Fix TotalDifficulty for post-merge networks in genesis

src/Nethermind/Nethermind.Merge.Plugin.Test/EngineModuleTests.Synchronization.cs

@@ -77,6 +77,8 @@ public async Task forkChoiceUpdatedV1_unknown_block_initiates_syncing()
         chain.BeaconSync.IsBeaconSyncHeadersFinished().Should().BeFalse();
         chain.BeaconSync.IsBeaconSyncFinished(chain.BlockTree.FindBlock(block.Hash!)?.Header).Should().BeFalse();
         AssertBeaconPivotValues(chain.BeaconPivot, block.Header);
+
+        block.Header.TotalDifficulty = 0;
         pointers.LowestInsertedBeaconHeader = block.Header;
         pointers.BestKnownBeaconBlock = block.Number;
         pointers.LowestInsertedHeader = block.Header;
@@ -151,6 +153,7 @@ public async Task forkChoiceUpdatedV1_unknown_block_parent_while_syncing_initiat
         chain.BeaconSync.IsBeaconSyncFinished(chain.BlockTree.FindBlock(block.Hash!)?.Header).Should().BeFalse();
         AssertBeaconPivotValues(chain.BeaconPivot, block.Header);
 
+        block.Header.TotalDifficulty = 0;
         pointers.LowestInsertedBeaconHeader = block.Header;
         pointers.BestKnownBeaconBlock = block.Number;
         pointers.LowestInsertedHeader = block.Header;
@@ -167,6 +170,7 @@ public async Task forkChoiceUpdatedV1_unknown_block_parent_while_syncing_initiat
         chain.BeaconSync.IsBeaconSyncFinished(chain.BlockTree.FindBlock(nextUnconnectedBlock.Hash!)?.Header).Should().BeFalse();
         AssertBeaconPivotValues(chain.BeaconPivot, nextUnconnectedBlock.Header);
 
+        nextUnconnectedBlock.Header.TotalDifficulty = 0;
         pointers.LowestInsertedBeaconHeader = nextUnconnectedBlock.Header;
         pointers.BestKnownBeaconBlock = nextUnconnectedBlock.Number;
         AssertBlockTreePointers(chain.BlockTree, pointers);
@@ -967,7 +971,7 @@ private void AssertBeaconPivotValues(IBeaconPivot beaconPivot, BlockHeader block
         beaconPivot.BeaconPivotExists().Should().BeTrue();
         beaconPivot.PivotNumber.Should().Be(blockHeader.Number);
         beaconPivot.PivotHash.Should().Be(blockHeader.Hash ?? blockHeader.CalculateHash());
-        beaconPivot.PivotTotalDifficulty.Should().Be(null);
+        beaconPivot.PivotTotalDifficulty.Should().Be((UInt256)0);
     }
 
     private class BlockTreePointers

src/Nethermind/Nethermind.Merge.Plugin.Test/PoSSwitcherTests.cs

@@ -2,6 +2,7 @@
 // SPDX-License-Identifier: LGPL-3.0-only
 
 using System.IO;
+using FluentAssertions;
 using Nethermind.Blockchain;
 using Nethermind.Blockchain.Synchronization;
 using Nethermind.Core;
@@ -222,6 +223,45 @@ public void Can_load_parameters_after_the_restart()
             Assert.That(newPoSSwitcher.HasEverReachedTerminalBlock(), Is.EqualTo(true));
         }
 
+        [Test]
+        public void No_final_difficulty_if_conditions_are_not_met()
+        {
+            AssertFinalTotalDifficulty(10005, 10000, 10000, null);
+        }
+
+        [TestCase(0, 1)]
+        [TestCase(0, 0)]
+        [TestCase(5000, 6000)]
+        public void Can_set_final_total_difficulty_for_post_merge_networks(long ttd, long genesisDifficulty)
+        {
+            AssertFinalTotalDifficulty(ttd, genesisDifficulty, null, genesisDifficulty);
+        }
+
+        [TestCase(0, 1)]
+        [TestCase(0, 0)]
+        [TestCase(5000, 6000)]
+        public void Can_set_final_total_difficulty_based_on_sync_pivot(long ttd, long pivotTotalDifficulty)
+        {
+            AssertFinalTotalDifficulty(ttd, 0, pivotTotalDifficulty, pivotTotalDifficulty);
+        }
+
+        private void AssertFinalTotalDifficulty(long ttd, long genesisDifficulty, long? pivotTotalDifficulty, long? expectedFinalTotalDifficulty)
+        {
+            TestSpecProvider specProvider = new(London.Instance);
+            specProvider.TerminalTotalDifficulty = (UInt256)ttd;
+            Block genesisBlock = Build.A.Block.WithNumber(0).WithDifficulty((UInt256)genesisDifficulty).TestObject;
+            BlockTree blockTree = Build.A.BlockTree(genesisBlock, specProvider).OfChainLength(4).TestObject;
+            SyncConfig syncConfig = new();
+            if (pivotTotalDifficulty != null)
+                syncConfig = new SyncConfig() { PivotTotalDifficulty = $"{(UInt256)pivotTotalDifficulty}" };
+            PoSSwitcher poSSwitcher = new PoSSwitcher(new MergeConfig(), syncConfig, new MemDb(), blockTree, specProvider, LimboLogs.Instance);
+            if (expectedFinalTotalDifficulty != null)
+                poSSwitcher.FinalTotalDifficulty.Should().Be((UInt256)expectedFinalTotalDifficulty);
+            else
+                poSSwitcher.FinalTotalDifficulty.Should().BeNull();
+        }
+
+
         private static PoSSwitcher CreatePosSwitcher(IBlockTree blockTree, IDb? db = null, ISpecProvider? specProvider = null)
         {
             db ??= new MemDb();

src/Nethermind/Nethermind.Merge.Plugin/PoSSwitcher.cs

@@ -88,11 +88,22 @@ private void LoadFinalTotalDifficulty()
         {
             _finalTotalDifficulty = _mergeConfig.FinalTotalDifficultyParsed;
 
+            if (TerminalTotalDifficulty is null)
+                return;
+
             // pivot post TTD, so we know FinalTotalDifficulty
-            if (_syncConfig.PivotTotalDifficultyParsed != 0 && TerminalTotalDifficulty is not null && _syncConfig.PivotTotalDifficultyParsed >= TerminalTotalDifficulty)
+            if (_syncConfig.PivotTotalDifficultyParsed != 0 && _syncConfig.PivotTotalDifficultyParsed >= TerminalTotalDifficulty)
             {
                 _finalTotalDifficulty = _syncConfig.PivotTotalDifficultyParsed;
             }
+            else
+            {
+                UInt256 genesisDifficulty = _blockTree.Genesis?.Difficulty ?? 0;
+                if (genesisDifficulty >= TerminalTotalDifficulty) // networks with the merge in genesis
+                {
+                    _finalTotalDifficulty = genesisDifficulty;
+                }
+            }
         }
 
         private void CheckIfTerminalBlockReached(object? sender, BlockEventArgs e)

src/Nethermind/Nethermind.Runner/configs/holesky.cfg

@@ -26,7 +26,6 @@
         "EngineEnabledModules": "net,eth,subscribe,engine,web3,client"
     },
     "Merge": {
-        "Enabled": true,
-        "FinalTotalDifficulty": "1"
+        "Enabled": true
     }
 }

src/Nethermind/Nethermind.Runner/configs/holesky_archive.cfg

@@ -27,7 +27,6 @@
         "EngineEnabledModules": "net,eth,subscribe,engine,web3,client"
     },
     "Merge": {
-        "Enabled": true,
-        "FinalTotalDifficulty": "1"
+        "Enabled": true
     }
 }