Ensure correct enumeration indices in the dict

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index 57882a4d20a0f8f3a64c9919c39d94c86f64df30..34d3364cfb159434827d3d7206d24b81d3b8d61f 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -487,11 +487,20 @@ MaybeObject* JSObject::SetNormalizedProperty(String* name,
     set_properties(StringDictionary::cast(dict));
     return value;
   }
-  // Preserve enumeration index.
+
+  PropertyDetails original_details = property_dictionary()->DetailsAt(entry);
+  int enumeration_index;
+  // Preserve the enumeration index unless the property was deleted.
+  if (original_details.IsDeleted()) {
+    enumeration_index = property_dictionary()->NextEnumerationIndex();
+    property_dictionary()->SetNextEnumerationIndex(enumeration_index + 1);
+  } else {
+    enumeration_index = original_details.dictionary_index();
+    ASSERT(enumeration_index != 0);
+  }
+
   details = PropertyDetails(
-      details.attributes(),
-      details.type(),
-      property_dictionary()->DetailsAt(entry).dictionary_index());
+      details.attributes(), details.type(), enumeration_index);
 
   if (IsGlobalObject()) {
     JSGlobalPropertyCell* cell =
@@ -9392,8 +9401,15 @@ MaybeObject* JSObject::SetDictionaryElement(uint32_t index,
       // is read-only (a declared const that has not been initialized).  If a
       // value is being defined we skip attribute checks completely.
       if (set_mode == DEFINE_PROPERTY) {
+        int enumeration_index;
+        if (details.dictionary_index() == 0 && !(attributes & DONT_ENUM)) {

[Michael Starzinger, 2012/09/12 17:06:55]

Why do we check for DONT_ENUM here? Do we do that anywhere else in the code? If
not I would just allocate enumeration indices. If we change the DONT_ENUM
attribute after the fact, the enumeration order will be screwed up because we
didn't hand out an index when the property was defined.

However I am not sure if my comment even applies to elements as opposed to
properties.

Also I don't understand why we check for dictionary_index == 0 instead of
IsDeleted() here. Shouldn't the invariant be that every non-deleted property has
a valid enumeration index?

[Toon Verwaest, 2012/09/13 08:46:32]

You are right, this code is unnecessary for elements. It just invalidly
triggered the ASSERT in DetailsAtPut, which is now removed. We only have to
ensure enumeration indices for properties.

On 2012/09/12 17:06:55, Michael Starzinger wrote:

+          enumeration_index = dictionary->NextEnumerationIndex();
+          dictionary->SetNextEnumerationIndex(enumeration_index + 1);
+        } else {
+          enumeration_index = details.dictionary_index();
+        }
         details = PropertyDetails(
-            attributes, NORMAL, details.dictionary_index());
+            attributes, NORMAL, enumeration_index);
         dictionary->DetailsAtPut(entry, details);
       } else if (details.IsReadOnly() && !element->IsTheHole()) {
         if (strict_mode == kNonStrictMode) {