file is part of Substrate.
+
+// Copyright (C) 2017-2020 Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: Apache-2.0
+
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// 	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use sp_std::vec::Vec;
+use sp_core::H160;
+use evm::{ExitError, ExitSucceed};
+use impl_trait_for_tuples::impl_for_tuples;
+
+/// Custom precompiles to be used by EVM engine.
+pub trait Precompiles {
+	/// Try to execute the code address as precompile. If the code address is not
+	/// a precompile or the precompile is not yet available, return `None`.
+	/// Otherwise, calculate the amount of gas needed with given `input` and
+	/// `target_gas`. Return `Some(Ok(status, output, gas_used))` if the execution
+	/// is successful. Otherwise return `Some(Err(_))`.
+	fn execute(
+		address: H160,
+		input: &[u8],
+		target_gas: Option<usize>,
+	) -> Option<core::result::Result<(ExitSucceed, Vec<u8>, usize), ExitError>>;
+}
+
+/// One single precompile used by EVM engine.
+pub trait Precompile {
+	/// Try to execute the precompile. Calculate the amount of gas needed with given `input` and
+	/// `target_gas`. Return `Ok(status, output, gas_used)` if the execution is
+	/// successful. Otherwise return `Err(_)`.
+	fn execute(
+		input: &[u8],
+		target_gas: Option<usize>,
+	) -> core::result::Result<(ExitSucceed, Vec<u8>, usize), ExitError>;
+}
+
+#[impl_for_tuples(16)]
+#[tuple_types_no_default_trait_bound]
+impl Precompiles for Tuple {
+	for_tuples!( where #( Tuple: Precompile )* );
+
+	fn execute(
+		address: H160,
+		input: &[u8],
+		target_gas: Option<usize>,
+	) -> Option<core::result::Result<(ExitSucceed, Vec<u8>, usize), ExitError>> {
+		let mut index = 0;
+
+		for_tuples!( #(
+			index += 1;
+			if address == H160::from_low_u64_be(index) {
+				return Some(Tuple::execute(input, target_gas))
+			}
+		)* );
+
+		None
+	}
+}