op-service, op-deployer: Support marshaling systemconfig in pre-Holocene format (#12619)

op-deployer generates rollup configs, and those rollup configs are currently broken for older versions of op-node that don't support reading the EIP1559Params field in the SystemConfig. This PR adds a meta field within the SystemConfig that, when enabled, marshals the SystemConfig without the EIP1559Params field. This solution is backwards-compatible and minimally invasive, requiring no changes to the consensus-critical code that consumes the SystemConfig elsewhere.

Closes https://github.com/ethereum-optimism/optimism/issues/12615.

op-deployer/pkg/deployer/inspect/rollup.go

@@ -22,6 +22,9 @@ func RollupCLI(cliCtx *cli.Context) error {
 	}
 
 	_, rollupConfig, err := GenesisAndRollup(globalState, cfg.ChainID)
+	if rollupConfig.HoloceneTime == nil {
+		rollupConfig.Genesis.SystemConfig.MarshalPreHolocene = true
+	}
 	if err != nil {
 		return fmt.Errorf("failed to generate rollup config: %w", err)
 	}

op-service/eth/types.go

@@ -3,6 +3,7 @@ package eth
 import (
 	"bytes"
 	"encoding/binary"
+	"encoding/json"
 	"errors"
 	"fmt"
 	"math"
@@ -419,8 +420,42 @@ type SystemConfig struct {
 	// EIP1559Params contains the Holocene-encoded EIP-1559 parameters. This
 	// value will be 0 if Holocene is not active, or if derivation has yet to
 	// process any EIP_1559_PARAMS system config update events.
-	EIP1559Params Bytes8 `json:"eip1559Params,omitempty"`
+	EIP1559Params Bytes8 `json:"eip1559Params"`
 	// More fields can be added for future SystemConfig versions.
+
+	// MarshalPreHolocene indicates whether or not this struct should be
+	// marshaled in the pre-Holocene format. The pre-Holocene format does
+	// not marshal the EIP1559Params field. The presence of this field in
+	// pre-Holocene codebases causes the rollup config to be rejected.
+	MarshalPreHolocene bool `json:"-"`
+}
+
+func (sysCfg SystemConfig) MarshalJSON() ([]byte, error) {
+	if sysCfg.MarshalPreHolocene {
+		return jsonMarshalPreHolocene(sysCfg)
+	}
+	return jsonMarshalHolocene(sysCfg)
+}
+
+func jsonMarshalHolocene(sysCfg SystemConfig) ([]byte, error) {
+	type sysCfgMarshaling SystemConfig
+	return json.Marshal(sysCfgMarshaling(sysCfg))
+}
+
+func jsonMarshalPreHolocene(sysCfg SystemConfig) ([]byte, error) {
+	type sysCfgMarshaling struct {
+		BatcherAddr common.Address `json:"batcherAddr"`
+		Overhead    Bytes32        `json:"overhead"`
+		Scalar      Bytes32        `json:"scalar"`
+		GasLimit    uint64         `json:"gasLimit"`
+	}
+	sc := sysCfgMarshaling{
+		BatcherAddr: sysCfg.BatcherAddr,
+		Overhead:    sysCfg.Overhead,
+		Scalar:      sysCfg.Scalar,
+		GasLimit:    sysCfg.GasLimit,
+	}
+	return json.Marshal(sc)
 }
 
 // The Ecotone upgrade introduces a versioned L1 scalar format

op-service/eth/types_test.go

 package eth
 
 import (
+	"encoding/json"
 	"errors"
 	"math"
 	"testing"
 
+	"github.com/ethereum/go-ethereum/common"
+
 	"github.com/stretchr/testify/require"
 )
 
@@ -66,3 +69,21 @@ func FuzzEncodeScalar(f *testing.F) {
 		require.Equal(t, baseFeeScalar, scalars.BaseFeeScalar)
 	})
 }
+
+func TestSystemConfigMarshaling(t *testing.T) {
+	sysConfig := SystemConfig{
+		BatcherAddr: common.Address{'A'},
+		Overhead:    Bytes32{0x4, 0x5, 0x6},
+		Scalar:      Bytes32{0x7, 0x8, 0x9},
+		GasLimit:    1234,
+		// Leave EIP1559 params empty to prove that the
+		// zero value is sent.
+	}
+	j, err := json.Marshal(sysConfig)
+	require.NoError(t, err)
+	require.Equal(t, `{"batcherAddr":"0x4100000000000000000000000000000000000000","overhead":"0x0405060000000000000000000000000000000000000000000000000000000000","scalar":"0x0708090000000000000000000000000000000000000000000000000000000000","gasLimit":1234,"eip1559Params":"0x0000000000000000"}`, string(j))
+	sysConfig.MarshalPreHolocene = true
+	j, err = json.Marshal(sysConfig)
+	require.NoError(t, err)
+	require.Equal(t, `{"batcherAddr":"0x4100000000000000000000000000000000000000","overhead":"0x0405060000000000000000000000000000000000000000000000000000000000","scalar":"0x0708090000000000000000000000000000000000000000000000000000000000","gasLimit":1234}`, string(j))
+}