Adding upstream version 124.0.1.upstream/124.0.1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1133 insertions, 0 deletions

diff --git a/js/src/vm/JSObject.h b/js/src/vm/JSObject.h
new file mode 100644
index 0000000000..bbd3d98e1c
--- /dev/null
+++ b/js/src/vm/JSObject.h
@@ -0,0 +1,1133 @@
+/* -*- 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_JSObject_h
+#define vm_JSObject_h
+
+#include "mozilla/MemoryReporting.h"
+
+#include "jsfriendapi.h"
+
+#include "js/friend/ErrorMessages.h"  // JSErrNum
+#include "js/GCVector.h"
+#include "js/shadow/Zone.h"  // JS::shadow::Zone
+#include "js/Wrapper.h"
+#include "vm/Shape.h"
+
+namespace JS {
+struct ClassInfo;
+}  // namespace JS
+
+namespace js {
+
+using PropertyDescriptorVector = JS::GCVector<JS::PropertyDescriptor>;
+class GCMarker;
+class JS_PUBLIC_API GenericPrinter;
+class JSONPrinter;
+class Nursery;
+struct AutoEnterOOMUnsafeRegion;
+
+namespace gc {
+class RelocationOverlay;
+}  // namespace gc
+
+/****************************************************************************/
+
+class GlobalObject;
+class NativeObject;
+
+enum class IntegrityLevel { Sealed, Frozen };
+
+/*
+ * The NewObjectKind allows an allocation site to specify the lifetime
+ * requirements that must be fixed at allocation time.
+ */
+enum NewObjectKind {
+  /* This is the default. Most objects are generic. */
+  GenericObject,
+
+  /*
+   * Objects which will not benefit from being allocated in the nursery
+   * (e.g. because they are known to have a long lifetime) may be allocated
+   * with this kind to place them immediately into the tenured generation.
+   */
+  TenuredObject
+};
+
+// Forward declarations, required for later friend declarations.
+bool PreventExtensions(JSContext* cx, JS::HandleObject obj,
+                       JS::ObjectOpResult& result);
+bool SetImmutablePrototype(JSContext* cx, JS::HandleObject obj,
+                           bool* succeeded);
+
+} /* namespace js */
+
+/*
+ * [SMDOC] JSObject layout
+ *
+ * A JavaScript object.
+ *
+ * This is the base class for all objects exposed to JS script (as well as some
+ * objects that are only accessed indirectly). Subclasses add additional fields
+ * and execution semantics. The runtime class of an arbitrary JSObject is
+ * identified by JSObject::getClass().
+ *
+ * All objects have a non-null Shape, stored in the cell header, which describes
+ * the current layout and set of property keys of the object.
+ *
+ * Each Shape has a pointer to a BaseShape. The BaseShape contains the object's
+ * prototype object, its class, and its realm.
+ *
+ * NOTE: Some operations can change the contents of an object (including class)
+ *       in-place so avoid assuming an object with same pointer has same class
+ *       as before.
+ *       - JSObject::swap()
+ */
+class JSObject
+    : public js::gc::CellWithTenuredGCPointer<js::gc::Cell, js::Shape> {
+ public:
+  // The Shape is stored in the cell header.
+  js::Shape* shape() const { return headerPtr(); }
+
+  // Like shape(), but uses getAtomic to read the header word.
+  js::Shape* shapeMaybeForwarded() const { return headerPtrAtomic(); }
+
+#ifndef JS_64BIT
+  // Ensure fixed slots have 8-byte alignment on 32-bit platforms.
+  uint32_t padding_;
+#endif
+
+ private:
+  friend class js::GCMarker;
+  friend class js::GlobalObject;
+  friend class js::Nursery;
+  friend class js::gc::RelocationOverlay;
+  friend bool js::PreventExtensions(JSContext* cx, JS::HandleObject obj,
+                                    JS::ObjectOpResult& result);
+  friend bool js::SetImmutablePrototype(JSContext* cx, JS::HandleObject obj,
+                                        bool* succeeded);
+
+ public:
+  const JSClass* getClass() const { return shape()->getObjectClass(); }
+  bool hasClass(const JSClass* c) const { return getClass() == c; }
+
+  js::LookupPropertyOp getOpsLookupProperty() const {
+    return getClass()->getOpsLookupProperty();
+  }
+  js::DefinePropertyOp getOpsDefineProperty() const {
+    return getClass()->getOpsDefineProperty();
+  }
+  js::HasPropertyOp getOpsHasProperty() const {
+    return getClass()->getOpsHasProperty();
+  }
+  js::GetPropertyOp getOpsGetProperty() const {
+    return getClass()->getOpsGetProperty();
+  }
+  js::SetPropertyOp getOpsSetProperty() const {
+    return getClass()->getOpsSetProperty();
+  }
+  js::GetOwnPropertyOp getOpsGetOwnPropertyDescriptor() const {
+    return getClass()->getOpsGetOwnPropertyDescriptor();
+  }
+  js::DeletePropertyOp getOpsDeleteProperty() const {
+    return getClass()->getOpsDeleteProperty();
+  }
+  js::GetElementsOp getOpsGetElements() const {
+    return getClass()->getOpsGetElements();
+  }
+  JSFunToStringOp getOpsFunToString() const {
+    return getClass()->getOpsFunToString();
+  }
+
+  JS::Compartment* compartment() const { return shape()->compartment(); }
+  JS::Compartment* maybeCompartment() const { return compartment(); }
+
+  void initShape(js::Shape* shape) {
+    // Note: use Cell::Zone() instead of zone() because zone() relies on the
+    // shape we still have to initialize.
+    MOZ_ASSERT(Cell::zone() == shape->zone());
+    initHeaderPtr(shape);
+  }
+  void setShape(js::Shape* shape) {
+    MOZ_ASSERT(maybeCCWRealm() == shape->realm());
+    setHeaderPtr(shape);
+  }
+
+  static bool setFlag(JSContext* cx, JS::HandleObject obj, js::ObjectFlag flag);
+
+  bool hasFlag(js::ObjectFlag flag) const {
+    return shape()->hasObjectFlag(flag);
+  }
+
+  bool hasAnyFlag(js::ObjectFlags flags) const {
+    return shape()->objectFlags().hasAnyFlag(flags);
+  }
+
+  // Change this object's shape for a prototype mutation.
+  //
+  // Note: the caller must ensure the object has a mutable proto, is extensible,
+  // etc.
+  static bool setProtoUnchecked(JSContext* cx, JS::HandleObject obj,
+                                js::Handle<js::TaggedProto> proto);
+
+  // An object is marked IsUsedAsPrototype if it is (or was) another object's
+  // prototype. Optimization heuristics will make use of this flag.
+  //
+  // This flag is only relevant for static prototypes. Proxy traps can return
+  // objects without this flag set.
+  //
+  // NOTE: it's important to call setIsUsedAsPrototype *after* initializing the
+  // object's properties, because that avoids unnecessary shadowing checks and
+  // reshaping.
+  //
+  // See: ReshapeForProtoMutation, ReshapeForShadowedProp
+  bool isUsedAsPrototype() const {
+    return hasFlag(js::ObjectFlag::IsUsedAsPrototype);
+  }
+  static bool setIsUsedAsPrototype(JSContext* cx, JS::HandleObject obj) {
+    return setFlag(cx, obj, js::ObjectFlag::IsUsedAsPrototype);
+  }
+
+  bool useWatchtowerTestingLog() const {
+    return hasFlag(js::ObjectFlag::UseWatchtowerTestingLog);
+  }
+  static bool setUseWatchtowerTestingLog(JSContext* cx, JS::HandleObject obj) {
+    return setFlag(cx, obj, js::ObjectFlag::UseWatchtowerTestingLog);
+  }
+
+  bool isGenerationCountedGlobal() const {
+    return hasFlag(js::ObjectFlag::GenerationCountedGlobal);
+  }
+  static bool setGenerationCountedGlobal(JSContext* cx, JS::HandleObject obj) {
+    return setFlag(cx, obj, js::ObjectFlag::GenerationCountedGlobal);
+  }
+
+  bool hasFuseProperty() const {
+    return hasFlag(js::ObjectFlag::HasFuseProperty);
+  }
+  static bool setHasFuseProperty(JSContext* cx, JS::HandleObject obj) {
+    return setFlag(cx, obj, js::ObjectFlag::HasFuseProperty);
+  }
+
+  // A "qualified" varobj is the object on which "qualified" variable
+  // declarations (i.e., those defined with "var") are kept.
+  //
+  // Conceptually, when a var binding is defined, it is defined on the
+  // innermost qualified varobj on the scope chain.
+  //
+  // Function scopes (CallObjects) are qualified varobjs, and there can be
+  // no other qualified varobj that is more inner for var bindings in that
+  // function. As such, all references to local var bindings in a function
+  // may be statically bound to the function scope. This is subject to
+  // further optimization. Unaliased bindings inside functions reside
+  // entirely on the frame, not in CallObjects.
+  //
+  // Global scopes are also qualified varobjs. It is possible to statically
+  // know, for a given script, that are no more inner qualified varobjs, so
+  // free variable references can be statically bound to the global.
+  //
+  // Finally, there are non-syntactic qualified varobjs used by embedders
+  // (e.g., Gecko and XPConnect), as they often wish to run scripts under a
+  // scope that captures var bindings.
+  inline bool isQualifiedVarObj() const;
+  static bool setQualifiedVarObj(JSContext* cx, JS::HandleObject obj) {
+    return setFlag(cx, obj, js::ObjectFlag::QualifiedVarObj);
+  }
+
+  // An "unqualified" varobj is the object on which "unqualified"
+  // assignments (i.e., bareword assignments for which the LHS does not
+  // exist on the scope chain) are kept.
+  inline bool isUnqualifiedVarObj() const;
+
+  // Once the "invalidated teleporting" flag is set for an object, it is never
+  // cleared and it may cause the JITs to insert additional guards when
+  // accessing properties on this object. While the flag remains clear, the
+  // shape teleporting optimization can be used to avoid those extra checks.
+  //
+  // The flag is set on the object if either:
+  //
+  // * Its own proto was mutated or it was on the proto chain of an object that
+  //   had its proto mutated.
+  //
+  // * It was on the proto chain of an object that started shadowing a property
+  //   on this object.
+  //
+  // See:
+  // - ReshapeForProtoMutation
+  // - ReshapeForShadowedProp
+  // - ProtoChainSupportsTeleporting
+  inline bool hasInvalidatedTeleporting() const;
+  static bool setInvalidatedTeleporting(JSContext* cx, JS::HandleObject obj) {
+    MOZ_ASSERT(obj->isUsedAsPrototype());
+    MOZ_ASSERT(obj->hasStaticPrototype(),
+               "teleporting as a concept is only applicable to static "
+               "(not dynamically-computed) prototypes");
+    return setFlag(cx, obj, js::ObjectFlag::InvalidatedTeleporting);
+  }
+
+  /*
+   * Whether there may be "interesting symbol" properties on this object. An
+   * interesting symbol is a symbol for which symbol->isInterestingSymbol()
+   * returns true.
+   */
+  MOZ_ALWAYS_INLINE bool maybeHasInterestingSymbolProperty() const;
+
+  inline bool needsProxyGetSetResultValidation() const;
+
+  /* GC support. */
+
+  void traceChildren(JSTracer* trc);
+
+  void fixupAfterMovingGC() {}
+
+  static const JS::TraceKind TraceKind = JS::TraceKind::Object;
+
+  static constexpr size_t thingSize(js::gc::AllocKind kind);
+
+  MOZ_ALWAYS_INLINE JS::Zone* zone() const {
+    MOZ_ASSERT_IF(!isTenured(), nurseryZone() == shape()->zone());
+    return shape()->zone();
+  }
+  MOZ_ALWAYS_INLINE JS::shadow::Zone* shadowZone() const {
+    return JS::shadow::Zone::from(zone());
+  }
+  MOZ_ALWAYS_INLINE JS::Zone* zoneFromAnyThread() const {
+    MOZ_ASSERT_IF(!isTenured(),
+                  nurseryZoneFromAnyThread() == shape()->zoneFromAnyThread());
+    return shape()->zoneFromAnyThread();
+  }
+  MOZ_ALWAYS_INLINE JS::shadow::Zone* shadowZoneFromAnyThread() const {
+    return JS::shadow::Zone::from(zoneFromAnyThread());
+  }
+  static MOZ_ALWAYS_INLINE void postWriteBarrier(void* cellp, JSObject* prev,
+                                                 JSObject* next) {
+    js::gc::PostWriteBarrierImpl<JSObject>(cellp, prev, next);
+  }
+
+  /* Return the allocKind we would use if we were to tenure this object. */
+  js::gc::AllocKind allocKindForTenure(const js::Nursery& nursery) const;
+
+  bool canHaveFixedElements() const;
+
+  size_t tenuredSizeOfThis() const {
+    MOZ_ASSERT(isTenured());
+    return js::gc::Arena::thingSize(asTenured().getAllocKind());
+  }
+
+  void addSizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf,
+                              JS::ClassInfo* info,
+                              JS::RuntimeSizes* runtimeSizes);
+
+  // We can only use addSizeOfExcludingThis on tenured objects: it assumes it
+  // can apply mallocSizeOf to bits and pieces of the object, whereas objects
+  // in the nursery may have those bits and pieces allocated in the nursery
+  // along with them, and are not each their own malloc blocks.
+  size_t sizeOfIncludingThisInNursery() const;
+
+#ifdef DEBUG
+  static void debugCheckNewObject(js::Shape* shape, js::gc::AllocKind allocKind,
+                                  js::gc::Heap heap);
+#else
+  static void debugCheckNewObject(js::Shape* shape, js::gc::AllocKind allocKind,
+                                  js::gc::Heap heap) {}
+#endif
+
+  /*
+   * We permit proxies to dynamically compute their prototype if desired.
+   * (Not all proxies will so desire: in particular, most DOM proxies can
+   * track their prototype with a single, nullable JSObject*.)  If a proxy
+   * so desires, we store (JSObject*)0x1 in the proto field of the object's
+   * group.
+   *
+   * We offer three ways to get an object's prototype:
+   *
+   * 1. obj->staticPrototype() returns the prototype, but it asserts if obj
+   *    is a proxy, and the proxy has opted to dynamically compute its
+   *    prototype using a getPrototype() handler.
+   * 2. obj->taggedProto() returns a TaggedProto, which can be tested to
+   *    check if the proto is an object, nullptr, or lazily computed.
+   * 3. js::GetPrototype(cx, obj, &proto) computes the proto of an object.
+   *    If obj is a proxy with dynamically-computed prototype, this code may
+   *    perform arbitrary behavior (allocation, GC, run JS) while computing
+   *    the proto.
+   */
+
+  js::TaggedProto taggedProto() const { return shape()->proto(); }
+
+  bool uninlinedIsProxyObject() const;
+
+  JSObject* staticPrototype() const {
+    MOZ_ASSERT(hasStaticPrototype());
+    return taggedProto().toObjectOrNull();
+  }
+
+  // Normal objects and a subset of proxies have an uninteresting, static
+  // (albeit perhaps mutable) [[Prototype]].  For such objects the
+  // [[Prototype]] is just a value returned when needed for accesses, or
+  // modified in response to requests.  These objects store the
+  // [[Prototype]] directly within |obj->group()|.
+  bool hasStaticPrototype() const { return !hasDynamicPrototype(); }
+
+  // The remaining proxies have a [[Prototype]] requiring dynamic computation
+  // for every access, going through the proxy handler {get,set}Prototype and
+  // setImmutablePrototype methods.  (Wrappers particularly use this to keep
+  // the wrapper/wrappee [[Prototype]]s consistent.)
+  bool hasDynamicPrototype() const {
+    bool dynamic = taggedProto().isDynamic();
+    MOZ_ASSERT_IF(dynamic, uninlinedIsProxyObject());
+    return dynamic;
+  }
+
+  // True iff this object's [[Prototype]] is immutable.  Must be called only
+  // on objects with a static [[Prototype]]!
+  inline bool staticPrototypeIsImmutable() const;
+
+  /*
+   * Environment chains.
+   *
+   * The environment chain of an object is the link in the search path when
+   * a script does a name lookup on an environment object. For JS internal
+   * environment objects --- Call, LexicalEnvironment, and WithEnvironment
+   * --- the chain is stored in the first fixed slot of the object.  For
+   * other environment objects, the chain goes directly to the global.
+   *
+   * In code which is not marked hasNonSyntacticScope, environment chains
+   * can contain only syntactic environment objects (see
+   * IsSyntacticEnvironment) with a global object at the root as the
+   * environment of the outermost non-function script. In
+   * hasNonSyntacticScope code, the environment of the outermost
+   * non-function script might not be a global object, and can have a mix of
+   * other objects above it before the global object is reached.
+   */
+
+  /*
+   * Get the enclosing environment of an object. When called on a
+   * non-EnvironmentObject, this will just be the global (the name
+   * "enclosing environment" still applies in this situation because
+   * non-EnvironmentObjects can be on the environment chain).
+   */
+  inline JSObject* enclosingEnvironment() const;
+
+  // Cross-compartment wrappers are not associated with a single realm/global,
+  // so these methods assert the object is not a CCW.
+  inline js::GlobalObject& nonCCWGlobal() const;
+
+  JS::Realm* nonCCWRealm() const {
+    MOZ_ASSERT(!js::UninlinedIsCrossCompartmentWrapper(this));
+    return shape()->realm();
+  }
+  bool hasSameRealmAs(JSContext* cx) const;
+
+  // Returns the object's realm even if the object is a CCW (be careful, in
+  // this case the realm is not very meaningful because wrappers are shared by
+  // all realms in the compartment).
+  JS::Realm* maybeCCWRealm() const { return shape()->realm(); }
+
+  /*
+   * ES5 meta-object properties and operations.
+   */
+
+ public:
+  // Indicates whether a non-proxy is extensible.  Don't call on proxies!
+  // This method really shouldn't exist -- but there are a few internal
+  // places that want it (JITs and the like), and it'd be a pain to mark them
+  // all as friends.
+  inline bool nonProxyIsExtensible() const;
+  bool uninlinedNonProxyIsExtensible() const;
+
+ public:
+  /*
+   * Back to generic stuff.
+   */
+  MOZ_ALWAYS_INLINE bool isCallable() const;
+  MOZ_ALWAYS_INLINE bool isConstructor() const;
+  MOZ_ALWAYS_INLINE JSNative callHook() const;
+  MOZ_ALWAYS_INLINE JSNative constructHook() const;
+
+  bool isBackgroundFinalized() const;
+
+  MOZ_ALWAYS_INLINE void finalize(JS::GCContext* gcx);
+
+ public:
+  static bool nonNativeSetProperty(JSContext* cx, js::HandleObject obj,
+                                   js::HandleId id, js::HandleValue v,
+                                   js::HandleValue receiver,
+                                   JS::ObjectOpResult& result);
+  static bool nonNativeSetElement(JSContext* cx, js::HandleObject obj,
+                                  uint32_t index, js::HandleValue v,
+                                  js::HandleValue receiver,
+                                  JS::ObjectOpResult& result);
+
+  static void swap(JSContext* cx, JS::HandleObject a, JS::HandleObject b,
+                   js::AutoEnterOOMUnsafeRegion& oomUnsafe);
+
+  /*
+   * In addition to the generic object interface provided by JSObject,
+   * specific types of objects may provide additional operations. To access,
+   * these addition operations, callers should use the pattern:
+   *
+   *   if (obj.is<XObject>()) {
+   *     XObject& x = obj.as<XObject>();
+   *     x.foo();
+   *   }
+   *
+   * These XObject classes form a hierarchy. For example, for a cloned block
+   * object, the following predicates are true: is<ClonedBlockObject>,
+   * is<NestedScopeObject> and is<ScopeObject>. Each of these has a
+   * respective class that derives and adds operations.
+   *
+   * A class XObject is defined in a vm/XObject{.h, .cpp, -inl.h} file
+   * triplet (along with any class YObject that derives XObject).
+   *
+   * Note that X represents a low-level representation and does not query the
+   * [[Class]] property of object defined by the spec: use |JS::GetBuiltinClass|
+   * for this.
+   */
+
+  template <class T>
+  inline bool is() const {
+    return getClass() == &T::class_;
+  }
+
+  template <class T>
+  T& as() {
+    MOZ_ASSERT(this->is<T>());
+    return *static_cast<T*>(this);
+  }
+
+  template <class T>
+  const T& as() const {
+    MOZ_ASSERT(this->is<T>());
+    return *static_cast<const T*>(this);
+  }
+
+  /*
+   * True if either this or CheckedUnwrap(this) is an object of class T.
+   * (Only two objects are checked, regardless of how many wrappers there
+   * are.)
+   *
+   * /!\ Note: This can be true at one point, but false later for the same
+   * object, thanks to js::NukeCrossCompartmentWrapper and friends.
+   */
+  template <class T>
+  bool canUnwrapAs();
+
+  /*
+   * Unwrap and downcast to class T.
+   *
+   * Precondition: `this->canUnwrapAs<T>()`. Note that it's not enough to
+   * have checked this at some point in the past; if there's any doubt as to
+   * whether js::Nuke* could have been called in the meantime, check again.
+   */
+  template <class T>
+  T& unwrapAs();
+
+  /*
+   * Tries to unwrap and downcast to class T. Returns nullptr if (and only if) a
+   * wrapper with a security policy is involved. Crashes in all builds if the
+   * (possibly unwrapped) object is not of class T (for example, because it's a
+   * dead wrapper).
+   */
+  template <class T>
+  inline T* maybeUnwrapAs();
+
+  /*
+   * Tries to unwrap and downcast to an object with class |clasp|.  Returns
+   * nullptr if (and only if) a wrapper with a security policy is involved.
+   * Crashes in all builds if the (possibly unwrapped) object doesn't have class
+   * |clasp| (for example, because it's a dead wrapper).
+   */
+  inline JSObject* maybeUnwrapAs(const JSClass* clasp);
+
+  /*
+   * Tries to unwrap and downcast to class T. Returns nullptr if a wrapper with
+   * a security policy is involved or if the object does not have class T.
+   */
+  template <class T>
+  T* maybeUnwrapIf();
+
+#if defined(DEBUG) || defined(JS_JITSPEW)
+  void dump() const;
+  void dump(js::GenericPrinter& out) const;
+  void dump(js::JSONPrinter& json) const;
+
+  void dumpFields(js::JSONPrinter& json) const;
+  void dumpStringContent(js::GenericPrinter& out) const;
+#endif
+
+  // Maximum size in bytes of a JSObject.
+#ifdef JS_64BIT
+  static constexpr size_t MAX_BYTE_SIZE =
+      3 * sizeof(void*) + 16 * sizeof(JS::Value);
+#else
+  static constexpr size_t MAX_BYTE_SIZE =
+      4 * sizeof(void*) + 16 * sizeof(JS::Value);
+#endif
+
+ protected:
+  // JIT Accessors.
+  //
+  // To help avoid writing Spectre-unsafe code, we only allow MacroAssembler
+  // to call the method below.
+  friend class js::jit::MacroAssembler;
+
+  static constexpr size_t offsetOfShape() { return offsetOfHeaderPtr(); }
+
+ private:
+  JSObject(const JSObject& other) = delete;
+  void operator=(const JSObject& other) = delete;
+
+ protected:
+  // For the allocator only, to be used with placement new.
+  friend class js::gc::GCRuntime;
+  JSObject() = default;
+};
+
+template <>
+inline bool JSObject::is<JSObject>() const {
+  return true;
+}
+
+template <typename Wrapper>
+template <typename U>
+MOZ_ALWAYS_INLINE JS::Handle<U*> js::RootedOperations<JSObject*, Wrapper>::as()
+    const {
+  const Wrapper& self = *static_cast<const Wrapper*>(this);
+  MOZ_ASSERT(self->template is<U>());
+  return Handle<U*>::fromMarkedLocation(
+      reinterpret_cast<U* const*>(self.address()));
+}
+
+template <typename Wrapper>
+template <class U>
+MOZ_ALWAYS_INLINE JS::Handle<U*> js::HandleOperations<JSObject*, Wrapper>::as()
+    const {
+  const JS::Handle<JSObject*>& self =
+      *static_cast<const JS::Handle<JSObject*>*>(this);
+  MOZ_ASSERT(self->template is<U>());
+  return Handle<U*>::fromMarkedLocation(
+      reinterpret_cast<U* const*>(self.address()));
+}
+
+template <class T>
+bool JSObject::canUnwrapAs() {
+  static_assert(!std::is_convertible_v<T*, js::Wrapper*>,
+                "T can't be a Wrapper type; this function discards wrappers");
+
+  if (is<T>()) {
+    return true;
+  }
+  JSObject* obj = js::CheckedUnwrapStatic(this);
+  return obj && obj->is<T>();
+}
+
+template <class T>
+T& JSObject::unwrapAs() {
+  static_assert(!std::is_convertible_v<T*, js::Wrapper*>,
+                "T can't be a Wrapper type; this function discards wrappers");
+
+  if (is<T>()) {
+    return as<T>();
+  }
+
+  // Since the caller just called canUnwrapAs<T>(), which does a
+  // CheckedUnwrap, this does not need to repeat the security check.
+  JSObject* unwrapped = js::UncheckedUnwrap(this);
+  MOZ_ASSERT(js::CheckedUnwrapStatic(this) == unwrapped,
+             "check that the security check we skipped really is redundant");
+  return unwrapped->as<T>();
+}
+
+template <class T>
+inline T* JSObject::maybeUnwrapAs() {
+  static_assert(!std::is_convertible_v<T*, js::Wrapper*>,
+                "T can't be a Wrapper type; this function discards wrappers");
+
+  if (is<T>()) {
+    return &as<T>();
+  }
+
+  JSObject* unwrapped = js::CheckedUnwrapStatic(this);
+  if (!unwrapped) {
+    return nullptr;
+  }
+
+  if (MOZ_LIKELY(unwrapped->is<T>())) {
+    return &unwrapped->as<T>();
+  }
+
+  MOZ_CRASH("Invalid object. Dead wrapper?");
+}
+
+inline JSObject* JSObject::maybeUnwrapAs(const JSClass* clasp) {
+  if (hasClass(clasp)) {
+    return this;
+  }
+
+  JSObject* unwrapped = js::CheckedUnwrapStatic(this);
+  if (!unwrapped) {
+    return nullptr;
+  }
+
+  if (MOZ_LIKELY(unwrapped->hasClass(clasp))) {
+    return unwrapped;
+  }
+
+  MOZ_CRASH("Invalid object. Dead wrapper?");
+}
+
+template <class T>
+T* JSObject::maybeUnwrapIf() {
+  static_assert(!std::is_convertible_v<T*, js::Wrapper*>,
+                "T can't be a Wrapper type; this function discards wrappers");
+
+  if (is<T>()) {
+    return &as<T>();
+  }
+
+  JSObject* unwrapped = js::CheckedUnwrapStatic(this);
+  return (unwrapped && unwrapped->is<T>()) ? &unwrapped->as<T>() : nullptr;
+}
+
+/*
+ * The only sensible way to compare JSObject with == is by identity. We use
+ * const& instead of * as a syntactic way to assert non-null. This leads to an
+ * abundance of address-of operators to identity. Hence this overload.
+ */
+static MOZ_ALWAYS_INLINE bool operator==(const JSObject& lhs,
+                                         const JSObject& rhs) {
+  return &lhs == &rhs;
+}
+
+static MOZ_ALWAYS_INLINE bool operator!=(const JSObject& lhs,
+                                         const JSObject& rhs) {
+  return &lhs != &rhs;
+}
+
+// Size of the various GC thing allocation sizes used for objects.
+struct JSObject_Slots0 : JSObject {
+  void* data[2];
+};
+struct JSObject_Slots2 : JSObject {
+  void* data[2];
+  js::Value fslots[2];
+};
+struct JSObject_Slots4 : JSObject {
+  void* data[2];
+  js::Value fslots[4];
+};
+struct JSObject_Slots7 : JSObject {
+  // Only used for extended functions which are required to have exactly seven
+  // fixed slots due to JIT assumptions.
+  void* data[2];
+  js::Value fslots[7];
+};
+struct JSObject_Slots8 : JSObject {
+  void* data[2];
+  js::Value fslots[8];
+};
+struct JSObject_Slots12 : JSObject {
+  void* data[2];
+  js::Value fslots[12];
+};
+struct JSObject_Slots16 : JSObject {
+  void* data[2];
+  js::Value fslots[16];
+};
+
+/* static */
+constexpr size_t JSObject::thingSize(js::gc::AllocKind kind) {
+  MOZ_ASSERT(IsObjectAllocKind(kind));
+  constexpr uint8_t objectSizes[] = {
+#define EXPAND_OJBECT_SIZE(_1, _2, _3, sizedType, _4, _5, _6) sizeof(sizedType),
+      FOR_EACH_OBJECT_ALLOCKIND(EXPAND_OJBECT_SIZE)};
+  return objectSizes[size_t(kind)];
+}
+
+namespace js {
+
+// Returns true if object may possibly use JSObject::swap. The JITs may better
+// optimize objects that can never swap (and thus change their type).
+//
+// If ObjectMayBeSwapped is false, it is safe to guard on pointer identity to
+// test immutable features of the object. For example, the target of a
+// JSFunction will not change. Note: the object can still be moved by GC.
+extern bool ObjectMayBeSwapped(const JSObject* obj);
+
+extern bool DefineFunctions(JSContext* cx, HandleObject obj,
+                            const JSFunctionSpec* fs);
+
+/* ES6 draft rev 36 (2015 March 17) 7.1.1 ToPrimitive(vp[, preferredType]) */
+extern bool ToPrimitiveSlow(JSContext* cx, JSType hint, MutableHandleValue vp);
+
+inline bool ToPrimitive(JSContext* cx, MutableHandleValue vp) {
+  if (vp.isPrimitive()) {
+    return true;
+  }
+  return ToPrimitiveSlow(cx, JSTYPE_UNDEFINED, vp);
+}
+
+inline bool ToPrimitive(JSContext* cx, JSType preferredType,
+                        MutableHandleValue vp) {
+  if (vp.isPrimitive()) {
+    return true;
+  }
+  return ToPrimitiveSlow(cx, preferredType, vp);
+}
+
+/*
+ * toString support. (This isn't called GetClassName because there's a macro in
+ * <windows.h> with that name.)
+ */
+MOZ_ALWAYS_INLINE const char* GetObjectClassName(JSContext* cx,
+                                                 HandleObject obj);
+
+/*
+ * Prepare a |this| object to be returned to script. This includes replacing
+ * Windows with their corresponding WindowProxy.
+ *
+ * Helpers are also provided to first extract the |this| from specific
+ * types of environment.
+ */
+JSObject* GetThisObject(JSObject* obj);
+
+JSObject* GetThisObjectOfLexical(JSObject* env);
+
+JSObject* GetThisObjectOfWith(JSObject* env);
+
+} /* namespace js */
+
+namespace js {
+
+// ES6 9.1.15 GetPrototypeFromConstructor.
+extern bool GetPrototypeFromConstructor(JSContext* cx,
+                                        js::HandleObject newTarget,
+                                        JSProtoKey intrinsicDefaultProto,
+                                        js::MutableHandleObject proto);
+
+// https://tc39.github.io/ecma262/#sec-getprototypefromconstructor
+//
+// Determine which [[Prototype]] to use when creating a new object using a
+// builtin constructor.
+//
+// This sets `proto` to `nullptr` to mean "the builtin prototype object for
+// this type in the current realm", the common case.
+//
+// We could set it to `cx->global()->getOrCreatePrototype(protoKey)`, but
+// nullptr gets a fast path in e.g. js::NewObjectWithClassProtoCommon.
+//
+// intrinsicDefaultProto can be JSProto_Null if there's no appropriate
+// JSProtoKey enum; but we then select the wrong prototype object in a
+// multi-realm corner case (see bug 1515167).
+MOZ_ALWAYS_INLINE bool GetPrototypeFromBuiltinConstructor(
+    JSContext* cx, const CallArgs& args, JSProtoKey intrinsicDefaultProto,
+    js::MutableHandleObject proto) {
+  // We can skip the "prototype" lookup in the two common cases:
+  // 1.  Builtin constructor called without `new`, as in `obj = Object();`.
+  // 2.  Builtin constructor called with `new`, as in `obj = new Object();`.
+  //
+  // Cases that can't take the fast path include `new MySubclassOfObject()`,
+  // `new otherGlobal.Object()`, and `Reflect.construct(Object, [], Date)`.
+  if (!args.isConstructing() ||
+      &args.newTarget().toObject() == &args.callee()) {
+    MOZ_ASSERT(args.callee().hasSameRealmAs(cx));
+    proto.set(nullptr);
+    return true;
+  }
+
+  // We're calling this constructor from a derived class, retrieve the
+  // actual prototype from newTarget.
+  RootedObject newTarget(cx, &args.newTarget().toObject());
+  return GetPrototypeFromConstructor(cx, newTarget, intrinsicDefaultProto,
+                                     proto);
+}
+
+/* ES6 draft rev 32 (2015 Feb 2) 6.2.4.5 ToPropertyDescriptor(Obj) */
+bool ToPropertyDescriptor(JSContext* cx, HandleValue descval,
+                          bool checkAccessors,
+                          MutableHandle<JS::PropertyDescriptor> desc);
+
+/*
+ * Throw a TypeError if desc.getter() or setter() is not
+ * callable. This performs exactly the checks omitted by ToPropertyDescriptor
+ * when checkAccessors is false.
+ */
+Result<> CheckPropertyDescriptorAccessors(JSContext* cx,
+                                          Handle<JS::PropertyDescriptor> desc);
+
+void CompletePropertyDescriptor(MutableHandle<JS::PropertyDescriptor> desc);
+
+/*
+ * Read property descriptors from props, as for Object.defineProperties. See
+ * ES5 15.2.3.7 steps 3-5.
+ */
+extern bool ReadPropertyDescriptors(
+    JSContext* cx, HandleObject props, bool checkAccessors,
+    MutableHandleIdVector ids, MutableHandle<PropertyDescriptorVector> descs);
+
+/* Read the name using a dynamic lookup on the scopeChain. */
+extern bool LookupName(JSContext* cx, Handle<PropertyName*> name,
+                       HandleObject scopeChain, MutableHandleObject objp,
+                       MutableHandleObject pobjp, PropertyResult* propp);
+
+extern bool LookupNameNoGC(JSContext* cx, PropertyName* name,
+                           JSObject* scopeChain, JSObject** objp,
+                           NativeObject** pobjp, PropertyResult* propp);
+
+/*
+ * Like LookupName except returns the global object if 'name' is not found in
+ * any preceding scope.
+ *
+ * Additionally, pobjp and propp are not needed by callers so they are not
+ * returned.
+ */
+extern bool LookupNameWithGlobalDefault(JSContext* cx,
+                                        Handle<PropertyName*> name,
+                                        HandleObject scopeChain,
+                                        MutableHandleObject objp);
+
+/*
+ * Like LookupName except returns the unqualified var object if 'name' is not
+ * found in any preceding scope. Normally the unqualified var object is the
+ * global. If the value for the name in the looked-up scope is an
+ * uninitialized lexical, an UninitializedLexicalObject is returned.
+ *
+ * Additionally, pobjp is not needed by callers so it is not returned.
+ */
+extern bool LookupNameUnqualified(JSContext* cx, Handle<PropertyName*> name,
+                                  HandleObject scopeChain,
+                                  MutableHandleObject objp);
+
+}  // namespace js
+
+namespace js {
+
+/*
+ * Family of Pure property lookup functions. The bool return does NOT have the
+ * standard SpiderMonkey semantics. The return value means "can this operation
+ * be performed and produce a valid result without any side effects?". If any of
+ * these return true, then the outparam can be inspected to determine the
+ * result.
+ */
+
+bool LookupPropertyPure(JSContext* cx, JSObject* obj, jsid id,
+                        NativeObject** objp, PropertyResult* propp);
+
+bool LookupOwnPropertyPure(JSContext* cx, JSObject* obj, jsid id,
+                           PropertyResult* propp);
+
+bool GetPropertyPure(JSContext* cx, JSObject* obj, jsid id, Value* vp);
+
+bool GetOwnPropertyPure(JSContext* cx, JSObject* obj, jsid id, Value* vp,
+                        bool* found);
+
+bool GetGetterPure(JSContext* cx, JSObject* obj, jsid id, JSFunction** fp);
+
+bool GetOwnGetterPure(JSContext* cx, JSObject* obj, jsid id, JSFunction** fp);
+
+bool GetOwnNativeGetterPure(JSContext* cx, JSObject* obj, jsid id,
+                            JSNative* native);
+
+bool HasOwnDataPropertyPure(JSContext* cx, JSObject* obj, jsid id,
+                            bool* result);
+
+/*
+ * Like JS::FromPropertyDescriptor, but ignore desc.object() and always set vp
+ * to an object on success.
+ *
+ * Use JS::FromPropertyDescriptor for getOwnPropertyDescriptor, since
+ * desc.object() is used to indicate whether a result was found or not.  Use
+ * this instead for defineProperty: it would be senseless to define a "missing"
+ * property.
+ */
+extern bool FromPropertyDescriptorToObject(JSContext* cx,
+                                           Handle<JS::PropertyDescriptor> desc,
+                                           MutableHandleValue vp);
+
+// obj is a JSObject*, but we root it immediately up front. We do it
+// that way because we need a Rooted temporary in this method anyway.
+extern bool IsPrototypeOf(JSContext* cx, HandleObject protoObj, JSObject* obj,
+                          bool* result);
+
+/* Wrap boolean, number or string as Boolean, Number or String object. */
+extern JSObject* PrimitiveToObject(JSContext* cx, const Value& v);
+extern JSProtoKey PrimitiveToProtoKey(JSContext* cx, const Value& v);
+
+} /* namespace js */
+
+namespace js {
+
+JSObject* ToObjectSlowForPropertyAccess(JSContext* cx, JS::HandleValue val,
+                                        int valIndex, HandleId key);
+JSObject* ToObjectSlowForPropertyAccess(JSContext* cx, JS::HandleValue val,
+                                        int valIndex,
+                                        Handle<PropertyName*> key);
+JSObject* ToObjectSlowForPropertyAccess(JSContext* cx, JS::HandleValue val,
+                                        int valIndex, HandleValue keyValue);
+
+MOZ_ALWAYS_INLINE JSObject* ToObjectFromStackForPropertyAccess(JSContext* cx,
+                                                               HandleValue vp,
+                                                               int vpIndex,
+                                                               HandleId key) {
+  if (vp.isObject()) {
+    return &vp.toObject();
+  }
+  return js::ToObjectSlowForPropertyAccess(cx, vp, vpIndex, key);
+}
+MOZ_ALWAYS_INLINE JSObject* ToObjectFromStackForPropertyAccess(
+    JSContext* cx, HandleValue vp, int vpIndex, Handle<PropertyName*> key) {
+  if (vp.isObject()) {
+    return &vp.toObject();
+  }
+  return js::ToObjectSlowForPropertyAccess(cx, vp, vpIndex, key);
+}
+MOZ_ALWAYS_INLINE JSObject* ToObjectFromStackForPropertyAccess(
+    JSContext* cx, HandleValue vp, int vpIndex, HandleValue key) {
+  if (vp.isObject()) {
+    return &vp.toObject();
+  }
+  return js::ToObjectSlowForPropertyAccess(cx, vp, vpIndex, key);
+}
+
+/*
+ * Report a TypeError: "so-and-so is not an object".
+ * Using NotNullObject is usually less code.
+ */
+extern void ReportNotObject(JSContext* cx, const Value& v);
+
+inline JSObject* RequireObject(JSContext* cx, HandleValue v) {
+  if (v.isObject()) {
+    return &v.toObject();
+  }
+  ReportNotObject(cx, v);
+  return nullptr;
+}
+
+/*
+ * Report a TypeError: "SOMETHING must be an object, got VALUE".
+ * Using NotNullObject is usually less code.
+ *
+ * By default this function will attempt to report the expression which computed
+ * the value which given as argument. This can be disabled by using
+ * JSDVG_IGNORE_STACK.
+ */
+extern void ReportNotObject(JSContext* cx, JSErrNum err, int spindex,
+                            HandleValue v);
+
+inline JSObject* RequireObject(JSContext* cx, JSErrNum err, int spindex,
+                               HandleValue v) {
+  if (v.isObject()) {
+    return &v.toObject();
+  }
+  ReportNotObject(cx, err, spindex, v);
+  return nullptr;
+}
+
+extern void ReportNotObject(JSContext* cx, JSErrNum err, HandleValue v);
+
+inline JSObject* RequireObject(JSContext* cx, JSErrNum err, HandleValue v) {
+  if (v.isObject()) {
+    return &v.toObject();
+  }
+  ReportNotObject(cx, err, v);
+  return nullptr;
+}
+
+/*
+ * Report a TypeError: "N-th argument of FUN must be an object, got VALUE".
+ * Using NotNullObjectArg is usually less code.
+ */
+extern void ReportNotObjectArg(JSContext* cx, const char* nth, const char* fun,
+                               HandleValue v);
+
+inline JSObject* RequireObjectArg(JSContext* cx, const char* nth,
+                                  const char* fun, HandleValue v) {
+  if (v.isObject()) {
+    return &v.toObject();
+  }
+  ReportNotObjectArg(cx, nth, fun, v);
+  return nullptr;
+}
+
+extern bool GetFirstArgumentAsObject(JSContext* cx, const CallArgs& args,
+                                     const char* method,
+                                     MutableHandleObject objp);
+
+/* Helper for throwing, always returns false. */
+extern bool Throw(JSContext* cx, HandleId id, unsigned errorNumber,
+                  const char* details = nullptr);
+
+/*
+ * ES6 rev 29 (6 Dec 2014) 7.3.13. Mark obj as non-extensible, and adjust each
+ * of obj's own properties' attributes appropriately: each property becomes
+ * non-configurable, and if level == Frozen, data properties become
+ * non-writable as well.
+ */
+extern bool SetIntegrityLevel(JSContext* cx, HandleObject obj,
+                              IntegrityLevel level);
+
+inline bool FreezeObject(JSContext* cx, HandleObject obj) {
+  return SetIntegrityLevel(cx, obj, IntegrityLevel::Frozen);
+}
+
+/*
+ * ES6 rev 29 (6 Dec 2014) 7.3.14. Code shared by Object.isSealed and
+ * Object.isFrozen.
+ */
+extern bool TestIntegrityLevel(JSContext* cx, HandleObject obj,
+                               IntegrityLevel level, bool* resultp);
+
+[[nodiscard]] extern JSObject* SpeciesConstructor(
+    JSContext* cx, HandleObject obj, HandleObject defaultCtor,
+    bool (*isDefaultSpecies)(JSContext*, JSFunction*));
+
+[[nodiscard]] extern JSObject* SpeciesConstructor(
+    JSContext* cx, HandleObject obj, JSProtoKey ctorKey,
+    bool (*isDefaultSpecies)(JSContext*, JSFunction*));
+
+extern bool GetObjectFromIncumbentGlobal(JSContext* cx,
+                                         MutableHandleObject obj);
+
+#ifdef DEBUG
+inline bool IsObjectValueInCompartment(const Value& v, JS::Compartment* comp) {
+  if (!v.isObject()) {
+    return true;
+  }
+  return v.toObject().compartment() == comp;
+}
+#endif
+
+/*
+ * A generic trace hook that calls the object's 'trace' method.
+ *
+ * If you are introducing a new JSObject subclass, MyObject, that needs a custom
+ * JSClassOps::trace function, it's often helpful to write `trace` as a
+ * non-static member function, since `this` will the correct type. In this case,
+ * you can use `CallTraceMethod<MyObject>` as your JSClassOps::trace value.
+ */
+template <typename ObjectSubclass>
+void CallTraceMethod(JSTracer* trc, JSObject* obj) {
+  obj->as<ObjectSubclass>().trace(trc);
+}
+
+#ifdef JS_HAS_CTYPES
+
+namespace ctypes {
+
+extern size_t SizeOfDataIfCDataObject(mozilla::MallocSizeOf mallocSizeOf,
+                                      JSObject* obj);
+
+}  // namespace ctypes
+
+#endif
+
+#ifdef DEBUG
+void AssertJSClassInvariants(const JSClass* clasp);
+#endif
+
+} /* namespace js */
+
+#endif /* vm_JSObject_h */