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diff --git a/Source/JavaScriptCore/runtime/AbstractModuleRecord.h b/Source/JavaScriptCore/runtime/AbstractModuleRecord.h
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+++ b/Source/JavaScriptCore/runtime/AbstractModuleRecord.h
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+/*
+ * Copyright (C) 2015 Apple Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
+ * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include "Identifier.h"
+#include "JSDestructibleObject.h"
+#include "SourceCode.h"
+#include "VariableEnvironment.h"
+#include <wtf/HashMap.h>
+#include <wtf/ListHashSet.h>
+#include <wtf/Optional.h>
+
+namespace JSC {
+
+class JSModuleEnvironment;
+class JSModuleNamespaceObject;
+class JSMap;
+
+// Based on the Source Text Module Record
+// http://www.ecma-international.org/ecma-262/6.0/#sec-source-text-module-records
+class AbstractModuleRecord : public JSDestructibleObject {
+    friend class LLIntOffsetsExtractor;
+public:
+    typedef JSDestructibleObject Base;
+
+    // https://tc39.github.io/ecma262/#sec-source-text-module-records
+    struct ExportEntry {
+        enum class Type {
+            Local,
+            Indirect
+        };
+
+        static ExportEntry createLocal(const Identifier& exportName, const Identifier& localName);
+        static ExportEntry createIndirect(const Identifier& exportName, const Identifier& importName, const Identifier& moduleName);
+
+        Type type;
+        Identifier exportName;
+        Identifier moduleName;
+        Identifier importName;
+        Identifier localName;
+    };
+
+    struct ImportEntry {
+        Identifier moduleRequest;
+        Identifier importName;
+        Identifier localName;
+
+        bool isNamespace(VM& vm) const
+        {
+            return importName == vm.propertyNames->timesIdentifier;
+        }
+    };
+
+    typedef WTF::ListHashSet<RefPtr<UniquedStringImpl>, IdentifierRepHash> OrderedIdentifierSet;
+    typedef HashMap<RefPtr<UniquedStringImpl>, ImportEntry, IdentifierRepHash, HashTraits<RefPtr<UniquedStringImpl>>> ImportEntries;
+    typedef HashMap<RefPtr<UniquedStringImpl>, ExportEntry, IdentifierRepHash, HashTraits<RefPtr<UniquedStringImpl>>> ExportEntries;
+
+    DECLARE_EXPORT_INFO;
+
+    void appendRequestedModule(const Identifier&);
+    void addStarExportEntry(const Identifier&);
+    void addImportEntry(const ImportEntry&);
+    void addExportEntry(const ExportEntry&);
+
+    std::optional<ImportEntry> tryGetImportEntry(UniquedStringImpl* localName);
+    std::optional<ExportEntry> tryGetExportEntry(UniquedStringImpl* exportName);
+
+    const Identifier& moduleKey() const { return m_moduleKey; }
+    const OrderedIdentifierSet& requestedModules() const { return m_requestedModules; }
+    const ExportEntries& exportEntries() const { return m_exportEntries; }
+    const ImportEntries& importEntries() const { return m_importEntries; }
+    const OrderedIdentifierSet& starExportEntries() const { return m_starExportEntries; }
+
+    void dump();
+
+    struct Resolution {
+        enum class Type { Resolved, NotFound, Ambiguous, Error };
+
+        static Resolution notFound();
+        static Resolution error();
+        static Resolution ambiguous();
+
+        Type type;
+        AbstractModuleRecord* moduleRecord;
+        Identifier localName;
+    };
+
+    Resolution resolveExport(ExecState*, const Identifier& exportName);
+    Resolution resolveImport(ExecState*, const Identifier& localName);
+
+    AbstractModuleRecord* hostResolveImportedModule(ExecState*, const Identifier& moduleName);
+
+    JSModuleNamespaceObject* getModuleNamespace(ExecState*);
+    
+    JSModuleEnvironment* moduleEnvironment()
+    {
+        ASSERT(m_moduleEnvironment);
+        return m_moduleEnvironment.get();
+    }
+
+protected:
+    AbstractModuleRecord(VM&, Structure*, const Identifier&);
+    void finishCreation(ExecState*, VM&);
+
+    static void visitChildren(JSCell*, SlotVisitor&);
+    static void destroy(JSCell*);
+
+    WriteBarrier<JSModuleEnvironment> m_moduleEnvironment;
+
+private:
+    struct ResolveQuery;
+    static Resolution resolveExportImpl(ExecState*, const ResolveQuery&);
+    std::optional<Resolution> tryGetCachedResolution(UniquedStringImpl* exportName);
+    void cacheResolution(UniquedStringImpl* exportName, const Resolution&);
+
+    // The loader resolves the given module name to the module key. The module key is the unique value to represent this module.
+    Identifier m_moduleKey;
+
+    // Currently, we don't keep the occurrence order of the import / export entries.
+    // So, we does not guarantee the order of the errors.
+    // e.g. The import declaration that occurr later than the another import declaration may
+    //      throw the error even if the former import declaration also has the invalid content.
+    //
+    //      import ... // (1) this has some invalid content.
+    //      import ... // (2) this also has some invalid content.
+    //
+    //      In the above case, (2) may throw the error earlier than (1)
+    //
+    // But, in all the cases, we will throw the syntax error. So except for the content of the syntax error,
+    // there are no difference.
+
+    // Map localName -> ImportEntry.
+    ImportEntries m_importEntries;
+
+    // Map exportName -> ExportEntry.
+    ExportEntries m_exportEntries;
+
+    // Save the occurrence order since resolveExport requires it.
+    OrderedIdentifierSet m_starExportEntries;
+
+    // Save the occurrence order since the module loader loads and runs the modules in this order.
+    // http://www.ecma-international.org/ecma-262/6.0/#sec-moduleevaluation
+    OrderedIdentifierSet m_requestedModules;
+
+    WriteBarrier<JSMap> m_dependenciesMap;
+    
+    WriteBarrier<JSModuleNamespaceObject> m_moduleNamespaceObject;
+
+    // We assume that all the AbstractModuleRecord are retained by JSModuleLoader's registry.
+    // So here, we don't visit each object for GC. The resolution cache map caches the once
+    // looked up correctly resolved resolution, since (1) we rarely looked up the non-resolved one,
+    // and (2) if we cache all the attempts the size of the map becomes infinitely large.
+    typedef HashMap<RefPtr<UniquedStringImpl>, Resolution, IdentifierRepHash, HashTraits<RefPtr<UniquedStringImpl>>> Resolutions;
+    Resolutions m_resolutionCache;
+};
+
+} // namespace JSC