Transaction: Prepare txRefundGas to support txCallEvm

There's only one call left to `refundGas(Transaction, ...)`, and the
similarity to the tail of `rpcEstimateGas` is obvious.

Gather this into `call_evm`: `refundGas` -> `txRefundGas`.

Signed-off-by: Jamie Lokier <jamie@shareable.org>

nimbus/p2p/executor.nim

@@ -72,7 +72,7 @@ proc processTransaction*(tx: Transaction, sender: EthAddress, vmState: BaseVMSta
 
     result = tx.gasLimit
     if not c.shouldBurnGas:
-      c.refundGas(tx, sender)
+      txRefundGas(tx, sender, c)
       result -= c.gasMeter.gasRemaining
 
   vmState.cumulativeGasUsed += result

nimbus/transaction/call_evm.nim

@@ -10,7 +10,8 @@ import
   eth/common/eth_types, stint, options, stew/byteutils,
   ".."/[vm_types, vm_types2, vm_state, vm_computation, utils],
   ".."/[db/db_chain, config, vm_state_transactions, rpc/hexstrings],
-  ".."/[db/accounts_cache, transaction, vm_precompiles, vm_gas_costs], eth/trie/db
+  ".."/[db/accounts_cache, transaction, vm_precompiles, vm_gas_costs], eth/trie/db,
+  ".."/vm_internals
 
 type
   RpcCallData* = object
@@ -172,3 +173,10 @@ proc txSetupComputation*(tx: Transaction, sender: EthAddress, vmState: BaseVMSta
 
   result = newComputation(vmState, msg)
   doAssert result.isOriginComputation
+
+proc txRefundGas*(tx: Transaction, sender: EthAddress, c: Computation) =
+  let maxRefund = (tx.gasLimit - c.gasMeter.gasRemaining) div 2
+  let refund = min(c.getGasRefund(), maxRefund)
+  c.gasMeter.returnGas(refund)
+  c.vmState.mutateStateDB:
+    db.addBalance(sender, c.gasMeter.gasRemaining.u256 * tx.gasPrice.u256)

nimbus/vm/state_transactions.nim

@@ -25,9 +25,3 @@ proc execComputation*(c: Computation) =
     c.vmState.touchedAccounts.incl c.touchedAccounts
 
   c.vmstate.status = c.isSuccess
-
-proc refundGas*(c: Computation, tx: Transaction, sender: EthAddress) =
-  let maxRefund = (tx.gasLimit - c.gasMeter.gasRemaining) div 2
-  c.gasMeter.returnGas min(c.getGasRefund(), maxRefund)
-  c.vmState.mutateStateDB:
-    db.addBalance(sender, c.gasMeter.gasRemaining.u256 * tx.gasPrice.u256)

nimbus/vm_state_transactions.nim

@@ -16,7 +16,6 @@ else:
     vm2/state_transactions as vmx
 
 export
-  vmx.execComputation,
-  vmx.refundGas
+  vmx.execComputation
 
 # End