Force Interpreter VM when VM tracing requested.

Fixes https://github.com/ethereum/cpp-ethereum/issues/2585.

libethereum/State.cpp

@@ -1137,6 +1137,12 @@ bool State::isTrieGood(bool _enforceRefs, bool _requireNoLeftOvers) const
 
 ExecutionResult State::execute(LastHashes const& _lh, Transaction const& _t, Permanence _p, OnOpFunc const& _onOp)
 {
+	auto onOp = _onOp;
+#if ETH_VMTRACE
+	if (isChannelVisible<VMTraceChannel>())
+		onOp = Executive::simpleTrace(); // override tracer
+#endif
+
 #if ETH_PARANOIA
 	paranoia("start of execution.", true);
 	State old(*this);
@@ -1161,16 +1167,11 @@ ExecutionResult State::execute(LastHashes const& _lh, Transaction const& _t, Per
 	ctrace << toHex(e.t().rlp());
 #endif
 	if (!e.execute())
-#if ETH_VMTRACE
 	{
-		if (isChannelVisible<VMTraceChannel>())
-			e.go(e.simpleTrace());
-		else
-			e.go(_onOp);
+		if (onOp)
+			VMFactory::setKind(VMKind::Interpreter); // force interpreter if a trace is wanted
+		e.go(onOp);
 	}
-#else
-		e.go(_onOp);
-#endif
 	e.finalize();
 
 #if ETH_PARANOIA
@@ -1183,13 +1184,13 @@ ExecutionResult State::execute(LastHashes const& _lh, Transaction const& _t, Per
 	else
 	{
 		commit();
-	
+
 #if ETH_PARANOIA && !ETH_FATDB
 		ctrace << "Executed; now" << rootHash();
 		ctrace << old.diff(*this);
-	
+
 		paranoia("after execution commit.", true);
-	
+
 		if (e.t().receiveAddress())
 		{
 			EnforceRefs r(m_db, true);
@@ -1200,9 +1201,9 @@ ExecutionResult State::execute(LastHashes const& _lh, Transaction const& _t, Per
 			}
 		}
 #endif
-	
+
 		// TODO: CHECK TRIE after level DB flush to make sure exactly the same.
-	
+
 		// Add to the user-originated transactions that we've executed.
 		m_transactions.push_back(e.t());
 		m_receipts.push_back(TransactionReceipt(rootHash(), startGasUsed + e.gasUsed(), e.logs()));