core/types/bal: change code change type to list (#33774)

To align with the latest spec of EIP-7928:

```
# CodeChange: [block_access_index, new_code]
CodeChange = [BlockAccessIndex, Bytecode]
```

core/types/bal/bal.go

@@ -24,13 +24,6 @@ import (
 	"github.com/holiman/uint256"
 )
 
-// CodeChange contains the runtime bytecode deployed at an address and the
-// transaction index where the deployment took place.
-type CodeChange struct {
-	TxIndex uint16
-	Code    []byte `json:"code,omitempty"`
-}
-
 // ConstructionAccountAccess contains post-block account state for mutations as well as
 // all storage keys that were read during execution.  It is used when building block
 // access list during execution.
@@ -55,9 +48,9 @@ type ConstructionAccountAccess struct {
 	// by tx index.
 	NonceChanges map[uint16]uint64 `json:"nonceChanges,omitempty"`
 
-	// CodeChange is only set for contract accounts which were deployed in
-	// the block.
-	CodeChange *CodeChange `json:"codeChange,omitempty"`
+	// CodeChange contains the post-state contract code of an account keyed
+	// by tx index.
+	CodeChange map[uint16][]byte `json:"codeChange,omitempty"`
 }
 
 // NewConstructionAccountAccess initializes the account access object.
@@ -67,6 +60,7 @@ func NewConstructionAccountAccess() *ConstructionAccountAccess {
 		StorageReads:   make(map[common.Hash]struct{}),
 		BalanceChanges: make(map[uint16]*uint256.Int),
 		NonceChanges:   make(map[uint16]uint64),
+		CodeChange:     make(map[uint16][]byte),
 	}
 }
 
@@ -120,10 +114,8 @@ func (b *ConstructionBlockAccessList) CodeChange(address common.Address, txIndex
 	if _, ok := b.Accounts[address]; !ok {
 		b.Accounts[address] = NewConstructionAccountAccess()
 	}
-	b.Accounts[address].CodeChange = &CodeChange{
-		TxIndex: txIndex,
-		Code:    bytes.Clone(code),
-	}
+	// TODO(rjl493456442) is it essential to deep-copy the code?
+	b.Accounts[address].CodeChange[txIndex] = bytes.Clone(code)
 }
 
 // NonceChange records tx post-state nonce of any contract-like accounts whose
@@ -170,12 +162,11 @@ func (b *ConstructionBlockAccessList) Copy() *ConstructionBlockAccessList {
 		aaCopy.BalanceChanges = balances
 		aaCopy.NonceChanges = maps.Clone(aa.NonceChanges)
 
-		if aa.CodeChange != nil {
-			aaCopy.CodeChange = &CodeChange{
-				TxIndex: aa.CodeChange.TxIndex,
-				Code:    bytes.Clone(aa.CodeChange.Code),
-			}
+		codes := make(map[uint16][]byte, len(aa.CodeChange))
+		for index, code := range aa.CodeChange {
+			codes[index] = bytes.Clone(code)
 		}
+		aaCopy.CodeChange = codes
 		res.Accounts[addr] = &aaCopy
 	}
 	return &res

core/types/bal/bal_encoding.go

@@ -119,6 +119,13 @@ func (e *encodingSlotWrites) validate() error {
 	return errors.New("storage write tx indices not in order")
 }
 
+// encodingCodeChange contains the runtime bytecode deployed at an address
+// and the transaction index where the deployment took place.
+type encodingCodeChange struct {
+	TxIndex uint16 `ssz-size:"2"`
+	Code    []byte `ssz-max:"300000"` // TODO(rjl493456442) shall we put the limit here? The limit will be increased gradually
+}
+
 // AccountAccess is the encoding format of ConstructionAccountAccess.
 type AccountAccess struct {
 	Address        [20]byte                `ssz-size:"20"`    // 20-byte Ethereum address
@@ -126,7 +133,7 @@ type AccountAccess struct {
 	StorageReads   [][32]byte              `ssz-max:"300000"` // Read-only storage keys
 	BalanceChanges []encodingBalanceChange `ssz-max:"300000"` // Balance changes ([tx_index -> post_balance])
 	NonceChanges   []encodingAccountNonce  `ssz-max:"300000"` // Nonce changes ([tx_index -> new_nonce])
-	Code           []CodeChange            `ssz-max:"1"`      // Code changes ([tx_index -> new_code])
+	CodeChanges    []encodingCodeChange    `ssz-max:"300000"` // Code changes ([tx_index -> new_code])
 }
 
 // validate converts the account accesses out of encoding format.
@@ -166,9 +173,16 @@ func (e *AccountAccess) validate() error {
 		return errors.New("nonce changes not in ascending order by tx index")
 	}
 
-	// Convert code change
-	if len(e.Code) == 1 {
-		if len(e.Code[0].Code) > params.MaxCodeSize {
+	// Check the code changes are sorted in order
+	if !slices.IsSortedFunc(e.CodeChanges, func(a, b encodingCodeChange) int {
+		return cmp.Compare[uint16](a.TxIndex, b.TxIndex)
+	}) {
+		return errors.New("code changes not in ascending order by tx index")
+	}
+	for _, change := range e.CodeChanges {
+		// TODO(rjl493456442): This check should be fork-aware, since the limit may
+		// differ across forks.
+		if len(change.Code) > params.MaxCodeSize {
 			return errors.New("code change contained oversized code")
 		}
 	}
@@ -182,6 +196,8 @@ func (e *AccountAccess) Copy() AccountAccess {
 		StorageReads:   slices.Clone(e.StorageReads),
 		BalanceChanges: slices.Clone(e.BalanceChanges),
 		NonceChanges:   slices.Clone(e.NonceChanges),
+		StorageWrites:  make([]encodingSlotWrites, 0, len(e.StorageWrites)),
+		CodeChanges:    make([]encodingCodeChange, 0, len(e.CodeChanges)),
 	}
 	for _, storageWrite := range e.StorageWrites {
 		res.StorageWrites = append(res.StorageWrites, encodingSlotWrites{
@@ -189,13 +205,11 @@ func (e *AccountAccess) Copy() AccountAccess {
 			Accesses: slices.Clone(storageWrite.Accesses),
 		})
 	}
-	if len(e.Code) == 1 {
-		res.Code = []CodeChange{
-			{
-				e.Code[0].TxIndex,
-				bytes.Clone(e.Code[0].Code),
-			},
-		}
+	for _, codeChange := range e.CodeChanges {
+		res.CodeChanges = append(res.CodeChanges, encodingCodeChange{
+			TxIndex: codeChange.TxIndex,
+			Code:    bytes.Clone(codeChange.Code),
+		})
 	}
 	return res
 }
@@ -212,11 +226,11 @@ var _ rlp.Encoder = &ConstructionBlockAccessList{}
 func (a *ConstructionAccountAccess) toEncodingObj(addr common.Address) AccountAccess {
 	res := AccountAccess{
 		Address:        addr,
-		StorageWrites:  make([]encodingSlotWrites, 0),
-		StorageReads:   make([][32]byte, 0),
-		BalanceChanges: make([]encodingBalanceChange, 0),
-		NonceChanges:   make([]encodingAccountNonce, 0),
-		Code:           nil,
+		StorageWrites:  make([]encodingSlotWrites, 0, len(a.StorageWrites)),
+		StorageReads:   make([][32]byte, 0, len(a.StorageReads)),
+		BalanceChanges: make([]encodingBalanceChange, 0, len(a.BalanceChanges)),
+		NonceChanges:   make([]encodingAccountNonce, 0, len(a.NonceChanges)),
+		CodeChanges:    make([]encodingCodeChange, 0, len(a.CodeChange)),
 	}
 
 	// Convert write slots
@@ -268,13 +282,13 @@ func (a *ConstructionAccountAccess) toEncodingObj(addr common.Address) AccountAc
 	}
 
 	// Convert code change
-	if a.CodeChange != nil {
-		res.Code = []CodeChange{
-			{
-				a.CodeChange.TxIndex,
-				bytes.Clone(a.CodeChange.Code),
-			},
-		}
+	codeIndices := slices.Collect(maps.Keys(a.CodeChange))
+	slices.SortFunc(codeIndices, cmp.Compare[uint16])
+	for _, idx := range codeIndices {
+		res.CodeChanges = append(res.CodeChanges, encodingCodeChange{
+			TxIndex: idx,
+			Code:    a.CodeChange[idx],
+		})
 	}
 	return res
 }
@@ -327,9 +341,9 @@ func (e *BlockAccessList) PrettyPrint() string {
 			printWithIndent(2, fmt.Sprintf("%d: %d", change.TxIdx, change.Nonce))
 		}
 
-		if len(accountDiff.Code) > 0 {
-			printWithIndent(1, "code:")
-			printWithIndent(2, fmt.Sprintf("%d: %x", accountDiff.Code[0].TxIndex, accountDiff.Code[0].Code))
+		printWithIndent(1, "code changes:")
+		for _, change := range accountDiff.CodeChanges {
+			printWithIndent(2, fmt.Sprintf("%d: %x", change.TxIndex, change.Code))
 		}
 	}
 	return res.String()

core/types/bal/bal_encoding_rlp_generated.go

@@ -49,7 +49,7 @@ func (obj *BlockAccessList) EncodeRLP(_w io.Writer) error {
 		}
 		w.ListEnd(_tmp15)
 		_tmp18 := w.List()
-		for _, _tmp19 := range _tmp2.Code {
+		for _, _tmp19 := range _tmp2.CodeChanges {
 			_tmp20 := w.List()
 			w.WriteUint64(uint64(_tmp19.TxIndex))
 			w.WriteBytes(_tmp19.Code)
@@ -228,13 +228,13 @@ func (obj *BlockAccessList) DecodeRLP(dec *rlp.Stream) error {
 					return err
 				}
 				_tmp2.NonceChanges = _tmp17
-				// Code:
-				var _tmp21 []CodeChange
+				// CodeChanges:
+				var _tmp21 []encodingCodeChange
 				if _, err := dec.List(); err != nil {
 					return err
 				}
 				for dec.MoreDataInList() {
-					var _tmp22 CodeChange
+					var _tmp22 encodingCodeChange
 					{
 						if _, err := dec.List(); err != nil {
 							return err
@@ -260,7 +260,7 @@ func (obj *BlockAccessList) DecodeRLP(dec *rlp.Stream) error {
 				if err := dec.ListEnd(); err != nil {
 					return err
 				}
-				_tmp2.Code = _tmp21
+				_tmp2.CodeChanges = _tmp21
 				if err := dec.ListEnd(); err != nil {
 					return err
 				}

core/types/bal/bal_test.go

@@ -60,9 +60,8 @@ func makeTestConstructionBAL() *ConstructionBlockAccessList {
 					1: 2,
 					2: 6,
 				},
-				CodeChange: &CodeChange{
-					TxIndex: 0,
-					Code:    common.Hex2Bytes("deadbeef"),
+				CodeChange: map[uint16][]byte{
+					0: common.Hex2Bytes("deadbeef"),
 				},
 			},
 			common.BytesToAddress([]byte{0xff, 0xff, 0xff}): {
@@ -85,6 +84,9 @@ func makeTestConstructionBAL() *ConstructionBlockAccessList {
 				NonceChanges: map[uint16]uint64{
 					1: 2,
 				},
+				CodeChange: map[uint16][]byte{
+					0: common.Hex2Bytes("deadbeef"),
+				},
 			},
 		},
 	}
@@ -179,7 +181,7 @@ func makeTestAccountAccess(sort bool) AccountAccess {
 		StorageReads:   storageReads,
 		BalanceChanges: balances,
 		NonceChanges:   nonces,
-		Code: []CodeChange{
+		CodeChanges: []encodingCodeChange{
 			{
 				TxIndex: 100,
 				Code:    testrand.Bytes(256),