Implement ES6 @@isConcatSpreadable / Array.prototype.concat

Add support for Symbol.isConcatSpreadable in Array.prototype.concat. This enables spreading non-Array objects with the symbol.

LOG=N
R=dslomov@chromium.org
BUG=

Review URL: https://codereview.chromium.org/771483002

Cr-Commit-Position: refs/heads/master@{#25808}

src/harmony-array.js

@@ -192,6 +192,17 @@ function ArrayOf() {
 
 // -------------------------------------------------------------------
 
+function HarmonyArrayExtendSymbolPrototype() {
+  %CheckIsBootstrapping();
+
+  InstallConstants($Symbol, $Array(
+    // TODO(dslomov, caitp): Move to symbol.js when shipping
+   "isConcatSpreadable", symbolIsConcatSpreadable
+  ));
+}
+
+HarmonyArrayExtendSymbolPrototype();
+
 function HarmonyArrayExtendArrayPrototype() {
   %CheckIsBootstrapping();
 

src/runtime.js

@@ -626,6 +626,15 @@ function IsPrimitive(x) {
 }
 
 
+// ES6, draft 10-14-14, section 22.1.3.1.1
+function IsConcatSpreadable(O) {
+  if (!IS_SPEC_OBJECT(O)) return false;
+  var spreadable = O[symbolIsConcatSpreadable];
+  if (IS_UNDEFINED(spreadable)) return IS_ARRAY(O);
+  return ToBoolean(spreadable);
+}
+
+
 // ECMA-262, section 8.6.2.6, page 28.
 function DefaultNumber(x) {
   if (!IS_SYMBOL_WRAPPER(x)) {

src/runtime/runtime-array.cc

@@ -289,11 +289,11 @@ static uint32_t EstimateElementCount(Handle<JSArray> array) {
 
 
 template <class ExternalArrayClass, class ElementType>
-static void IterateExternalArrayElements(Isolate* isolate,
-                                         Handle<JSObject> receiver,
-                                         bool elements_are_ints,
-                                         bool elements_are_guaranteed_smis,
-                                         ArrayConcatVisitor* visitor) {
+static void IterateTypedArrayElements(Isolate* isolate,
+                                      Handle<JSObject> receiver,
+                                      bool elements_are_ints,
+                                      bool elements_are_guaranteed_smis,
+                                      ArrayConcatVisitor* visitor) {
   Handle<ExternalArrayClass> array(
       ExternalArrayClass::cast(receiver->elements()));
   uint32_t len = static_cast<uint32_t>(array->length());
@@ -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:
@@ -552,55 +565,132 @@ static bool IterateElements(Isolate* isolate, Handle<JSArray> receiver,
       }
       break;
     }
+    case UINT8_CLAMPED_ELEMENTS: {
+      Handle<FixedUint8ClampedArray> pixels(
+      FixedUint8ClampedArray::cast(receiver->elements()));
+      for (uint32_t j = 0; j < length; j++) {
+        Handle<Smi> e(Smi::FromInt(pixels->get_scalar(j)), isolate);
+        visitor->visit(j, e);
+      }
+      break;
+    }
     case EXTERNAL_INT8_ELEMENTS: {
-      IterateExternalArrayElements<ExternalInt8Array, int8_t>(
+      IterateTypedArrayElements<ExternalInt8Array, int8_t>(
           isolate, receiver, true, true, visitor);
       break;
     }
+    case INT8_ELEMENTS: {
+      IterateTypedArrayElements<FixedInt8Array, int8_t>(
+      isolate, receiver, true, true, visitor);
+      break;
+    }
     case EXTERNAL_UINT8_ELEMENTS: {
-      IterateExternalArrayElements<ExternalUint8Array, uint8_t>(
+      IterateTypedArrayElements<ExternalUint8Array, uint8_t>(
           isolate, receiver, true, true, visitor);
       break;
     }
+    case UINT8_ELEMENTS: {
+      IterateTypedArrayElements<FixedUint8Array, uint8_t>(
+      isolate, receiver, true, true, visitor);
+      break;
+    }
     case EXTERNAL_INT16_ELEMENTS: {
-      IterateExternalArrayElements<ExternalInt16Array, int16_t>(
+      IterateTypedArrayElements<ExternalInt16Array, int16_t>(
           isolate, receiver, true, true, visitor);
       break;
     }
+    case INT16_ELEMENTS: {
+      IterateTypedArrayElements<FixedInt16Array, int16_t>(
+      isolate, receiver, true, true, visitor);
+      break;
+    }
     case EXTERNAL_UINT16_ELEMENTS: {
-      IterateExternalArrayElements<ExternalUint16Array, uint16_t>(
+      IterateTypedArrayElements<ExternalUint16Array, uint16_t>(
           isolate, receiver, true, true, visitor);
       break;
     }
+    case UINT16_ELEMENTS: {
+      IterateTypedArrayElements<FixedUint16Array, uint16_t>(
+      isolate, receiver, true, true, visitor);
+      break;
+    }
     case EXTERNAL_INT32_ELEMENTS: {
-      IterateExternalArrayElements<ExternalInt32Array, int32_t>(
+      IterateTypedArrayElements<ExternalInt32Array, int32_t>(
           isolate, receiver, true, false, visitor);
       break;
     }
+    case INT32_ELEMENTS: {
+      IterateTypedArrayElements<FixedInt32Array, int32_t>(
+      isolate, receiver, true, false, visitor);
+      break;
+    }
     case EXTERNAL_UINT32_ELEMENTS: {
-      IterateExternalArrayElements<ExternalUint32Array, uint32_t>(
+      IterateTypedArrayElements<ExternalUint32Array, uint32_t>(
           isolate, receiver, true, false, visitor);
       break;
     }
+    case UINT32_ELEMENTS: {
+      IterateTypedArrayElements<FixedUint32Array, uint32_t>(
+      isolate, receiver, true, false, visitor);
+      break;
+    }
     case EXTERNAL_FLOAT32_ELEMENTS: {
-      IterateExternalArrayElements<ExternalFloat32Array, float>(
+      IterateTypedArrayElements<ExternalFloat32Array, float>(
           isolate, receiver, false, false, visitor);
       break;
     }
+    case FLOAT32_ELEMENTS: {
+      IterateTypedArrayElements<FixedFloat32Array, float>(
+      isolate, receiver, false, false, visitor);
+      break;
+    }
     case EXTERNAL_FLOAT64_ELEMENTS: {
-      IterateExternalArrayElements<ExternalFloat64Array, double>(
+      IterateTypedArrayElements<ExternalFloat64Array, double>(
           isolate, receiver, false, false, visitor);
       break;
     }
-    default:
-      UNREACHABLE();
+    case FLOAT64_ELEMENTS: {
+      IterateTypedArrayElements<FixedFloat64Array, double>(
+      isolate, receiver, false, false, visitor);
       break;
+    }
+    case SLOPPY_ARGUMENTS_ELEMENTS: {
+      ElementsAccessor* accessor = receiver->GetElementsAccessor();
+      for (uint32_t index = 0; index < length; index++) {
+        HandleScope loop_scope(isolate);
+        if (accessor->HasElement(receiver, receiver, index)) {
+          Handle<Object> element;
+          ASSIGN_RETURN_ON_EXCEPTION_VALUE(
+              isolate, element, accessor->Get(receiver, receiver, index),
+              false);
+          visitor->visit(index, element);
+        }
+      }
+      break;
+    }
   }
   visitor->increase_index_offset(length);
   return true;
 }
 
 
+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 +861,11 @@ 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 {