[builtins] move String.prototype[@@iterator] to C++ builtin

src/bootstrapper.cc

Index: src/bootstrapper.cc
diff --git a/src/bootstrapper.cc b/src/bootstrapper.cc
index 14fe8b0a5b67b9c058cf437de1d44c6931c3d555..6acd1e71206f3f9b3b9b103b7003b0eb1bddd909 100644
--- a/src/bootstrapper.cc
+++ b/src/bootstrapper.cc
@@ -660,6 +660,16 @@ void Genesis::CreateIteratorMaps(Handle<JSFunction> empty) {
   // Create iterator-related meta-objects.
   Handle<JSObject> iterator_prototype =
       factory()->NewJSObject(isolate()->object_function(), TENURED);
+
+  Handle<JSFunction> iterator_prototype_iterator = SimpleCreateFunction(

[caitp, 2016/09/15 19:02:39]

The full %IteratorPrototype% is now set up here, so this allows deleting
src/js/iterator-prototype.js

+      isolate(), factory()->NewStringFromAsciiChecked("[Symbol.iterator]"),
+      Builtins::kIteratorPrototypeIterator, 0, false);
+  iterator_prototype_iterator->shared()->set_native(true);
+
+  JSObject::AddProperty(iterator_prototype, factory()->iterator_symbol(),
+                        iterator_prototype_iterator, DONT_ENUM);
+  native_context()->set_initial_iterator_prototype(*iterator_prototype);
+
   Handle<JSObject> generator_object_prototype =
       factory()->NewJSObject(isolate()->object_function(), TENURED);
   native_context()->set_initial_generator_prototype(
@@ -1406,6 +1416,38 @@ void Genesis::InitializeGlobal(Handle<JSGlobalObject> global_object,
                           Builtins::kStringPrototypeTrimRight, 0, false);
     SimpleInstallFunction(prototype, "valueOf",
                           Builtins::kStringPrototypeValueOf, 0, true);
+
+    Handle<JSFunction> iterator = SimpleCreateFunction(
+        isolate, factory->NewStringFromAsciiChecked("[Symbol.iterator]"),
+        Builtins::kStringPrototypeIterator, 0, true);
+    iterator->shared()->set_native(true);
+    JSObject::AddProperty(prototype, factory->iterator_symbol(), iterator,
+                          static_cast<PropertyAttributes>(DONT_ENUM));
+  }
+
+  {  // --- S t r i n g I t e r a t o r ---
+    Handle<JSObject> iterator_prototype(
+        native_context()->initial_iterator_prototype());
+
+    Handle<JSObject> string_iterator_prototype =
+        factory->NewJSObject(isolate->object_function(), TENURED);
+    JSObject::ForceSetPrototype(string_iterator_prototype, iterator_prototype);

[caitp, 2016/09/15 19:02:39]

TODO: use JSObject::SetPrototype()

[caitp, 2016/09/15 19:14:57]

JSObject::SetPrototype actually doesn't seem like the better option, it looks
like ForceSetObject will copy and migrate the map as expected, without any of
the extra functionality that the API or JS needs. Most of the callers in
bootstrapper use ForceSetMap for this reason, I guess.

[Benedikt Meurer, 2016/09/16 03:16:37]

Acknowledged.

+
+    JSObject::AddProperty(
+        string_iterator_prototype, factory->to_string_tag_symbol(),
+        factory->NewStringFromAsciiChecked("String Iterator"),
+        static_cast<PropertyAttributes>(DONT_ENUM | READ_ONLY));
+
+    InstallFunction(string_iterator_prototype, "next", JS_OBJECT_TYPE,
+                    JSObject::kHeaderSize, MaybeHandle<JSObject>(),
+                    Builtins::kStringIteratorPrototypeNext);
+
+    Handle<JSFunction> string_iterator_function = CreateFunction(
+        isolate, factory->NewStringFromAsciiChecked("StringIterator"),

[caitp, 2016/09/15 19:02:39]

I assume this string is actually used for something, but it's not clear what.

+        JS_STRING_ITERATOR_TYPE, JSStringIterator::kSize,
+        string_iterator_prototype, Builtins::kIllegal);
+    native_context()->set_string_iterator_map(
+        string_iterator_function->initial_map());
   }
 
   {
@@ -2466,17 +2508,12 @@ void Bootstrapper::ExportFromRuntime(Isolate* isolate,
     native_context->set_object_to_string(*to_string);
   }
 
-  Handle<JSObject> iterator_prototype;
-
-  {
-    PrototypeIterator iter(native_context->generator_object_prototype_map());
-    iter.Advance();  // Advance to the prototype of generator_object_prototype.
-    iterator_prototype = Handle<JSObject>(iter.GetCurrent<JSObject>());
+  Handle<JSObject> iterator_prototype(

[caitp, 2016/09/15 19:02:39]

This stuff is still used by collections iterators

+      native_context->initial_iterator_prototype());
 
-    JSObject::AddProperty(container,
-                          factory->InternalizeUtf8String("IteratorPrototype"),
-                          iterator_prototype, NONE);
-  }
+  JSObject::AddProperty(container,
+                        factory->InternalizeUtf8String("IteratorPrototype"),
+                        iterator_prototype, NONE);
 
   {
     PrototypeIterator iter(native_context->sloppy_generator_function_map());