op-node/rollup/derive: Add L2BlockToBlockRef

This is similar to PayloadToBlockRef but takes an interface instead that
e.g. a types.Block fulfills. This way, we can directly extract L2BlockRefs
from type.Blocks that have a valid L1 Info Deposit tx as first tx.

A block could also be converted into an ExecutionPayload, but this would make an
inefficient roundtrip, marshalling and unmarshalling all transactions.

op-node/rollup/derive/l2block_util.go

+package derive
+
+import (
+	"fmt"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/core/types"
+
+	"github.com/ethereum-optimism/optimism/op-node/eth"
+	"github.com/ethereum-optimism/optimism/op-node/rollup"
+)
+
+// L2BlockRefSource is a source for the generation of a L2BlockRef. E.g. a
+// *types.Block is a L2BlockRefSource.
+//
+// L2BlockToBlockRef extracts L2BlockRef from a L2BlockRefSource. The first
+// transaction of a source must be a Deposit transaction.
+type L2BlockRefSource interface {
+	Hash() common.Hash
+	ParentHash() common.Hash
+	NumberU64() uint64
+	Time() uint64
+	Transactions() types.Transactions
+}
+
+// PayloadToBlockRef extracts the essential L2BlockRef information from an L2
+// block ref source, falling back to genesis information if necessary.
+func L2BlockToBlockRef(block L2BlockRefSource, genesis *rollup.Genesis) (eth.L2BlockRef, error) {
+	hash, number := block.Hash(), block.NumberU64()
+
+	var l1Origin eth.BlockID
+	var sequenceNumber uint64
+	if number == genesis.L2.Number {
+		if hash != genesis.L2.Hash {
+			return eth.L2BlockRef{}, fmt.Errorf("expected L2 genesis hash to match L2 block at genesis block number %d: %s <> %s", genesis.L2.Number, hash, genesis.L2.Hash)
+		}
+		l1Origin = genesis.L1
+		sequenceNumber = 0
+	} else {
+		txs := block.Transactions()
+		if txs.Len() == 0 {
+			return eth.L2BlockRef{}, fmt.Errorf("l2 block is missing L1 info deposit tx, block hash: %s", hash)
+		}
+		tx := txs[0]
+		if tx.Type() != types.DepositTxType {
+			return eth.L2BlockRef{}, fmt.Errorf("first payload tx has unexpected tx type: %d", tx.Type())
+		}
+		info, err := L1InfoDepositTxData(tx.Data())
+		if err != nil {
+			return eth.L2BlockRef{}, fmt.Errorf("failed to parse L1 info deposit tx from L2 block: %w", err)
+		}
+		l1Origin = eth.BlockID{Hash: info.BlockHash, Number: info.Number}
+		sequenceNumber = info.SequenceNumber
+	}
+
+	return eth.L2BlockRef{
+		Hash:           hash,
+		Number:         number,
+		ParentHash:     block.ParentHash(),
+		Time:           block.Time(),
+		L1Origin:       l1Origin,
+		SequenceNumber: sequenceNumber,
+	}, nil
+}