Fixtures: Make fixture "vm json tests" use new function fixtureCallEvm

Move the EVM setup and call in fixtures "vm json tests" to new function
`fixtureCallEvm` in `call_evm`.  Extra return values needed for testing are
returned specially.

This entry point is different from all other `..CallEvm` type functions,
because it uses `executeOpcodes` instead of `execComputation`, so it doesn't
update the account balance or nonce on entry and exit from the EVM.

The new code is a bit redundant and simplistic intentionally, as the purpose is
to move functionality to `call_evm` with high confidence nothing really
changed.  The calls will be jointly refactored afterwards to merge differences.

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

nimbus/transaction/call_evm.nim

@@ -283,7 +283,7 @@ proc asmCallEvm*(blockNumber: Uint256, chainDB: BaseChainDB, code, data: seq[byt
   result.vmState         = c.vmState
   result.contractAddress = c.msg.contractAddress
 
-proc fixtureSetupComputation*(vmState: BaseVMState, call: RpcCallData, origin: EthAddress): Computation =
+proc fixtureSetupComputation(vmState: BaseVMState, call: RpcCallData, origin: EthAddress): Computation =
   vmState.setupTxContext(
     origin = origin,          # Differs from `rpcSetupComputation`
     gasPrice = call.gasPrice,
@@ -302,3 +302,28 @@ proc fixtureSetupComputation*(vmState: BaseVMState, call: RpcCallData, origin: E
   )
 
   return newComputation(vmState, msg)
+
+type
+  FixtureResult* = object
+    isError*:         bool
+    error*:           Error
+    gasRemaining*:    GasInt
+    output*:          seq[byte]
+    vmState*:         BaseVMState
+    logEntries*:      seq[Log]
+
+proc fixtureCallEvm*(vmState: BaseVMState, call: RpcCallData, origin: EthAddress): FixtureResult =
+  var c = fixtureSetupComputation(vmState, call, origin)
+
+  # Next line differs from all the other EVM calls.  With `execComputation`,
+  # most "vm json tests" fail with either `balanceDiff` or `nonceDiff` errors.
+  c.executeOpcodes()
+
+  # Some of these are extra returned state, for testing, that a normal EVMC API
+  # computation doesn't return.  We'll have to obtain them outside EVMC.
+  result.isError         = c.isError
+  result.error           = c.error
+  result.gasRemaining    = c.gasMeter.gasRemaining
+  result.output          = c.output
+  result.vmState         = c.vmState
+  shallowCopy(result.logEntries, c.logEntries)

tests/test_vm_json.nim

@@ -59,16 +59,15 @@ proc testFixture(fixtures: JsonNode, testStatusIMPL: var TestStatus) =
   # assume ZERO_ADDRESS is a contract creation
   call.contractCreation = (toAddress == ZERO_ADDRESS)
 
-  var computation = fixtureSetupComputation(vmState, call, origin)
-  computation.executeOpcodes()
+  var fixtureResult = fixtureCallEvm(vmState, call, origin)
 
   if not fixture{"post"}.isNil:
     # Success checks
-    check(not computation.isError)
-    if computation.isError:
-      echo "Computation error: ", computation.error.info
+    check(not fixtureResult.isError)
+    if fixtureResult.isError:
+      echo "Computation error: ", fixtureResult.error.info
 
-    let logEntries = computation.logEntries
+    let logEntries = fixtureResult.logEntries
     if not fixture{"logs"}.isNil:
       let actualLogsHash = hashLogEntries(logEntries)
       let expectedLogsHash = toLowerAscii(fixture{"logs"}.getStr)
@@ -78,21 +77,20 @@ proc testFixture(fixtures: JsonNode, testStatusIMPL: var TestStatus) =
       fail()
 
     let expectedOutput = fixture{"out"}.getStr
-    check(computation.output.bytesToHex == expectedOutput)
-    let gasMeter = computation.gasMeter
+    check(fixtureResult.output.bytesToHex == expectedOutput)
 
     let expectedGasRemaining = fixture{"gas"}.getHexadecimalInt
-    let actualGasRemaining = gasMeter.gasRemaining
+    let actualGasRemaining = fixtureResult.gasRemaining
     checkpoint(&"Remaining: {actualGasRemaining} - Expected: {expectedGasRemaining}")
     check(actualGasRemaining == expectedGasRemaining)
 
     if not fixture{"post"}.isNil:
-      verifyStateDb(fixture{"post"}, computation.vmState.readOnlyStateDB)
+      verifyStateDb(fixture{"post"}, fixtureResult.vmState.readOnlyStateDB)
   else:
     # Error checks
-    check(computation.isError)
+    check(fixtureResult.isError)
     if not fixture{"pre"}.isNil:
-      verifyStateDb(fixture{"pre"}, computation.vmState.readOnlyStateDB)
+      verifyStateDb(fixture{"pre"}, fixtureResult.vmState.readOnlyStateDB)
 
 when isMainModule:
   vmJsonMain()