Add m-esr52 at 52.6.0

1 files changed, 1578 insertions, 0 deletions

diff --git a/js/src/jsiter.cpp b/js/src/jsiter.cpp
new file mode 100644
index 0000000000..63c81e6af8
--- /dev/null
+++ b/js/src/jsiter.cpp
@@ -0,0 +1,1578 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/* JavaScript iterators. */
+
+#include "jsiter.h"
+
+#include "mozilla/ArrayUtils.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/MemoryReporting.h"
+#include "mozilla/PodOperations.h"
+
+#include "jsarray.h"
+#include "jsatom.h"
+#include "jscntxt.h"
+#include "jsgc.h"
+#include "jsobj.h"
+#include "jsopcode.h"
+#include "jsscript.h"
+#include "jstypes.h"
+#include "jsutil.h"
+
+#include "ds/Sort.h"
+#include "gc/Marking.h"
+#include "js/Proxy.h"
+#include "vm/GeneratorObject.h"
+#include "vm/GlobalObject.h"
+#include "vm/Interpreter.h"
+#include "vm/Shape.h"
+#include "vm/StopIterationObject.h"
+#include "vm/TypedArrayCommon.h"
+
+#include "jsscriptinlines.h"
+
+#include "vm/NativeObject-inl.h"
+#include "vm/Stack-inl.h"
+#include "vm/String-inl.h"
+
+using namespace js;
+using namespace js::gc;
+using JS::ForOfIterator;
+
+using mozilla::ArrayLength;
+using mozilla::Maybe;
+using mozilla::PodCopy;
+using mozilla::PodZero;
+
+typedef Rooted<PropertyIteratorObject*> RootedPropertyIteratorObject;
+
+static const gc::AllocKind ITERATOR_FINALIZE_KIND = gc::AllocKind::OBJECT2_BACKGROUND;
+
+void
+NativeIterator::trace(JSTracer* trc)
+{
+    for (GCPtrFlatString* str = begin(); str < end(); str++)
+        TraceNullableEdge(trc, str, "prop");
+    TraceNullableEdge(trc, &obj, "obj");
+
+    for (size_t i = 0; i < guard_length; i++)
+        guard_array[i].trace(trc);
+
+    // The SuppressDeletedPropertyHelper loop can GC, so make sure that if the
+    // GC removes any elements from the list, it won't remove this one.
+    if (iterObj_)
+        TraceManuallyBarrieredEdge(trc, &iterObj_, "iterObj");
+}
+
+typedef HashSet<jsid, DefaultHasher<jsid>> IdSet;
+
+static inline bool
+NewKeyValuePair(JSContext* cx, jsid id, const Value& val, MutableHandleValue rval)
+{
+    return NewValuePair(cx, IdToValue(id), val, rval);
+}
+
+static inline bool
+Enumerate(JSContext* cx, HandleObject pobj, jsid id,
+          bool enumerable, unsigned flags, Maybe<IdSet>& ht, AutoIdVector* props)
+{
+    // Allow duplicate properties from Proxy's [[OwnPropertyKeys]].
+    bool proxyOwnProperty = pobj->is<ProxyObject>() && (flags & JSITER_OWNONLY);
+
+    if (!proxyOwnProperty && (!(flags & JSITER_OWNONLY) || pobj->is<ProxyObject>() ||
+        pobj->getOpsEnumerate()))
+    {
+        if (!ht) {
+            ht.emplace(cx);
+            // Most of the time there are only a handful of entries.
+            if (!ht->init(5))
+                return false;
+        }
+
+        // If we've already seen this, we definitely won't add it.
+        IdSet::AddPtr p = ht->lookupForAdd(id);
+        if (MOZ_UNLIKELY(!!p))
+            return true;
+
+        // It's not necessary to add properties to the hash table at the end of
+        // the prototype chain, but custom enumeration behaviors might return
+        // duplicated properties, so always add in such cases.
+        if (pobj->is<ProxyObject>() || pobj->staticPrototype() || pobj->getOpsEnumerate()) {
+            if (!ht->add(p, id))
+                return false;
+        }
+    }
+
+    // Symbol-keyed properties and nonenumerable properties are skipped unless
+    // the caller specifically asks for them. A caller can also filter out
+    // non-symbols by asking for JSITER_SYMBOLSONLY.
+    if (JSID_IS_SYMBOL(id) ? !(flags & JSITER_SYMBOLS) : (flags & JSITER_SYMBOLSONLY))
+        return true;
+    if (!enumerable && !(flags & JSITER_HIDDEN))
+        return true;
+
+    return props->append(id);
+}
+
+static bool
+EnumerateExtraProperties(JSContext* cx, HandleObject obj, unsigned flags, Maybe<IdSet>& ht,
+                         AutoIdVector* props)
+{
+    MOZ_ASSERT(obj->getOpsEnumerate());
+
+    AutoIdVector properties(cx);
+    bool enumerableOnly = !(flags & JSITER_HIDDEN);
+    if (!obj->getOpsEnumerate()(cx, obj, properties, enumerableOnly))
+        return false;
+
+    RootedId id(cx);
+    for (size_t n = 0; n < properties.length(); n++) {
+        id = properties[n];
+
+        // The enumerate hook does not indicate whether the properties
+        // it returns are enumerable or not. Since we already passed
+        // `enumerableOnly` to the hook to filter out non-enumerable
+        // properties, it doesn't really matter what we pass here.
+        bool enumerable = true;
+        if (!Enumerate(cx, obj, id, enumerable, flags, ht, props))
+            return false;
+    }
+
+    return true;
+}
+
+static bool
+SortComparatorIntegerIds(jsid a, jsid b, bool* lessOrEqualp)
+{
+    uint32_t indexA, indexB;
+    MOZ_ALWAYS_TRUE(IdIsIndex(a, &indexA));
+    MOZ_ALWAYS_TRUE(IdIsIndex(b, &indexB));
+    *lessOrEqualp = (indexA <= indexB);
+    return true;
+}
+
+static bool
+EnumerateNativeProperties(JSContext* cx, HandleNativeObject pobj, unsigned flags, Maybe<IdSet>& ht,
+                          AutoIdVector* props, Handle<UnboxedPlainObject*> unboxed = nullptr)
+{
+    bool enumerateSymbols;
+    if (flags & JSITER_SYMBOLSONLY) {
+        enumerateSymbols = true;
+    } else {
+        /* Collect any dense elements from this object. */
+        size_t firstElemIndex = props->length();
+        size_t initlen = pobj->getDenseInitializedLength();
+        const Value* vp = pobj->getDenseElements();
+        bool hasHoles = false;
+        for (size_t i = 0; i < initlen; ++i, ++vp) {
+            if (vp->isMagic(JS_ELEMENTS_HOLE)) {
+                hasHoles = true;
+            } else {
+                /* Dense arrays never get so large that i would not fit into an integer id. */
+                if (!Enumerate(cx, pobj, INT_TO_JSID(i), /* enumerable = */ true, flags, ht, props))
+                    return false;
+            }
+        }
+
+        /* Collect any typed array or shared typed array elements from this object. */
+        if (pobj->is<TypedArrayObject>()) {
+            size_t len = pobj->as<TypedArrayObject>().length();
+            for (size_t i = 0; i < len; i++) {
+                if (!Enumerate(cx, pobj, INT_TO_JSID(i), /* enumerable = */ true, flags, ht, props))
+                    return false;
+            }
+        }
+
+        // Collect any sparse elements from this object.
+        bool isIndexed = pobj->isIndexed();
+        if (isIndexed) {
+            // If the dense elements didn't have holes, we don't need to include
+            // them in the sort.
+            if (!hasHoles)
+                firstElemIndex = props->length();
+
+            for (Shape::Range<NoGC> r(pobj->lastProperty()); !r.empty(); r.popFront()) {
+                Shape& shape = r.front();
+                jsid id = shape.propid();
+                uint32_t dummy;
+                if (IdIsIndex(id, &dummy)) {
+                    if (!Enumerate(cx, pobj, id, shape.enumerable(), flags, ht, props))
+                        return false;
+                }
+            }
+
+            MOZ_ASSERT(firstElemIndex <= props->length());
+
+            jsid* ids = props->begin() + firstElemIndex;
+            size_t n = props->length() - firstElemIndex;
+
+            AutoIdVector tmp(cx);
+            if (!tmp.resize(n))
+                return false;
+            PodCopy(tmp.begin(), ids, n);
+
+            if (!MergeSort(ids, n, tmp.begin(), SortComparatorIntegerIds))
+                return false;
+        }
+
+        if (unboxed) {
+            // If |unboxed| is set then |pobj| is the expando for an unboxed
+            // plain object we are enumerating. Add the unboxed properties
+            // themselves here since they are all property names that were
+            // given to the object before any of the expando's properties.
+            MOZ_ASSERT(pobj->is<UnboxedExpandoObject>());
+            if (!EnumerateExtraProperties(cx, unboxed, flags, ht, props))
+                return false;
+        }
+
+        size_t initialLength = props->length();
+
+        /* Collect all unique property names from this object's shape. */
+        bool symbolsFound = false;
+        Shape::Range<NoGC> r(pobj->lastProperty());
+        for (; !r.empty(); r.popFront()) {
+            Shape& shape = r.front();
+            jsid id = shape.propid();
+
+            if (JSID_IS_SYMBOL(id)) {
+                symbolsFound = true;
+                continue;
+            }
+
+            uint32_t dummy;
+            if (isIndexed && IdIsIndex(id, &dummy))
+                continue;
+
+            if (!Enumerate(cx, pobj, id, shape.enumerable(), flags, ht, props))
+                return false;
+        }
+        ::Reverse(props->begin() + initialLength, props->end());
+
+        enumerateSymbols = symbolsFound && (flags & JSITER_SYMBOLS);
+    }
+
+    if (enumerateSymbols) {
+        // Do a second pass to collect symbols. ES6 draft rev 25 (2014 May 22)
+        // 9.1.12 requires that all symbols appear after all strings in the
+        // result.
+        size_t initialLength = props->length();
+        for (Shape::Range<NoGC> r(pobj->lastProperty()); !r.empty(); r.popFront()) {
+            Shape& shape = r.front();
+            jsid id = shape.propid();
+            if (JSID_IS_SYMBOL(id)) {
+                if (!Enumerate(cx, pobj, id, shape.enumerable(), flags, ht, props))
+                    return false;
+            }
+        }
+        ::Reverse(props->begin() + initialLength, props->end());
+    }
+
+    return true;
+}
+
+#ifdef JS_MORE_DETERMINISTIC
+
+struct SortComparatorIds
+{
+    JSContext*  const cx;
+
+    SortComparatorIds(JSContext* cx)
+      : cx(cx) {}
+
+    bool operator()(jsid a, jsid b, bool* lessOrEqualp)
+    {
+        // Pick an arbitrary order on jsids that is as stable as possible
+        // across executions.
+        if (a == b) {
+            *lessOrEqualp = true;
+            return true;
+        }
+
+        size_t ta = JSID_BITS(a) & JSID_TYPE_MASK;
+        size_t tb = JSID_BITS(b) & JSID_TYPE_MASK;
+        if (ta != tb) {
+            *lessOrEqualp = (ta <= tb);
+            return true;
+        }
+
+        if (JSID_IS_INT(a)) {
+            *lessOrEqualp = (JSID_TO_INT(a) <= JSID_TO_INT(b));
+            return true;
+        }
+
+        RootedString astr(cx), bstr(cx);
+        if (JSID_IS_SYMBOL(a)) {
+            MOZ_ASSERT(JSID_IS_SYMBOL(b));
+            JS::SymbolCode ca = JSID_TO_SYMBOL(a)->code();
+            JS::SymbolCode cb = JSID_TO_SYMBOL(b)->code();
+            if (ca != cb) {
+                *lessOrEqualp = uint32_t(ca) <= uint32_t(cb);
+                return true;
+            }
+            MOZ_ASSERT(ca == JS::SymbolCode::InSymbolRegistry || ca == JS::SymbolCode::UniqueSymbol);
+            astr = JSID_TO_SYMBOL(a)->description();
+            bstr = JSID_TO_SYMBOL(b)->description();
+            if (!astr || !bstr) {
+                *lessOrEqualp = !astr;
+                return true;
+            }
+
+            // Fall through to string comparison on the descriptions. The sort
+            // order is nondeterministic if two different unique symbols have
+            // the same description.
+        } else {
+            astr = IdToString(cx, a);
+            if (!astr)
+                return false;
+            bstr = IdToString(cx, b);
+            if (!bstr)
+                return false;
+        }
+
+        int32_t result;
+        if (!CompareStrings(cx, astr, bstr, &result))
+            return false;
+
+        *lessOrEqualp = (result <= 0);
+        return true;
+    }
+};
+
+#endif /* JS_MORE_DETERMINISTIC */
+
+static bool
+Snapshot(JSContext* cx, HandleObject pobj_, unsigned flags, AutoIdVector* props)
+{
+    // We initialize |ht| lazily (in Enumerate()) because it ends up unused
+    // anywhere from 67--99.9% of the time.
+    Maybe<IdSet> ht;
+    RootedObject pobj(cx, pobj_);
+
+    do {
+        if (pobj->getOpsEnumerate()) {
+            if (pobj->is<UnboxedPlainObject>() && pobj->as<UnboxedPlainObject>().maybeExpando()) {
+                // Special case unboxed objects with an expando object.
+                RootedNativeObject expando(cx, pobj->as<UnboxedPlainObject>().maybeExpando());
+                if (!EnumerateNativeProperties(cx, expando, flags, ht, props,
+                                               pobj.as<UnboxedPlainObject>()))
+                {
+                    return false;
+                }
+            } else {
+                if (!EnumerateExtraProperties(cx, pobj, flags, ht, props))
+                    return false;
+
+                if (pobj->isNative()) {
+                    if (!EnumerateNativeProperties(cx, pobj.as<NativeObject>(), flags, ht, props))
+                        return false;
+                }
+            }
+        } else if (pobj->isNative()) {
+            // Give the object a chance to resolve all lazy properties
+            if (JSEnumerateOp enumerate = pobj->getClass()->getEnumerate()) {
+                if (!enumerate(cx, pobj.as<NativeObject>()))
+                    return false;
+            }
+            if (!EnumerateNativeProperties(cx, pobj.as<NativeObject>(), flags, ht, props))
+                return false;
+        } else if (pobj->is<ProxyObject>()) {
+            AutoIdVector proxyProps(cx);
+            if (flags & JSITER_HIDDEN || flags & JSITER_SYMBOLS) {
+                // This gets all property keys, both strings and
+                // symbols.  The call to Enumerate in the loop below
+                // will filter out unwanted keys, per the flags.
+                if (!Proxy::ownPropertyKeys(cx, pobj, proxyProps))
+                    return false;
+
+                Rooted<PropertyDescriptor> desc(cx);
+                for (size_t n = 0, len = proxyProps.length(); n < len; n++) {
+                    bool enumerable = false;
+
+                    // We need to filter, if the caller just wants enumerable
+                    // symbols.
+                    if (!(flags & JSITER_HIDDEN)) {
+                        if (!Proxy::getOwnPropertyDescriptor(cx, pobj, proxyProps[n], &desc))
+                            return false;
+                        enumerable = desc.enumerable();
+                    }
+
+                    if (!Enumerate(cx, pobj, proxyProps[n], enumerable, flags, ht, props))
+                        return false;
+                }
+            } else {
+                // Returns enumerable property names (no symbols).
+                if (!Proxy::getOwnEnumerablePropertyKeys(cx, pobj, proxyProps))
+                    return false;
+
+                for (size_t n = 0, len = proxyProps.length(); n < len; n++) {
+                    if (!Enumerate(cx, pobj, proxyProps[n], true, flags, ht, props))
+                        return false;
+                }
+            }
+        } else {
+            MOZ_CRASH("non-native objects must have an enumerate op");
+        }
+
+        if (flags & JSITER_OWNONLY)
+            break;
+
+        if (!GetPrototype(cx, pobj, &pobj))
+            return false;
+
+    } while (pobj != nullptr);
+
+#ifdef JS_MORE_DETERMINISTIC
+
+    /*
+     * In some cases the enumeration order for an object depends on the
+     * execution mode (interpreter vs. JIT), especially for native objects
+     * with a class enumerate hook (where resolving a property changes the
+     * resulting enumeration order). These aren't really bugs, but the
+     * differences can change the generated output and confuse correctness
+     * fuzzers, so we sort the ids if such a fuzzer is running.
+     *
+     * We don't do this in the general case because (a) doing so is slow,
+     * and (b) it also breaks the web, which expects enumeration order to
+     * follow the order in which properties are added, in certain cases.
+     * Since ECMA does not specify an enumeration order for objects, both
+     * behaviors are technically correct to do.
+     */
+
+    jsid* ids = props->begin();
+    size_t n = props->length();
+
+    AutoIdVector tmp(cx);
+    if (!tmp.resize(n))
+        return false;
+    PodCopy(tmp.begin(), ids, n);
+
+    if (!MergeSort(ids, n, tmp.begin(), SortComparatorIds(cx)))
+        return false;
+
+#endif /* JS_MORE_DETERMINISTIC */
+
+    return true;
+}
+
+JS_FRIEND_API(bool)
+js::GetPropertyKeys(JSContext* cx, HandleObject obj, unsigned flags, AutoIdVector* props)
+{
+    return Snapshot(cx, obj,
+                    flags & (JSITER_OWNONLY | JSITER_HIDDEN | JSITER_SYMBOLS | JSITER_SYMBOLSONLY),
+                    props);
+}
+
+size_t sCustomIteratorCount = 0;
+
+static inline bool
+GetCustomIterator(JSContext* cx, HandleObject obj, unsigned flags, MutableHandleObject objp)
+{
+    JS_CHECK_RECURSION(cx, return false);
+
+    RootedValue rval(cx);
+    /* Check whether we have a valid __iterator__ method. */
+    HandlePropertyName name = cx->names().iteratorIntrinsic;
+    if (!GetProperty(cx, obj, obj, name, &rval))
+        return false;
+
+    /* If there is no custom __iterator__ method, we are done here. */
+    if (!rval.isObject()) {
+        objp.set(nullptr);
+        return true;
+    }
+
+    if (!cx->runningWithTrustedPrincipals())
+        ++sCustomIteratorCount;
+
+    /* Otherwise call it and return that object. */
+    {
+        FixedInvokeArgs<1> args(cx);
+
+        args[0].setBoolean((flags & JSITER_FOREACH) == 0);
+
+        RootedValue thisv(cx, ObjectValue(*obj));
+        if (!js::Call(cx, rval, thisv, args, &rval))
+            return false;
+    }
+
+    if (rval.isPrimitive()) {
+        // Ignore the stack when throwing. We can't tell whether we were
+        // supposed to skip over a new.target or not.
+        JSAutoByteString bytes;
+        if (!AtomToPrintableString(cx, name, &bytes))
+            return false;
+        RootedValue val(cx, ObjectValue(*obj));
+        ReportValueError2(cx, JSMSG_BAD_TRAP_RETURN_VALUE,
+                          JSDVG_IGNORE_STACK, val, nullptr, bytes.ptr());
+        return false;
+    }
+    objp.set(&rval.toObject());
+    return true;
+}
+
+template <typename T>
+static inline bool
+Compare(T* a, T* b, size_t c)
+{
+    size_t n = (c + size_t(7)) / size_t(8);
+    switch (c % 8) {
+      case 0: do { if (*a++ != *b++) return false; MOZ_FALLTHROUGH;
+      case 7:      if (*a++ != *b++) return false; MOZ_FALLTHROUGH;
+      case 6:      if (*a++ != *b++) return false; MOZ_FALLTHROUGH;
+      case 5:      if (*a++ != *b++) return false; MOZ_FALLTHROUGH;
+      case 4:      if (*a++ != *b++) return false; MOZ_FALLTHROUGH;
+      case 3:      if (*a++ != *b++) return false; MOZ_FALLTHROUGH;
+      case 2:      if (*a++ != *b++) return false; MOZ_FALLTHROUGH;
+      case 1:      if (*a++ != *b++) return false;
+              } while (--n > 0);
+    }
+    return true;
+}
+
+static bool legacy_iterator_next(JSContext* cx, unsigned argc, Value* vp);
+
+static inline PropertyIteratorObject*
+NewPropertyIteratorObject(JSContext* cx, unsigned flags)
+{
+    if (flags & JSITER_ENUMERATE) {
+        RootedObjectGroup group(cx, ObjectGroup::defaultNewGroup(cx, &PropertyIteratorObject::class_,
+                                                                 TaggedProto(nullptr)));
+        if (!group)
+            return nullptr;
+
+        const Class* clasp = &PropertyIteratorObject::class_;
+        RootedShape shape(cx, EmptyShape::getInitialShape(cx, clasp, TaggedProto(nullptr),
+                                                          ITERATOR_FINALIZE_KIND));
+        if (!shape)
+            return nullptr;
+
+        JSObject* obj = JSObject::create(cx, ITERATOR_FINALIZE_KIND,
+                                         GetInitialHeap(GenericObject, clasp), shape, group);
+        if (!obj)
+            return nullptr;
+
+        PropertyIteratorObject* res = &obj->as<PropertyIteratorObject>();
+
+        MOZ_ASSERT(res->numFixedSlots() == JSObject::ITER_CLASS_NFIXED_SLOTS);
+        return res;
+    }
+
+    Rooted<PropertyIteratorObject*> res(cx, NewBuiltinClassInstance<PropertyIteratorObject>(cx));
+    if (!res)
+        return nullptr;
+
+    if (flags == 0) {
+        // Redefine next as an own property. This ensure that deleting the
+        // next method on the prototype doesn't break cross-global for .. in.
+        // We don't have to do this for JSITER_ENUMERATE because that object always
+        // takes an optimized path.
+        RootedFunction next(cx, NewNativeFunction(cx, legacy_iterator_next, 0,
+                                                  HandlePropertyName(cx->names().next)));
+        if (!next)
+            return nullptr;
+
+        RootedValue value(cx, ObjectValue(*next));
+        if (!DefineProperty(cx, res, cx->names().next, value))
+            return nullptr;
+    }
+
+    return res;
+}
+
+NativeIterator*
+NativeIterator::allocateIterator(JSContext* cx, uint32_t numGuards, uint32_t plength)
+{
+    JS_STATIC_ASSERT(sizeof(ReceiverGuard) == 2 * sizeof(void*));
+
+    size_t extraLength = plength + numGuards * 2;
+    NativeIterator* ni = cx->zone()->pod_malloc_with_extra<NativeIterator, void*>(extraLength);
+    if (!ni) {
+        ReportOutOfMemory(cx);
+        return nullptr;
+    }
+
+    void** extra = reinterpret_cast<void**>(ni + 1);
+    PodZero(ni);
+    PodZero(extra, extraLength);
+    ni->props_array = ni->props_cursor = reinterpret_cast<GCPtrFlatString*>(extra);
+    ni->props_end = ni->props_array + plength;
+    return ni;
+}
+
+NativeIterator*
+NativeIterator::allocateSentinel(JSContext* maybecx)
+{
+    NativeIterator* ni = js_pod_malloc<NativeIterator>();
+    if (!ni) {
+        if (maybecx)
+            ReportOutOfMemory(maybecx);
+        return nullptr;
+    }
+
+    PodZero(ni);
+
+    ni->next_ = ni;
+    ni->prev_ = ni;
+    return ni;
+}
+
+inline void
+NativeIterator::init(JSObject* obj, JSObject* iterObj, unsigned flags, uint32_t numGuards, uint32_t key)
+{
+    this->obj.init(obj);
+    this->iterObj_ = iterObj;
+    this->flags = flags;
+    this->guard_array = (HeapReceiverGuard*) this->props_end;
+    this->guard_length = numGuards;
+    this->guard_key = key;
+}
+
+bool
+NativeIterator::initProperties(JSContext* cx, Handle<PropertyIteratorObject*> obj,
+                               const AutoIdVector& props)
+{
+    // The obj parameter is just so that we can ensure that this object will get
+    // traced if we GC.
+    MOZ_ASSERT(this == obj->getNativeIterator());
+
+    size_t plength = props.length();
+    MOZ_ASSERT(plength == size_t(end() - begin()));
+
+    for (size_t i = 0; i < plength; i++) {
+        JSFlatString* str = IdToString(cx, props[i]);
+        if (!str)
+            return false;
+        props_array[i].init(str);
+    }
+
+    return true;
+}
+
+static inline void
+RegisterEnumerator(JSContext* cx, PropertyIteratorObject* iterobj, NativeIterator* ni)
+{
+    /* Register non-escaping native enumerators (for-in) with the current context. */
+    if (ni->flags & JSITER_ENUMERATE) {
+        ni->link(cx->compartment()->enumerators);
+
+        MOZ_ASSERT(!(ni->flags & JSITER_ACTIVE));
+        ni->flags |= JSITER_ACTIVE;
+    }
+}
+
+static inline bool
+VectorToKeyIterator(JSContext* cx, HandleObject obj, unsigned flags, AutoIdVector& keys,
+                    uint32_t numGuards, uint32_t key, MutableHandleObject objp)
+{
+    MOZ_ASSERT(!(flags & JSITER_FOREACH));
+
+    if (obj->isSingleton() && !obj->setIteratedSingleton(cx))
+        return false;
+    MarkObjectGroupFlags(cx, obj, OBJECT_FLAG_ITERATED);
+
+    Rooted<PropertyIteratorObject*> iterobj(cx, NewPropertyIteratorObject(cx, flags));
+    if (!iterobj)
+        return false;
+
+    NativeIterator* ni = NativeIterator::allocateIterator(cx, numGuards, keys.length());
+    if (!ni)
+        return false;
+
+    iterobj->setNativeIterator(ni);
+    ni->init(obj, iterobj, flags, numGuards, key);
+    if (!ni->initProperties(cx, iterobj, keys))
+        return false;
+
+    if (numGuards) {
+        // Fill in the guard array from scratch.
+        JSObject* pobj = obj;
+        size_t ind = 0;
+        do {
+            ni->guard_array[ind++].init(ReceiverGuard(pobj));
+
+            // The one caller of this method that passes |numGuards > 0|, does
+            // so only if the entire chain consists of cacheable objects (that
+            // necessarily have static prototypes).
+            pobj = pobj->staticPrototype();
+        } while (pobj);
+        MOZ_ASSERT(ind == numGuards);
+    }
+
+    objp.set(iterobj);
+
+    RegisterEnumerator(cx, iterobj, ni);
+    return true;
+}
+
+static bool
+VectorToValueIterator(JSContext* cx, HandleObject obj, unsigned flags, AutoIdVector& keys,
+                      MutableHandleObject objp)
+{
+    MOZ_ASSERT(flags & JSITER_FOREACH);
+
+    if (obj->isSingleton() && !obj->setIteratedSingleton(cx))
+        return false;
+    MarkObjectGroupFlags(cx, obj, OBJECT_FLAG_ITERATED);
+
+    Rooted<PropertyIteratorObject*> iterobj(cx, NewPropertyIteratorObject(cx, flags));
+    if (!iterobj)
+        return false;
+
+    NativeIterator* ni = NativeIterator::allocateIterator(cx, 0, keys.length());
+    if (!ni)
+        return false;
+
+    iterobj->setNativeIterator(ni);
+    ni->init(obj, iterobj, flags, 0, 0);
+    if (!ni->initProperties(cx, iterobj, keys))
+        return false;
+
+    objp.set(iterobj);
+
+    RegisterEnumerator(cx, iterobj, ni);
+    return true;
+}
+
+bool
+js::EnumeratedIdVectorToIterator(JSContext* cx, HandleObject obj, unsigned flags,
+                                 AutoIdVector& props, MutableHandleObject objp)
+{
+    if (!(flags & JSITER_FOREACH))
+        return VectorToKeyIterator(cx, obj, flags, props, 0, 0, objp);
+
+    return VectorToValueIterator(cx, obj, flags, props, objp);
+}
+
+// Mainly used for .. in over null/undefined
+bool
+js::NewEmptyPropertyIterator(JSContext* cx, unsigned flags, MutableHandleObject objp)
+{
+    Rooted<PropertyIteratorObject*> iterobj(cx, NewPropertyIteratorObject(cx, flags));
+    if (!iterobj)
+        return false;
+
+    AutoIdVector keys(cx); // Empty
+    NativeIterator* ni = NativeIterator::allocateIterator(cx, 0, keys.length());
+    if (!ni)
+        return false;
+
+    iterobj->setNativeIterator(ni);
+    ni->init(nullptr, iterobj, flags, 0, 0);
+    if (!ni->initProperties(cx, iterobj, keys))
+        return false;
+
+    objp.set(iterobj);
+
+    RegisterEnumerator(cx, iterobj, ni);
+    return true;
+}
+
+static inline void
+UpdateNativeIterator(NativeIterator* ni, JSObject* obj)
+{
+    // Update the object for which the native iterator is associated, so
+    // SuppressDeletedPropertyHelper will recognize the iterator as a match.
+    ni->obj = obj;
+}
+
+static inline bool
+CanCompareIterableObjectToCache(JSObject* obj)
+{
+    if (obj->isNative())
+        return obj->as<NativeObject>().hasEmptyElements();
+    if (obj->is<UnboxedPlainObject>()) {
+        if (UnboxedExpandoObject* expando = obj->as<UnboxedPlainObject>().maybeExpando())
+            return expando->hasEmptyElements();
+        return true;
+    }
+    return false;
+}
+
+static inline bool
+CanCacheIterableObject(JSContext* cx, JSObject* obj)
+{
+    if (!CanCompareIterableObjectToCache(obj))
+        return false;
+    if (obj->isNative()) {
+        if (obj->is<TypedArrayObject>() ||
+            obj->hasUncacheableProto() ||
+            obj->getOpsEnumerate() ||
+            obj->getClass()->getEnumerate() ||
+            obj->as<NativeObject>().containsPure(cx->names().iteratorIntrinsic))
+        {
+            return false;
+        }
+    }
+    return true;
+}
+
+bool
+js::GetIterator(JSContext* cx, HandleObject obj, unsigned flags, MutableHandleObject objp)
+{
+    if (obj->is<PropertyIteratorObject>() || obj->is<LegacyGeneratorObject>()) {
+        objp.set(obj);
+        return true;
+    }
+
+    // We should only call the enumerate trap for "for-in".
+    // Or when we call GetIterator from the Proxy [[Enumerate]] hook.
+    // JSITER_ENUMERATE is just an optimization and the same
+    // as flags == 0 otherwise.
+    if (flags == 0 || flags == JSITER_ENUMERATE) {
+        if (obj->is<ProxyObject>())
+            return Proxy::enumerate(cx, obj, objp);
+    }
+
+    Vector<ReceiverGuard, 8> guards(cx);
+    uint32_t key = 0;
+    if (flags == JSITER_ENUMERATE) {
+        // Check to see if this is the same as the most recent object which was
+        // iterated over.
+        if (PropertyIteratorObject* last = cx->compartment()->lastCachedNativeIterator) {
+            NativeIterator* lastni = last->getNativeIterator();
+            if (!(lastni->flags & (JSITER_ACTIVE|JSITER_UNREUSABLE)) &&
+                CanCompareIterableObjectToCache(obj) &&
+                ReceiverGuard(obj) == lastni->guard_array[0])
+            {
+                JSObject* proto = obj->staticPrototype();
+                if (CanCompareIterableObjectToCache(proto) &&
+                    ReceiverGuard(proto) == lastni->guard_array[1] &&
+                    !proto->staticPrototype())
+                {
+                    objp.set(last);
+                    assertSameCompartment(cx, objp);
+                    UpdateNativeIterator(lastni, obj);
+                    RegisterEnumerator(cx, last, lastni);
+                    return true;
+                }
+            }
+        }
+
+        // The iterator object for JSITER_ENUMERATE never escapes, so we don't
+        // care that the "proper" prototype is set.  This also lets us reuse an
+        // old, inactive iterator object.
+        {
+            JSObject* pobj = obj;
+            do {
+                if (!CanCacheIterableObject(cx, pobj)) {
+                    guards.clear();
+                    goto miss;
+                }
+
+                ReceiverGuard guard(pobj);
+                key = (key + (key << 16)) ^ guard.hash();
+                if (!guards.append(guard))
+                    return false;
+
+                pobj = pobj->staticPrototype();
+            } while (pobj);
+        }
+
+        if (PropertyIteratorObject* iterobj = cx->caches.nativeIterCache.get(key)) {
+            NativeIterator* ni = iterobj->getNativeIterator();
+            if (!(ni->flags & (JSITER_ACTIVE|JSITER_UNREUSABLE)) &&
+                ni->guard_key == key &&
+                ni->guard_length == guards.length() &&
+                Compare(reinterpret_cast<ReceiverGuard*>(ni->guard_array),
+                        guards.begin(), ni->guard_length) &&
+                iterobj->compartment() == cx->compartment())
+            {
+                objp.set(iterobj);
+
+                UpdateNativeIterator(ni, obj);
+                RegisterEnumerator(cx, iterobj, ni);
+                if (guards.length() == 2)
+                    cx->compartment()->lastCachedNativeIterator = iterobj;
+                return true;
+            }
+        }
+    }
+
+  miss:
+    if (!GetCustomIterator(cx, obj, flags, objp))
+        return false;
+    if (objp) {
+        assertSameCompartment(cx, objp);
+        return true;
+    }
+
+    AutoIdVector keys(cx);
+    if (flags & JSITER_FOREACH) {
+        MOZ_ASSERT(guards.empty());
+
+        if (!Snapshot(cx, obj, flags, &keys))
+            return false;
+        if (!VectorToValueIterator(cx, obj, flags, keys, objp))
+            return false;
+    } else {
+        if (!Snapshot(cx, obj, flags, &keys))
+            return false;
+        if (!VectorToKeyIterator(cx, obj, flags, keys, guards.length(), key, objp))
+            return false;
+    }
+
+    PropertyIteratorObject* iterobj = &objp->as<PropertyIteratorObject>();
+    assertSameCompartment(cx, iterobj);
+
+    /* Cache the iterator object if possible. */
+    if (guards.length())
+        cx->caches.nativeIterCache.set(key, iterobj);
+
+    if (guards.length() == 2)
+        cx->compartment()->lastCachedNativeIterator = iterobj;
+    return true;
+}
+
+JSObject*
+js::GetIteratorObject(JSContext* cx, HandleObject obj, uint32_t flags)
+{
+    RootedObject iterator(cx);
+    if (!GetIterator(cx, obj, flags, &iterator))
+        return nullptr;
+    return iterator;
+}
+
+JSObject*
+js::CreateItrResultObject(JSContext* cx, HandleValue value, bool done)
+{
+    // FIXME: We can cache the iterator result object shape somewhere.
+    AssertHeapIsIdle(cx);
+
+    RootedObject proto(cx, cx->global()->getOrCreateObjectPrototype(cx));
+    if (!proto)
+        return nullptr;
+
+    RootedPlainObject obj(cx, NewObjectWithGivenProto<PlainObject>(cx, proto));
+    if (!obj)
+        return nullptr;
+
+    if (!DefineProperty(cx, obj, cx->names().value, value))
+        return nullptr;
+
+    RootedValue doneBool(cx, BooleanValue(done));
+    if (!DefineProperty(cx, obj, cx->names().done, doneBool))
+        return nullptr;
+
+    return obj;
+}
+
+bool
+js::ThrowStopIteration(JSContext* cx)
+{
+    MOZ_ASSERT(!JS_IsExceptionPending(cx));
+
+    // StopIteration isn't a constructor, but it's stored in GlobalObject
+    // as one, out of laziness. Hence the GetBuiltinConstructor call here.
+    RootedObject ctor(cx);
+    if (GetBuiltinConstructor(cx, JSProto_StopIteration, &ctor))
+        cx->setPendingException(ObjectValue(*ctor));
+    return false;
+}
+
+/*** Iterator objects ****************************************************************************/
+
+bool
+js::IteratorConstructor(JSContext* cx, unsigned argc, Value* vp)
+{
+    CallArgs args = CallArgsFromVp(argc, vp);
+    if (args.length() == 0) {
+        ReportMissingArg(cx, args.calleev(), 0);
+        return false;
+    }
+
+    bool keyonly = false;
+    if (args.length() >= 2)
+        keyonly = ToBoolean(args[1]);
+    unsigned flags = JSITER_OWNONLY | (keyonly ? 0 : (JSITER_FOREACH | JSITER_KEYVALUE));
+
+    RootedObject iterobj(cx, ValueToIterator(cx, flags, args[0]));
+    if (!iterobj)
+        return false;
+    args.rval().setObject(*iterobj);
+    return true;
+}
+
+MOZ_ALWAYS_INLINE bool
+NativeIteratorNext(JSContext* cx, NativeIterator* ni, MutableHandleValue rval, bool* done)
+{
+    *done = false;
+
+    if (ni->props_cursor >= ni->props_end) {
+        *done = true;
+        return true;
+    }
+
+    if (MOZ_LIKELY(ni->isKeyIter())) {
+        rval.setString(*ni->current());
+        ni->incCursor();
+        return true;
+    }
+
+    // Non-standard Iterator for "for each"
+    RootedId id(cx);
+    RootedValue current(cx, StringValue(*ni->current()));
+    if (!ValueToId<CanGC>(cx, current, &id))
+        return false;
+    ni->incCursor();
+    RootedObject obj(cx, ni->obj);
+    if (!GetProperty(cx, obj, obj, id, rval))
+        return false;
+
+    // JS 1.7 only: for each (let [k, v] in obj)
+    if (ni->flags & JSITER_KEYVALUE)
+        return NewKeyValuePair(cx, id, rval, rval);
+    return true;
+}
+
+MOZ_ALWAYS_INLINE bool
+IsIterator(HandleValue v)
+{
+    return v.isObject() && v.toObject().hasClass(&PropertyIteratorObject::class_);
+}
+
+MOZ_ALWAYS_INLINE bool
+legacy_iterator_next_impl(JSContext* cx, const CallArgs& args)
+{
+    MOZ_ASSERT(IsIterator(args.thisv()));
+
+    RootedObject thisObj(cx, &args.thisv().toObject());
+
+    NativeIterator* ni = thisObj.as<PropertyIteratorObject>()->getNativeIterator();
+    RootedValue value(cx);
+    bool done;
+    if (!NativeIteratorNext(cx, ni, &value, &done))
+         return false;
+
+    // Use old iterator protocol for compatibility reasons.
+    if (done) {
+        ThrowStopIteration(cx);
+        return false;
+    }
+
+    args.rval().set(value);
+    return true;
+}
+
+static bool
+legacy_iterator_next(JSContext* cx, unsigned argc, Value* vp)
+{
+    CallArgs args = CallArgsFromVp(argc, vp);
+    return CallNonGenericMethod<IsIterator, legacy_iterator_next_impl>(cx, args);
+}
+
+static const JSFunctionSpec legacy_iterator_methods[] = {
+    JS_SELF_HOSTED_SYM_FN(iterator, "LegacyIteratorShim", 0, 0),
+    JS_FN("next",      legacy_iterator_next,       0, 0),
+    JS_FS_END
+};
+
+size_t
+PropertyIteratorObject::sizeOfMisc(mozilla::MallocSizeOf mallocSizeOf) const
+{
+    return mallocSizeOf(getPrivate());
+}
+
+void
+PropertyIteratorObject::trace(JSTracer* trc, JSObject* obj)
+{
+    if (NativeIterator* ni = obj->as<PropertyIteratorObject>().getNativeIterator())
+        ni->trace(trc);
+}
+
+void
+PropertyIteratorObject::finalize(FreeOp* fop, JSObject* obj)
+{
+    if (NativeIterator* ni = obj->as<PropertyIteratorObject>().getNativeIterator())
+        fop->free_(ni);
+}
+
+const ClassOps PropertyIteratorObject::classOps_ = {
+    nullptr, /* addProperty */
+    nullptr, /* delProperty */
+    nullptr, /* getProperty */
+    nullptr, /* setProperty */
+    nullptr, /* enumerate */
+    nullptr, /* resolve */
+    nullptr, /* mayResolve */
+    finalize,
+    nullptr, /* call        */
+    nullptr, /* hasInstance */
+    nullptr, /* construct   */
+    trace
+};
+
+const Class PropertyIteratorObject::class_ = {
+    "Iterator",
+    JSCLASS_HAS_CACHED_PROTO(JSProto_Iterator) |
+    JSCLASS_HAS_PRIVATE |
+    JSCLASS_BACKGROUND_FINALIZE,
+    &PropertyIteratorObject::classOps_
+};
+
+static const Class ArrayIteratorPrototypeClass = {
+    "Array Iterator",
+    0
+};
+
+enum {
+    ArrayIteratorSlotIteratedObject,
+    ArrayIteratorSlotNextIndex,
+    ArrayIteratorSlotItemKind,
+    ArrayIteratorSlotCount
+};
+
+const Class ArrayIteratorObject::class_ = {
+    "Array Iterator",
+    JSCLASS_HAS_RESERVED_SLOTS(ArrayIteratorSlotCount)
+};
+
+static const JSFunctionSpec array_iterator_methods[] = {
+    JS_SELF_HOSTED_FN("next", "ArrayIteratorNext", 0, 0),
+    JS_FS_END
+};
+
+static const Class StringIteratorPrototypeClass = {
+    "String Iterator",
+    0
+};
+
+enum {
+    StringIteratorSlotIteratedObject,
+    StringIteratorSlotNextIndex,
+    StringIteratorSlotCount
+};
+
+const Class StringIteratorObject::class_ = {
+    "String Iterator",
+    JSCLASS_HAS_RESERVED_SLOTS(StringIteratorSlotCount)
+};
+
+static const JSFunctionSpec string_iterator_methods[] = {
+    JS_SELF_HOSTED_FN("next", "StringIteratorNext", 0, 0),
+    JS_FS_END
+};
+
+enum {
+    ListIteratorSlotIteratedObject,
+    ListIteratorSlotNextIndex,
+    ListIteratorSlotNextMethod,
+    ListIteratorSlotCount
+};
+
+const Class ListIteratorObject::class_ = {
+    "List Iterator",
+    JSCLASS_HAS_RESERVED_SLOTS(ListIteratorSlotCount)
+};
+
+JSObject*
+js::ValueToIterator(JSContext* cx, unsigned flags, HandleValue vp)
+{
+    /* JSITER_KEYVALUE must always come with JSITER_FOREACH */
+    MOZ_ASSERT_IF(flags & JSITER_KEYVALUE, flags & JSITER_FOREACH);
+
+    RootedObject obj(cx);
+    if (vp.isObject()) {
+        /* Common case. */
+        obj = &vp.toObject();
+    } else if ((flags & JSITER_ENUMERATE) && vp.isNullOrUndefined()) {
+        /*
+         * Enumerating over null and undefined gives an empty enumerator, so
+         * that |for (var p in <null or undefined>) <loop>;| never executes
+         * <loop>, per ES5 12.6.4.
+         */
+        RootedObject iter(cx);
+        if (!NewEmptyPropertyIterator(cx, flags, &iter))
+            return nullptr;
+        return iter;
+    } else {
+        obj = ToObject(cx, vp);
+        if (!obj)
+            return nullptr;
+    }
+
+    RootedObject iter(cx);
+    if (!GetIterator(cx, obj, flags, &iter))
+        return nullptr;
+    return iter;
+}
+
+bool
+js::CloseIterator(JSContext* cx, HandleObject obj)
+{
+    if (obj->is<PropertyIteratorObject>()) {
+        /* Remove enumerators from the active list, which is a stack. */
+        NativeIterator* ni = obj->as<PropertyIteratorObject>().getNativeIterator();
+
+        if (ni->flags & JSITER_ENUMERATE) {
+            ni->unlink();
+
+            MOZ_ASSERT(ni->flags & JSITER_ACTIVE);
+            ni->flags &= ~JSITER_ACTIVE;
+
+            /*
+             * Reset the enumerator; it may still be in the cached iterators
+             * for this thread, and can be reused.
+             */
+            ni->props_cursor = ni->props_array;
+        }
+    } else if (obj->is<LegacyGeneratorObject>()) {
+        Rooted<LegacyGeneratorObject*> genObj(cx, &obj->as<LegacyGeneratorObject>());
+        if (genObj->isClosed())
+            return true;
+        if (genObj->isRunning() || genObj->isClosing()) {
+            // Nothing sensible to do.
+            return true;
+        }
+        return LegacyGeneratorObject::close(cx, obj);
+    }
+    return true;
+}
+
+bool
+js::UnwindIteratorForException(JSContext* cx, HandleObject obj)
+{
+    RootedValue v(cx);
+    bool getOk = cx->getPendingException(&v);
+    cx->clearPendingException();
+    if (!CloseIterator(cx, obj))
+        return false;
+    if (!getOk)
+        return false;
+    cx->setPendingException(v);
+    return true;
+}
+
+void
+js::UnwindIteratorForUncatchableException(JSContext* cx, JSObject* obj)
+{
+    if (obj->is<PropertyIteratorObject>()) {
+        NativeIterator* ni = obj->as<PropertyIteratorObject>().getNativeIterator();
+        if (ni->flags & JSITER_ENUMERATE)
+            ni->unlink();
+    }
+}
+
+/*
+ * Suppress enumeration of deleted properties. This function must be called
+ * when a property is deleted and there might be active enumerators.
+ *
+ * We maintain a list of active non-escaping for-in enumerators. To suppress
+ * a property, we check whether each active enumerator contains the (obj, id)
+ * pair and has not yet enumerated |id|. If so, and |id| is the next property,
+ * we simply advance the cursor. Otherwise, we delete |id| from the list.
+ *
+ * We do not suppress enumeration of a property deleted along an object's
+ * prototype chain. Only direct deletions on the object are handled.
+ *
+ * This function can suppress multiple properties at once. The |predicate|
+ * argument is an object which can be called on an id and returns true or
+ * false. It also must have a method |matchesAtMostOne| which allows us to
+ * stop searching after the first deletion if true.
+ */
+template<typename StringPredicate>
+static bool
+SuppressDeletedPropertyHelper(JSContext* cx, HandleObject obj, StringPredicate predicate)
+{
+    NativeIterator* enumeratorList = cx->compartment()->enumerators;
+    NativeIterator* ni = enumeratorList->next();
+
+    while (ni != enumeratorList) {
+      again:
+        /* This only works for identified suppressed keys, not values. */
+        if (ni->isKeyIter() && ni->obj == obj && ni->props_cursor < ni->props_end) {
+            /* Check whether id is still to come. */
+            GCPtrFlatString* props_cursor = ni->current();
+            GCPtrFlatString* props_end = ni->end();
+            for (GCPtrFlatString* idp = props_cursor; idp < props_end; ++idp) {
+                if (predicate(*idp)) {
+                    /*
+                     * Check whether another property along the prototype chain
+                     * became visible as a result of this deletion.
+                     */
+                    RootedObject proto(cx);
+                    if (!GetPrototype(cx, obj, &proto))
+                        return false;
+                    if (proto) {
+                        RootedId id(cx);
+                        RootedValue idv(cx, StringValue(*idp));
+                        if (!ValueToId<CanGC>(cx, idv, &id))
+                            return false;
+
+                        Rooted<PropertyDescriptor> desc(cx);
+                        if (!GetPropertyDescriptor(cx, proto, id, &desc))
+                            return false;
+
+                        if (desc.object()) {
+                            if (desc.enumerable())
+                                continue;
+                        }
+                    }
+
+                    /*
+                     * If GetPropertyDescriptorById above removed a property from
+                     * ni, start over.
+                     */
+                    if (props_end != ni->props_end || props_cursor != ni->props_cursor)
+                        goto again;
+
+                    /*
+                     * No property along the prototype chain stepped in to take the
+                     * property's place, so go ahead and delete id from the list.
+                     * If it is the next property to be enumerated, just skip it.
+                     */
+                    if (idp == props_cursor) {
+                        ni->incCursor();
+                    } else {
+                        for (GCPtrFlatString* p = idp; p + 1 != props_end; p++)
+                            *p = *(p + 1);
+                        ni->props_end = ni->end() - 1;
+
+                        /*
+                         * This invokes the pre barrier on this element, since
+                         * it's no longer going to be marked, and ensures that
+                         * any existing remembered set entry will be dropped.
+                         */
+                        *ni->props_end = nullptr;
+                    }
+
+                    /* Don't reuse modified native iterators. */
+                    ni->flags |= JSITER_UNREUSABLE;
+
+                    if (predicate.matchesAtMostOne())
+                        break;
+                }
+            }
+        }
+        ni = ni->next();
+    }
+    return true;
+}
+
+namespace {
+
+class SingleStringPredicate {
+    Handle<JSFlatString*> str;
+public:
+    explicit SingleStringPredicate(Handle<JSFlatString*> str) : str(str) {}
+
+    bool operator()(JSFlatString* str) { return EqualStrings(str, this->str); }
+    bool matchesAtMostOne() { return true; }
+};
+
+} /* anonymous namespace */
+
+bool
+js::SuppressDeletedProperty(JSContext* cx, HandleObject obj, jsid id)
+{
+    if (JSID_IS_SYMBOL(id))
+        return true;
+
+    Rooted<JSFlatString*> str(cx, IdToString(cx, id));
+    if (!str)
+        return false;
+    return SuppressDeletedPropertyHelper(cx, obj, SingleStringPredicate(str));
+}
+
+bool
+js::SuppressDeletedElement(JSContext* cx, HandleObject obj, uint32_t index)
+{
+    RootedId id(cx);
+    if (!IndexToId(cx, index, &id))
+        return false;
+    return SuppressDeletedProperty(cx, obj, id);
+}
+
+bool
+js::IteratorMore(JSContext* cx, HandleObject iterobj, MutableHandleValue rval)
+{
+    // Fast path for native iterators.
+    if (iterobj->is<PropertyIteratorObject>()) {
+        NativeIterator* ni = iterobj->as<PropertyIteratorObject>().getNativeIterator();
+        bool done;
+        if (!NativeIteratorNext(cx, ni, rval, &done))
+            return false;
+
+        if (done)
+            rval.setMagic(JS_NO_ITER_VALUE);
+        return true;
+    }
+
+    // We're reentering below and can call anything.
+    JS_CHECK_RECURSION(cx, return false);
+
+    // Call the iterator object's .next method.
+    if (!GetProperty(cx, iterobj, iterobj, cx->names().next, rval))
+        return false;
+
+    // Call the .next method.  Fall through to the error-handling cases in the
+    // unlikely event that either one of the fallible operations performed
+    // during the call process fails.
+    FixedInvokeArgs<0> args(cx);
+    RootedValue iterval(cx, ObjectValue(*iterobj));
+    if (!js::Call(cx, rval, iterval, args, rval)) {
+        // Check for StopIteration.
+        if (!cx->isExceptionPending())
+            return false;
+        RootedValue exception(cx);
+        if (!cx->getPendingException(&exception))
+            return false;
+        if (!JS_IsStopIteration(exception))
+            return false;
+
+        cx->clearPendingException();
+        rval.setMagic(JS_NO_ITER_VALUE);
+    }
+
+    return true;
+}
+
+static bool
+stopiter_hasInstance(JSContext* cx, HandleObject obj, MutableHandleValue v, bool* bp)
+{
+    *bp = JS_IsStopIteration(v);
+    return true;
+}
+
+static const ClassOps StopIterationObjectClassOps = {
+    nullptr, /* addProperty */
+    nullptr, /* delProperty */
+    nullptr, /* getProperty */
+    nullptr, /* setProperty */
+    nullptr, /* enumerate */
+    nullptr, /* resolve */
+    nullptr, /* mayResolve */
+    nullptr, /* finalize */
+    nullptr, /* call */
+    stopiter_hasInstance
+};
+
+const Class StopIterationObject::class_ = {
+    "StopIteration",
+    JSCLASS_HAS_CACHED_PROTO(JSProto_StopIteration),
+    &StopIterationObjectClassOps
+};
+
+static const JSFunctionSpec iterator_proto_methods[] = {
+    JS_SELF_HOSTED_SYM_FN(iterator, "IteratorIdentity", 0, 0),
+    JS_FS_END
+};
+
+/* static */ bool
+GlobalObject::initIteratorProto(JSContext* cx, Handle<GlobalObject*> global)
+{
+    if (global->getReservedSlot(ITERATOR_PROTO).isObject())
+        return true;
+
+    RootedObject proto(cx, global->createBlankPrototype<PlainObject>(cx));
+    if (!proto || !DefinePropertiesAndFunctions(cx, proto, nullptr, iterator_proto_methods))
+        return false;
+
+    global->setReservedSlot(ITERATOR_PROTO, ObjectValue(*proto));
+    return true;
+}
+
+/* static */ bool
+GlobalObject::initArrayIteratorProto(JSContext* cx, Handle<GlobalObject*> global)
+{
+    if (global->getReservedSlot(ARRAY_ITERATOR_PROTO).isObject())
+        return true;
+
+    RootedObject iteratorProto(cx, GlobalObject::getOrCreateIteratorPrototype(cx, global));
+    if (!iteratorProto)
+        return false;
+
+    const Class* cls = &ArrayIteratorPrototypeClass;
+    RootedObject proto(cx, global->createBlankPrototypeInheriting(cx, cls, iteratorProto));
+    if (!proto ||
+        !DefinePropertiesAndFunctions(cx, proto, nullptr, array_iterator_methods) ||
+        !DefineToStringTag(cx, proto, cx->names().ArrayIterator))
+    {
+        return false;
+    }
+
+    global->setReservedSlot(ARRAY_ITERATOR_PROTO, ObjectValue(*proto));
+    return true;
+}
+
+/* static */ bool
+GlobalObject::initStringIteratorProto(JSContext* cx, Handle<GlobalObject*> global)
+{
+    if (global->getReservedSlot(STRING_ITERATOR_PROTO).isObject())
+        return true;
+
+    RootedObject iteratorProto(cx, GlobalObject::getOrCreateIteratorPrototype(cx, global));
+    if (!iteratorProto)
+        return false;
+
+    const Class* cls = &StringIteratorPrototypeClass;
+    RootedObject proto(cx, global->createBlankPrototypeInheriting(cx, cls, iteratorProto));
+    if (!proto ||
+        !DefinePropertiesAndFunctions(cx, proto, nullptr, string_iterator_methods) ||
+        !DefineToStringTag(cx, proto, cx->names().StringIterator))
+    {
+        return false;
+    }
+
+    global->setReservedSlot(STRING_ITERATOR_PROTO, ObjectValue(*proto));
+    return true;
+}
+
+JSObject*
+js::InitLegacyIteratorClass(JSContext* cx, HandleObject obj)
+{
+    Handle<GlobalObject*> global = obj.as<GlobalObject>();
+
+    if (global->getPrototype(JSProto_Iterator).isObject())
+        return &global->getPrototype(JSProto_Iterator).toObject();
+
+    RootedObject iteratorProto(cx);
+    iteratorProto = global->createBlankPrototype(cx, &PropertyIteratorObject::class_);
+    if (!iteratorProto)
+        return nullptr;
+
+    NativeIterator* ni = NativeIterator::allocateIterator(cx, 0, 0);
+    if (!ni)
+        return nullptr;
+
+    iteratorProto->as<PropertyIteratorObject>().setNativeIterator(ni);
+    ni->init(nullptr, nullptr, 0 /* flags */, 0, 0);
+
+    Rooted<JSFunction*> ctor(cx);
+    ctor = global->createConstructor(cx, IteratorConstructor, cx->names().Iterator, 2);
+    if (!ctor)
+        return nullptr;
+    if (!LinkConstructorAndPrototype(cx, ctor, iteratorProto))
+        return nullptr;
+    if (!DefinePropertiesAndFunctions(cx, iteratorProto, nullptr, legacy_iterator_methods))
+        return nullptr;
+    if (!GlobalObject::initBuiltinConstructor(cx, global, JSProto_Iterator,
+                                              ctor, iteratorProto))
+    {
+        return nullptr;
+    }
+
+    return &global->getPrototype(JSProto_Iterator).toObject();
+}
+
+JSObject*
+js::InitStopIterationClass(JSContext* cx, HandleObject obj)
+{
+    Handle<GlobalObject*> global = obj.as<GlobalObject>();
+    if (!global->getPrototype(JSProto_StopIteration).isObject()) {
+        RootedObject proto(cx, global->createBlankPrototype(cx, &StopIterationObject::class_));
+        if (!proto || !FreezeObject(cx, proto))
+            return nullptr;
+
+        // This should use a non-JSProtoKey'd slot, but this is easier for now.
+        if (!GlobalObject::initBuiltinConstructor(cx, global, JSProto_StopIteration, proto, proto))
+            return nullptr;
+
+        global->setConstructor(JSProto_StopIteration, ObjectValue(*proto));
+    }
+
+    return &global->getPrototype(JSProto_StopIteration).toObject();
+}