Implement ES6 @@isConcatSpreadable

src/runtime/runtime-array.cc

Index: src/runtime/runtime-array.cc
diff --git a/src/runtime/runtime-array.cc b/src/runtime/runtime-array.cc
index 523d8f5faa30653a0aae97e5d58096ef53bd3c4c..74d43f23ea764391cd8a523a4a07727253261f94 100644
--- a/src/runtime/runtime-array.cc
+++ b/src/runtime/runtime-array.cc
@@ -440,7 +440,7 @@ static void CollectElementIndices(Handle<JSObject> object, uint32_t range,
 
 
 /**
- * A helper function that visits elements of a JSArray in numerical
+ * A helper function that visits elements of a JSObject in numerical
  * order.
  *
  * The visitor argument called for each existing element in the array
@@ -449,9 +449,22 @@ static void CollectElementIndices(Handle<JSObject> object, uint32_t range,
  * length.
  * Returns false if any access threw an exception, otherwise true.
  */
-static bool IterateElements(Isolate* isolate, Handle<JSArray> receiver,
+static bool IterateElements(Isolate* isolate, Handle<JSObject> receiver,
                             ArrayConcatVisitor* visitor) {
-  uint32_t length = static_cast<uint32_t>(receiver->length()->Number());
+  uint32_t length = 0;
+
+  if (receiver->IsJSArray()) {
+    Handle<JSArray> array(Handle<JSArray>::cast(receiver));
+    length = static_cast<uint32_t>(array->length()->Number());
+  } else {
+    Handle<Object> val;
+    Handle<Object> key(isolate->heap()->length_string(), isolate);
+    ASSIGN_RETURN_ON_EXCEPTION_VALUE(isolate, val,
+        Runtime::GetObjectProperty(isolate, receiver, key), false);
+    // TODO(caitp): implement ToLength() abstract operation for C++
+    val->ToUint32(&length);
+  }
+
   switch (receiver->GetElementsKind()) {
     case FAST_SMI_ELEMENTS:
     case FAST_ELEMENTS:
@@ -601,6 +614,23 @@ static bool IterateElements(Isolate* isolate, Handle<JSArray> receiver,
 }
 
 
+static bool IsConcatSpreadable(Isolate* isolate, Handle<Object> obj) {
+  HandleScope handle_scope(isolate);
+  if (!obj->IsSpecObject()) return false;
+  if (obj->IsJSArray()) return true;
+  if (FLAG_harmony_arrays) {
+    Handle<Symbol> key(isolate->factory()->is_concat_spreadable_symbol());
+    Handle<Object> value;
+    MaybeHandle<Object> maybeValue =
+        i::Runtime::GetObjectProperty(isolate, obj, key);
+    if (maybeValue.ToHandle(&value)) {
+      return value->BooleanValue();
+    }
+  }
+  return false;
+}
+
+
 /**
  * Array::concat implementation.
  * See ECMAScript 262, 15.4.4.4.
@@ -771,9 +801,11 @@ RUNTIME_FUNCTION(Runtime_ArrayConcat) {
 
   for (int i = 0; i < argument_count; i++) {
     Handle<Object> obj(elements->get(i), isolate);
-    if (obj->IsJSArray()) {
-      Handle<JSArray> array = Handle<JSArray>::cast(obj);
-      if (!IterateElements(isolate, array, &visitor)) {
+    bool spreadable = IsConcatSpreadable(isolate, obj);
+    if (isolate->has_pending_exception()) return isolate->heap()->exception();
+    if (spreadable) {
+      Handle<JSObject> object = Handle<JSObject>::cast(obj);
+      if (!IterateElements(isolate, object, &visitor)) {
         return isolate->heap()->exception();
       }
     } else {