harmony_scoping: Implement lexical bindings at top level

src/contexts.h

Index: src/contexts.h
diff --git a/src/contexts.h b/src/contexts.h
index dc77861b2578be34e1169ae932c50554adfbfa76..4023c0b51eec352cbfa4bf83a8865bd7f1c53399 100644
--- a/src/contexts.h
+++ b/src/contexts.h
@@ -183,7 +183,43 @@ enum BindingFlags {
   V(SET_ITERATOR_MAP_INDEX, Map, set_iterator_map)                             \
   V(ITERATOR_SYMBOL_INDEX, Symbol, iterator_symbol)                            \
   V(UNSCOPABLES_SYMBOL_INDEX, Symbol, unscopables_symbol)                      \
-  V(ARRAY_VALUES_ITERATOR_INDEX, JSFunction, array_values_iterator)
+  V(ARRAY_VALUES_ITERATOR_INDEX, JSFunction, array_values_iterator)            \
+  V(GLOBAL_CONTEXT_TABLE_INDEX, GlobalContextTable, global_context_table)
+
+
+class GlobalContextTable : public FixedArray {

[adamk, 2014/11/06 20:18:06]

Please add a comment for this class. What is it for? What's the layout?

[Dmitry Lomov (no reviews), 2014/11/07 10:18:48]

Done.

+ public:
+  // Conversions.
+  static GlobalContextTable* cast(Object* context) {
+    DCHECK(context->IsGlobalContextTable());
+    return reinterpret_cast<GlobalContextTable*>(context);
+  }
+
+  struct LookupResult {
+    int context_index;
+    int slot_index;
+    VariableMode mode;
+    InitializationFlag init_flag;
+    MaybeAssignedFlag maybe_assigned_flag;
+  };
+
+  int size() const { return Smi::cast(get(kSizeSlot))->value(); }

[adamk, 2014/11/06 20:18:05]

Just a question: are const methods that common? I do see a few in objects.h now
that I look. What's the best practice here?

[Dmitry Lomov (no reviews), 2014/11/07 10:18:47]

Make methods 'const' if possible is the parctice

+
+  static Handle<Context> GetContext(Handle<GlobalContextTable> table, int i) {
+    DCHECK(i < table->size());
+    return Handle<Context>::cast(FixedArray::get(table, i + 1));

[adamk, 2014/11/06 20:18:06]

This and the various other +1s in the .cc file might benefit from a constant or
a private helper method, but I could imagine that's too much overhead for a
simple case like this. I leave it up to you.

[Dmitry Lomov (no reviews), 2014/11/07 10:18:47]

Yes, I think it is too much fuss.

+  }
+
+  static bool Lookup(Handle<GlobalContextTable> table, Handle<String> name,

[adamk, 2014/11/06 20:18:06]

This method could use a comment, at least for the return value. It's notable
that result ends up with garbage in it when this returns false (MUST_USE_RESULT
wouldn't be a bad idea here for that reason).

[Dmitry Lomov (no reviews), 2014/11/07 10:18:47]

Done.

+                     LookupResult* result);
+
+  // table may be null.

[adamk, 2014/11/06 20:18:05]

Not clear what this means, it certainly can't be a null handle.

[Dmitry Lomov (no reviews), 2014/11/07 10:18:47]

Stray comment, removed.

+  static Handle<GlobalContextTable> Extend(Handle<GlobalContextTable> table,

[adamk, 2014/11/06 20:18:05]

MUST_USE_RESULT?

[Dmitry Lomov (no reviews), 2014/11/07 10:18:47]

Done.

+                                           Handle<Context> global_context);
+
+ private:
+  static const int kSizeSlot = 0;
+};

[adamk, 2014/11/06 20:18:05]

nit: DISALLOW_IMPLICIT_CONSTRUCTORS

[Dmitry Lomov (no reviews), 2014/11/07 10:18:47]

Done.

 
 // JSFunctions are pairs (context, function code), sometimes also called
 // closures. A Context object is used to represent function contexts and
@@ -360,6 +396,7 @@ class Context: public FixedArray {
     ITERATOR_SYMBOL_INDEX,
     UNSCOPABLES_SYMBOL_INDEX,
     ARRAY_VALUES_ITERATOR_INDEX,
+    GLOBAL_CONTEXT_TABLE_INDEX,
 
     // Properties from here are treated as weak references by the full GC.
     // Scavenge treats them as strong references.
@@ -555,7 +592,6 @@ class Context: public FixedArray {
   STATIC_ASSERT(kHeaderSize == Internals::kContextHeaderSize);
   STATIC_ASSERT(EMBEDDER_DATA_INDEX == Internals::kContextEmbedderDataIndex);
 };
-
 } }  // namespace v8::internal
 
 #endif  // V8_CONTEXTS_H_