Adding upstream version 1:115.7.0.upstream/1%115.7.0upstream

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

1 files changed, 2548 insertions, 0 deletions

diff --git a/js/src/builtin/ModuleObject.cpp b/js/src/builtin/ModuleObject.cpp
new file mode 100644
index 0000000000..f227728f98
--- /dev/null
+++ b/js/src/builtin/ModuleObject.cpp
@@ -0,0 +1,2548 @@
+/* -*- 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/. */
+
+#include "builtin/ModuleObject.h"
+
+#include "mozilla/DebugOnly.h"
+#include "mozilla/EnumSet.h"
+#include "mozilla/ScopeExit.h"
+
+#include "builtin/Promise.h"
+#include "builtin/SelfHostingDefines.h"
+#include "frontend/ParseNode.h"
+#include "frontend/ParserAtom.h"  // TaggedParserAtomIndex, ParserAtomsTable, ParserAtom
+#include "frontend/SharedContext.h"
+#include "frontend/Stencil.h"
+#include "gc/GCContext.h"
+#include "gc/Tracer.h"
+#include "js/friend/ErrorMessages.h"  // JSMSG_*
+#include "js/Modules.h"  // JS::GetModulePrivate, JS::ModuleDynamicImportHook
+#include "vm/EqualityOperations.h"  // js::SameValue
+#include "vm/Interpreter.h"    // Execute, Lambda, ReportRuntimeLexicalError
+#include "vm/ModuleBuilder.h"  // js::ModuleBuilder
+#include "vm/Modules.h"
+#include "vm/PlainObject.h"    // js::PlainObject
+#include "vm/PromiseObject.h"  // js::PromiseObject
+#include "vm/SharedStencil.h"  // js::GCThingIndex
+
+#include "builtin/HandlerFunction-inl.h"  // js::ExtraValueFromHandler, js::NewHandler{,WithExtraValue}, js::TargetFromHandler
+#include "gc/GCContext-inl.h"
+#include "vm/JSObject-inl.h"
+#include "vm/JSScript-inl.h"
+#include "vm/List-inl.h"
+#include "vm/NativeObject-inl.h"
+
+using namespace js;
+
+using mozilla::Maybe;
+using mozilla::Nothing;
+using mozilla::Some;
+using mozilla::Span;
+
+static_assert(ModuleStatus::Unlinked < ModuleStatus::Linking &&
+                  ModuleStatus::Linking < ModuleStatus::Linked &&
+                  ModuleStatus::Linked < ModuleStatus::Evaluating &&
+                  ModuleStatus::Evaluating < ModuleStatus::EvaluatingAsync &&
+                  ModuleStatus::EvaluatingAsync < ModuleStatus::Evaluated &&
+                  ModuleStatus::Evaluated < ModuleStatus::Evaluated_Error,
+              "Module statuses are ordered incorrectly");
+
+static Value StringOrNullValue(JSString* maybeString) {
+  return maybeString ? StringValue(maybeString) : NullValue();
+}
+
+#define DEFINE_ATOM_ACCESSOR_METHOD(cls, name, slot) \
+  JSAtom* cls::name() const {                        \
+    Value value = getReservedSlot(slot);             \
+    return &value.toString()->asAtom();              \
+  }
+
+#define DEFINE_ATOM_OR_NULL_ACCESSOR_METHOD(cls, name, slot) \
+  JSAtom* cls::name() const {                                \
+    Value value = getReservedSlot(slot);                     \
+    if (value.isNull()) {                                    \
+      return nullptr;                                        \
+    }                                                        \
+    return &value.toString()->asAtom();                      \
+  }
+
+#define DEFINE_UINT32_ACCESSOR_METHOD(cls, name, slot) \
+  uint32_t cls::name() const {                         \
+    Value value = getReservedSlot(slot);               \
+    MOZ_ASSERT(value.toNumber() >= 0);                 \
+    if (value.isInt32()) {                             \
+      return value.toInt32();                          \
+    }                                                  \
+    return JS::ToUint32(value.toDouble());             \
+  }
+
+///////////////////////////////////////////////////////////////////////////
+// ImportEntry
+
+ImportEntry::ImportEntry(Handle<ModuleRequestObject*> moduleRequest,
+                         Handle<JSAtom*> maybeImportName,
+                         Handle<JSAtom*> localName, uint32_t lineNumber,
+                         uint32_t columnNumber)
+    : moduleRequest_(moduleRequest),
+      importName_(maybeImportName),
+      localName_(localName),
+      lineNumber_(lineNumber),
+      columnNumber_(columnNumber) {}
+
+void ImportEntry::trace(JSTracer* trc) {
+  TraceEdge(trc, &moduleRequest_, "ImportEntry::moduleRequest_");
+  TraceNullableEdge(trc, &importName_, "ImportEntry::importName_");
+  TraceNullableEdge(trc, &localName_, "ImportEntry::localName_");
+}
+
+///////////////////////////////////////////////////////////////////////////
+// ExportEntry
+
+ExportEntry::ExportEntry(Handle<JSAtom*> maybeExportName,
+                         Handle<ModuleRequestObject*> moduleRequest,
+                         Handle<JSAtom*> maybeImportName,
+                         Handle<JSAtom*> maybeLocalName, uint32_t lineNumber,
+                         uint32_t columnNumber)
+    : exportName_(maybeExportName),
+      moduleRequest_(moduleRequest),
+      importName_(maybeImportName),
+      localName_(maybeLocalName),
+      lineNumber_(lineNumber),
+      columnNumber_(columnNumber) {
+  // Line and column numbers are optional for export entries since direct
+  // entries are checked at parse time.
+}
+
+void ExportEntry::trace(JSTracer* trc) {
+  TraceNullableEdge(trc, &exportName_, "ExportEntry::exportName_");
+  TraceNullableEdge(trc, &moduleRequest_, "ExportEntry::moduleRequest_");
+  TraceNullableEdge(trc, &importName_, "ExportEntry::importName_");
+  TraceNullableEdge(trc, &localName_, "ExportEntry::localName_");
+}
+
+///////////////////////////////////////////////////////////////////////////
+// RequestedModule
+
+/* static */
+RequestedModule::RequestedModule(Handle<ModuleRequestObject*> moduleRequest,
+                                 uint32_t lineNumber, uint32_t columnNumber)
+    : moduleRequest_(moduleRequest),
+      lineNumber_(lineNumber),
+      columnNumber_(columnNumber) {}
+
+void RequestedModule::trace(JSTracer* trc) {
+  TraceEdge(trc, &moduleRequest_, "ExportEntry::moduleRequest_");
+}
+
+///////////////////////////////////////////////////////////////////////////
+// ResolvedBindingObject
+
+/* static */ const JSClass ResolvedBindingObject::class_ = {
+    "ResolvedBinding",
+    JSCLASS_HAS_RESERVED_SLOTS(ResolvedBindingObject::SlotCount)};
+
+ModuleObject* ResolvedBindingObject::module() const {
+  Value value = getReservedSlot(ModuleSlot);
+  return &value.toObject().as<ModuleObject>();
+}
+
+JSAtom* ResolvedBindingObject::bindingName() const {
+  Value value = getReservedSlot(BindingNameSlot);
+  return &value.toString()->asAtom();
+}
+
+/* static */
+bool ResolvedBindingObject::isInstance(HandleValue value) {
+  return value.isObject() && value.toObject().is<ResolvedBindingObject>();
+}
+
+/* static */
+ResolvedBindingObject* ResolvedBindingObject::create(
+    JSContext* cx, Handle<ModuleObject*> module, Handle<JSAtom*> bindingName) {
+  ResolvedBindingObject* self =
+      NewObjectWithGivenProto<ResolvedBindingObject>(cx, nullptr);
+  if (!self) {
+    return nullptr;
+  }
+
+  self->initReservedSlot(ModuleSlot, ObjectValue(*module));
+  self->initReservedSlot(BindingNameSlot, StringValue(bindingName));
+  return self;
+}
+
+///////////////////////////////////////////////////////////////////////////
+// ModuleRequestObject
+/* static */ const JSClass ModuleRequestObject::class_ = {
+    "ModuleRequest",
+    JSCLASS_HAS_RESERVED_SLOTS(ModuleRequestObject::SlotCount)};
+
+DEFINE_ATOM_OR_NULL_ACCESSOR_METHOD(ModuleRequestObject, specifier,
+                                    SpecifierSlot)
+
+ArrayObject* ModuleRequestObject::assertions() const {
+  JSObject* obj = getReservedSlot(AssertionSlot).toObjectOrNull();
+  if (!obj) {
+    return nullptr;
+  }
+
+  return &obj->as<ArrayObject>();
+}
+
+/* static */
+bool ModuleRequestObject::isInstance(HandleValue value) {
+  return value.isObject() && value.toObject().is<ModuleRequestObject>();
+}
+
+/* static */
+ModuleRequestObject* ModuleRequestObject::create(
+    JSContext* cx, Handle<JSAtom*> specifier,
+    Handle<ArrayObject*> maybeAssertions) {
+  ModuleRequestObject* self =
+      NewObjectWithGivenProto<ModuleRequestObject>(cx, nullptr);
+  if (!self) {
+    return nullptr;
+  }
+
+  self->initReservedSlot(SpecifierSlot, StringOrNullValue(specifier));
+  self->initReservedSlot(AssertionSlot, ObjectOrNullValue(maybeAssertions));
+  return self;
+}
+
+///////////////////////////////////////////////////////////////////////////
+// IndirectBindingMap
+
+IndirectBindingMap::Binding::Binding(ModuleEnvironmentObject* environment,
+                                     jsid targetName, PropertyInfo prop)
+    : environment(environment),
+#ifdef DEBUG
+      targetName(targetName),
+#endif
+      prop(prop) {
+}
+
+void IndirectBindingMap::trace(JSTracer* trc) {
+  if (!map_) {
+    return;
+  }
+
+  for (Map::Enum e(*map_); !e.empty(); e.popFront()) {
+    Binding& b = e.front().value();
+    TraceEdge(trc, &b.environment, "module bindings environment");
+#ifdef DEBUG
+    TraceEdge(trc, &b.targetName, "module bindings target name");
+#endif
+    mozilla::DebugOnly<jsid> prev(e.front().key());
+    TraceEdge(trc, &e.front().mutableKey(), "module bindings binding name");
+    MOZ_ASSERT(e.front().key() == prev);
+  }
+}
+
+bool IndirectBindingMap::put(JSContext* cx, HandleId name,
+                             Handle<ModuleEnvironmentObject*> environment,
+                             HandleId targetName) {
+  if (!map_) {
+    map_.emplace(cx->zone());
+  }
+
+  mozilla::Maybe<PropertyInfo> prop = environment->lookup(cx, targetName);
+  MOZ_ASSERT(prop.isSome());
+  if (!map_->put(name, Binding(environment, targetName, *prop))) {
+    ReportOutOfMemory(cx);
+    return false;
+  }
+
+  return true;
+}
+
+bool IndirectBindingMap::lookup(jsid name, ModuleEnvironmentObject** envOut,
+                                mozilla::Maybe<PropertyInfo>* propOut) const {
+  if (!map_) {
+    return false;
+  }
+
+  auto ptr = map_->lookup(name);
+  if (!ptr) {
+    return false;
+  }
+
+  const Binding& binding = ptr->value();
+  MOZ_ASSERT(binding.environment);
+  MOZ_ASSERT(
+      binding.environment->containsPure(binding.targetName, binding.prop));
+  *envOut = binding.environment;
+  *propOut = Some(binding.prop);
+  return true;
+}
+
+///////////////////////////////////////////////////////////////////////////
+// ModuleNamespaceObject
+
+/* static */
+const ModuleNamespaceObject::ProxyHandler ModuleNamespaceObject::proxyHandler;
+
+/* static */
+bool ModuleNamespaceObject::isInstance(HandleValue value) {
+  return value.isObject() && value.toObject().is<ModuleNamespaceObject>();
+}
+
+/* static */
+ModuleNamespaceObject* ModuleNamespaceObject::create(
+    JSContext* cx, Handle<ModuleObject*> module,
+    MutableHandle<UniquePtr<ExportNameVector>> exports,
+    MutableHandle<UniquePtr<IndirectBindingMap>> bindings) {
+  RootedValue priv(cx, ObjectValue(*module));
+  ProxyOptions options;
+  options.setLazyProto(true);
+
+  RootedObject object(
+      cx, NewProxyObject(cx, &proxyHandler, priv, nullptr, options));
+  if (!object) {
+    return nullptr;
+  }
+
+  SetProxyReservedSlot(object, ExportsSlot,
+                       PrivateValue(exports.get().release()));
+  AddCellMemory(object, sizeof(ExportNameVector), MemoryUse::ModuleExports);
+
+  SetProxyReservedSlot(object, BindingsSlot,
+                       PrivateValue(bindings.get().release()));
+  AddCellMemory(object, sizeof(IndirectBindingMap),
+                MemoryUse::ModuleBindingMap);
+
+  return &object->as<ModuleNamespaceObject>();
+}
+
+ModuleObject& ModuleNamespaceObject::module() {
+  return GetProxyPrivate(this).toObject().as<ModuleObject>();
+}
+
+const ExportNameVector& ModuleNamespaceObject::exports() const {
+  Value value = GetProxyReservedSlot(this, ExportsSlot);
+  auto* exports = static_cast<ExportNameVector*>(value.toPrivate());
+  MOZ_ASSERT(exports);
+  return *exports;
+}
+
+ExportNameVector& ModuleNamespaceObject::mutableExports() {
+  // Get a non-const reference for tracing/destruction. Do not actually mutate
+  // this vector!  This would be incorrect without adding barriers.
+  return const_cast<ExportNameVector&>(exports());
+}
+
+IndirectBindingMap& ModuleNamespaceObject::bindings() {
+  Value value = GetProxyReservedSlot(this, BindingsSlot);
+  auto* bindings = static_cast<IndirectBindingMap*>(value.toPrivate());
+  MOZ_ASSERT(bindings);
+  return *bindings;
+}
+
+bool ModuleNamespaceObject::hasExports() const {
+  // Exports may not be present if we hit OOM in initialization.
+  return !GetProxyReservedSlot(this, ExportsSlot).isUndefined();
+}
+
+bool ModuleNamespaceObject::hasBindings() const {
+  // Import bindings may not be present if we hit OOM in initialization.
+  return !GetProxyReservedSlot(this, BindingsSlot).isUndefined();
+}
+
+bool ModuleNamespaceObject::addBinding(JSContext* cx,
+                                       Handle<JSAtom*> exportedName,
+                                       Handle<ModuleObject*> targetModule,
+                                       Handle<JSAtom*> targetName) {
+  Rooted<ModuleEnvironmentObject*> environment(
+      cx, &targetModule->initialEnvironment());
+  RootedId exportedNameId(cx, AtomToId(exportedName));
+  RootedId targetNameId(cx, AtomToId(targetName));
+  return bindings().put(cx, exportedNameId, environment, targetNameId);
+}
+
+const char ModuleNamespaceObject::ProxyHandler::family = 0;
+
+ModuleNamespaceObject::ProxyHandler::ProxyHandler()
+    : BaseProxyHandler(&family, false) {}
+
+bool ModuleNamespaceObject::ProxyHandler::getPrototype(
+    JSContext* cx, HandleObject proxy, MutableHandleObject protop) const {
+  protop.set(nullptr);
+  return true;
+}
+
+bool ModuleNamespaceObject::ProxyHandler::setPrototype(
+    JSContext* cx, HandleObject proxy, HandleObject proto,
+    ObjectOpResult& result) const {
+  if (!proto) {
+    return result.succeed();
+  }
+  return result.failCantSetProto();
+}
+
+bool ModuleNamespaceObject::ProxyHandler::getPrototypeIfOrdinary(
+    JSContext* cx, HandleObject proxy, bool* isOrdinary,
+    MutableHandleObject protop) const {
+  *isOrdinary = false;
+  return true;
+}
+
+bool ModuleNamespaceObject::ProxyHandler::setImmutablePrototype(
+    JSContext* cx, HandleObject proxy, bool* succeeded) const {
+  *succeeded = true;
+  return true;
+}
+
+bool ModuleNamespaceObject::ProxyHandler::isExtensible(JSContext* cx,
+                                                       HandleObject proxy,
+                                                       bool* extensible) const {
+  *extensible = false;
+  return true;
+}
+
+bool ModuleNamespaceObject::ProxyHandler::preventExtensions(
+    JSContext* cx, HandleObject proxy, ObjectOpResult& result) const {
+  result.succeed();
+  return true;
+}
+
+bool ModuleNamespaceObject::ProxyHandler::getOwnPropertyDescriptor(
+    JSContext* cx, HandleObject proxy, HandleId id,
+    MutableHandle<mozilla::Maybe<PropertyDescriptor>> desc) const {
+  Rooted<ModuleNamespaceObject*> ns(cx, &proxy->as<ModuleNamespaceObject>());
+  if (id.isSymbol()) {
+    if (id.isWellKnownSymbol(JS::SymbolCode::toStringTag)) {
+      desc.set(Some(PropertyDescriptor::Data(StringValue(cx->names().Module))));
+      return true;
+    }
+
+    desc.reset();
+    return true;
+  }
+
+  const IndirectBindingMap& bindings = ns->bindings();
+  ModuleEnvironmentObject* env;
+  mozilla::Maybe<PropertyInfo> prop;
+  if (!bindings.lookup(id, &env, &prop)) {
+    // Not found.
+    desc.reset();
+    return true;
+  }
+
+  RootedValue value(cx, env->getSlot(prop->slot()));
+  if (value.isMagic(JS_UNINITIALIZED_LEXICAL)) {
+    ReportRuntimeLexicalError(cx, JSMSG_UNINITIALIZED_LEXICAL, id);
+    return false;
+  }
+
+  desc.set(
+      Some(PropertyDescriptor::Data(value, {JS::PropertyAttribute::Enumerable,
+                                            JS::PropertyAttribute::Writable})));
+  return true;
+}
+
+static bool ValidatePropertyDescriptor(
+    JSContext* cx, Handle<PropertyDescriptor> desc, bool expectedWritable,
+    bool expectedEnumerable, bool expectedConfigurable,
+    HandleValue expectedValue, ObjectOpResult& result) {
+  if (desc.isAccessorDescriptor()) {
+    return result.fail(JSMSG_CANT_REDEFINE_PROP);
+  }
+
+  if (desc.hasWritable() && desc.writable() != expectedWritable) {
+    return result.fail(JSMSG_CANT_REDEFINE_PROP);
+  }
+
+  if (desc.hasEnumerable() && desc.enumerable() != expectedEnumerable) {
+    return result.fail(JSMSG_CANT_REDEFINE_PROP);
+  }
+
+  if (desc.hasConfigurable() && desc.configurable() != expectedConfigurable) {
+    return result.fail(JSMSG_CANT_REDEFINE_PROP);
+  }
+
+  if (desc.hasValue()) {
+    bool same;
+    if (!SameValue(cx, desc.value(), expectedValue, &same)) {
+      return false;
+    }
+    if (!same) {
+      return result.fail(JSMSG_CANT_REDEFINE_PROP);
+    }
+  }
+
+  return result.succeed();
+}
+
+bool ModuleNamespaceObject::ProxyHandler::defineProperty(
+    JSContext* cx, HandleObject proxy, HandleId id,
+    Handle<PropertyDescriptor> desc, ObjectOpResult& result) const {
+  if (id.isSymbol()) {
+    if (id.isWellKnownSymbol(JS::SymbolCode::toStringTag)) {
+      RootedValue value(cx, StringValue(cx->names().Module));
+      return ValidatePropertyDescriptor(cx, desc, false, false, false, value,
+                                        result);
+    }
+    return result.fail(JSMSG_CANT_DEFINE_PROP_OBJECT_NOT_EXTENSIBLE);
+  }
+
+  const IndirectBindingMap& bindings =
+      proxy->as<ModuleNamespaceObject>().bindings();
+  ModuleEnvironmentObject* env;
+  mozilla::Maybe<PropertyInfo> prop;
+  if (!bindings.lookup(id, &env, &prop)) {
+    return result.fail(JSMSG_CANT_DEFINE_PROP_OBJECT_NOT_EXTENSIBLE);
+  }
+
+  RootedValue value(cx, env->getSlot(prop->slot()));
+  if (value.isMagic(JS_UNINITIALIZED_LEXICAL)) {
+    ReportRuntimeLexicalError(cx, JSMSG_UNINITIALIZED_LEXICAL, id);
+    return false;
+  }
+
+  return ValidatePropertyDescriptor(cx, desc, true, true, false, value, result);
+}
+
+bool ModuleNamespaceObject::ProxyHandler::has(JSContext* cx, HandleObject proxy,
+                                              HandleId id, bool* bp) const {
+  Rooted<ModuleNamespaceObject*> ns(cx, &proxy->as<ModuleNamespaceObject>());
+  if (id.isSymbol()) {
+    *bp = id.isWellKnownSymbol(JS::SymbolCode::toStringTag);
+    return true;
+  }
+
+  *bp = ns->bindings().has(id);
+  return true;
+}
+
+bool ModuleNamespaceObject::ProxyHandler::get(JSContext* cx, HandleObject proxy,
+                                              HandleValue receiver, HandleId id,
+                                              MutableHandleValue vp) const {
+  Rooted<ModuleNamespaceObject*> ns(cx, &proxy->as<ModuleNamespaceObject>());
+  if (id.isSymbol()) {
+    if (id.isWellKnownSymbol(JS::SymbolCode::toStringTag)) {
+      vp.setString(cx->names().Module);
+      return true;
+    }
+
+    vp.setUndefined();
+    return true;
+  }
+
+  ModuleEnvironmentObject* env;
+  mozilla::Maybe<PropertyInfo> prop;
+  if (!ns->bindings().lookup(id, &env, &prop)) {
+    vp.setUndefined();
+    return true;
+  }
+
+  RootedValue value(cx, env->getSlot(prop->slot()));
+  if (value.isMagic(JS_UNINITIALIZED_LEXICAL)) {
+    ReportRuntimeLexicalError(cx, JSMSG_UNINITIALIZED_LEXICAL, id);
+    return false;
+  }
+
+  vp.set(value);
+  return true;
+}
+
+bool ModuleNamespaceObject::ProxyHandler::set(JSContext* cx, HandleObject proxy,
+                                              HandleId id, HandleValue v,
+                                              HandleValue receiver,
+                                              ObjectOpResult& result) const {
+  return result.failReadOnly();
+}
+
+bool ModuleNamespaceObject::ProxyHandler::delete_(
+    JSContext* cx, HandleObject proxy, HandleId id,
+    ObjectOpResult& result) const {
+  Rooted<ModuleNamespaceObject*> ns(cx, &proxy->as<ModuleNamespaceObject>());
+  if (id.isSymbol()) {
+    if (id.isWellKnownSymbol(JS::SymbolCode::toStringTag)) {
+      return result.failCantDelete();
+    }
+
+    return result.succeed();
+  }
+
+  if (ns->bindings().has(id)) {
+    return result.failCantDelete();
+  }
+
+  return result.succeed();
+}
+
+bool ModuleNamespaceObject::ProxyHandler::ownPropertyKeys(
+    JSContext* cx, HandleObject proxy, MutableHandleIdVector props) const {
+  Rooted<ModuleNamespaceObject*> ns(cx, &proxy->as<ModuleNamespaceObject>());
+  uint32_t count = ns->exports().length();
+  if (!props.reserve(props.length() + count + 1)) {
+    return false;
+  }
+
+  for (JSAtom* atom : ns->exports()) {
+    props.infallibleAppend(AtomToId(atom));
+  }
+  props.infallibleAppend(
+      PropertyKey::Symbol(cx->wellKnownSymbols().toStringTag));
+
+  return true;
+}
+
+void ModuleNamespaceObject::ProxyHandler::trace(JSTracer* trc,
+                                                JSObject* proxy) const {
+  auto& self = proxy->as<ModuleNamespaceObject>();
+
+  if (self.hasExports()) {
+    self.mutableExports().trace(trc);
+  }
+
+  if (self.hasBindings()) {
+    self.bindings().trace(trc);
+  }
+}
+
+void ModuleNamespaceObject::ProxyHandler::finalize(JS::GCContext* gcx,
+                                                   JSObject* proxy) const {
+  auto& self = proxy->as<ModuleNamespaceObject>();
+
+  if (self.hasExports()) {
+    gcx->delete_(proxy, &self.mutableExports(), MemoryUse::ModuleExports);
+  }
+
+  if (self.hasBindings()) {
+    gcx->delete_(proxy, &self.bindings(), MemoryUse::ModuleBindingMap);
+  }
+}
+
+///////////////////////////////////////////////////////////////////////////
+// CyclicModuleFields
+
+// The fields of a cyclic module record, as described in:
+// https://tc39.es/ecma262/#sec-cyclic-module-records
+class js::CyclicModuleFields {
+ public:
+  ModuleStatus status = ModuleStatus::Unlinked;
+
+  bool hasTopLevelAwait : 1;
+
+ private:
+  // Flag bits that determine whether other fields are present.
+  bool hasDfsIndex : 1;
+  bool hasDfsAncestorIndex : 1;
+  bool isAsyncEvaluating : 1;
+  bool hasPendingAsyncDependencies : 1;
+
+  // Fields whose presence is conditional on the flag bits above.
+  uint32_t dfsIndex = 0;
+  uint32_t dfsAncestorIndex = 0;
+  uint32_t asyncEvaluatingPostOrder = 0;
+  uint32_t pendingAsyncDependencies = 0;
+
+  // Fields describing the layout of exportEntries.
+  uint32_t indirectExportEntriesStart = 0;
+  uint32_t starExportEntriesStart = 0;
+
+ public:
+  HeapPtr<Value> evaluationError;
+  HeapPtr<JSObject*> metaObject;
+  HeapPtr<ScriptSourceObject*> scriptSourceObject;
+  RequestedModuleVector requestedModules;
+  ImportEntryVector importEntries;
+  ExportEntryVector exportEntries;
+  IndirectBindingMap importBindings;
+  UniquePtr<FunctionDeclarationVector> functionDeclarations;
+  HeapPtr<PromiseObject*> topLevelCapability;
+  HeapPtr<ListObject*> asyncParentModules;
+  HeapPtr<ModuleObject*> cycleRoot;
+
+ public:
+  CyclicModuleFields();
+
+  void trace(JSTracer* trc);
+
+  void initExportEntries(MutableHandle<ExportEntryVector> allEntries,
+                         uint32_t localExportCount,
+                         uint32_t indirectExportCount,
+                         uint32_t starExportCount);
+  Span<const ExportEntry> localExportEntries() const;
+  Span<const ExportEntry> indirectExportEntries() const;
+  Span<const ExportEntry> starExportEntries() const;
+
+  void setDfsIndex(uint32_t index);
+  Maybe<uint32_t> maybeDfsIndex() const;
+  void setDfsAncestorIndex(uint32_t index);
+  Maybe<uint32_t> maybeDfsAncestorIndex() const;
+  void clearDfsIndexes();
+
+  void setAsyncEvaluating(uint32_t postOrder);
+  bool getIsAsyncEvaluating() const;
+  Maybe<uint32_t> maybeAsyncEvaluatingPostOrder() const;
+  void clearAsyncEvaluatingPostOrder();
+
+  void setPendingAsyncDependencies(uint32_t newValue);
+  Maybe<uint32_t> maybePendingAsyncDependencies() const;
+};
+
+CyclicModuleFields::CyclicModuleFields()
+    : hasTopLevelAwait(false),
+      hasDfsIndex(false),
+      hasDfsAncestorIndex(false),
+      isAsyncEvaluating(false),
+      hasPendingAsyncDependencies(false) {}
+
+void CyclicModuleFields::trace(JSTracer* trc) {
+  TraceEdge(trc, &evaluationError, "CyclicModuleFields::evaluationError");
+  TraceNullableEdge(trc, &metaObject, "CyclicModuleFields::metaObject");
+  TraceNullableEdge(trc, &scriptSourceObject,
+                    "CyclicModuleFields::scriptSourceObject");
+  requestedModules.trace(trc);
+  importEntries.trace(trc);
+  exportEntries.trace(trc);
+  importBindings.trace(trc);
+  TraceNullableEdge(trc, &topLevelCapability,
+                    "CyclicModuleFields::topLevelCapability");
+  TraceNullableEdge(trc, &asyncParentModules,
+                    "CyclicModuleFields::asyncParentModules");
+  TraceNullableEdge(trc, &cycleRoot, "CyclicModuleFields::cycleRoot");
+}
+
+void CyclicModuleFields::initExportEntries(
+    MutableHandle<ExportEntryVector> allEntries, uint32_t localExportCount,
+    uint32_t indirectExportCount, uint32_t starExportCount) {
+  MOZ_ASSERT(allEntries.length() ==
+             localExportCount + indirectExportCount + starExportCount);
+
+  exportEntries = std::move(allEntries.get());
+  indirectExportEntriesStart = localExportCount;
+  starExportEntriesStart = indirectExportEntriesStart + indirectExportCount;
+}
+
+Span<const ExportEntry> CyclicModuleFields::localExportEntries() const {
+  MOZ_ASSERT(indirectExportEntriesStart <= exportEntries.length());
+  return Span(exportEntries.begin(),
+              exportEntries.begin() + indirectExportEntriesStart);
+}
+
+Span<const ExportEntry> CyclicModuleFields::indirectExportEntries() const {
+  MOZ_ASSERT(indirectExportEntriesStart <= starExportEntriesStart);
+  MOZ_ASSERT(starExportEntriesStart <= exportEntries.length());
+  return Span(exportEntries.begin() + indirectExportEntriesStart,
+              exportEntries.begin() + starExportEntriesStart);
+}
+
+Span<const ExportEntry> CyclicModuleFields::starExportEntries() const {
+  MOZ_ASSERT(starExportEntriesStart <= exportEntries.length());
+  return Span(exportEntries.begin() + starExportEntriesStart,
+              exportEntries.end());
+}
+
+void CyclicModuleFields::setDfsIndex(uint32_t index) {
+  dfsIndex = index;
+  hasDfsIndex = true;
+}
+
+Maybe<uint32_t> CyclicModuleFields::maybeDfsIndex() const {
+  return hasDfsIndex ? Some(dfsIndex) : Nothing();
+}
+
+void CyclicModuleFields::setDfsAncestorIndex(uint32_t index) {
+  dfsAncestorIndex = index;
+  hasDfsAncestorIndex = true;
+}
+
+Maybe<uint32_t> CyclicModuleFields::maybeDfsAncestorIndex() const {
+  return hasDfsAncestorIndex ? Some(dfsAncestorIndex) : Nothing();
+}
+
+void CyclicModuleFields::clearDfsIndexes() {
+  dfsIndex = 0;
+  hasDfsIndex = false;
+  dfsAncestorIndex = 0;
+  hasDfsAncestorIndex = false;
+}
+
+void CyclicModuleFields::setAsyncEvaluating(uint32_t postOrder) {
+  isAsyncEvaluating = true;
+  asyncEvaluatingPostOrder = postOrder;
+}
+
+bool CyclicModuleFields::getIsAsyncEvaluating() const {
+  return isAsyncEvaluating;
+}
+
+Maybe<uint32_t> CyclicModuleFields::maybeAsyncEvaluatingPostOrder() const {
+  if (!isAsyncEvaluating ||
+      asyncEvaluatingPostOrder == ASYNC_EVALUATING_POST_ORDER_CLEARED) {
+    return Nothing();
+  }
+
+  return Some(asyncEvaluatingPostOrder);
+}
+
+void CyclicModuleFields::clearAsyncEvaluatingPostOrder() {
+  asyncEvaluatingPostOrder = ASYNC_EVALUATING_POST_ORDER_CLEARED;
+}
+
+void CyclicModuleFields::setPendingAsyncDependencies(uint32_t newValue) {
+  pendingAsyncDependencies = newValue;
+  hasPendingAsyncDependencies = true;
+}
+
+Maybe<uint32_t> CyclicModuleFields::maybePendingAsyncDependencies() const {
+  return hasPendingAsyncDependencies ? Some(pendingAsyncDependencies)
+                                     : Nothing();
+}
+
+///////////////////////////////////////////////////////////////////////////
+// ModuleObject
+
+/* static */ const JSClassOps ModuleObject::classOps_ = {
+    nullptr,                 // addProperty
+    nullptr,                 // delProperty
+    nullptr,                 // enumerate
+    nullptr,                 // newEnumerate
+    nullptr,                 // resolve
+    nullptr,                 // mayResolve
+    ModuleObject::finalize,  // finalize
+    nullptr,                 // call
+    nullptr,                 // construct
+    ModuleObject::trace,     // trace
+};
+
+/* static */ const JSClass ModuleObject::class_ = {
+    "Module",
+    JSCLASS_HAS_RESERVED_SLOTS(ModuleObject::SlotCount) |
+        JSCLASS_BACKGROUND_FINALIZE,
+    &ModuleObject::classOps_};
+
+/* static */
+bool ModuleObject::isInstance(HandleValue value) {
+  return value.isObject() && value.toObject().is<ModuleObject>();
+}
+
+bool ModuleObject::hasCyclicModuleFields() const {
+  // This currently only returns false if we GC during initialization.
+  return !getReservedSlot(CyclicModuleFieldsSlot).isUndefined();
+}
+
+CyclicModuleFields* ModuleObject::cyclicModuleFields() {
+  void* ptr = getReservedSlot(CyclicModuleFieldsSlot).toPrivate();
+  MOZ_ASSERT(ptr);
+  return static_cast<CyclicModuleFields*>(ptr);
+}
+const CyclicModuleFields* ModuleObject::cyclicModuleFields() const {
+  return const_cast<ModuleObject*>(this)->cyclicModuleFields();
+}
+
+Span<const RequestedModule> ModuleObject::requestedModules() const {
+  return cyclicModuleFields()->requestedModules;
+}
+
+Span<const ImportEntry> ModuleObject::importEntries() const {
+  return cyclicModuleFields()->importEntries;
+}
+
+Span<const ExportEntry> ModuleObject::localExportEntries() const {
+  return cyclicModuleFields()->localExportEntries();
+}
+
+Span<const ExportEntry> ModuleObject::indirectExportEntries() const {
+  return cyclicModuleFields()->indirectExportEntries();
+}
+
+Span<const ExportEntry> ModuleObject::starExportEntries() const {
+  return cyclicModuleFields()->starExportEntries();
+}
+
+void ModuleObject::initFunctionDeclarations(
+    UniquePtr<FunctionDeclarationVector> decls) {
+  cyclicModuleFields()->functionDeclarations = std::move(decls);
+}
+
+/* static */
+ModuleObject* ModuleObject::create(JSContext* cx) {
+  Rooted<UniquePtr<CyclicModuleFields>> fields(cx);
+  fields = cx->make_unique<CyclicModuleFields>();
+  if (!fields) {
+    return nullptr;
+  }
+
+  Rooted<ModuleObject*> self(
+      cx, NewObjectWithGivenProto<ModuleObject>(cx, nullptr));
+  if (!self) {
+    return nullptr;
+  }
+
+  InitReservedSlot(self, CyclicModuleFieldsSlot, fields.release(),
+                   MemoryUse::ModuleCyclicFields);
+
+  return self;
+}
+
+/* static */
+void ModuleObject::finalize(JS::GCContext* gcx, JSObject* obj) {
+  ModuleObject* self = &obj->as<ModuleObject>();
+  if (self->hasCyclicModuleFields()) {
+    gcx->delete_(obj, self->cyclicModuleFields(),
+                 MemoryUse::ModuleCyclicFields);
+  }
+}
+
+ModuleEnvironmentObject& ModuleObject::initialEnvironment() const {
+  Value value = getReservedSlot(EnvironmentSlot);
+  return value.toObject().as<ModuleEnvironmentObject>();
+}
+
+ModuleEnvironmentObject* ModuleObject::environment() const {
+  // Note that this it's valid to call this even if there was an error
+  // evaluating the module.
+
+  // According to the spec the environment record is created during linking, but
+  // we create it earlier than that.
+  if (status() < ModuleStatus::Linked) {
+    return nullptr;
+  }
+
+  return &initialEnvironment();
+}
+
+IndirectBindingMap& ModuleObject::importBindings() {
+  return cyclicModuleFields()->importBindings;
+}
+
+ModuleNamespaceObject* ModuleObject::namespace_() {
+  Value value = getReservedSlot(NamespaceSlot);
+  if (value.isUndefined()) {
+    return nullptr;
+  }
+  return &value.toObject().as<ModuleNamespaceObject>();
+}
+
+ScriptSourceObject* ModuleObject::scriptSourceObject() const {
+  return cyclicModuleFields()->scriptSourceObject;
+}
+
+void ModuleObject::initAsyncSlots(JSContext* cx, bool hasTopLevelAwait,
+                                  Handle<ListObject*> asyncParentModules) {
+  cyclicModuleFields()->hasTopLevelAwait = hasTopLevelAwait;
+  cyclicModuleFields()->asyncParentModules = asyncParentModules;
+}
+
+static uint32_t NextPostOrder(JSRuntime* rt) {
+  uint32_t ordinal = rt->moduleAsyncEvaluatingPostOrder;
+  MOZ_ASSERT(ordinal != ASYNC_EVALUATING_POST_ORDER_CLEARED);
+  MOZ_ASSERT(ordinal < MAX_UINT32);
+  rt->moduleAsyncEvaluatingPostOrder++;
+  return ordinal;
+}
+
+// Reset the runtime's moduleAsyncEvaluatingPostOrder counter when the last
+// module that was async evaluating is finished.
+//
+// The graph is not re-entrant and any future modules will be independent from
+// this one.
+static void MaybeResetPostOrderCounter(JSRuntime* rt,
+                                       uint32_t finishedPostOrder) {
+  if (rt->moduleAsyncEvaluatingPostOrder == finishedPostOrder + 1) {
+    rt->moduleAsyncEvaluatingPostOrder = ASYNC_EVALUATING_POST_ORDER_INIT;
+  }
+}
+
+void ModuleObject::setAsyncEvaluating() {
+  MOZ_ASSERT(!isAsyncEvaluating());
+  uint32_t postOrder = NextPostOrder(runtimeFromMainThread());
+  cyclicModuleFields()->setAsyncEvaluating(postOrder);
+}
+
+void ModuleObject::initScriptSlots(HandleScript script) {
+  MOZ_ASSERT(script);
+  MOZ_ASSERT(script->sourceObject());
+  initReservedSlot(ScriptSlot, PrivateGCThingValue(script));
+  cyclicModuleFields()->scriptSourceObject = script->sourceObject();
+}
+
+void ModuleObject::setInitialEnvironment(
+    Handle<ModuleEnvironmentObject*> initialEnvironment) {
+  initReservedSlot(EnvironmentSlot, ObjectValue(*initialEnvironment));
+}
+
+void ModuleObject::initImportExportData(
+    MutableHandle<RequestedModuleVector> requestedModules,
+    MutableHandle<ImportEntryVector> importEntries,
+    MutableHandle<ExportEntryVector> exportEntries, uint32_t localExportCount,
+    uint32_t indirectExportCount, uint32_t starExportCount) {
+  cyclicModuleFields()->requestedModules = std::move(requestedModules.get());
+  cyclicModuleFields()->importEntries = std::move(importEntries.get());
+  cyclicModuleFields()->initExportEntries(exportEntries, localExportCount,
+                                          indirectExportCount, starExportCount);
+}
+
+/* static */
+bool ModuleObject::Freeze(JSContext* cx, Handle<ModuleObject*> self) {
+  return FreezeObject(cx, self);
+}
+
+#ifdef DEBUG
+/* static */ inline bool ModuleObject::AssertFrozen(
+    JSContext* cx, Handle<ModuleObject*> self) {
+  bool frozen = false;
+  if (!TestIntegrityLevel(cx, self, IntegrityLevel::Frozen, &frozen)) {
+    return false;
+  }
+  MOZ_ASSERT(frozen);
+
+  return true;
+}
+#endif
+
+JSScript* ModuleObject::maybeScript() const {
+  Value value = getReservedSlot(ScriptSlot);
+  if (value.isUndefined()) {
+    return nullptr;
+  }
+  BaseScript* script = value.toGCThing()->as<BaseScript>();
+  MOZ_ASSERT(script->hasBytecode(),
+             "Module scripts should always have bytecode");
+  return script->asJSScript();
+}
+
+JSScript* ModuleObject::script() const {
+  JSScript* ptr = maybeScript();
+  MOZ_RELEASE_ASSERT(ptr);
+  return ptr;
+}
+
+static inline void AssertValidModuleStatus(ModuleStatus status) {
+  MOZ_ASSERT(status >= ModuleStatus::Unlinked &&
+             status <= ModuleStatus::Evaluated_Error);
+}
+
+ModuleStatus ModuleObject::status() const {
+  // TODO: When implementing synthetic module records it may be convenient to
+  // make this method always return a ModuleStatus::Evaluated for such a module
+  // so we can assert a module's status without checking which kind it is, even
+  // though synthetic modules don't have this field according to the spec.
+
+  ModuleStatus status = cyclicModuleFields()->status;
+  AssertValidModuleStatus(status);
+
+  if (status == ModuleStatus::Evaluated_Error) {
+    return ModuleStatus::Evaluated;
+  }
+
+  return status;
+}
+
+void ModuleObject::setStatus(ModuleStatus newStatus) {
+  AssertValidModuleStatus(newStatus);
+
+  // Note that under OOM conditions we can fail the module linking process even
+  // after modules have been marked as linked.
+  MOZ_ASSERT((status() <= ModuleStatus::Linked &&
+              newStatus == ModuleStatus::Unlinked) ||
+                 newStatus > status(),
+             "New module status inconsistent with current status");
+
+  cyclicModuleFields()->status = newStatus;
+}
+
+bool ModuleObject::hasTopLevelAwait() const {
+  return cyclicModuleFields()->hasTopLevelAwait;
+}
+
+bool ModuleObject::isAsyncEvaluating() const {
+  return cyclicModuleFields()->getIsAsyncEvaluating();
+}
+
+Maybe<uint32_t> ModuleObject::maybeDfsIndex() const {
+  return cyclicModuleFields()->maybeDfsIndex();
+}
+
+uint32_t ModuleObject::dfsIndex() const { return maybeDfsIndex().value(); }
+
+void ModuleObject::setDfsIndex(uint32_t index) {
+  cyclicModuleFields()->setDfsIndex(index);
+}
+
+Maybe<uint32_t> ModuleObject::maybeDfsAncestorIndex() const {
+  return cyclicModuleFields()->maybeDfsAncestorIndex();
+}
+
+uint32_t ModuleObject::dfsAncestorIndex() const {
+  return maybeDfsAncestorIndex().value();
+}
+
+void ModuleObject::setDfsAncestorIndex(uint32_t index) {
+  cyclicModuleFields()->setDfsAncestorIndex(index);
+}
+
+void ModuleObject::clearDfsIndexes() {
+  cyclicModuleFields()->clearDfsIndexes();
+}
+
+PromiseObject* ModuleObject::maybeTopLevelCapability() const {
+  return cyclicModuleFields()->topLevelCapability;
+}
+
+PromiseObject* ModuleObject::topLevelCapability() const {
+  PromiseObject* capability = maybeTopLevelCapability();
+  MOZ_RELEASE_ASSERT(capability);
+  return capability;
+}
+
+// static
+PromiseObject* ModuleObject::createTopLevelCapability(
+    JSContext* cx, Handle<ModuleObject*> module) {
+  MOZ_ASSERT(!module->maybeTopLevelCapability());
+
+  Rooted<PromiseObject*> resultPromise(cx, CreatePromiseObjectForAsync(cx));
+  if (!resultPromise) {
+    return nullptr;
+  }
+
+  module->setInitialTopLevelCapability(resultPromise);
+  return resultPromise;
+}
+
+void ModuleObject::setInitialTopLevelCapability(
+    Handle<PromiseObject*> capability) {
+  cyclicModuleFields()->topLevelCapability = capability;
+}
+
+ListObject* ModuleObject::asyncParentModules() const {
+  return cyclicModuleFields()->asyncParentModules;
+}
+
+bool ModuleObject::appendAsyncParentModule(JSContext* cx,
+                                           Handle<ModuleObject*> self,
+                                           Handle<ModuleObject*> parent) {
+  Rooted<Value> parentValue(cx, ObjectValue(*parent));
+  return self->asyncParentModules()->append(cx, parentValue);
+}
+
+Maybe<uint32_t> ModuleObject::maybePendingAsyncDependencies() const {
+  return cyclicModuleFields()->maybePendingAsyncDependencies();
+}
+
+uint32_t ModuleObject::pendingAsyncDependencies() const {
+  return maybePendingAsyncDependencies().value();
+}
+
+Maybe<uint32_t> ModuleObject::maybeAsyncEvaluatingPostOrder() const {
+  return cyclicModuleFields()->maybeAsyncEvaluatingPostOrder();
+}
+
+uint32_t ModuleObject::getAsyncEvaluatingPostOrder() const {
+  return cyclicModuleFields()->maybeAsyncEvaluatingPostOrder().value();
+}
+
+void ModuleObject::clearAsyncEvaluatingPostOrder() {
+  MOZ_ASSERT(status() == ModuleStatus::Evaluated);
+
+  JSRuntime* rt = runtimeFromMainThread();
+  MaybeResetPostOrderCounter(rt, getAsyncEvaluatingPostOrder());
+
+  cyclicModuleFields()->clearAsyncEvaluatingPostOrder();
+}
+
+void ModuleObject::setPendingAsyncDependencies(uint32_t newValue) {
+  cyclicModuleFields()->setPendingAsyncDependencies(newValue);
+}
+
+void ModuleObject::setCycleRoot(ModuleObject* cycleRoot) {
+  cyclicModuleFields()->cycleRoot = cycleRoot;
+}
+
+ModuleObject* ModuleObject::getCycleRoot() const {
+  MOZ_RELEASE_ASSERT(cyclicModuleFields()->cycleRoot);
+  return cyclicModuleFields()->cycleRoot;
+}
+
+bool ModuleObject::hasTopLevelCapability() const {
+  return cyclicModuleFields()->topLevelCapability;
+}
+
+bool ModuleObject::hadEvaluationError() const {
+  ModuleStatus fullStatus = cyclicModuleFields()->status;
+  return fullStatus == ModuleStatus::Evaluated_Error;
+}
+
+void ModuleObject::setEvaluationError(HandleValue newValue) {
+  MOZ_ASSERT(status() != ModuleStatus::Unlinked);
+  MOZ_ASSERT(!hadEvaluationError());
+
+  cyclicModuleFields()->status = ModuleStatus::Evaluated_Error;
+  cyclicModuleFields()->evaluationError = newValue;
+
+  MOZ_ASSERT(status() == ModuleStatus::Evaluated);
+  MOZ_ASSERT(hadEvaluationError());
+}
+
+Value ModuleObject::maybeEvaluationError() const {
+  return cyclicModuleFields()->evaluationError;
+}
+
+Value ModuleObject::evaluationError() const {
+  MOZ_ASSERT(hadEvaluationError());
+  return maybeEvaluationError();
+}
+
+JSObject* ModuleObject::metaObject() const {
+  return cyclicModuleFields()->metaObject;
+}
+
+void ModuleObject::setMetaObject(JSObject* obj) {
+  MOZ_ASSERT(obj);
+  MOZ_ASSERT(!metaObject());
+  cyclicModuleFields()->metaObject = obj;
+}
+
+/* static */
+void ModuleObject::trace(JSTracer* trc, JSObject* obj) {
+  ModuleObject& module = obj->as<ModuleObject>();
+  if (module.hasCyclicModuleFields()) {
+    module.cyclicModuleFields()->trace(trc);
+  }
+}
+
+/* static */
+bool ModuleObject::instantiateFunctionDeclarations(JSContext* cx,
+                                                   Handle<ModuleObject*> self) {
+#ifdef DEBUG
+  MOZ_ASSERT(self->status() == ModuleStatus::Linking);
+  if (!AssertFrozen(cx, self)) {
+    return false;
+  }
+#endif
+  // |self| initially manages this vector.
+  UniquePtr<FunctionDeclarationVector>& funDecls =
+      self->cyclicModuleFields()->functionDeclarations;
+  if (!funDecls) {
+    JS_ReportErrorASCII(
+        cx, "Module function declarations have already been instantiated");
+    return false;
+  }
+
+  Rooted<ModuleEnvironmentObject*> env(cx, &self->initialEnvironment());
+  RootedObject obj(cx);
+  RootedValue value(cx);
+  RootedFunction fun(cx);
+  Rooted<PropertyName*> name(cx);
+
+  for (GCThingIndex funIndex : *funDecls) {
+    fun.set(self->script()->getFunction(funIndex));
+    obj = Lambda(cx, fun, env);
+    if (!obj) {
+      return false;
+    }
+
+    name = fun->explicitName()->asPropertyName();
+    value = ObjectValue(*obj);
+    if (!SetProperty(cx, env, name, value)) {
+      return false;
+    }
+  }
+
+  // Free the vector, now its contents are no longer needed.
+  funDecls.reset();
+
+  return true;
+}
+
+/* static */
+bool ModuleObject::execute(JSContext* cx, Handle<ModuleObject*> self) {
+#ifdef DEBUG
+  MOZ_ASSERT(self->status() == ModuleStatus::Evaluating ||
+             self->status() == ModuleStatus::EvaluatingAsync ||
+             self->status() == ModuleStatus::Evaluated);
+  MOZ_ASSERT(!self->hadEvaluationError());
+  if (!AssertFrozen(cx, self)) {
+    return false;
+  }
+#endif
+
+  RootedScript script(cx, self->script());
+
+  auto guardA = mozilla::MakeScopeExit([&] {
+    if (self->hasTopLevelAwait()) {
+      // Handled in AsyncModuleExecutionFulfilled and
+      // AsyncModuleExecutionRejected.
+      return;
+    }
+    ModuleObject::onTopLevelEvaluationFinished(self);
+  });
+
+  Rooted<ModuleEnvironmentObject*> env(cx, self->environment());
+  if (!env) {
+    JS_ReportErrorASCII(cx,
+                        "Module declarations have not yet been instantiated");
+    return false;
+  }
+
+  Rooted<Value> ignored(cx);
+  return Execute(cx, script, env, &ignored);
+}
+
+/* static */
+void ModuleObject::onTopLevelEvaluationFinished(ModuleObject* module) {
+  // ScriptSlot is used by debugger to access environments during evaluating
+  // the top-level script.
+  // Clear the reference at exit to prevent us keeping this alive unnecessarily.
+  module->setReservedSlot(ScriptSlot, UndefinedValue());
+}
+
+/* static */
+ModuleNamespaceObject* ModuleObject::createNamespace(
+    JSContext* cx, Handle<ModuleObject*> self,
+    MutableHandle<UniquePtr<ExportNameVector>> exports) {
+  MOZ_ASSERT(!self->namespace_());
+
+  Rooted<UniquePtr<IndirectBindingMap>> bindings(cx);
+  bindings = cx->make_unique<IndirectBindingMap>();
+  if (!bindings) {
+    return nullptr;
+  }
+
+  auto* ns = ModuleNamespaceObject::create(cx, self, exports, &bindings);
+  if (!ns) {
+    return nullptr;
+  }
+
+  self->initReservedSlot(NamespaceSlot, ObjectValue(*ns));
+  return ns;
+}
+
+/* static */
+bool ModuleObject::createEnvironment(JSContext* cx,
+                                     Handle<ModuleObject*> self) {
+  Rooted<ModuleEnvironmentObject*> env(
+      cx, ModuleEnvironmentObject::create(cx, self));
+  if (!env) {
+    return false;
+  }
+
+  self->setInitialEnvironment(env);
+  return true;
+}
+
+///////////////////////////////////////////////////////////////////////////
+// ModuleBuilder
+
+ModuleBuilder::ModuleBuilder(FrontendContext* fc,
+                             const frontend::EitherParser& eitherParser)
+    : fc_(fc),
+      eitherParser_(eitherParser),
+      requestedModuleSpecifiers_(fc),
+      importEntries_(fc),
+      exportEntries_(fc),
+      exportNames_(fc) {}
+
+bool ModuleBuilder::noteFunctionDeclaration(FrontendContext* fc,
+                                            uint32_t funIndex) {
+  if (!functionDecls_.emplaceBack(funIndex)) {
+    js::ReportOutOfMemory(fc);
+    return false;
+  }
+  return true;
+}
+
+void ModuleBuilder::noteAsync(frontend::StencilModuleMetadata& metadata) {
+  metadata.isAsync = true;
+}
+
+bool ModuleBuilder::buildTables(frontend::StencilModuleMetadata& metadata) {
+  // https://tc39.es/ecma262/#sec-parsemodule
+  // 15.2.1.17.1 ParseModule, Steps 4-11.
+
+  // Step 4.
+  metadata.moduleRequests = std::move(moduleRequests_);
+  metadata.requestedModules = std::move(requestedModules_);
+
+  // Step 5.
+  if (!metadata.importEntries.reserve(importEntries_.count())) {
+    js::ReportOutOfMemory(fc_);
+    return false;
+  }
+  for (auto r = importEntries_.all(); !r.empty(); r.popFront()) {
+    frontend::StencilModuleEntry& entry = r.front().value();
+    metadata.importEntries.infallibleAppend(entry);
+  }
+
+  // Steps 6-11.
+  for (const frontend::StencilModuleEntry& exp : exportEntries_) {
+    if (!exp.moduleRequest) {
+      frontend::StencilModuleEntry* importEntry = importEntryFor(exp.localName);
+      if (!importEntry) {
+        if (!metadata.localExportEntries.append(exp)) {
+          js::ReportOutOfMemory(fc_);
+          return false;
+        }
+      } else {
+        if (!importEntry->importName) {
+          if (!metadata.localExportEntries.append(exp)) {
+            js::ReportOutOfMemory(fc_);
+            return false;
+          }
+        } else {
+          // All names should have already been marked as used-by-stencil.
+          auto entry = frontend::StencilModuleEntry::exportFromEntry(
+              importEntry->moduleRequest, importEntry->importName,
+              exp.exportName, exp.lineno, exp.column);
+          if (!metadata.indirectExportEntries.append(entry)) {
+            js::ReportOutOfMemory(fc_);
+            return false;
+          }
+        }
+      }
+    } else if (!exp.importName && !exp.exportName) {
+      if (!metadata.starExportEntries.append(exp)) {
+        js::ReportOutOfMemory(fc_);
+        return false;
+      }
+    } else {
+      if (!metadata.indirectExportEntries.append(exp)) {
+        js::ReportOutOfMemory(fc_);
+        return false;
+      }
+    }
+  }
+
+  return true;
+}
+
+void ModuleBuilder::finishFunctionDecls(
+    frontend::StencilModuleMetadata& metadata) {
+  metadata.functionDecls = std::move(functionDecls_);
+}
+
+bool frontend::StencilModuleMetadata::createModuleRequestObjects(
+    JSContext* cx, CompilationAtomCache& atomCache,
+    MutableHandle<ModuleRequestVector> output) const {
+  if (!output.reserve(moduleRequests.length())) {
+    ReportOutOfMemory(cx);
+    return false;
+  }
+
+  Rooted<ModuleRequestObject*> object(cx);
+  for (const StencilModuleRequest& request : moduleRequests) {
+    object = createModuleRequestObject(cx, atomCache, request);
+    if (!object) {
+      return false;
+    }
+
+    output.infallibleEmplaceBack(object);
+  }
+
+  return true;
+}
+
+ModuleRequestObject* frontend::StencilModuleMetadata::createModuleRequestObject(
+    JSContext* cx, CompilationAtomCache& atomCache,
+    const StencilModuleRequest& request) const {
+  Rooted<ArrayObject*> assertionArray(cx);
+  uint32_t numberOfAssertions = request.assertions.length();
+  if (numberOfAssertions > 0) {
+    assertionArray = NewDenseFullyAllocatedArray(cx, numberOfAssertions);
+    if (!assertionArray) {
+      return nullptr;
+    }
+    assertionArray->ensureDenseInitializedLength(0, numberOfAssertions);
+
+    Rooted<PlainObject*> assertionObject(cx);
+    RootedId assertionKey(cx);
+    RootedValue assertionValue(cx);
+    for (uint32_t j = 0; j < numberOfAssertions; ++j) {
+      assertionObject = NewPlainObject(cx);
+      if (!assertionObject) {
+        return nullptr;
+      }
+
+      JSAtom* jsatom =
+          atomCache.getExistingAtomAt(cx, request.assertions[j].key);
+      MOZ_ASSERT(jsatom);
+      assertionKey = AtomToId(jsatom);
+
+      jsatom = atomCache.getExistingAtomAt(cx, request.assertions[j].value);
+      MOZ_ASSERT(jsatom);
+      assertionValue = StringValue(jsatom);
+
+      if (!DefineDataProperty(cx, assertionObject, assertionKey, assertionValue,
+                              JSPROP_ENUMERATE)) {
+        return nullptr;
+      }
+
+      assertionArray->initDenseElement(j, ObjectValue(*assertionObject));
+    }
+  }
+
+  Rooted<JSAtom*> specifier(cx,
+                            atomCache.getExistingAtomAt(cx, request.specifier));
+  MOZ_ASSERT(specifier);
+
+  return ModuleRequestObject::create(cx, specifier, assertionArray);
+}
+
+bool frontend::StencilModuleMetadata::createImportEntries(
+    JSContext* cx, CompilationAtomCache& atomCache,
+    Handle<ModuleRequestVector> moduleRequests,
+    MutableHandle<ImportEntryVector> output) const {
+  if (!output.reserve(importEntries.length())) {
+    ReportOutOfMemory(cx);
+    return false;
+  }
+
+  for (const StencilModuleEntry& entry : importEntries) {
+    Rooted<ModuleRequestObject*> moduleRequest(cx);
+    moduleRequest = moduleRequests[entry.moduleRequest.value()].get();
+    MOZ_ASSERT(moduleRequest);
+
+    Rooted<JSAtom*> localName(cx);
+    if (entry.localName) {
+      localName = atomCache.getExistingAtomAt(cx, entry.localName);
+      MOZ_ASSERT(localName);
+    }
+
+    Rooted<JSAtom*> importName(cx);
+    if (entry.importName) {
+      importName = atomCache.getExistingAtomAt(cx, entry.importName);
+      MOZ_ASSERT(importName);
+    }
+
+    MOZ_ASSERT(!entry.exportName);
+
+    output.infallibleEmplaceBack(moduleRequest, importName, localName,
+                                 entry.lineno, entry.column);
+  }
+
+  return true;
+}
+
+bool frontend::StencilModuleMetadata::createExportEntries(
+    JSContext* cx, frontend::CompilationAtomCache& atomCache,
+    Handle<ModuleRequestVector> moduleRequests,
+    const frontend::StencilModuleMetadata::EntryVector& input,
+    MutableHandle<ExportEntryVector> output) const {
+  if (!output.reserve(output.length() + input.length())) {
+    ReportOutOfMemory(cx);
+    return false;
+  }
+
+  for (const frontend::StencilModuleEntry& entry : input) {
+    Rooted<JSAtom*> exportName(cx);
+    if (entry.exportName) {
+      exportName = atomCache.getExistingAtomAt(cx, entry.exportName);
+      MOZ_ASSERT(exportName);
+    }
+
+    Rooted<ModuleRequestObject*> moduleRequestObject(cx);
+    if (entry.moduleRequest) {
+      moduleRequestObject = moduleRequests[entry.moduleRequest.value()].get();
+      MOZ_ASSERT(moduleRequestObject);
+    }
+
+    Rooted<JSAtom*> localName(cx);
+    if (entry.localName) {
+      localName = atomCache.getExistingAtomAt(cx, entry.localName);
+      MOZ_ASSERT(localName);
+    }
+
+    Rooted<JSAtom*> importName(cx);
+    if (entry.importName) {
+      importName = atomCache.getExistingAtomAt(cx, entry.importName);
+      MOZ_ASSERT(importName);
+    }
+
+    output.infallibleEmplaceBack(exportName, moduleRequestObject, importName,
+                                 localName, entry.lineno, entry.column);
+  }
+
+  return true;
+}
+
+bool frontend::StencilModuleMetadata::createRequestedModules(
+    JSContext* cx, CompilationAtomCache& atomCache,
+    Handle<ModuleRequestVector> moduleRequests,
+    MutableHandle<RequestedModuleVector> output) const {
+  if (!output.reserve(requestedModules.length())) {
+    ReportOutOfMemory(cx);
+    return false;
+  }
+
+  for (const frontend::StencilModuleEntry& entry : requestedModules) {
+    Rooted<ModuleRequestObject*> moduleRequest(cx);
+    moduleRequest = moduleRequests[entry.moduleRequest.value()].get();
+    MOZ_ASSERT(moduleRequest);
+
+    MOZ_ASSERT(!entry.localName);
+    MOZ_ASSERT(!entry.importName);
+    MOZ_ASSERT(!entry.exportName);
+
+    output.infallibleEmplaceBack(moduleRequest, entry.lineno, entry.column);
+  }
+
+  return true;
+}
+
+// Use StencilModuleMetadata data to fill in ModuleObject
+bool frontend::StencilModuleMetadata::initModule(
+    JSContext* cx, FrontendContext* fc,
+    frontend::CompilationAtomCache& atomCache,
+    JS::Handle<ModuleObject*> module) const {
+  Rooted<ModuleRequestVector> moduleRequestsVector(cx);
+  if (!createModuleRequestObjects(cx, atomCache, &moduleRequestsVector)) {
+    return false;
+  }
+
+  Rooted<RequestedModuleVector> requestedModulesVector(cx);
+  if (!createRequestedModules(cx, atomCache, moduleRequestsVector,
+                              &requestedModulesVector)) {
+    return false;
+  }
+
+  Rooted<ImportEntryVector> importEntriesVector(cx);
+  if (!createImportEntries(cx, atomCache, moduleRequestsVector,
+                           &importEntriesVector)) {
+    return false;
+  }
+
+  Rooted<ExportEntryVector> exportEntriesVector(cx);
+  if (!createExportEntries(cx, atomCache, moduleRequestsVector,
+                           localExportEntries, &exportEntriesVector)) {
+    return false;
+  }
+
+  Rooted<ExportEntryVector> indirectExportEntriesVector(cx);
+  if (!createExportEntries(cx, atomCache, moduleRequestsVector,
+                           indirectExportEntries, &exportEntriesVector)) {
+    return false;
+  }
+
+  Rooted<ExportEntryVector> starExportEntriesVector(cx);
+  if (!createExportEntries(cx, atomCache, moduleRequestsVector,
+                           starExportEntries, &exportEntriesVector)) {
+    return false;
+  }
+
+  // Copy the vector of declarations to the ModuleObject.
+  auto functionDeclsCopy = MakeUnique<FunctionDeclarationVector>();
+  if (!functionDeclsCopy || !functionDeclsCopy->appendAll(functionDecls)) {
+    js::ReportOutOfMemory(fc);
+    return false;
+  }
+  module->initFunctionDeclarations(std::move(functionDeclsCopy));
+
+  Rooted<ListObject*> asyncParentModulesList(cx, ListObject::create(cx));
+  if (!asyncParentModulesList) {
+    return false;
+  }
+
+  module->initAsyncSlots(cx, isAsync, asyncParentModulesList);
+
+  module->initImportExportData(
+      &requestedModulesVector, &importEntriesVector, &exportEntriesVector,
+      localExportEntries.length(), indirectExportEntries.length(),
+      starExportEntries.length());
+
+  return true;
+}
+
+bool ModuleBuilder::isAssertionSupported(JS::ImportAssertion supportedAssertion,
+                                         frontend::TaggedParserAtomIndex key) {
+  if (!key.isWellKnownAtomId()) {
+    return false;
+  }
+
+  bool result = false;
+
+  switch (supportedAssertion) {
+    case JS::ImportAssertion::Type:
+      result = key.toWellKnownAtomId() == WellKnownAtomId::type;
+      break;
+  }
+
+  return result;
+}
+
+bool ModuleBuilder::processAssertions(frontend::StencilModuleRequest& request,
+                                      frontend::ListNode* assertionList) {
+  using namespace js::frontend;
+
+  for (ParseNode* assertionItem : assertionList->contents()) {
+    BinaryNode* assertion = &assertionItem->as<BinaryNode>();
+    MOZ_ASSERT(assertion->isKind(ParseNodeKind::ImportAssertion));
+
+    auto key = assertion->left()->as<NameNode>().atom();
+    auto value = assertion->right()->as<NameNode>().atom();
+
+    for (JS::ImportAssertion assertion : fc_->getSupportedImportAssertions()) {
+      if (isAssertionSupported(assertion, key)) {
+        markUsedByStencil(key);
+        markUsedByStencil(value);
+
+        StencilModuleAssertion assertionStencil(key, value);
+        if (!request.assertions.append(assertionStencil)) {
+          js::ReportOutOfMemory(fc_);
+          return false;
+        }
+      }
+    }
+  }
+
+  return true;
+}
+
+bool ModuleBuilder::processImport(frontend::BinaryNode* importNode) {
+  using namespace js::frontend;
+
+  MOZ_ASSERT(importNode->isKind(ParseNodeKind::ImportDecl));
+
+  auto* specList = &importNode->left()->as<ListNode>();
+  MOZ_ASSERT(specList->isKind(ParseNodeKind::ImportSpecList));
+
+  auto* moduleRequest = &importNode->right()->as<BinaryNode>();
+  MOZ_ASSERT(moduleRequest->isKind(ParseNodeKind::ImportModuleRequest));
+
+  auto* moduleSpec = &moduleRequest->left()->as<NameNode>();
+  MOZ_ASSERT(moduleSpec->isKind(ParseNodeKind::StringExpr));
+
+  auto* assertionList = &moduleRequest->right()->as<ListNode>();
+  MOZ_ASSERT(assertionList->isKind(ParseNodeKind::ImportAssertionList));
+
+  auto specifier = moduleSpec->atom();
+  MaybeModuleRequestIndex moduleRequestIndex =
+      appendModuleRequest(specifier, assertionList);
+  if (!moduleRequestIndex.isSome()) {
+    return false;
+  }
+
+  if (!maybeAppendRequestedModule(moduleRequestIndex, moduleSpec)) {
+    return false;
+  }
+
+  for (ParseNode* item : specList->contents()) {
+    uint32_t line;
+    uint32_t column;
+    eitherParser_.computeLineAndColumn(item->pn_pos.begin, &line, &column);
+
+    StencilModuleEntry entry;
+    TaggedParserAtomIndex localName;
+    if (item->isKind(ParseNodeKind::ImportSpec)) {
+      auto* spec = &item->as<BinaryNode>();
+
+      auto* importNameNode = &spec->left()->as<NameNode>();
+      auto* localNameNode = &spec->right()->as<NameNode>();
+
+      auto importName = importNameNode->atom();
+      localName = localNameNode->atom();
+
+      markUsedByStencil(localName);
+      markUsedByStencil(importName);
+      entry = StencilModuleEntry::importEntry(moduleRequestIndex, localName,
+                                              importName, line, column);
+    } else {
+      MOZ_ASSERT(item->isKind(ParseNodeKind::ImportNamespaceSpec));
+      auto* spec = &item->as<UnaryNode>();
+
+      auto* localNameNode = &spec->kid()->as<NameNode>();
+
+      localName = localNameNode->atom();
+
+      markUsedByStencil(localName);
+      entry = StencilModuleEntry::importNamespaceEntry(moduleRequestIndex,
+                                                       localName, line, column);
+    }
+
+    if (!importEntries_.put(localName, entry)) {
+      return false;
+    }
+  }
+
+  return true;
+}
+
+bool ModuleBuilder::processExport(frontend::ParseNode* exportNode) {
+  using namespace js::frontend;
+
+  MOZ_ASSERT(exportNode->isKind(ParseNodeKind::ExportStmt) ||
+             exportNode->isKind(ParseNodeKind::ExportDefaultStmt));
+
+  bool isDefault = exportNode->isKind(ParseNodeKind::ExportDefaultStmt);
+  ParseNode* kid = isDefault ? exportNode->as<BinaryNode>().left()
+                             : exportNode->as<UnaryNode>().kid();
+
+  if (isDefault && exportNode->as<BinaryNode>().right()) {
+    // This is an export default containing an expression.
+    auto localName = TaggedParserAtomIndex::WellKnown::default_();
+    auto exportName = TaggedParserAtomIndex::WellKnown::default_();
+    return appendExportEntry(exportName, localName);
+  }
+
+  switch (kid->getKind()) {
+    case ParseNodeKind::ExportSpecList: {
+      MOZ_ASSERT(!isDefault);
+      for (ParseNode* item : kid->as<ListNode>().contents()) {
+        BinaryNode* spec = &item->as<BinaryNode>();
+        MOZ_ASSERT(spec->isKind(ParseNodeKind::ExportSpec));
+
+        NameNode* localNameNode = &spec->left()->as<NameNode>();
+        NameNode* exportNameNode = &spec->right()->as<NameNode>();
+
+        auto localName = localNameNode->atom();
+        auto exportName = exportNameNode->atom();
+
+        if (!appendExportEntry(exportName, localName, spec)) {
+          return false;
+        }
+      }
+      break;
+    }
+
+    case ParseNodeKind::ClassDecl: {
+      const ClassNode& cls = kid->as<ClassNode>();
+      MOZ_ASSERT(cls.names());
+      auto localName = cls.names()->innerBinding()->atom();
+      auto exportName =
+          isDefault ? TaggedParserAtomIndex::WellKnown::default_() : localName;
+      if (!appendExportEntry(exportName, localName)) {
+        return false;
+      }
+      break;
+    }
+
+    case ParseNodeKind::VarStmt:
+    case ParseNodeKind::ConstDecl:
+    case ParseNodeKind::LetDecl: {
+      for (ParseNode* binding : kid->as<ListNode>().contents()) {
+        if (binding->isKind(ParseNodeKind::AssignExpr)) {
+          binding = binding->as<AssignmentNode>().left();
+        } else {
+          MOZ_ASSERT(binding->isKind(ParseNodeKind::Name));
+        }
+
+        if (binding->isKind(ParseNodeKind::Name)) {
+          auto localName = binding->as<NameNode>().atom();
+          auto exportName = isDefault
+                                ? TaggedParserAtomIndex::WellKnown::default_()
+                                : localName;
+          if (!appendExportEntry(exportName, localName)) {
+            return false;
+          }
+        } else if (binding->isKind(ParseNodeKind::ArrayExpr)) {
+          if (!processExportArrayBinding(&binding->as<ListNode>())) {
+            return false;
+          }
+        } else {
+          MOZ_ASSERT(binding->isKind(ParseNodeKind::ObjectExpr));
+          if (!processExportObjectBinding(&binding->as<ListNode>())) {
+            return false;
+          }
+        }
+      }
+      break;
+    }
+
+    case ParseNodeKind::Function: {
+      FunctionBox* box = kid->as<FunctionNode>().funbox();
+      MOZ_ASSERT(!box->isArrow());
+      auto localName = box->explicitName();
+      auto exportName =
+          isDefault ? TaggedParserAtomIndex::WellKnown::default_() : localName;
+      if (!appendExportEntry(exportName, localName)) {
+        return false;
+      }
+      break;
+    }
+
+    default:
+      MOZ_CRASH("Unexpected parse node");
+  }
+
+  return true;
+}
+
+bool ModuleBuilder::processExportBinding(frontend::ParseNode* binding) {
+  using namespace js::frontend;
+
+  if (binding->isKind(ParseNodeKind::Name)) {
+    auto name = binding->as<NameNode>().atom();
+    return appendExportEntry(name, name);
+  }
+
+  if (binding->isKind(ParseNodeKind::ArrayExpr)) {
+    return processExportArrayBinding(&binding->as<ListNode>());
+  }
+
+  MOZ_ASSERT(binding->isKind(ParseNodeKind::ObjectExpr));
+  return processExportObjectBinding(&binding->as<ListNode>());
+}
+
+bool ModuleBuilder::processExportArrayBinding(frontend::ListNode* array) {
+  using namespace js::frontend;
+
+  MOZ_ASSERT(array->isKind(ParseNodeKind::ArrayExpr));
+
+  for (ParseNode* node : array->contents()) {
+    if (node->isKind(ParseNodeKind::Elision)) {
+      continue;
+    }
+
+    if (node->isKind(ParseNodeKind::Spread)) {
+      node = node->as<UnaryNode>().kid();
+    } else if (node->isKind(ParseNodeKind::AssignExpr)) {
+      node = node->as<AssignmentNode>().left();
+    }
+
+    if (!processExportBinding(node)) {
+      return false;
+    }
+  }
+
+  return true;
+}
+
+bool ModuleBuilder::processExportObjectBinding(frontend::ListNode* obj) {
+  using namespace js::frontend;
+
+  MOZ_ASSERT(obj->isKind(ParseNodeKind::ObjectExpr));
+
+  for (ParseNode* node : obj->contents()) {
+    MOZ_ASSERT(node->isKind(ParseNodeKind::MutateProto) ||
+               node->isKind(ParseNodeKind::PropertyDefinition) ||
+               node->isKind(ParseNodeKind::Shorthand) ||
+               node->isKind(ParseNodeKind::Spread));
+
+    ParseNode* target;
+    if (node->isKind(ParseNodeKind::Spread)) {
+      target = node->as<UnaryNode>().kid();
+    } else {
+      if (node->isKind(ParseNodeKind::MutateProto)) {
+        target = node->as<UnaryNode>().kid();
+      } else {
+        target = node->as<BinaryNode>().right();
+      }
+
+      if (target->isKind(ParseNodeKind::AssignExpr)) {
+        target = target->as<AssignmentNode>().left();
+      }
+    }
+
+    if (!processExportBinding(target)) {
+      return false;
+    }
+  }
+
+  return true;
+}
+
+bool ModuleBuilder::processExportFrom(frontend::BinaryNode* exportNode) {
+  using namespace js::frontend;
+
+  MOZ_ASSERT(exportNode->isKind(ParseNodeKind::ExportFromStmt));
+
+  auto* specList = &exportNode->left()->as<ListNode>();
+  MOZ_ASSERT(specList->isKind(ParseNodeKind::ExportSpecList));
+
+  auto* moduleRequest = &exportNode->right()->as<BinaryNode>();
+  MOZ_ASSERT(moduleRequest->isKind(ParseNodeKind::ImportModuleRequest));
+
+  auto* moduleSpec = &moduleRequest->left()->as<NameNode>();
+  MOZ_ASSERT(moduleSpec->isKind(ParseNodeKind::StringExpr));
+
+  auto* assertionList = &moduleRequest->right()->as<ListNode>();
+  MOZ_ASSERT(assertionList->isKind(ParseNodeKind::ImportAssertionList));
+
+  auto specifier = moduleSpec->atom();
+  MaybeModuleRequestIndex moduleRequestIndex =
+      appendModuleRequest(specifier, assertionList);
+  if (!moduleRequestIndex.isSome()) {
+    return false;
+  }
+
+  if (!maybeAppendRequestedModule(moduleRequestIndex, moduleSpec)) {
+    return false;
+  }
+
+  for (ParseNode* spec : specList->contents()) {
+    uint32_t line;
+    uint32_t column;
+    eitherParser_.computeLineAndColumn(spec->pn_pos.begin, &line, &column);
+
+    StencilModuleEntry entry;
+    TaggedParserAtomIndex exportName;
+    if (spec->isKind(ParseNodeKind::ExportSpec)) {
+      auto* importNameNode = &spec->as<BinaryNode>().left()->as<NameNode>();
+      auto* exportNameNode = &spec->as<BinaryNode>().right()->as<NameNode>();
+
+      auto importName = importNameNode->atom();
+      exportName = exportNameNode->atom();
+
+      markUsedByStencil(importName);
+      markUsedByStencil(exportName);
+      entry = StencilModuleEntry::exportFromEntry(
+          moduleRequestIndex, importName, exportName, line, column);
+    } else if (spec->isKind(ParseNodeKind::ExportNamespaceSpec)) {
+      auto* exportNameNode = &spec->as<UnaryNode>().kid()->as<NameNode>();
+
+      exportName = exportNameNode->atom();
+
+      markUsedByStencil(exportName);
+      entry = StencilModuleEntry::exportNamespaceFromEntry(
+          moduleRequestIndex, exportName, line, column);
+    } else {
+      MOZ_ASSERT(spec->isKind(ParseNodeKind::ExportBatchSpecStmt));
+
+      entry = StencilModuleEntry::exportBatchFromEntry(moduleRequestIndex, line,
+                                                       column);
+    }
+
+    if (!exportEntries_.append(entry)) {
+      return false;
+    }
+    if (exportName && !exportNames_.put(exportName)) {
+      return false;
+    }
+  }
+
+  return true;
+}
+
+frontend::StencilModuleEntry* ModuleBuilder::importEntryFor(
+    frontend::TaggedParserAtomIndex localName) const {
+  MOZ_ASSERT(localName);
+  auto ptr = importEntries_.lookup(localName);
+  if (!ptr) {
+    return nullptr;
+  }
+
+  return &ptr->value();
+}
+
+bool ModuleBuilder::hasExportedName(
+    frontend::TaggedParserAtomIndex name) const {
+  MOZ_ASSERT(name);
+  return exportNames_.has(name);
+}
+
+bool ModuleBuilder::appendExportEntry(
+    frontend::TaggedParserAtomIndex exportName,
+    frontend::TaggedParserAtomIndex localName, frontend::ParseNode* node) {
+  uint32_t line = 0;
+  uint32_t column = 0;
+  if (node) {
+    eitherParser_.computeLineAndColumn(node->pn_pos.begin, &line, &column);
+  }
+
+  markUsedByStencil(localName);
+  markUsedByStencil(exportName);
+  auto entry = frontend::StencilModuleEntry::exportAsEntry(
+      localName, exportName, line, column);
+  if (!exportEntries_.append(entry)) {
+    return false;
+  }
+
+  if (!exportNames_.put(exportName)) {
+    return false;
+  }
+
+  return true;
+}
+
+frontend::MaybeModuleRequestIndex ModuleBuilder::appendModuleRequest(
+    frontend::TaggedParserAtomIndex specifier,
+    frontend::ListNode* assertionList) {
+  markUsedByStencil(specifier);
+  auto request = frontend::StencilModuleRequest(specifier);
+
+  if (!processAssertions(request, assertionList)) {
+    return MaybeModuleRequestIndex();
+  }
+
+  uint32_t index = moduleRequests_.length();
+  if (!moduleRequests_.append(request)) {
+    js::ReportOutOfMemory(fc_);
+    return MaybeModuleRequestIndex();
+  }
+
+  return MaybeModuleRequestIndex(index);
+}
+
+bool ModuleBuilder::maybeAppendRequestedModule(
+    MaybeModuleRequestIndex moduleRequest, frontend::ParseNode* node) {
+  auto specifier = moduleRequests_[moduleRequest.value()].specifier;
+  if (requestedModuleSpecifiers_.has(specifier)) {
+    return true;
+  }
+
+  uint32_t line;
+  uint32_t column;
+  eitherParser_.computeLineAndColumn(node->pn_pos.begin, &line, &column);
+
+  auto entry = frontend::StencilModuleEntry::requestedModule(moduleRequest,
+                                                             line, column);
+
+  if (!requestedModules_.append(entry)) {
+    js::ReportOutOfMemory(fc_);
+    return false;
+  }
+
+  return requestedModuleSpecifiers_.put(specifier);
+}
+
+void ModuleBuilder::markUsedByStencil(frontend::TaggedParserAtomIndex name) {
+  // Imported/exported identifiers must be atomized.
+  eitherParser_.parserAtoms().markUsedByStencil(
+      name, frontend::ParserAtom::Atomize::Yes);
+}
+
+JSObject* js::GetOrCreateModuleMetaObject(JSContext* cx,
+                                          HandleObject moduleArg) {
+  Handle<ModuleObject*> module = moduleArg.as<ModuleObject>();
+  if (JSObject* obj = module->metaObject()) {
+    return obj;
+  }
+
+  RootedObject metaObject(cx, NewPlainObjectWithProto(cx, nullptr));
+  if (!metaObject) {
+    return nullptr;
+  }
+
+  JS::ModuleMetadataHook func = cx->runtime()->moduleMetadataHook;
+  if (!func) {
+    JS_ReportErrorASCII(cx, "Module metadata hook not set");
+    return nullptr;
+  }
+
+  RootedValue modulePrivate(cx, JS::GetModulePrivate(module));
+  if (!func(cx, modulePrivate, metaObject)) {
+    return nullptr;
+  }
+
+  module->setMetaObject(metaObject);
+
+  return metaObject;
+}
+
+ModuleObject* js::CallModuleResolveHook(JSContext* cx,
+                                        HandleValue referencingPrivate,
+                                        HandleObject moduleRequest) {
+  JS::ModuleResolveHook moduleResolveHook = cx->runtime()->moduleResolveHook;
+  if (!moduleResolveHook) {
+    JS_ReportErrorASCII(cx, "Module resolve hook not set");
+    return nullptr;
+  }
+
+  RootedObject result(cx,
+                      moduleResolveHook(cx, referencingPrivate, moduleRequest));
+  if (!result) {
+    return nullptr;
+  }
+
+  if (!result->is<ModuleObject>()) {
+    JS_ReportErrorASCII(cx, "Module resolve hook did not return Module object");
+    return nullptr;
+  }
+
+  return &result->as<ModuleObject>();
+}
+
+bool ModuleObject::topLevelCapabilityResolve(JSContext* cx,
+                                             Handle<ModuleObject*> module) {
+  RootedValue rval(cx);
+  Rooted<PromiseObject*> promise(
+      cx, &module->topLevelCapability()->as<PromiseObject>());
+  return AsyncFunctionReturned(cx, promise, rval);
+}
+
+bool ModuleObject::topLevelCapabilityReject(JSContext* cx,
+                                            Handle<ModuleObject*> module,
+                                            HandleValue error) {
+  Rooted<PromiseObject*> promise(
+      cx, &module->topLevelCapability()->as<PromiseObject>());
+  return AsyncFunctionThrown(cx, promise, error);
+}
+
+// https://tc39.es/proposal-import-assertions/#sec-evaluate-import-call
+// NOTE: The caller needs to handle the promise.
+static bool EvaluateDynamicImportOptions(
+    JSContext* cx, HandleValue optionsArg,
+    MutableHandle<ArrayObject*> assertionArrayArg) {
+  // Step 10. If options is not undefined, then.
+  if (optionsArg.isUndefined()) {
+    return true;
+  }
+
+  // Step 10.a. If Type(options) is not Object,
+  if (!optionsArg.isObject()) {
+    JS_ReportErrorNumberASCII(
+        cx, GetErrorMessage, nullptr, JSMSG_NOT_EXPECTED_TYPE, "import",
+        "object or undefined", InformalValueTypeName(optionsArg));
+    return false;
+  }
+
+  RootedObject assertWrapperObject(cx, &optionsArg.toObject());
+  RootedValue assertValue(cx);
+
+  // Step 10.b. Let assertionsObj be Get(options, "assert").
+  RootedId assertId(cx, NameToId(cx->names().assert_));
+  if (!GetProperty(cx, assertWrapperObject, assertWrapperObject, assertId,
+                   &assertValue)) {
+    return false;
+  }
+
+  // Step 10.d. If assertionsObj is not undefined.
+  if (assertValue.isUndefined()) {
+    return true;
+  }
+
+  // Step 10.d.i. If Type(assertionsObj) is not Object.
+  if (!assertValue.isObject()) {
+    JS_ReportErrorNumberASCII(
+        cx, GetErrorMessage, nullptr, JSMSG_NOT_EXPECTED_TYPE, "import",
+        "object or undefined", InformalValueTypeName(assertValue));
+    return false;
+  }
+
+  // Step 10.d.i. Let keys be EnumerableOwnPropertyNames(assertionsObj, key).
+  RootedObject assertObject(cx, &assertValue.toObject());
+  RootedIdVector assertions(cx);
+  if (!GetPropertyKeys(cx, assertObject, JSITER_OWNONLY, &assertions)) {
+    return false;
+  }
+
+  uint32_t numberOfAssertions = assertions.length();
+  if (numberOfAssertions == 0) {
+    return true;
+  }
+
+  // Step 9 (reordered). Let assertions be a new empty List.
+  Rooted<ArrayObject*> assertionArray(
+      cx, NewDenseFullyAllocatedArray(cx, numberOfAssertions));
+  if (!assertionArray) {
+    return false;
+  }
+  assertionArray->ensureDenseInitializedLength(0, numberOfAssertions);
+
+  // Step 10.d.iv. Let supportedAssertions be
+  // !HostGetSupportedImportAssertions().
+  const JS::ImportAssertionVector& supportedAssertions =
+      cx->runtime()->supportedImportAssertions;
+
+  size_t numberOfValidAssertions = 0;
+
+  // Step 10.d.v. For each String key of keys,
+  RootedId key(cx);
+  for (size_t i = 0; i < numberOfAssertions; i++) {
+    key = assertions[i];
+
+    // Step 10.d.v.1. Let value be Get(assertionsObj, key).
+    RootedValue value(cx);
+    if (!GetProperty(cx, assertObject, assertObject, key, &value)) {
+      return false;
+    }
+
+    // Step 10.d.v.3. If Type(value) is not String, then.
+    if (!value.isString()) {
+      JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                                JSMSG_NOT_EXPECTED_TYPE, "import", "string",
+                                InformalValueTypeName(value));
+      return false;
+    }
+
+    // Step 10.d.v.4. If supportedAssertions contains key, then Append {
+    // [[Key]]: key, [[Value]]: value } to assertions.
+    for (JS::ImportAssertion assertion : supportedAssertions) {
+      bool supported = false;
+      switch (assertion) {
+        case JS::ImportAssertion::Type: {
+          supported = key.toAtom() == cx->names().type;
+        } break;
+      }
+
+      if (supported) {
+        Rooted<PlainObject*> assertionObj(cx, NewPlainObject(cx));
+        if (!assertionObj) {
+          return false;
+        }
+
+        if (!DefineDataProperty(cx, assertionObj, key, value,
+                                JSPROP_ENUMERATE)) {
+          return false;
+        }
+
+        assertionArray->initDenseElement(numberOfValidAssertions,
+                                         ObjectValue(*assertionObj));
+        ++numberOfValidAssertions;
+      }
+    }
+  }
+
+  if (numberOfValidAssertions == 0) {
+    return true;
+  }
+
+  assertionArray->setLength(numberOfValidAssertions);
+  assertionArrayArg.set(assertionArray);
+
+  return true;
+}
+
+JSObject* js::StartDynamicModuleImport(JSContext* cx, HandleScript script,
+                                       HandleValue specifierArg,
+                                       HandleValue optionsArg) {
+  RootedObject promiseConstructor(cx, JS::GetPromiseConstructor(cx));
+  if (!promiseConstructor) {
+    return nullptr;
+  }
+
+  RootedObject promiseObject(cx, JS::NewPromiseObject(cx, nullptr));
+  if (!promiseObject) {
+    return nullptr;
+  }
+
+  Handle<PromiseObject*> promise = promiseObject.as<PromiseObject>();
+
+  JS::ModuleDynamicImportHook importHook =
+      cx->runtime()->moduleDynamicImportHook;
+
+  if (!importHook) {
+    // Dynamic import can be disabled by a pref and is not supported in all
+    // contexts (e.g. web workers).
+    JS_ReportErrorASCII(
+        cx,
+        "Dynamic module import is disabled or not supported in this context");
+    if (!RejectPromiseWithPendingError(cx, promise)) {
+      return nullptr;
+    }
+    return promise;
+  }
+
+  RootedString specifier(cx, ToString(cx, specifierArg));
+  if (!specifier) {
+    if (!RejectPromiseWithPendingError(cx, promise)) {
+      return nullptr;
+    }
+    return promise;
+  }
+
+  RootedValue referencingPrivate(cx, script->sourceObject()->getPrivate());
+  cx->runtime()->addRefScriptPrivate(referencingPrivate);
+
+  Rooted<JSAtom*> specifierAtom(cx, AtomizeString(cx, specifier));
+  if (!specifierAtom) {
+    if (!RejectPromiseWithPendingError(cx, promise)) {
+      return nullptr;
+    }
+    return promise;
+  }
+
+  Rooted<ArrayObject*> assertionArray(cx);
+  if (!EvaluateDynamicImportOptions(cx, optionsArg, &assertionArray)) {
+    if (!RejectPromiseWithPendingError(cx, promise)) {
+      return nullptr;
+    }
+    return promise;
+  }
+
+  RootedObject moduleRequest(
+      cx, ModuleRequestObject::create(cx, specifierAtom, assertionArray));
+  if (!moduleRequest) {
+    if (!RejectPromiseWithPendingError(cx, promise)) {
+      return nullptr;
+    }
+    return promise;
+  }
+
+  if (!importHook(cx, referencingPrivate, moduleRequest, promise)) {
+    cx->runtime()->releaseScriptPrivate(referencingPrivate);
+
+    // If there's no exception pending then the script is terminating
+    // anyway, so just return nullptr.
+    if (!cx->isExceptionPending() ||
+        !RejectPromiseWithPendingError(cx, promise)) {
+      return nullptr;
+    }
+    return promise;
+  }
+
+  return promise;
+}
+
+static bool OnRootModuleRejected(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+  HandleValue error = args.get(0);
+
+  ReportExceptionClosure reportExn(error);
+  PrepareScriptEnvironmentAndInvoke(cx, cx->global(), reportExn);
+
+  args.rval().setUndefined();
+  return true;
+};
+
+bool js::OnModuleEvaluationFailure(JSContext* cx,
+                                   HandleObject evaluationPromise,
+                                   JS::ModuleErrorBehaviour errorBehaviour) {
+  if (evaluationPromise == nullptr) {
+    return false;
+  }
+
+  // To allow module evaluation to happen synchronously throw the error
+  // immediately. This assumes that any error will already have caused the
+  // promise to be rejected, and doesn't support top-level await.
+  if (errorBehaviour == JS::ThrowModuleErrorsSync) {
+    JS::PromiseState state = JS::GetPromiseState(evaluationPromise);
+    MOZ_DIAGNOSTIC_ASSERT(state == JS::PromiseState::Rejected ||
+                          state == JS::PromiseState::Fulfilled);
+
+    JS::SetSettledPromiseIsHandled(cx, evaluationPromise);
+    if (state == JS::PromiseState::Fulfilled) {
+      return true;
+    }
+
+    RootedValue error(cx, JS::GetPromiseResult(evaluationPromise));
+    JS_SetPendingException(cx, error);
+    return false;
+  }
+
+  RootedFunction onRejected(
+      cx, NewHandler(cx, OnRootModuleRejected, evaluationPromise));
+  if (!onRejected) {
+    return false;
+  }
+
+  return JS::AddPromiseReactions(cx, evaluationPromise, nullptr, onRejected);
+}
+
+// Adjustment for Top-level await;
+// See: https://github.com/tc39/proposal-dynamic-import/pull/71/files
+static bool OnResolvedDynamicModule(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+  MOZ_ASSERT(args.get(0).isUndefined());
+
+  // This is a hack to allow us to have the 2 extra variables needed
+  // for FinishDynamicModuleImport in the resolve callback.
+  Rooted<ListObject*> resolvedModuleParams(cx,
+                                           ExtraFromHandler<ListObject>(args));
+  MOZ_ASSERT(resolvedModuleParams->length() == 2);
+  RootedValue referencingPrivate(cx, resolvedModuleParams->get(0));
+
+  Rooted<JSAtom*> specifier(
+      cx, AtomizeString(cx, resolvedModuleParams->get(1).toString()));
+  if (!specifier) {
+    return false;
+  }
+
+  Rooted<PromiseObject*> promise(cx, TargetFromHandler<PromiseObject>(args));
+
+  auto releasePrivate = mozilla::MakeScopeExit(
+      [&] { cx->runtime()->releaseScriptPrivate(referencingPrivate); });
+
+  RootedObject moduleRequest(
+      cx, ModuleRequestObject::create(cx, specifier, nullptr));
+  if (!moduleRequest) {
+    return RejectPromiseWithPendingError(cx, promise);
+  }
+
+  RootedObject result(
+      cx, CallModuleResolveHook(cx, referencingPrivate, moduleRequest));
+
+  if (!result) {
+    return RejectPromiseWithPendingError(cx, promise);
+  }
+
+  Rooted<ModuleObject*> module(cx, &result->as<ModuleObject>());
+  if (module->status() != ModuleStatus::EvaluatingAsync &&
+      module->status() != ModuleStatus::Evaluated) {
+    JS_ReportErrorASCII(
+        cx, "Unevaluated or errored module returned by module resolve hook");
+    return RejectPromiseWithPendingError(cx, promise);
+  }
+
+  MOZ_ASSERT(module->getCycleRoot()
+                 ->topLevelCapability()
+                 ->as<PromiseObject>()
+                 .state() == JS::PromiseState::Fulfilled);
+
+  RootedObject ns(cx, GetOrCreateModuleNamespace(cx, module));
+  if (!ns) {
+    return RejectPromiseWithPendingError(cx, promise);
+  }
+
+  args.rval().setUndefined();
+  RootedValue value(cx, ObjectValue(*ns));
+  return PromiseObject::resolve(cx, promise, value);
+};
+
+static bool OnRejectedDynamicModule(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+  HandleValue error = args.get(0);
+
+  RootedValue referencingPrivate(cx, ExtraValueFromHandler(args));
+  Rooted<PromiseObject*> promise(cx, TargetFromHandler<PromiseObject>(args));
+
+  auto releasePrivate = mozilla::MakeScopeExit(
+      [&] { cx->runtime()->releaseScriptPrivate(referencingPrivate); });
+
+  args.rval().setUndefined();
+  return PromiseObject::reject(cx, promise, error);
+};
+
+bool FinishDynamicModuleImport_impl(JSContext* cx,
+                                    HandleObject evaluationPromise,
+                                    HandleValue referencingPrivate,
+                                    HandleObject moduleRequest,
+                                    HandleObject promiseArg) {
+  Rooted<ListObject*> resolutionArgs(cx, ListObject::create(cx));
+  if (!resolutionArgs->append(cx, referencingPrivate)) {
+    return false;
+  }
+  Rooted<Value> stringValue(
+      cx, StringValue(moduleRequest->as<ModuleRequestObject>().specifier()));
+  if (!resolutionArgs->append(cx, stringValue)) {
+    return false;
+  }
+
+  Rooted<Value> resolutionArgsValue(cx, ObjectValue(*resolutionArgs));
+
+  RootedFunction onResolved(
+      cx, NewHandlerWithExtraValue(cx, OnResolvedDynamicModule, promiseArg,
+                                   resolutionArgsValue));
+  if (!onResolved) {
+    return false;
+  }
+
+  RootedFunction onRejected(
+      cx, NewHandlerWithExtraValue(cx, OnRejectedDynamicModule, promiseArg,
+                                   referencingPrivate));
+  if (!onRejected) {
+    return false;
+  }
+
+  return JS::AddPromiseReactionsIgnoringUnhandledRejection(
+      cx, evaluationPromise, onResolved, onRejected);
+}
+
+bool js::FinishDynamicModuleImport(JSContext* cx,
+                                   HandleObject evaluationPromise,
+                                   HandleValue referencingPrivate,
+                                   HandleObject moduleRequest,
+                                   HandleObject promiseArg) {
+  // If we do not have an evaluation promise or a module request for the module,
+  // we can assume that evaluation has failed or been interrupted -- we can
+  // reject the dynamic module.
+  auto releasePrivate = mozilla::MakeScopeExit(
+      [&] { cx->runtime()->releaseScriptPrivate(referencingPrivate); });
+
+  if (!evaluationPromise || !moduleRequest) {
+    Handle<PromiseObject*> promise = promiseArg.as<PromiseObject>();
+    return RejectPromiseWithPendingError(cx, promise);
+  }
+
+  if (!FinishDynamicModuleImport_impl(cx, evaluationPromise, referencingPrivate,
+                                      moduleRequest, promiseArg)) {
+    return false;
+  }
+
+  releasePrivate.release();
+  return true;
+}