Ensure correct enumeration indices in the dict

src/objects.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 469 matching lines @@
       if (!maybe_store_value->ToObject(&store_value)) return maybe_store_value;
     }
     Object* dict;
     { MaybeObject* maybe_dict =
           property_dictionary()->Add(name, store_value, details);
       if (!maybe_dict->ToObject(&dict)) return maybe_dict;
     }
     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 =
         JSGlobalPropertyCell::cast(property_dictionary()->ValueAt(entry));
     cell->set_value(value);
     // Please note we have to update the property details.
     property_dictionary()->DetailsAtPut(entry, details);
   } else {
     property_dictionary()->SetEntry(entry, name, value, details);
   }
@@ skipping 8880 matching lines @@
     Object* element = dictionary->ValueAt(entry);
     PropertyDetails details = dictionary->DetailsAt(entry);
     if (details.type() == CALLBACKS && set_mode == SET_PROPERTY) {
       return SetElementWithCallback(element, index, value, this, strict_mode);
     } else {
       dictionary->UpdateMaxNumberKey(index);
       // If a value has not been initialized we allow writing to it even if it
       // 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) {
           return isolate->heap()->undefined_value();
         } else {
           Handle<Object> holder(this);
           Handle<Object> number = isolate->factory()->NewNumberFromUint(index);
           Handle<Object> args[2] = { number, holder };
           Handle<Object> error =
               isolate->factory()->NewTypeError("strict_read_only_property",
@@ skipping 3805 matching lines @@
   set_year(Smi::FromInt(year), SKIP_WRITE_BARRIER);
   set_month(Smi::FromInt(month), SKIP_WRITE_BARRIER);
   set_day(Smi::FromInt(day), SKIP_WRITE_BARRIER);
   set_weekday(Smi::FromInt(weekday), SKIP_WRITE_BARRIER);
   set_hour(Smi::FromInt(hour), SKIP_WRITE_BARRIER);
   set_min(Smi::FromInt(min), SKIP_WRITE_BARRIER);
   set_sec(Smi::FromInt(sec), SKIP_WRITE_BARRIER);
 }
 
 } }  // namespace v8::internal