incremental commit, manual changes to support merge

eth/ethconfig/config.go

@@ -186,3 +186,20 @@ func CreateConsensusEngine(config *params.ChainConfig, db ethdb.Database) (conse
 	}
 	return beacon.New(ethash.NewFaker()), nil
 }
+
+// CreateConsensusEngine creates a consensus engine for the given chain config.
+// Clique is allowed for now to live standalone, but ethash is forbidden and can
+// only exist on already merged networks.
+func CreateConsensusEngine(config *params.ChainConfig, db ethdb.Database) (consensus.Engine, error) {
+	// If proof-of-authority is requested, set it up
+	if config.Clique != nil {
+		return beacon.New(clique.New(config.Clique, db)), nil
+	}
+	// If defaulting to proof-of-work, enforce an already merged network since
+	// we cannot run PoW algorithms and more, so we cannot even follow a chain
+	// not coordinated by a beacon node.
+	if !config.TerminalTotalDifficultyPassed {
+		return nil, errors.New("ethash is only supported as a historical component of already merged networks")
+	}
+	return beacon.New(ethash.NewFaker()), nil
+}