vm: accept only object as arg of .createContext()

Converting strings and others to objects is very slow and essentially
wrong.

src/node_script.cc

@@ -257,9 +257,14 @@ Handle<Value> WrappedScript::CreateContext(const Arguments& args) {
   Local<Object> context = WrappedContext::NewInstance();
 
   if (args.Length() > 0) {
-    Local<Object> sandbox = args[0]->ToObject();
+    if (args[0]->IsObject()) {
+      Local<Object> sandbox = args[0].As<Object>();
 
-    CloneObject(args.This(), sandbox, context);
+      CloneObject(args.This(), sandbox, context);
+    } else {
+      return ThrowException(Exception::TypeError(String::New(
+          "createContext() accept only object as first argument.")));
+    }
   }
 
 

test/simple/test-vm-create-context-arg.js

@@ -0,0 +1,33 @@
+// Copyright Joyent, Inc. and other Node contributors.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the
+// "Software"), to deal in the Software without restriction, including
+// without limitation the rights to use, copy, modify, merge, publish,
+// distribute, sublicense, and/or sell copies of the Software, and to permit
+// persons to whom the Software is furnished to do so, subject to the
+// following conditions:
+//
+// The above copyright notice and this permission notice shall be included
+// in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
+// NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
+// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
+// USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+var common = require('../common');
+var assert = require('assert');
+var vm = require('vm');
+
+assert.throws(function() {
+  var ctx = vm.createContext('string is not supported');
+});
+
+assert.doesNotThrow(function() {
+  var ctx = vm.createContext({ a: 1 });
+  ctx = vm.createContext([0, 1, 2, 3]);
+});