Add custom type for `LocalContext` - @tynes review

Co-Authored-By: Mark Tyneway <mark.tyneway@gmail.com>

cannon/mipsevm/evm.go

@@ -28,6 +28,21 @@ var (
 	LoadLocalDataBytes4             []byte
 )
 
+func init() {
+	mipsAbi, err := bindings.MIPSMetaData.GetAbi()
+	if err != nil {
+		panic(fmt.Errorf("failed to load MIPS ABI: %w", err))
+	}
+	StepBytes4 = mipsAbi.Methods["step"].ID[:4]
+
+	preimageAbi, err := bindings.PreimageOracleMetaData.GetAbi()
+	if err != nil {
+		panic(fmt.Errorf("failed to load pre-image oracle ABI: %w", err))
+	}
+	LoadKeccak256PreimagePartBytes4 = preimageAbi.Methods["loadKeccak256PreimagePart"].ID[:4]
+	LoadLocalDataBytes4 = preimageAbi.Methods["loadLocalData"].ID[:4]
+}
+
 // LoadContracts loads the Cannon contracts, from op-bindings package
 func LoadContracts() (*Contracts, error) {
 	var mips, oracle Contract
@@ -35,9 +50,6 @@ func LoadContracts() (*Contracts, error) {
 	mips.DeployedBytecode.SourceMap = bindings.MIPSDeployedSourceMap
 	oracle.DeployedBytecode.Object = hexutil.MustDecode(bindings.PreimageOracleDeployedBin)
 	oracle.DeployedBytecode.SourceMap = bindings.PreimageOracleDeployedSourceMap
-	if err := InitSelectors(); err != nil {
-		return nil, err
-	}
 	return &Contracts{
 		MIPS:   &mips,
 		Oracle: &oracle,
@@ -54,32 +66,12 @@ func LoadContractsFromFiles() (*Contracts, error) {
 	if err != nil {
 		return nil, err
 	}
-	if err := InitSelectors(); err != nil {
-		return nil, err
-	}
 	return &Contracts{
 		MIPS:   mips,
 		Oracle: oracle,
 	}, nil
 }
 
-func InitSelectors() error {
-	mipsAbi, err := bindings.MIPSMetaData.GetAbi()
-	if err != nil {
-		return fmt.Errorf("failed to load MIPS ABI: %w", err)
-	}
-	StepBytes4 = mipsAbi.Methods["step"].ID[:4]
-
-	preimageAbi, err := bindings.PreimageOracleMetaData.GetAbi()
-	if err != nil {
-		return fmt.Errorf("failed to load pre-image oracle ABI: %w", err)
-	}
-	LoadKeccak256PreimagePartBytes4 = preimageAbi.Methods["loadKeccak256PreimagePart"].ID[:4]
-	LoadLocalDataBytes4 = preimageAbi.Methods["loadLocalData"].ID[:4]
-
-	return nil
-}
-
 func LoadContract(name string) (*Contract, error) {
 	dat, err := os.ReadFile(fmt.Sprintf("../../packages/contracts-bedrock/forge-artifacts/%s.sol/%s.json", name, name))
 	if err != nil {

cannon/mipsevm/witness.go

@@ -8,6 +8,8 @@ import (
 	preimage "github.com/ethereum-optimism/optimism/op-preimage"
 )
 
+type LocalContext uint64
+
 type StepWitness struct {
 	// encoded state witness
 	State []byte
@@ -25,7 +27,7 @@ func uint32ToBytes32(v uint32) []byte {
 	return out[:]
 }
 
-func (wit *StepWitness) EncodeStepInput(localContext uint32) []byte {
+func (wit *StepWitness) EncodeStepInput(localContext LocalContext) []byte {
 	abiStateLen := len(wit.State)
 	if abiStateLen%32 != 0 {
 		abiStateLen += 32 - (abiStateLen % 32)
@@ -38,7 +40,7 @@ func (wit *StepWitness) EncodeStepInput(localContext uint32) []byte {
 	input = append(input, StepBytes4...)
 	input = append(input, uint32ToBytes32(32*3)...)                          // state data offset in bytes
 	input = append(input, uint32ToBytes32(32*3+32+uint32(len(abiState)))...) // proof data offset in bytes
-	input = append(input, uint32ToBytes32(localContext)...)                  // local context in bytes
+	input = append(input, uint32ToBytes32(uint32(localContext))...)          // local context in bytes
 
 	input = append(input, uint32ToBytes32(uint32(len(wit.State)))...) // state data length in bytes
 	input = append(input, abiState[:]...)
@@ -51,7 +53,7 @@ func (wit *StepWitness) HasPreimage() bool {
 	return wit.PreimageKey != ([32]byte{})
 }
 
-func (wit *StepWitness) EncodePreimageOracleInput(localContext uint32) ([]byte, error) {
+func (wit *StepWitness) EncodePreimageOracleInput(localContext LocalContext) ([]byte, error) {
 	if wit.PreimageKey == ([32]byte{}) {
 		return nil, errors.New("cannot encode pre-image oracle input, witness has no pre-image to proof")
 	}
@@ -64,7 +66,7 @@ func (wit *StepWitness) EncodePreimageOracleInput(localContext uint32) ([]byte,
 		var input []byte
 		input = append(input, LoadLocalDataBytes4...)
 		input = append(input, wit.PreimageKey[:]...)
-		input = append(input, uint32ToBytes32(localContext)...) // local context in bytes
+		input = append(input, uint32ToBytes32(uint32(localContext))...) // local context in bytes
 
 		preimagePart := wit.PreimageValue[8:]
 		var tmp [32]byte

op-challenger/game/fault/trace/cannon/updater_test.go

@@ -6,6 +6,7 @@ import (
 	"math/big"
 	"testing"
 
+	"github.com/ethereum-optimism/optimism/op-bindings/bindings"
 	"github.com/ethereum-optimism/optimism/op-challenger/game/fault/types"
 	"github.com/ethereum-optimism/optimism/op-service/testlog"
 
@@ -104,7 +105,9 @@ func TestCannonUpdater_BuildLocalOracleData(t *testing.T) {
 	txData, err := updater.BuildLocalOracleData(oracleData)
 	require.NoError(t, err)
 
-	var addLocalDataBytes4 = crypto.Keccak256([]byte("addLocalData(uint256,uint256,uint256)"))[:4]
+	fdgAbi, err := bindings.FaultDisputeGameMetaData.GetAbi()
+	require.NoError(t, err)
+	addLocalDataBytes4 := fdgAbi.Methods["addLocalData"].ID[:4]
 
 	// Pack the tx data manually.
 	var expected []byte