Adding upstream version 115.7.0esr.upstream/115.7.0esrupstream

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

1 files changed, 3649 insertions, 0 deletions

diff --git a/js/src/vm/JSObject.cpp b/js/src/vm/JSObject.cpp
new file mode 100644
index 0000000000..292971cf3e
--- /dev/null
+++ b/js/src/vm/JSObject.cpp
@@ -0,0 +1,3649 @@
+/* -*- 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/. */
+
+/*
+ * JS object implementation.
+ */
+
+#include "vm/JSObject-inl.h"
+
+#include "mozilla/MemoryReporting.h"
+
+#include <string.h>
+
+#include "jsapi.h"
+#include "jsexn.h"
+#include "jsfriendapi.h"
+#include "jsnum.h"
+#include "jstypes.h"
+
+#include "builtin/BigInt.h"
+#include "builtin/MapObject.h"
+#include "builtin/Object.h"
+#include "builtin/String.h"
+#include "builtin/Symbol.h"
+#include "builtin/WeakSetObject.h"
+#include "gc/AllocKind.h"
+#include "gc/GC.h"
+#include "js/CharacterEncoding.h"
+#include "js/friend/DumpFunctions.h"  // js::DumpObject
+#include "js/friend/ErrorMessages.h"  // JSErrNum, js::GetErrorMessage, JSMSG_*
+#include "js/friend/WindowProxy.h"    // js::IsWindow, js::ToWindowProxyIfWindow
+#include "js/MemoryMetrics.h"
+#include "js/PropertyDescriptor.h"  // JS::FromPropertyDescriptor
+#include "js/PropertySpec.h"        // JSPropertySpec
+#include "js/Proxy.h"
+#include "js/Result.h"
+#include "js/UbiNode.h"
+#include "js/Wrapper.h"
+#include "proxy/DeadObjectProxy.h"
+#include "util/Memory.h"
+#include "util/Text.h"
+#include "util/WindowsWrapper.h"
+#include "vm/ArgumentsObject.h"
+#include "vm/BytecodeUtil.h"
+#include "vm/Compartment.h"
+#include "vm/DateObject.h"
+#include "vm/Interpreter.h"
+#include "vm/Iteration.h"
+#include "vm/JSAtom.h"
+#include "vm/JSContext.h"
+#include "vm/JSFunction.h"
+#include "vm/JSScript.h"
+#include "vm/ProxyObject.h"
+#include "vm/RegExpObject.h"
+#include "vm/Shape.h"
+#include "vm/TypedArrayObject.h"
+#include "vm/Watchtower.h"
+#include "vm/WellKnownAtom.h"  // js_*_str
+#include "vm/WrapperObject.h"
+#ifdef ENABLE_RECORD_TUPLE
+#  include "builtin/RecordObject.h"
+#  include "builtin/TupleObject.h"
+#  include "vm/RecordType.h"
+#  include "vm/TupleType.h"
+#endif
+#include "wasm/WasmGcObject.h"
+
+#include "gc/StableCellHasher-inl.h"
+#include "vm/BooleanObject-inl.h"
+#include "vm/EnvironmentObject-inl.h"
+#include "vm/Interpreter-inl.h"
+#include "vm/JSAtom-inl.h"
+#include "vm/JSContext-inl.h"
+#include "vm/NativeObject-inl.h"
+#include "vm/NumberObject-inl.h"
+#include "vm/ObjectFlags-inl.h"
+#include "vm/Realm-inl.h"
+#include "vm/StringObject-inl.h"
+#include "vm/TypedArrayObject-inl.h"
+
+using namespace js;
+
+using mozilla::Maybe;
+
+void js::ReportNotObject(JSContext* cx, JSErrNum err, int spindex,
+                         HandleValue v) {
+  MOZ_ASSERT(!v.isObject());
+  ReportValueError(cx, err, spindex, v, nullptr);
+}
+
+void js::ReportNotObject(JSContext* cx, JSErrNum err, HandleValue v) {
+  ReportNotObject(cx, err, JSDVG_SEARCH_STACK, v);
+}
+
+void js::ReportNotObject(JSContext* cx, const Value& v) {
+  RootedValue value(cx, v);
+  ReportNotObject(cx, JSMSG_OBJECT_REQUIRED, value);
+}
+
+void js::ReportNotObjectArg(JSContext* cx, const char* nth, const char* fun,
+                            HandleValue v) {
+  MOZ_ASSERT(!v.isObject());
+
+  UniqueChars bytes;
+  if (const char* chars = ValueToSourceForError(cx, v, bytes)) {
+    JS_ReportErrorNumberLatin1(cx, GetErrorMessage, nullptr,
+                               JSMSG_OBJECT_REQUIRED_ARG, nth, fun, chars);
+  }
+}
+
+JS_PUBLIC_API const char* JS::InformalValueTypeName(const Value& v) {
+  switch (v.type()) {
+    case ValueType::Double:
+    case ValueType::Int32:
+      return "number";
+    case ValueType::Boolean:
+      return "boolean";
+    case ValueType::Undefined:
+      return "undefined";
+    case ValueType::Null:
+      return "null";
+    case ValueType::String:
+      return "string";
+    case ValueType::Symbol:
+      return "symbol";
+    case ValueType::BigInt:
+      return "bigint";
+    case ValueType::Object:
+#ifdef ENABLE_RECORD_TUPLE
+    case ValueType::ExtendedPrimitive:
+#endif
+      return v.getObjectPayload().getClass()->name;
+    case ValueType::Magic:
+      return "magic";
+    case ValueType::PrivateGCThing:
+      break;
+  }
+
+  MOZ_CRASH("unexpected type");
+}
+
+// ES6 draft rev37 6.2.4.4 FromPropertyDescriptor
+JS_PUBLIC_API bool JS::FromPropertyDescriptor(
+    JSContext* cx, Handle<Maybe<PropertyDescriptor>> desc_,
+    MutableHandleValue vp) {
+  AssertHeapIsIdle();
+  CHECK_THREAD(cx);
+  cx->check(desc_);
+
+  // Step 1.
+  if (desc_.isNothing()) {
+    vp.setUndefined();
+    return true;
+  }
+
+  Rooted<PropertyDescriptor> desc(cx, *desc_);
+  return FromPropertyDescriptorToObject(cx, desc, vp);
+}
+
+bool js::FromPropertyDescriptorToObject(JSContext* cx,
+                                        Handle<PropertyDescriptor> desc,
+                                        MutableHandleValue vp) {
+  // Step 2-3.
+  RootedObject obj(cx, NewPlainObject(cx));
+  if (!obj) {
+    return false;
+  }
+
+  const JSAtomState& names = cx->names();
+
+  // Step 4.
+  if (desc.hasValue()) {
+    if (!DefineDataProperty(cx, obj, names.value, desc.value())) {
+      return false;
+    }
+  }
+
+  // Step 5.
+  RootedValue v(cx);
+  if (desc.hasWritable()) {
+    v.setBoolean(desc.writable());
+    if (!DefineDataProperty(cx, obj, names.writable, v)) {
+      return false;
+    }
+  }
+
+  // Step 6.
+  if (desc.hasGetter()) {
+    if (JSObject* get = desc.getter()) {
+      v.setObject(*get);
+    } else {
+      v.setUndefined();
+    }
+    if (!DefineDataProperty(cx, obj, names.get, v)) {
+      return false;
+    }
+  }
+
+  // Step 7.
+  if (desc.hasSetter()) {
+    if (JSObject* set = desc.setter()) {
+      v.setObject(*set);
+    } else {
+      v.setUndefined();
+    }
+    if (!DefineDataProperty(cx, obj, names.set, v)) {
+      return false;
+    }
+  }
+
+  // Step 8.
+  if (desc.hasEnumerable()) {
+    v.setBoolean(desc.enumerable());
+    if (!DefineDataProperty(cx, obj, names.enumerable, v)) {
+      return false;
+    }
+  }
+
+  // Step 9.
+  if (desc.hasConfigurable()) {
+    v.setBoolean(desc.configurable());
+    if (!DefineDataProperty(cx, obj, names.configurable, v)) {
+      return false;
+    }
+  }
+
+  vp.setObject(*obj);
+  return true;
+}
+
+bool js::GetFirstArgumentAsObject(JSContext* cx, const CallArgs& args,
+                                  const char* method,
+                                  MutableHandleObject objp) {
+  if (!args.requireAtLeast(cx, method, 1)) {
+    return false;
+  }
+
+  HandleValue v = args[0];
+  if (!v.isObject()) {
+    UniqueChars bytes =
+        DecompileValueGenerator(cx, JSDVG_SEARCH_STACK, v, nullptr);
+    if (!bytes) {
+      return false;
+    }
+    JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
+                             JSMSG_UNEXPECTED_TYPE, bytes.get(),
+                             "not an object");
+    return false;
+  }
+
+  objp.set(&v.toObject());
+  return true;
+}
+
+static bool GetPropertyIfPresent(JSContext* cx, HandleObject obj, HandleId id,
+                                 MutableHandleValue vp, bool* foundp) {
+  if (!HasProperty(cx, obj, id, foundp)) {
+    return false;
+  }
+  if (!*foundp) {
+    vp.setUndefined();
+    return true;
+  }
+
+  return GetProperty(cx, obj, obj, id, vp);
+}
+
+bool js::Throw(JSContext* cx, HandleId id, unsigned errorNumber,
+               const char* details) {
+  MOZ_ASSERT(js_ErrorFormatString[errorNumber].argCount == (details ? 2 : 1));
+  MOZ_ASSERT_IF(details, JS::StringIsASCII(details));
+
+  UniqueChars bytes =
+      IdToPrintableUTF8(cx, id, IdToPrintableBehavior::IdIsPropertyKey);
+  if (!bytes) {
+    return false;
+  }
+
+  if (details) {
+    JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr, errorNumber,
+                             bytes.get(), details);
+  } else {
+    JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr, errorNumber,
+                             bytes.get());
+  }
+
+  return false;
+}
+
+/*** PropertyDescriptor operations and DefineProperties *********************/
+
+#ifndef ENABLE_DECORATORS
+// These are defined by CommonPropertyNames.h and WellKnownAtom.{cpp,h}
+// when decorators are enabled.
+static const char js_getter_str[] = "getter";
+static const char js_setter_str[] = "setter";
+#endif
+
+static Result<> CheckCallable(JSContext* cx, JSObject* obj,
+                              const char* fieldName) {
+  if (obj && !obj->isCallable()) {
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                              JSMSG_BAD_GET_SET_FIELD, fieldName);
+    return cx->alreadyReportedError();
+  }
+  return Ok();
+}
+
+// 6.2.5.5 ToPropertyDescriptor(Obj)
+bool js::ToPropertyDescriptor(JSContext* cx, HandleValue descval,
+                              bool checkAccessors,
+                              MutableHandle<PropertyDescriptor> desc_) {
+  // Step 1.
+  RootedObject obj(cx,
+                   RequireObject(cx, JSMSG_OBJECT_REQUIRED_PROP_DESC, descval));
+  if (!obj) {
+    return false;
+  }
+
+  // Step 2.
+  Rooted<PropertyDescriptor> desc(cx, PropertyDescriptor::Empty());
+
+  RootedId id(cx);
+  RootedValue v(cx);
+
+  // Steps 3-4.
+  id = NameToId(cx->names().enumerable);
+  bool hasEnumerable = false;
+  if (!GetPropertyIfPresent(cx, obj, id, &v, &hasEnumerable)) {
+    return false;
+  }
+  if (hasEnumerable) {
+    desc.setEnumerable(ToBoolean(v));
+  }
+
+  // Steps 5-6.
+  id = NameToId(cx->names().configurable);
+  bool hasConfigurable = false;
+  if (!GetPropertyIfPresent(cx, obj, id, &v, &hasConfigurable)) {
+    return false;
+  }
+  if (hasConfigurable) {
+    desc.setConfigurable(ToBoolean(v));
+  }
+
+  // Steps 7-8.
+  id = NameToId(cx->names().value);
+  bool hasValue = false;
+  if (!GetPropertyIfPresent(cx, obj, id, &v, &hasValue)) {
+    return false;
+  }
+  if (hasValue) {
+    desc.setValue(v);
+  }
+
+  // Steps 9-10.
+  id = NameToId(cx->names().writable);
+  bool hasWritable = false;
+  if (!GetPropertyIfPresent(cx, obj, id, &v, &hasWritable)) {
+    return false;
+  }
+  if (hasWritable) {
+    desc.setWritable(ToBoolean(v));
+  }
+
+  // Steps 11-12.
+  id = NameToId(cx->names().get);
+  bool hasGet = false;
+  if (!GetPropertyIfPresent(cx, obj, id, &v, &hasGet)) {
+    return false;
+  }
+  RootedObject getter(cx);
+  if (hasGet) {
+    if (v.isObject()) {
+      if (checkAccessors) {
+        JS_TRY_OR_RETURN_FALSE(cx,
+                               CheckCallable(cx, &v.toObject(), js_getter_str));
+      }
+      getter = &v.toObject();
+    } else if (v.isUndefined()) {
+      getter = nullptr;
+    } else {
+      JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                                JSMSG_BAD_GET_SET_FIELD, js_getter_str);
+      return false;
+    }
+  }
+
+  // Steps 13-14.
+  id = NameToId(cx->names().set);
+  bool hasSet = false;
+  if (!GetPropertyIfPresent(cx, obj, id, &v, &hasSet)) {
+    return false;
+  }
+  RootedObject setter(cx);
+  if (hasSet) {
+    if (v.isObject()) {
+      if (checkAccessors) {
+        JS_TRY_OR_RETURN_FALSE(cx,
+                               CheckCallable(cx, &v.toObject(), js_setter_str));
+      }
+      setter = &v.toObject();
+    } else if (v.isUndefined()) {
+      setter = nullptr;
+    } else {
+      JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                                JSMSG_BAD_GET_SET_FIELD, js_setter_str);
+      return false;
+    }
+  }
+
+  // Step 15.
+  if (hasGet || hasSet) {
+    if (hasValue || hasWritable) {
+      JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                                JSMSG_INVALID_DESCRIPTOR);
+      return false;
+    }
+
+    // We delay setGetter/setSetter after the previous check,
+    // because otherwise we would assert.
+    if (hasGet) {
+      desc.setGetter(getter);
+    }
+    if (hasSet) {
+      desc.setSetter(setter);
+    }
+  }
+
+  desc.assertValid();
+  desc_.set(desc);
+  return true;
+}
+
+Result<> js::CheckPropertyDescriptorAccessors(JSContext* cx,
+                                              Handle<PropertyDescriptor> desc) {
+  if (desc.hasGetter()) {
+    MOZ_TRY(CheckCallable(cx, desc.getter(), js_getter_str));
+  }
+
+  if (desc.hasSetter()) {
+    MOZ_TRY(CheckCallable(cx, desc.setter(), js_setter_str));
+  }
+
+  return Ok();
+}
+
+// 6.2.5.6 CompletePropertyDescriptor(Desc)
+void js::CompletePropertyDescriptor(MutableHandle<PropertyDescriptor> desc) {
+  // Step 1.
+  desc.assertValid();
+
+  // Step 2.
+  // Let like be the Record { [[Value]]: undefined, [[Writable]]: false,
+  //                          [[Get]]: undefined, [[Set]]: undefined,
+  //                          [[Enumerable]]: false, [[Configurable]]: false }.
+
+  // Step 3.
+  if (desc.isGenericDescriptor() || desc.isDataDescriptor()) {
+    // Step 3.a.
+    if (!desc.hasValue()) {
+      desc.setValue(UndefinedHandleValue);
+    }
+    // Step 3.b.
+    if (!desc.hasWritable()) {
+      desc.setWritable(false);
+    }
+  } else {
+    // Step 4.a.
+    if (!desc.hasGetter()) {
+      desc.setGetter(nullptr);
+    }
+    // Step 4.b.
+    if (!desc.hasSetter()) {
+      desc.setSetter(nullptr);
+    }
+  }
+
+  // Step 5.
+  if (!desc.hasEnumerable()) {
+    desc.setEnumerable(false);
+  }
+
+  // Step 6.
+  if (!desc.hasConfigurable()) {
+    desc.setConfigurable(false);
+  }
+
+  desc.assertComplete();
+}
+
+bool js::ReadPropertyDescriptors(
+    JSContext* cx, HandleObject props, bool checkAccessors,
+    MutableHandleIdVector ids, MutableHandle<PropertyDescriptorVector> descs) {
+  if (!GetPropertyKeys(cx, props, JSITER_OWNONLY | JSITER_SYMBOLS, ids)) {
+    return false;
+  }
+
+  RootedId id(cx);
+  for (size_t i = 0, len = ids.length(); i < len; i++) {
+    id = ids[i];
+    Rooted<PropertyDescriptor> desc(cx);
+    RootedValue v(cx);
+    if (!GetProperty(cx, props, props, id, &v) ||
+        !ToPropertyDescriptor(cx, v, checkAccessors, &desc) ||
+        !descs.append(desc)) {
+      return false;
+    }
+  }
+  return true;
+}
+
+/*** Seal and freeze ********************************************************/
+
+/* ES6 draft rev 29 (6 Dec 2014) 7.3.13. */
+bool js::SetIntegrityLevel(JSContext* cx, HandleObject obj,
+                           IntegrityLevel level) {
+  cx->check(obj);
+
+  // Steps 3-5. (Steps 1-2 are redundant assertions.)
+  if (!PreventExtensions(cx, obj)) {
+    return false;
+  }
+
+  // Steps 6-9, loosely interpreted.
+  if (obj->is<NativeObject>() && !obj->is<TypedArrayObject>() &&
+      !obj->is<MappedArgumentsObject>()) {
+    Handle<NativeObject*> nobj = obj.as<NativeObject>();
+
+    // Use a fast path to seal/freeze properties. This has the benefit of
+    // creating shared property maps if possible, whereas the slower/generic
+    // implementation below ends up converting non-empty objects to dictionary
+    // mode.
+    if (nobj->shape()->propMapLength() > 0) {
+      if (!NativeObject::freezeOrSealProperties(cx, nobj, level)) {
+        return false;
+      }
+    }
+
+    // Ordinarily ArraySetLength handles this, but we're going behind its back
+    // right now, so we must do this manually.
+    if (level == IntegrityLevel::Frozen && obj->is<ArrayObject>()) {
+      obj->as<ArrayObject>().setNonWritableLength(cx);
+    }
+  } else {
+    // Steps 6-7.
+    RootedIdVector keys(cx);
+    if (!GetPropertyKeys(
+            cx, obj, JSITER_HIDDEN | JSITER_OWNONLY | JSITER_SYMBOLS, &keys)) {
+      return false;
+    }
+
+    RootedId id(cx);
+    Rooted<PropertyDescriptor> desc(cx, PropertyDescriptor::Empty());
+
+    // 8.a/9.a. The two different loops are merged here.
+    for (size_t i = 0; i < keys.length(); i++) {
+      id = keys[i];
+
+      if (level == IntegrityLevel::Sealed) {
+        // 8.a.i.
+        desc.setConfigurable(false);
+      } else {
+        // 9.a.i-ii.
+        Rooted<Maybe<PropertyDescriptor>> currentDesc(cx);
+        if (!GetOwnPropertyDescriptor(cx, obj, id, &currentDesc)) {
+          return false;
+        }
+
+        // 9.a.iii.
+        if (currentDesc.isNothing()) {
+          continue;
+        }
+
+        // 9.a.iii.1-2
+        desc = PropertyDescriptor::Empty();
+        if (currentDesc->isAccessorDescriptor()) {
+          desc.setConfigurable(false);
+        } else {
+          desc.setConfigurable(false);
+          desc.setWritable(false);
+        }
+      }
+
+      // 8.a.i-ii. / 9.a.iii.3-4
+      if (!DefineProperty(cx, obj, id, desc)) {
+        return false;
+      }
+    }
+  }
+
+  // Finally, freeze or seal the dense elements.
+  if (obj->is<NativeObject>()) {
+    if (!ObjectElements::FreezeOrSeal(cx, obj.as<NativeObject>(), level)) {
+      return false;
+    }
+  }
+
+  return true;
+}
+
+static bool ResolveLazyProperties(JSContext* cx, Handle<NativeObject*> obj) {
+  const JSClass* clasp = obj->getClass();
+  if (JSEnumerateOp enumerate = clasp->getEnumerate()) {
+    if (!enumerate(cx, obj)) {
+      return false;
+    }
+  }
+  if (clasp->getNewEnumerate() && clasp->getResolve()) {
+    RootedIdVector properties(cx);
+    if (!clasp->getNewEnumerate()(cx, obj, &properties,
+                                  /* enumerableOnly = */ false)) {
+      return false;
+    }
+
+    RootedId id(cx);
+    for (size_t i = 0; i < properties.length(); i++) {
+      id = properties[i];
+      bool found;
+      if (!HasOwnProperty(cx, obj, id, &found)) {
+        return false;
+      }
+    }
+  }
+  return true;
+}
+
+// ES6 draft rev33 (12 Feb 2015) 7.3.15
+bool js::TestIntegrityLevel(JSContext* cx, HandleObject obj,
+                            IntegrityLevel level, bool* result) {
+  // Steps 3-6. (Steps 1-2 are redundant assertions.)
+  bool status;
+  if (!IsExtensible(cx, obj, &status)) {
+    return false;
+  }
+  if (status) {
+    *result = false;
+    return true;
+  }
+
+  // Fast path for native objects.
+  if (obj->is<NativeObject>()) {
+    Handle<NativeObject*> nobj = obj.as<NativeObject>();
+
+    // Force lazy properties to be resolved.
+    if (!ResolveLazyProperties(cx, nobj)) {
+      return false;
+    }
+
+    // Typed array elements are configurable, writable properties, so if any
+    // elements are present, the typed array can neither be sealed nor frozen.
+    if (nobj->is<TypedArrayObject>() &&
+        nobj->as<TypedArrayObject>().length() > 0) {
+      *result = false;
+      return true;
+    }
+
+    bool hasDenseElements = false;
+    for (size_t i = 0; i < nobj->getDenseInitializedLength(); i++) {
+      if (nobj->containsDenseElement(i)) {
+        hasDenseElements = true;
+        break;
+      }
+    }
+
+    if (hasDenseElements) {
+      // Unless the sealed flag is set, dense elements are configurable.
+      if (!nobj->denseElementsAreSealed()) {
+        *result = false;
+        return true;
+      }
+
+      // Unless the frozen flag is set, dense elements are writable.
+      if (level == IntegrityLevel::Frozen && !nobj->denseElementsAreFrozen()) {
+        *result = false;
+        return true;
+      }
+    }
+
+    // Steps 7-9.
+    for (ShapePropertyIter<NoGC> iter(nobj->shape()); !iter.done(); iter++) {
+      // Steps 9.c.i-ii.
+      if (iter->configurable() ||
+          (level == IntegrityLevel::Frozen && iter->isDataDescriptor() &&
+           iter->writable())) {
+        // Private fields on objects don't participate in the frozen state, and
+        // so should be elided from checking for frozen state.
+        if (iter->key().isPrivateName()) {
+          continue;
+        }
+
+        *result = false;
+        return true;
+      }
+    }
+  } else {
+    // Steps 7-8.
+    RootedIdVector props(cx);
+    if (!GetPropertyKeys(
+            cx, obj, JSITER_HIDDEN | JSITER_OWNONLY | JSITER_SYMBOLS, &props)) {
+      return false;
+    }
+
+    // Step 9.
+    RootedId id(cx);
+    Rooted<Maybe<PropertyDescriptor>> desc(cx);
+    for (size_t i = 0, len = props.length(); i < len; i++) {
+      id = props[i];
+
+      // Steps 9.a-b.
+      if (!GetOwnPropertyDescriptor(cx, obj, id, &desc)) {
+        return false;
+      }
+
+      // Step 9.c.
+      if (desc.isNothing()) {
+        continue;
+      }
+
+      // Steps 9.c.i-ii.
+      if (desc->configurable() ||
+          (level == IntegrityLevel::Frozen && desc->isDataDescriptor() &&
+           desc->writable())) {
+        // Since we don't request JSITER_PRIVATE in GetPropertyKeys above, we
+        // should never see a private name here.
+        MOZ_ASSERT(!id.isPrivateName());
+        *result = false;
+        return true;
+      }
+    }
+  }
+
+  // Step 10.
+  *result = true;
+  return true;
+}
+
+/* * */
+
+static MOZ_ALWAYS_INLINE NativeObject* NewObject(JSContext* cx,
+                                                 const JSClass* clasp,
+                                                 Handle<TaggedProto> proto,
+                                                 gc::AllocKind kind,
+                                                 NewObjectKind newKind) {
+  MOZ_ASSERT(clasp->isNativeObject());
+
+  // Some classes have specialized allocation functions and shouldn't end up
+  // here.
+  MOZ_ASSERT(clasp != &ArrayObject::class_);
+  MOZ_ASSERT(clasp != &PlainObject::class_);
+  MOZ_ASSERT(!clasp->isJSFunction());
+
+  // Computing nfixed based on the AllocKind isn't right for objects which can
+  // store fixed data inline (TypedArrays and ArrayBuffers) so for simplicity
+  // and performance reasons we don't support such objects here.
+  MOZ_ASSERT(!ClassCanHaveFixedData(clasp));
+  size_t nfixed = GetGCKindSlots(kind);
+
+  if (CanChangeToBackgroundAllocKind(kind, clasp)) {
+    kind = ForegroundToBackgroundAllocKind(kind);
+  }
+
+  Rooted<SharedShape*> shape(
+      cx, SharedShape::getInitialShape(cx, clasp, cx->realm(), proto, nfixed,
+                                       ObjectFlags()));
+  if (!shape) {
+    return nullptr;
+  }
+
+  gc::Heap heap = GetInitialHeap(newKind, clasp);
+  NativeObject* obj = NativeObject::create(cx, kind, heap, shape);
+  if (!obj) {
+    return nullptr;
+  }
+
+  probes::CreateObject(cx, obj);
+  return obj;
+}
+
+NativeObject* js::NewObjectWithGivenTaggedProto(JSContext* cx,
+                                                const JSClass* clasp,
+                                                Handle<TaggedProto> proto,
+                                                gc::AllocKind allocKind,
+                                                NewObjectKind newKind) {
+  return NewObject(cx, clasp, proto, allocKind, newKind);
+}
+
+NativeObject* js::NewObjectWithClassProto(JSContext* cx, const JSClass* clasp,
+                                          HandleObject protoArg,
+                                          gc::AllocKind allocKind,
+                                          NewObjectKind newKind) {
+  if (protoArg) {
+    return NewObjectWithGivenTaggedProto(cx, clasp, AsTaggedProto(protoArg),
+                                         allocKind, newKind);
+  }
+
+  // Find the appropriate proto for clasp. Built-in classes have a cached
+  // proto on cx->global(); all others get %ObjectPrototype%.
+  JSProtoKey protoKey = JSCLASS_CACHED_PROTO_KEY(clasp);
+  if (protoKey == JSProto_Null) {
+    protoKey = JSProto_Object;
+  }
+
+  JSObject* proto = GlobalObject::getOrCreatePrototype(cx, protoKey);
+  if (!proto) {
+    return nullptr;
+  }
+
+  Rooted<TaggedProto> taggedProto(cx, TaggedProto(proto));
+  return NewObject(cx, clasp, taggedProto, allocKind, newKind);
+}
+
+bool js::GetPrototypeFromConstructor(JSContext* cx, HandleObject newTarget,
+                                     JSProtoKey intrinsicDefaultProto,
+                                     MutableHandleObject proto) {
+  RootedValue protov(cx);
+  if (!GetProperty(cx, newTarget, newTarget, cx->names().prototype, &protov)) {
+    return false;
+  }
+  if (protov.isObject()) {
+    proto.set(&protov.toObject());
+  } else if (newTarget->is<JSFunction>() &&
+             newTarget->as<JSFunction>().realm() == cx->realm()) {
+    // Steps 4.a-b fetch the builtin prototype of the current realm, which we
+    // represent as nullptr.
+    proto.set(nullptr);
+  } else if (intrinsicDefaultProto == JSProto_Null) {
+    // Bug 1317416. The caller did not pass a reasonable JSProtoKey, so let the
+    // caller select a prototype object. Most likely they will choose one from
+    // the wrong realm.
+    proto.set(nullptr);
+  } else {
+    // Step 4.a: Let realm be ? GetFunctionRealm(constructor);
+    Realm* realm = JS::GetFunctionRealm(cx, newTarget);
+    if (!realm) {
+      return false;
+    }
+
+    // Step 4.b: Set proto to realm's intrinsic object named
+    //           intrinsicDefaultProto.
+    {
+      Maybe<AutoRealm> ar;
+      if (cx->realm() != realm) {
+        ar.emplace(cx, realm->maybeGlobal());
+      }
+      proto.set(GlobalObject::getOrCreatePrototype(cx, intrinsicDefaultProto));
+    }
+    if (!proto) {
+      return false;
+    }
+    if (!cx->compartment()->wrap(cx, proto)) {
+      return false;
+    }
+  }
+  return true;
+}
+
+/* static */
+bool JSObject::nonNativeSetProperty(JSContext* cx, HandleObject obj,
+                                    HandleId id, HandleValue v,
+                                    HandleValue receiver,
+                                    ObjectOpResult& result) {
+  return obj->getOpsSetProperty()(cx, obj, id, v, receiver, result);
+}
+
+/* static */
+bool JSObject::nonNativeSetElement(JSContext* cx, HandleObject obj,
+                                   uint32_t index, HandleValue v,
+                                   HandleValue receiver,
+                                   ObjectOpResult& result) {
+  RootedId id(cx);
+  if (!IndexToId(cx, index, &id)) {
+    return false;
+  }
+  return nonNativeSetProperty(cx, obj, id, v, receiver, result);
+}
+
+static bool CopyPropertyFrom(JSContext* cx, HandleId id, HandleObject target,
+                             HandleObject obj) {
+  // |target| must not be a CCW because we need to enter its realm below and
+  // CCWs are not associated with a single realm.
+  MOZ_ASSERT(!IsCrossCompartmentWrapper(target));
+
+  // |obj| and |cx| are generally not same-compartment with |target| here.
+  cx->check(obj, id);
+  Rooted<mozilla::Maybe<PropertyDescriptor>> desc(cx);
+
+  if (!GetOwnPropertyDescriptor(cx, obj, id, &desc)) {
+    return false;
+  }
+  MOZ_ASSERT(desc.isSome());
+
+  JSAutoRealm ar(cx, target);
+  cx->markId(id);
+  RootedId wrappedId(cx, id);
+  if (!cx->compartment()->wrap(cx, &desc)) {
+    return false;
+  }
+
+  Rooted<PropertyDescriptor> desc_(cx, *desc);
+  return DefineProperty(cx, target, wrappedId, desc_);
+}
+
+JS_PUBLIC_API bool JS_CopyOwnPropertiesAndPrivateFields(JSContext* cx,
+                                                        HandleObject target,
+                                                        HandleObject obj) {
+  // Both |obj| and |target| must not be CCWs because we need to enter their
+  // realms below and CCWs are not associated with a single realm.
+  MOZ_ASSERT(!IsCrossCompartmentWrapper(obj));
+  MOZ_ASSERT(!IsCrossCompartmentWrapper(target));
+
+  JSAutoRealm ar(cx, obj);
+
+  RootedIdVector props(cx);
+  if (!GetPropertyKeys(
+          cx, obj,
+          JSITER_PRIVATE | JSITER_OWNONLY | JSITER_HIDDEN | JSITER_SYMBOLS,
+          &props)) {
+    return false;
+  }
+
+  for (size_t i = 0; i < props.length(); ++i) {
+    if (!CopyPropertyFrom(cx, props[i], target, obj)) {
+      return false;
+    }
+  }
+
+  return true;
+}
+
+static bool InitializePropertiesFromCompatibleNativeObject(
+    JSContext* cx, Handle<NativeObject*> dst, Handle<NativeObject*> src) {
+  cx->check(src, dst);
+  MOZ_ASSERT(src->getClass() == dst->getClass());
+  MOZ_ASSERT(dst->shape()->objectFlags().isEmpty());
+  MOZ_ASSERT(src->numFixedSlots() == dst->numFixedSlots());
+  MOZ_ASSERT(!src->inDictionaryMode());
+  MOZ_ASSERT(!dst->inDictionaryMode());
+
+  if (!dst->ensureElements(cx, src->getDenseInitializedLength())) {
+    return false;
+  }
+
+  uint32_t initialized = src->getDenseInitializedLength();
+  for (uint32_t i = 0; i < initialized; ++i) {
+    dst->setDenseInitializedLength(i + 1);
+    dst->initDenseElement(i, src->getDenseElement(i));
+  }
+
+  // If there are no properties to copy, we're done.
+  if (!src->sharedShape()->propMap()) {
+    return true;
+  }
+
+  Rooted<SharedShape*> shape(cx);
+  if (src->staticPrototype() == dst->staticPrototype()) {
+    shape = src->sharedShape();
+  } else {
+    // We need to generate a new shape for dst that has dst's proto but all
+    // the property information from src.  Note that we asserted above that
+    // dst's object flags are empty.
+    SharedShape* srcShape = src->sharedShape();
+    ObjectFlags objFlags;
+    objFlags = CopyPropMapObjectFlags(objFlags, srcShape->objectFlags());
+    Rooted<SharedPropMap*> map(cx, srcShape->propMap());
+    uint32_t mapLength = srcShape->propMapLength();
+    shape = SharedShape::getPropMapShape(cx, dst->shape()->base(),
+                                         dst->numFixedSlots(), map, mapLength,
+                                         objFlags);
+    if (!shape) {
+      return false;
+    }
+  }
+
+  uint32_t oldSpan = dst->sharedShape()->slotSpan();
+  uint32_t newSpan = shape->slotSpan();
+  if (!dst->setShapeAndAddNewSlots(cx, shape, oldSpan, newSpan)) {
+    return false;
+  }
+  for (size_t i = JSCLASS_RESERVED_SLOTS(src->getClass()); i < newSpan; i++) {
+    dst->setSlot(i, src->getSlot(i));
+  }
+
+  return true;
+}
+
+JS_PUBLIC_API bool JS_InitializePropertiesFromCompatibleNativeObject(
+    JSContext* cx, HandleObject dst, HandleObject src) {
+  return InitializePropertiesFromCompatibleNativeObject(
+      cx, dst.as<NativeObject>(), src.as<NativeObject>());
+}
+
+bool js::ObjectMayBeSwapped(const JSObject* obj) {
+  const JSClass* clasp = obj->getClass();
+
+  // We want to optimize Window/globals and Gecko doesn't require transplanting
+  // them (only the WindowProxy around them). A Window may be a DOMClass, so we
+  // explicitly check if this is a global.
+  if (clasp->isGlobal()) {
+    return false;
+  }
+
+  // WindowProxy, Wrapper, DeadProxyObject, DOMProxy, and DOMClass (non-global)
+  // types may be swapped. It is hard to detect DOMProxy from shell, so target
+  // proxies in general.
+  return clasp->isProxyObject() || clasp->isDOMClass();
+}
+
+bool NativeObject::prepareForSwap(JSContext* cx,
+                                  MutableHandleValueVector slotValuesOut) {
+  MOZ_ASSERT(slotValuesOut.empty());
+
+  for (size_t i = 0; i < slotSpan(); i++) {
+    if (!slotValuesOut.append(getSlot(i))) {
+      return false;
+    }
+  }
+
+  if (hasDynamicSlots()) {
+    ObjectSlots* slotsHeader = getSlotsHeader();
+    size_t size = ObjectSlots::allocSize(slotsHeader->capacity());
+    RemoveCellMemory(this, size, MemoryUse::ObjectSlots);
+    if (!cx->nursery().isInside(slotsHeader)) {
+      if (!isTenured()) {
+        cx->nursery().removeMallocedBuffer(slotsHeader, size);
+      }
+      js_free(slotsHeader);
+    }
+    setEmptyDynamicSlots(0);
+  }
+
+  if (hasDynamicElements()) {
+    ObjectElements* elements = getElementsHeader();
+    void* allocatedElements = getUnshiftedElementsHeader();
+    size_t count = elements->numAllocatedElements();
+    size_t size = count * sizeof(HeapSlot);
+
+    if (isTenured()) {
+      RemoveCellMemory(this, size, MemoryUse::ObjectElements);
+    } else if (cx->nursery().isInside(allocatedElements)) {
+      // Move nursery allocated elements in case they end up in a tenured
+      // object.
+      ObjectElements* newElements =
+          reinterpret_cast<ObjectElements*>(js_pod_malloc<HeapSlot>(count));
+      if (!newElements) {
+        return false;
+      }
+
+      memmove(newElements, elements, size);
+      elements_ = newElements->elements();
+    } else {
+      cx->nursery().removeMallocedBuffer(allocatedElements, size);
+    }
+    MOZ_ASSERT(hasDynamicElements());
+  }
+
+  return true;
+}
+
+/* static */
+bool NativeObject::fixupAfterSwap(JSContext* cx, Handle<NativeObject*> obj,
+                                  gc::AllocKind kind,
+                                  HandleValueVector slotValues) {
+  // This object has just been swapped with some other object, and its shape
+  // no longer reflects its allocated size. Correct this information and
+  // fill the slots in with the specified values.
+  MOZ_ASSERT_IF(!obj->inDictionaryMode(),
+                obj->slotSpan() == slotValues.length());
+
+  // Make sure the shape's numFixedSlots() is correct.
+  size_t nfixed = gc::GetGCKindSlots(kind);
+  if (nfixed != obj->shape()->numFixedSlots()) {
+    if (!NativeObject::changeNumFixedSlotsAfterSwap(cx, obj, nfixed)) {
+      return false;
+    }
+    MOZ_ASSERT(obj->shape()->numFixedSlots() == nfixed);
+  }
+
+  uint32_t oldDictionarySlotSpan =
+      obj->inDictionaryMode() ? slotValues.length() : 0;
+
+  MOZ_ASSERT(!obj->hasUniqueId());
+  size_t ndynamic =
+      calculateDynamicSlots(nfixed, slotValues.length(), obj->getClass());
+  size_t currentSlots = obj->getSlotsHeader()->capacity();
+  MOZ_ASSERT(ndynamic >= currentSlots);
+  if (ndynamic > currentSlots) {
+    if (!obj->growSlots(cx, currentSlots, ndynamic)) {
+      return false;
+    }
+  }
+
+  if (obj->inDictionaryMode()) {
+    obj->setDictionaryModeSlotSpan(oldDictionarySlotSpan);
+  }
+
+  for (size_t i = 0, len = slotValues.length(); i < len; i++) {
+    obj->initSlotUnchecked(i, slotValues[i]);
+  }
+
+  if (obj->hasDynamicElements()) {
+    ObjectElements* elements = obj->getElementsHeader();
+    void* allocatedElements = obj->getUnshiftedElementsHeader();
+    MOZ_ASSERT(!cx->nursery().isInside(allocatedElements));
+    size_t size = elements->numAllocatedElements() * sizeof(HeapSlot);
+    if (obj->isTenured()) {
+      AddCellMemory(obj, size, MemoryUse::ObjectElements);
+    } else if (!cx->nursery().registerMallocedBuffer(allocatedElements, size)) {
+      return false;
+    }
+  }
+
+  return true;
+}
+
+[[nodiscard]] bool ProxyObject::prepareForSwap(
+    JSContext* cx, MutableHandleValueVector valuesOut) {
+  MOZ_ASSERT(valuesOut.empty());
+
+  // Remove the GCPtr<Value>s we're about to swap from the store buffer, to
+  // ensure we don't trace bogus values.
+  gc::StoreBuffer& sb = cx->runtime()->gc.storeBuffer();
+
+  // Reserve space for the expando, private slot and the reserved slots.
+  if (!valuesOut.reserve(2 + numReservedSlots())) {
+    return false;
+  }
+
+  js::detail::ProxyValueArray* valArray = data.values();
+  sb.unputValue(&valArray->expandoSlot);
+  sb.unputValue(&valArray->privateSlot);
+  valuesOut.infallibleAppend(valArray->expandoSlot);
+  valuesOut.infallibleAppend(valArray->privateSlot);
+
+  for (size_t i = 0; i < numReservedSlots(); i++) {
+    sb.unputValue(&valArray->reservedSlots.slots[i]);
+    valuesOut.infallibleAppend(valArray->reservedSlots.slots[i]);
+  }
+
+  if (isTenured() && !usingInlineValueArray()) {
+    size_t count = detail::ProxyValueArray::allocCount(numReservedSlots());
+    RemoveCellMemory(this, count * sizeof(Value),
+                     MemoryUse::ProxyExternalValueArray);
+    js_free(valArray);
+    data.reservedSlots = nullptr;
+  }
+
+  return true;
+}
+
+bool ProxyObject::fixupAfterSwap(JSContext* cx,
+                                 const HandleValueVector values) {
+  MOZ_ASSERT(getClass()->isProxyObject());
+
+  size_t nreserved = numReservedSlots();
+
+  // |values| contains the expando slot, private slot and the reserved slots.
+  MOZ_ASSERT(values.length() == 2 + nreserved);
+
+  // Allocate the external value array in malloc memory, even for nursery
+  // proxies.
+  size_t count = detail::ProxyValueArray::allocCount(nreserved);
+  auto* allocation = js_pod_malloc<JS::Value>(count);
+  if (!allocation) {
+    return false;
+  }
+
+  size_t size = count * sizeof(Value);
+  if (isTenured()) {
+    AddCellMemory(&asTenured(), size, MemoryUse::ProxyExternalValueArray);
+  } else if (!cx->nursery().registerMallocedBuffer(allocation, size)) {
+    js_free(allocation);
+    return false;
+  }
+
+  auto* valArray = reinterpret_cast<js::detail::ProxyValueArray*>(allocation);
+
+  valArray->expandoSlot = values[0];
+  valArray->privateSlot = values[1];
+
+  for (size_t i = 0; i < nreserved; i++) {
+    valArray->reservedSlots.slots[i] = values[i + 2];
+  }
+
+  data.reservedSlots = &valArray->reservedSlots;
+  MOZ_ASSERT(!usingInlineValueArray());
+  return true;
+}
+
+static gc::AllocKind SwappableObjectAllocKind(JSObject* obj) {
+  MOZ_ASSERT(ObjectMayBeSwapped(obj));
+
+  if (obj->isTenured()) {
+    return obj->asTenured().getAllocKind();
+  }
+
+  if (obj->is<NativeObject>()) {
+    return obj->as<NativeObject>().allocKindForTenure();
+  }
+
+  return obj->as<ProxyObject>().allocKindForTenure();
+}
+
+/* Use this method with extreme caution. It trades the guts of two objects. */
+void JSObject::swap(JSContext* cx, HandleObject a, HandleObject b,
+                    AutoEnterOOMUnsafeRegion& oomUnsafe) {
+  // Ensure swap doesn't cause a finalizer to be run at the wrong time.
+  MOZ_ASSERT(a->isBackgroundFinalized() == b->isBackgroundFinalized());
+
+  MOZ_ASSERT(a->compartment() == b->compartment());
+
+  // You must have entered the objects' compartment before calling this.
+  MOZ_ASSERT(cx->compartment() == a->compartment());
+
+  // Only certain types of objects are allowed to be swapped. This allows the
+  // JITs to better optimize objects that can never swap and rules out most
+  // builtin objects that have special behaviour.
+  MOZ_RELEASE_ASSERT(js::ObjectMayBeSwapped(a));
+  MOZ_RELEASE_ASSERT(js::ObjectMayBeSwapped(b));
+
+  if (!Watchtower::watchObjectSwap(cx, a, b)) {
+    oomUnsafe.crash("watchObjectSwap");
+  }
+
+  // Ensure we update any embedded nursery pointers in either object.
+  gc::StoreBuffer& storeBuffer = cx->runtime()->gc.storeBuffer();
+  if (a->isTenured()) {
+    storeBuffer.putWholeCell(a);
+  }
+  if (b->isTenured()) {
+    storeBuffer.putWholeCell(b);
+  }
+  if (a->isTenured() || b->isTenured()) {
+    if (a->zone()->wasGCStarted()) {
+      storeBuffer.setMayHavePointersToDeadCells();
+    }
+  }
+
+  unsigned r = NotifyGCPreSwap(a, b);
+
+  ProxyObject* pa = a->is<ProxyObject>() ? &a->as<ProxyObject>() : nullptr;
+  ProxyObject* pb = b->is<ProxyObject>() ? &b->as<ProxyObject>() : nullptr;
+  bool aIsProxyWithInlineValues = pa && pa->usingInlineValueArray();
+  bool bIsProxyWithInlineValues = pb && pb->usingInlineValueArray();
+
+  bool aIsUsedAsPrototype = a->isUsedAsPrototype();
+  bool bIsUsedAsPrototype = b->isUsedAsPrototype();
+
+  // Swap element associations.
+  Zone* zone = a->zone();
+
+  // Record any associated unique IDs and prepare for swap.
+  //
+  // Note that unique IDs are NOT swapped but remain associated with the
+  // original address.
+  uint64_t aid = 0;
+  uint64_t bid = 0;
+  (void)gc::MaybeGetUniqueId(a, &aid);
+  (void)gc::MaybeGetUniqueId(b, &bid);
+  NativeObject* na = a->is<NativeObject>() ? &a->as<NativeObject>() : nullptr;
+  NativeObject* nb = b->is<NativeObject>() ? &b->as<NativeObject>() : nullptr;
+  if ((aid || bid) && (na || nb)) {
+    // We can't remove unique IDs from native objects when they are swapped with
+    // objects without an ID. Instead ensure they both have IDs so we always
+    // have something to overwrite the old ID with.
+    if (!gc::GetOrCreateUniqueId(a, &aid) ||
+        !gc::GetOrCreateUniqueId(b, &bid)) {
+      oomUnsafe.crash("Failed to create unique ID during swap");
+    }
+
+    // IDs stored in NativeObjects could shadow those stored in the zone
+    // table. Remove any zone table IDs first.
+    if (pa && aid) {
+      gc::RemoveUniqueId(a);
+    }
+    if (pb && bid) {
+      gc::RemoveUniqueId(b);
+    }
+  }
+
+  gc::AllocKind ka = SwappableObjectAllocKind(a);
+  gc::AllocKind kb = SwappableObjectAllocKind(b);
+
+  size_t sa = gc::Arena::thingSize(ka);
+  size_t sb = gc::Arena::thingSize(kb);
+  if (sa == sb && a->isTenured() == b->isTenured()) {
+    // When both objects are the same size and in the same heap, just do a plain
+    // swap of their contents.
+
+    // Swap slot associations.
+    zone->swapCellMemory(a, b, MemoryUse::ObjectSlots);
+
+    size_t size = sa;
+    char tmp[sizeof(JSObject_Slots16)];
+    MOZ_ASSERT(size <= sizeof(tmp));
+
+    js_memcpy(tmp, a, size);
+    js_memcpy(a, b, size);
+    js_memcpy(b, tmp, size);
+
+    zone->swapCellMemory(a, b, MemoryUse::ObjectElements);
+    zone->swapCellMemory(a, b, MemoryUse::ProxyExternalValueArray);
+
+    if (aIsProxyWithInlineValues) {
+      b->as<ProxyObject>().setInlineValueArray();
+    }
+    if (bIsProxyWithInlineValues) {
+      a->as<ProxyObject>().setInlineValueArray();
+    }
+  } else {
+    // Avoid GC in here to avoid confusing the tracing code with our
+    // intermediate state.
+    gc::AutoSuppressGC suppress(cx);
+
+    // When the objects have different sizes, they will have different numbers
+    // of fixed slots before and after the swap, so the slots for native objects
+    // will need to be rearranged. Remember the original values from the
+    // objects.
+    RootedValueVector avals(cx);
+    RootedValueVector bvals(cx);
+    if (na && !na->prepareForSwap(cx, &avals)) {
+      oomUnsafe.crash("NativeObject::prepareForSwap");
+    }
+    if (nb && !nb->prepareForSwap(cx, &bvals)) {
+      oomUnsafe.crash("NativeObject::prepareForSwap");
+    }
+
+    // Do the same for proxy value arrays.
+    if (pa && !pa->prepareForSwap(cx, &avals)) {
+      oomUnsafe.crash("ProxyObject::prepareForSwap");
+    }
+    if (pb && !pb->prepareForSwap(cx, &bvals)) {
+      oomUnsafe.crash("ProxyObject::prepareForSwap");
+    }
+
+    // Swap the main fields of the objects, whether they are native objects or
+    // proxies.
+    char tmp[sizeof(JSObject_Slots0)];
+    js_memcpy(&tmp, a, sizeof tmp);
+    js_memcpy(a, b, sizeof tmp);
+    js_memcpy(b, &tmp, sizeof tmp);
+
+    if (na &&
+        !NativeObject::fixupAfterSwap(cx, b.as<NativeObject>(), kb, avals)) {
+      oomUnsafe.crash("NativeObject::fixupAfterSwap");
+    }
+    if (nb &&
+        !NativeObject::fixupAfterSwap(cx, a.as<NativeObject>(), ka, bvals)) {
+      oomUnsafe.crash("NativeObject::fixupAfterSwap");
+    }
+
+    if (pa && !b->as<ProxyObject>().fixupAfterSwap(cx, avals)) {
+      oomUnsafe.crash("ProxyObject::fixupAfterSwap");
+    }
+    if (pb && !a->as<ProxyObject>().fixupAfterSwap(cx, bvals)) {
+      oomUnsafe.crash("ProxyObject::fixupAfterSwap");
+    }
+  }
+
+  // Restore original unique IDs.
+  if ((aid || bid) && (na || nb)) {
+    if ((aid && !gc::SetOrUpdateUniqueId(cx, a, aid)) ||
+        (bid && !gc::SetOrUpdateUniqueId(cx, b, bid))) {
+      oomUnsafe.crash("Failed to set unique ID after swap");
+    }
+  }
+  MOZ_ASSERT_IF(aid, gc::GetUniqueIdInfallible(a) == aid);
+  MOZ_ASSERT_IF(bid, gc::GetUniqueIdInfallible(b) == bid);
+
+  // Preserve the IsUsedAsPrototype flag on the objects.
+  if (aIsUsedAsPrototype) {
+    if (!JSObject::setIsUsedAsPrototype(cx, a)) {
+      oomUnsafe.crash("setIsUsedAsPrototype");
+    }
+  }
+  if (bIsUsedAsPrototype) {
+    if (!JSObject::setIsUsedAsPrototype(cx, b)) {
+      oomUnsafe.crash("setIsUsedAsPrototype");
+    }
+  }
+
+  /*
+   * We need a write barrier here. If |a| was marked and |b| was not, then
+   * after the swap, |b|'s guts would never be marked. The write barrier
+   * solves this.
+   *
+   * Normally write barriers happen before the write. However, that's not
+   * necessary here because nothing is being destroyed. We're just swapping.
+   */
+  PreWriteBarrier(zone, a.get(), [](JSTracer* trc, JSObject* obj) {
+    obj->traceChildren(trc);
+  });
+  PreWriteBarrier(zone, b.get(), [](JSTracer* trc, JSObject* obj) {
+    obj->traceChildren(trc);
+  });
+
+  NotifyGCPostSwap(a, b, r);
+}
+
+static NativeObject* DefineConstructorAndPrototype(
+    JSContext* cx, HandleObject obj, Handle<JSAtom*> atom,
+    HandleObject protoProto, const JSClass* clasp, Native constructor,
+    unsigned nargs, const JSPropertySpec* ps, const JSFunctionSpec* fs,
+    const JSPropertySpec* static_ps, const JSFunctionSpec* static_fs,
+    NativeObject** ctorp) {
+  // Create the prototype object.
+  Rooted<NativeObject*> proto(
+      cx, GlobalObject::createBlankPrototypeInheriting(cx, clasp, protoProto));
+  if (!proto) {
+    return nullptr;
+  }
+
+  Rooted<NativeObject*> ctor(cx);
+  if (!constructor) {
+    ctor = proto;
+  } else {
+    ctor = NewNativeConstructor(cx, constructor, nargs, atom);
+    if (!ctor) {
+      return nullptr;
+    }
+
+    if (!LinkConstructorAndPrototype(cx, ctor, proto)) {
+      return nullptr;
+    }
+  }
+
+  if (!DefinePropertiesAndFunctions(cx, proto, ps, fs) ||
+      (ctor != proto &&
+       !DefinePropertiesAndFunctions(cx, ctor, static_ps, static_fs))) {
+    return nullptr;
+  }
+
+  RootedId id(cx, AtomToId(atom));
+  RootedValue value(cx, ObjectValue(*ctor));
+  if (!DefineDataProperty(cx, obj, id, value, 0)) {
+    return nullptr;
+  }
+
+  if (ctorp) {
+    *ctorp = ctor;
+  }
+  return proto;
+}
+
+NativeObject* js::InitClass(JSContext* cx, HandleObject obj,
+                            const JSClass* protoClass, HandleObject protoProto_,
+                            const char* name, Native constructor,
+                            unsigned nargs, const JSPropertySpec* ps,
+                            const JSFunctionSpec* fs,
+                            const JSPropertySpec* static_ps,
+                            const JSFunctionSpec* static_fs,
+                            NativeObject** ctorp) {
+  Rooted<JSAtom*> atom(cx, Atomize(cx, name, strlen(name)));
+  if (!atom) {
+    return nullptr;
+  }
+
+  /*
+   * All instances of the class will inherit properties from the prototype
+   * object we are about to create (in DefineConstructorAndPrototype), which
+   * in turn will inherit from protoProto.
+   *
+   * If protoProto is nullptr, default to Object.prototype.
+   * If protoClass is nullptr, default to PlainObject.
+   */
+  RootedObject protoProto(cx, protoProto_);
+  if (!protoProto) {
+    protoProto = &cx->global()->getObjectPrototype();
+  }
+  if (!protoClass) {
+    protoClass = &PlainObject::class_;
+  }
+
+  return DefineConstructorAndPrototype(cx, obj, atom, protoProto, protoClass,
+                                       constructor, nargs, ps, fs, static_ps,
+                                       static_fs, ctorp);
+}
+
+/**
+ * Returns the original Object.prototype from the embedding-provided incumbent
+ * global.
+ *
+ * Really, we want the incumbent global itself so we can pass it to other
+ * embedding hooks which need it. Specifically, the enqueue promise hook
+ * takes an incumbent global so it can set that on the PromiseCallbackJob
+ * it creates.
+ *
+ * The reason for not just returning the global itself is that we'd need to
+ * wrap it into the current compartment, and later unwrap it. Unwrapping
+ * globals is tricky, though: we might accidentally unwrap through an inner
+ * to its outer window and end up with the wrong global. Plain objects don't
+ * have this problem, so we use the global's Object.prototype. The code using
+ * it - e.g. EnqueuePromiseReactionJob - can then unwrap the object and get
+ * its global without fear of unwrapping too far.
+ */
+bool js::GetObjectFromIncumbentGlobal(JSContext* cx, MutableHandleObject obj) {
+  Rooted<GlobalObject*> globalObj(cx, cx->runtime()->getIncumbentGlobal(cx));
+  if (!globalObj) {
+    obj.set(nullptr);
+    return true;
+  }
+
+  obj.set(&globalObj->getObjectPrototype());
+
+  // The object might be from a different compartment, so wrap it.
+  if (obj && !cx->compartment()->wrap(cx, obj)) {
+    return false;
+  }
+
+  return true;
+}
+
+static bool IsStandardPrototype(JSObject* obj, JSProtoKey key) {
+  return obj->nonCCWGlobal().maybeGetPrototype(key) == obj;
+}
+
+JSProtoKey JS::IdentifyStandardInstance(JSObject* obj) {
+  // Note: The prototype shares its JSClass with instances.
+  MOZ_ASSERT(!obj->is<CrossCompartmentWrapperObject>());
+  JSProtoKey key = StandardProtoKeyOrNull(obj);
+  if (key != JSProto_Null && !IsStandardPrototype(obj, key)) {
+    return key;
+  }
+  return JSProto_Null;
+}
+
+JSProtoKey JS::IdentifyStandardPrototype(JSObject* obj) {
+  // Note: The prototype shares its JSClass with instances.
+  MOZ_ASSERT(!obj->is<CrossCompartmentWrapperObject>());
+  JSProtoKey key = StandardProtoKeyOrNull(obj);
+  if (key != JSProto_Null && IsStandardPrototype(obj, key)) {
+    return key;
+  }
+  return JSProto_Null;
+}
+
+JSProtoKey JS::IdentifyStandardInstanceOrPrototype(JSObject* obj) {
+  return StandardProtoKeyOrNull(obj);
+}
+
+JSProtoKey JS::IdentifyStandardConstructor(JSObject* obj) {
+  // Note that isNativeConstructor does not imply that we are a standard
+  // constructor, but the converse is true (at least until we start having
+  // self-hosted constructors for standard classes). This lets us avoid a costly
+  // loop for many functions (which, depending on the call site, may be the
+  // common case).
+  if (!obj->is<JSFunction>() ||
+      !(obj->as<JSFunction>().flags().isNativeConstructor())) {
+    return JSProto_Null;
+  }
+
+  static_assert(JSProto_Null == 0,
+                "Loop below can start at 1 to skip JSProto_Null");
+
+  GlobalObject& global = obj->as<JSFunction>().global();
+  for (size_t k = 1; k < JSProto_LIMIT; ++k) {
+    JSProtoKey key = static_cast<JSProtoKey>(k);
+    if (global.maybeGetConstructor(key) == obj) {
+      return key;
+    }
+  }
+
+  return JSProto_Null;
+}
+
+bool js::LookupProperty(JSContext* cx, HandleObject obj, js::HandleId id,
+                        MutableHandleObject objp, PropertyResult* propp) {
+  if (LookupPropertyOp op = obj->getOpsLookupProperty()) {
+    return op(cx, obj, id, objp, propp);
+  }
+  return NativeLookupPropertyInline<CanGC>(cx, obj.as<NativeObject>(), id, objp,
+                                           propp);
+}
+
+bool js::LookupName(JSContext* cx, Handle<PropertyName*> name,
+                    HandleObject envChain, MutableHandleObject objp,
+                    MutableHandleObject pobjp, PropertyResult* propp) {
+  RootedId id(cx, NameToId(name));
+
+  for (RootedObject env(cx, envChain); env; env = env->enclosingEnvironment()) {
+    if (!LookupProperty(cx, env, id, pobjp, propp)) {
+      return false;
+    }
+    if (propp->isFound()) {
+      objp.set(env);
+      return true;
+    }
+  }
+
+  objp.set(nullptr);
+  pobjp.set(nullptr);
+  propp->setNotFound();
+  return true;
+}
+
+bool js::LookupNameNoGC(JSContext* cx, PropertyName* name, JSObject* envChain,
+                        JSObject** objp, NativeObject** pobjp,
+                        PropertyResult* propp) {
+  AutoAssertNoPendingException nogc(cx);
+
+  MOZ_ASSERT(!*objp && !*pobjp && propp->isNotFound());
+
+  for (JSObject* env = envChain; env; env = env->enclosingEnvironment()) {
+    if (env->getOpsLookupProperty()) {
+      return false;
+    }
+    if (!NativeLookupPropertyInline<NoGC>(cx, &env->as<NativeObject>(),
+                                          NameToId(name), pobjp, propp)) {
+      return false;
+    }
+    if (propp->isFound()) {
+      *objp = env;
+      return true;
+    }
+  }
+
+  return true;
+}
+
+bool js::LookupNameWithGlobalDefault(JSContext* cx, Handle<PropertyName*> name,
+                                     HandleObject envChain,
+                                     MutableHandleObject objp) {
+  RootedId id(cx, NameToId(name));
+
+  RootedObject pobj(cx);
+  PropertyResult prop;
+
+  RootedObject env(cx, envChain);
+  for (; !env->is<GlobalObject>(); env = env->enclosingEnvironment()) {
+    if (!LookupProperty(cx, env, id, &pobj, &prop)) {
+      return false;
+    }
+    if (prop.isFound()) {
+      break;
+    }
+  }
+
+  objp.set(env);
+  return true;
+}
+
+bool js::LookupNameUnqualified(JSContext* cx, Handle<PropertyName*> name,
+                               HandleObject envChain,
+                               MutableHandleObject objp) {
+  RootedId id(cx, NameToId(name));
+
+  RootedObject pobj(cx);
+  PropertyResult prop;
+
+  RootedObject env(cx, envChain);
+  for (; !env->isUnqualifiedVarObj(); env = env->enclosingEnvironment()) {
+    if (!LookupProperty(cx, env, id, &pobj, &prop)) {
+      return false;
+    }
+    if (prop.isFound()) {
+      break;
+    }
+  }
+
+  // See note above RuntimeLexicalErrorObject.
+  if (pobj == env) {
+    bool isTDZ = false;
+    if (prop.isFound() && name != cx->names().dotThis) {
+      // Treat Debugger environments specially for TDZ checks, as they
+      // look like non-native environments but in fact wrap native
+      // environments.
+      if (env->is<DebugEnvironmentProxy>()) {
+        RootedValue v(cx);
+        Rooted<DebugEnvironmentProxy*> envProxy(
+            cx, &env->as<DebugEnvironmentProxy>());
+        if (!DebugEnvironmentProxy::getMaybeSentinelValue(cx, envProxy, id,
+                                                          &v)) {
+          return false;
+        }
+        isTDZ = IsUninitializedLexical(v);
+      } else {
+        isTDZ = IsUninitializedLexicalSlot(env, prop);
+      }
+    }
+
+    if (isTDZ) {
+      env = RuntimeLexicalErrorObject::create(cx, env,
+                                              JSMSG_UNINITIALIZED_LEXICAL);
+      if (!env) {
+        return false;
+      }
+    } else if (env->is<LexicalEnvironmentObject>() &&
+               !prop.propertyInfo().writable()) {
+      // Assigning to a named lambda callee name is a no-op in sloppy mode.
+      if (!(env->is<BlockLexicalEnvironmentObject>() &&
+            env->as<BlockLexicalEnvironmentObject>().scope().kind() ==
+                ScopeKind::NamedLambda)) {
+        MOZ_ASSERT(name != cx->names().dotThis);
+        env =
+            RuntimeLexicalErrorObject::create(cx, env, JSMSG_BAD_CONST_ASSIGN);
+        if (!env) {
+          return false;
+        }
+      }
+    }
+  }
+
+  objp.set(env);
+  return true;
+}
+
+bool js::HasOwnProperty(JSContext* cx, HandleObject obj, HandleId id,
+                        bool* result) {
+  if (obj->is<ProxyObject>()) {
+    return Proxy::hasOwn(cx, obj, id, result);
+  }
+
+  if (GetOwnPropertyOp op = obj->getOpsGetOwnPropertyDescriptor()) {
+    Rooted<mozilla::Maybe<PropertyDescriptor>> desc(cx);
+    if (!op(cx, obj, id, &desc)) {
+      return false;
+    }
+    *result = desc.isSome();
+    return true;
+  }
+
+  PropertyResult prop;
+  if (!NativeLookupOwnProperty<CanGC>(cx, obj.as<NativeObject>(), id, &prop)) {
+    return false;
+  }
+  *result = prop.isFound();
+  return true;
+}
+
+bool js::LookupPropertyPure(JSContext* cx, JSObject* obj, jsid id,
+                            NativeObject** objp, PropertyResult* propp) {
+  if (obj->getOpsLookupProperty()) {
+    return false;
+  }
+  return NativeLookupPropertyInline<NoGC, LookupResolveMode::CheckMayResolve>(
+      cx, &obj->as<NativeObject>(), id, objp, propp);
+}
+
+bool js::LookupOwnPropertyPure(JSContext* cx, JSObject* obj, jsid id,
+                               PropertyResult* propp) {
+  if (obj->getOpsLookupProperty()) {
+    return false;
+  }
+  return NativeLookupOwnPropertyInline<NoGC,
+                                       LookupResolveMode::CheckMayResolve>(
+      cx, &obj->as<NativeObject>(), id, propp);
+}
+
+static inline bool NativeGetPureInline(NativeObject* pobj, jsid id,
+                                       PropertyResult prop, Value* vp,
+                                       JSContext* cx) {
+  if (prop.isDenseElement()) {
+    *vp = pobj->getDenseElement(prop.denseElementIndex());
+    return true;
+  }
+  if (prop.isTypedArrayElement()) {
+    size_t idx = prop.typedArrayElementIndex();
+    return pobj->as<TypedArrayObject>().getElement<NoGC>(cx, idx, vp);
+  }
+
+  // Fail if we have a custom getter.
+  PropertyInfo propInfo = prop.propertyInfo();
+  if (!propInfo.isDataProperty()) {
+    return false;
+  }
+
+  *vp = pobj->getSlot(propInfo.slot());
+  MOZ_ASSERT(!vp->isMagic());
+  return true;
+}
+
+bool js::GetPropertyPure(JSContext* cx, JSObject* obj, jsid id, Value* vp) {
+  NativeObject* pobj;
+  PropertyResult prop;
+  if (!LookupPropertyPure(cx, obj, id, &pobj, &prop)) {
+    return false;
+  }
+
+  if (prop.isNotFound()) {
+    vp->setUndefined();
+    return true;
+  }
+
+  return NativeGetPureInline(pobj, id, prop, vp, cx);
+}
+
+bool js::GetOwnPropertyPure(JSContext* cx, JSObject* obj, jsid id, Value* vp,
+                            bool* found) {
+  PropertyResult prop;
+  if (!LookupOwnPropertyPure(cx, obj, id, &prop)) {
+    return false;
+  }
+
+  if (prop.isNotFound()) {
+    *found = false;
+    vp->setUndefined();
+    return true;
+  }
+
+  *found = true;
+  return obj->is<NativeObject>() &&
+         NativeGetPureInline(&obj->as<NativeObject>(), id, prop, vp, cx);
+}
+
+static inline bool NativeGetGetterPureInline(NativeObject* holder,
+                                             PropertyResult prop,
+                                             JSFunction** fp) {
+  MOZ_ASSERT(prop.isNativeProperty());
+
+  PropertyInfo propInfo = prop.propertyInfo();
+  if (holder->hasGetter(propInfo)) {
+    JSObject* getter = holder->getGetter(propInfo);
+    if (getter->is<JSFunction>()) {
+      *fp = &getter->as<JSFunction>();
+      return true;
+    }
+  }
+
+  *fp = nullptr;
+  return true;
+}
+
+bool js::GetGetterPure(JSContext* cx, JSObject* obj, jsid id, JSFunction** fp) {
+  /* Just like GetPropertyPure, but get getter function, without invoking
+   * it. */
+  NativeObject* pobj;
+  PropertyResult prop;
+  if (!LookupPropertyPure(cx, obj, id, &pobj, &prop)) {
+    return false;
+  }
+
+  if (prop.isNotFound()) {
+    *fp = nullptr;
+    return true;
+  }
+
+  return prop.isNativeProperty() && NativeGetGetterPureInline(pobj, prop, fp);
+}
+
+bool js::GetOwnGetterPure(JSContext* cx, JSObject* obj, jsid id,
+                          JSFunction** fp) {
+  JS::AutoCheckCannotGC nogc;
+  PropertyResult prop;
+  if (!LookupOwnPropertyPure(cx, obj, id, &prop)) {
+    return false;
+  }
+
+  if (prop.isNotFound()) {
+    *fp = nullptr;
+    return true;
+  }
+
+  return prop.isNativeProperty() &&
+         NativeGetGetterPureInline(&obj->as<NativeObject>(), prop, fp);
+}
+
+bool js::GetOwnNativeGetterPure(JSContext* cx, JSObject* obj, jsid id,
+                                JSNative* native) {
+  JS::AutoCheckCannotGC nogc;
+  *native = nullptr;
+  PropertyResult prop;
+  if (!LookupOwnPropertyPure(cx, obj, id, &prop)) {
+    return false;
+  }
+
+  if (!prop.isNativeProperty()) {
+    return true;
+  }
+
+  PropertyInfo propInfo = prop.propertyInfo();
+
+  NativeObject* nobj = &obj->as<NativeObject>();
+  if (!nobj->hasGetter(propInfo)) {
+    return true;
+  }
+
+  JSObject* getterObj = nobj->getGetter(propInfo);
+  if (!getterObj->is<JSFunction>()) {
+    return true;
+  }
+
+  JSFunction* getter = &getterObj->as<JSFunction>();
+  if (!getter->isNativeFun()) {
+    return true;
+  }
+
+  *native = getter->native();
+  return true;
+}
+
+bool js::HasOwnDataPropertyPure(JSContext* cx, JSObject* obj, jsid id,
+                                bool* result) {
+  PropertyResult prop;
+  if (!LookupOwnPropertyPure(cx, obj, id, &prop)) {
+    return false;
+  }
+
+  *result = prop.isNativeProperty() && prop.propertyInfo().isDataProperty();
+  return true;
+}
+
+bool js::GetPrototypeIfOrdinary(JSContext* cx, HandleObject obj,
+                                bool* isOrdinary, MutableHandleObject protop) {
+  if (obj->is<js::ProxyObject>()) {
+    return js::Proxy::getPrototypeIfOrdinary(cx, obj, isOrdinary, protop);
+  }
+
+  *isOrdinary = true;
+  protop.set(obj->staticPrototype());
+  return true;
+}
+
+/*** ES6 standard internal methods ******************************************/
+
+bool js::SetPrototype(JSContext* cx, HandleObject obj, HandleObject proto,
+                      JS::ObjectOpResult& result) {
+  // The proxy trap subsystem fully handles prototype-setting for proxies
+  // with dynamic [[Prototype]]s.
+  if (obj->hasDynamicPrototype()) {
+    MOZ_ASSERT(obj->is<ProxyObject>());
+    return Proxy::setPrototype(cx, obj, proto, result);
+  }
+
+  /*
+   * ES6 9.1.2 step 3-4 if |obj.[[Prototype]]| has SameValue as |proto| return
+   * true. Since the values in question are objects, we can just compare
+   * pointers.
+   */
+  if (proto == obj->staticPrototype()) {
+    return result.succeed();
+  }
+
+  /* Disallow mutation of immutable [[Prototype]]s. */
+  if (obj->staticPrototypeIsImmutable()) {
+    return result.fail(JSMSG_CANT_SET_PROTO);
+  }
+
+  /*
+   * Disallow mutating the [[Prototype]] on Typed Objects, per the spec.
+   */
+  if (obj->is<WasmGcObject>()) {
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                              JSMSG_CANT_SET_PROTO_OF,
+                              "incompatible WebAssembly object");
+    return false;
+  }
+
+  /* ES6 9.1.2 step 5 forbids changing [[Prototype]] if not [[Extensible]]. */
+  bool extensible;
+  if (!IsExtensible(cx, obj, &extensible)) {
+    return false;
+  }
+  if (!extensible) {
+    return result.fail(JSMSG_CANT_SET_PROTO);
+  }
+
+  /*
+   * ES6 9.1.2 step 6 forbids generating cyclical prototype chains. But we
+   * have to do this comparison on the observable WindowProxy, not on the
+   * possibly-Window object we're setting the proto on.
+   */
+  RootedObject objMaybeWindowProxy(cx, ToWindowProxyIfWindow(obj));
+  RootedObject obj2(cx, proto);
+  while (obj2) {
+    MOZ_ASSERT(!IsWindow(obj2));
+    if (obj2 == objMaybeWindowProxy) {
+      return result.fail(JSMSG_CANT_SET_PROTO_CYCLE);
+    }
+
+    bool isOrdinary;
+    if (!GetPrototypeIfOrdinary(cx, obj2, &isOrdinary, &obj2)) {
+      return false;
+    }
+    if (!isOrdinary) {
+      break;
+    }
+  }
+
+  Rooted<TaggedProto> taggedProto(cx, TaggedProto(proto));
+  if (!JSObject::setProtoUnchecked(cx, obj, taggedProto)) {
+    return false;
+  }
+
+  return result.succeed();
+}
+
+bool js::SetPrototype(JSContext* cx, HandleObject obj, HandleObject proto) {
+  ObjectOpResult result;
+  return SetPrototype(cx, obj, proto, result) && result.checkStrict(cx, obj);
+}
+
+bool js::PreventExtensions(JSContext* cx, HandleObject obj,
+                           ObjectOpResult& result) {
+  if (obj->is<ProxyObject>()) {
+    return js::Proxy::preventExtensions(cx, obj, result);
+  }
+
+  if (!obj->nonProxyIsExtensible()) {
+    // If the following assertion fails, there's somewhere else a missing
+    // call to shrinkCapacityToInitializedLength() which needs to be found
+    // and fixed.
+    MOZ_ASSERT_IF(obj->is<NativeObject>(),
+                  obj->as<NativeObject>().getDenseInitializedLength() ==
+                      obj->as<NativeObject>().getDenseCapacity());
+
+    return result.succeed();
+  }
+
+  if (obj->is<NativeObject>()) {
+    // Force lazy properties to be resolved.
+    Handle<NativeObject*> nobj = obj.as<NativeObject>();
+    if (!ResolveLazyProperties(cx, nobj)) {
+      return false;
+    }
+
+    // Prepare the elements. We have to do this before we mark the object
+    // non-extensible; that's fine because these changes are not observable.
+    ObjectElements::PrepareForPreventExtensions(cx, nobj);
+  }
+
+  // Finally, set the NotExtensible flag on the Shape and ObjectElements.
+  if (!JSObject::setFlag(cx, obj, ObjectFlag::NotExtensible)) {
+    return false;
+  }
+  if (obj->is<NativeObject>()) {
+    ObjectElements::PreventExtensions(&obj->as<NativeObject>());
+  }
+
+  return result.succeed();
+}
+
+bool js::PreventExtensions(JSContext* cx, HandleObject obj) {
+  ObjectOpResult result;
+  return PreventExtensions(cx, obj, result) && result.checkStrict(cx, obj);
+}
+
+bool js::GetOwnPropertyDescriptor(
+    JSContext* cx, HandleObject obj, HandleId id,
+    MutableHandle<Maybe<PropertyDescriptor>> desc) {
+  if (GetOwnPropertyOp op = obj->getOpsGetOwnPropertyDescriptor()) {
+    bool ok = op(cx, obj, id, desc);
+    if (ok && desc.isSome()) {
+      desc->assertComplete();
+    }
+    return ok;
+  }
+
+  return NativeGetOwnPropertyDescriptor(cx, obj.as<NativeObject>(), id, desc);
+}
+
+bool js::DefineProperty(JSContext* cx, HandleObject obj, HandleId id,
+                        Handle<PropertyDescriptor> desc) {
+  ObjectOpResult result;
+  return DefineProperty(cx, obj, id, desc, result) &&
+         result.checkStrict(cx, obj, id);
+}
+
+bool js::DefineProperty(JSContext* cx, HandleObject obj, HandleId id,
+                        Handle<PropertyDescriptor> desc,
+                        ObjectOpResult& result) {
+  desc.assertValid();
+  if (DefinePropertyOp op = obj->getOpsDefineProperty()) {
+    return op(cx, obj, id, desc, result);
+  }
+  return NativeDefineProperty(cx, obj.as<NativeObject>(), id, desc, result);
+}
+
+bool js::DefineAccessorProperty(JSContext* cx, HandleObject obj, HandleId id,
+                                HandleObject getter, HandleObject setter,
+                                unsigned attrs, ObjectOpResult& result) {
+  Rooted<PropertyDescriptor> desc(
+      cx, PropertyDescriptor::Accessor(
+              getter ? mozilla::Some(getter) : mozilla::Nothing(),
+              setter ? mozilla::Some(setter) : mozilla::Nothing(), attrs));
+
+  if (DefinePropertyOp op = obj->getOpsDefineProperty()) {
+    MOZ_ASSERT(!cx->isHelperThreadContext());
+    return op(cx, obj, id, desc, result);
+  }
+  return NativeDefineProperty(cx, obj.as<NativeObject>(), id, desc, result);
+}
+
+bool js::DefineDataProperty(JSContext* cx, HandleObject obj, HandleId id,
+                            HandleValue value, unsigned attrs,
+                            ObjectOpResult& result) {
+  Rooted<PropertyDescriptor> desc(cx, PropertyDescriptor::Data(value, attrs));
+  if (DefinePropertyOp op = obj->getOpsDefineProperty()) {
+    MOZ_ASSERT(!cx->isHelperThreadContext());
+    return op(cx, obj, id, desc, result);
+  }
+  return NativeDefineProperty(cx, obj.as<NativeObject>(), id, desc, result);
+}
+
+bool js::DefineAccessorProperty(JSContext* cx, HandleObject obj, HandleId id,
+                                HandleObject getter, HandleObject setter,
+                                unsigned attrs) {
+  ObjectOpResult result;
+  if (!DefineAccessorProperty(cx, obj, id, getter, setter, attrs, result)) {
+    return false;
+  }
+  if (!result) {
+    MOZ_ASSERT(!cx->isHelperThreadContext());
+    result.reportError(cx, obj, id);
+    return false;
+  }
+  return true;
+}
+
+bool js::DefineDataProperty(JSContext* cx, HandleObject obj, HandleId id,
+                            HandleValue value, unsigned attrs) {
+  ObjectOpResult result;
+  if (!DefineDataProperty(cx, obj, id, value, attrs, result)) {
+    return false;
+  }
+  if (!result) {
+    MOZ_ASSERT(!cx->isHelperThreadContext());
+    result.reportError(cx, obj, id);
+    return false;
+  }
+  return true;
+}
+
+bool js::DefineDataProperty(JSContext* cx, HandleObject obj, PropertyName* name,
+                            HandleValue value, unsigned attrs) {
+  RootedId id(cx, NameToId(name));
+  return DefineDataProperty(cx, obj, id, value, attrs);
+}
+
+bool js::DefineDataElement(JSContext* cx, HandleObject obj, uint32_t index,
+                           HandleValue value, unsigned attrs) {
+  RootedId id(cx);
+  if (!IndexToId(cx, index, &id)) {
+    return false;
+  }
+  return DefineDataProperty(cx, obj, id, value, attrs);
+}
+
+/*** SpiderMonkey nonstandard internal methods ******************************/
+
+// Mark an object as having an immutable prototype
+//
+// NOTE: This does not correspond to the SetImmutablePrototype ECMAScript
+//       method.
+bool js::SetImmutablePrototype(JSContext* cx, HandleObject obj,
+                               bool* succeeded) {
+  if (obj->hasDynamicPrototype()) {
+    MOZ_ASSERT(!cx->isHelperThreadContext());
+    return Proxy::setImmutablePrototype(cx, obj, succeeded);
+  }
+
+  if (!JSObject::setFlag(cx, obj, ObjectFlag::ImmutablePrototype)) {
+    return false;
+  }
+  *succeeded = true;
+  return true;
+}
+
+bool js::GetPropertyDescriptor(
+    JSContext* cx, HandleObject obj, HandleId id,
+    MutableHandle<mozilla::Maybe<PropertyDescriptor>> desc,
+    MutableHandleObject holder) {
+  RootedObject pobj(cx);
+  for (pobj = obj; pobj;) {
+    if (!GetOwnPropertyDescriptor(cx, pobj, id, desc)) {
+      return false;
+    }
+
+    if (desc.isSome()) {
+      holder.set(pobj);
+      return true;
+    }
+
+    if (!GetPrototype(cx, pobj, &pobj)) {
+      return false;
+    }
+  }
+
+  MOZ_ASSERT(desc.isNothing());
+  holder.set(nullptr);
+  return true;
+}
+
+/* * */
+
+extern bool PropertySpecNameToId(JSContext* cx, JSPropertySpec::Name name,
+                                 MutableHandleId id);
+
+// If a property or method is part of an experimental feature that can be
+// disabled at run-time by a preference, we keep it in the JSFunctionSpec /
+// JSPropertySpec list, but omit the definition if the preference is off.
+JS_PUBLIC_API bool js::ShouldIgnorePropertyDefinition(JSContext* cx,
+                                                      JSProtoKey key, jsid id) {
+  if (!cx->realm()->creationOptions().getToSourceEnabled() &&
+      (id == NameToId(cx->names().toSource) ||
+       id == NameToId(cx->names().uneval))) {
+    return true;
+  }
+
+  if (key == JSProto_FinalizationRegistry &&
+      cx->realm()->creationOptions().getWeakRefsEnabled() ==
+          JS::WeakRefSpecifier::EnabledWithoutCleanupSome &&
+      id == NameToId(cx->names().cleanupSome)) {
+    return true;
+  }
+
+#ifdef NIGHTLY_BUILD
+  if (key == JSProto_Array &&
+      !cx->realm()->creationOptions().getArrayGroupingEnabled() &&
+      (id == NameToId(cx->names().group) ||
+       id == NameToId(cx->names().groupToMap))) {
+    return true;
+  }
+#endif
+
+  // It's gently surprising that this is JSProto_Function, but the trick
+  // to realize is that this is a -constructor function-, not a function
+  // on the prototype; and the proto of the constructor is JSProto_Function.
+  if (key == JSProto_Function &&
+      !cx->realm()->creationOptions().getArrayFromAsyncEnabled() &&
+      id == NameToId(cx->names().fromAsync)) {
+    return true;
+  }
+
+  if (key == JSProto_Array &&
+      !cx->realm()->creationOptions().getChangeArrayByCopyEnabled() &&
+      (id == NameToId(cx->names().with) ||
+       id == NameToId(cx->names().toReversed) ||
+       id == NameToId(cx->names().toSorted) ||
+       id == NameToId(cx->names().toSpliced))) {
+    return true;
+  }
+
+  if (key == JSProto_TypedArray &&
+      !cx->realm()->creationOptions().getChangeArrayByCopyEnabled() &&
+      (id == NameToId(cx->names().with) ||
+       id == NameToId(cx->names().toReversed) ||
+       id == NameToId(cx->names().toSorted))) {
+    return true;
+  }
+
+#ifdef ENABLE_NEW_SET_METHODS
+  if (key == JSProto_Set &&
+      !cx->realm()->creationOptions().getNewSetMethodsEnabled() &&
+      (id == NameToId(cx->names().union_) ||
+       id == NameToId(cx->names().difference) ||
+       id == NameToId(cx->names().intersection) ||
+       id == NameToId(cx->names().isSubsetOf) ||
+       id == NameToId(cx->names().isSupersetOf) ||
+       id == NameToId(cx->names().isDisjointFrom) ||
+       id == NameToId(cx->names().symmetricDifference))) {
+    return true;
+  }
+#endif
+
+  return false;
+}
+
+static bool DefineFunctionFromSpec(JSContext* cx, HandleObject obj,
+                                   const JSFunctionSpec* fs) {
+  RootedId id(cx);
+  if (!PropertySpecNameToId(cx, fs->name, &id)) {
+    return false;
+  }
+
+  if (ShouldIgnorePropertyDefinition(cx, StandardProtoKeyOrNull(obj), id)) {
+    return true;
+  }
+
+  JSFunction* fun = NewFunctionFromSpec(cx, fs, id);
+  if (!fun) {
+    return false;
+  }
+
+  RootedValue funVal(cx, ObjectValue(*fun));
+  return DefineDataProperty(cx, obj, id, funVal, fs->flags & ~JSFUN_FLAGS_MASK);
+}
+
+bool js::DefineFunctions(JSContext* cx, HandleObject obj,
+                         const JSFunctionSpec* fs) {
+  for (; fs->name; fs++) {
+    if (!DefineFunctionFromSpec(cx, obj, fs)) {
+      return false;
+    }
+  }
+  return true;
+}
+
+/*** ToPrimitive ************************************************************/
+
+/*
+ * Gets |obj[id]|.  If that value's not callable, returns true and stores an
+ * object value in *vp.  If it's callable, calls it with no arguments and |obj|
+ * as |this|, returning the result in *vp.
+ *
+ * This is a mini-abstraction for ES6 draft rev 36 (2015 Mar 17),
+ * 7.1.1, second algorithm (OrdinaryToPrimitive), steps 5.a-c.
+ */
+static bool MaybeCallMethod(JSContext* cx, HandleObject obj, HandleId id,
+                            MutableHandleValue vp) {
+  if (!GetProperty(cx, obj, obj, id, vp)) {
+    return false;
+  }
+  if (!IsCallable(vp)) {
+    vp.setObject(*obj);
+    return true;
+  }
+
+  return js::Call(cx, vp, obj, vp);
+}
+
+static bool ReportCantConvert(JSContext* cx, unsigned errorNumber,
+                              HandleObject obj, JSType hint) {
+  const JSClass* clasp = obj->getClass();
+
+  // Avoid recursive death when decompiling in ReportValueError.
+  RootedString str(cx);
+  if (hint == JSTYPE_STRING) {
+    str = JS_AtomizeString(cx, clasp->name);
+    if (!str) {
+      return false;
+    }
+  } else {
+    str = nullptr;
+  }
+
+  RootedValue val(cx, ObjectValue(*obj));
+  ReportValueError(cx, errorNumber, JSDVG_SEARCH_STACK, val, str,
+                   hint == JSTYPE_UNDEFINED ? "primitive type"
+                   : hint == JSTYPE_STRING  ? "string"
+                                            : "number");
+  return false;
+}
+
+bool JS::OrdinaryToPrimitive(JSContext* cx, HandleObject obj, JSType hint,
+                             MutableHandleValue vp) {
+  MOZ_ASSERT(hint == JSTYPE_NUMBER || hint == JSTYPE_STRING ||
+             hint == JSTYPE_UNDEFINED);
+
+  Rooted<jsid> id(cx);
+
+  const JSClass* clasp = obj->getClass();
+  if (hint == JSTYPE_STRING) {
+    id = NameToId(cx->names().toString);
+
+    bool calledToString = false;
+    if (clasp == &StringObject::class_) {
+      // Optimize (new String(...)).toString().
+      StringObject* nobj = &obj->as<StringObject>();
+      if (HasNativeMethodPure(nobj, cx->names().toString, str_toString, cx)) {
+        vp.setString(nobj->unbox());
+        return true;
+      }
+    } else if (clasp == &PlainObject::class_) {
+      JSFunction* fun;
+      if (GetPropertyPure(cx, obj, id, vp.address()) &&
+          IsFunctionObject(vp, &fun)) {
+        // Common case: we have a toString function. Try to short-circuit if
+        // it's Object.prototype.toString and there's no @@toStringTag.
+        if (fun->maybeNative() == obj_toString &&
+            !MaybeHasInterestingSymbolProperty(
+                cx, obj, cx->wellKnownSymbols().toStringTag)) {
+          vp.setString(cx->names().objectObject);
+          return true;
+        }
+        if (!js::Call(cx, vp, obj, vp)) {
+          return false;
+        }
+        calledToString = true;
+      }
+    }
+
+    if (!calledToString) {
+      if (!MaybeCallMethod(cx, obj, id, vp)) {
+        return false;
+      }
+    }
+    if (vp.isPrimitive()) {
+      return true;
+    }
+
+    id = NameToId(cx->names().valueOf);
+    if (!MaybeCallMethod(cx, obj, id, vp)) {
+      return false;
+    }
+    if (vp.isPrimitive()) {
+      return true;
+    }
+  } else {
+    id = NameToId(cx->names().valueOf);
+
+    if (clasp == &StringObject::class_) {
+      // Optimize new String(...).valueOf().
+      StringObject* nobj = &obj->as<StringObject>();
+      if (HasNativeMethodPure(nobj, cx->names().valueOf, str_toString, cx)) {
+        vp.setString(nobj->unbox());
+        return true;
+      }
+    } else if (clasp == &NumberObject::class_) {
+      // Optimize new Number(...).valueOf().
+      NumberObject* nobj = &obj->as<NumberObject>();
+      if (HasNativeMethodPure(nobj, cx->names().valueOf, num_valueOf, cx)) {
+        vp.setNumber(nobj->unbox());
+        return true;
+      }
+    }
+
+    if (!MaybeCallMethod(cx, obj, id, vp)) {
+      return false;
+    }
+    if (vp.isPrimitive()) {
+      return true;
+    }
+
+    id = NameToId(cx->names().toString);
+    if (!MaybeCallMethod(cx, obj, id, vp)) {
+      return false;
+    }
+    if (vp.isPrimitive()) {
+      return true;
+    }
+  }
+
+  return ReportCantConvert(cx, JSMSG_CANT_CONVERT_TO, obj, hint);
+}
+
+bool js::ToPrimitiveSlow(JSContext* cx, JSType preferredType,
+                         MutableHandleValue vp) {
+  // Step numbers refer to the first algorithm listed in ES6 draft rev 36
+  // (2015 Mar 17) 7.1.1 ToPrimitive.
+  MOZ_ASSERT(preferredType == JSTYPE_UNDEFINED ||
+             preferredType == JSTYPE_STRING || preferredType == JSTYPE_NUMBER);
+  RootedObject obj(cx, &vp.toObject());
+
+  // Steps 4-5.
+  RootedValue method(cx);
+  if (!GetInterestingSymbolProperty(cx, obj, cx->wellKnownSymbols().toPrimitive,
+                                    &method)) {
+    return false;
+  }
+
+  // Step 6.
+  if (!method.isNullOrUndefined()) {
+    // Step 6 of GetMethod. js::Call() below would do this check and throw a
+    // TypeError anyway, but this produces a better error message.
+    if (!IsCallable(method)) {
+      return ReportCantConvert(cx, JSMSG_TOPRIMITIVE_NOT_CALLABLE, obj,
+                               preferredType);
+    }
+
+    // Steps 1-3, 6.a-b.
+    RootedValue arg0(
+        cx,
+        StringValue(preferredType == JSTYPE_STRING   ? cx->names().string
+                    : preferredType == JSTYPE_NUMBER ? cx->names().number
+                                                     : cx->names().default_));
+
+    if (!js::Call(cx, method, vp, arg0, vp)) {
+      return false;
+    }
+
+    // Steps 6.c-d.
+    if (vp.isObject()) {
+      return ReportCantConvert(cx, JSMSG_TOPRIMITIVE_RETURNED_OBJECT, obj,
+                               preferredType);
+    }
+    return true;
+  }
+
+  return OrdinaryToPrimitive(cx, obj, preferredType, vp);
+}
+
+/* ES6 draft rev 28 (2014 Oct 14) 7.1.14 */
+bool js::ToPropertyKeySlow(JSContext* cx, HandleValue argument,
+                           MutableHandleId result) {
+  MOZ_ASSERT(argument.isObject());
+
+  // Steps 1-2.
+  RootedValue key(cx, argument);
+  if (!ToPrimitiveSlow(cx, JSTYPE_STRING, &key)) {
+    return false;
+  }
+
+  // Steps 3-4.
+  return PrimitiveValueToId<CanGC>(cx, key, result);
+}
+
+/* * */
+
+bool js::IsPrototypeOf(JSContext* cx, HandleObject protoObj, JSObject* obj,
+                       bool* result) {
+  RootedObject obj2(cx, obj);
+  for (;;) {
+    // The [[Prototype]] chain might be cyclic.
+    if (!CheckForInterrupt(cx)) {
+      return false;
+    }
+    if (!GetPrototype(cx, obj2, &obj2)) {
+      return false;
+    }
+    if (!obj2) {
+      *result = false;
+      return true;
+    }
+    if (obj2 == protoObj) {
+      *result = true;
+      return true;
+    }
+  }
+}
+
+JSObject* js::PrimitiveToObject(JSContext* cx, const Value& v) {
+  MOZ_ASSERT(v.isPrimitive());
+
+  switch (v.type()) {
+    case ValueType::String: {
+      Rooted<JSString*> str(cx, v.toString());
+      return StringObject::create(cx, str);
+    }
+    case ValueType::Double:
+    case ValueType::Int32:
+      return NumberObject::create(cx, v.toNumber());
+    case ValueType::Boolean:
+      return BooleanObject::create(cx, v.toBoolean());
+    case ValueType::Symbol: {
+      RootedSymbol symbol(cx, v.toSymbol());
+      return SymbolObject::create(cx, symbol);
+    }
+    case ValueType::BigInt: {
+      RootedBigInt bigInt(cx, v.toBigInt());
+      return BigIntObject::create(cx, bigInt);
+    }
+#ifdef ENABLE_RECORD_TUPLE
+    case ValueType::ExtendedPrimitive: {
+      JSObject& obj = v.toExtendedPrimitive();
+
+      if (obj.is<RecordType>()) {
+        Rooted<RecordType*> rec(cx, &obj.as<RecordType>());
+        return RecordObject::create(cx, rec);
+      }
+      if (obj.is<TupleType>()) {
+        Rooted<TupleType*> tuple(cx, &obj.as<TupleType>());
+        return TupleObject::create(cx, tuple);
+      }
+
+      MOZ_CRASH("Unexpected ExtendedPrimitive type.");
+    }
+#endif
+    case ValueType::Undefined:
+    case ValueType::Null:
+    case ValueType::Magic:
+    case ValueType::PrivateGCThing:
+    case ValueType::Object:
+      break;
+  }
+
+  MOZ_CRASH("unexpected type");
+}
+
+// Like PrimitiveToObject, but returns the JSProtoKey of the prototype that
+// would be used without actually creating the object.
+JSProtoKey js::PrimitiveToProtoKey(JSContext* cx, const Value& v) {
+  MOZ_ASSERT(v.isPrimitive());
+
+  switch (v.type()) {
+    case ValueType::String:
+      return JSProto_String;
+    case ValueType::Double:
+    case ValueType::Int32:
+      return JSProto_Number;
+    case ValueType::Boolean:
+      return JSProto_Boolean;
+    case ValueType::Symbol:
+      return JSProto_Symbol;
+    case ValueType::BigInt:
+      return JSProto_BigInt;
+#ifdef ENABLE_RECORD_TUPLE
+    case ValueType::ExtendedPrimitive:
+      if (v.toExtendedPrimitive().is<TupleType>()) {
+        return JSProto_Tuple;
+      }
+      if (v.toExtendedPrimitive().is<RecordType>()) {
+        return JSProto_Null;
+      }
+      MOZ_CRASH("Unsupported ExtendedPrimitive");
+#endif
+    case ValueType::Undefined:
+    case ValueType::Null:
+    case ValueType::Magic:
+    case ValueType::PrivateGCThing:
+    case ValueType::Object:
+      break;
+  }
+
+  MOZ_CRASH("unexpected type");
+}
+
+/*
+ * Invokes the ES5 ToObject algorithm on vp, returning the result. If vp might
+ * already be an object, use ToObject. reportScanStack controls how null and
+ * undefined errors are reported.
+ *
+ * Callers must handle the already-object case.
+ */
+JSObject* js::ToObjectSlow(JSContext* cx, JS::HandleValue val,
+                           bool reportScanStack) {
+  MOZ_ASSERT(!val.isMagic());
+  MOZ_ASSERT(!val.isObject());
+
+  if (val.isNullOrUndefined()) {
+    ReportIsNullOrUndefinedForPropertyAccess(
+        cx, val, reportScanStack ? JSDVG_SEARCH_STACK : JSDVG_IGNORE_STACK);
+    return nullptr;
+  }
+
+  return PrimitiveToObject(cx, val);
+}
+
+JSObject* js::ToObjectSlowForPropertyAccess(JSContext* cx, JS::HandleValue val,
+                                            int valIndex, HandleId key) {
+  MOZ_ASSERT(!val.isMagic());
+  MOZ_ASSERT(!val.isObject());
+
+  if (val.isNullOrUndefined()) {
+    ReportIsNullOrUndefinedForPropertyAccess(cx, val, valIndex, key);
+    return nullptr;
+  }
+
+  return PrimitiveToObject(cx, val);
+}
+
+JSObject* js::ToObjectSlowForPropertyAccess(JSContext* cx, JS::HandleValue val,
+                                            int valIndex,
+                                            Handle<PropertyName*> key) {
+  MOZ_ASSERT(!val.isMagic());
+  MOZ_ASSERT(!val.isObject());
+
+  if (val.isNullOrUndefined()) {
+    RootedId keyId(cx, NameToId(key));
+    ReportIsNullOrUndefinedForPropertyAccess(cx, val, valIndex, keyId);
+    return nullptr;
+  }
+
+  return PrimitiveToObject(cx, val);
+}
+
+JSObject* js::ToObjectSlowForPropertyAccess(JSContext* cx, JS::HandleValue val,
+                                            int valIndex,
+                                            HandleValue keyValue) {
+  MOZ_ASSERT(!val.isMagic());
+  MOZ_ASSERT(!val.isObject());
+
+  if (val.isNullOrUndefined()) {
+    RootedId key(cx);
+    if (keyValue.isPrimitive()) {
+      if (!PrimitiveValueToId<CanGC>(cx, keyValue, &key)) {
+        return nullptr;
+      }
+      ReportIsNullOrUndefinedForPropertyAccess(cx, val, valIndex, key);
+    } else {
+      ReportIsNullOrUndefinedForPropertyAccess(cx, val, valIndex);
+    }
+    return nullptr;
+  }
+
+  return PrimitiveToObject(cx, val);
+}
+
+JSObject* js::GetThisObject(JSObject* obj) {
+  // Use the WindowProxy if the global is a Window, as Window must never be
+  // exposed to script.
+  if (obj->is<GlobalObject>()) {
+    return ToWindowProxyIfWindow(obj);
+  }
+
+  // We should not expose any environments except NSVOs to script. The NSVO is
+  // pretending to be the global object in this case.
+  MOZ_ASSERT(obj->is<NonSyntacticVariablesObject>() ||
+             !obj->is<EnvironmentObject>());
+
+  return obj;
+}
+
+JSObject* js::GetThisObjectOfLexical(JSObject* env) {
+  return env->as<ExtensibleLexicalEnvironmentObject>().thisObject();
+}
+
+JSObject* js::GetThisObjectOfWith(JSObject* env) {
+  MOZ_ASSERT(env->is<WithEnvironmentObject>());
+  return GetThisObject(env->as<WithEnvironmentObject>().withThis());
+}
+
+class GetObjectSlotNameFunctor : public JS::TracingContext::Functor {
+  JSObject* obj;
+
+ public:
+  explicit GetObjectSlotNameFunctor(JSObject* ctx) : obj(ctx) {}
+  virtual void operator()(JS::TracingContext* trc, char* buf,
+                          size_t bufsize) override;
+};
+
+void GetObjectSlotNameFunctor::operator()(JS::TracingContext* tcx, char* buf,
+                                          size_t bufsize) {
+  MOZ_ASSERT(tcx->index() != JS::TracingContext::InvalidIndex);
+
+  uint32_t slot = uint32_t(tcx->index());
+
+  Maybe<PropertyKey> key;
+  if (obj->is<NativeObject>()) {
+    NativeShape* shape = obj->as<NativeObject>().shape();
+    for (ShapePropertyIter<NoGC> iter(shape); !iter.done(); iter++) {
+      if (iter->hasSlot() && iter->slot() == slot) {
+        key.emplace(iter->key());
+        break;
+      }
+    }
+  }
+
+  if (key.isNothing()) {
+    do {
+      const char* slotname = nullptr;
+      const char* pattern = nullptr;
+      if (obj->is<GlobalObject>()) {
+        pattern = "CLASS_OBJECT(%s)";
+        if (false) {
+          ;
+        }
+#define TEST_SLOT_MATCHES_PROTOTYPE(name, clasp) \
+  else if ((JSProto_##name) == slot) {           \
+    slotname = js_##name##_str;                  \
+  }
+        JS_FOR_EACH_PROTOTYPE(TEST_SLOT_MATCHES_PROTOTYPE)
+#undef TEST_SLOT_MATCHES_PROTOTYPE
+      } else {
+        pattern = "%s";
+        if (obj->is<EnvironmentObject>()) {
+          if (slot == EnvironmentObject::enclosingEnvironmentSlot()) {
+            slotname = "enclosing_environment";
+          } else if (obj->is<CallObject>()) {
+            if (slot == CallObject::calleeSlot()) {
+              slotname = "callee_slot";
+            }
+          } else if (obj->is<WithEnvironmentObject>()) {
+            if (slot == WithEnvironmentObject::objectSlot()) {
+              slotname = "with_object";
+            } else if (slot == WithEnvironmentObject::thisSlot()) {
+              slotname = "with_this";
+            }
+          }
+        }
+      }
+
+      if (slotname) {
+        snprintf(buf, bufsize, pattern, slotname);
+      } else {
+        snprintf(buf, bufsize, "**UNKNOWN SLOT %" PRIu32 "**", slot);
+      }
+    } while (false);
+  } else {
+    if (key->isInt()) {
+      snprintf(buf, bufsize, "%" PRId32, key->toInt());
+    } else if (key->isAtom()) {
+      PutEscapedString(buf, bufsize, key->toAtom(), 0);
+    } else if (key->isSymbol()) {
+      snprintf(buf, bufsize, "**SYMBOL KEY**");
+    } else {
+      snprintf(buf, bufsize, "**FINALIZED ATOM KEY**");
+    }
+  }
+}
+
+/*** Debugging routines *****************************************************/
+
+#if defined(DEBUG) || defined(JS_JITSPEW)
+
+/*
+ * Routines to print out values during debugging.  These are FRIEND_API to help
+ * the debugger find them and to support temporarily hacking js::Dump* calls
+ * into other code.
+ */
+
+static void dumpValue(const Value& v, js::GenericPrinter& out) {
+  switch (v.type()) {
+    case ValueType::Null:
+      out.put("null");
+      break;
+    case ValueType::Undefined:
+      out.put("undefined");
+      break;
+    case ValueType::Int32:
+      out.printf("%d", v.toInt32());
+      break;
+    case ValueType::Double:
+      out.printf("%g", v.toDouble());
+      break;
+    case ValueType::String:
+      v.toString()->dumpNoNewline(out);
+      break;
+    case ValueType::Symbol:
+      v.toSymbol()->dump(out);
+      break;
+    case ValueType::BigInt:
+      v.toBigInt()->dump(out);
+      break;
+    case ValueType::Object:
+      if (v.toObject().is<JSFunction>()) {
+        JSFunction* fun = &v.toObject().as<JSFunction>();
+        if (fun->displayAtom()) {
+          out.put("<function ");
+          EscapedStringPrinter(out, fun->displayAtom(), 0);
+        } else {
+          out.put("<unnamed function");
+        }
+        if (fun->hasBaseScript()) {
+          BaseScript* script = fun->baseScript();
+          out.printf(" (%s:%u)", script->filename() ? script->filename() : "",
+                     script->lineno());
+        }
+        out.printf(" at %p>", (void*)fun);
+      } else {
+        JSObject* obj = &v.toObject();
+        const JSClass* clasp = obj->getClass();
+        out.printf("<%s%s at %p>", clasp->name,
+                   (clasp == &PlainObject::class_) ? "" : " object",
+                   (void*)obj);
+      }
+      break;
+#  ifdef ENABLE_RECORD_TUPLE
+    case ValueType::ExtendedPrimitive: {
+      JSObject* obj = &v.toExtendedPrimitive();
+      out.printf("<%s at %p>", obj->getClass()->name, (void*)obj);
+      break;
+    }
+#  endif
+    case ValueType::Boolean:
+      if (v.toBoolean()) {
+        out.put("true");
+      } else {
+        out.put("false");
+      }
+      break;
+    case ValueType::Magic:
+      out.put("<magic");
+      switch (v.whyMagic()) {
+        case JS_ELEMENTS_HOLE:
+          out.put(" elements hole");
+          break;
+        case JS_NO_ITER_VALUE:
+          out.put(" no iter value");
+          break;
+        case JS_GENERATOR_CLOSING:
+          out.put(" generator closing");
+          break;
+        case JS_OPTIMIZED_OUT:
+          out.put(" optimized out");
+          break;
+        default:
+          out.put(" ?!");
+          break;
+      }
+      out.putChar('>');
+      break;
+    case ValueType::PrivateGCThing:
+      out.printf("<PrivateGCThing %p>", v.toGCThing());
+      break;
+  }
+}
+
+namespace js {
+
+// We don't want jsfriendapi.h to depend on GenericPrinter,
+// so these functions are declared directly in the cpp.
+
+JS_PUBLIC_API void DumpValue(const JS::Value& val, js::GenericPrinter& out);
+
+JS_PUBLIC_API void DumpId(jsid id, js::GenericPrinter& out);
+
+JS_PUBLIC_API void DumpInterpreterFrame(JSContext* cx, js::GenericPrinter& out,
+                                        InterpreterFrame* start = nullptr);
+
+}  // namespace js
+
+JS_PUBLIC_API void js::DumpValue(const Value& val, js::GenericPrinter& out) {
+  dumpValue(val, out);
+  out.putChar('\n');
+}
+
+JS_PUBLIC_API void js::DumpId(jsid id, js::GenericPrinter& out) {
+  out.printf("jsid %p = ", (void*)id.asRawBits());
+  dumpValue(IdToValue(id), out);
+  out.putChar('\n');
+}
+
+static void DumpProperty(const NativeObject* obj, PropMap* map, uint32_t index,
+                         js::GenericPrinter& out) {
+  PropertyInfoWithKey prop = map->getPropertyInfoWithKey(index);
+  jsid id = prop.key();
+  if (id.isAtom()) {
+    id.toAtom()->dumpCharsNoNewline(out);
+  } else if (id.isInt()) {
+    out.printf("%d", id.toInt());
+  } else if (id.isSymbol()) {
+    id.toSymbol()->dump(out);
+  } else {
+    out.printf("id %p", reinterpret_cast<void*>(id.asRawBits()));
+  }
+
+  if (prop.isDataProperty()) {
+    out.printf(": ");
+    dumpValue(obj->getSlot(prop.slot()), out);
+  } else if (prop.isAccessorProperty()) {
+    out.printf(": getter %p setter %p", obj->getGetter(prop),
+               obj->getSetter(prop));
+  }
+
+  out.printf(" (map %p/%u", map, index);
+
+  if (prop.enumerable()) {
+    out.put(" enumerable");
+  }
+  if (prop.configurable()) {
+    out.put(" configurable");
+  }
+  if (prop.isDataDescriptor() && prop.writable()) {
+    out.put(" writable");
+  }
+
+  if (prop.isCustomDataProperty()) {
+    out.printf(" <custom-data-prop>");
+  }
+
+  if (prop.hasSlot()) {
+    out.printf(" slot %u", prop.slot());
+  }
+
+  out.printf(")\n");
+}
+
+bool JSObject::hasSameRealmAs(JSContext* cx) const {
+  return nonCCWRealm() == cx->realm();
+}
+
+bool JSObject::uninlinedIsProxyObject() const { return is<ProxyObject>(); }
+
+bool JSObject::uninlinedNonProxyIsExtensible() const {
+  return nonProxyIsExtensible();
+}
+
+void JSObject::dump(js::GenericPrinter& out) const {
+  const JSObject* obj = this;
+  out.printf("object %p\n", obj);
+
+  if (IsCrossCompartmentWrapper(this)) {
+    out.printf("  compartment %p\n", compartment());
+  } else {
+    JSObject* globalObj = &nonCCWGlobal();
+    out.printf("  global %p [%s]\n", globalObj, globalObj->getClass()->name);
+  }
+
+  const JSClass* clasp = obj->getClass();
+  out.printf("  class %p %s\n", clasp, clasp->name);
+
+  if (IsProxy(obj)) {
+    auto* handler = GetProxyHandler(obj);
+    out.printf("    handler %p", handler);
+    if (IsDeadProxyObject(obj)) {
+      out.printf(" (DeadObjectProxy)");
+    } else if (IsCrossCompartmentWrapper(obj)) {
+      out.printf(" (CCW)");
+    }
+    out.putChar('\n');
+
+    Value priv = GetProxyPrivate(obj);
+    if (!priv.isUndefined()) {
+      out.printf("    private ");
+      dumpValue(priv, out);
+      out.putChar('\n');
+    }
+
+    Value expando = GetProxyExpando(obj);
+    if (!expando.isNull()) {
+      out.printf("    expando ");
+      dumpValue(expando, out);
+      out.putChar('\n');
+    }
+  }
+
+  const Shape* shape = obj->shape();
+  out.printf("  shape %p\n", shape);
+
+  out.put("  flags:");
+  if (obj->isUsedAsPrototype()) {
+    out.put(" used_as_prototype");
+  }
+  if (!obj->is<ProxyObject>() && !obj->nonProxyIsExtensible()) {
+    out.put(" not_extensible");
+  }
+  if (obj->maybeHasInterestingSymbolProperty()) {
+    out.put(" maybe_has_interesting_symbol");
+  }
+  if (obj->isQualifiedVarObj()) {
+    out.put(" varobj");
+  }
+  if (obj->isUnqualifiedVarObj()) {
+    out.put(" unqualified_varobj");
+  }
+  if (obj->hasInvalidatedTeleporting()) {
+    out.put(" invalidated_teleporting");
+  }
+  if (obj->hasStaticPrototype() && obj->staticPrototypeIsImmutable()) {
+    out.put(" immutable_prototype");
+  }
+
+  const NativeObject* nobj =
+      obj->is<NativeObject>() ? &obj->as<NativeObject>() : nullptr;
+  if (nobj) {
+    if (nobj->inDictionaryMode()) {
+      out.put(" inDictionaryMode");
+    }
+    if (nobj->hadGetterSetterChange()) {
+      out.put(" had_getter_setter_change");
+    }
+    if (nobj->isIndexed()) {
+      out.put(" indexed");
+    }
+    if (nobj->hasEnumerableProperty()) {
+      out.put(" has_enumerable");
+    }
+    if (nobj->is<PlainObject>() &&
+        nobj->as<PlainObject>().hasNonWritableOrAccessorPropExclProto()) {
+      out.put(" has_non_writable_or_accessor_prop_excl_proto");
+    }
+    if (!nobj->denseElementsArePacked()) {
+      out.put(" non_packed_elements");
+    }
+    if (nobj->getElementsHeader()->isNotExtensible()) {
+      out.put(" not_extensible");
+    }
+    if (nobj->getElementsHeader()->isSealed()) {
+      out.put(" sealed_elements");
+    }
+    if (nobj->getElementsHeader()->isFrozen()) {
+      out.put(" frozen_elements");
+    }
+    if (nobj->getElementsHeader()->maybeInIteration()) {
+      out.put(" elements_maybe_in_iteration");
+    }
+  } else {
+    out.put(" not_native");
+  }
+  out.putChar('\n');
+
+  out.put("  proto ");
+  TaggedProto proto = obj->taggedProto();
+  if (proto.isDynamic()) {
+    out.put("<dynamic>");
+  } else {
+    dumpValue(ObjectOrNullValue(proto.toObjectOrNull()), out);
+  }
+  out.putChar('\n');
+
+  if (nobj) {
+    uint32_t reserved = JSCLASS_RESERVED_SLOTS(clasp);
+    if (reserved) {
+      out.printf("  reserved slots:\n");
+      for (uint32_t i = 0; i < reserved; i++) {
+        out.printf("    %3u ", i);
+        out.put(": ");
+        dumpValue(nobj->getSlot(i), out);
+        out.putChar('\n');
+      }
+    }
+
+    out.put("  properties:\n");
+
+    if (PropMap* map = nobj->shape()->propMap()) {
+      Vector<PropMap*, 8, SystemAllocPolicy> maps;
+      while (true) {
+        if (!maps.append(map)) {
+          out.printf("(OOM while appending maps)\n");
+          break;
+        }
+        if (!map->hasPrevious()) {
+          break;
+        }
+        map = map->asLinked()->previous();
+      }
+
+      for (size_t i = maps.length(); i > 0; i--) {
+        size_t index = i - 1;
+        uint32_t len =
+            (index == 0) ? nobj->shape()->propMapLength() : PropMap::Capacity;
+        for (uint32_t j = 0; j < len; j++) {
+          PropMap* map = maps[index];
+          if (!map->hasKey(j)) {
+            MOZ_ASSERT(map->isDictionary());
+            continue;
+          }
+          out.printf("    ");
+          DumpProperty(nobj, map, j, out);
+        }
+      }
+    }
+
+    uint32_t slots = nobj->getDenseInitializedLength();
+    if (slots) {
+      out.put("  elements:\n");
+      for (uint32_t i = 0; i < slots; i++) {
+        out.printf("    %3u: ", i);
+        dumpValue(nobj->getDenseElement(i), out);
+        out.putChar('\n');
+      }
+    }
+  }
+}
+
+// For debuggers.
+void JSObject::dump() const {
+  Fprinter out(stderr);
+  dump(out);
+}
+
+static void MaybeDumpScope(Scope* scope, js::GenericPrinter& out) {
+  if (scope) {
+    out.printf("  scope: %s\n", ScopeKindString(scope->kind()));
+    for (BindingIter bi(scope); bi; bi++) {
+      out.put("    ");
+      dumpValue(StringValue(bi.name()), out);
+      out.putChar('\n');
+    }
+  }
+}
+
+static void MaybeDumpValue(const char* name, const Value& v,
+                           js::GenericPrinter& out) {
+  if (!v.isNull()) {
+    out.printf("  %s: ", name);
+    dumpValue(v, out);
+    out.putChar('\n');
+  }
+}
+
+JS_PUBLIC_API void js::DumpInterpreterFrame(JSContext* cx,
+                                            js::GenericPrinter& out,
+                                            InterpreterFrame* start) {
+  /* This should only called during live debugging. */
+  ScriptFrameIter i(cx);
+  if (!start) {
+    if (i.done()) {
+      out.printf("no stack for cx = %p\n", (void*)cx);
+      return;
+    }
+  } else {
+    while (!i.done() && !i.isJSJit() && i.interpFrame() != start) {
+      ++i;
+    }
+
+    if (i.done()) {
+      out.printf("fp = %p not found in cx = %p\n", (void*)start, (void*)cx);
+      return;
+    }
+  }
+
+  for (; !i.done(); ++i) {
+    if (i.isJSJit()) {
+      out.put("JIT frame\n");
+    } else {
+      out.printf("InterpreterFrame at %p\n", (void*)i.interpFrame());
+    }
+
+    if (i.isFunctionFrame()) {
+      out.put("callee fun: ");
+      RootedValue v(cx);
+      JSObject* fun = i.callee(cx);
+      v.setObject(*fun);
+      dumpValue(v, out);
+    } else {
+      out.put("global or eval frame, no callee");
+    }
+    out.putChar('\n');
+
+    out.printf("file %s line %u\n", i.script()->filename(),
+               i.script()->lineno());
+
+    if (jsbytecode* pc = i.pc()) {
+      out.printf("  pc = %p\n", pc);
+      out.printf("  current op: %s\n", CodeName(JSOp(*pc)));
+      MaybeDumpScope(i.script()->lookupScope(pc), out);
+    }
+    if (i.isFunctionFrame()) {
+      MaybeDumpValue("this", i.thisArgument(cx), out);
+    }
+    if (!i.isJSJit()) {
+      out.put("  rval: ");
+      dumpValue(i.interpFrame()->returnValue(), out);
+      out.putChar('\n');
+    }
+
+    out.put("  flags:");
+    if (i.isConstructing()) {
+      out.put(" constructing");
+    }
+    if (!i.isJSJit() && i.interpFrame()->isDebuggerEvalFrame()) {
+      out.put(" debugger eval");
+    }
+    if (i.isEvalFrame()) {
+      out.put(" eval");
+    }
+    out.putChar('\n');
+
+    out.printf("  envChain: (JSObject*) %p\n", (void*)i.environmentChain(cx));
+
+    out.putChar('\n');
+  }
+}
+
+#endif /* defined(DEBUG) || defined(JS_JITSPEW) */
+
+JS_PUBLIC_API void js::DumpBacktrace(JSContext* cx, FILE* fp) {
+  Fprinter out(fp);
+  js::DumpBacktrace(cx, out);
+}
+
+JS_PUBLIC_API void js::DumpBacktrace(JSContext* cx, js::GenericPrinter& out) {
+  size_t depth = 0;
+  for (AllFramesIter i(cx); !i.done(); ++i, ++depth) {
+    const char* filename;
+    unsigned line;
+    if (i.hasScript()) {
+      filename = JS_GetScriptFilename(i.script());
+      line = PCToLineNumber(i.script(), i.pc());
+    } else {
+      filename = i.filename();
+      line = i.computeLine();
+    }
+    char frameType = i.isInterp()     ? 'i'
+                     : i.isBaseline() ? 'b'
+                     : i.isIon()      ? 'I'
+                     : i.isWasm()     ? 'W'
+                                      : '?';
+
+    out.printf("#%zu %14p %c   %s:%u", depth, i.rawFramePtr(), frameType,
+               filename, line);
+
+    if (i.hasScript()) {
+      out.printf(" (%p @ %zu)\n", i.script(), i.script()->pcToOffset(i.pc()));
+    } else {
+      out.printf(" (%p)\n", i.pc());
+    }
+  }
+}
+
+JS_PUBLIC_API void js::DumpBacktrace(JSContext* cx) {
+  DumpBacktrace(cx, stdout);
+}
+
+/* * */
+
+bool JSObject::isBackgroundFinalized() const {
+  if (isTenured()) {
+    return js::gc::IsBackgroundFinalized(asTenured().getAllocKind());
+  }
+
+  js::Nursery& nursery = runtimeFromMainThread()->gc.nursery();
+  return js::gc::IsBackgroundFinalized(allocKindForTenure(nursery));
+}
+
+js::gc::AllocKind JSObject::allocKindForTenure(
+    const js::Nursery& nursery) const {
+  using namespace js::gc;
+
+  MOZ_ASSERT(IsInsideNursery(this));
+
+  if (canHaveFixedElements()) {
+    const NativeObject& nobj = as<NativeObject>();
+    MOZ_ASSERT(nobj.numFixedSlots() == 0);
+
+    /* Use minimal size object if we are just going to copy the pointer. */
+    if (!nursery.isInside(nobj.getUnshiftedElementsHeader())) {
+      return gc::AllocKind::OBJECT0_BACKGROUND;
+    }
+
+    size_t nelements = nobj.getDenseCapacity();
+    return ForegroundToBackgroundAllocKind(GetGCArrayKind(nelements));
+  }
+
+  if (is<JSFunction>()) {
+    return as<JSFunction>().getAllocKind();
+  }
+
+  /*
+   * Typed arrays in the nursery may have a lazily allocated buffer, make
+   * sure there is room for the array's fixed data when moving the array.
+   */
+  if (is<TypedArrayObject>() && !as<TypedArrayObject>().hasBuffer()) {
+    gc::AllocKind allocKind;
+    if (as<TypedArrayObject>().hasInlineElements()) {
+      size_t nbytes = as<TypedArrayObject>().byteLength();
+      allocKind = TypedArrayObject::AllocKindForLazyBuffer(nbytes);
+    } else {
+      allocKind = GetGCObjectKind(getClass());
+    }
+    return ForegroundToBackgroundAllocKind(allocKind);
+  }
+
+  // Proxies that are CrossCompartmentWrappers may be nursery allocated.
+  if (is<ProxyObject>()) {
+    return as<ProxyObject>().allocKindForTenure();
+  }
+
+  // WasmStructObjects have a variable-length tail which contains the first
+  // few data fields, so make sure we copy it all over to the new object.
+  if (is<WasmStructObject>()) {
+    // Figure out the size of this object, from the object's TypeDef.
+    const wasm::TypeDef* typeDef = &as<WasmStructObject>().typeDef();
+    return WasmStructObject::allocKindForTypeDef(typeDef);
+  }
+
+  if (is<WasmArrayObject>()) {
+    return WasmArrayObject::allocKind();
+  }
+
+  // All nursery allocatable non-native objects are handled above.
+  return as<NativeObject>().allocKindForTenure();
+}
+
+void JSObject::addSizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf,
+                                      JS::ClassInfo* info,
+                                      JS::RuntimeSizes* runtimeSizes) {
+  if (is<NativeObject>() && as<NativeObject>().hasDynamicSlots()) {
+    info->objectsMallocHeapSlots +=
+        mallocSizeOf(as<NativeObject>().getSlotsHeader());
+  }
+
+  if (is<NativeObject>() && as<NativeObject>().hasDynamicElements()) {
+    void* allocatedElements = as<NativeObject>().getUnshiftedElementsHeader();
+    info->objectsMallocHeapElementsNormal += mallocSizeOf(allocatedElements);
+  }
+
+  // Other things may be measured in the future if DMD indicates it is
+  // worthwhile.
+  if (is<JSFunction>() || is<PlainObject>() || is<ArrayObject>() ||
+      is<CallObject>() || is<RegExpObject>() || is<ProxyObject>()) {
+    // Do nothing.  But this function is hot, and we win by getting the
+    // common cases out of the way early.  Some stats on the most common
+    // classes, as measured during a vanilla browser session:
+    // - (53.7%, 53.7%): Function
+    // - (18.0%, 71.7%): Object
+    // - (16.9%, 88.6%): Array
+    // - ( 3.9%, 92.5%): Call
+    // - ( 2.8%, 95.3%): RegExp
+    // - ( 1.0%, 96.4%): Proxy
+
+    // Note that any JSClass that is special cased below likely needs to
+    // specify the JSCLASS_DELAY_METADATA_BUILDER flag, or else we will
+    // probably crash if the object metadata callback attempts to get the
+    // size of the new object (which Debugger code does) before private
+    // slots are initialized.
+  } else if (is<ArgumentsObject>()) {
+    info->objectsMallocHeapMisc +=
+        as<ArgumentsObject>().sizeOfMisc(mallocSizeOf);
+  } else if (is<MapObject>()) {
+    info->objectsMallocHeapMisc += as<MapObject>().sizeOfData(mallocSizeOf);
+  } else if (is<SetObject>()) {
+    info->objectsMallocHeapMisc += as<SetObject>().sizeOfData(mallocSizeOf);
+  } else if (is<PropertyIteratorObject>()) {
+    info->objectsMallocHeapMisc +=
+        as<PropertyIteratorObject>().sizeOfMisc(mallocSizeOf);
+  } else if (is<ArrayBufferObject>()) {
+    ArrayBufferObject::addSizeOfExcludingThis(this, mallocSizeOf, info,
+                                              runtimeSizes);
+  } else if (is<SharedArrayBufferObject>()) {
+    SharedArrayBufferObject::addSizeOfExcludingThis(this, mallocSizeOf, info,
+                                                    runtimeSizes);
+  } else if (is<GlobalObject>()) {
+    as<GlobalObject>().addSizeOfData(mallocSizeOf, info);
+  } else if (is<WeakCollectionObject>()) {
+    info->objectsMallocHeapMisc +=
+        as<WeakCollectionObject>().sizeOfExcludingThis(mallocSizeOf);
+  }
+#ifdef JS_HAS_CTYPES
+  else {
+    // This must be the last case.
+    info->objectsMallocHeapMisc += ctypes::SizeOfDataIfCDataObject(
+        mallocSizeOf, const_cast<JSObject*>(this));
+  }
+#endif
+}
+
+size_t JSObject::sizeOfIncludingThisInNursery() const {
+  // This function doesn't concern itself yet with typed objects (bug 1133593).
+
+  MOZ_ASSERT(!isTenured());
+
+  const Nursery& nursery = runtimeFromMainThread()->gc.nursery();
+  size_t size = gc::Arena::thingSize(allocKindForTenure(nursery));
+
+  if (is<NativeObject>()) {
+    const NativeObject& native = as<NativeObject>();
+
+    size += native.numDynamicSlots() * sizeof(Value);
+
+    if (native.hasDynamicElements()) {
+      js::ObjectElements& elements = *native.getElementsHeader();
+      size += (elements.capacity + elements.numShiftedElements()) *
+              sizeof(HeapSlot);
+    }
+
+    if (is<ArgumentsObject>()) {
+      size += as<ArgumentsObject>().sizeOfData();
+    }
+  }
+
+  return size;
+}
+
+JS::ubi::Node::Size JS::ubi::Concrete<JSObject>::size(
+    mozilla::MallocSizeOf mallocSizeOf) const {
+  JSObject& obj = get();
+
+  if (!obj.isTenured()) {
+    return obj.sizeOfIncludingThisInNursery();
+  }
+
+  JS::ClassInfo info;
+  obj.addSizeOfExcludingThis(mallocSizeOf, &info, nullptr);
+  return obj.tenuredSizeOfThis() + info.sizeOfAllThings();
+}
+
+const char16_t JS::ubi::Concrete<JSObject>::concreteTypeName[] = u"JSObject";
+
+void JSObject::traceChildren(JSTracer* trc) {
+  TraceCellHeaderEdge(trc, this, "shape");
+
+  Shape* objShape = shape();
+  if (objShape->isNative()) {
+    NativeObject* nobj = &as<NativeObject>();
+
+    {
+      GetObjectSlotNameFunctor func(nobj);
+      JS::AutoTracingDetails ctx(trc, func);
+      JS::AutoTracingIndex index(trc);
+      // Tracing can mutate the target but cannot change the slot count,
+      // but the compiler has no way of knowing this.
+      const uint32_t nslots = nobj->slotSpan();
+      for (uint32_t i = 0; i < nslots; ++i) {
+        TraceEdge(trc, &nobj->getSlotRef(i), "object slot");
+        ++index;
+      }
+      MOZ_ASSERT(nslots == nobj->slotSpan());
+    }
+
+    TraceRange(trc, nobj->getDenseInitializedLength(),
+               static_cast<HeapSlot*>(nobj->getDenseElements()),
+               "objectElements");
+  }
+
+  // Call the trace hook at the end so that during a moving GC the trace hook
+  // will see updated fields and slots.
+  const JSClass* clasp = objShape->getObjectClass();
+  if (clasp->hasTrace()) {
+    clasp->doTrace(trc, this);
+  }
+}
+
+// ES 2016 7.3.20.
+[[nodiscard]] JSObject* js::SpeciesConstructor(
+    JSContext* cx, HandleObject obj, HandleObject defaultCtor,
+    bool (*isDefaultSpecies)(JSContext*, JSFunction*)) {
+  // Step 1 (implicit).
+
+  // Fast-path for steps 2 - 8. Applies if all of the following conditions
+  // are met:
+  // - obj.constructor can be retrieved without side-effects.
+  // - obj.constructor[[@@species]] can be retrieved without side-effects.
+  // - obj.constructor[[@@species]] is the builtin's original @@species
+  //   getter.
+  RootedValue ctor(cx);
+  bool ctorGetSucceeded = GetPropertyPure(
+      cx, obj, NameToId(cx->names().constructor), ctor.address());
+  if (ctorGetSucceeded && ctor.isObject() && &ctor.toObject() == defaultCtor) {
+    jsid speciesId = PropertyKey::Symbol(cx->wellKnownSymbols().species);
+    JSFunction* getter;
+    if (GetGetterPure(cx, defaultCtor, speciesId, &getter) && getter &&
+        isDefaultSpecies(cx, getter)) {
+      return defaultCtor;
+    }
+  }
+
+  // Step 2.
+  if (!ctorGetSucceeded &&
+      !GetProperty(cx, obj, obj, cx->names().constructor, &ctor)) {
+    return nullptr;
+  }
+
+  // Step 3.
+  if (ctor.isUndefined()) {
+    return defaultCtor;
+  }
+
+  // Step 4.
+  if (!ctor.isObject()) {
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                              JSMSG_OBJECT_REQUIRED,
+                              "object's 'constructor' property");
+    return nullptr;
+  }
+
+  // Step 5.
+  RootedObject ctorObj(cx, &ctor.toObject());
+  RootedValue s(cx);
+  RootedId speciesId(cx, PropertyKey::Symbol(cx->wellKnownSymbols().species));
+  if (!GetProperty(cx, ctorObj, ctor, speciesId, &s)) {
+    return nullptr;
+  }
+
+  // Step 6.
+  if (s.isNullOrUndefined()) {
+    return defaultCtor;
+  }
+
+  // Step 7.
+  if (IsConstructor(s)) {
+    return &s.toObject();
+  }
+
+  // Step 8.
+  JS_ReportErrorNumberASCII(
+      cx, GetErrorMessage, nullptr, JSMSG_NOT_CONSTRUCTOR,
+      "[Symbol.species] property of object's constructor");
+  return nullptr;
+}
+
+[[nodiscard]] JSObject* js::SpeciesConstructor(
+    JSContext* cx, HandleObject obj, JSProtoKey ctorKey,
+    bool (*isDefaultSpecies)(JSContext*, JSFunction*)) {
+  RootedObject defaultCtor(cx,
+                           GlobalObject::getOrCreateConstructor(cx, ctorKey));
+  if (!defaultCtor) {
+    return nullptr;
+  }
+  return SpeciesConstructor(cx, obj, defaultCtor, isDefaultSpecies);
+}
+
+bool js::Unbox(JSContext* cx, HandleObject obj, MutableHandleValue vp) {
+  if (MOZ_UNLIKELY(obj->is<ProxyObject>())) {
+    return Proxy::boxedValue_unbox(cx, obj, vp);
+  }
+
+  if (obj->is<BooleanObject>()) {
+    vp.setBoolean(obj->as<BooleanObject>().unbox());
+  } else if (obj->is<NumberObject>()) {
+    vp.setNumber(obj->as<NumberObject>().unbox());
+  } else if (obj->is<StringObject>()) {
+    vp.setString(obj->as<StringObject>().unbox());
+  } else if (obj->is<DateObject>()) {
+    vp.set(obj->as<DateObject>().UTCTime());
+  } else if (obj->is<SymbolObject>()) {
+    vp.setSymbol(obj->as<SymbolObject>().unbox());
+  } else if (obj->is<BigIntObject>()) {
+    vp.setBigInt(obj->as<BigIntObject>().unbox());
+#ifdef ENABLE_RECORD_TUPLE
+  } else if (obj->is<RecordObject>()) {
+    vp.setExtendedPrimitive(*obj->as<RecordObject>().unbox());
+  } else if (obj->is<TupleObject>()) {
+    vp.setExtendedPrimitive(obj->as<TupleObject>().unbox());
+#endif
+  } else {
+    vp.setUndefined();
+  }
+
+  return true;
+}
+
+#ifdef DEBUG
+void js::AssertJSClassInvariants(const JSClass* clasp) {
+  MOZ_ASSERT(JS::StringIsASCII(clasp->name));
+
+  // Native objects shouldn't use the property operation hooks in ObjectOps.
+  // Doing so could violate JIT invariants.
+  //
+  // Environment objects unfortunately use these hooks, but environment objects
+  // are not exposed directly to script so they're generally less of an issue.
+  if (clasp->isNativeObject() && clasp != &WithEnvironmentObject::class_ &&
+      clasp != &ModuleEnvironmentObject::class_ &&
+      clasp != &RuntimeLexicalErrorObject::class_) {
+    MOZ_ASSERT(!clasp->getOpsLookupProperty());
+    MOZ_ASSERT_IF(clasp != &MappedArgumentsObject::class_,
+                  !clasp->getOpsDefineProperty());
+    MOZ_ASSERT(!clasp->getOpsHasProperty());
+    MOZ_ASSERT(!clasp->getOpsGetProperty());
+    MOZ_ASSERT(!clasp->getOpsSetProperty());
+    MOZ_ASSERT(!clasp->getOpsGetOwnPropertyDescriptor());
+    MOZ_ASSERT(!clasp->getOpsDeleteProperty());
+  }
+}
+
+/* static */
+void JSObject::debugCheckNewObject(Shape* shape, js::gc::AllocKind allocKind,
+                                   js::gc::Heap heap) {
+  const JSClass* clasp = shape->getObjectClass();
+
+  if (!ClassCanHaveFixedData(clasp)) {
+    NativeShape* nshape = &shape->asNative();
+    if (clasp == &ArrayObject::class_) {
+      // Arrays can store the ObjectElements header inline.
+      MOZ_ASSERT(nshape->numFixedSlots() == 0);
+    } else {
+      MOZ_ASSERT(gc::GetGCKindSlots(allocKind) == nshape->numFixedSlots());
+    }
+  }
+
+  // Assert background finalization is used when possible.
+  MOZ_ASSERT(!CanChangeToBackgroundAllocKind(allocKind, clasp));
+
+  // Classes with a finalizer must specify whether instances will be finalized
+  // on the main thread or in the background, except proxies whose behaviour
+  // depends on the target object.
+  static const uint32_t FinalizeMask =
+      JSCLASS_FOREGROUND_FINALIZE | JSCLASS_BACKGROUND_FINALIZE;
+  uint32_t flags = clasp->flags;
+  uint32_t finalizeFlags = flags & FinalizeMask;
+  if (clasp->hasFinalize() && !clasp->isProxyObject()) {
+    MOZ_ASSERT(finalizeFlags == JSCLASS_FOREGROUND_FINALIZE ||
+               finalizeFlags == JSCLASS_BACKGROUND_FINALIZE);
+    MOZ_ASSERT((finalizeFlags == JSCLASS_BACKGROUND_FINALIZE) ==
+               IsBackgroundFinalized(allocKind));
+  } else {
+    MOZ_ASSERT(finalizeFlags == 0);
+  }
+
+  MOZ_ASSERT_IF(clasp->hasFinalize(),
+                heap == gc::Heap::Tenured ||
+                    CanNurseryAllocateFinalizedClass(clasp) ||
+                    clasp->isProxyObject());
+
+  MOZ_ASSERT(!shape->isDictionary());
+  MOZ_ASSERT(!shape->realm()->hasObjectPendingMetadata());
+
+  // Non-native classes manage their own data and slots, so numFixedSlots is
+  // always 0. Note that proxy classes can have reserved slots but they're not
+  // included in numFixedSlots.
+  if (!clasp->isNativeObject()) {
+    MOZ_ASSERT_IF(!clasp->isProxyObject(), JSCLASS_RESERVED_SLOTS(clasp) == 0);
+  }
+}
+#endif