From 47104429415c4c580cea8da4a3e3e7bf32338775 Mon Sep 17 00:00:00 2001
From: Jeremy Roman <jbroman@chromium.org>
Date: Tue, 16 Jan 2018 14:00:27 -0500
Subject: [PATCH] Implement v8::Object::SetLazyDataProperty.

It is analogous to Template::SetLazyDataProperty, but for a single
existing object. Similar to how SetNativeDataProperty exists on both.

Bug: v8:7303
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_chromium_rel_ng
Change-Id: I634358ee455e28150198bd87a2bd79dc59e3e449
Reviewed-on: https://chromium-review.googlesource.com/867474
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Jeremy Roman <jbroman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50841}
---
 include/v8.h                  | 13 +++++++++++++
 src/api.cc                    | 20 +++++++++++++++-----
 test/cctest/test-accessors.cc | 35 +++++++++++++++++++++++++++++++++++
 3 files changed, 63 insertions(+), 5 deletions(-)

diff --git a/include/v8.h b/include/v8.h
index c0f9679c8b..75d15ce1ce 100644
--- a/include/v8.h
+++ b/include/v8.h
@@ -3198,6 +3198,19 @@ class V8_EXPORT Object : public Value {
       AccessorNameSetterCallback setter = nullptr,
       Local<Value> data = Local<Value>(), PropertyAttribute attributes = None);
 
+  /**
+   * Attempts to create a property with the given name which behaves like a data
+   * property, except that the provided getter is invoked (and provided with the
+   * data value) to supply its value the first time it is read. After the
+   * property is accessed once, it is replaced with an ordinary data property.
+   *
+   * Analogous to Template::SetLazyDataProperty.
+   */
+  V8_WARN_UNUSED_RESULT Maybe<bool> SetLazyDataProperty(
+      Local<Context> context, Local<Name> name,
+      AccessorNameGetterCallback getter, Local<Value> data = Local<Value>(),
+      PropertyAttribute attributes = None);
+
   /**
    * Functionality for private properties.
    * This is an experimental feature, use at your own risk.
diff --git a/src/api.cc b/src/api.cc
index 66f38f0e98..4cc96d6df8 100644
--- a/src/api.cc
+++ b/src/api.cc
@@ -4765,14 +4765,14 @@ Maybe<bool> v8::Object::Has(Local<Context> context, uint32_t index) {
   return maybe;
 }
 
-
 template <typename Getter, typename Setter, typename Data>
 static Maybe<bool> ObjectSetAccessor(Local<Context> context, Object* self,
                                      Local<Name> name, Getter getter,
                                      Setter setter, Data data,
                                      AccessControl settings,
                                      PropertyAttribute attributes,
-                                     bool is_special_data_property) {
+                                     bool is_special_data_property,
+                                     bool replace_on_access) {
   auto isolate = reinterpret_cast<i::Isolate*>(context->GetIsolate());
   ENTER_V8_NO_SCRIPT(isolate, context, Object, SetAccessor, Nothing<bool>(),
                      i::HandleScope);
@@ -4782,7 +4782,7 @@ static Maybe<bool> ObjectSetAccessor(Local<Context> context, Object* self,
   v8::Local<AccessorSignature> signature;
   i::Handle<i::AccessorInfo> info =
       MakeAccessorInfo(isolate, name, getter, setter, data, settings, signature,
-                       is_special_data_property, false);
+                       is_special_data_property, replace_on_access);
   if (info.is_null()) return Nothing<bool>();
   bool fast = obj->HasFastProperties();
   i::Handle<i::Object> result;
@@ -4808,7 +4808,7 @@ Maybe<bool> Object::SetAccessor(Local<Context> context, Local<Name> name,
                                 PropertyAttribute attribute) {
   return ObjectSetAccessor(context, this, name, getter, setter,
                            data.FromMaybe(Local<Value>()), settings, attribute,
-                           i::FLAG_disable_old_api_accessors);
+                           i::FLAG_disable_old_api_accessors, false);
 }
 
 
@@ -4838,7 +4838,17 @@ Maybe<bool> Object::SetNativeDataProperty(v8::Local<v8::Context> context,
                                           v8::Local<Value> data,
                                           PropertyAttribute attributes) {
   return ObjectSetAccessor(context, this, name, getter, setter, data, DEFAULT,
-                           attributes, true);
+                           attributes, true, false);
+}
+
+Maybe<bool> Object::SetLazyDataProperty(v8::Local<v8::Context> context,
+                                        v8::Local<Name> name,
+                                        AccessorNameGetterCallback getter,
+                                        v8::Local<Value> data,
+                                        PropertyAttribute attributes) {
+  return ObjectSetAccessor(context, this, name, getter,
+                           static_cast<AccessorNameSetterCallback>(nullptr),
+                           data, DEFAULT, attributes, true, true);
 }
 
 Maybe<bool> v8::Object::HasOwnProperty(Local<Context> context,
diff --git a/test/cctest/test-accessors.cc b/test/cctest/test-accessors.cc
index 6a68ef1e38..b21c611a25 100644
--- a/test/cctest/test-accessors.cc
+++ b/test/cctest/test-accessors.cc
@@ -821,3 +821,38 @@ TEST(Regress609134) {
       "var a = 42;"
       "for (var i = 0; i<3; i++) { a.foo; }");
 }
+
+TEST(ObjectSetLazyDataProperty) {
+  LocalContext env;
+  v8::Isolate* isolate = env->GetIsolate();
+  v8::HandleScope scope(isolate);
+  v8::Local<v8::Object> obj = v8::Object::New(isolate);
+  CHECK(env->Global()->Set(env.local(), v8_str("obj"), obj).FromJust());
+
+  // Despite getting the property multiple times, the getter should only be
+  // called once and data property reads should continue to produce the same
+  // value.
+  static int getter_call_count;
+  getter_call_count = 0;
+  auto result = obj->SetLazyDataProperty(
+      env.local(), v8_str("foo"),
+      [](Local<Name> name, const v8::PropertyCallbackInfo<v8::Value>& info) {
+        getter_call_count++;
+        info.GetReturnValue().Set(getter_call_count);
+      });
+  CHECK(result.FromJust());
+  CHECK_EQ(0, getter_call_count);
+  for (int i = 0; i < 2; i++) {
+    ExpectInt32("obj.foo", 1);
+    CHECK_EQ(1, getter_call_count);
+  }
+
+  // Setting should overwrite the data property.
+  result = obj->SetLazyDataProperty(
+      env.local(), v8_str("bar"),
+      [](Local<Name> name, const v8::PropertyCallbackInfo<v8::Value>& info) {
+        CHECK(false);
+      });
+  CHECK(result.FromJust());
+  ExpectInt32("obj.bar = -1; obj.bar;", -1);
+}