vm: fix property descriptors of sandbox properties

The GlobalPropertyQueryCallback was changed in 2010 to return an
integer instead of a boolean:

https://groups.google.com/forum/#!topic/v8-users/OOjHJrix-cU

This integer communicates the property descriptors of the property,
instead of just its presence or absence. However, the original
contextify code was probably written before this change, and it was
not updated when porting to Node.js.

Credit to @smikes for the test and the original PR of #885.

Fixes: https://github.com/nodejs/io.js/pull/864
Fixes: https://github.com/nodejs/io.js/pull/885
PR-URL: https://github.com/nodejs/io.js/pull/1773
Reviewed-By: Fedor Indutny <fedor@indutny.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

src/node_contextify.cc

@@ -30,6 +30,7 @@ using v8::None;
 using v8::Object;
 using v8::ObjectTemplate;
 using v8::Persistent;
+using v8::PropertyAttribute;
 using v8::PropertyCallbackInfo;
 using v8::Script;
 using v8::ScriptCompiler;
@@ -406,10 +407,15 @@ class ContextifyContext {
     Local<Object> proxy_global = PersistentToLocal(isolate,
                                                    ctx->proxy_global_);
 
-    bool in_sandbox = sandbox->GetRealNamedProperty(property).IsEmpty();
-    bool in_proxy_global =
-        proxy_global->GetRealNamedProperty(property).IsEmpty();
-    if (!in_sandbox || !in_proxy_global) {
+    if (sandbox->HasRealNamedProperty(property)) {
+      PropertyAttribute propAttr =
+          sandbox->GetRealNamedPropertyAttributes(property).FromJust();
+      args.GetReturnValue().Set(propAttr);
+    } else if (proxy_global->HasRealNamedProperty(property)) {
+      PropertyAttribute propAttr =
+          proxy_global->GetRealNamedPropertyAttributes(property).FromJust();
+      args.GetReturnValue().Set(propAttr);
+    } else {
       args.GetReturnValue().Set(None);
     }
   }

test/parallel/test-vm-preserves-property.js

@@ -0,0 +1,25 @@
+'use strict';
+
+var common = require('../common');
+var assert = require('assert');
+
+var vm = require('vm');
+
+var x = {};
+Object.defineProperty(x, 'prop', {
+  configurable: false,
+  enumerable: false,
+  writable: false,
+  value: 'val'
+});
+var o = vm.createContext(x);
+
+var code = 'Object.getOwnPropertyDescriptor(this, "prop")';
+var res = vm.runInContext(code, o, 'test');
+
+assert(res);
+assert.equal(typeof res, 'object');
+assert.equal(res.value, 'val');
+assert.equal(res.configurable, false, 'should not be configurable');
+assert.equal(res.enumerable, false, 'should not be enumerable');
+assert.equal(res.writable, false, 'should not be writable');