feat: legacy package for backwards-compatible type support

Author: ARR4N

core/vm/contracts.libevm_test.go

@@ -39,6 +39,7 @@ import (
 	"github.com/ava-labs/libevm/libevm"
 	"github.com/ava-labs/libevm/libevm/ethtest"
 	"github.com/ava-labs/libevm/libevm/hookstest"
+	"github.com/ava-labs/libevm/libevm/legacy"
 	"github.com/ava-labs/libevm/params"
 )
 
@@ -146,16 +147,13 @@ func TestNewStatefulPrecompile(t *testing.T) {
 	const gasLimit = 1e6
 	gasCost := rng.Uint64n(gasLimit)
 
-	run := func(env vm.PrecompileEnvironment, input []byte) ([]byte, error) {
+	run := func(env vm.PrecompileEnvironment, input []byte, suppliedGas uint64) ([]byte, uint64, error) {
 		if got, want := env.StateDB() != nil, !env.ReadOnly(); got != want {
-			return nil, fmt.Errorf("PrecompileEnvironment().StateDB() must be non-nil i.f.f. not read-only; got non-nil? %t; want %t", got, want)
+			return nil, suppliedGas, fmt.Errorf("PrecompileEnvironment().StateDB() must be non-nil i.f.f. not read-only; got non-nil? %t; want %t", got, want)
 		}
 		hdr, err := env.BlockHeader()
 		if err != nil {
-			return nil, err
-		}
-		if !env.UseGas(gasCost) {
-			return nil, vm.ErrOutOfGas
+			return nil, suppliedGas, err
 		}
 
 		out := &statefulPrecompileOutput{
@@ -169,11 +167,15 @@ func TestNewStatefulPrecompile(t *testing.T) {
 			Input:            input,
 			IncomingCallType: env.IncomingCallType(),
 		}
-		return out.Bytes(), nil
+		return out.Bytes(), suppliedGas - gasCost, nil
 	}
 	hooks := &hookstest.Stub{
 		PrecompileOverrides: map[common.Address]libevm.PrecompiledContract{
-			precompile: vm.NewStatefulPrecompile(run),
+			precompile: vm.NewStatefulPrecompile(
+				// In production, the new function signature should be used, but
+				// this just exercises the converter.
+				legacy.PrecompiledStatefulContract(run).Upgrade(),
+			),
 		},
 	}
 	hooks.Register(t)

libevm/legacy/legacy.go

@@ -0,0 +1,39 @@
+// Copyright 2024 the libevm authors.
+//
+// The libevm additions to go-ethereum are free software: you can redistribute
+// them and/or modify them under the terms of the GNU Lesser General Public License
+// as published by the Free Software Foundation, either version 3 of the License,
+// or (at your option) any later version.
+//
+// The libevm additions are distributed in the hope that they will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser
+// General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see
+// <http://www.gnu.org/licenses/>.
+
+// Package legacy provides converters between legacy types and their refactored
+// equivalents.
+package legacy
+
+import "github.com/ava-labs/libevm/core/vm"
+
+// PrecompiledStatefulContract is the legacy signature of
+// [vm.PrecompiledStatefulContract], which explicitly accepts and returns gas
+// values. Instances SHOULD NOT use the [vm.PrecompileEnvironment]
+// gas-management methods as this may result in unexpected behaviour.
+type PrecompiledStatefulContract func(env vm.PrecompileEnvironment, input []byte, suppliedGas uint64) (ret []byte, remainingGas uint64, err error)
+
+// Upgrade converts the legacy precompile signature into the now-required form.
+func (c PrecompiledStatefulContract) Upgrade() vm.PrecompiledStatefulContract {
+	return func(env vm.PrecompileEnvironment, input []byte) ([]byte, error) {
+		gas := env.Gas()
+		ret, remainingGas, err := c(env, input, env.Gas())
+		if used := gas - remainingGas; used < gas {
+			env.UseGas(used)
+		}
+		return ret, err
+	}
+}