Source/JavaScriptCore/runtime/JSPropertyNameEnumerator.h

/*
 * Copyright (C) 2014-2021 Apple Inc. All rights reserved.
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#pragma once

#include "JSCast.h"
#include "Operations.h"
#include "PropertyNameArray.h"
#include "StructureChain.h"

namespace JSC {

class JSPropertyNameEnumerator final : public JSCell {
public:
    using Base = JSCell;
    static constexpr unsigned StructureFlags = Base::StructureFlags | StructureIsImmortal;

    enum Flag : uint8_t {
        InitMode = 0,
        IndexedMode = 1 << 0,
        OwnStructureMode = 1 << 1,
        GenericMode = 1 << 2,
        // Profiling Only
        HasSeenOwnStructureModeStructureMismatch = 1 << 3,
    };

    static constexpr uint8_t enumerationModeMask = (GenericMode << 1) - 1;

    template<typename CellType, SubspaceAccess mode>
    static IsoSubspace* subspaceFor(VM& vm)
    {
        return &vm.propertyNameEnumeratorSpace();
    }

    static JSPropertyNameEnumerator* create(VM&, Structure*, uint32_t, uint32_t, PropertyNameArray&&);

    static Structure* createStructure(VM& vm, JSGlobalObject* globalObject, JSValue prototype)
    {
        return Structure::create(vm, globalObject, prototype, TypeInfo(CellType, StructureFlags), info());
    }

    DECLARE_EXPORT_INFO;

    JSString* propertyNameAtIndex(uint32_t index)
    {
        if (index >= sizeOfPropertyNames())
            return nullptr;
        return m_propertyNames.get()[index].get();
    }

    Structure* cachedStructure(VM& vm) const
    {
        if (!m_cachedStructureID)
            return nullptr;
        return vm.heap.structureIDTable().get(m_cachedStructureID);
    }
    StructureID cachedStructureID() const { return m_cachedStructureID; }
    uint32_t indexedLength() const { return m_indexedLength; }
    uint32_t endStructurePropertyIndex() const { return m_endStructurePropertyIndex; }
    uint32_t endGenericPropertyIndex() const { return m_endGenericPropertyIndex; }
    uint32_t cachedInlineCapacity() const { return m_cachedInlineCapacity; }
    uint32_t sizeOfPropertyNames() const { return endGenericPropertyIndex(); }
    uint32_t flags() const { return m_flags; }
    static ptrdiff_t cachedStructureIDOffset() { return OBJECT_OFFSETOF(JSPropertyNameEnumerator, m_cachedStructureID); }
    static ptrdiff_t indexedLengthOffset() { return OBJECT_OFFSETOF(JSPropertyNameEnumerator, m_indexedLength); }
    static ptrdiff_t endStructurePropertyIndexOffset() { return OBJECT_OFFSETOF(JSPropertyNameEnumerator, m_endStructurePropertyIndex); }
    static ptrdiff_t endGenericPropertyIndexOffset() { return OBJECT_OFFSETOF(JSPropertyNameEnumerator, m_endGenericPropertyIndex); }
    static ptrdiff_t cachedInlineCapacityOffset() { return OBJECT_OFFSETOF(JSPropertyNameEnumerator, m_cachedInlineCapacity); }
    static ptrdiff_t flagsOffset() { return OBJECT_OFFSETOF(JSPropertyNameEnumerator, m_flags); }
    static ptrdiff_t cachedPropertyNamesVectorOffset()
    {
        return OBJECT_OFFSETOF(JSPropertyNameEnumerator, m_propertyNames);
    }

    JSString* computeNext(JSGlobalObject*, JSObject* base, uint32_t& currentIndex, Flag&, bool shouldAllocateIndexedNameString = true);

    DECLARE_VISIT_CHILDREN;

private:
    friend class LLIntOffsetsExtractor;

    JSPropertyNameEnumerator(VM&, Structure*, uint32_t, uint32_t, WriteBarrier<JSString>*, unsigned);
    void finishCreation(VM&, RefPtr<PropertyNameArrayData>&&);

    // JSPropertyNameEnumerator is immutable data structure, which allows VM to cache the empty one.
    // After instantiating JSPropertyNameEnumerator, we must not change any fields.
    AuxiliaryBarrier<WriteBarrier<JSString>*> m_propertyNames;
    StructureID m_cachedStructureID;
    uint32_t m_indexedLength;
    uint32_t m_endStructurePropertyIndex;
    uint32_t m_endGenericPropertyIndex;
    uint32_t m_cachedInlineCapacity;
    uint32_t m_flags { 0 };
};

void getEnumerablePropertyNames(JSGlobalObject*, JSObject*, PropertyNameArray&, uint32_t& indexedLength, uint32_t& structurePropertyCount);

inline JSPropertyNameEnumerator* propertyNameEnumerator(JSGlobalObject* globalObject, JSObject* base)
{
    VM& vm = getVM(globalObject);
    auto scope = DECLARE_THROW_SCOPE(vm);

    uint32_t indexedLength = base->getEnumerableLength(globalObject);

    Structure* structure = base->structure(vm);
    if (!indexedLength) {
        uintptr_t enumeratorAndFlag = structure->cachedPropertyNameEnumeratorAndFlag();
        if (enumeratorAndFlag) {
            if (!(enumeratorAndFlag & StructureRareData::cachedPropertyNameEnumeratorIsValidatedViaTraversingFlag))
                return bitwise_cast<JSPropertyNameEnumerator*>(enumeratorAndFlag);
            structure->prototypeChain(vm, globalObject, base); // Refresh cached structure chain.
            if (auto* enumerator = structure->cachedPropertyNameEnumerator())
                return enumerator;
        }
    }

    uint32_t numberStructureProperties = 0;
    PropertyNameArray propertyNames(vm, PropertyNameMode::Strings, PrivateSymbolMode::Exclude);
    getEnumerablePropertyNames(globalObject, base, propertyNames, indexedLength, numberStructureProperties);
    RETURN_IF_EXCEPTION(scope, nullptr);

    ASSERT(propertyNames.size() < UINT32_MAX);

    bool sawPolyProto;
    bool successfullyNormalizedChain = normalizePrototypeChain(globalObject, base, sawPolyProto) != InvalidPrototypeChain;

    Structure* structureAfterGettingPropertyNames = base->structure(vm);
    if (!structureAfterGettingPropertyNames->canAccessPropertiesQuicklyForEnumeration()) {
        indexedLength = 0;
        numberStructureProperties = 0;
    }

    JSPropertyNameEnumerator* enumerator = nullptr;
    if (!indexedLength && !propertyNames.size())
        enumerator = vm.emptyPropertyNameEnumerator();
    else
        enumerator = JSPropertyNameEnumerator::create(vm, structureAfterGettingPropertyNames, indexedLength, numberStructureProperties, WTFMove(propertyNames));
    if (!indexedLength && successfullyNormalizedChain && structureAfterGettingPropertyNames == structure) {
        StructureChain* chain = structure->prototypeChain(vm, globalObject, base);
        if (structure->canCachePropertyNameEnumerator(vm))
            structure->setCachedPropertyNameEnumerator(vm, enumerator, chain);
    }
    return enumerator;
}

using EnumeratorMetadata = std::underlying_type_t<JSPropertyNameEnumerator::Flag>;

} // namespace JSC