gecko-dev/js/public/Class.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/. */

/* JSClass definition and its component types, plus related interfaces. */

#ifndef js_Class_h
#define js_Class_h

#include "mozilla/Attributes.h"

#include "jstypes.h"

#include "js/CallArgs.h"
#include "js/Id.h"
#include "js/TypeDecls.h"

/*
 * A JSClass acts as a vtable for JS objects that allows JSAPI clients to
 * control various aspects of the behavior of an object like property lookup.
 * js::Class is an engine-private extension that allows more control over
 * object behavior and, e.g., allows custom slow layout.
 */

struct JSAtomState;
struct JSFreeOp;
struct JSFunctionSpec;

namespace js {

struct Class;
class FreeOp;
class Shape;

// This is equal to JSFunction::class_.  Use it in places where you don't want
// to #include jsfun.h.
extern JS_FRIEND_DATA const js::Class* const FunctionClassPtr;

}  // namespace js

namespace JS {

/**
 * The answer to a successful query as to whether an object is an Array per
 * ES6's internal |IsArray| operation (as exposed by |Array.isArray|).
 */
enum class IsArrayAnswer { Array, NotArray, RevokedProxy };

/**
 * ES6 7.2.2.
 *
 * Returns false on failure, otherwise returns true and sets |*isArray|
 * indicating whether the object passes ECMAScript's IsArray test.  This is the
 * same test performed by |Array.isArray|.
 *
 * This is NOT the same as asking whether |obj| is an Array or a wrapper around
 * one.  If |obj| is a proxy created by |Proxy.revocable()| and has been
 * revoked, or if |obj| is a proxy whose target (at any number of hops) is a
 * revoked proxy, this method throws a TypeError and returns false.
 */
extern JS_PUBLIC_API bool IsArray(JSContext* cx, HandleObject obj,
                                  bool* isArray);

/**
 * Identical to IsArray above, but the nature of the object (if successfully
 * determined) is communicated via |*answer|.  In particular this method
 * returns true and sets |*answer = IsArrayAnswer::RevokedProxy| when called on
 * a revoked proxy.
 *
 * Most users will want the overload above, not this one.
 */
extern JS_PUBLIC_API bool IsArray(JSContext* cx, HandleObject obj,
                                  IsArrayAnswer* answer);

/**
 * Per ES6, the [[DefineOwnProperty]] internal method has three different
 * possible outcomes:
 *
 * -   It can throw an exception (which we indicate by returning false).
 *
 * -   It can return true, indicating unvarnished success.
 *
 * -   It can return false, indicating "strict failure". The property could
 *     not be defined. It's an error, but no exception was thrown.
 *
 * It's not just [[DefineOwnProperty]]: all the mutating internal methods have
 * the same three outcomes. (The other affected internal methods are [[Set]],
 * [[Delete]], [[SetPrototypeOf]], and [[PreventExtensions]].)
 *
 * If you think this design is awful, you're not alone.  But as it's the
 * standard, we must represent these boolean "success" values somehow.
 * ObjectOpSuccess is the class for this. It's like a bool, but when it's false
 * it also stores an error code.
 *
 * Typical usage:
 *
 *     ObjectOpResult result;
 *     if (!DefineProperty(cx, obj, id, ..., result)) {
 *         return false;
 *     }
 *     if (!result) {
 *         return result.reportError(cx, obj, id);
 *     }
 *
 * Users don't have to call `result.report()`; another possible ending is:
 *
 *     argv.rval().setBoolean(result.reallyOk());
 *     return true;
 */
class ObjectOpResult {
 private:
  /**
   * code_ is either one of the special codes OkCode or Uninitialized, or
   * an error code. For now the error codes are private to the JS engine;
   * they're defined in js/src/js.msg.
   *
   * code_ is uintptr_t (rather than uint32_t) for the convenience of the
   * JITs, which would otherwise have to deal with either padding or stack
   * alignment on 64-bit platforms.
   */
  uintptr_t code_;

 public:
  enum SpecialCodes : uintptr_t { OkCode = 0, Uninitialized = uintptr_t(-1) };

  static const uintptr_t SoftFailBit = uintptr_t(1)
                                       << (sizeof(uintptr_t) * 8 - 1);

  ObjectOpResult() : code_(Uninitialized) {}

  /* Return true if succeed() or failSoft() was called. */
  bool ok() const {
    MOZ_ASSERT(code_ != Uninitialized);
    return code_ == OkCode || (code_ & SoftFailBit);
  }

  explicit operator bool() const { return ok(); }

  /* Return true if succeed() was called. */
  bool reallyOk() const {
    MOZ_ASSERT(code_ != Uninitialized);
    return code_ == OkCode;
  }

  /* Set this ObjectOpResult to true and return true. */
  bool succeed() {
    code_ = OkCode;
    return true;
  }

  /*
   * Set this ObjectOpResult to false with an error code.
   *
   * Always returns true, as a convenience. Typical usage will be:
   *
   *     if (funny condition) {
   *         return result.fail(JSMSG_CANT_DO_THE_THINGS);
   *     }
   *
   * The true return value indicates that no exception is pending, and it
   * would be OK to ignore the failure and continue.
   */
  bool fail(uint32_t msg) {
    MOZ_ASSERT(msg != OkCode);
    MOZ_ASSERT((msg & SoftFailBit) == 0);
    code_ = msg;
    return true;
  }

  /*
   * DEPRECATED: This is a non-standard compatibility hack.
   *
   * Set this ObjectOpResult to true, but remembers an error code.
   * This is used for situations where we really want to fail,
   * but can't for legacy reasons.
   *
   * Always returns true, as a convenience.
   */
  bool failSoft(uint32_t msg) {
    // The msg code is currently never extracted again.
    code_ = msg | SoftFailBit;
    return true;
  }

  JS_PUBLIC_API bool failCantRedefineProp();
  JS_PUBLIC_API bool failReadOnly();
  JS_PUBLIC_API bool failGetterOnly();
  JS_PUBLIC_API bool failCantDelete();

  JS_PUBLIC_API bool failCantSetInterposed();
  JS_PUBLIC_API bool failCantDefineWindowElement();
  JS_PUBLIC_API bool failCantDeleteWindowElement();
  JS_PUBLIC_API bool failCantDeleteWindowNamedProperty();
  JS_PUBLIC_API bool failCantPreventExtensions();
  JS_PUBLIC_API bool failCantSetProto();
  JS_PUBLIC_API bool failNoNamedSetter();
  JS_PUBLIC_API bool failNoIndexedSetter();
  JS_PUBLIC_API bool failNotDataDescriptor();

  // Careful: This case has special handling in Object.defineProperty.
  JS_PUBLIC_API bool failCantDefineWindowNonConfigurable();

  uint32_t failureCode() const {
    MOZ_ASSERT(!ok());
    return uint32_t(code_);
  }

  /*
   * Report an error or warning if necessary; return true to proceed and
   * false if an error was reported. Call this when failure should cause
   * a warning if extraWarnings are enabled.
   *
   * The precise rules are like this:
   *
   * -   If ok(), then we succeeded. Do nothing and return true.
   * -   Otherwise, if |strict| is true, or if cx has both extraWarnings and
   *     werrorOption enabled, throw a TypeError and return false.
   * -   Otherwise, if cx has extraWarnings enabled, emit a warning and
   *     return true.
   * -   Otherwise, do nothing and return true.
   */
  bool checkStrictErrorOrWarning(JSContext* cx, HandleObject obj, HandleId id,
                                 bool strict) {
    if (ok()) {
      return true;
    }
    return reportStrictErrorOrWarning(cx, obj, id, strict);
  }

  /*
   * The same as checkStrictErrorOrWarning(cx, id, strict), except the
   * operation is not associated with a particular property id. This is
   * used for [[PreventExtensions]] and [[SetPrototypeOf]]. failureCode()
   * must not be an error that has "{0}" in the error message.
   */
  bool checkStrictErrorOrWarning(JSContext* cx, HandleObject obj, bool strict) {
    return ok() || reportStrictErrorOrWarning(cx, obj, strict);
  }

  /* Throw a TypeError. Call this only if !ok(). */
  bool reportError(JSContext* cx, HandleObject obj, HandleId id) {
    return reportStrictErrorOrWarning(cx, obj, id, true);
  }

  /*
   * The same as reportError(cx, obj, id), except the operation is not
   * associated with a particular property id.
   */
  bool reportError(JSContext* cx, HandleObject obj) {
    return reportStrictErrorOrWarning(cx, obj, true);
  }

  /* Helper function for checkStrictErrorOrWarning's slow path. */
  JS_PUBLIC_API bool reportStrictErrorOrWarning(JSContext* cx, HandleObject obj,
                                                HandleId id, bool strict);
  JS_PUBLIC_API bool reportStrictErrorOrWarning(JSContext* cx, HandleObject obj,
                                                bool strict);

  /*
   * Convenience method. Return true if ok() or if strict is false; otherwise
   * throw a TypeError and return false.
   */
  bool checkStrict(JSContext* cx, HandleObject obj, HandleId id) {
    return checkStrictErrorOrWarning(cx, obj, id, true);
  }

  /*
   * Convenience method. The same as checkStrict(cx, id), except the
   * operation is not associated with a particular property id.
   */
  bool checkStrict(JSContext* cx, HandleObject obj) {
    return checkStrictErrorOrWarning(cx, obj, true);
  }
};

class PropertyResult {
  union {
    js::Shape* shape_;
    uintptr_t bits_;
  };

  static const uintptr_t NotFound = 0;
  static const uintptr_t NonNativeProperty = 1;
  static const uintptr_t DenseOrTypedArrayElement = 1;

 public:
  PropertyResult() : bits_(NotFound) {}

  explicit PropertyResult(js::Shape* propertyShape) : shape_(propertyShape) {
    MOZ_ASSERT(!isFound() || isNativeProperty());
  }

  explicit operator bool() const { return isFound(); }

  bool isFound() const { return bits_ != NotFound; }

  bool isNonNativeProperty() const { return bits_ == NonNativeProperty; }

  bool isDenseOrTypedArrayElement() const {
    return bits_ == DenseOrTypedArrayElement;
  }

  bool isNativeProperty() const { return isFound() && !isNonNativeProperty(); }

  js::Shape* maybeShape() const {
    MOZ_ASSERT(!isNonNativeProperty());
    return isFound() ? shape_ : nullptr;
  }

  js::Shape* shape() const {
    MOZ_ASSERT(isNativeProperty());
    return shape_;
  }

  void setNotFound() { bits_ = NotFound; }

  void setNativeProperty(js::Shape* propertyShape) {
    shape_ = propertyShape;
    MOZ_ASSERT(isNativeProperty());
  }

  void setNonNativeProperty() { bits_ = NonNativeProperty; }

  void setDenseOrTypedArrayElement() { bits_ = DenseOrTypedArrayElement; }

  void trace(JSTracer* trc);
};

}  // namespace JS

namespace js {

template <class Wrapper>
class WrappedPtrOperations<JS::PropertyResult, Wrapper> {
  const JS::PropertyResult& value() const {
    return static_cast<const Wrapper*>(this)->get();
  }

 public:
  bool isFound() const { return value().isFound(); }
  explicit operator bool() const { return bool(value()); }
  js::Shape* maybeShape() const { return value().maybeShape(); }
  js::Shape* shape() const { return value().shape(); }
  bool isNativeProperty() const { return value().isNativeProperty(); }
  bool isNonNativeProperty() const { return value().isNonNativeProperty(); }
  bool isDenseOrTypedArrayElement() const {
    return value().isDenseOrTypedArrayElement();
  }
  js::Shape* asTaggedShape() const { return value().asTaggedShape(); }
};

template <class Wrapper>
class MutableWrappedPtrOperations<JS::PropertyResult, Wrapper>
    : public WrappedPtrOperations<JS::PropertyResult, Wrapper> {
  JS::PropertyResult& value() { return static_cast<Wrapper*>(this)->get(); }

 public:
  void setNotFound() { value().setNotFound(); }
  void setNativeProperty(js::Shape* shape) { value().setNativeProperty(shape); }
  void setNonNativeProperty() { value().setNonNativeProperty(); }
  void setDenseOrTypedArrayElement() { value().setDenseOrTypedArrayElement(); }
};

}  // namespace js

// JSClass operation signatures.

/**
 * Get a property named by id in obj.  Note the jsid id type -- id may
 * be a string (Unicode property identifier) or an int (element index).  The
 * *vp out parameter, on success, is the new property value after the action.
 */
typedef bool (*JSGetterOp)(JSContext* cx, JS::HandleObject obj, JS::HandleId id,
                           JS::MutableHandleValue vp);

/** Add a property named by id to obj. */
typedef bool (*JSAddPropertyOp)(JSContext* cx, JS::HandleObject obj,
                                JS::HandleId id, JS::HandleValue v);

/**
 * Set a property named by id in obj, treating the assignment as strict
 * mode code if strict is true. Note the jsid id type -- id may be a string
 * (Unicode property identifier) or an int (element index).
 */
typedef bool (*JSSetterOp)(JSContext* cx, JS::HandleObject obj, JS::HandleId id,
                           JS::HandleValue v, JS::ObjectOpResult& result);

/**
 * Delete a property named by id in obj.
 *
 * If an error occurred, return false as per normal JSAPI error practice.
 *
 * If no error occurred, but the deletion attempt wasn't allowed (perhaps
 * because the property was non-configurable), call result.fail() and
 * return true.  This will cause |delete obj[id]| to evaluate to false in
 * non-strict mode code, and to throw a TypeError in strict mode code.
 *
 * If no error occurred and the deletion wasn't disallowed (this is *not* the
 * same as saying that a deletion actually occurred -- deleting a non-existent
 * property, or an inherited property, is allowed -- it's just pointless),
 * call result.succeed() and return true.
 */
typedef bool (*JSDeletePropertyOp)(JSContext* cx, JS::HandleObject obj,
                                   JS::HandleId id, JS::ObjectOpResult& result);

/**
 * The type of ObjectOps::enumerate. This callback overrides a portion of
 * SpiderMonkey's default [[Enumerate]] internal method. When an ordinary object
 * is enumerated, that object and each object on its prototype chain is tested
 * for an enumerate op, and those ops are called in order. The properties each
 * op adds to the 'properties' vector are added to the set of values the for-in
 * loop will iterate over. All of this is nonstandard.
 *
 * An object is "enumerated" when it's the target of a for-in loop or
 * JS_Enumerate(). The callback's job is to populate 'properties' with the
 * object's property keys. If `enumerableOnly` is true, the callback should only
 * add enumerable properties.
 */
typedef bool (*JSNewEnumerateOp)(JSContext* cx, JS::HandleObject obj,
                                 JS::AutoIdVector& properties,
                                 bool enumerableOnly);

/**
 * The old-style JSClass.enumerate op should define all lazy properties not
 * yet reflected in obj.
 */
typedef bool (*JSEnumerateOp)(JSContext* cx, JS::HandleObject obj);

/**
 * The type of ObjectOps::funToString.  This callback allows an object to
 * provide a custom string to use when Function.prototype.toString is invoked on
 * that object.  A null return value means OOM.
 */
typedef JSString* (*JSFunToStringOp)(JSContext* cx, JS::HandleObject obj,
                                     bool isToSource);

/**
 * Resolve a lazy property named by id in obj by defining it directly in obj.
 * Lazy properties are those reflected from some peer native property space
 * (e.g., the DOM attributes for a given node reflected as obj) on demand.
 *
 * JS looks for a property in an object, and if not found, tries to resolve
 * the given id. *resolvedp should be set to true iff the property was defined
 * on |obj|.
 */
typedef bool (*JSResolveOp)(JSContext* cx, JS::HandleObject obj,
                            JS::HandleId id, bool* resolvedp);

/**
 * A class with a resolve hook can optionally have a mayResolve hook. This hook
 * must have no side effects and must return true for a given id if the resolve
 * hook may resolve this id. This is useful when we're doing a "pure" lookup: if
 * mayResolve returns false, we know we don't have to call the effectful resolve
 * hook.
 *
 * maybeObj, if non-null, is the object on which we're doing the lookup. This
 * can be nullptr: during JIT compilation we sometimes know the Class but not
 * the object.
 */
typedef bool (*JSMayResolveOp)(const JSAtomState& names, jsid id,
                               JSObject* maybeObj);

/**
 * Finalize obj, which the garbage collector has determined to be unreachable
 * from other live objects or from GC roots.  Obviously, finalizers must never
 * store a reference to obj.
 */
typedef void (*JSFinalizeOp)(JSFreeOp* fop, JSObject* obj);

/**
 * Check whether v is an instance of obj.  Return false on error or exception,
 * true on success with true in *bp if v is an instance of obj, false in
 * *bp otherwise.
 */
typedef bool (*JSHasInstanceOp)(JSContext* cx, JS::HandleObject obj,
                                JS::MutableHandleValue vp, bool* bp);

/**
 * Function type for trace operation of the class called to enumerate all
 * traceable things reachable from obj's private data structure. For each such
 * thing, a trace implementation must call JS::TraceEdge on the thing's
 * location.
 *
 * JSTraceOp implementation can assume that no other threads mutates object
 * state. It must not change state of the object or corresponding native
 * structures. The only exception for this rule is the case when the embedding
 * needs a tight integration with GC. In that case the embedding can check if
 * the traversal is a part of the marking phase through calling
 * JS_IsGCMarkingTracer and apply a special code like emptying caches or
 * marking its native structures.
 */
typedef void (*JSTraceOp)(JSTracer* trc, JSObject* obj);

typedef size_t (*JSObjectMovedOp)(JSObject* obj, JSObject* old);

/* js::Class operation signatures. */

namespace js {

typedef bool (*LookupPropertyOp)(JSContext* cx, JS::HandleObject obj,
                                 JS::HandleId id, JS::MutableHandleObject objp,
                                 JS::MutableHandle<JS::PropertyResult> propp);
typedef bool (*DefinePropertyOp)(JSContext* cx, JS::HandleObject obj,
                                 JS::HandleId id,
                                 JS::Handle<JS::PropertyDescriptor> desc,
                                 JS::ObjectOpResult& result);
typedef bool (*HasPropertyOp)(JSContext* cx, JS::HandleObject obj,
                              JS::HandleId id, bool* foundp);
typedef bool (*GetPropertyOp)(JSContext* cx, JS::HandleObject obj,
                              JS::HandleValue receiver, JS::HandleId id,
                              JS::MutableHandleValue vp);
typedef bool (*SetPropertyOp)(JSContext* cx, JS::HandleObject obj,
                              JS::HandleId id, JS::HandleValue v,
                              JS::HandleValue receiver,
                              JS::ObjectOpResult& result);
typedef bool (*GetOwnPropertyOp)(
    JSContext* cx, JS::HandleObject obj, JS::HandleId id,
    JS::MutableHandle<JS::PropertyDescriptor> desc);
typedef bool (*DeletePropertyOp)(JSContext* cx, JS::HandleObject obj,
                                 JS::HandleId id, JS::ObjectOpResult& result);

class JS_FRIEND_API ElementAdder {
 public:
  enum GetBehavior {
    // Check if the element exists before performing the Get and preserve
    // holes.
    CheckHasElemPreserveHoles,

    // Perform a Get operation, like obj[index] in JS.
    GetElement
  };

 private:
  // Only one of these is used.
  JS::RootedObject resObj_;
  JS::Value* vp_;

  uint32_t index_;
#ifdef DEBUG
  uint32_t length_;
#endif
  GetBehavior getBehavior_;

 public:
  ElementAdder(JSContext* cx, JSObject* obj, uint32_t length,
               GetBehavior behavior)
      : resObj_(cx, obj),
        vp_(nullptr),
        index_(0),
#ifdef DEBUG
        length_(length),
#endif
        getBehavior_(behavior) {
  }
  ElementAdder(JSContext* cx, JS::Value* vp, uint32_t length,
               GetBehavior behavior)
      : resObj_(cx),
        vp_(vp),
        index_(0),
#ifdef DEBUG
        length_(length),
#endif
        getBehavior_(behavior) {
  }

  GetBehavior getBehavior() const { return getBehavior_; }

  bool append(JSContext* cx, JS::HandleValue v);
  void appendHole();
};

typedef bool (*GetElementsOp)(JSContext* cx, JS::HandleObject obj,
                              uint32_t begin, uint32_t end,
                              ElementAdder* adder);

typedef void (*FinalizeOp)(FreeOp* fop, JSObject* obj);

// The special treatment of |finalize| and |trace| is necessary because if we
// assign either of those hooks to a local variable and then call it -- as is
// done with the other hooks -- the GC hazard analysis gets confused.
#define JS_CLASS_MEMBERS(ClassOpsType, FreeOpType)                             \
  const char* name;                                                            \
  uint32_t flags;                                                              \
  const ClassOpsType* cOps;                                                    \
                                                                               \
  JSAddPropertyOp getAddProperty() const {                                     \
    return cOps ? cOps->addProperty : nullptr;                                 \
  }                                                                            \
  JSDeletePropertyOp getDelProperty() const {                                  \
    return cOps ? cOps->delProperty : nullptr;                                 \
  }                                                                            \
  JSEnumerateOp getEnumerate() const {                                         \
    return cOps ? cOps->enumerate : nullptr;                                   \
  }                                                                            \
  JSNewEnumerateOp getNewEnumerate() const {                                   \
    return cOps ? cOps->newEnumerate : nullptr;                                \
  }                                                                            \
  JSResolveOp getResolve() const { return cOps ? cOps->resolve : nullptr; }    \
  JSMayResolveOp getMayResolve() const {                                       \
    return cOps ? cOps->mayResolve : nullptr;                                  \
  }                                                                            \
  JSNative getCall() const { return cOps ? cOps->call : nullptr; }             \
  JSHasInstanceOp getHasInstance() const {                                     \
    return cOps ? cOps->hasInstance : nullptr;                                 \
  }                                                                            \
  JSNative getConstruct() const { return cOps ? cOps->construct : nullptr; }   \
                                                                               \
  bool hasFinalize() const { return cOps && cOps->finalize; }                  \
  bool hasTrace() const { return cOps && cOps->trace; }                        \
                                                                               \
  bool isTrace(JSTraceOp trace) const { return cOps && cOps->trace == trace; } \
                                                                               \
  void doFinalize(FreeOpType* fop, JSObject* obj) const {                      \
    MOZ_ASSERT(cOps && cOps->finalize);                                        \
    cOps->finalize(fop, obj);                                                  \
  }                                                                            \
  void doTrace(JSTracer* trc, JSObject* obj) const {                           \
    MOZ_ASSERT(cOps && cOps->trace);                                           \
    cOps->trace(trc, obj);                                                     \
  }

struct MOZ_STATIC_CLASS ClassOps {
  /* Function pointer members (may be null). */
  JSAddPropertyOp addProperty;
  JSDeletePropertyOp delProperty;
  JSEnumerateOp enumerate;
  JSNewEnumerateOp newEnumerate;
  JSResolveOp resolve;
  JSMayResolveOp mayResolve;
  FinalizeOp finalize;
  JSNative call;
  JSHasInstanceOp hasInstance;
  JSNative construct;
  JSTraceOp trace;
};

/** Callback for the creation of constructor and prototype objects. */
typedef JSObject* (*ClassObjectCreationOp)(JSContext* cx, JSProtoKey key);

/**
 * Callback for custom post-processing after class initialization via
 * ClassSpec.
 */
typedef bool (*FinishClassInitOp)(JSContext* cx, JS::HandleObject ctor,
                                  JS::HandleObject proto);

const size_t JSCLASS_CACHED_PROTO_WIDTH = 6;

struct MOZ_STATIC_CLASS ClassSpec {
  ClassObjectCreationOp createConstructor;
  ClassObjectCreationOp createPrototype;
  const JSFunctionSpec* constructorFunctions;
  const JSPropertySpec* constructorProperties;
  const JSFunctionSpec* prototypeFunctions;
  const JSPropertySpec* prototypeProperties;
  FinishClassInitOp finishInit;
  uintptr_t flags;

  static const size_t ProtoKeyWidth = JSCLASS_CACHED_PROTO_WIDTH;

  static const uintptr_t ProtoKeyMask = (1 << ProtoKeyWidth) - 1;
  static const uintptr_t DontDefineConstructor = 1 << ProtoKeyWidth;

  bool defined() const { return !!createConstructor; }

  // The ProtoKey this class inherits from.
  JSProtoKey inheritanceProtoKey() const {
    MOZ_ASSERT(defined());
    static_assert(JSProto_Null == 0, "zeroed key must be null");

    // Default: Inherit from Object.
    if (!(flags & ProtoKeyMask)) {
      return JSProto_Object;
    }

    return JSProtoKey(flags & ProtoKeyMask);
  }

  bool shouldDefineConstructor() const {
    MOZ_ASSERT(defined());
    return !(flags & DontDefineConstructor);
  }
};

struct MOZ_STATIC_CLASS ClassExtension {
  /**
   * Optional hook called when an object is moved by generational or
   * compacting GC.
   *
   * There may exist weak pointers to an object that are not traced through
   * when the normal trace APIs are used, for example objects in the wrapper
   * cache. This hook allows these pointers to be updated.
   *
   * Note that this hook can be called before JS_NewObject() returns if a GC
   * is triggered during construction of the object. This can happen for
   * global objects for example.
   *
   * The function should return the difference between nursery bytes used and
   * tenured bytes used, which may be nonzero e.g. if some nursery-allocated
   * data beyond the actual GC thing is moved into malloced memory.
   *
   * This is used to compute the nursery promotion rate.
   */
  JSObjectMovedOp objectMovedOp;
};

#define JS_NULL_CLASS_SPEC nullptr
#define JS_NULL_CLASS_EXT nullptr

struct MOZ_STATIC_CLASS ObjectOps {
  LookupPropertyOp lookupProperty;
  DefinePropertyOp defineProperty;
  HasPropertyOp hasProperty;
  GetPropertyOp getProperty;
  SetPropertyOp setProperty;
  GetOwnPropertyOp getOwnPropertyDescriptor;
  DeletePropertyOp deleteProperty;
  GetElementsOp getElements;
  JSFunToStringOp funToString;
};

#define JS_NULL_OBJECT_OPS nullptr

}  // namespace js

// Classes, objects, and properties.

typedef void (*JSClassInternal)();

struct MOZ_STATIC_CLASS JSClassOps {
  /* Function pointer members (may be null). */
  JSAddPropertyOp addProperty;
  JSDeletePropertyOp delProperty;
  JSEnumerateOp enumerate;
  JSNewEnumerateOp newEnumerate;
  JSResolveOp resolve;
  JSMayResolveOp mayResolve;
  JSFinalizeOp finalize;
  JSNative call;
  JSHasInstanceOp hasInstance;
  JSNative construct;
  JSTraceOp trace;
};

#define JS_NULL_CLASS_OPS nullptr

struct JSClass {
  JS_CLASS_MEMBERS(JSClassOps, JSFreeOp);

  void* reserved[3];
};

// Objects have private slot.
static const uint32_t JSCLASS_HAS_PRIVATE = 1 << 0;

// Class's initialization code will call `SetNewObjectMetadata` itself.
static const uint32_t JSCLASS_DELAY_METADATA_BUILDER = 1 << 1;

// Class is an XPCWrappedNative. WeakMaps use this to override the wrapper
// disposal mechanism.
static const uint32_t JSCLASS_IS_WRAPPED_NATIVE = 1 << 2;

// Private is `nsISupports*`.
static const uint32_t JSCLASS_PRIVATE_IS_NSISUPPORTS = 1 << 3;

// Objects are DOM.
static const uint32_t JSCLASS_IS_DOMJSCLASS = 1 << 4;

// If wrapped by an xray wrapper, the builtin class's constructor won't be
// unwrapped and invoked. Instead, the constructor is resolved in the caller's
// compartment and invoked with a wrapped newTarget. The constructor has to
// detect and handle this situation. See PromiseConstructor for details.
static const uint32_t JSCLASS_HAS_XRAYED_CONSTRUCTOR = 1 << 5;

// Objects of this class act like the value undefined, in some contexts.
static const uint32_t JSCLASS_EMULATES_UNDEFINED = 1 << 6;

// Reserved for embeddings.
static const uint32_t JSCLASS_USERBIT1 = 1 << 7;

// To reserve slots fetched and stored via JS_Get/SetReservedSlot, bitwise-or
// JSCLASS_HAS_RESERVED_SLOTS(n) into the initializer for JSClass.flags, where n
// is a constant in [1, 255]. Reserved slots are indexed from 0 to n-1.

// Room for 8 flags below ...
static const uintptr_t JSCLASS_RESERVED_SLOTS_SHIFT = 8;
// ... and 16 above this field.
static const uint32_t JSCLASS_RESERVED_SLOTS_WIDTH = 8;

static const uint32_t JSCLASS_RESERVED_SLOTS_MASK =
    JS_BITMASK(JSCLASS_RESERVED_SLOTS_WIDTH);

#define JSCLASS_HAS_RESERVED_SLOTS(n) \
  (((n)&JSCLASS_RESERVED_SLOTS_MASK) << JSCLASS_RESERVED_SLOTS_SHIFT)
#define JSCLASS_RESERVED_SLOTS(clasp)                 \
  (((clasp)->flags >> JSCLASS_RESERVED_SLOTS_SHIFT) & \
   JSCLASS_RESERVED_SLOTS_MASK)

#define JSCLASS_HIGH_FLAGS_SHIFT \
  (JSCLASS_RESERVED_SLOTS_SHIFT + JSCLASS_RESERVED_SLOTS_WIDTH)

static const uint32_t JSCLASS_IS_ANONYMOUS = 1
                                             << (JSCLASS_HIGH_FLAGS_SHIFT + 0);
static const uint32_t JSCLASS_IS_GLOBAL = 1 << (JSCLASS_HIGH_FLAGS_SHIFT + 1);
static const uint32_t JSCLASS_INTERNAL_FLAG2 =
    1 << (JSCLASS_HIGH_FLAGS_SHIFT + 2);
static const uint32_t JSCLASS_INTERNAL_FLAG3 =
    1 << (JSCLASS_HIGH_FLAGS_SHIFT + 3);
static const uint32_t JSCLASS_IS_PROXY = 1 << (JSCLASS_HIGH_FLAGS_SHIFT + 4);
static const uint32_t JSCLASS_SKIP_NURSERY_FINALIZE =
    1 << (JSCLASS_HIGH_FLAGS_SHIFT + 5);

// Reserved for embeddings.
static const uint32_t JSCLASS_USERBIT2 = 1 << (JSCLASS_HIGH_FLAGS_SHIFT + 6);
static const uint32_t JSCLASS_USERBIT3 = 1 << (JSCLASS_HIGH_FLAGS_SHIFT + 7);

static const uint32_t JSCLASS_BACKGROUND_FINALIZE =
    1 << (JSCLASS_HIGH_FLAGS_SHIFT + 8);
static const uint32_t JSCLASS_FOREGROUND_FINALIZE =
    1 << (JSCLASS_HIGH_FLAGS_SHIFT + 9);

// Bits 26 through 31 are reserved for the CACHED_PROTO_KEY mechanism, see
// below.

// ECMA-262 requires that most constructors used internally create objects
// with "the original Foo.prototype value" as their [[Prototype]] (__proto__)
// member initial value.  The "original ... value" verbiage is there because
// in ECMA-262, global properties naming class objects are read/write and
// deleteable, for the most part.
//
// Implementing this efficiently requires that global objects have classes
// with the following flags. Failure to use JSCLASS_GLOBAL_FLAGS was
// previously allowed, but is now an ES5 violation and thus unsupported.
//
// JSCLASS_GLOBAL_APPLICATION_SLOTS is the number of slots reserved at
// the beginning of every global object's slots for use by the
// application.
static const uint32_t JSCLASS_GLOBAL_APPLICATION_SLOTS = 5;
static const uint32_t JSCLASS_GLOBAL_SLOT_COUNT =
    JSCLASS_GLOBAL_APPLICATION_SLOTS + JSProto_LIMIT * 2 + 38;

#define JSCLASS_GLOBAL_FLAGS_WITH_SLOTS(n) \
  (JSCLASS_IS_GLOBAL |                     \
   JSCLASS_HAS_RESERVED_SLOTS(JSCLASS_GLOBAL_SLOT_COUNT + (n)))
#define JSCLASS_GLOBAL_FLAGS JSCLASS_GLOBAL_FLAGS_WITH_SLOTS(0)
#define JSCLASS_HAS_GLOBAL_FLAG_AND_SLOTS(clasp) \
  (((clasp)->flags & JSCLASS_IS_GLOBAL) &&       \
   JSCLASS_RESERVED_SLOTS(clasp) >= JSCLASS_GLOBAL_SLOT_COUNT)

// Fast access to the original value of each standard class's prototype.
static const uint32_t JSCLASS_CACHED_PROTO_SHIFT =
    JSCLASS_HIGH_FLAGS_SHIFT + 10;
static const uint32_t JSCLASS_CACHED_PROTO_MASK =
    JS_BITMASK(js::JSCLASS_CACHED_PROTO_WIDTH);

#define JSCLASS_HAS_CACHED_PROTO(key) \
  (uint32_t(key) << JSCLASS_CACHED_PROTO_SHIFT)
#define JSCLASS_CACHED_PROTO_KEY(clasp)                          \
  ((JSProtoKey)(((clasp)->flags >> JSCLASS_CACHED_PROTO_SHIFT) & \
                JSCLASS_CACHED_PROTO_MASK))

// Initializer for unused members of statically initialized JSClass structs.
#define JSCLASS_NO_INTERNAL_MEMBERS \
  { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 }
#define JSCLASS_NO_OPTIONAL_MEMBERS 0, 0, 0, 0, 0, JSCLASS_NO_INTERNAL_MEMBERS

namespace js {

struct MOZ_STATIC_CLASS Class {
  JS_CLASS_MEMBERS(js::ClassOps, FreeOp);
  const ClassSpec* spec;
  const ClassExtension* ext;
  const ObjectOps* oOps;

  /*
   * Objects of this class aren't native objects. They don't have Shapes that
   * describe their properties and layout. Classes using this flag must
   * provide their own property behavior, either by being proxy classes (do
   * this) or by overriding all the ObjectOps except getElements
   * (don't do this).
   */
  static const uint32_t NON_NATIVE = JSCLASS_INTERNAL_FLAG2;

  bool isNative() const { return !(flags & NON_NATIVE); }

  bool hasPrivate() const { return !!(flags & JSCLASS_HAS_PRIVATE); }

  bool emulatesUndefined() const { return flags & JSCLASS_EMULATES_UNDEFINED; }

  bool isJSFunction() const { return this == js::FunctionClassPtr; }

  bool nonProxyCallable() const {
    MOZ_ASSERT(!isProxy());
    return isJSFunction() || getCall();
  }

  bool isProxy() const { return flags & JSCLASS_IS_PROXY; }

  bool isDOMClass() const { return flags & JSCLASS_IS_DOMJSCLASS; }

  bool shouldDelayMetadataBuilder() const {
    return flags & JSCLASS_DELAY_METADATA_BUILDER;
  }

  bool isWrappedNative() const { return flags & JSCLASS_IS_WRAPPED_NATIVE; }

  static size_t offsetOfFlags() { return offsetof(Class, flags); }

  bool specDefined() const { return spec ? spec->defined() : false; }
  JSProtoKey specInheritanceProtoKey() const {
    return spec ? spec->inheritanceProtoKey() : JSProto_Null;
  }
  bool specShouldDefineConstructor() const {
    return spec ? spec->shouldDefineConstructor() : true;
  }
  ClassObjectCreationOp specCreateConstructorHook() const {
    return spec ? spec->createConstructor : nullptr;
  }
  ClassObjectCreationOp specCreatePrototypeHook() const {
    return spec ? spec->createPrototype : nullptr;
  }
  const JSFunctionSpec* specConstructorFunctions() const {
    return spec ? spec->constructorFunctions : nullptr;
  }
  const JSPropertySpec* specConstructorProperties() const {
    return spec ? spec->constructorProperties : nullptr;
  }
  const JSFunctionSpec* specPrototypeFunctions() const {
    return spec ? spec->prototypeFunctions : nullptr;
  }
  const JSPropertySpec* specPrototypeProperties() const {
    return spec ? spec->prototypeProperties : nullptr;
  }
  FinishClassInitOp specFinishInitHook() const {
    return spec ? spec->finishInit : nullptr;
  }

  JSObjectMovedOp extObjectMovedOp() const {
    return ext ? ext->objectMovedOp : nullptr;
  }

  LookupPropertyOp getOpsLookupProperty() const {
    return oOps ? oOps->lookupProperty : nullptr;
  }
  DefinePropertyOp getOpsDefineProperty() const {
    return oOps ? oOps->defineProperty : nullptr;
  }
  HasPropertyOp getOpsHasProperty() const {
    return oOps ? oOps->hasProperty : nullptr;
  }
  GetPropertyOp getOpsGetProperty() const {
    return oOps ? oOps->getProperty : nullptr;
  }
  SetPropertyOp getOpsSetProperty() const {
    return oOps ? oOps->setProperty : nullptr;
  }
  GetOwnPropertyOp getOpsGetOwnPropertyDescriptor() const {
    return oOps ? oOps->getOwnPropertyDescriptor : nullptr;
  }
  DeletePropertyOp getOpsDeleteProperty() const {
    return oOps ? oOps->deleteProperty : nullptr;
  }
  GetElementsOp getOpsGetElements() const {
    return oOps ? oOps->getElements : nullptr;
  }
  JSFunToStringOp getOpsFunToString() const {
    return oOps ? oOps->funToString : nullptr;
  }
};

static_assert(offsetof(JSClassOps, addProperty) ==
                  offsetof(ClassOps, addProperty),
              "ClassOps and JSClassOps must be consistent");
static_assert(offsetof(JSClassOps, delProperty) ==
                  offsetof(ClassOps, delProperty),
              "ClassOps and JSClassOps must be consistent");
static_assert(offsetof(JSClassOps, enumerate) == offsetof(ClassOps, enumerate),
              "ClassOps and JSClassOps must be consistent");
static_assert(offsetof(JSClassOps, newEnumerate) ==
                  offsetof(ClassOps, newEnumerate),
              "ClassOps and JSClassOps must be consistent");
static_assert(offsetof(JSClassOps, resolve) == offsetof(ClassOps, resolve),
              "ClassOps and JSClassOps must be consistent");
static_assert(offsetof(JSClassOps, mayResolve) ==
                  offsetof(ClassOps, mayResolve),
              "ClassOps and JSClassOps must be consistent");
static_assert(offsetof(JSClassOps, finalize) == offsetof(ClassOps, finalize),
              "ClassOps and JSClassOps must be consistent");
static_assert(offsetof(JSClassOps, call) == offsetof(ClassOps, call),
              "ClassOps and JSClassOps must be consistent");
static_assert(offsetof(JSClassOps, construct) == offsetof(ClassOps, construct),
              "ClassOps and JSClassOps must be consistent");
static_assert(offsetof(JSClassOps, hasInstance) ==
                  offsetof(ClassOps, hasInstance),
              "ClassOps and JSClassOps must be consistent");
static_assert(offsetof(JSClassOps, trace) == offsetof(ClassOps, trace),
              "ClassOps and JSClassOps must be consistent");
static_assert(sizeof(JSClassOps) == sizeof(ClassOps),
              "ClassOps and JSClassOps must be consistent");

static_assert(offsetof(JSClass, name) == offsetof(Class, name),
              "Class and JSClass must be consistent");
static_assert(offsetof(JSClass, flags) == offsetof(Class, flags),
              "Class and JSClass must be consistent");
static_assert(offsetof(JSClass, cOps) == offsetof(Class, cOps),
              "Class and JSClass must be consistent");
static_assert(sizeof(JSClass) == sizeof(Class),
              "Class and JSClass must be consistent");

static MOZ_ALWAYS_INLINE const JSClass* Jsvalify(const Class* c) {
  return (const JSClass*)c;
}

static MOZ_ALWAYS_INLINE const Class* Valueify(const JSClass* c) {
  return (const Class*)c;
}

/**
 * Enumeration describing possible values of the [[Class]] internal property
 * value of objects.
 */
enum class ESClass {
  Object,
  Array,
  Number,
  String,
  Boolean,
  RegExp,
  ArrayBuffer,
  SharedArrayBuffer,
  Date,
  Set,
  Map,
  Promise,
  MapIterator,
  SetIterator,
  Arguments,
  Error,
#ifdef ENABLE_BIGINT
  BigInt,
#endif

  /** None of the above. */
  Other
};

/* Fills |vp| with the unboxed value for boxed types, or undefined otherwise. */
bool Unbox(JSContext* cx, JS::HandleObject obj, JS::MutableHandleValue vp);

#ifdef DEBUG
JS_FRIEND_API bool HasObjectMovedOp(JSObject* obj);
#endif

} /* namespace js */

#endif /* js_Class_h */