Stop sending Object.observe notifications for API accessor properties

src/v8natives.js

 // Copyright 2012 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.
 
 // This file relies on the fact that the following declarations have been made
 // in runtime.js:
 // var $Object = global.Object;
 // var $Boolean = global.Boolean;
 // var $Number = global.Number;
 // var $Function = global.Function;
@@ skipping 822 matching lines @@
       setter = current.getSet();
     }
     %DefineAccessorPropertyUnchecked(obj, p, getter, setter, flag);
   }
   return true;
 }
 
 
 // ES5 section 15.4.5.1.
 function DefineArrayProperty(obj, p, desc, should_throw) {
-  // Note that the length of an array is not actually stored as part of the
-  // property, hence we use generated code throughout this function instead of
-  // DefineObjectProperty() to modify its value.
-
-  // Step 3 - Special handling for length property.

[Jakob Kummerow, 2014/12/11 11:41:40]

Some of this code was ~3 years old and seems unrelated to Object.observe, e.g.
as modified by https://codereview.chromium.org/8890015. Are you sure we don't
need it any more?

[adamk, 2014/12/11 16:47:26]

Arg, you're right, test262 not being in make check gets me half the time.

-  if (p === "length") {
-    var length = obj.length;
-    var old_length = length;
-    if (!desc.hasValue()) {
-      return DefineObjectProperty(obj, "length", desc, should_throw);
-    }
-    var new_length = ToUint32(desc.getValue());
-    if (new_length != ToNumber(desc.getValue())) {
-      throw new $RangeError('defineProperty() array length out of range');
-    }
-    var length_desc = GetOwnPropertyJS(obj, "length");
-    if (new_length != length && !length_desc.isWritable()) {
-      if (should_throw) {
-        throw MakeTypeError("redefine_disallowed", [p]);
-      } else {
-        return false;
-      }
-    }
-    var threw = false;
-
-    var emit_splice = %IsObserved(obj) && new_length !== old_length;
-    var removed;
-    if (emit_splice) {
-      BeginPerformSplice(obj);
-      removed = [];
-      if (new_length < old_length)
-        removed.length = old_length - new_length;
-    }
-
-    while (new_length < length--) {
-      var index = ToString(length);
-      if (emit_splice) {
-        var deletedDesc = GetOwnPropertyJS(obj, index);
-        if (deletedDesc && deletedDesc.hasValue())
-          removed[length - new_length] = deletedDesc.getValue();
-      }
-      if (!Delete(obj, index, false)) {
-        new_length = length + 1;
-        threw = true;
-        break;
-      }
-    }
-    // Make sure the below call to DefineObjectProperty() doesn't overwrite
-    // any magic "length" property by removing the value.
-    // TODO(mstarzinger): This hack should be removed once we have addressed the
-    // respective TODO in Runtime_DefineDataPropertyUnchecked.
-    // For the time being, we need a hack to prevent Object.observe from
-    // generating two change records.
-    obj.length = new_length;
-    desc.value_ = UNDEFINED;
-    desc.hasValue_ = false;
-    threw = !DefineObjectProperty(obj, "length", desc, should_throw) || threw;
-    if (emit_splice) {
-      EndPerformSplice(obj);
-      EnqueueSpliceRecord(obj,
-          new_length < old_length ? new_length : old_length,
-          removed,
-          new_length > old_length ? new_length - old_length : 0);
-    }
-    if (threw) {
-      if (should_throw) {
-        throw MakeTypeError("redefine_disallowed", [p]);
-      } else {
-        return false;
-      }
-    }
-    return true;
-  }
-
-  // Step 4 - Special handling for array index.
+  // Special handling for array index.
   if (!IS_SYMBOL(p)) {
     var index = ToUint32(p);
     var emit_splice = false;
     if (ToString(index) == p && index != 4294967295) {
       var length = obj.length;
       if (index >= length && %IsObserved(obj)) {
         emit_splice = true;
         BeginPerformSplice(obj);
       }
 
@@ skipping 12 matching lines @@
         obj.length = index + 1;
       }
       if (emit_splice) {
         EndPerformSplice(obj);
         EnqueueSpliceRecord(obj, length, [], index + 1 - length);
       }
       return true;
     }
   }
 
-  // Step 5 - Fallback to default implementation.
+  // Fallback to default implementation.
   return DefineObjectProperty(obj, p, desc, should_throw);
 }
 
 
 // ES5 section 8.12.9, ES5 section 15.4.5.1 and Harmony proxies.
 function DefineOwnProperty(obj, p, desc, should_throw) {
   if (%_IsJSProxy(obj)) {
     // TODO(rossberg): adjust once there is a story for symbols vs proxies.
     if (IS_SYMBOL(p)) return false;
 
@@ skipping 936 matching lines @@
   }
   if (!IS_SPEC_FUNCTION(method)) {
     throw MakeTypeError('not_iterable', [obj]);
   }
   var iterator = %_CallFunction(obj, method);
   if (!IS_SPEC_OBJECT(iterator)) {
     throw MakeTypeError('not_an_iterator', [iterator]);
   }
   return iterator;
 }