[runtime] PreventExtensionsWithTransition: before adding the new

src/objects.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/objects.h"
 
 #include <cmath>
 #include <iomanip>
 #include <memory>
 #include <sstream>
@@ skipping 7404 matching lines @@
 }
 
 
 Maybe<bool> JSReceiver::SetIntegrityLevel(Handle<JSReceiver> receiver,
                                           IntegrityLevel level,
                                           ShouldThrow should_throw) {
   DCHECK(level == SEALED || level == FROZEN);
 
   if (receiver->IsJSObject()) {
     Handle<JSObject> object = Handle<JSObject>::cast(receiver);
+
+    // prevent memory leaks by adding unnecessary transitions

[Toon Verwaest, 2017/06/13 09:57:05]

Prevent ... *not* adding ... transitions. :)

[kris.selden, 2017/06/16 22:32:12]

Done.

+    Maybe<bool> test = JSObject::TestIntegrityLevel(object, level);
+    MAYBE_RETURN(test, Nothing<bool>());
+    if (test.FromJust()) return Just(true);
+
     if (!object->HasSloppyArgumentsElements()) {  // Fast path.
       if (level == SEALED) {
         return JSObject::PreventExtensionsWithTransition<SEALED>(object,
                                                                  should_throw);
       } else {
         return JSObject::PreventExtensionsWithTransition<FROZEN>(object,
                                                                  should_throw);
       }
     }
   }
@@ skipping 36 matching lines @@
               ? no_conf
               : no_conf_no_write;
       MAYBE_RETURN(
           DefineOwnProperty(isolate, receiver, key, &desc, THROW_ON_ERROR),
           Nothing<bool>());
     }
   }
   return Just(true);
 }
 
-
 Maybe<bool> JSReceiver::TestIntegrityLevel(Handle<JSReceiver> object,
                                            IntegrityLevel level) {
+  if (object->IsJSObject()) {
+    return JSObject::TestIntegrityLevel(Handle<JSObject>::cast(object), level);
+  }
+
   DCHECK(level == SEALED || level == FROZEN);
   Isolate* isolate = object->GetIsolate();
 
   Maybe<bool> extensible = JSReceiver::IsExtensible(object);
   MAYBE_RETURN(extensible, Nothing<bool>());
   if (extensible.FromJust()) return Just(false);
 
   Handle<FixedArray> keys;
   ASSIGN_RETURN_ON_EXCEPTION_VALUE(
       isolate, keys, JSReceiver::OwnPropertyKeys(object), Nothing<bool>());
 
   for (int i = 0; i < keys->length(); ++i) {
     Handle<Object> key(keys->get(i), isolate);
     PropertyDescriptor current_desc;
     Maybe<bool> owned = JSReceiver::GetOwnPropertyDescriptor(
         isolate, object, key, &current_desc);
     MAYBE_RETURN(owned, Nothing<bool>());
     if (owned.FromJust()) {
       if (current_desc.configurable()) return Just(false);
       if (level == FROZEN &&
           PropertyDescriptor::IsDataDescriptor(&current_desc) &&
           current_desc.writable()) {
         return Just(false);
       }
     }
   }
   return Just(true);
 }
 
+Maybe<bool> JSObject::TestIntegrityLevel(Handle<JSObject> object,
+                                         IntegrityLevel level) {
+  DCHECK(level == SEALED || level == FROZEN);
+
+  if (JSObject::IsExtensible(object)) return Just(false);
+
+  if (object->HasFastProperties() &&
+      IsFastObjectElementsKind(object->GetElementsKind())) {
+    ElementsAccessor* accessor = object->GetElementsAccessor();

[Toon Verwaest, 2017/06/13 09:57:06]

If we only support fast elements, finding any element makes it false.

[Toon Verwaest, 2017/06/16 10:03:02]

Come to think of it; if we ever followed the fast transition, we always end up
with slow elements. See CopyForPreventExtensions; it always sets the elements
kind to something slow (except typed arrays).

[kris.selden, 2017/06/16 22:32:12]

I think what I did addresses this but I need your review.

+    JSObject* rawobj = *object;
+    uint32_t number_of_elements = accessor->NumberOfElements(rawobj);
+    for (uint32_t i = 0; i < number_of_elements; i++) {
+      PropertyDetails details = accessor->GetDetails(rawobj, i);
+      if (details.IsConfigurable()) return Just(false);
+      if (level == FROZEN && details.kind() == kData && !details.IsReadOnly()) {
+        return Just(false);
+      }
+    }
+    Map* map = object->map();
+    DescriptorArray* descriptors = map->instance_descriptors();
+    int number_of_own_descriptors = map->NumberOfOwnDescriptors();
+    for (int i = 0; i < number_of_own_descriptors; i++) {
+      PropertyDetails details = descriptors->GetDetails(i);
+      if (details.IsConfigurable()) return Just(false);
+      if (level == FROZEN && details.kind() == kData && !details.IsReadOnly()) {
+        return Just(false);
+      }
+    }
+    return Just(true);
+  }
+
+  Handle<JSReceiver> receiver = Handle<JSReceiver>::cast(object);

[Toon Verwaest, 2017/06/13 09:57:05]

We definitely want to share this slow path with the code for JSReceiver above.

[kris.selden, 2017/06/16 22:32:12]

Done.

+  Isolate* isolate = object->GetIsolate();
+  Handle<FixedArray> keys;
+  ASSIGN_RETURN_ON_EXCEPTION_VALUE(
+      isolate, keys, JSObject::OwnPropertyKeys(receiver), Nothing<bool>());
+
+  for (int i = 0; i < keys->length(); ++i) {
+    Handle<Object> key(keys->get(i), isolate);
+    PropertyDescriptor current_desc;
+    Maybe<bool> owned = JSReceiver::GetOwnPropertyDescriptor(
+        isolate, receiver, key, &current_desc);
+    MAYBE_RETURN(owned, Nothing<bool>());
+    if (owned.FromJust()) {
+      if (current_desc.configurable()) return Just(false);
+      if (level == FROZEN &&
+          PropertyDescriptor::IsDataDescriptor(&current_desc) &&
+          current_desc.writable()) {
+        return Just(false);
+      }
+    }
+  }
+  return Just(true);
+}
 
 Maybe<bool> JSReceiver::PreventExtensions(Handle<JSReceiver> object,
                                           ShouldThrow should_throw) {
   if (object->IsJSProxy()) {
     return JSProxy::PreventExtensions(Handle<JSProxy>::cast(object),
                                       should_throw);
   }
   DCHECK(object->IsJSObject());
   return JSObject::PreventExtensions(Handle<JSObject>::cast(object),
                                      should_throw);
@@ skipping 13045 matching lines @@
       // not
       // depend on this.
       return DICTIONARY_ELEMENTS;
     }
     DCHECK_LE(kind, LAST_ELEMENTS_KIND);
     return kind;
   }
 }
 }  // namespace internal
 }  // namespace v8