gecko-dev/js/src/jscompartment.h

/* -*- 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/. */

#ifndef jscompartment_h
#define jscompartment_h

#include "mozilla/MemoryReporting.h"

#include "prmjtime.h"
#include "builtin/RegExp.h"
#include "gc/Zone.h"
#include "vm/GlobalObject.h"
#include "vm/PIC.h"
#include "vm/SavedStacks.h"

namespace js {

namespace jit {
class JitCompartment;
}

namespace gc {
template<class Node> class ComponentFinder;
}

struct NativeIterator;

/*
 * A single-entry cache for some base-10 double-to-string conversions. This
 * helps date-format-xparb.js.  It also avoids skewing the results for
 * v8-splay.js when measured by the SunSpider harness, where the splay tree
 * initialization (which includes many repeated double-to-string conversions)
 * is erroneously included in the measurement; see bug 562553.
 */
class DtoaCache {
    double       d;
    int          base;
    JSFlatString* s;      // if s==nullptr, d and base are not valid

  public:
    DtoaCache() : s(nullptr) {}
    void purge() { s = nullptr; }

    JSFlatString* lookup(int base, double d) {
        return this->s && base == this->base && d == this->d ? this->s : nullptr;
    }

    void cache(int base, double d, JSFlatString* s) {
        this->base = base;
        this->d = d;
        this->s = s;
    }
};

struct CrossCompartmentKey
{
    enum Kind {
        ObjectWrapper,
        StringWrapper,
        DebuggerScript,
        DebuggerSource,
        DebuggerObject,
        DebuggerEnvironment
    };

    Kind kind;
    JSObject* debugger;
    js::gc::Cell* wrapped;

    explicit CrossCompartmentKey(JSObject* wrapped)
      : kind(ObjectWrapper), debugger(nullptr), wrapped(wrapped)
    {
        MOZ_RELEASE_ASSERT(wrapped);
    }
    explicit CrossCompartmentKey(JSString* wrapped)
      : kind(StringWrapper), debugger(nullptr), wrapped(wrapped)
    {
        MOZ_RELEASE_ASSERT(wrapped);
    }
    explicit CrossCompartmentKey(Value wrappedArg)
      : kind(wrappedArg.isString() ? StringWrapper : ObjectWrapper),
        debugger(nullptr),
        wrapped((js::gc::Cell*)wrappedArg.toGCThing())
    {
        MOZ_RELEASE_ASSERT(wrappedArg.isString() || wrappedArg.isObject());
        MOZ_RELEASE_ASSERT(wrapped);
    }
    explicit CrossCompartmentKey(const RootedValue& wrappedArg)
      : kind(wrappedArg.get().isString() ? StringWrapper : ObjectWrapper),
        debugger(nullptr),
        wrapped((js::gc::Cell*)wrappedArg.get().toGCThing())
    {
        MOZ_RELEASE_ASSERT(wrappedArg.isString() || wrappedArg.isObject());
        MOZ_RELEASE_ASSERT(wrapped);
    }
    CrossCompartmentKey(Kind kind, JSObject* dbg, js::gc::Cell* wrapped)
      : kind(kind), debugger(dbg), wrapped(wrapped)
    {
        MOZ_RELEASE_ASSERT(dbg);
        MOZ_RELEASE_ASSERT(wrapped);
    }

  private:
    CrossCompartmentKey() = delete;
};

struct WrapperHasher : public DefaultHasher<CrossCompartmentKey>
{
    static HashNumber hash(const CrossCompartmentKey& key) {
        static_assert(sizeof(HashNumber) == sizeof(uint32_t),
                      "subsequent code assumes a four-byte hash");
        return uint32_t(uintptr_t(key.wrapped)) | uint32_t(key.kind);
    }

    static bool match(const CrossCompartmentKey& l, const CrossCompartmentKey& k) {
        return l.kind == k.kind && l.debugger == k.debugger && l.wrapped == k.wrapped;
    }
};

typedef HashMap<CrossCompartmentKey, ReadBarrieredValue,
                WrapperHasher, SystemAllocPolicy> WrapperMap;

} /* namespace js */

namespace js {
class DebugScopes;
class ObjectWeakMap;
class WatchpointMap;
class WeakMapBase;
}

struct JSCompartment
{
    JS::CompartmentOptions       options_;

  private:
    JS::Zone*                    zone_;
    JSRuntime*                   runtime_;

  public:
    /*
     * The principals associated with this compartment. Note that the
     * same several compartments may share the same principals and
     * that a compartment may change principals during its lifetime
     * (e.g. in case of lazy parsing).
     */
    inline JSPrincipals* principals() {
        return principals_;
    }
    inline void setPrincipals(JSPrincipals* principals) {
        if (principals_ == principals)
            return;

        // If we change principals, we need to unlink immediately this
        // compartment from its PerformanceGroup. For one thing, the
        // performance data we collect should not be improperly associated
        // with a group to which we do not belong anymore. For another thing,
        // we use `principals()` as part of the key to map compartments
        // to a `PerformanceGroup`, so if we do not unlink now, this will
        // be too late once we have updated `principals_`.
        performanceMonitoring.unlink();
        principals_ = principals;
    }
    inline bool isSystem() const {
        return isSystem_;
    }
    inline void setIsSystem(bool isSystem) {
        if (isSystem_ == isSystem)
            return;

        // If we change `isSystem*(`, we need to unlink immediately this
        // compartment from its PerformanceGroup. For one thing, the
        // performance data we collect should not be improperly associated
        // to a group to which we do not belong anymore. For another thing,
        // we use `isSystem()` as part of the key to map compartments
        // to a `PerformanceGroup`, so if we do not unlink now, this will
        // be too late once we have updated `isSystem_`.
        performanceMonitoring.unlink();
        isSystem_ = isSystem;
    }
  private:
    JSPrincipals*                principals_;
    bool                         isSystem_;
  public:
    bool                         isSelfHosting;
    bool                         marked;
    bool                         warnedAboutNoSuchMethod;
    bool                         warnedAboutFlagsArgument;

    // A null add-on ID means that the compartment is not associated with an
    // add-on.
    JSAddonId*                   const addonId;

#ifdef DEBUG
    bool                         firedOnNewGlobalObject;
#endif

    void mark() { marked = true; }

  private:
    friend struct JSRuntime;
    friend struct JSContext;
    friend class js::ExclusiveContext;
    js::ReadBarrieredGlobalObject global_;

    unsigned                     enterCompartmentDepth;
    int64_t                      startInterval;

  public:
    js::PerformanceGroupHolder performanceMonitoring;

    void enter() {
        enterCompartmentDepth++;
    }
    void leave() {
        enterCompartmentDepth--;
    }
    bool hasBeenEntered() { return !!enterCompartmentDepth; }

    JS::Zone* zone() { return zone_; }
    const JS::Zone* zone() const { return zone_; }
    JS::CompartmentOptions& options() { return options_; }
    const JS::CompartmentOptions& options() const { return options_; }

    JSRuntime* runtimeFromMainThread() {
        MOZ_ASSERT(CurrentThreadCanAccessRuntime(runtime_));
        return runtime_;
    }

    // Note: Unrestricted access to the zone's runtime from an arbitrary
    // thread can easily lead to races. Use this method very carefully.
    JSRuntime* runtimeFromAnyThread() const {
        return runtime_;
    }

    /*
     * Nb: global_ might be nullptr, if (a) it's the atoms compartment, or
     * (b) the compartment's global has been collected.  The latter can happen
     * if e.g. a string in a compartment is rooted but no object is, and thus
     * the global isn't rooted, and thus the global can be finalized while the
     * compartment lives on.
     *
     * In contrast, JSObject::global() is infallible because marking a JSObject
     * always marks its global as well.
     * TODO: add infallible JSScript::global()
     */
    inline js::GlobalObject* maybeGlobal() const;

    /* An unbarriered getter for use while tracing. */
    inline js::GlobalObject* unsafeUnbarrieredMaybeGlobal() const;

    inline void initGlobal(js::GlobalObject& global);

  public:
    void*                        data;

  private:
    js::ObjectMetadataCallback   objectMetadataCallback;

    js::SavedStacks              savedStacks_;

    js::WrapperMap               crossCompartmentWrappers;

  public:
    /* Last time at which an animation was played for a global in this compartment. */
    int64_t                      lastAnimationTime;

    js::RegExpCompartment        regExps;

    /*
     * For generational GC, record whether a write barrier has added this
     * compartment's global to the store buffer since the last minor GC.
     *
     * This is used to avoid adding it to the store buffer on every write, which
     * can quickly fill the buffer and also cause performance problems.
     */
    bool                         globalWriteBarriered;

    // Non-zero if any typed objects in this compartment might be neutered.
    int32_t                      neuteredTypedObjects;

  public:
    void addSizeOfIncludingThis(mozilla::MallocSizeOf mallocSizeOf,
                                size_t* tiAllocationSiteTables,
                                size_t* tiArrayTypeTables,
                                size_t* tiObjectTypeTables,
                                size_t* compartmentObject,
                                size_t* compartmentTables,
                                size_t* innerViews,
                                size_t* lazyArrayBuffers,
                                size_t* objectMetadataTables,
                                size_t* crossCompartmentWrappers,
                                size_t* regexpCompartment,
                                size_t* savedStacksSet);

    /*
     * Shared scope property tree, and arena-pool for allocating its nodes.
     */
    js::PropertyTree             propertyTree;

    /* Set of all unowned base shapes in the compartment. */
    js::BaseShapeSet             baseShapes;
    void sweepBaseShapeTable();

    /* Set of initial shapes in the compartment. */
    js::InitialShapeSet          initialShapes;
    void sweepInitialShapeTable();

    // Object group tables and other state in the compartment.
    js::ObjectGroupCompartment   objectGroups;

#ifdef JSGC_HASH_TABLE_CHECKS
    void checkInitialShapesTableAfterMovingGC();
    void checkWrapperMapAfterMovingGC();
    void checkBaseShapeTableAfterMovingGC();
#endif

    /*
     * Lazily initialized script source object to use for scripts cloned
     * from the self-hosting global.
     */
    js::ReadBarrieredScriptSourceObject selfHostingScriptSource;

    // Keep track of the metadata objects which can be associated with each JS
    // object. Both keys and values are in this compartment.
    js::ObjectWeakMap* objectMetadataTable;

    // Map from array buffers to views sharing that storage.
    js::InnerViewTable innerViews;

    // Inline transparent typed objects do not initially have an array buffer,
    // but can have that buffer created lazily if it is accessed later. This
    // table manages references from such typed objects to their buffers.
    js::ObjectWeakMap* lazyArrayBuffers;

    // All unboxed layouts in the compartment.
    mozilla::LinkedList<js::UnboxedLayout> unboxedLayouts;

    /* During GC, stores the index of this compartment in rt->compartments. */
    unsigned                     gcIndex;

    /*
     * During GC, stores the head of a list of incoming pointers from gray cells.
     *
     * The objects in the list are either cross-compartment wrappers, or
     * debugger wrapper objects.  The list link is either in the second extra
     * slot for the former, or a special slot for the latter.
     */
    JSObject*                    gcIncomingGrayPointers;

    /* Linked list of live weakmaps in this compartment. */
    js::WeakMapBase*             gcWeakMapList;

  private:
    /* Whether to preserve JIT code on non-shrinking GCs. */
    bool                         gcPreserveJitCode;

    enum {
        IsDebuggee = 1 << 0,
        DebuggerObservesAllExecution = 1 << 1,
        DebuggerObservesAsmJS = 1 << 2,
        DebuggerNeedsDelazification = 1 << 3
    };

    unsigned                     debugModeBits;

    static const unsigned DebuggerObservesMask = IsDebuggee |
                                                 DebuggerObservesAllExecution |
                                                 DebuggerObservesAsmJS;

    void updateDebuggerObservesFlag(unsigned flag);

  public:
    JSCompartment(JS::Zone* zone, const JS::CompartmentOptions& options);
    ~JSCompartment();

    bool init(JSContext* maybecx);

    /* Mark cross-compartment wrappers. */
    void markCrossCompartmentWrappers(JSTracer* trc);

    inline bool wrap(JSContext* cx, JS::MutableHandleValue vp,
                     JS::HandleObject existing = nullptr);

    bool wrap(JSContext* cx, js::MutableHandleString strp);
    bool wrap(JSContext* cx, JS::MutableHandleObject obj,
              JS::HandleObject existingArg = nullptr);
    bool wrap(JSContext* cx, JS::MutableHandle<js::PropertyDescriptor> desc);

    template<typename T> bool wrap(JSContext* cx, JS::AutoVectorRooter<T>& vec) {
        for (size_t i = 0; i < vec.length(); ++i) {
            if (!wrap(cx, vec[i]))
                return false;
        }
        return true;
    };

    bool putWrapper(JSContext* cx, const js::CrossCompartmentKey& wrapped, const js::Value& wrapper);

    js::WrapperMap::Ptr lookupWrapper(const js::Value& wrapped) const {
        return crossCompartmentWrappers.lookup(js::CrossCompartmentKey(wrapped));
    }

    void removeWrapper(js::WrapperMap::Ptr p) {
        crossCompartmentWrappers.remove(p);
    }

    struct WrapperEnum : public js::WrapperMap::Enum {
        explicit WrapperEnum(JSCompartment* c) : js::WrapperMap::Enum(c->crossCompartmentWrappers) {}
    };

    void trace(JSTracer* trc);
    void markRoots(JSTracer* trc);
    bool preserveJitCode() { return gcPreserveJitCode; }

    void sweepInnerViews();
    void sweepCrossCompartmentWrappers();
    void sweepSavedStacks();
    void sweepGlobalObject(js::FreeOp* fop);
    void sweepSelfHostingScriptSource();
    void sweepJitCompartment(js::FreeOp* fop);
    void sweepRegExps();
    void sweepDebugScopes();
    void sweepWeakMaps();
    void sweepNativeIterators();

    void purge();
    void clearTables();

    void fixupInitialShapeTable();
    void fixupAfterMovingGC();
    void fixupGlobal();

    bool hasObjectMetadataCallback() const { return objectMetadataCallback; }
    js::ObjectMetadataCallback getObjectMetadataCallback() const { return objectMetadataCallback; }
    void setObjectMetadataCallback(js::ObjectMetadataCallback callback);
    void forgetObjectMetadataCallback() {
        objectMetadataCallback = nullptr;
    }
    void setNewObjectMetadata(JSContext* cx, JSObject* obj);
    void clearObjectMetadata();
    const void* addressOfMetadataCallback() const {
        return &objectMetadataCallback;
    }

    js::SavedStacks& savedStacks() { return savedStacks_; }

    void findOutgoingEdges(js::gc::ComponentFinder<JS::Zone>& finder);

    js::DtoaCache dtoaCache;

    /* Random number generator state, used by jsmath.cpp. */
    uint64_t rngState;

    static size_t offsetOfRngState() {
        return offsetof(JSCompartment, rngState);
    }

  private:
    JSCompartment* thisForCtor() { return this; }

  public:
    //
    // The Debugger observes execution on a frame-by-frame basis. The
    // invariants of JSCompartment's debug mode bits, JSScript::isDebuggee,
    // InterpreterFrame::isDebuggee, and BaselineFrame::isDebuggee are
    // enumerated below.
    //
    // 1. When a compartment's isDebuggee() == true, relazification and lazy
    //    parsing are disabled.
    //
    //    Whether AOT asm.js is disabled is togglable by the Debugger API. By
    //    default it is disabled. See debuggerObservesAsmJS below.
    //
    // 2. When a compartment's debuggerObservesAllExecution() == true, all of
    //    the compartment's scripts are considered debuggee scripts.
    //
    // 3. A script is considered a debuggee script either when, per above, its
    //    compartment is observing all execution, or if it has breakpoints set.
    //
    // 4. A debuggee script always pushes a debuggee frame.
    //
    // 5. A debuggee frame calls all slow path Debugger hooks in the
    //    Interpreter and Baseline. A debuggee frame implies that its script's
    //    BaselineScript, if extant, has been compiled with debug hook calls.
    //
    // 6. A debuggee script or a debuggee frame (i.e., during OSR) ensures
    //    that the compiled BaselineScript is compiled with debug hook calls
    //    when attempting to enter Baseline.
    //
    // 7. A debuggee script or a debuggee frame (i.e., during OSR) does not
    //    attempt to enter Ion.
    //
    // Note that a debuggee frame may exist without its script being a
    // debuggee script. e.g., Debugger.Frame.prototype.eval only marks the
    // frame in which it is evaluating as a debuggee frame.
    //

    // True if this compartment's global is a debuggee of some Debugger
    // object.
    bool isDebuggee() const { return !!(debugModeBits & IsDebuggee); }
    void setIsDebuggee() { debugModeBits |= IsDebuggee; }
    void unsetIsDebuggee();

    // True if this compartment's global is a debuggee of some Debugger
    // object with a live hook that observes all execution; e.g.,
    // onEnterFrame.
    bool debuggerObservesAllExecution() const {
        static const unsigned Mask = IsDebuggee | DebuggerObservesAllExecution;
        return (debugModeBits & Mask) == Mask;
    }
    void updateDebuggerObservesAllExecution() {
        updateDebuggerObservesFlag(DebuggerObservesAllExecution);
    }

    // True if this compartment's global is a debuggee of some Debugger object
    // whose allowUnobservedAsmJS flag is false.
    //
    // Note that since AOT asm.js functions cannot bail out, this flag really
    // means "observe asm.js from this point forward". We cannot make
    // already-compiled asm.js code observable to Debugger.
    bool debuggerObservesAsmJS() const {
        static const unsigned Mask = IsDebuggee | DebuggerObservesAsmJS;
        return (debugModeBits & Mask) == Mask;
    }
    void updateDebuggerObservesAsmJS() {
        updateDebuggerObservesFlag(DebuggerObservesAsmJS);
    }

    bool needsDelazificationForDebugger() const {
        return debugModeBits & DebuggerNeedsDelazification;
    }

    /*
     * Schedule the compartment to be delazified. Called from
     * LazyScript::Create.
     */
    void scheduleDelazificationForDebugger() { debugModeBits |= DebuggerNeedsDelazification; }

    /*
     * If we scheduled delazification for turning on debug mode, delazify all
     * scripts.
     */
    bool ensureDelazifyScriptsForDebugger(JSContext* cx);

    void clearBreakpointsIn(js::FreeOp* fop, js::Debugger* dbg, JS::HandleObject handler);

  private:
    void sweepBreakpoints(js::FreeOp* fop);

  public:
    js::WatchpointMap* watchpointMap;

    js::ScriptCountsMap* scriptCountsMap;

    js::DebugScriptMap* debugScriptMap;

    /* Bookkeeping information for debug scope objects. */
    js::DebugScopes* debugScopes;

    /*
     * List of potentially active iterators that may need deleted property
     * suppression.
     */
    js::NativeIterator* enumerators;

    /* Used by memory reporters and invalid otherwise. */
    void*              compartmentStats;

    // These flags help us to discover if a compartment that shouldn't be alive
    // manages to outlive a GC.
    bool scheduledForDestruction;
    bool maybeAlive;

  private:
    js::jit::JitCompartment* jitCompartment_;

  public:
    bool ensureJitCompartmentExists(JSContext* cx);
    js::jit::JitCompartment* jitCompartment() {
        return jitCompartment_;
    }

    enum DeprecatedLanguageExtension {
        DeprecatedForEach = 0,              // JS 1.6+
        // NO LONGER USING 1
        DeprecatedLegacyGenerator = 2,      // JS 1.7+
        DeprecatedExpressionClosure = 3,    // Added in JS 1.8
        DeprecatedLetBlock = 4,             // Added in JS 1.7
        // NO LONGER USING 5
        DeprecatedNoSuchMethod = 6,         // JS 1.7+
        DeprecatedFlagsArgument = 7,        // JS 1.3 or older
        RegExpSourceProperty = 8,           // ES5
        DeprecatedLanguageExtensionCount
    };

  private:
    // Used for collecting telemetry on SpiderMonkey's deprecated language extensions.
    bool sawDeprecatedLanguageExtension[DeprecatedLanguageExtensionCount];

    void reportTelemetry();

  public:
    void addTelemetry(const char* filename, DeprecatedLanguageExtension e);
};

inline bool
JSRuntime::isAtomsZone(const JS::Zone* zone) const
{
    return zone == atomsCompartment_->zone();
}

namespace js {

// We only set the maybeAlive flag for objects and scripts. It's assumed that,
// if a compartment is alive, then it will have at least some live object or
// script it in. Even if we get this wrong, the worst that will happen is that
// scheduledForDestruction will be set on the compartment, which will cause
// some extra GC activity to try to free the compartment.
template<typename T> inline void SetMaybeAliveFlag(T* thing) {}
template<> inline void SetMaybeAliveFlag(JSObject* thing) {thing->compartment()->maybeAlive = true;}
template<> inline void SetMaybeAliveFlag(JSScript* thing) {thing->compartment()->maybeAlive = true;}

inline js::Handle<js::GlobalObject*>
ExclusiveContext::global() const
{
    /*
     * It's safe to use |unsafeGet()| here because any compartment that is
     * on-stack will be marked automatically, so there's no need for a read
     * barrier on it. Once the compartment is popped, the handle is no longer
     * safe to use.
     */
    MOZ_ASSERT(compartment_, "Caller needs to enter a compartment first");
    return Handle<GlobalObject*>::fromMarkedLocation(compartment_->global_.unsafeGet());
}

class AssertCompartmentUnchanged
{
  public:
    explicit AssertCompartmentUnchanged(JSContext* cx
                                        MOZ_GUARD_OBJECT_NOTIFIER_PARAM)
      : cx(cx), oldCompartment(cx->compartment())
    {
        MOZ_GUARD_OBJECT_NOTIFIER_INIT;
    }

    ~AssertCompartmentUnchanged() {
        MOZ_ASSERT(cx->compartment() == oldCompartment);
    }

  protected:
    JSContext * const cx;
    JSCompartment * const oldCompartment;
    MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER
};

class AutoCompartment
{
    ExclusiveContext * const cx_;
    JSCompartment * const origin_;

  public:
    inline AutoCompartment(ExclusiveContext* cx, JSObject* target);
    inline AutoCompartment(ExclusiveContext* cx, JSCompartment* target);
    inline ~AutoCompartment();

    ExclusiveContext* context() const { return cx_; }
    JSCompartment* origin() const { return origin_; }

  private:
    AutoCompartment(const AutoCompartment&) = delete;
    AutoCompartment & operator=(const AutoCompartment&) = delete;
};

/*
 * Use this to change the behavior of an AutoCompartment slightly on error. If
 * the exception happens to be an Error object, copy it to the origin compartment
 * instead of wrapping it.
 */
class ErrorCopier
{
    mozilla::Maybe<AutoCompartment>& ac;

  public:
    explicit ErrorCopier(mozilla::Maybe<AutoCompartment>& ac)
      : ac(ac) {}
    ~ErrorCopier();
};

/*
 * AutoWrapperVector and AutoWrapperRooter can be used to store wrappers that
 * are obtained from the cross-compartment map. However, these classes should
 * not be used if the wrapper will escape. For example, it should not be stored
 * in the heap.
 *
 * The AutoWrapper rooters are different from other autorooters because their
 * wrappers are marked on every GC slice rather than just the first one. If
 * there's some wrapper that we want to use temporarily without causing it to be
 * marked, we can use these AutoWrapper classes. If we get unlucky and a GC
 * slice runs during the code using the wrapper, the GC will mark the wrapper so
 * that it doesn't get swept out from under us. Otherwise, the wrapper needn't
 * be marked. This is useful in functions like JS_TransplantObject that
 * manipulate wrappers in compartments that may no longer be alive.
 */

/*
 * This class stores the data for AutoWrapperVector and AutoWrapperRooter. It
 * should not be used in any other situations.
 */
struct WrapperValue
{
    /*
     * We use unsafeGet() in the constructors to avoid invoking a read barrier
     * on the wrapper, which may be dead (see the comment about bug 803376 in
     * jsgc.cpp regarding this). If there is an incremental GC while the wrapper
     * is in use, the AutoWrapper rooter will ensure the wrapper gets marked.
     */
    explicit WrapperValue(const WrapperMap::Ptr& ptr)
      : value(*ptr->value().unsafeGet())
    {}

    explicit WrapperValue(const WrapperMap::Enum& e)
      : value(*e.front().value().unsafeGet())
    {}

    Value& get() { return value; }
    Value get() const { return value; }
    operator const Value&() const { return value; }
    JSObject& toObject() const { return value.toObject(); }

  private:
    Value value;
};

class AutoWrapperVector : public JS::AutoVectorRooterBase<WrapperValue>
{
  public:
    explicit AutoWrapperVector(JSContext* cx
                               MOZ_GUARD_OBJECT_NOTIFIER_PARAM)
        : AutoVectorRooterBase<WrapperValue>(cx, WRAPVECTOR)
    {
        MOZ_GUARD_OBJECT_NOTIFIER_INIT;
    }

    MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER
};

class AutoWrapperRooter : private JS::AutoGCRooter {
  public:
    AutoWrapperRooter(JSContext* cx, WrapperValue v
                      MOZ_GUARD_OBJECT_NOTIFIER_PARAM)
      : JS::AutoGCRooter(cx, WRAPPER), value(v)
    {
        MOZ_GUARD_OBJECT_NOTIFIER_INIT;
    }

    operator JSObject*() const {
        return value.get().toObjectOrNull();
    }

    friend void JS::AutoGCRooter::trace(JSTracer* trc);

  private:
    WrapperValue value;
    MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER
};

} /* namespace js */

#endif /* jscompartment_h */