consensus/beacon: remove TestingTTDBlock (#31153)

This removes the method `TestingTTDBlock` introduced by #30744. It was
added to make the beacon consensus engine aware of the merge block in
tests without relying on the total difficulty. However, tracking the
merge block this way is very annoying. We usually configure forks in the
`ChainConfig`, but the method is on the consensus engine, which isn't
always created in the same place. By sidestepping the `ChainConfig` we
don't get the usual fork-order checking, so it's possible to enable the
merge before the London fork, for example. This in turn can lead to very
hard-to-debug outputs and validation errors.

So here I'm changing the consensus engine to check the
`MergeNetsplitBlock` instead. Alternatively, we assume a network is
merged if it has a `TerminalTotalDifficulty` of zero, which is a very
common configuration in tests.

consensus/beacon/consensus.go

@@ -61,8 +61,7 @@ var (
 // is only used for necessary consensus checks. The legacy consensus engine can be any
 // engine implements the consensus interface (except the beacon itself).
 type Beacon struct {
-	ethone   consensus.Engine // Original consensus engine used in eth1, e.g. ethash or clique
-	ttdblock *uint64          // Merge block-number for testchain generation without TTDs
+	ethone consensus.Engine // Original consensus engine used in eth1, e.g. ethash or clique
 }
 
 // New creates a consensus engine with the given embedded eth1 engine.
@@ -73,16 +72,12 @@ func New(ethone consensus.Engine) *Beacon {
 	return &Beacon{ethone: ethone}
 }
 
-// TestingTTDBlock is a replacement mechanism for TTD-based pre-/post-merge
-// splitting. With chain history deletion, TD calculations become impossible.
-// This is fine for progressing the live chain, but to be able to generate test
-// chains, we do need a split point. This method supports setting an explicit
-// block number to use as the splitter *for testing*, instead of having to keep
-// the notion of TDs in the client just for testing.
-//
-// The block with supplied number is regarded as the last pre-merge block.
-func (beacon *Beacon) TestingTTDBlock(number uint64) {
-	beacon.ttdblock = &number
+// isPostMerge reports whether the given block number is assumed to be post-merge.
+// Here we check the MergeNetsplitBlock to allow configuring networks with a PoW or
+// PoA chain for unit testing purposes.
+func isPostMerge(config *params.ChainConfig, block uint64) bool {
+	mergedAtGenesis := config.TerminalTotalDifficulty != nil && config.TerminalTotalDifficulty.Sign() == 0
+	return mergedAtGenesis || config.MergeNetsplitBlock != nil && block >= config.MergeNetsplitBlock.Uint64()
 }
 
 // Author implements consensus.Engine, returning the verified author of the block.
@@ -332,15 +327,7 @@ func (beacon *Beacon) verifyHeaders(chain consensus.ChainHeaderReader, headers [
 // Prepare implements consensus.Engine, initializing the difficulty field of a
 // header to conform to the beacon protocol. The changes are done inline.
 func (beacon *Beacon) Prepare(chain consensus.ChainHeaderReader, header *types.Header) error {
-	// The beacon engine requires access to total difficulties to be able to
-	// seal pre-merge and post-merge blocks. With the transition to removing
-	// old blocks, TDs become unaccessible, thus making TTD based pre-/post-
-	// merge decisions impossible.
-	//
-	// We do not need to seal non-merge blocks anymore live, but we do need
-	// to be able to generate test chains, thus we're reverting to a testing-
-	// settable field to direct that.
-	if beacon.ttdblock != nil && *beacon.ttdblock >= header.Number.Uint64() {
+	if !isPostMerge(chain.Config(), header.Number.Uint64()) {
 		return beacon.ethone.Prepare(chain, header)
 	}
 	header.Difficulty = beaconDifficulty
@@ -450,15 +437,7 @@ func (beacon *Beacon) SealHash(header *types.Header) common.Hash {
 // the difficulty that a new block should have when created at time
 // given the parent block's time and difficulty.
 func (beacon *Beacon) CalcDifficulty(chain consensus.ChainHeaderReader, time uint64, parent *types.Header) *big.Int {
-	// The beacon engine requires access to total difficulties to be able to
-	// seal pre-merge and post-merge blocks. With the transition to removing
-	// old blocks, TDs become unaccessible, thus making TTD based pre-/post-
-	// merge decisions impossible.
-	//
-	// We do not need to seal non-merge blocks anymore live, but we do need
-	// to be able to generate test chains, thus we're reverting to a testing-
-	// settable field to direct that.
-	if beacon.ttdblock != nil && *beacon.ttdblock > parent.Number.Uint64() {
+	if !isPostMerge(chain.Config(), parent.Number.Uint64()+1) {
 		return beacon.ethone.CalcDifficulty(chain, time, parent)
 	}
 	return beaconDifficulty

eth/catalyst/api_test.go

@@ -64,9 +64,12 @@ func generateMergeChain(n int, merged bool) (*core.Genesis, []*types.Block) {
 	engine := beacon.New(ethash.NewFaker())
 	if merged {
 		config.TerminalTotalDifficulty = common.Big0
+		config.MergeNetsplitBlock = common.Big0
 	} else {
-		engine.TestingTTDBlock(uint64(n))
+		// When !merged, the tests expect the next block after the generated chain to be in PoS.
+		config.MergeNetsplitBlock = big.NewInt(int64(n + 1))
 	}
+
 	genesis := &core.Genesis{
 		Config: &config,
 		Alloc: types.GenesisAlloc{

eth/gasprice/gasprice_test.go

@@ -147,11 +147,11 @@ func newTestBackend(t *testing.T, londonBlock *big.Int, cancunBlock *big.Int, pe
 	config.LondonBlock = londonBlock
 	config.ArrowGlacierBlock = londonBlock
 	config.GrayGlacierBlock = londonBlock
-
+	if cancunBlock != nil {
+		// Enable the merge with cancun fork.
+		config.MergeNetsplitBlock = cancunBlock
+	}
 	engine := beacon.New(ethash.NewFaker())
-	engine.TestingTTDBlock(testHead + 1)
-
-	td := params.GenesisDifficulty.Uint64()
 
 	if cancunBlock != nil {
 		ts := gspec.Timestamp + cancunBlock.Uint64()*10 // fixed 10 sec block time in blockgen
@@ -209,10 +209,9 @@ func newTestBackend(t *testing.T, londonBlock *big.Int, cancunBlock *big.Int, pe
 				b.AddTx(types.MustSignNewTx(key, signer, blobTx))
 			}
 		}
-		td += b.Difficulty().Uint64()
 	})
+
 	// Construct testing chain
-	gspec.Config.TerminalTotalDifficulty = new(big.Int).SetUint64(td)
 	chain, err := core.NewBlockChain(db, &core.CacheConfig{TrieCleanNoPrefetch: true}, gspec, nil, engine, vm.Config{}, nil)
 	if err != nil {
 		t.Fatalf("Failed to create local chain, %v", err)

eth/protocols/eth/handler_test.go

@@ -74,9 +74,7 @@ func newTestBackendWithGenerator(blocks int, shanghai bool, generator func(int,
 		config = params.TestChainConfig
 		engine = beacon.New(ethash.NewFaker())
 	)
-	if !shanghai {
-		engine.TestingTTDBlock(math.MaxUint64)
-	} else {
+	if shanghai {
 		config = &params.ChainConfig{
 			ChainID:                 big.NewInt(1),
 			HomesteadBlock:          big.NewInt(0),

eth/tracers/internal/tracetest/supply_test.go

@@ -75,8 +75,6 @@ func TestSupplyOmittedFields(t *testing.T) {
 		}
 	)
 
-	gspec.Config.TerminalTotalDifficulty = big.NewInt(0)
-
 	out, _, err := testSupplyTracer(t, gspec, func(b *core.BlockGen) {
 		b.SetPoS()
 	})
@@ -546,7 +544,6 @@ func TestSupplySelfdestructItselfAndRevert(t *testing.T) {
 
 func testSupplyTracer(t *testing.T, genesis *core.Genesis, gen func(*core.BlockGen)) ([]supplyInfo, *core.BlockChain, error) {
 	engine := beacon.New(ethash.NewFaker())
-	engine.TestingTTDBlock(1)
 
 	traceOutputPath := filepath.ToSlash(t.TempDir())
 	traceOutputFilename := path.Join(traceOutputPath, "supply.jsonl")

graphql/graphql_test.go

@@ -21,7 +21,6 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
-	"math"
 	"math/big"
 	"net/http"
 	"strings"
@@ -459,15 +458,13 @@ func newGQLService(t *testing.T, stack *node.Node, shanghai bool, gspec *core.Ge
 	var engine = beacon.New(ethash.NewFaker())
 	if shanghai {
 		gspec.Config.TerminalTotalDifficulty = common.Big0
+		gspec.Config.MergeNetsplitBlock = common.Big0
 		// GenerateChain will increment timestamps by 10.
 		// Shanghai upgrade at block 1.
 		shanghaiTime := uint64(5)
 		gspec.Config.ShanghaiTime = &shanghaiTime
-	} else {
-		// set an arbitrary large ttd as chains are required to be known to be merged
-		gspec.Config.TerminalTotalDifficulty = big.NewInt(math.MaxInt64)
-		engine.TestingTTDBlock(math.MaxUint64)
 	}
+
 	ethBackend, err := eth.New(stack, ethConf)
 	if err != nil {
 		t.Fatalf("could not create eth backend: %v", err)