Object.observe support for Function 'prototype' property

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index 405867a908f3f34f91841dbaafac7fa86519f34c..a5d83436ec5ba3c9acb6f0e2771ca15128a3da94 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -27,6 +27,7 @@
 
 #include "v8.h"
 
+#include "accessors.h"
 #include "api.h"
 #include "arguments.h"
 #include "bootstrapper.h"
@@ -3104,9 +3105,18 @@ MaybeObject* JSObject::SetLocalPropertyIgnoreAttributes(
 
   Handle<Object> old_value(isolate->heap()->the_hole_value(), isolate);
   PropertyAttributes old_attributes = ABSENT;
-  if (FLAG_harmony_observation && map()->is_observed()) {
-    old_value = handle(lookup.GetLazyValue(), isolate);
-    old_attributes = lookup.GetAttributes();
+  bool is_observed = FLAG_harmony_observation && self->map()->is_observed();
+  if (is_observed) {
+    // Function prototypes are stored specially
+    if (self->IsJSFunction() &&
+        JSFunction::cast(*self)->should_have_prototype() &&
+        name->Equals(isolate->heap()->prototype_symbol())) {
+      MaybeObject* maybe = Accessors::FunctionGetPrototype(*self, NULL);
+      if (!maybe->ToHandle(&old_value, isolate)) return maybe;

[rossberg, 2012/12/05 12:02:29]

I don't understand why this works. How come you don't have to set old_attributes
in this case?

[adamk, 2012/12/05 17:38:17]

Hmm, I don't understand either. Added a test that should tickle it, but doesn't.
Moved the attributes-setting outside the inner if statement for now, but would
like to figure out a test that would result in different behavior...

[adamk, 2012/12/05 19:47:38]

Ah, here's why: there's that special case in %DefineOrRedefineDataProperty when
the lookup result is a callback property and the attributes aren't being
changed. So this code is run only when attributes are changing. In any case, I
think always setting old_attributes is more semantically correct.

And hopefully the TODO in %DefineOrRedefineDataProperty will be fixed and this
code can be removed.

+    } else {
+      old_value = handle(lookup.GetLazyValue(), isolate);
+      old_attributes = lookup.GetAttributes();
+    }
   }
 
   // Check of IsReadOnly removed from here in clone.
@@ -3169,7 +3179,7 @@ MaybeObject* JSObject::SetLocalPropertyIgnoreAttributes(
   Handle<Object> hresult;
   if (!result->ToHandle(&hresult, isolate)) return result;
 
-  if (FLAG_harmony_observation && map()->is_observed()) {
+  if (is_observed) {
     if (lookup.IsTransition()) {
       EnqueueChangeRecord(self, "new", name, old_value);
     } else {