[api] Support sharing prototypes between FunctionTemplates

src/api-natives.cc

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/api-natives.h"
 
 #include "src/api.h"
 #include "src/isolate-inl.h"
 #include "src/lookup.h"
 #include "src/messages.h"
@@ skipping 377 matching lines @@
   // TODO(dcarney): is this necessary?
   JSObject::MigrateSlowToFast(result, 0, "ApiNatives::InstantiateObject");
 
   if (serial_number) {
     CacheTemplateInstantiation(isolate, serial_number, result);
     result = isolate->factory()->CopyJSObject(result);
   }
   return result;
 }
 
+namespace {
+MaybeHandle<Object> GetInstancePrototype(Isolate* isolate,
+                                         Object* function_template) {
+  // Enter a new scope.  Recursion could otherwise create a lot of handles.
+  HandleScope scope(isolate);
+  Handle<JSFunction> parent_instance;
+  ASSIGN_RETURN_ON_EXCEPTION(
+      isolate, parent_instance,
+      InstantiateFunction(
+          isolate,
+          handle(FunctionTemplateInfo::cast(function_template), isolate)),
+      JSFunction);
+  Handle<Object> instance_prototype;
+  // TODO(cbruni): decide what to do here.
+  ASSIGN_RETURN_ON_EXCEPTION(
+      isolate, instance_prototype,
+      JSObject::GetProperty(parent_instance,
+                            isolate->factory()->prototype_string()),
+      JSFunction);
+  return scope.CloseAndEscape(instance_prototype);
+}
+}  // namespace
 
 MaybeHandle<JSFunction> InstantiateFunction(Isolate* isolate,
                                             Handle<FunctionTemplateInfo> data,
                                             Handle<Name> name) {
   int serial_number = Smi::cast(data->serial_number())->value();
   if (serial_number) {
     Handle<JSObject> result;
     if (ProbeInstantiationsCache(isolate, serial_number).ToHandle(&result)) {
       return Handle<JSFunction>::cast(result);
     }
   }
-  Handle<JSObject> prototype;
+  Handle<Object> prototype;
   if (!data->remove_prototype()) {
     Object* prototype_templ = data->prototype_template();
     if (prototype_templ->IsUndefined(isolate)) {
-      prototype = isolate->factory()->NewJSObject(isolate->object_function());
+      Object* protoype_provider_templ = data->prototype_provider_template();
+      if (protoype_provider_templ->IsUndefined(isolate)) {
+        prototype = isolate->factory()->NewJSObject(isolate->object_function());
+      } else {
+        ASSIGN_RETURN_ON_EXCEPTION(
+            isolate, prototype,
+            GetInstancePrototype(isolate, protoype_provider_templ), JSFunction);
+      }
     } else {
       ASSIGN_RETURN_ON_EXCEPTION(
           isolate, prototype,
           InstantiateObject(
               isolate,
               handle(ObjectTemplateInfo::cast(prototype_templ), isolate),
               Handle<JSReceiver>(), data->hidden_prototype()),
           JSFunction);
     }
     Object* parent = data->parent_template();
     if (!parent->IsUndefined(isolate)) {
-      // Enter a new scope.  Recursion could otherwise create a lot of handles.
-      HandleScope scope(isolate);
-      Handle<JSFunction> parent_instance;
-      ASSIGN_RETURN_ON_EXCEPTION(
-          isolate, parent_instance,
-          InstantiateFunction(
-              isolate, handle(FunctionTemplateInfo::cast(parent), isolate)),
-          JSFunction);
-      // TODO(dcarney): decide what to do here.
       Handle<Object> parent_prototype;
-      ASSIGN_RETURN_ON_EXCEPTION(
-          isolate, parent_prototype,
-          JSObject::GetProperty(parent_instance,
-                                isolate->factory()->prototype_string()),
-          JSFunction);
-      JSObject::ForceSetPrototype(prototype, parent_prototype);
+      ASSIGN_RETURN_ON_EXCEPTION(isolate, parent_prototype,
+                                 GetInstancePrototype(isolate, parent),
+                                 JSFunction);
+      JSObject::ForceSetPrototype(Handle<JSObject>::cast(prototype),
+                                  parent_prototype);
     }
   }
   Handle<JSFunction> function = ApiNatives::CreateApiFunction(
       isolate, data, prototype, ApiNatives::JavaScriptObjectType);
   if (!name.is_null() && name->IsString()) {
     function->shared()->set_name(*name);
   }
   if (serial_number) {
     // Cache the function.
     CacheTemplateInstantiation(isolate, serial_number, function);
@@ skipping 148 matching lines @@
 
   // Down from here is only valid for API functions that can be used as a
   // constructor (don't set the "remove prototype" flag).
 
   if (obj->read_only_prototype()) {
     result->set_map(*isolate->sloppy_function_with_readonly_prototype_map());
   }
 
   if (prototype->IsTheHole(isolate)) {
     prototype = isolate->factory()->NewFunctionPrototype(result);
-  } else {
+  } else if (obj->prototype_provider_template()->IsUndefined(isolate)) {
     JSObject::AddProperty(Handle<JSObject>::cast(prototype),
                           isolate->factory()->constructor_string(), result,
                           DONT_ENUM);
   }
 
   int internal_field_count = 0;
   bool immutable_proto = false;
   if (!obj->instance_template()->IsUndefined(isolate)) {
     Handle<ObjectTemplateInfo> instance_template = Handle<ObjectTemplateInfo>(
         ObjectTemplateInfo::cast(obj->instance_template()));
@@ skipping 58 matching lines @@
     map->set_is_constructor(true);
   }
 
   if (immutable_proto) map->set_immutable_proto(true);
 
   return result;
 }
 
 }  // namespace internal
 }  // namespace v8