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diff --git a/js/src/builtin/ModuleObject.h b/js/src/builtin/ModuleObject.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: set ts=8 sts=2 et sw=2 tw=80:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef builtin_ModuleObject_h
+#define builtin_ModuleObject_h
+
+#include "mozilla/HashTable.h"  // mozilla::{HashMap, DefaultHasher}
+#include "mozilla/Maybe.h"      // mozilla::Maybe
+#include "mozilla/Span.h"
+
+#include <stddef.h>  // size_t
+#include <stdint.h>  // int32_t, uint32_t
+
+#include "gc/Barrier.h"        // HeapPtr
+#include "gc/ZoneAllocator.h"  // CellAllocPolicy
+#include "js/Class.h"          // JSClass, ObjectOpResult
+#include "js/GCVector.h"
+#include "js/Id.h"  // jsid
+#include "js/Modules.h"
+#include "js/Proxy.h"       // BaseProxyHandler
+#include "js/RootingAPI.h"  // Rooted, Handle, MutableHandle
+#include "js/TypeDecls.h"  // HandleValue, HandleId, HandleObject, HandleScript, MutableHandleValue, MutableHandleIdVector, MutableHandleObject
+#include "js/UniquePtr.h"  // UniquePtr
+#include "vm/JSObject.h"   // JSObject
+#include "vm/NativeObject.h"   // NativeObject
+#include "vm/ProxyObject.h"    // ProxyObject
+#include "vm/SharedStencil.h"  // FunctionDeclarationVector
+
+class JSAtom;
+class JSScript;
+class JSTracer;
+
+namespace JS {
+class PropertyDescriptor;
+class Value;
+}  // namespace JS
+
+namespace js {
+
+class ArrayObject;
+class CyclicModuleFields;
+class ListObject;
+class ModuleEnvironmentObject;
+class ModuleObject;
+class PromiseObject;
+class ScriptSourceObject;
+
+class ModuleRequestObject : public NativeObject {
+ public:
+  enum { SpecifierSlot = 0, AssertionSlot, SlotCount };
+
+  static const JSClass class_;
+  static bool isInstance(HandleValue value);
+  [[nodiscard]] static ModuleRequestObject* create(
+      JSContext* cx, Handle<JSAtom*> specifier,
+      Handle<ArrayObject*> maybeAssertions);
+
+  JSAtom* specifier() const;
+  ArrayObject* assertions() const;
+};
+
+using ModuleRequestVector =
+    GCVector<HeapPtr<ModuleRequestObject*>, 0, SystemAllocPolicy>;
+
+class ImportEntry {
+  const HeapPtr<ModuleRequestObject*> moduleRequest_;
+  const HeapPtr<JSAtom*> importName_;
+  const HeapPtr<JSAtom*> localName_;
+  const uint32_t lineNumber_;
+  const uint32_t columnNumber_;
+
+ public:
+  ImportEntry(Handle<ModuleRequestObject*> moduleRequest,
+              Handle<JSAtom*> maybeImportName, Handle<JSAtom*> localName,
+              uint32_t lineNumber, uint32_t columnNumber);
+
+  ModuleRequestObject* moduleRequest() const { return moduleRequest_; }
+  JSAtom* importName() const { return importName_; }
+  JSAtom* localName() const { return localName_; }
+  uint32_t lineNumber() const { return lineNumber_; }
+  uint32_t columnNumber() const { return columnNumber_; }
+
+  void trace(JSTracer* trc);
+};
+
+using ImportEntryVector = GCVector<ImportEntry, 0, SystemAllocPolicy>;
+
+class ExportEntry {
+  const HeapPtr<JSAtom*> exportName_;
+  const HeapPtr<ModuleRequestObject*> moduleRequest_;
+  const HeapPtr<JSAtom*> importName_;
+  const HeapPtr<JSAtom*> localName_;
+  const uint32_t lineNumber_;
+  const uint32_t columnNumber_;
+
+ public:
+  ExportEntry(Handle<JSAtom*> maybeExportName,
+              Handle<ModuleRequestObject*> maybeModuleRequest,
+              Handle<JSAtom*> maybeImportName, Handle<JSAtom*> maybeLocalName,
+              uint32_t lineNumber, uint32_t columnNumber);
+  JSAtom* exportName() const { return exportName_; }
+  ModuleRequestObject* moduleRequest() const { return moduleRequest_; }
+  JSAtom* importName() const { return importName_; }
+  JSAtom* localName() const { return localName_; }
+  uint32_t lineNumber() const { return lineNumber_; }
+  uint32_t columnNumber() const { return columnNumber_; }
+
+  void trace(JSTracer* trc);
+};
+
+using ExportEntryVector = GCVector<ExportEntry, 0, SystemAllocPolicy>;
+
+class RequestedModule {
+  const HeapPtr<ModuleRequestObject*> moduleRequest_;
+  const uint32_t lineNumber_;
+  const uint32_t columnNumber_;
+
+ public:
+  RequestedModule(Handle<ModuleRequestObject*> moduleRequest,
+                  uint32_t lineNumber, uint32_t columnNumber);
+  ModuleRequestObject* moduleRequest() const { return moduleRequest_; }
+  uint32_t lineNumber() const { return lineNumber_; }
+  uint32_t columnNumber() const { return columnNumber_; }
+
+  void trace(JSTracer* trc);
+};
+
+using RequestedModuleVector = GCVector<RequestedModule, 0, SystemAllocPolicy>;
+
+class ResolvedBindingObject : public NativeObject {
+ public:
+  enum { ModuleSlot = 0, BindingNameSlot, SlotCount };
+
+  static const JSClass class_;
+  static bool isInstance(HandleValue value);
+  static ResolvedBindingObject* create(JSContext* cx,
+                                       Handle<ModuleObject*> module,
+                                       Handle<JSAtom*> bindingName);
+  ModuleObject* module() const;
+  JSAtom* bindingName() const;
+};
+
+class IndirectBindingMap {
+ public:
+  void trace(JSTracer* trc);
+
+  bool put(JSContext* cx, HandleId name,
+           Handle<ModuleEnvironmentObject*> environment, HandleId targetName);
+
+  size_t count() const { return map_ ? map_->count() : 0; }
+
+  bool has(jsid name) const { return map_ ? map_->has(name) : false; }
+
+  bool lookup(jsid name, ModuleEnvironmentObject** envOut,
+              mozilla::Maybe<PropertyInfo>* propOut) const;
+
+  template <typename Func>
+  void forEachExportedName(Func func) const {
+    if (!map_) {
+      return;
+    }
+
+    for (auto r = map_->all(); !r.empty(); r.popFront()) {
+      func(r.front().key());
+    }
+  }
+
+ private:
+  struct Binding {
+    Binding(ModuleEnvironmentObject* environment, jsid targetName,
+            PropertyInfo prop);
+    HeapPtr<ModuleEnvironmentObject*> environment;
+#ifdef DEBUG
+    HeapPtr<jsid> targetName;
+#endif
+    PropertyInfo prop;
+  };
+
+  using Map = mozilla::HashMap<PreBarriered<jsid>, Binding,
+                               mozilla::DefaultHasher<PreBarriered<jsid>>,
+                               CellAllocPolicy>;
+
+  mozilla::Maybe<Map> map_;
+};
+
+// Vector of atoms representing the names exported from a module namespace.
+//
+// This is used both on the stack and in the heap.
+using ExportNameVector = GCVector<HeapPtr<JSAtom*>, 0, SystemAllocPolicy>;
+
+class ModuleNamespaceObject : public ProxyObject {
+ public:
+  enum ModuleNamespaceSlot { ExportsSlot = 0, BindingsSlot };
+
+  static bool isInstance(HandleValue value);
+  static ModuleNamespaceObject* create(
+      JSContext* cx, Handle<ModuleObject*> module,
+      MutableHandle<UniquePtr<ExportNameVector>> exports,
+      MutableHandle<UniquePtr<IndirectBindingMap>> bindings);
+
+  ModuleObject& module();
+  const ExportNameVector& exports() const;
+  IndirectBindingMap& bindings();
+
+  bool addBinding(JSContext* cx, Handle<JSAtom*> exportedName,
+                  Handle<ModuleObject*> targetModule,
+                  Handle<JSAtom*> targetName);
+
+ private:
+  struct ProxyHandler : public BaseProxyHandler {
+    ProxyHandler();
+
+    bool getOwnPropertyDescriptor(
+        JSContext* cx, HandleObject proxy, HandleId id,
+        MutableHandle<mozilla::Maybe<PropertyDescriptor>> desc) const override;
+    bool defineProperty(JSContext* cx, HandleObject proxy, HandleId id,
+                        Handle<PropertyDescriptor> desc,
+                        ObjectOpResult& result) const override;
+    bool ownPropertyKeys(JSContext* cx, HandleObject proxy,
+                         MutableHandleIdVector props) const override;
+    bool delete_(JSContext* cx, HandleObject proxy, HandleId id,
+                 ObjectOpResult& result) const override;
+    bool getPrototype(JSContext* cx, HandleObject proxy,
+                      MutableHandleObject protop) const override;
+    bool setPrototype(JSContext* cx, HandleObject proxy, HandleObject proto,
+                      ObjectOpResult& result) const override;
+    bool getPrototypeIfOrdinary(JSContext* cx, HandleObject proxy,
+                                bool* isOrdinary,
+                                MutableHandleObject protop) const override;
+    bool setImmutablePrototype(JSContext* cx, HandleObject proxy,
+                               bool* succeeded) const override;
+
+    bool preventExtensions(JSContext* cx, HandleObject proxy,
+                           ObjectOpResult& result) const override;
+    bool isExtensible(JSContext* cx, HandleObject proxy,
+                      bool* extensible) const override;
+    bool has(JSContext* cx, HandleObject proxy, HandleId id,
+             bool* bp) const override;
+    bool get(JSContext* cx, HandleObject proxy, HandleValue receiver,
+             HandleId id, MutableHandleValue vp) const override;
+    bool set(JSContext* cx, HandleObject proxy, HandleId id, HandleValue v,
+             HandleValue receiver, ObjectOpResult& result) const override;
+
+    void trace(JSTracer* trc, JSObject* proxy) const override;
+    void finalize(JS::GCContext* gcx, JSObject* proxy) const override;
+
+    static const char family;
+  };
+
+  bool hasBindings() const;
+  bool hasExports() const;
+
+  ExportNameVector& mutableExports();
+
+ public:
+  static const ProxyHandler proxyHandler;
+};
+
+// Value types of [[Status]] in a Cyclic Module Record
+// https://tc39.es/ecma262/#table-cyclic-module-fields
+enum class ModuleStatus : int8_t {
+  Unlinked,
+  Linking,
+  Linked,
+  Evaluating,
+  EvaluatingAsync,
+  Evaluated,
+
+  // Sub-state of Evaluated with error value set.
+  //
+  // This is not returned from ModuleObject::status(); use hadEvaluationError()
+  // to check this.
+  Evaluated_Error
+};
+
+// Special values for CyclicModuleFields' asyncEvaluatingPostOrderSlot field,
+// which is used as part of the implementation of the AsyncEvaluation field of
+// cyclic module records.
+//
+// The spec requires us to be able to tell the order in which the field was set
+// to true for async evaluating modules.
+//
+// This is arranged by using an integer to record the order. After evaluation is
+// complete the value is set to ASYNC_EVALUATING_POST_ORDER_CLEARED.
+//
+// See https://tc39.es/ecma262/#sec-cyclic-module-records for field defintion.
+// See https://tc39.es/ecma262/#sec-async-module-execution-fulfilled for sort
+// requirement.
+
+// Initial value for the runtime's counter used to generate these values.
+constexpr uint32_t ASYNC_EVALUATING_POST_ORDER_INIT = 1;
+
+// Value that the field is set to after being cleared.
+constexpr uint32_t ASYNC_EVALUATING_POST_ORDER_CLEARED = 0;
+
+class ModuleObject : public NativeObject {
+ public:
+  // Module fields including those for AbstractModuleRecords described by:
+  // https://tc39.es/ecma262/#sec-abstract-module-records
+  enum ModuleSlot {
+    ScriptSlot = 0,
+    EnvironmentSlot,
+    NamespaceSlot,
+    CyclicModuleFieldsSlot,
+    SlotCount
+  };
+
+  static const JSClass class_;
+
+  static bool isInstance(HandleValue value);
+
+  static ModuleObject* create(JSContext* cx);
+
+  // Initialize the slots on this object that are dependent on the script.
+  void initScriptSlots(HandleScript script);
+
+  void setInitialEnvironment(
+      Handle<ModuleEnvironmentObject*> initialEnvironment);
+
+  void initFunctionDeclarations(UniquePtr<FunctionDeclarationVector> decls);
+  void initImportExportData(
+      MutableHandle<RequestedModuleVector> requestedModules,
+      MutableHandle<ImportEntryVector> importEntries,
+      MutableHandle<ExportEntryVector> exportEntries, uint32_t localExportCount,
+      uint32_t indirectExportCount, uint32_t starExportCount);
+  static bool Freeze(JSContext* cx, Handle<ModuleObject*> self);
+#ifdef DEBUG
+  static bool AssertFrozen(JSContext* cx, Handle<ModuleObject*> self);
+#endif
+
+  JSScript* maybeScript() const;
+  JSScript* script() const;
+  ModuleEnvironmentObject& initialEnvironment() const;
+  ModuleEnvironmentObject* environment() const;
+  ModuleNamespaceObject* namespace_();
+  ModuleStatus status() const;
+  mozilla::Maybe<uint32_t> maybeDfsIndex() const;
+  uint32_t dfsIndex() const;
+  mozilla::Maybe<uint32_t> maybeDfsAncestorIndex() const;
+  uint32_t dfsAncestorIndex() const;
+  bool hadEvaluationError() const;
+  Value maybeEvaluationError() const;
+  Value evaluationError() const;
+  JSObject* metaObject() const;
+  ScriptSourceObject* scriptSourceObject() const;
+  mozilla::Span<const RequestedModule> requestedModules() const;
+  mozilla::Span<const ImportEntry> importEntries() const;
+  mozilla::Span<const ExportEntry> localExportEntries() const;
+  mozilla::Span<const ExportEntry> indirectExportEntries() const;
+  mozilla::Span<const ExportEntry> starExportEntries() const;
+  IndirectBindingMap& importBindings();
+
+  void setStatus(ModuleStatus newStatus);
+  void setDfsIndex(uint32_t index);
+  void setDfsAncestorIndex(uint32_t index);
+  void clearDfsIndexes();
+
+  static PromiseObject* createTopLevelCapability(JSContext* cx,
+                                                 Handle<ModuleObject*> module);
+  bool hasTopLevelAwait() const;
+  bool isAsyncEvaluating() const;
+  void setAsyncEvaluating();
+  void setEvaluationError(HandleValue newValue);
+  void setPendingAsyncDependencies(uint32_t newValue);
+  void setInitialTopLevelCapability(Handle<PromiseObject*> capability);
+  bool hasTopLevelCapability() const;
+  PromiseObject* maybeTopLevelCapability() const;
+  PromiseObject* topLevelCapability() const;
+  ListObject* asyncParentModules() const;
+  mozilla::Maybe<uint32_t> maybePendingAsyncDependencies() const;
+  uint32_t pendingAsyncDependencies() const;
+  mozilla::Maybe<uint32_t> maybeAsyncEvaluatingPostOrder() const;
+  uint32_t getAsyncEvaluatingPostOrder() const;
+  void clearAsyncEvaluatingPostOrder();
+  void setCycleRoot(ModuleObject* cycleRoot);
+  ModuleObject* getCycleRoot() const;
+
+  static void onTopLevelEvaluationFinished(ModuleObject* module);
+
+  static bool appendAsyncParentModule(JSContext* cx, Handle<ModuleObject*> self,
+                                      Handle<ModuleObject*> parent);
+
+  [[nodiscard]] static bool topLevelCapabilityResolve(
+      JSContext* cx, Handle<ModuleObject*> module);
+  [[nodiscard]] static bool topLevelCapabilityReject(
+      JSContext* cx, Handle<ModuleObject*> module, HandleValue error);
+
+  void setMetaObject(JSObject* obj);
+
+  static bool instantiateFunctionDeclarations(JSContext* cx,
+                                              Handle<ModuleObject*> self);
+
+  static bool execute(JSContext* cx, Handle<ModuleObject*> self);
+
+  static ModuleNamespaceObject* createNamespace(
+      JSContext* cx, Handle<ModuleObject*> self,
+      MutableHandle<UniquePtr<ExportNameVector>> exports);
+
+  static bool createEnvironment(JSContext* cx, Handle<ModuleObject*> self);
+
+  void initAsyncSlots(JSContext* cx, bool hasTopLevelAwait,
+                      Handle<ListObject*> asyncParentModules);
+
+ private:
+  static const JSClassOps classOps_;
+
+  static void trace(JSTracer* trc, JSObject* obj);
+  static void finalize(JS::GCContext* gcx, JSObject* obj);
+
+  bool hasCyclicModuleFields() const;
+  CyclicModuleFields* cyclicModuleFields();
+  const CyclicModuleFields* cyclicModuleFields() const;
+};
+
+JSObject* GetOrCreateModuleMetaObject(JSContext* cx, HandleObject module);
+
+ModuleObject* CallModuleResolveHook(JSContext* cx,
+                                    HandleValue referencingPrivate,
+                                    HandleObject moduleRequest);
+
+JSObject* StartDynamicModuleImport(JSContext* cx, HandleScript script,
+                                   HandleValue specifier, HandleValue options);
+
+bool OnModuleEvaluationFailure(JSContext* cx, HandleObject evaluationPromise,
+                               JS::ModuleErrorBehaviour errorBehaviour);
+
+bool FinishDynamicModuleImport(JSContext* cx, HandleObject evaluationPromise,
+                               HandleValue referencingPrivate,
+                               HandleObject moduleRequest,
+                               HandleObject promise);
+
+}  // namespace js
+
+template <>
+inline bool JSObject::is<js::ModuleNamespaceObject>() const {
+  return js::IsDerivedProxyObject(this,
+                                  &js::ModuleNamespaceObject::proxyHandler);
+}
+
+#endif /* builtin_ModuleObject_h */