fixes regression caused by recent changes in eth state handling

detected when running hive consensus simulator.
when processing an invalid block header and then
a new valid block header with the same block number,
the state root of the stateDB object should be updated
or reverted to parent stateRoot.

using intermediate stateRoot will trigger the hexary trie assertion.

nimbus/p2p/chain/chain_desc.nim

@@ -43,6 +43,7 @@ type
     forkIds: array[ChainFork, ForkID]
     blockZeroHash: KeccakHash
     lastBlockHash: KeccakHash
+    parentStateRoot: KeccakHash
 
     extraValidation: bool ##\
       ## Trigger extra validation, currently within `persistBlocks()`
@@ -227,6 +228,10 @@ proc lastBlockHash*(c: Chain): auto {.inline.} =
   ## Getter
   c.lastBlockHash
 
+proc parentStateRoot*(c: Chain): auto {.inline.} =
+  ## Getter
+  c.parentStateRoot
+
 proc currentBlock*(c: Chain): BlockHeader
   {.gcsafe, raises: [Defect,CatchableError].} =
   ## currentBlock retrieves the current head block of the canonical chain.
@@ -253,6 +258,10 @@ proc `lastBlockHash=`*(c: Chain; blockHash: KeccakHash) {.inline.} =
   ## Setter.
   c.lastBlockHash = blockHash
 
+proc `parentStateRoot=`*(c: Chain; stateRoot: KeccakHash) {.inline.} =
+  ## Setter.
+  c.parentStateRoot = stateRoot
+
 # ------------------------------------------------------------------------------
 # End
 # ------------------------------------------------------------------------------

nimbus/p2p/chain/persist_blocks.nim

@@ -51,14 +51,17 @@ proc persistBlocksImpl(c: Chain; headers: openarray[BlockHeader];
     let (header, body) = (headers[i], bodies[i])
 
     if header.parentHash != c.lastBlockHash:
-      # reinit the stateDB if there is some interruption
       let parent = c.db.getBlockHeader(header.parentHash)
-      c.db.initStateDB(parent.stateRoot)
+      c.parentStateRoot = parent.stateRoot
+      
+    # initStateDB will return the last known state
+    # if the stateRoot is match
+    c.db.initStateDB(c.parentStateRoot)
 
-    let
+    let 
       vmState = newBaseVMState(c.db.stateDB, header, c.db)
       validationResult = vmState.processBlock(c.clique, header, body)
-
+    
     when not defined(release):
       if validationResult == ValidationResult.Error and
          body.transactions.calcTxRoot == header.txRoot:
@@ -99,8 +102,9 @@ proc persistBlocksImpl(c: Chain; headers: openarray[BlockHeader];
     # so the rpc return consistent result
     # between eth_blockNumber and eth_syncing
     c.db.currentBlock = header.blockNumber
-
-  c.lastBlockHash = headers[^1].blockHash
+    c.lastBlockHash = header.blockHash
+    c.parentStateRoot = header.stateRoot
+    
   transaction.commit()
 
 # ------------------------------------------------------------------------------