path: root/js/src/vm/Iteration.h

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
 * vim: set ts=8 sts=2 et sw=2 tw=80:
 * 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/. */

#ifndef vm_Iteration_h
#define vm_Iteration_h

/*
 * JavaScript iterators.
 */

#include "mozilla/ArrayUtils.h"
#include "mozilla/MemoryReporting.h"

#include "builtin/SelfHostingDefines.h"
#include "gc/Barrier.h"
#include "vm/NativeObject.h"

/*
 * [SMDOC] For-in enumeration
 *
 * A for-in loop in JS iterates over the string-valued, enumerable
 * property keys of an object and its prototype chain. The order in
 * which keys appear is specified to the extent that implementations
 * historically agreed, and implementation-defined beyond that. See
 * https://tc39.es/ecma262/#sec-enumerate-object-properties for the
 * gory details. Each key appears only once in the enumeration.
 *
 * We enumerate properties using PropertyEnumerator, which creates an
 * ordered list of PropertyKeys, using ShapePropertyIter for native
 * objects and calling enumerate hooks where necessary. This list is
 * used to create a NativeIterator, which contains (among other
 * things) a trailing array of strings representing the property keys
 * of the object, and a cursor pointing into that array. This
 * NativeIterator is wrapped in a PropertyIteratorObject, which is
 * pushed by JSOp::Iter and used by JSOp::MoreIter and JSOp::EndIter.
 *
 * While active, a NativeIterator is registered in a doubly linked
 * list, rooted in the compartment. When any property is deleted from
 * an object, this list is used to remove the deleted property from
 * any active enumerations. See SuppressDeletedProperty. This slows
 * down deletion but speeds up enumeration, which is generally a good
 * tradeoff.
 *
 * In many cases, objects with the same shape will have the same set
 * of property keys. (The most common exception is objects with dense
 * elements, which can be added or removed without changing the shape
 * of the object.) In such cases, we can reuse an existing iterator by
 * storing a pointer to the PropertyIteratorObject in the shape's
 * |cache_| pointer. Before reusing an iterator, we have to verify
 * that the prototype chain has not changed and no dense elements have
 * been added, which is done by storing a trailing array of prototype
 * shapes in the NativeIterator and comparing it against the shapes of
 * the prototype chain.
 *
 * One of the most frequent uses of for-in loops is in loops that look
 * like this, which iterate over each property of an object and do
 * something with those values:
 *   for (var key in obj) {
 *     if (obj.hasOwnProperty(key)) {
 *       doSomethingWith(obj[key]);
 *     }
 *   }
 * Most objects don't have any enumerable properties on the prototype
 * chain. In such cases, we can speed up property access inside the
 * loop by precomputing some information and storing it in the
 * iterator.  When we see a pattern like this in Ion, we generate a
 * call to GetIteratorWithIndices instead of GetIterator. In this
 * case, in addition to the list of property keys, PropertyEnumerator
 * will try to generate a list of corresponding PropertyIndex values,
 * which represent the location of the own property key in the object
 * (fixed slot/dynamic slot/dense element + offset). This list will be
 * stored in NativeIterator as yet another trailing array. When
 * present, it can be used by Ion code to speed up property access
 * inside for-in loops. See OptimizeIteratorIndices in
 * IonAnalysis.cpp.
 */

namespace js {

class ArrayObject;
class PlainObject;
class PropertyIteratorObject;

// A PropertyIndex stores information about the location of an own data
// property in a format that can be stored in a NativeIterator and consumed by
// jitcode to access properties without needing to use the megamorphic cache.
struct PropertyIndex {
 private:
  uint32_t asBits_;

 public:
  enum class Kind : uint32_t { DynamicSlot, FixedSlot, Element, Invalid };

  PropertyIndex(Kind kind, uint32_t index) : asBits_(encode(kind, index)) {}

  static PropertyIndex Invalid() { return PropertyIndex(Kind::Invalid, 0); }

  static PropertyIndex ForElement(uint32_t index) {
    return PropertyIndex(Kind::Element, index);
  }

  static PropertyIndex ForSlot(NativeObject* obj, uint32_t index) {
    if (index < obj->numFixedSlots()) {
      return PropertyIndex(Kind::FixedSlot, index);
    } else {
      return PropertyIndex(Kind::DynamicSlot, index - obj->numFixedSlots());
    }
  }

  static constexpr uint32_t KindBits = 2;

  static constexpr uint32_t IndexBits = 32 - KindBits;
  static constexpr uint32_t IndexLimit = 1 << IndexBits;
  static constexpr uint32_t IndexMask = (1 << IndexBits) - 1;

  static constexpr uint32_t KindShift = IndexBits;

  static_assert(NativeObject::MAX_FIXED_SLOTS < IndexLimit);
  static_assert(NativeObject::MAX_SLOTS_COUNT < IndexLimit);
  static_assert(NativeObject::MAX_DENSE_ELEMENTS_COUNT < IndexLimit);

 private:
  uint32_t encode(Kind kind, uint32_t index) {
    MOZ_ASSERT(index < IndexLimit);
    return (uint32_t(kind) << KindShift) | index;
  }

 public:
  Kind kind() const { return Kind(asBits_ >> KindShift); }
  uint32_t index() const { return asBits_ & IndexMask; }
};

using PropertyIndexVector = js::Vector<PropertyIndex, 8, js::TempAllocPolicy>;

struct NativeIterator;

class NativeIteratorListNode {
 protected:
  // While in compartment->enumerators, these form a doubly linked list.
  NativeIteratorListNode* prev_ = nullptr;
  NativeIteratorListNode* next_ = nullptr;

 public:
  NativeIteratorListNode* prev() { return prev_; }
  NativeIteratorListNode* next() { return next_; }

  void setPrev(NativeIteratorListNode* prev) { prev_ = prev; }
  void setNext(NativeIteratorListNode* next) { next_ = next; }

  static constexpr size_t offsetOfNext() {
    return offsetof(NativeIteratorListNode, next_);
  }

  static constexpr size_t offsetOfPrev() {
    return offsetof(NativeIteratorListNode, prev_);
  }

 private:
  NativeIterator* asNativeIterator() {
    return reinterpret_cast<NativeIterator*>(this);
  }

  friend class NativeIteratorListIter;
};

class NativeIteratorListHead : public NativeIteratorListNode {
 private:
  // Initialize a |Compartment::enumerators| sentinel.
  NativeIteratorListHead() { prev_ = next_ = this; }
  friend class JS::Compartment;
};

class NativeIteratorListIter {
 private:
  NativeIteratorListHead* head_;
  NativeIteratorListNode* curr_;

 public:
  explicit NativeIteratorListIter(NativeIteratorListHead* head)
      : head_(head), curr_(head->next()) {}

  bool done() const { return curr_ == head_; }

  NativeIterator* next() {
    MOZ_ASSERT(!done());
    NativeIterator* result = curr_->asNativeIterator();
    curr_ = curr_->next();
    return result;
  }
};

// If an object only has own data properties, we can store a list of
// PropertyIndex that can be used in Ion to more efficiently access those
// properties in cases like `for (var key in obj) { ...obj[key]... }`.
enum class NativeIteratorIndices : uint32_t {
  // The object being iterated does not support indices.
  Unavailable = 0,

  // The object being iterated supports indices, but none have been
  // allocated, because it has not yet been iterated by Ion code that
  // can use indices-based access.
  AvailableOnRequest = 1,

  // The object being iterated had indices allocated, but they were
  // disabled due to a deleted property.
  Disabled = 2,

  // The object being iterated had indices allocated, and they are
  // still valid.
  Valid = 3
};

struct NativeIterator : public NativeIteratorListNode {
 private:
  // Object being iterated.  Non-null except in NativeIterator sentinels,
  // the empty iterator singleton (for iterating |null| or |undefined|), and
  // inactive iterators.
  GCPtr<JSObject*> objectBeingIterated_ = {};

  // Internal iterator object.
  const GCPtr<JSObject*> iterObj_ = {};

  // The end of GCPtr<Shape*>s that appear directly after |this|, as part of an
  // overall allocation that stores |*this|, shapes, iterated strings, and maybe
  // indices. Once this has been fully initialized, it also equals the start of
  // iterated strings.
  GCPtr<Shape*>* shapesEnd_;  // initialized by constructor

  // The next property, pointing into an array of strings directly after any
  // GCPtr<Shape*>s that appear directly after |*this|, as part of an overall
  // allocation that stores |*this|, shapes, iterated strings, and maybe
  // indices.
  GCPtr<JSLinearString*>* propertyCursor_;  // initialized by constructor

  // The limit/end of properties to iterate. Once |this| has been fully
  // initialized, it also equals the start of indices, if indices are present,
  // or the end of the full allocation storing |*this|, shapes, and strings, if
  // indices are not present. Beware! This value may change as properties are
  // deleted from the observed object.
  GCPtr<JSLinearString*>* propertiesEnd_;  // initialized by constructor

  HashNumber shapesHash_;  // initialized by constructor

 public:
  // For cacheable native iterators, whether the iterator is currently
  // active.  Not serialized by XDR.
  struct Flags {
    // This flag is set when all shapes and properties associated with this
    // NativeIterator have been initialized, such that |shapesEnd_|, in
    // addition to being the end of shapes, is also the beginning of
    // properties.
    //
    // This flag is only *not* set when a NativeIterator is in the process
    // of being constructed.  At such time |shapesEnd_| accounts only for
    // shapes that have been initialized -- potentially none of them.
    // Instead, |propertyCursor_| is initialized to the ultimate/actual
    // start of properties and must be used instead of |propertiesBegin()|,
    // which asserts that this flag is present to guard against misuse.
    static constexpr uint32_t Initialized = 0x1;

    // This flag indicates that this NativeIterator is currently being used
    // to enumerate an object's properties and has not yet been closed.
    static constexpr uint32_t Active = 0x2;

    // This flag indicates that the object being enumerated by this
    // |NativeIterator| had a property deleted from it before it was
    // visited, forcing the properties array in this to be mutated to
    // remove it.
    static constexpr uint32_t HasUnvisitedPropertyDeletion = 0x4;

    // Whether this is the shared empty iterator object used for iterating over
    // null/undefined.
    static constexpr uint32_t IsEmptyIteratorSingleton = 0x8;

    // If any of these bits are set on a |NativeIterator|, it isn't
    // currently reusable.  (An active |NativeIterator| can't be stolen
    // *right now*; a |NativeIterator| that's had its properties mutated
    // can never be reused, because it would give incorrect results.)
    static constexpr uint32_t NotReusable =
        Active | HasUnvisitedPropertyDeletion;
  };

 private:
  static constexpr uint32_t FlagsBits = 4;
  static constexpr uint32_t IndicesBits = 2;

  static constexpr uint32_t FlagsMask = (1 << FlagsBits) - 1;

  static constexpr uint32_t PropCountShift = IndicesBits + FlagsBits;
  static constexpr uint32_t PropCountBits = 32 - PropCountShift;

 public:
  static constexpr uint32_t IndicesShift = FlagsBits;
  static constexpr uint32_t IndicesMask = ((1 << IndicesBits) - 1)
                                          << IndicesShift;

  static constexpr uint32_t PropCountLimit = 1 << PropCountBits;

 private:
  // Stores Flags bits and indices state in the lower bits and the initial
  // property count above them.
  uint32_t flagsAndCount_ = 0;

#ifdef DEBUG
  // If true, this iterator may contain indexed properties that came from
  // objects on the prototype chain. This is used by certain debug assertions.
  bool maybeHasIndexedPropertiesFromProto_ = false;
#endif

  // END OF PROPERTIES

  // No further fields appear after here *in NativeIterator*, but this class is
  // always allocated with space tacked on immediately after |this| to store
  // shapes p to |shapesEnd_|, iterated property names after that up to
  // |propertiesEnd_|, and maybe PropertyIndex values up to |indices_end()|.

 public:
  /**
   * Initialize a NativeIterator properly allocated for |props.length()|
   * properties and |numShapes| shapes. If |indices| is non-null, also
   * allocates room for |indices.length()| PropertyIndex values. In this case,
   * |indices.length()| must equal |props.length()|.
   *
   * Despite being a constructor, THIS FUNCTION CAN REPORT ERRORS.  Users
   * MUST set |*hadError = false| on entry and consider |*hadError| on return
   * to mean this function failed.
   */
  NativeIterator(JSContext* cx, Handle<PropertyIteratorObject*> propIter,
                 Handle<JSObject*> objBeingIterated, HandleIdVector props,
                 bool supportsIndices, PropertyIndexVector* indices,
                 uint32_t numShapes, bool* hadError);

  JSObject* objectBeingIterated() const { return objectBeingIterated_; }

  void initObjectBeingIterated(JSObject& obj) {
    MOZ_ASSERT(!objectBeingIterated_);
    objectBeingIterated_.init(&obj);
  }
  void clearObjectBeingIterated() {
    MOZ_ASSERT(objectBeingIterated_);
    objectBeingIterated_ = nullptr;
  }

  GCPtr<Shape*>* shapesBegin() const {
    static_assert(
        alignof(GCPtr<Shape*>) <= alignof(NativeIterator),
        "NativeIterator must be aligned to begin storing "
        "GCPtr<Shape*>s immediately after it with no required padding");
    const NativeIterator* immediatelyAfter = this + 1;
    auto* afterNonConst = const_cast<NativeIterator*>(immediatelyAfter);
    return reinterpret_cast<GCPtr<Shape*>*>(afterNonConst);
  }

  GCPtr<Shape*>* shapesEnd() const { return shapesEnd_; }

  uint32_t shapeCount() const {
    return mozilla::PointerRangeSize(shapesBegin(), shapesEnd());
  }

  GCPtr<JSLinearString*>* propertiesBegin() const {
    static_assert(
        alignof(GCPtr<Shape*>) >= alignof(GCPtr<JSLinearString*>),
        "GCPtr<JSLinearString*>s for properties must be able to appear "
        "directly after any GCPtr<Shape*>s after this NativeIterator, "
        "with no padding space required for correct alignment");
    static_assert(
        alignof(NativeIterator) >= alignof(GCPtr<JSLinearString*>),
        "GCPtr<JSLinearString*>s for properties must be able to appear "
        "directly after this NativeIterator when no GCPtr<Shape*>s are "
        "present, with no padding space required for correct "
        "alignment");

    // We *could* just check the assertion below if we wanted, but the
    // incompletely-initialized NativeIterator case matters for so little
    // code that we prefer not imposing the condition-check on every single
    // user.
    MOZ_ASSERT(isInitialized(),
               "NativeIterator must be initialized, or else |shapesEnd_| "
               "isn't necessarily the start of properties and instead "
               "|propertyCursor_| is");

    return reinterpret_cast<GCPtr<JSLinearString*>*>(shapesEnd_);
  }

  GCPtr<JSLinearString*>* propertiesEnd() const { return propertiesEnd_; }

  GCPtr<JSLinearString*>* nextProperty() const { return propertyCursor_; }

  PropertyIndex* indicesBegin() const {
    // PropertyIndex must be able to be appear directly after the properties
    // array, with no padding required for correct alignment.
    static_assert(alignof(GCPtr<JSLinearString*>) >= alignof(PropertyIndex));
    return reinterpret_cast<PropertyIndex*>(propertiesEnd_);
  }

  PropertyIndex* indicesEnd() const {
    MOZ_ASSERT(indicesState() == NativeIteratorIndices::Valid);
    return indicesBegin() + numKeys() * sizeof(PropertyIndex);
  }

  MOZ_ALWAYS_INLINE JS::Value nextIteratedValueAndAdvance() {
    if (propertyCursor_ >= propertiesEnd_) {
      MOZ_ASSERT(propertyCursor_ == propertiesEnd_);
      return JS::MagicValue(JS_NO_ITER_VALUE);
    }

    JSLinearString* str = *propertyCursor_;
    incCursor();
    return JS::StringValue(str);
  }

  void resetPropertyCursorForReuse() {
    MOZ_ASSERT(isInitialized());

    // This function is called unconditionally on IteratorClose, so
    // unvisited properties might have been deleted, so we can't assert
    // this NativeIterator is reusable.  (Should we not bother resetting
    // the cursor in that case?)

    // Note: JIT code inlines |propertyCursor_| resetting when an iterator
    //       ends: see |CodeGenerator::visitIteratorEnd|.
    propertyCursor_ = propertiesBegin();
  }

  bool previousPropertyWas(JS::Handle<JSLinearString*> str) {
    MOZ_ASSERT(isInitialized());
    return propertyCursor_ > propertiesBegin() && propertyCursor_[-1] == str;
  }

  size_t numKeys() const {
    return mozilla::PointerRangeSize(propertiesBegin(), propertiesEnd());
  }

  void trimLastProperty() {
    MOZ_ASSERT(isInitialized());
    propertiesEnd_--;

    // This invokes the pre barrier on this property, since it's no longer
    // going to be marked, and it ensures that any existing remembered set
    // entry will be dropped.
    *propertiesEnd_ = nullptr;

    // Indices are no longer valid.
    disableIndices();
  }

  JSObject* iterObj() const { return iterObj_; }
  GCPtr<JSLinearString*>* currentProperty() const {
    MOZ_ASSERT(propertyCursor_ < propertiesEnd());
    return propertyCursor_;
  }

  void incCursor() {
    MOZ_ASSERT(isInitialized());
    propertyCursor_++;
  }

  HashNumber shapesHash() const { return shapesHash_; }

  bool isInitialized() const { return flags() & Flags::Initialized; }

  size_t allocationSize() const;

#ifdef DEBUG
  void setMaybeHasIndexedPropertiesFromProto() {
    maybeHasIndexedPropertiesFromProto_ = true;
  }
  bool maybeHasIndexedPropertiesFromProto() const {
    return maybeHasIndexedPropertiesFromProto_;
  }
#endif

 private:
  uint32_t flags() const { return flagsAndCount_ & FlagsMask; }

  NativeIteratorIndices indicesState() const {
    return NativeIteratorIndices((flagsAndCount_ & IndicesMask) >>
                                 IndicesShift);
  }

  uint32_t initialPropertyCount() const {
    return flagsAndCount_ >> PropCountShift;
  }

  static uint32_t initialFlagsAndCount(uint32_t count) {
    // No flags are initially set.
    MOZ_ASSERT(count < PropCountLimit);
    return count << PropCountShift;
  }

  void setFlags(uint32_t flags) {
    MOZ_ASSERT((flags & ~FlagsMask) == 0);
    flagsAndCount_ = (flagsAndCount_ & ~FlagsMask) | flags;
  }

  void setIndicesState(NativeIteratorIndices indices) {
    uint32_t indicesBits = uint32_t(indices) << IndicesShift;
    flagsAndCount_ = (flagsAndCount_ & ~IndicesMask) | indicesBits;
  }

  bool indicesAllocated() const {
    return indicesState() >= NativeIteratorIndices::Disabled;
  }

  void markInitialized() {
    MOZ_ASSERT(flags() == 0);
    setFlags(Flags::Initialized);
  }

  bool isUnlinked() const { return !prev_ && !next_; }

 public:
  // Whether this is the shared empty iterator object used for iterating over
  // null/undefined.
  bool isEmptyIteratorSingleton() const {
    // Note: equivalent code is inlined in MacroAssembler::iteratorClose.
    bool res = flags() & Flags::IsEmptyIteratorSingleton;
    MOZ_ASSERT_IF(
        res, flags() == (Flags::Initialized | Flags::IsEmptyIteratorSingleton));
    MOZ_ASSERT_IF(res, !objectBeingIterated_);
    MOZ_ASSERT_IF(res, initialPropertyCount() == 0);
    MOZ_ASSERT_IF(res, shapeCount() == 0);
    MOZ_ASSERT_IF(res, isUnlinked());
    return res;
  }
  void markEmptyIteratorSingleton() {
    flagsAndCount_ |= Flags::IsEmptyIteratorSingleton;

    // isEmptyIteratorSingleton() has various debug assertions.
    MOZ_ASSERT(isEmptyIteratorSingleton());
  }

  bool isActive() const {
    MOZ_ASSERT(isInitialized());

    return flags() & Flags::Active;
  }

  void markActive() {
    MOZ_ASSERT(isInitialized());
    MOZ_ASSERT(!isEmptyIteratorSingleton());

    flagsAndCount_ |= Flags::Active;
  }

  void markInactive() {
    MOZ_ASSERT(isInitialized());
    MOZ_ASSERT(!isEmptyIteratorSingleton());

    flagsAndCount_ &= ~Flags::Active;
  }

  bool isReusable() const {
    MOZ_ASSERT(isInitialized());

    // Cached NativeIterators are reusable if they're not currently active
    // and their properties array hasn't been mutated, i.e. if only
    // |Flags::Initialized| is set.  Using |Flags::NotReusable| to test
    // would also work, but this formulation is safer against memory
    // corruption.
    return flags() == Flags::Initialized;
  }

  void markHasUnvisitedPropertyDeletion() {
    MOZ_ASSERT(isInitialized());
    MOZ_ASSERT(!isEmptyIteratorSingleton());

    flagsAndCount_ |= Flags::HasUnvisitedPropertyDeletion;
  }

  bool hasValidIndices() const {
    return indicesState() == NativeIteratorIndices::Valid;
  }

  bool indicesAvailableOnRequest() const {
    return indicesState() == NativeIteratorIndices::AvailableOnRequest;
  }

  void disableIndices() {
    // If we have allocated indices, set the state to Disabled.
    // This will ensure that we don't use them, but we still
    // free them correctly.
    if (indicesState() == NativeIteratorIndices::Valid) {
      setIndicesState(NativeIteratorIndices::Disabled);
    }
  }

  void link(NativeIteratorListNode* other) {
    MOZ_ASSERT(isInitialized());

    // The shared iterator used for for-in with null/undefined is immutable and
    // shouldn't be linked.
    MOZ_ASSERT(!isEmptyIteratorSingleton());

    // A NativeIterator cannot appear in the enumerator list twice.
    MOZ_ASSERT(isUnlinked());

    setNext(other);
    setPrev(other->prev());

    other->prev()->setNext(this);
    other->setPrev(this);
  }
  void unlink() {
    MOZ_ASSERT(isInitialized());
    MOZ_ASSERT(!isEmptyIteratorSingleton());

    next()->setPrev(prev());
    prev()->setNext(next());
    setNext(nullptr);
    setPrev(nullptr);
  }

  void trace(JSTracer* trc);

  static constexpr size_t offsetOfObjectBeingIterated() {
    return offsetof(NativeIterator, objectBeingIterated_);
  }

  static constexpr size_t offsetOfShapesEnd() {
    return offsetof(NativeIterator, shapesEnd_);
  }

  static constexpr size_t offsetOfPropertyCursor() {
    return offsetof(NativeIterator, propertyCursor_);
  }

  static constexpr size_t offsetOfPropertiesEnd() {
    return offsetof(NativeIterator, propertiesEnd_);
  }

  static constexpr size_t offsetOfFlagsAndCount() {
    return offsetof(NativeIterator, flagsAndCount_);
  }

  static constexpr size_t offsetOfFirstShape() {
    // Shapes are stored directly after |this|.
    return sizeof(NativeIterator);
  }
};

class PropertyIteratorObject : public NativeObject {
  static const JSClassOps classOps_;

  enum { IteratorSlot, SlotCount };

 public:
  static const JSClass class_;

  NativeIterator* getNativeIterator() const {
    return maybePtrFromReservedSlot<NativeIterator>(IteratorSlot);
  }
  void initNativeIterator(js::NativeIterator* ni) {
    initReservedSlot(IteratorSlot, PrivateValue(ni));
  }

  size_t sizeOfMisc(mozilla::MallocSizeOf mallocSizeOf) const;

  static size_t offsetOfIteratorSlot() {
    return getFixedSlotOffset(IteratorSlot);
  }

 private:
  static void trace(JSTracer* trc, JSObject* obj);
  static void finalize(JS::GCContext* gcx, JSObject* obj);
};

class ArrayIteratorObject : public NativeObject {
 public:
  static const JSClass class_;
};

ArrayIteratorObject* NewArrayIteratorTemplate(JSContext* cx);
ArrayIteratorObject* NewArrayIterator(JSContext* cx);

class StringIteratorObject : public NativeObject {
 public:
  static const JSClass class_;
};

StringIteratorObject* NewStringIteratorTemplate(JSContext* cx);
StringIteratorObject* NewStringIterator(JSContext* cx);

class RegExpStringIteratorObject : public NativeObject {
 public:
  static const JSClass class_;
};

RegExpStringIteratorObject* NewRegExpStringIteratorTemplate(JSContext* cx);
RegExpStringIteratorObject* NewRegExpStringIterator(JSContext* cx);

[[nodiscard]] bool EnumerateProperties(JSContext* cx, HandleObject obj,
                                       MutableHandleIdVector props);

PropertyIteratorObject* LookupInIteratorCache(JSContext* cx, HandleObject obj);

PropertyIteratorObject* GetIterator(JSContext* cx, HandleObject obj);
PropertyIteratorObject* GetIteratorWithIndices(JSContext* cx, HandleObject obj);

PropertyIteratorObject* ValueToIterator(JSContext* cx, HandleValue vp);

void CloseIterator(JSObject* obj);

bool IteratorCloseForException(JSContext* cx, HandleObject obj);

void UnwindIteratorForUncatchableException(JSObject* obj);

extern bool SuppressDeletedProperty(JSContext* cx, HandleObject obj, jsid id);

extern bool SuppressDeletedElement(JSContext* cx, HandleObject obj,
                                   uint32_t index);

#ifdef DEBUG
extern void AssertDenseElementsNotIterated(NativeObject* obj);
#else
inline void AssertDenseElementsNotIterated(NativeObject* obj) {}
#endif

/*
 * IteratorMore() returns the next iteration value. If no value is available,
 * MagicValue(JS_NO_ITER_VALUE) is returned.
 */
inline Value IteratorMore(JSObject* iterobj) {
  NativeIterator* ni =
      iterobj->as<PropertyIteratorObject>().getNativeIterator();
  return ni->nextIteratedValueAndAdvance();
}

/*
 * Create an object of the form { value: VALUE, done: DONE }.
 * ES 2017 draft 7.4.7.
 */
extern PlainObject* CreateIterResultObject(JSContext* cx, HandleValue value,
                                           bool done);

/*
 * Global Iterator constructor.
 * Iterator Helpers proposal 2.1.3.
 */
class IteratorObject : public NativeObject {
 public:
  static const JSClass class_;
  static const JSClass protoClass_;
};

/*
 * Wrapper for iterators created via Iterator.from.
 * Iterator Helpers proposal 2.1.3.3.1.1.
 */
class WrapForValidIteratorObject : public NativeObject {
 public:
  static const JSClass class_;

  enum { IteratedSlot, SlotCount };

  static_assert(
      IteratedSlot == ITERATED_SLOT,
      "IteratedSlot must match self-hosting define for iterated object slot.");
};

WrapForValidIteratorObject* NewWrapForValidIterator(JSContext* cx);

/*
 * Generator-esque object returned by Iterator Helper methods.
 */
class IteratorHelperObject : public NativeObject {
 public:
  static const JSClass class_;

  enum {
    // The implementation (an instance of one of the generators in
    // builtin/Iterator.js).
    // Never null.
    GeneratorSlot,

    SlotCount,
  };

  static_assert(GeneratorSlot == ITERATOR_HELPER_GENERATOR_SLOT,
                "GeneratorSlot must match self-hosting define for generator "
                "object slot.");
};

IteratorHelperObject* NewIteratorHelper(JSContext* cx);

bool IterableToArray(JSContext* cx, HandleValue iterable,
                     MutableHandle<ArrayObject*> array);

} /* namespace js */

#endif /* vm_Iteration_h */