Make global variable initialization consistent with Firefox and Safari

behavior.  Only force the introduction of a variable directly on the
global object if there is an explicit initial value in a variable
declaration.

BUG=http://crbug.com/12548
Review URL: http://codereview.chromium.org/151191

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@2326 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/runtime.cc

@@ -769,17 +769,23 @@ static Object* Runtime_InitializeVarGlobal(Arguments args) {
   PropertyAttributes attributes = DONT_DELETE;
 
   // Lookup the property locally in the global object. If it isn't
-  // there, we add the property and take special precautions to always
-  // add it as a local property even in case of callbacks in the
-  // prototype chain (this rules out using SetProperty).
-  // We have IgnoreAttributesAndSetLocalProperty for this.
+  // there, there is a property with this name in the prototype chain.
+  // We follow Safari and Firefox behavior and only set the property
+  // locally if there is an explicit initialization value that we have
+  // to assign to the property. When adding the property we take
+  // special precautions to always add it as a local property even in
+  // case of callbacks in the prototype chain (this rules out using
+  // SetProperty).  We have IgnoreAttributesAndSetLocalProperty for
+  // this.
   LookupResult lookup;
   global->LocalLookup(*name, &lookup);
   if (!lookup.IsProperty()) {
-    Object* value = (assign) ? args[1] : Heap::undefined_value();
-    return global->IgnoreAttributesAndSetLocalProperty(*name,
-                                                       value,
-                                                       attributes);
+    if (assign) {
+      return global->IgnoreAttributesAndSetLocalProperty(*name,
+                                                         args[1],
+                                                         attributes);
+    }
+    return Heap::undefined_value();
   }
 
   // Determine if this is a redeclaration of something read-only.

test/cctest/test-api.cc

@@ -7024,3 +7024,20 @@ THREADED_TEST(GetCallingContext) {
   calling_context1.Clear();
   calling_context2.Clear();
 }
+
+
+// Check that a variable declaration with no explicit initialization
+// value does not shadow an existing property in the prototype chain.
+//
+// This is consistent with Firefox and Safari.
+//
+// See http://crbug.com/12548.
+THREADED_TEST(InitGlobalVarInProtoChain) {
+  v8::HandleScope scope;
+  LocalContext context;
+  // Introduce a variable in the prototype chain.
+  CompileRun("__proto__.x = 42");
+  v8::Handle<v8::Value> result = CompileRun("var x; x");
+  CHECK(!result->IsUndefined());
+  CHECK_EQ(42, result->Int32Value());
+}

test/cctest/test-decls.cc

@@ -534,10 +534,10 @@ TEST(ExistsInPrototype) {
 
   { ExistsInPrototypeContext context;
     context.Check("var x; x",
-                  0,
+                  1,  // get
                   0,
                   1,  // declaration
-                  EXPECT_RESULT, Undefined());
+                  EXPECT_EXCEPTION);
   }
 
   { ExistsInPrototypeContext context;