Don't wrap StopIteration singleton, just translate it to the current global's StopIteration object and freeze StopIteration at birth (606573, r=mrbkap).

js/src/jsapi.h

@@ -1718,6 +1718,10 @@ struct JSClass {
 #define JSCLASS_MARK_IS_TRACE           (1<<(JSCLASS_HIGH_FLAGS_SHIFT+3))
 #define JSCLASS_INTERNAL_FLAG2          (1<<(JSCLASS_HIGH_FLAGS_SHIFT+4))
 
+/* Indicate whether the proto or ctor should be frozen. */
+#define JSCLASS_FREEZE_PROTO            (1<<(JSCLASS_HIGH_FLAGS_SHIFT+5))
+#define JSCLASS_FREEZE_CTOR             (1<<(JSCLASS_HIGH_FLAGS_SHIFT+6))
+
 /* Additional global reserved slots, beyond those for standard prototypes. */
 #define JSRESERVED_GLOBAL_SLOTS_COUNT     3
 #define JSRESERVED_GLOBAL_THIS            (JSProto_LIMIT * 3)

js/src/jscompartment.cpp

@@ -38,9 +38,10 @@
  *
  * ***** END LICENSE BLOCK ***** */
 
+#include "jscntxt.h"
 #include "jscompartment.h"
 #include "jsgc.h"
-#include "jscntxt.h"
+#include "jsiter.h"
 #include "jsproxy.h"
 #include "jsscope.h"
 #include "methodjit/PolyIC.h"
@@ -143,6 +144,10 @@ JSCompartment::wrap(JSContext *cx, Value *vp)
         if (obj->compartment() == this)
             return true;
 
+        /* Translate StopIteration singleton. */
+        if (obj->getClass() == &js_StopIterationClass)
+            return js_FindClassObject(cx, NULL, JSProto_StopIteration, vp);
+
         /* Don't unwrap an outer window proxy. */
         if (!obj->getClass()->ext.innerObject) {
             obj = vp->toObject().unwrap(&flags);

js/src/jsiter.cpp

@@ -624,6 +624,16 @@ GetIterator(JSContext *cx, JSObject *obj, uintN flags, Value *vp)
     bool keysOnly = (flags == JSITER_ENUMERATE);
 
     if (obj) {
+        /* Enumerate Iterator.prototype directly. */
+        JSIteratorOp op = obj->getClass()->ext.iteratorObject;
+        if (op && (obj->getClass() != &js_IteratorClass || obj->getNativeIterator())) {
+            JSObject *iterobj = op(cx, obj, !(flags & JSITER_FOREACH));
+            if (!iterobj)
+                return false;
+            vp->setObject(*iterobj);
+            return true;
+        }
+
         if (keysOnly) {
             /*
              * Check to see if this is the same as the most recent object which
@@ -813,8 +823,7 @@ js_ValueToIterator(JSContext *cx, uintN flags, Value *vp)
         if ((flags & JSITER_ENUMERATE)) {
             if (!js_ValueToObjectOrNull(cx, *vp, &obj))
                 return false;
-            if (!obj)
-                return GetIterator(cx, NULL, flags, vp);
+            /* fall through */
         } else {
             obj = js_ValueToNonNullObject(cx, *vp);
             if (!obj)
@@ -822,18 +831,6 @@ js_ValueToIterator(JSContext *cx, uintN flags, Value *vp)
         }
     }
 
-    AutoObjectRooter tvr(cx, obj);
-
-    /* Enumerate Iterator.prototype directly. */
-    JSIteratorOp op = obj->getClass()->ext.iteratorObject;
-    if (op && (obj->getClass() != &js_IteratorClass || obj->getNativeIterator())) {
-        JSObject *iterobj = op(cx, obj, !(flags & JSITER_FOREACH));
-        if (!iterobj)
-            return false;
-        vp->setObject(*iterobj);
-        return true;
-    }
-
     return GetIterator(cx, obj, flags, vp);
 }
 
@@ -1084,7 +1081,9 @@ stopiter_hasInstance(JSContext *cx, JSObject *obj, const Value *v, JSBool *bp)
 
 Class js_StopIterationClass = {
     js_StopIteration_str,
-    JSCLASS_HAS_CACHED_PROTO(JSProto_StopIteration),
+    JSCLASS_HAS_CACHED_PROTO(JSProto_StopIteration) |
+    JSCLASS_FREEZE_PROTO |
+    JSCLASS_FREEZE_CTOR,
     PropertyStub,   /* addProperty */
     PropertyStub,   /* delProperty */
     PropertyStub,   /* getProperty */

js/src/jsobj.cpp

@@ -3680,6 +3680,13 @@ js_InitClass(JSContext *cx, JSObject *obj, JSObject *parent_proto,
     if (!proto->getEmptyShape(cx, proto->clasp, FINALIZE_OBJECT0))
         goto bad;
 
+    if (clasp->flags & (JSCLASS_FREEZE_PROTO|JSCLASS_FREEZE_CTOR)) {
+        if (proto && (clasp->flags & JSCLASS_FREEZE_PROTO) && !proto->freeze(cx))
+            goto bad;
+        if (ctor && (clasp->flags & JSCLASS_FREEZE_CTOR) && !ctor->freeze(cx))
+            goto bad;
+    }
+
     /* If this is a standard class, cache its prototype. */
     if (key != JSProto_Null && !js_SetClassObject(cx, obj, key, ctor, proto))
         goto bad;