ASTImporter.cpp

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//===- ASTImporter.cpp - Importing ASTs from other Contexts ---------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
//  This file defines the ASTImporter class which imports AST nodes from one
//  context into another context.
//
//===----------------------------------------------------------------------===//

#include "clang/AST/ASTImporter.h"
#include "clang/AST/ASTImporterLookupTable.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/ASTDiagnostic.h"
#include "clang/AST/ASTStructuralEquivalence.h"
#include "clang/AST/Attr.h"
#include "clang/AST/Decl.h"
#include "clang/AST/DeclAccessPair.h"
#include "clang/AST/DeclBase.h"
#include "clang/AST/DeclCXX.h"
#include "clang/AST/DeclFriend.h"
#include "clang/AST/DeclGroup.h"
#include "clang/AST/DeclObjC.h"
#include "clang/AST/DeclTemplate.h"
#include "clang/AST/DeclVisitor.h"
#include "clang/AST/DeclarationName.h"
#include "clang/AST/Expr.h"
#include "clang/AST/ExprCXX.h"
#include "clang/AST/ExprObjC.h"
#include "clang/AST/ExternalASTSource.h"
#include "clang/AST/LambdaCapture.h"
#include "clang/AST/NestedNameSpecifier.h"
#include "clang/AST/OperationKinds.h"
#include "clang/AST/Stmt.h"
#include "clang/AST/StmtCXX.h"
#include "clang/AST/StmtObjC.h"
#include "clang/AST/StmtVisitor.h"
#include "clang/AST/TemplateBase.h"
#include "clang/AST/TemplateName.h"
#include "clang/AST/Type.h"
#include "clang/AST/TypeLoc.h"
#include "clang/AST/TypeVisitor.h"
#include "clang/AST/UnresolvedSet.h"
#include "clang/Basic/ExceptionSpecificationType.h"
#include "clang/Basic/FileManager.h"
#include "clang/Basic/IdentifierTable.h"
#include "clang/Basic/LLVM.h"
#include "clang/Basic/LangOptions.h"
#include "clang/Basic/SourceLocation.h"
#include "clang/Basic/SourceManager.h"
#include "clang/Basic/Specifiers.h"
#include "llvm/ADT/APSInt.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/None.h"
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/MemoryBuffer.h"
#include <algorithm>
#include <cassert>
#include <cstddef>
#include <memory>
#include <type_traits>
#include <utility>

namespace clang {

  using llvm::make_error;
  using llvm::Error;
  using llvm::Expected;
  using ExpectedType = llvm::Expected<QualType>;
  using ExpectedStmt = llvm::Expected<Stmt *>;
  using ExpectedExpr = llvm::Expected<Expr *>;
  using ExpectedDecl = llvm::Expected<Decl *>;
  using ExpectedSLoc = llvm::Expected<SourceLocation>;

  std::string ImportError::toString() const {
    // FIXME: Improve error texts.
    switch (Error) {
    case NameConflict:
      return "NameConflict";
    case UnsupportedConstruct:
      return "UnsupportedConstruct";
    case Unknown:
      return "Unknown error";
    }
    llvm_unreachable("Invalid error code.");
    return "Invalid error code.";
  }

  void ImportError::log(raw_ostream &OS) const {
    OS << toString();
  }

  std::error_code ImportError::convertToErrorCode() const {
    llvm_unreachable("Function not implemented.");
  }

  char ImportError::ID;

  template <class T>
  SmallVector<Decl *, 2>
  getCanonicalForwardRedeclChain(Redeclarable<T>* D) {
    SmallVector<Decl *, 2> Redecls;
    for (auto *R : D->getFirstDecl()->redecls()) {
      if (R != D->getFirstDecl())
        Redecls.push_back(R);
    }
    Redecls.push_back(D->getFirstDecl());
    std::reverse(Redecls.begin(), Redecls.end());
    return Redecls;
  }

  SmallVector<Decl*, 2> getCanonicalForwardRedeclChain(Decl* D) {
    if (auto *FD = dyn_cast<FunctionDecl>(D))
      return getCanonicalForwardRedeclChain<FunctionDecl>(FD);
    if (auto *VD = dyn_cast<VarDecl>(D))
      return getCanonicalForwardRedeclChain<VarDecl>(VD);
    if (auto *TD = dyn_cast<TagDecl>(D))
      return getCanonicalForwardRedeclChain<TagDecl>(TD);
    llvm_unreachable("Bad declaration kind");
  }

  void updateFlags(const Decl *From, Decl *To) {
    // Check if some flags or attrs are new in 'From' and copy into 'To'.
    // FIXME: Other flags or attrs?
    if (From->isUsed(false) && !To->isUsed(false))
      To->setIsUsed();
  }

  // FIXME: Temporary until every import returns Expected.
  template <>
  LLVM_NODISCARD Error
  ASTImporter::importInto(SourceLocation &To, const SourceLocation &From) {
    To = Import(From);
    if (From.isValid() && To.isInvalid())
        return llvm::make_error<ImportError>();
    return Error::success();
  }
  // FIXME: Temporary until every import returns Expected.
  template <>
  LLVM_NODISCARD Error
  ASTImporter::importInto(QualType &To, const QualType &From) {
    To = Import(From);
    if (!From.isNull() && To.isNull())
        return llvm::make_error<ImportError>();
    return Error::success();
  }

  class ASTNodeImporter : public TypeVisitor<ASTNodeImporter, ExpectedType>,
                          public DeclVisitor<ASTNodeImporter, ExpectedDecl>,
                          public StmtVisitor<ASTNodeImporter, ExpectedStmt> {
    ASTImporter &Importer;

    // Use this instead of Importer.importInto .
    template <typename ImportT>
    LLVM_NODISCARD Error importInto(ImportT &To, const ImportT &From) {
      return Importer.importInto(To, From);
    }

    // Use this to import pointers of specific type.
    template <typename ImportT>
    LLVM_NODISCARD Error importInto(ImportT *&To, ImportT *From) {
      auto ToI = Importer.Import(From);
      if (!ToI && From)
        return make_error<ImportError>();
      To = cast_or_null<ImportT>(ToI);
      return Error::success();
      // FIXME: This should be the final code.
      //auto ToOrErr = Importer.Import(From);
      //if (ToOrErr) {
      //  To = cast_or_null<ImportT>(*ToOrErr);
      //}
      //return ToOrErr.takeError();
    }

    // Call the import function of ASTImporter for a baseclass of type `T` and
    // cast the return value to `T`.
    template <typename T>
    Expected<T *> import(T *From) {
      auto *To = Importer.Import(From);
      if (!To && From)
        return make_error<ImportError>();
      return cast_or_null<T>(To);
      // FIXME: This should be the final code.
      //auto ToOrErr = Importer.Import(From);
      //if (!ToOrErr)
      //  return ToOrErr.takeError();
      //return cast_or_null<T>(*ToOrErr);
    }

    template <typename T>
    Expected<T *> import(const T *From) {
      return import(const_cast<T *>(From));
    }

    // Call the import function of ASTImporter for type `T`.
    template <typename T>
    Expected<T> import(const T &From) {
      T To = Importer.Import(From);
      T DefaultT;
      if (To == DefaultT && !(From == DefaultT))
        return make_error<ImportError>();
      return To;
      // FIXME: This should be the final code.
      //return Importer.Import(From);
    }

    template <class T>
    Expected<std::tuple<T>>
    importSeq(const T &From) {
      Expected<T> ToOrErr = import(From);
      if (!ToOrErr)
        return ToOrErr.takeError();
      return std::make_tuple<T>(std::move(*ToOrErr));
    }

    // Import multiple objects with a single function call.
    // This should work for every type for which a variant of `import` exists.
    // The arguments are processed from left to right and import is stopped on
    // first error.
    template <class THead, class... TTail>
    Expected<std::tuple<THead, TTail...>>
    importSeq(const THead &FromHead, const TTail &...FromTail) {
      Expected<std::tuple<THead>> ToHeadOrErr = importSeq(FromHead);
      if (!ToHeadOrErr)
        return ToHeadOrErr.takeError();
      Expected<std::tuple<TTail...>> ToTailOrErr = importSeq(FromTail...);
      if (!ToTailOrErr)
        return ToTailOrErr.takeError();
      return std::tuple_cat(*ToHeadOrErr, *ToTailOrErr);
    }

// Wrapper for an overload set.
    template <typename ToDeclT> struct CallOverloadedCreateFun {
      template <typename... Args>
      auto operator()(Args &&... args)
          -> decltype(ToDeclT::Create(std::forward<Args>(args)...)) {
        return ToDeclT::Create(std::forward<Args>(args)...);
      }
    };

    // Always use these functions to create a Decl during import. There are
    // certain tasks which must be done after the Decl was created, e.g. we
    // must immediately register that as an imported Decl.  The parameter `ToD`
    // will be set to the newly created Decl or if had been imported before
    // then to the already imported Decl.  Returns a bool value set to true if
    // the `FromD` had been imported before.
    template <typename ToDeclT, typename FromDeclT, typename... Args>
    LLVM_NODISCARD bool GetImportedOrCreateDecl(ToDeclT *&ToD, FromDeclT *FromD,
                                                Args &&... args) {
      // There may be several overloads of ToDeclT::Create. We must make sure
      // to call the one which would be chosen by the arguments, thus we use a
      // wrapper for the overload set.
      CallOverloadedCreateFun<ToDeclT> OC;
      return GetImportedOrCreateSpecialDecl(ToD, OC, FromD,
                                            std::forward<Args>(args)...);
    }
    // Use this overload if a special Type is needed to be created.  E.g if we
    // want to create a `TypeAliasDecl` and assign that to a `TypedefNameDecl`
    // then:
    // TypedefNameDecl *ToTypedef;
    // GetImportedOrCreateDecl<TypeAliasDecl>(ToTypedef, FromD, ...);
    template <typename NewDeclT, typename ToDeclT, typename FromDeclT,
              typename... Args>
    LLVM_NODISCARD bool GetImportedOrCreateDecl(ToDeclT *&ToD, FromDeclT *FromD,
                                                Args &&... args) {
      CallOverloadedCreateFun<NewDeclT> OC;
      return GetImportedOrCreateSpecialDecl(ToD, OC, FromD,
                                            std::forward<Args>(args)...);
    }
    // Use this version if a special create function must be
    // used, e.g. CXXRecordDecl::CreateLambda .
    template <typename ToDeclT, typename CreateFunT, typename FromDeclT,
              typename... Args>
    LLVM_NODISCARD bool
    GetImportedOrCreateSpecialDecl(ToDeclT *&ToD, CreateFunT CreateFun,
                                   FromDeclT *FromD, Args &&... args) {
      // FIXME: This code is needed later.
      //if (Importer.getImportDeclErrorIfAny(FromD)) {
      //  ToD = nullptr;
      //  return true; // Already imported but with error.
      //}
      ToD = cast_or_null<ToDeclT>(Importer.GetAlreadyImportedOrNull(FromD));
      if (ToD)
        return true; // Already imported.
      ToD = CreateFun(std::forward<Args>(args)...);
      // Keep track of imported Decls.
      Importer.MapImported(FromD, ToD);
      Importer.AddToLookupTable(ToD);
      InitializeImportedDecl(FromD, ToD);
      return false; // A new Decl is created.
    }

    void InitializeImportedDecl(Decl *FromD, Decl *ToD) {
      ToD->IdentifierNamespace = FromD->IdentifierNamespace;
      if (FromD->hasAttrs())
        for (const Attr *FromAttr : FromD->getAttrs())
          ToD->addAttr(Importer.Import(FromAttr));
      if (FromD->isUsed())
        ToD->setIsUsed();
      if (FromD->isImplicit())
        ToD->setImplicit();
    }

  public:
    explicit ASTNodeImporter(ASTImporter &Importer) : Importer(Importer) {}

    using TypeVisitor<ASTNodeImporter, ExpectedType>::Visit;
    using DeclVisitor<ASTNodeImporter, ExpectedDecl>::Visit;
    using StmtVisitor<ASTNodeImporter, ExpectedStmt>::Visit;

    // Importing types
    ExpectedType VisitType(const Type *T);
    ExpectedType VisitAtomicType(const AtomicType *T);
    ExpectedType VisitBuiltinType(const BuiltinType *T);
    ExpectedType VisitDecayedType(const DecayedType *T);
    ExpectedType VisitComplexType(const ComplexType *T);
    ExpectedType VisitPointerType(const PointerType *T);
    ExpectedType VisitBlockPointerType(const BlockPointerType *T);
    ExpectedType VisitLValueReferenceType(const LValueReferenceType *T);
    ExpectedType VisitRValueReferenceType(const RValueReferenceType *T);
    ExpectedType VisitMemberPointerType(const MemberPointerType *T);
    ExpectedType VisitConstantArrayType(const ConstantArrayType *T);
    ExpectedType VisitIncompleteArrayType(const IncompleteArrayType *T);
    ExpectedType VisitVariableArrayType(const VariableArrayType *T);
    ExpectedType VisitDependentSizedArrayType(const DependentSizedArrayType *T);
    // FIXME: DependentSizedExtVectorType
    ExpectedType VisitVectorType(const VectorType *T);
    ExpectedType VisitExtVectorType(const ExtVectorType *T);
    ExpectedType VisitFunctionNoProtoType(const FunctionNoProtoType *T);
    ExpectedType VisitFunctionProtoType(const FunctionProtoType *T);
    ExpectedType VisitUnresolvedUsingType(const UnresolvedUsingType *T);
    ExpectedType VisitParenType(const ParenType *T);
    ExpectedType VisitTypedefType(const TypedefType *T);
    ExpectedType VisitTypeOfExprType(const TypeOfExprType *T);
    // FIXME: DependentTypeOfExprType
    ExpectedType VisitTypeOfType(const TypeOfType *T);
    ExpectedType VisitDecltypeType(const DecltypeType *T);
    ExpectedType VisitUnaryTransformType(const UnaryTransformType *T);
    ExpectedType VisitAutoType(const AutoType *T);
    ExpectedType VisitInjectedClassNameType(const InjectedClassNameType *T);
    // FIXME: DependentDecltypeType
    ExpectedType VisitRecordType(const RecordType *T);
    ExpectedType VisitEnumType(const EnumType *T);
    ExpectedType VisitAttributedType(const AttributedType *T);
    ExpectedType VisitTemplateTypeParmType(const TemplateTypeParmType *T);
    ExpectedType VisitSubstTemplateTypeParmType(
        const SubstTemplateTypeParmType *T);
    ExpectedType VisitTemplateSpecializationType(
        const TemplateSpecializationType *T);
    ExpectedType VisitElaboratedType(const ElaboratedType *T);
    ExpectedType VisitDependentNameType(const DependentNameType *T);
    ExpectedType VisitPackExpansionType(const PackExpansionType *T);
    ExpectedType VisitDependentTemplateSpecializationType(
        const DependentTemplateSpecializationType *T);
    ExpectedType VisitObjCInterfaceType(const ObjCInterfaceType *T);
    ExpectedType VisitObjCObjectType(const ObjCObjectType *T);
    ExpectedType VisitObjCObjectPointerType(const ObjCObjectPointerType *T);

    // Importing declarations
    Error ImportDeclParts(
        NamedDecl *D, DeclContext *&DC, DeclContext *&LexicalDC,
        DeclarationName &Name, NamedDecl *&ToD, SourceLocation &Loc);
    Error ImportDefinitionIfNeeded(Decl *FromD, Decl *ToD = nullptr);
    Error ImportDeclarationNameLoc(
        const DeclarationNameInfo &From, DeclarationNameInfo &To);
    Error ImportDeclContext(DeclContext *FromDC, bool ForceImport = false);
    Error ImportDeclContext(
        Decl *From, DeclContext *&ToDC, DeclContext *&ToLexicalDC);
    Error ImportImplicitMethods(const CXXRecordDecl *From, CXXRecordDecl *To);

    Expected<CXXCastPath> ImportCastPath(CastExpr *E);

    using Designator = DesignatedInitExpr::Designator;

    /// What we should import from the definition.
    enum ImportDefinitionKind {
      /// Import the default subset of the definition, which might be
      /// nothing (if minimal import is set) or might be everything (if minimal
      /// import is not set).
      IDK_Default,
      /// Import everything.
      IDK_Everything,
      /// Import only the bare bones needed to establish a valid
      /// DeclContext.
      IDK_Basic
    };

    bool shouldForceImportDeclContext(ImportDefinitionKind IDK) {
      return IDK == IDK_Everything ||
             (IDK == IDK_Default && !Importer.isMinimalImport());
    }

    Error ImportInitializer(VarDecl *From, VarDecl *To);
    Error ImportDefinition(
        RecordDecl *From, RecordDecl *To,
        ImportDefinitionKind Kind = IDK_Default);
    Error ImportDefinition(
        EnumDecl *From, EnumDecl *To,
        ImportDefinitionKind Kind = IDK_Default);
    Error ImportDefinition(
        ObjCInterfaceDecl *From, ObjCInterfaceDecl *To,
        ImportDefinitionKind Kind = IDK_Default);
    Error ImportDefinition(
        ObjCProtocolDecl *From, ObjCProtocolDecl *To,
        ImportDefinitionKind Kind = IDK_Default);
    Expected<TemplateParameterList *> ImportTemplateParameterList(
        TemplateParameterList *Params);
    Error ImportTemplateArguments(
        const TemplateArgument *FromArgs, unsigned NumFromArgs,
        SmallVectorImpl<TemplateArgument> &ToArgs);
    Expected<TemplateArgument>
    ImportTemplateArgument(const TemplateArgument &From);

    template <typename InContainerTy>
    Error ImportTemplateArgumentListInfo(
        const InContainerTy &Container, TemplateArgumentListInfo &ToTAInfo);

    template<typename InContainerTy>
    Error ImportTemplateArgumentListInfo(
      SourceLocation FromLAngleLoc, SourceLocation FromRAngleLoc,
      const InContainerTy &Container, TemplateArgumentListInfo &Result);

    using TemplateArgsTy = SmallVector<TemplateArgument, 8>;
    using FunctionTemplateAndArgsTy =
        std::tuple<FunctionTemplateDecl *, TemplateArgsTy>;
    Expected<FunctionTemplateAndArgsTy>
    ImportFunctionTemplateWithTemplateArgsFromSpecialization(
        FunctionDecl *FromFD);

    Error ImportTemplateInformation(FunctionDecl *FromFD, FunctionDecl *ToFD);

    bool IsStructuralMatch(Decl *From, Decl *To, bool Complain);
    bool IsStructuralMatch(RecordDecl *FromRecord, RecordDecl *ToRecord,
                           bool Complain = true);
    bool IsStructuralMatch(VarDecl *FromVar, VarDecl *ToVar,
                           bool Complain = true);
    bool IsStructuralMatch(EnumDecl *FromEnum, EnumDecl *ToRecord);
    bool IsStructuralMatch(EnumConstantDecl *FromEC, EnumConstantDecl *ToEC);
    bool IsStructuralMatch(FunctionTemplateDecl *From,
                           FunctionTemplateDecl *To);
    bool IsStructuralMatch(FunctionDecl *From, FunctionDecl *To);
    bool IsStructuralMatch(ClassTemplateDecl *From, ClassTemplateDecl *To);
    bool IsStructuralMatch(VarTemplateDecl *From, VarTemplateDecl *To);
    ExpectedDecl VisitDecl(Decl *D);
    ExpectedDecl VisitImportDecl(ImportDecl *D);
    ExpectedDecl VisitEmptyDecl(EmptyDecl *D);
    ExpectedDecl VisitAccessSpecDecl(AccessSpecDecl *D);
    ExpectedDecl VisitStaticAssertDecl(StaticAssertDecl *D);
    ExpectedDecl VisitTranslationUnitDecl(TranslationUnitDecl *D);
    ExpectedDecl VisitNamespaceDecl(NamespaceDecl *D);
    ExpectedDecl VisitNamespaceAliasDecl(NamespaceAliasDecl *D);
    ExpectedDecl VisitTypedefNameDecl(TypedefNameDecl *D, bool IsAlias);
    ExpectedDecl VisitTypedefDecl(TypedefDecl *D);
    ExpectedDecl VisitTypeAliasDecl(TypeAliasDecl *D);
    ExpectedDecl VisitTypeAliasTemplateDecl(TypeAliasTemplateDecl *D);
    ExpectedDecl VisitLabelDecl(LabelDecl *D);
    ExpectedDecl VisitEnumDecl(EnumDecl *D);
    ExpectedDecl VisitRecordDecl(RecordDecl *D);
    ExpectedDecl VisitEnumConstantDecl(EnumConstantDecl *D);
    ExpectedDecl VisitFunctionDecl(FunctionDecl *D);
    ExpectedDecl VisitCXXMethodDecl(CXXMethodDecl *D);
    ExpectedDecl VisitCXXConstructorDecl(CXXConstructorDecl *D);
    ExpectedDecl VisitCXXDestructorDecl(CXXDestructorDecl *D);
    ExpectedDecl VisitCXXConversionDecl(CXXConversionDecl *D);
    ExpectedDecl VisitFieldDecl(FieldDecl *D);
    ExpectedDecl VisitIndirectFieldDecl(IndirectFieldDecl *D);
    ExpectedDecl VisitFriendDecl(FriendDecl *D);
    ExpectedDecl VisitObjCIvarDecl(ObjCIvarDecl *D);
    ExpectedDecl VisitVarDecl(VarDecl *D);
    ExpectedDecl VisitImplicitParamDecl(ImplicitParamDecl *D);
    ExpectedDecl VisitParmVarDecl(ParmVarDecl *D);
    ExpectedDecl VisitObjCMethodDecl(ObjCMethodDecl *D);
    ExpectedDecl VisitObjCTypeParamDecl(ObjCTypeParamDecl *D);
    ExpectedDecl VisitObjCCategoryDecl(ObjCCategoryDecl *D);
    ExpectedDecl VisitObjCProtocolDecl(ObjCProtocolDecl *D);
    ExpectedDecl VisitLinkageSpecDecl(LinkageSpecDecl *D);
    ExpectedDecl VisitUsingDecl(UsingDecl *D);
    ExpectedDecl VisitUsingShadowDecl(UsingShadowDecl *D);
    ExpectedDecl VisitUsingDirectiveDecl(UsingDirectiveDecl *D);
    ExpectedDecl VisitUnresolvedUsingValueDecl(UnresolvedUsingValueDecl *D);
    ExpectedDecl VisitUnresolvedUsingTypenameDecl(UnresolvedUsingTypenameDecl *D);

    Expected<ObjCTypeParamList *>
    ImportObjCTypeParamList(ObjCTypeParamList *list);

    ExpectedDecl VisitObjCInterfaceDecl(ObjCInterfaceDecl *D);
    ExpectedDecl VisitObjCCategoryImplDecl(ObjCCategoryImplDecl *D);
    ExpectedDecl VisitObjCImplementationDecl(ObjCImplementationDecl *D);
    ExpectedDecl VisitObjCPropertyDecl(ObjCPropertyDecl *D);
    ExpectedDecl VisitObjCPropertyImplDecl(ObjCPropertyImplDecl *D);
    ExpectedDecl VisitTemplateTypeParmDecl(TemplateTypeParmDecl *D);
    ExpectedDecl VisitNonTypeTemplateParmDecl(NonTypeTemplateParmDecl *D);
    ExpectedDecl VisitTemplateTemplateParmDecl(TemplateTemplateParmDecl *D);
    ExpectedDecl VisitClassTemplateDecl(ClassTemplateDecl *D);
    ExpectedDecl VisitClassTemplateSpecializationDecl(
                                            ClassTemplateSpecializationDecl *D);
    ExpectedDecl VisitVarTemplateDecl(VarTemplateDecl *D);
    ExpectedDecl VisitVarTemplateSpecializationDecl(VarTemplateSpecializationDecl *D);
    ExpectedDecl VisitFunctionTemplateDecl(FunctionTemplateDecl *D);

    // Importing statements
    ExpectedStmt VisitStmt(Stmt *S);
    ExpectedStmt VisitGCCAsmStmt(GCCAsmStmt *S);
    ExpectedStmt VisitDeclStmt(DeclStmt *S);
    ExpectedStmt VisitNullStmt(NullStmt *S);
    ExpectedStmt VisitCompoundStmt(CompoundStmt *S);
    ExpectedStmt VisitCaseStmt(CaseStmt *S);
    ExpectedStmt VisitDefaultStmt(DefaultStmt *S);
    ExpectedStmt VisitLabelStmt(LabelStmt *S);
    ExpectedStmt VisitAttributedStmt(AttributedStmt *S);
    ExpectedStmt VisitIfStmt(IfStmt *S);
    ExpectedStmt VisitSwitchStmt(SwitchStmt *S);
    ExpectedStmt VisitWhileStmt(WhileStmt *S);
    ExpectedStmt VisitDoStmt(DoStmt *S);
    ExpectedStmt VisitForStmt(ForStmt *S);
    ExpectedStmt VisitGotoStmt(GotoStmt *S);
    ExpectedStmt VisitIndirectGotoStmt(IndirectGotoStmt *S);
    ExpectedStmt VisitContinueStmt(ContinueStmt *S);
    ExpectedStmt VisitBreakStmt(BreakStmt *S);
    ExpectedStmt VisitReturnStmt(ReturnStmt *S);
    // FIXME: MSAsmStmt
    // FIXME: SEHExceptStmt
    // FIXME: SEHFinallyStmt
    // FIXME: SEHTryStmt
    // FIXME: SEHLeaveStmt
    // FIXME: CapturedStmt
    ExpectedStmt VisitCXXCatchStmt(CXXCatchStmt *S);
    ExpectedStmt VisitCXXTryStmt(CXXTryStmt *S);
    ExpectedStmt VisitCXXForRangeStmt(CXXForRangeStmt *S);
    // FIXME: MSDependentExistsStmt
    ExpectedStmt VisitObjCForCollectionStmt(ObjCForCollectionStmt *S);
    ExpectedStmt VisitObjCAtCatchStmt(ObjCAtCatchStmt *S);
    ExpectedStmt VisitObjCAtFinallyStmt(ObjCAtFinallyStmt *S);
    ExpectedStmt VisitObjCAtTryStmt(ObjCAtTryStmt *S);
    ExpectedStmt VisitObjCAtSynchronizedStmt(ObjCAtSynchronizedStmt *S);
    ExpectedStmt VisitObjCAtThrowStmt(ObjCAtThrowStmt *S);
    ExpectedStmt VisitObjCAutoreleasePoolStmt(ObjCAutoreleasePoolStmt *S);

    // Importing expressions
    ExpectedStmt VisitExpr(Expr *E);
    ExpectedStmt VisitVAArgExpr(VAArgExpr *E);
    ExpectedStmt VisitGNUNullExpr(GNUNullExpr *E);
    ExpectedStmt VisitPredefinedExpr(PredefinedExpr *E);
    ExpectedStmt VisitDeclRefExpr(DeclRefExpr *E);
    ExpectedStmt VisitImplicitValueInitExpr(ImplicitValueInitExpr *E);
    ExpectedStmt VisitDesignatedInitExpr(DesignatedInitExpr *E);
    ExpectedStmt VisitCXXNullPtrLiteralExpr(CXXNullPtrLiteralExpr *E);
    ExpectedStmt VisitIntegerLiteral(IntegerLiteral *E);
    ExpectedStmt VisitFloatingLiteral(FloatingLiteral *E);
    ExpectedStmt VisitImaginaryLiteral(ImaginaryLiteral *E);
    ExpectedStmt VisitCharacterLiteral(CharacterLiteral *E);
    ExpectedStmt VisitStringLiteral(StringLiteral *E);
    ExpectedStmt VisitCompoundLiteralExpr(CompoundLiteralExpr *E);
    ExpectedStmt VisitAtomicExpr(AtomicExpr *E);
    ExpectedStmt VisitAddrLabelExpr(AddrLabelExpr *E);
    ExpectedStmt VisitConstantExpr(ConstantExpr *E);
    ExpectedStmt VisitParenExpr(ParenExpr *E);
    ExpectedStmt VisitParenListExpr(ParenListExpr *E);
    ExpectedStmt VisitStmtExpr(StmtExpr *E);
    ExpectedStmt VisitUnaryOperator(UnaryOperator *E);
    ExpectedStmt VisitUnaryExprOrTypeTraitExpr(UnaryExprOrTypeTraitExpr *E);
    ExpectedStmt VisitBinaryOperator(BinaryOperator *E);
    ExpectedStmt VisitConditionalOperator(ConditionalOperator *E);
    ExpectedStmt VisitBinaryConditionalOperator(BinaryConditionalOperator *E);
    ExpectedStmt VisitOpaqueValueExpr(OpaqueValueExpr *E);
    ExpectedStmt VisitArrayTypeTraitExpr(ArrayTypeTraitExpr *E);
    ExpectedStmt VisitExpressionTraitExpr(ExpressionTraitExpr *E);
    ExpectedStmt VisitArraySubscriptExpr(ArraySubscriptExpr *E);
    ExpectedStmt VisitCompoundAssignOperator(CompoundAssignOperator *E);
    ExpectedStmt VisitImplicitCastExpr(ImplicitCastExpr *E);
    ExpectedStmt VisitExplicitCastExpr(ExplicitCastExpr *E);
    ExpectedStmt VisitOffsetOfExpr(OffsetOfExpr *OE);
    ExpectedStmt VisitCXXThrowExpr(CXXThrowExpr *E);
    ExpectedStmt VisitCXXNoexceptExpr(CXXNoexceptExpr *E);
    ExpectedStmt VisitCXXDefaultArgExpr(CXXDefaultArgExpr *E);
    ExpectedStmt VisitCXXScalarValueInitExpr(CXXScalarValueInitExpr *E);
    ExpectedStmt VisitCXXBindTemporaryExpr(CXXBindTemporaryExpr *E);
    ExpectedStmt VisitCXXTemporaryObjectExpr(CXXTemporaryObjectExpr *E);
    ExpectedStmt VisitMaterializeTemporaryExpr(MaterializeTemporaryExpr *E);
    ExpectedStmt VisitPackExpansionExpr(PackExpansionExpr *E);
    ExpectedStmt VisitSizeOfPackExpr(SizeOfPackExpr *E);
    ExpectedStmt VisitCXXNewExpr(CXXNewExpr *E);
    ExpectedStmt VisitCXXDeleteExpr(CXXDeleteExpr *E);
    ExpectedStmt VisitCXXConstructExpr(CXXConstructExpr *E);
    ExpectedStmt VisitCXXMemberCallExpr(CXXMemberCallExpr *E);
    ExpectedStmt VisitCXXDependentScopeMemberExpr(CXXDependentScopeMemberExpr *E);
    ExpectedStmt VisitDependentScopeDeclRefExpr(DependentScopeDeclRefExpr *E);
    ExpectedStmt VisitCXXUnresolvedConstructExpr(CXXUnresolvedConstructExpr *E);
    ExpectedStmt VisitUnresolvedLookupExpr(UnresolvedLookupExpr *E);
    ExpectedStmt VisitUnresolvedMemberExpr(UnresolvedMemberExpr *E);
    ExpectedStmt VisitExprWithCleanups(ExprWithCleanups *E);
    ExpectedStmt VisitCXXThisExpr(CXXThisExpr *E);
    ExpectedStmt VisitCXXBoolLiteralExpr(CXXBoolLiteralExpr *E);
    ExpectedStmt VisitCXXPseudoDestructorExpr(CXXPseudoDestructorExpr *E);
    ExpectedStmt VisitMemberExpr(MemberExpr *E);
    ExpectedStmt VisitCallExpr(CallExpr *E);
    ExpectedStmt VisitLambdaExpr(LambdaExpr *LE);
    ExpectedStmt VisitInitListExpr(InitListExpr *E);
    ExpectedStmt VisitCXXStdInitializerListExpr(CXXStdInitializerListExpr *E);
    ExpectedStmt VisitCXXInheritedCtorInitExpr(CXXInheritedCtorInitExpr *E);
    ExpectedStmt VisitArrayInitLoopExpr(ArrayInitLoopExpr *E);
    ExpectedStmt VisitArrayInitIndexExpr(ArrayInitIndexExpr *E);
    ExpectedStmt VisitCXXDefaultInitExpr(CXXDefaultInitExpr *E);
    ExpectedStmt VisitCXXNamedCastExpr(CXXNamedCastExpr *E);
    ExpectedStmt VisitSubstNonTypeTemplateParmExpr(SubstNonTypeTemplateParmExpr *E);
    ExpectedStmt VisitTypeTraitExpr(TypeTraitExpr *E);
    ExpectedStmt VisitCXXTypeidExpr(CXXTypeidExpr *E);

    template<typename IIter, typename OIter>
    Error ImportArrayChecked(IIter Ibegin, IIter Iend, OIter Obegin) {
      using ItemT = typename std::remove_reference<decltype(*Obegin)>::type;
      for (; Ibegin != Iend; ++Ibegin, ++Obegin) {
        Expected<ItemT> ToOrErr = import(*Ibegin);
        if (!ToOrErr)
          return ToOrErr.takeError();
        *Obegin = *ToOrErr;
      }
      return Error::success();
    }

    // Import every item from a container structure into an output container.
    // If error occurs, stops at first error and returns the error.
    // The output container should have space for all needed elements (it is not
    // expanded, new items are put into from the beginning).
    template<typename InContainerTy, typename OutContainerTy>
    Error ImportContainerChecked(
        const InContainerTy &InContainer, OutContainerTy &OutContainer) {
      return ImportArrayChecked(
          InContainer.begin(), InContainer.end(), OutContainer.begin());
    }

    template<typename InContainerTy, typename OIter>
    Error ImportArrayChecked(const InContainerTy &InContainer, OIter Obegin) {
      return ImportArrayChecked(InContainer.begin(), InContainer.end(), Obegin);
    }

    void ImportOverrides(CXXMethodDecl *ToMethod, CXXMethodDecl *FromMethod);

    Expected<FunctionDecl *> FindFunctionTemplateSpecialization(
        FunctionDecl *FromFD);
  };

// FIXME: Temporary until every import returns Expected.
template <>
Expected<TemplateName> ASTNodeImporter::import(const TemplateName &From) {
  TemplateName To = Importer.Import(From);
  if (To.isNull() && !From.isNull())
    return make_error<ImportError>();
  return To;
}

template <typename InContainerTy>
Error ASTNodeImporter::ImportTemplateArgumentListInfo(
    SourceLocation FromLAngleLoc, SourceLocation FromRAngleLoc,
    const InContainerTy &Container, TemplateArgumentListInfo &Result) {
  auto ToLAngleLocOrErr = import(FromLAngleLoc);
  if (!ToLAngleLocOrErr)
    return ToLAngleLocOrErr.takeError();
  auto ToRAngleLocOrErr = import(FromRAngleLoc);
  if (!ToRAngleLocOrErr)
    return ToRAngleLocOrErr.takeError();

  TemplateArgumentListInfo ToTAInfo(*ToLAngleLocOrErr, *ToRAngleLocOrErr);
  if (auto Err = ImportTemplateArgumentListInfo(Container, ToTAInfo))
    return Err;
  Result = ToTAInfo;
  return Error::success();
}

template <>
Error ASTNodeImporter::ImportTemplateArgumentListInfo<TemplateArgumentListInfo>(
    const TemplateArgumentListInfo &From, TemplateArgumentListInfo &Result) {
  return ImportTemplateArgumentListInfo(
      From.getLAngleLoc(), From.getRAngleLoc(), From.arguments(), Result);
}

template <>
Error ASTNodeImporter::ImportTemplateArgumentListInfo<
    ASTTemplateArgumentListInfo>(
        const ASTTemplateArgumentListInfo &From,
        TemplateArgumentListInfo &Result) {
  return ImportTemplateArgumentListInfo(
      From.LAngleLoc, From.RAngleLoc, From.arguments(), Result);
}

Expected<ASTNodeImporter::FunctionTemplateAndArgsTy>
ASTNodeImporter::ImportFunctionTemplateWithTemplateArgsFromSpecialization(
    FunctionDecl *FromFD) {
  assert(FromFD->getTemplatedKind() ==
      FunctionDecl::TK_FunctionTemplateSpecialization);

  FunctionTemplateAndArgsTy Result;

  auto *FTSInfo = FromFD->getTemplateSpecializationInfo();
  if (Error Err = importInto(std::get<0>(Result), FTSInfo->getTemplate()))
    return std::move(Err);

  // Import template arguments.
  auto TemplArgs = FTSInfo->TemplateArguments->asArray();
  if (Error Err = ImportTemplateArguments(TemplArgs.data(), TemplArgs.size(),
      std::get<1>(Result)))
    return std::move(Err);

  return Result;
}

template <>
Expected<TemplateParameterList *>
ASTNodeImporter::import(TemplateParameterList *From) {
  SmallVector<NamedDecl *, 4> To(From->size());
  if (Error Err = ImportContainerChecked(*From, To))
    return std::move(Err);

  ExpectedExpr ToRequiresClause = import(From->getRequiresClause());
  if (!ToRequiresClause)
    return ToRequiresClause.takeError();

  auto ToTemplateLocOrErr = import(From->getTemplateLoc());
  if (!ToTemplateLocOrErr)
    return ToTemplateLocOrErr.takeError();
  auto ToLAngleLocOrErr = import(From->getLAngleLoc());
  if (!ToLAngleLocOrErr)
    return ToLAngleLocOrErr.takeError();
  auto ToRAngleLocOrErr = import(From->getRAngleLoc());
  if (!ToRAngleLocOrErr)
    return ToRAngleLocOrErr.takeError();

  return TemplateParameterList::Create(
      Importer.getToContext(),
      *ToTemplateLocOrErr,
      *ToLAngleLocOrErr,
      To,
      *ToRAngleLocOrErr,
      *ToRequiresClause);
}

template <>
Expected<TemplateArgument>
ASTNodeImporter::import(const TemplateArgument &From) {
  switch (From.getKind()) {
  case TemplateArgument::Null:
    return TemplateArgument();

  case TemplateArgument::Type: {
    ExpectedType ToTypeOrErr = import(From.getAsType());
    if (!ToTypeOrErr)
      return ToTypeOrErr.takeError();
    return TemplateArgument(*ToTypeOrErr);
  }

  case TemplateArgument::Integral: {
    ExpectedType ToTypeOrErr = import(From.getIntegralType());
    if (!ToTypeOrErr)
      return ToTypeOrErr.takeError();
    return TemplateArgument(From, *ToTypeOrErr);
  }

  case TemplateArgument::Declaration: {
    Expected<ValueDecl *> ToOrErr = import(From.getAsDecl());
    if (!ToOrErr)
      return ToOrErr.takeError();
    ExpectedType ToTypeOrErr = import(From.getParamTypeForDecl());
    if (!ToTypeOrErr)
      return ToTypeOrErr.takeError();
    return TemplateArgument(*ToOrErr, *ToTypeOrErr);
  }

  case TemplateArgument::NullPtr: {
    ExpectedType ToTypeOrErr = import(From.getNullPtrType());
    if (!ToTypeOrErr)
      return ToTypeOrErr.takeError();
    return TemplateArgument(*ToTypeOrErr, /*isNullPtr*/true);
  }

  case TemplateArgument::Template: {
    Expected<TemplateName> ToTemplateOrErr = import(From.getAsTemplate());
    if (!ToTemplateOrErr)
      return ToTemplateOrErr.takeError();

    return TemplateArgument(*ToTemplateOrErr);
  }

  case TemplateArgument::TemplateExpansion: {
    Expected<TemplateName> ToTemplateOrErr =
        import(From.getAsTemplateOrTemplatePattern());
    if (!ToTemplateOrErr)
      return ToTemplateOrErr.takeError();

    return TemplateArgument(
        *ToTemplateOrErr, From.getNumTemplateExpansions());
  }

  case TemplateArgument::Expression:
    if (ExpectedExpr ToExpr = import(From.getAsExpr()))
      return TemplateArgument(*ToExpr);
    else
      return ToExpr.takeError();

  case TemplateArgument::Pack: {
    SmallVector<TemplateArgument, 2> ToPack;
    ToPack.reserve(From.pack_size());
    if (Error Err = ImportTemplateArguments(
        From.pack_begin(), From.pack_size(), ToPack))
      return std::move(Err);

    return TemplateArgument(
        llvm::makeArrayRef(ToPack).copy(Importer.getToContext()));
  }
  }

  llvm_unreachable("Invalid template argument kind");
}

template <>
Expected<TemplateArgumentLoc>
ASTNodeImporter::import(const TemplateArgumentLoc &TALoc) {
  Expected<TemplateArgument> ArgOrErr = import(TALoc.getArgument());
  if (!ArgOrErr)
    return ArgOrErr.takeError();
  TemplateArgument Arg = *ArgOrErr;

  TemplateArgumentLocInfo FromInfo = TALoc.getLocInfo();

  TemplateArgumentLocInfo ToInfo;
  if (Arg.getKind() == TemplateArgument::Expression) {
    ExpectedExpr E = import(FromInfo.getAsExpr());
    if (!E)
      return E.takeError();
    ToInfo = TemplateArgumentLocInfo(*E);
  } else if (Arg.getKind() == TemplateArgument::Type) {
    if (auto TSIOrErr = import(FromInfo.getAsTypeSourceInfo()))
      ToInfo = TemplateArgumentLocInfo(*TSIOrErr);
    else
      return TSIOrErr.takeError();
  } else {
    auto ToTemplateQualifierLocOrErr =
        import(FromInfo.getTemplateQualifierLoc());
    if (!ToTemplateQualifierLocOrErr)
      return ToTemplateQualifierLocOrErr.takeError();
    auto ToTemplateNameLocOrErr = import(FromInfo.getTemplateNameLoc());
    if (!ToTemplateNameLocOrErr)
      return ToTemplateNameLocOrErr.takeError();
    auto ToTemplateEllipsisLocOrErr =
        import(FromInfo.getTemplateEllipsisLoc());
    if (!ToTemplateEllipsisLocOrErr)
      return ToTemplateEllipsisLocOrErr.takeError();

    ToInfo = TemplateArgumentLocInfo(
          *ToTemplateQualifierLocOrErr,
          *ToTemplateNameLocOrErr,
          *ToTemplateEllipsisLocOrErr);
  }

  return TemplateArgumentLoc(Arg, ToInfo);
}

template <>
Expected<DeclGroupRef> ASTNodeImporter::import(const DeclGroupRef &DG) {
  if (DG.isNull())
    return DeclGroupRef::Create(Importer.getToContext(), nullptr, 0);
  size_t NumDecls = DG.end() - DG.begin();
  SmallVector<Decl *, 1> ToDecls;
  ToDecls.reserve(NumDecls);
  for (Decl *FromD : DG) {
    if (auto ToDOrErr = import(FromD))
      ToDecls.push_back(*ToDOrErr);
    else
      return ToDOrErr.takeError();
  }
  return DeclGroupRef::Create(Importer.getToContext(),
                              ToDecls.begin(),
                              NumDecls);
}

template <>
Expected<ASTNodeImporter::Designator>
ASTNodeImporter::import(const Designator &D) {
  if (D.isFieldDesignator()) {
    IdentifierInfo *ToFieldName = Importer.Import(D.getFieldName());

    ExpectedSLoc ToDotLocOrErr = import(D.getDotLoc());
    if (!ToDotLocOrErr)
      return ToDotLocOrErr.takeError();

    ExpectedSLoc ToFieldLocOrErr = import(D.getFieldLoc());
    if (!ToFieldLocOrErr)
      return ToFieldLocOrErr.takeError();

    return Designator(ToFieldName, *ToDotLocOrErr, *ToFieldLocOrErr);
  }

  ExpectedSLoc ToLBracketLocOrErr = import(D.getLBracketLoc());
  if (!ToLBracketLocOrErr)
    return ToLBracketLocOrErr.takeError();

  ExpectedSLoc ToRBracketLocOrErr = import(D.getRBracketLoc());
  if (!ToRBracketLocOrErr)
    return ToRBracketLocOrErr.takeError();

  if (D.isArrayDesignator())
    return Designator(D.getFirstExprIndex(),
                      *ToLBracketLocOrErr, *ToRBracketLocOrErr);

  ExpectedSLoc ToEllipsisLocOrErr = import(D.getEllipsisLoc());
  if (!ToEllipsisLocOrErr)
    return ToEllipsisLocOrErr.takeError();

  assert(D.isArrayRangeDesignator());
  return Designator(
      D.getFirstExprIndex(), *ToLBracketLocOrErr, *ToEllipsisLocOrErr,
      *ToRBracketLocOrErr);
}

template <>
Expected<LambdaCapture> ASTNodeImporter::import(const LambdaCapture &From) {
  VarDecl *Var = nullptr;
  if (From.capturesVariable()) {
    if (auto VarOrErr = import(From.getCapturedVar()))
      Var = *VarOrErr;
    else
      return VarOrErr.takeError();
  }

  auto LocationOrErr = import(From.getLocation());
  if (!LocationOrErr)
    return LocationOrErr.takeError();

  SourceLocation EllipsisLoc;
  if (From.isPackExpansion())
    if (Error Err = importInto(EllipsisLoc, From.getEllipsisLoc()))
      return std::move(Err);

  return LambdaCapture(
      *LocationOrErr, From.isImplicit(), From.getCaptureKind(), Var,
      EllipsisLoc);
}

} // namespace clang

//----------------------------------------------------------------------------
// Import Types
//----------------------------------------------------------------------------

using namespace clang;

ExpectedType ASTNodeImporter::VisitType(const Type *T) {
  Importer.FromDiag(SourceLocation(), diag::err_unsupported_ast_node)
    << T->getTypeClassName();
  return make_error<ImportError>(ImportError::UnsupportedConstruct);
}

ExpectedType ASTNodeImporter::VisitAtomicType(const AtomicType *T){
  ExpectedType UnderlyingTypeOrErr = import(T->getValueType());
  if (!UnderlyingTypeOrErr)
    return UnderlyingTypeOrErr.takeError();

  return Importer.getToContext().getAtomicType(*UnderlyingTypeOrErr);
}

ExpectedType ASTNodeImporter::VisitBuiltinType(const BuiltinType *T) {
  switch (T->getKind()) {
#define IMAGE_TYPE(ImgType, Id, SingletonId, Access, Suffix) \
  case BuiltinType::Id: \
    return Importer.getToContext().SingletonId;
#include "clang/Basic/OpenCLImageTypes.def"
#define EXT_OPAQUE_TYPE(ExtType, Id, Ext) \
  case BuiltinType::Id: \
    return Importer.getToContext().Id##Ty;
#include "clang/Basic/OpenCLExtensionTypes.def"
#define SHARED_SINGLETON_TYPE(Expansion)
#define BUILTIN_TYPE(Id, SingletonId) \
  case BuiltinType::Id: return Importer.getToContext().SingletonId;
#include "clang/AST/BuiltinTypes.def"

  // FIXME: for Char16, Char32, and NullPtr, make sure that the "to"
  // context supports C++.

  // FIXME: for ObjCId, ObjCClass, and ObjCSel, make sure that the "to"
  // context supports ObjC.

  case BuiltinType::Char_U:
    // The context we're importing from has an unsigned 'char'. If we're
    // importing into a context with a signed 'char', translate to
    // 'unsigned char' instead.
    if (Importer.getToContext().getLangOpts().CharIsSigned)
      return Importer.getToContext().UnsignedCharTy;

    return Importer.getToContext().CharTy;

  case BuiltinType::Char_S:
    // The context we're importing from has an unsigned 'char'. If we're
    // importing into a context with a signed 'char', translate to
    // 'unsigned char' instead.
    if (!Importer.getToContext().getLangOpts().CharIsSigned)
      return Importer.getToContext().SignedCharTy;

    return Importer.getToContext().CharTy;

  case BuiltinType::WChar_S:
  case BuiltinType::WChar_U:
    // FIXME: If not in C++, shall we translate to the C equivalent of
    // wchar_t?
    return Importer.getToContext().WCharTy;
  }

  llvm_unreachable("Invalid BuiltinType Kind!");
}

ExpectedType ASTNodeImporter::VisitDecayedType(const DecayedType *T) {
  ExpectedType ToOriginalTypeOrErr = import(T->getOriginalType());
  if (!ToOriginalTypeOrErr)
    return ToOriginalTypeOrErr.takeError();

  return Importer.getToContext().getDecayedType(*ToOriginalTypeOrErr);
}

ExpectedType ASTNodeImporter::VisitComplexType(const ComplexType *T) {
  ExpectedType ToElementTypeOrErr = import(T->getElementType());
  if (!ToElementTypeOrErr)
    return ToElementTypeOrErr.takeError();

  return Importer.getToContext().getComplexType(*ToElementTypeOrErr);
}

ExpectedType ASTNodeImporter::VisitPointerType(const PointerType *T) {
  ExpectedType ToPointeeTypeOrErr = import(T->getPointeeType());
  if (!ToPointeeTypeOrErr)
    return ToPointeeTypeOrErr.takeError();

  return Importer.getToContext().getPointerType(*ToPointeeTypeOrErr);
}

ExpectedType ASTNodeImporter::VisitBlockPointerType(const BlockPointerType *T) {
  // FIXME: Check for blocks support in "to" context.
  ExpectedType ToPointeeTypeOrErr = import(T->getPointeeType());
  if (!ToPointeeTypeOrErr)
    return ToPointeeTypeOrErr.takeError();

  return Importer.getToContext().getBlockPointerType(*ToPointeeTypeOrErr);
}

ExpectedType
ASTNodeImporter::VisitLValueReferenceType(const LValueReferenceType *T) {
  // FIXME: Check for C++ support in "to" context.
  ExpectedType ToPointeeTypeOrErr = import(T->getPointeeTypeAsWritten());
  if (!ToPointeeTypeOrErr)
    return ToPointeeTypeOrErr.takeError();

  return Importer.getToContext().getLValueReferenceType(*ToPointeeTypeOrErr);
}

ExpectedType
ASTNodeImporter::VisitRValueReferenceType(const RValueReferenceType *T) {
  // FIXME: Check for C++0x support in "to" context.
  ExpectedType ToPointeeTypeOrErr = import(T->getPointeeTypeAsWritten());
  if (!ToPointeeTypeOrErr)
    return ToPointeeTypeOrErr.takeError();

  return Importer.getToContext().getRValueReferenceType(*ToPointeeTypeOrErr);
}

ExpectedType
ASTNodeImporter::VisitMemberPointerType(const MemberPointerType *T) {
  // FIXME: Check for C++ support in "to" context.
  ExpectedType ToPointeeTypeOrErr = import(T->getPointeeType());
  if (!ToPointeeTypeOrErr)
    return ToPointeeTypeOrErr.takeError();

  ExpectedType ClassTypeOrErr = import(QualType(T->getClass(), 0));
  if (!ClassTypeOrErr)
    return ClassTypeOrErr.takeError();

  return Importer.getToContext().getMemberPointerType(
      *ToPointeeTypeOrErr, (*ClassTypeOrErr).getTypePtr());
}

ExpectedType
ASTNodeImporter::VisitConstantArrayType(const ConstantArrayType *T) {
  ExpectedType ToElementTypeOrErr = import(T->getElementType());
  if (!ToElementTypeOrErr)
    return ToElementTypeOrErr.takeError();

  return Importer.getToContext().getConstantArrayType(*ToElementTypeOrErr,
                                                      T->getSize(),
                                                      T->getSizeModifier(),
                                               T->getIndexTypeCVRQualifiers());
}

ExpectedType
ASTNodeImporter::VisitIncompleteArrayType(const IncompleteArrayType *T) {
  ExpectedType ToElementTypeOrErr = import(T->getElementType());
  if (!ToElementTypeOrErr)
    return ToElementTypeOrErr.takeError();

  return Importer.getToContext().getIncompleteArrayType(*ToElementTypeOrErr,
                                                        T->getSizeModifier(),
                                                T->getIndexTypeCVRQualifiers());
}

ExpectedType
ASTNodeImporter::VisitVariableArrayType(const VariableArrayType *T) {
  QualType ToElementType;
  Expr *ToSizeExpr;
  SourceRange ToBracketsRange;
  if (auto Imp = importSeq(
      T->getElementType(), T->getSizeExpr(), T->getBracketsRange()))
    std::tie(ToElementType, ToSizeExpr, ToBracketsRange) = *Imp;
  else
    return Imp.takeError();

  return Importer.getToContext().getVariableArrayType(
      ToElementType, ToSizeExpr, T->getSizeModifier(),
      T->getIndexTypeCVRQualifiers(), ToBracketsRange);
}

ExpectedType ASTNodeImporter::VisitDependentSizedArrayType(
    const DependentSizedArrayType *T) {
  QualType ToElementType;
  Expr *ToSizeExpr;
  SourceRange ToBracketsRange;
  if (auto Imp = importSeq(
      T->getElementType(), T->getSizeExpr(), T->getBracketsRange()))
    std::tie(ToElementType, ToSizeExpr, ToBracketsRange) = *Imp;
  else
    return Imp.takeError();
  // SizeExpr may be null if size is not specified directly.
  // For example, 'int a[]'.

  return Importer.getToContext().getDependentSizedArrayType(
      ToElementType, ToSizeExpr, T->getSizeModifier(),
      T->getIndexTypeCVRQualifiers(), ToBracketsRange);
}

ExpectedType ASTNodeImporter::VisitVectorType(const VectorType *T) {
  ExpectedType ToElementTypeOrErr = import(T->getElementType());
  if (!ToElementTypeOrErr)
    return ToElementTypeOrErr.takeError();

  return Importer.getToContext().getVectorType(*ToElementTypeOrErr,
                                               T->getNumElements(),
                                               T->getVectorKind());
}

ExpectedType ASTNodeImporter::VisitExtVectorType(const ExtVectorType *T) {
  ExpectedType ToElementTypeOrErr = import(T->getElementType());
  if (!ToElementTypeOrErr)
    return ToElementTypeOrErr.takeError();

  return Importer.getToContext().getExtVectorType(*ToElementTypeOrErr,
                                                  T->getNumElements());
}

ExpectedType
ASTNodeImporter::VisitFunctionNoProtoType(const FunctionNoProtoType *T) {
  // FIXME: What happens if we're importing a function without a prototype
  // into C++? Should we make it variadic?
  ExpectedType ToReturnTypeOrErr = import(T->getReturnType());
  if (!ToReturnTypeOrErr)
    return ToReturnTypeOrErr.takeError();

  return Importer.getToContext().getFunctionNoProtoType(*ToReturnTypeOrErr,
                                                        T->getExtInfo());
}

ExpectedType
ASTNodeImporter::VisitFunctionProtoType(const FunctionProtoType *T) {
  ExpectedType ToReturnTypeOrErr = import(T->getReturnType());
  if (!ToReturnTypeOrErr)
    return ToReturnTypeOrErr.takeError();

  // Import argument types
  SmallVector<QualType, 4> ArgTypes;
  for (const auto &A : T->param_types()) {
    ExpectedType TyOrErr = import(A);
    if (!TyOrErr)
      return TyOrErr.takeError();
    ArgTypes.push_back(*TyOrErr);
  }

  // Import exception types
  SmallVector<QualType, 4> ExceptionTypes;
  for (const auto &E : T->exceptions()) {
    ExpectedType TyOrErr = import(E);
    if (!TyOrErr)
      return TyOrErr.takeError();
    ExceptionTypes.push_back(*TyOrErr);
  }

  FunctionProtoType::ExtProtoInfo FromEPI = T->getExtProtoInfo();
  FunctionProtoType::ExtProtoInfo ToEPI;

  auto Imp = importSeq(
      FromEPI.ExceptionSpec.NoexceptExpr,
      FromEPI.ExceptionSpec.SourceDecl,
      FromEPI.ExceptionSpec.SourceTemplate);
  if (!Imp)
    return Imp.takeError();

  ToEPI.ExtInfo = FromEPI.ExtInfo;
  ToEPI.Variadic = FromEPI.Variadic;
  ToEPI.HasTrailingReturn = FromEPI.HasTrailingReturn;
  ToEPI.TypeQuals = FromEPI.TypeQuals;
  ToEPI.RefQualifier = FromEPI.RefQualifier;
  ToEPI.ExceptionSpec.Type = FromEPI.ExceptionSpec.Type;
  ToEPI.ExceptionSpec.Exceptions = ExceptionTypes;
  std::tie(
      ToEPI.ExceptionSpec.NoexceptExpr,
      ToEPI.ExceptionSpec.SourceDecl,
      ToEPI.ExceptionSpec.SourceTemplate) = *Imp;

  return Importer.getToContext().getFunctionType(
      *ToReturnTypeOrErr, ArgTypes, ToEPI);
}

ExpectedType ASTNodeImporter::VisitUnresolvedUsingType(
    const UnresolvedUsingType *T) {
  UnresolvedUsingTypenameDecl *ToD;
  Decl *ToPrevD;
  if (auto Imp = importSeq(T->getDecl(), T->getDecl()->getPreviousDecl()))
    std::tie(ToD, ToPrevD) = *Imp;
  else
    return Imp.takeError();

  return Importer.getToContext().getTypeDeclType(
      ToD, cast_or_null<TypeDecl>(ToPrevD));
}

ExpectedType ASTNodeImporter::VisitParenType(const ParenType *T) {
  ExpectedType ToInnerTypeOrErr = import(T->getInnerType());
  if (!ToInnerTypeOrErr)
    return ToInnerTypeOrErr.takeError();

  return Importer.getToContext().getParenType(*ToInnerTypeOrErr);
}

ExpectedType ASTNodeImporter::VisitTypedefType(const TypedefType *T) {
  Expected<TypedefNameDecl *> ToDeclOrErr = import(T->getDecl());
  if (!ToDeclOrErr)
    return ToDeclOrErr.takeError();

  return Importer.getToContext().getTypeDeclType(*ToDeclOrErr);
}

ExpectedType ASTNodeImporter::VisitTypeOfExprType(const TypeOfExprType *T) {
  ExpectedExpr ToExprOrErr = import(T->getUnderlyingExpr());
  if (!ToExprOrErr)
    return ToExprOrErr.takeError();

  return Importer.getToContext().getTypeOfExprType(*ToExprOrErr);
}

ExpectedType ASTNodeImporter::VisitTypeOfType(const TypeOfType *T) {
  ExpectedType ToUnderlyingTypeOrErr = import(T->getUnderlyingType());
  if (!ToUnderlyingTypeOrErr)
    return ToUnderlyingTypeOrErr.takeError();

  return Importer.getToContext().getTypeOfType(*ToUnderlyingTypeOrErr);
}

ExpectedType ASTNodeImporter::VisitDecltypeType(const DecltypeType *T) {
  // FIXME: Make sure that the "to" context supports C++0x!
  ExpectedExpr ToExprOrErr = import(T->getUnderlyingExpr());
  if (!ToExprOrErr)
    return ToExprOrErr.takeError();

  ExpectedType ToUnderlyingTypeOrErr = import(T->getUnderlyingType());
  if (!ToUnderlyingTypeOrErr)
    return ToUnderlyingTypeOrErr.takeError();

  return Importer.getToContext().getDecltypeType(
      *ToExprOrErr, *ToUnderlyingTypeOrErr);
}

ExpectedType
ASTNodeImporter::VisitUnaryTransformType(const UnaryTransformType *T) {
  ExpectedType ToBaseTypeOrErr = import(T->getBaseType());
  if (!ToBaseTypeOrErr)
    return ToBaseTypeOrErr.takeError();

  ExpectedType ToUnderlyingTypeOrErr = import(T->getUnderlyingType());
  if (!ToUnderlyingTypeOrErr)
    return ToUnderlyingTypeOrErr.takeError();

  return Importer.getToContext().getUnaryTransformType(
      *ToBaseTypeOrErr, *ToUnderlyingTypeOrErr, T->getUTTKind());
}

ExpectedType ASTNodeImporter::VisitAutoType(const AutoType *T) {
  // FIXME: Make sure that the "to" context supports C++11!
  ExpectedType ToDeducedTypeOrErr = import(T->getDeducedType());
  if (!ToDeducedTypeOrErr)
    return ToDeducedTypeOrErr.takeError();

  return Importer.getToContext().getAutoType(*ToDeducedTypeOrErr,
                                             T->getKeyword(),
                                             /*IsDependent*/false);
}

ExpectedType ASTNodeImporter::VisitInjectedClassNameType(
    const InjectedClassNameType *T) {
  Expected<CXXRecordDecl *> ToDeclOrErr = import(T->getDecl());
  if (!ToDeclOrErr)
    return ToDeclOrErr.takeError();

  ExpectedType ToInjTypeOrErr = import(T->getInjectedSpecializationType());
  if (!ToInjTypeOrErr)
    return ToInjTypeOrErr.takeError();

  // FIXME: ASTContext::getInjectedClassNameType is not suitable for AST reading
  // See comments in InjectedClassNameType definition for details
  // return Importer.getToContext().getInjectedClassNameType(D, InjType);
  enum {
    TypeAlignmentInBits = 4,
    TypeAlignment = 1 << TypeAlignmentInBits
  };

  return QualType(new (Importer.getToContext(), TypeAlignment)
                  InjectedClassNameType(*ToDeclOrErr, *ToInjTypeOrErr), 0);
}

ExpectedType ASTNodeImporter::VisitRecordType(const RecordType *T) {
  Expected<RecordDecl *> ToDeclOrErr = import(T->getDecl());
  if (!ToDeclOrErr)
    return ToDeclOrErr.takeError();

  return Importer.getToContext().getTagDeclType(*ToDeclOrErr);
}

ExpectedType ASTNodeImporter::VisitEnumType(const EnumType *T) {
  Expected<EnumDecl *> ToDeclOrErr = import(T->getDecl());
  if (!ToDeclOrErr)
    return ToDeclOrErr.takeError();

  return Importer.getToContext().getTagDeclType(*ToDeclOrErr);
}

ExpectedType ASTNodeImporter::VisitAttributedType(const AttributedType *T) {
  ExpectedType ToModifiedTypeOrErr = import(T->getModifiedType());
  if (!ToModifiedTypeOrErr)
    return ToModifiedTypeOrErr.takeError();
  ExpectedType ToEquivalentTypeOrErr = import(T->getEquivalentType());
  if (!ToEquivalentTypeOrErr)
    return ToEquivalentTypeOrErr.takeError();

  return Importer.getToContext().getAttributedType(T->getAttrKind(),
      *ToModifiedTypeOrErr, *ToEquivalentTypeOrErr);
}

ExpectedType ASTNodeImporter::VisitTemplateTypeParmType(
    const TemplateTypeParmType *T) {
  Expected<TemplateTypeParmDecl *> ToDeclOrErr = import(T->getDecl());
  if (!ToDeclOrErr)
    return ToDeclOrErr.takeError();

  return Importer.getToContext().getTemplateTypeParmType(
      T->getDepth(), T->getIndex(), T->isParameterPack(), *ToDeclOrErr);
}

ExpectedType ASTNodeImporter::VisitSubstTemplateTypeParmType(
    const SubstTemplateTypeParmType *T) {
  ExpectedType ReplacedOrErr = import(QualType(T->getReplacedParameter(), 0));
  if (!ReplacedOrErr)
    return ReplacedOrErr.takeError();
  const TemplateTypeParmType *Replaced =
      cast<TemplateTypeParmType>((*ReplacedOrErr).getTypePtr());

  ExpectedType ToReplacementTypeOrErr = import(T->getReplacementType());
  if (!ToReplacementTypeOrErr)
    return ToReplacementTypeOrErr.takeError();

  return Importer.getToContext().getSubstTemplateTypeParmType(
        Replaced, (*ToReplacementTypeOrErr).getCanonicalType());
}

ExpectedType ASTNodeImporter::VisitTemplateSpecializationType(
                                       const TemplateSpecializationType *T) {
  auto ToTemplateOrErr = import(T->getTemplateName());
  if (!ToTemplateOrErr)
    return ToTemplateOrErr.takeError();

  SmallVector<TemplateArgument, 2> ToTemplateArgs;
  if (Error Err = ImportTemplateArguments(
      T->getArgs(), T->getNumArgs(), ToTemplateArgs))
    return std::move(Err);

  QualType ToCanonType;
  if (!QualType(T, 0).isCanonical()) {
    QualType FromCanonType
      = Importer.getFromContext().getCanonicalType(QualType(T, 0));
    if (ExpectedType TyOrErr = import(FromCanonType))
      ToCanonType = *TyOrErr;
    else
      return TyOrErr.takeError();
  }
  return Importer.getToContext().getTemplateSpecializationType(*ToTemplateOrErr,
                                                               ToTemplateArgs,
                                                               ToCanonType);
}

ExpectedType ASTNodeImporter::VisitElaboratedType(const ElaboratedType *T) {
  // Note: the qualifier in an ElaboratedType is optional.
  auto ToQualifierOrErr = import(T->getQualifier());
  if (!ToQualifierOrErr)
    return ToQualifierOrErr.takeError();

  ExpectedType ToNamedTypeOrErr = import(T->getNamedType());
  if (!ToNamedTypeOrErr)
    return ToNamedTypeOrErr.takeError();

  Expected<TagDecl *> ToOwnedTagDeclOrErr = import(T->getOwnedTagDecl());
  if (!ToOwnedTagDeclOrErr)
    return ToOwnedTagDeclOrErr.takeError();

  return Importer.getToContext().getElaboratedType(T->getKeyword(),
                                                   *ToQualifierOrErr,
                                                   *ToNamedTypeOrErr,
                                                   *ToOwnedTagDeclOrErr);
}

ExpectedType
ASTNodeImporter::VisitPackExpansionType(const PackExpansionType *T) {
  ExpectedType ToPatternOrErr = import(T->getPattern());
  if (!ToPatternOrErr)
    return ToPatternOrErr.takeError();

  return Importer.getToContext().getPackExpansionType(*ToPatternOrErr,
                                                      T->getNumExpansions());
}

ExpectedType ASTNodeImporter::VisitDependentTemplateSpecializationType(
    const DependentTemplateSpecializationType *T) {
  auto ToQualifierOrErr = import(T->getQualifier());
  if (!ToQualifierOrErr)
    return ToQualifierOrErr.takeError();

  IdentifierInfo *ToName = Importer.Import(T->getIdentifier());

  SmallVector<TemplateArgument, 2> ToPack;
  ToPack.reserve(T->getNumArgs());
  if (Error Err = ImportTemplateArguments(
      T->getArgs(), T->getNumArgs(), ToPack))
    return std::move(Err);

  return Importer.getToContext().getDependentTemplateSpecializationType(
      T->getKeyword(), *ToQualifierOrErr, ToName, ToPack);
}

ExpectedType
ASTNodeImporter::VisitDependentNameType(const DependentNameType *T) {
  auto ToQualifierOrErr = import(T->getQualifier());
  if (!ToQualifierOrErr)
    return ToQualifierOrErr.takeError();

  IdentifierInfo *Name = Importer.Import(T->getIdentifier());

  QualType Canon;
  if (T != T->getCanonicalTypeInternal().getTypePtr()) {
    if (ExpectedType TyOrErr = import(T->getCanonicalTypeInternal()))
      Canon = (*TyOrErr).getCanonicalType();
    else
      return TyOrErr.takeError();
  }

  return Importer.getToContext().getDependentNameType(T->getKeyword(),
                                                      *ToQualifierOrErr,
                                                      Name, Canon);
}

ExpectedType
ASTNodeImporter::VisitObjCInterfaceType(const ObjCInterfaceType *T) {
  Expected<ObjCInterfaceDecl *> ToDeclOrErr = import(T->getDecl());
  if (!ToDeclOrErr)
    return ToDeclOrErr.takeError();

  return Importer.getToContext().getObjCInterfaceType(*ToDeclOrErr);
}

ExpectedType ASTNodeImporter::VisitObjCObjectType(const ObjCObjectType *T) {
  ExpectedType ToBaseTypeOrErr = import(T->getBaseType());
  if (!ToBaseTypeOrErr)
    return ToBaseTypeOrErr.takeError();

  SmallVector<QualType, 4> TypeArgs;
  for (auto TypeArg : T->getTypeArgsAsWritten()) {
    if (ExpectedType TyOrErr = import(TypeArg))
      TypeArgs.push_back(*TyOrErr);
    else
      return TyOrErr.takeError();
  }

  SmallVector<ObjCProtocolDecl *, 4> Protocols;
  for (auto *P : T->quals()) {
    if (Expected<ObjCProtocolDecl *> ProtocolOrErr = import(P))
      Protocols.push_back(*ProtocolOrErr);
    else
      return ProtocolOrErr.takeError();

  }

  return Importer.getToContext().getObjCObjectType(*ToBaseTypeOrErr, TypeArgs,
                                                   Protocols,
                                                   T->isKindOfTypeAsWritten());
}

ExpectedType
ASTNodeImporter::VisitObjCObjectPointerType(const ObjCObjectPointerType *T) {
  ExpectedType ToPointeeTypeOrErr = import(T->getPointeeType());
  if (!ToPointeeTypeOrErr)
    return ToPointeeTypeOrErr.takeError();

  return Importer.getToContext().getObjCObjectPointerType(*ToPointeeTypeOrErr);
}

//----------------------------------------------------------------------------
// Import Declarations
//----------------------------------------------------------------------------
Error ASTNodeImporter::ImportDeclParts(
    NamedDecl *D, DeclContext *&DC, DeclContext *&LexicalDC,
    DeclarationName &Name, NamedDecl *&ToD, SourceLocation &Loc) {
  // Check if RecordDecl is in FunctionDecl parameters to avoid infinite loop.
  // example: int struct_in_proto(struct data_t{int a;int b;} *d);
  DeclContext *OrigDC = D->getDeclContext();
  FunctionDecl *FunDecl;
  if (isa<RecordDecl>(D) && (FunDecl = dyn_cast<FunctionDecl>(OrigDC)) &&
      FunDecl->hasBody()) {
    auto getLeafPointeeType = [](const Type *T) {
      while (T->isPointerType() || T->isArrayType()) {
        T = T->getPointeeOrArrayElementType();
      }
      return T;
    };
    for (const ParmVarDecl *P : FunDecl->parameters()) {
      const Type *LeafT =
          getLeafPointeeType(P->getType().getCanonicalType().getTypePtr());
      auto *RT = dyn_cast<RecordType>(LeafT);
      if (RT && RT->getDecl() == D) {
        Importer.FromDiag(D->getLocation(), diag::err_unsupported_ast_node)
            << D->getDeclKindName();
        return make_error<ImportError>(ImportError::UnsupportedConstruct);
      }
    }
  }

  // Import the context of this declaration.
  if (Error Err = ImportDeclContext(D, DC, LexicalDC))
    return Err;

  // Import the name of this declaration.
  if (Error Err = importInto(Name, D->getDeclName()))
    return Err;

  // Import the location of this declaration.
  if (Error Err = importInto(Loc, D->getLocation()))
    return Err;

  ToD = cast_or_null<NamedDecl>(Importer.GetAlreadyImportedOrNull(D));
  if (ToD)
    if (Error Err = ASTNodeImporter(*this).ImportDefinitionIfNeeded(D, ToD))
      return Err;

  return Error::success();
}

Error ASTNodeImporter::ImportDefinitionIfNeeded(Decl *FromD, Decl *ToD) {
  if (!FromD)
    return Error::success();

  if (!ToD)
    if (Error Err = importInto(ToD, FromD))
      return Err;

  if (RecordDecl *FromRecord = dyn_cast<RecordDecl>(FromD)) {
    if (RecordDecl *ToRecord = cast<RecordDecl>(ToD)) {
      if (FromRecord->getDefinition() && FromRecord->isCompleteDefinition() &&
          !ToRecord->getDefinition()) {
        if (Error Err = ImportDefinition(FromRecord, ToRecord))
          return Err;
      }
    }
    return Error::success();
  }

  if (EnumDecl *FromEnum = dyn_cast<EnumDecl>(FromD)) {
    if (EnumDecl *ToEnum = cast<EnumDecl>(ToD)) {
      if (FromEnum->getDefinition() && !ToEnum->getDefinition()) {
        if (Error Err = ImportDefinition(FromEnum, ToEnum))
          return Err;
      }
    }
    return Error::success();
  }

  return Error::success();
}

Error
ASTNodeImporter::ImportDeclarationNameLoc(
    const DeclarationNameInfo &From, DeclarationNameInfo& To) {
  // NOTE: To.Name and To.Loc are already imported.
  // We only have to import To.LocInfo.
  switch (To.getName().getNameKind()) {
  case DeclarationName::Identifier:
  case DeclarationName::ObjCZeroArgSelector:
  case DeclarationName::ObjCOneArgSelector:
  case DeclarationName::ObjCMultiArgSelector:
  case DeclarationName::CXXUsingDirective:
  case DeclarationName::CXXDeductionGuideName:
    return Error::success();

  case DeclarationName::CXXOperatorName: {
    if (auto ToRangeOrErr = import(From.getCXXOperatorNameRange()))
      To.setCXXOperatorNameRange(*ToRangeOrErr);
    else
      return ToRangeOrErr.takeError();
    return Error::success();
  }
  case DeclarationName::CXXLiteralOperatorName: {
    if (ExpectedSLoc LocOrErr = import(From.getCXXLiteralOperatorNameLoc()))
      To.setCXXLiteralOperatorNameLoc(*LocOrErr);
    else
      return LocOrErr.takeError();
    return Error::success();
  }
  case DeclarationName::CXXConstructorName:
  case DeclarationName::CXXDestructorName:
  case DeclarationName::CXXConversionFunctionName: {
    if (auto ToTInfoOrErr = import(From.getNamedTypeInfo()))
      To.setNamedTypeInfo(*ToTInfoOrErr);
    else
      return ToTInfoOrErr.takeError();
    return Error::success();
  }
  }
  llvm_unreachable("Unknown name kind.");
}

Error
ASTNodeImporter::ImportDeclContext(DeclContext *FromDC, bool ForceImport) {
  if (Importer.isMinimalImport() && !ForceImport) {
    auto ToDCOrErr = Importer.ImportContext(FromDC);
    return ToDCOrErr.takeError();
  }
  llvm::SmallVector<Decl *, 8> ImportedDecls;
  for (auto *From : FromDC->decls()) {
    ExpectedDecl ImportedOrErr = import(From);
    if (!ImportedOrErr)
      // Ignore the error, continue with next Decl.
      // FIXME: Handle this case somehow better.
      consumeError(ImportedOrErr.takeError());
  }

  return Error::success();
}

Error ASTNodeImporter::ImportDeclContext(
    Decl *FromD, DeclContext *&ToDC, DeclContext *&ToLexicalDC) {
  auto ToDCOrErr = Importer.ImportContext(FromD->getDeclContext());
  if (!ToDCOrErr)
    return ToDCOrErr.takeError();
  ToDC = *ToDCOrErr;

  if (FromD->getDeclContext() != FromD->getLexicalDeclContext()) {
    auto ToLexicalDCOrErr = Importer.ImportContext(
        FromD->getLexicalDeclContext());
    if (!ToLexicalDCOrErr)
      return ToLexicalDCOrErr.takeError();
    ToLexicalDC = *ToLexicalDCOrErr;
  } else
    ToLexicalDC = ToDC;

  return Error::success();
}

Error ASTNodeImporter::ImportImplicitMethods(
    const CXXRecordDecl *From, CXXRecordDecl *To) {
  assert(From->isCompleteDefinition() && To->getDefinition() == To &&
      "Import implicit methods to or from non-definition");

  for (CXXMethodDecl *FromM : From->methods())
    if (FromM->isImplicit()) {
      Expected<CXXMethodDecl *> ToMOrErr = import(FromM);
      if (!ToMOrErr)
        return ToMOrErr.takeError();
    }

  return Error::success();
}

static Error setTypedefNameForAnonDecl(TagDecl *From, TagDecl *To,
                                       ASTImporter &Importer) {
  if (TypedefNameDecl *FromTypedef = From->getTypedefNameForAnonDecl()) {
    Decl *ToTypedef = Importer.Import(FromTypedef);
    if (!ToTypedef)
      return make_error<ImportError>();
    To->setTypedefNameForAnonDecl(cast<TypedefNameDecl>(ToTypedef));
    // FIXME: This should be the final code.
    //if (Expected<Decl *> ToTypedefOrErr = Importer.Import(FromTypedef))
    //  To->setTypedefNameForAnonDecl(cast<TypedefNameDecl>(*ToTypedefOrErr));
    //else
    //  return ToTypedefOrErr.takeError();
  }
  return Error::success();
}

Error ASTNodeImporter::ImportDefinition(
    RecordDecl *From, RecordDecl *To, ImportDefinitionKind Kind) {
  if (To->getDefinition() || To->isBeingDefined()) {
    if (Kind == IDK_Everything)
      return ImportDeclContext(From, /*ForceImport=*/true);

    return Error::success();
  }

  To->startDefinition();

  if (Error Err = setTypedefNameForAnonDecl(From, To, Importer))
    return Err;

  // Add base classes.
  auto *ToCXX = dyn_cast<CXXRecordDecl>(To);
  auto *FromCXX = dyn_cast<CXXRecordDecl>(From);
  if (ToCXX && FromCXX && ToCXX->dataPtr() && FromCXX->dataPtr()) {

    struct CXXRecordDecl::DefinitionData &ToData = ToCXX->data();
    struct CXXRecordDecl::DefinitionData &FromData = FromCXX->data();
    ToData.UserDeclaredConstructor = FromData.UserDeclaredConstructor;
    ToData.UserDeclaredSpecialMembers = FromData.UserDeclaredSpecialMembers;
    ToData.Aggregate = FromData.Aggregate;
    ToData.PlainOldData = FromData.PlainOldData;
    ToData.Empty = FromData.Empty;
    ToData.Polymorphic = FromData.Polymorphic;
    ToData.Abstract = FromData.Abstract;
    ToData.IsStandardLayout = FromData.IsStandardLayout;
    ToData.IsCXX11StandardLayout = FromData.IsCXX11StandardLayout;
    ToData.HasBasesWithFields = FromData.HasBasesWithFields;
    ToData.HasBasesWithNonStaticDataMembers =
        FromData.HasBasesWithNonStaticDataMembers;
    ToData.HasPrivateFields = FromData.HasPrivateFields;
    ToData.HasProtectedFields = FromData.HasProtectedFields;
    ToData.HasPublicFields = FromData.HasPublicFields;
    ToData.HasMutableFields = FromData.HasMutableFields;
    ToData.HasVariantMembers = FromData.HasVariantMembers;
    ToData.HasOnlyCMembers = FromData.HasOnlyCMembers;
    ToData.HasInClassInitializer = FromData.HasInClassInitializer;
    ToData.HasUninitializedReferenceMember
      = FromData.HasUninitializedReferenceMember;
    ToData.HasUninitializedFields = FromData.HasUninitializedFields;
    ToData.HasInheritedConstructor = FromData.HasInheritedConstructor;
    ToData.HasInheritedAssignment = FromData.HasInheritedAssignment;
    ToData.NeedOverloadResolutionForCopyConstructor
      = FromData.NeedOverloadResolutionForCopyConstructor;
    ToData.NeedOverloadResolutionForMoveConstructor
      = FromData.NeedOverloadResolutionForMoveConstructor;
    ToData.NeedOverloadResolutionForMoveAssignment
      = FromData.NeedOverloadResolutionForMoveAssignment;
    ToData.NeedOverloadResolutionForDestructor
      = FromData.NeedOverloadResolutionForDestructor;
    ToData.DefaultedCopyConstructorIsDeleted
      = FromData.DefaultedCopyConstructorIsDeleted;
    ToData.DefaultedMoveConstructorIsDeleted
      = FromData.DefaultedMoveConstructorIsDeleted;
    ToData.DefaultedMoveAssignmentIsDeleted
      = FromData.DefaultedMoveAssignmentIsDeleted;
    ToData.DefaultedDestructorIsDeleted = FromData.DefaultedDestructorIsDeleted;
    ToData.HasTrivialSpecialMembers = FromData.HasTrivialSpecialMembers;
    ToData.HasIrrelevantDestructor = FromData.HasIrrelevantDestructor;
    ToData.HasConstexprNonCopyMoveConstructor
      = FromData.HasConstexprNonCopyMoveConstructor;
    ToData.HasDefaultedDefaultConstructor
      = FromData.HasDefaultedDefaultConstructor;
    ToData.DefaultedDefaultConstructorIsConstexpr
      = FromData.DefaultedDefaultConstructorIsConstexpr;
    ToData.HasConstexprDefaultConstructor
      = FromData.HasConstexprDefaultConstructor;
    ToData.HasNonLiteralTypeFieldsOrBases
      = FromData.HasNonLiteralTypeFieldsOrBases;
    // ComputedVisibleConversions not imported.
    ToData.UserProvidedDefaultConstructor
      = FromData.UserProvidedDefaultConstructor;
    ToData.DeclaredSpecialMembers = FromData.DeclaredSpecialMembers;
    ToData.ImplicitCopyConstructorCanHaveConstParamForVBase
      = FromData.ImplicitCopyConstructorCanHaveConstParamForVBase;
    ToData.ImplicitCopyConstructorCanHaveConstParamForNonVBase
      = FromData.ImplicitCopyConstructorCanHaveConstParamForNonVBase;
    ToData.ImplicitCopyAssignmentHasConstParam
      = FromData.ImplicitCopyAssignmentHasConstParam;
    ToData.HasDeclaredCopyConstructorWithConstParam
      = FromData.HasDeclaredCopyConstructorWithConstParam;
    ToData.HasDeclaredCopyAssignmentWithConstParam
      = FromData.HasDeclaredCopyAssignmentWithConstParam;

    SmallVector<CXXBaseSpecifier *, 4> Bases;
    for (const auto &Base1 : FromCXX->bases()) {
      ExpectedType TyOrErr = import(Base1.getType());
      if (!TyOrErr)
        return TyOrErr.takeError();

      SourceLocation EllipsisLoc;
      if (Base1.isPackExpansion()) {
        if (ExpectedSLoc LocOrErr = import(Base1.getEllipsisLoc()))
          EllipsisLoc = *LocOrErr;
        else
          return LocOrErr.takeError();
      }

      // Ensure that we have a definition for the base.
      if (Error Err =
          ImportDefinitionIfNeeded(Base1.getType()->getAsCXXRecordDecl()))
        return Err;

      auto RangeOrErr = import(Base1.getSourceRange());
      if (!RangeOrErr)
        return RangeOrErr.takeError();

      auto TSIOrErr = import(Base1.getTypeSourceInfo());
      if (!TSIOrErr)
        return TSIOrErr.takeError();

      Bases.push_back(
          new (Importer.getToContext()) CXXBaseSpecifier(
              *RangeOrErr,
              Base1.isVirtual(),
              Base1.isBaseOfClass(),
              Base1.getAccessSpecifierAsWritten(),
              *TSIOrErr,
              EllipsisLoc));
    }
    if (!Bases.empty())
      ToCXX->setBases(Bases.data(), Bases.size());
  }

  if (shouldForceImportDeclContext(Kind))
    if (Error Err = ImportDeclContext(From, /*ForceImport=*/true))
      return Err;

  To->completeDefinition();
  return Error::success();
}

Error ASTNodeImporter::ImportInitializer(VarDecl *From, VarDecl *To) {
  if (To->getAnyInitializer())
    return Error::success();

  Expr *FromInit = From->getInit();
  if (!FromInit)
    return Error::success();

  ExpectedExpr ToInitOrErr = import(FromInit);
  if (!ToInitOrErr)
    return ToInitOrErr.takeError();

  To->setInit(*ToInitOrErr);
  if (From->isInitKnownICE()) {
    EvaluatedStmt *Eval = To->ensureEvaluatedStmt();
    Eval->CheckedICE = true;
    Eval->IsICE = From->isInitICE();
  }

  // FIXME: Other bits to merge?
  return Error::success();
}

Error ASTNodeImporter::ImportDefinition(
    EnumDecl *From, EnumDecl *To, ImportDefinitionKind Kind) {
  if (To->getDefinition() || To->isBeingDefined()) {
    if (Kind == IDK_Everything)
      return ImportDeclContext(From, /*ForceImport=*/true);
    return Error::success();
  }

  To->startDefinition();

  if (Error Err = setTypedefNameForAnonDecl(From, To, Importer))
    return Err;

  ExpectedType ToTypeOrErr =
      import(Importer.getFromContext().getTypeDeclType(From));
  if (!ToTypeOrErr)
    return ToTypeOrErr.takeError();

  ExpectedType ToPromotionTypeOrErr = import(From->getPromotionType());
  if (!ToPromotionTypeOrErr)
    return ToPromotionTypeOrErr.takeError();

  if (shouldForceImportDeclContext(Kind))
    if (Error Err = ImportDeclContext(From, /*ForceImport=*/true))
      return Err;

  // FIXME: we might need to merge the number of positive or negative bits
  // if the enumerator lists don't match.
  To->completeDefinition(*ToTypeOrErr, *ToPromotionTypeOrErr,
                         From->getNumPositiveBits(),
                         From->getNumNegativeBits());
  return Error::success();
}

// FIXME: Remove this, use `import` instead.
Expected<TemplateParameterList *> ASTNodeImporter::ImportTemplateParameterList(
    TemplateParameterList *Params) {
  SmallVector<NamedDecl *, 4> ToParams(Params->size());
  if (Error Err = ImportContainerChecked(*Params, ToParams))
    return std::move(Err);

  Expr *ToRequiresClause;
  if (Expr *const R = Params->getRequiresClause()) {
    if (Error Err = importInto(ToRequiresClause, R))
      return std::move(Err);
  } else {
    ToRequiresClause = nullptr;
  }

  auto ToTemplateLocOrErr = import(Params->getTemplateLoc());
  if (!ToTemplateLocOrErr)
    return ToTemplateLocOrErr.takeError();
  auto ToLAngleLocOrErr = import(Params->getLAngleLoc());
  if (!ToLAngleLocOrErr)
    return ToLAngleLocOrErr.takeError();
  auto ToRAngleLocOrErr = import(Params->getRAngleLoc());
  if (!ToRAngleLocOrErr)
    return ToRAngleLocOrErr.takeError();

  return TemplateParameterList::Create(
      Importer.getToContext(),
      *ToTemplateLocOrErr,
      *ToLAngleLocOrErr,
      ToParams,
      *ToRAngleLocOrErr,
      ToRequiresClause);
}

Error ASTNodeImporter::ImportTemplateArguments(
    const TemplateArgument *FromArgs, unsigned NumFromArgs,
    SmallVectorImpl<TemplateArgument> &ToArgs) {
  for (unsigned I = 0; I != NumFromArgs; ++I) {
    if (auto ToOrErr = import(FromArgs[I]))
      ToArgs.push_back(*ToOrErr);
    else
      return ToOrErr.takeError();
  }

  return Error::success();
}

// FIXME: Do not forget to remove this and use only 'import'.
Expected<TemplateArgument>
ASTNodeImporter::ImportTemplateArgument(const TemplateArgument &From) {
  return import(From);
}

template <typename InContainerTy>
Error ASTNodeImporter::ImportTemplateArgumentListInfo(
    const InContainerTy &Container, TemplateArgumentListInfo &ToTAInfo) {
  for (const auto &FromLoc : Container) {
    if (auto ToLocOrErr = import(FromLoc))
      ToTAInfo.addArgument(*ToLocOrErr);
    else
      return ToLocOrErr.takeError();
  }
  return Error::success();
}

static StructuralEquivalenceKind
getStructuralEquivalenceKind(const ASTImporter &Importer) {
  return Importer.isMinimalImport() ? StructuralEquivalenceKind::Minimal
                                    : StructuralEquivalenceKind::Default;
}

bool ASTNodeImporter::IsStructuralMatch(Decl *From, Decl *To, bool Complain) {
  StructuralEquivalenceContext Ctx(
      Importer.getFromContext(), Importer.getToContext(),
      Importer.getNonEquivalentDecls(), getStructuralEquivalenceKind(Importer),
      false, Complain);
  return Ctx.IsEquivalent(From, To);
}

bool ASTNodeImporter::IsStructuralMatch(RecordDecl *FromRecord,
                                        RecordDecl *ToRecord, bool Complain) {
  // Eliminate a potential failure point where we attempt to re-import
  // something we're trying to import while completing ToRecord.
  Decl *ToOrigin = Importer.GetOriginalDecl(ToRecord);
  if (ToOrigin) {
    auto *ToOriginRecord = dyn_cast<RecordDecl>(ToOrigin);
    if (ToOriginRecord)
      ToRecord = ToOriginRecord;
  }

  StructuralEquivalenceContext Ctx(Importer.getFromContext(),
                                   ToRecord->getASTContext(),
                                   Importer.getNonEquivalentDecls(),
                                   getStructuralEquivalenceKind(Importer),
                                   false, Complain);
  return Ctx.IsEquivalent(FromRecord, ToRecord);
}

bool ASTNodeImporter::IsStructuralMatch(VarDecl *FromVar, VarDecl *ToVar,
                                        bool Complain) {
  StructuralEquivalenceContext Ctx(
      Importer.getFromContext(), Importer.getToContext(),
      Importer.getNonEquivalentDecls(), getStructuralEquivalenceKind(Importer),
      false, Complain);
  return Ctx.IsEquivalent(FromVar, ToVar);
}

bool ASTNodeImporter::IsStructuralMatch(EnumDecl *FromEnum, EnumDecl *ToEnum) {
  StructuralEquivalenceContext Ctx(
      Importer.getFromContext(), Importer.getToContext(),
      Importer.getNonEquivalentDecls(), getStructuralEquivalenceKind(Importer));
  return Ctx.IsEquivalent(FromEnum, ToEnum);
}

bool ASTNodeImporter::IsStructuralMatch(FunctionTemplateDecl *From,
                                        FunctionTemplateDecl *To) {
  StructuralEquivalenceContext Ctx(
      Importer.getFromContext(), Importer.getToContext(),
      Importer.getNonEquivalentDecls(), getStructuralEquivalenceKind(Importer),
      false, false);
  return Ctx.IsEquivalent(From, To);
}

bool ASTNodeImporter::IsStructuralMatch(FunctionDecl *From, FunctionDecl *To) {
  StructuralEquivalenceContext Ctx(
      Importer.getFromContext(), Importer.getToContext(),
      Importer.getNonEquivalentDecls(), getStructuralEquivalenceKind(Importer),
      false, false);
  return Ctx.IsEquivalent(From, To);
}

bool ASTNodeImporter::IsStructuralMatch(EnumConstantDecl *FromEC,
                                        EnumConstantDecl *ToEC) {
  const llvm::APSInt &FromVal = FromEC->getInitVal();
  const llvm::APSInt &ToVal = ToEC->getInitVal();

  return FromVal.isSigned() == ToVal.isSigned() &&
         FromVal.getBitWidth() == ToVal.getBitWidth() &&
         FromVal == ToVal;
}

bool ASTNodeImporter::IsStructuralMatch(ClassTemplateDecl *From,
                                        ClassTemplateDecl *To) {
  StructuralEquivalenceContext Ctx(Importer.getFromContext(),
                                   Importer.getToContext(),
                                   Importer.getNonEquivalentDecls(),
                                   getStructuralEquivalenceKind(Importer));
  return Ctx.IsEquivalent(From, To);
}

bool ASTNodeImporter::IsStructuralMatch(VarTemplateDecl *From,
                                        VarTemplateDecl *To) {
  StructuralEquivalenceContext Ctx(Importer.getFromContext(),
                                   Importer.getToContext(),
                                   Importer.getNonEquivalentDecls(),
                                   getStructuralEquivalenceKind(Importer));
  return Ctx.IsEquivalent(From, To);
}

ExpectedDecl ASTNodeImporter::VisitDecl(Decl *D) {
  Importer.FromDiag(D->getLocation(), diag::err_unsupported_ast_node)
    << D->getDeclKindName();
  return make_error<ImportError>(ImportError::UnsupportedConstruct);
}

ExpectedDecl ASTNodeImporter::VisitImportDecl(ImportDecl *D) {
  Importer.FromDiag(D->getLocation(), diag::err_unsupported_ast_node)
      << D->getDeclKindName();
  return make_error<ImportError>(ImportError::UnsupportedConstruct);
}

ExpectedDecl ASTNodeImporter::VisitEmptyDecl(EmptyDecl *D) {
  // Import the context of this declaration.
  DeclContext *DC, *LexicalDC;
  if (Error Err = ImportDeclContext(D, DC, LexicalDC))
    return std::move(Err);

  // Import the location of this declaration.
  ExpectedSLoc LocOrErr = import(D->getLocation());
  if (!LocOrErr)
    return LocOrErr.takeError();

  EmptyDecl *ToD;
  if (GetImportedOrCreateDecl(ToD, D, Importer.getToContext(), DC, *LocOrErr))
    return ToD;

  ToD->setLexicalDeclContext(LexicalDC);
  LexicalDC->addDeclInternal(ToD);
  return ToD;
}

ExpectedDecl ASTNodeImporter::VisitTranslationUnitDecl(TranslationUnitDecl *D) {
  TranslationUnitDecl *ToD =
    Importer.getToContext().getTranslationUnitDecl();

  Importer.MapImported(D, ToD);

  return ToD;
}

ExpectedDecl ASTNodeImporter::VisitAccessSpecDecl(AccessSpecDecl *D) {
  ExpectedSLoc LocOrErr = import(D->getLocation());
  if (!LocOrErr)
    return LocOrErr.takeError();
  auto ColonLocOrErr = import(D->getColonLoc());
  if (!ColonLocOrErr)
    return ColonLocOrErr.takeError();

  // Import the context of this declaration.
  auto DCOrErr = Importer.ImportContext(D->getDeclContext());
  if (!DCOrErr)
    return DCOrErr.takeError();
  DeclContext *DC = *DCOrErr;

  AccessSpecDecl *ToD;
  if (GetImportedOrCreateDecl(ToD, D, Importer.getToContext(), D->getAccess(),
                              DC, *LocOrErr, *ColonLocOrErr))
    return ToD;

  // Lexical DeclContext and Semantic DeclContext
  // is always the same for the accessSpec.
  ToD->setLexicalDeclContext(DC);
  DC->addDeclInternal(ToD);

  return ToD;
}

ExpectedDecl ASTNodeImporter::VisitStaticAssertDecl(StaticAssertDecl *D) {
  auto DCOrErr = Importer.ImportContext(D->getDeclContext());
  if (!DCOrErr)
    return DCOrErr.takeError();
  DeclContext *DC = *DCOrErr;
  DeclContext *LexicalDC = DC;

  SourceLocation ToLocation, ToRParenLoc;
  Expr *ToAssertExpr;
  StringLiteral *ToMessage;
  if (auto Imp = importSeq(
      D->getLocation(), D->getAssertExpr(), D->getMessage(), D->getRParenLoc()))
    std::tie(ToLocation, ToAssertExpr, ToMessage, ToRParenLoc) = *Imp;
  else
    return Imp.takeError();

  StaticAssertDecl *ToD;
  if (GetImportedOrCreateDecl(
      ToD, D, Importer.getToContext(), DC, ToLocation, ToAssertExpr, ToMessage,
      ToRParenLoc, D->isFailed()))
    return ToD;

  ToD->setLexicalDeclContext(LexicalDC);
  LexicalDC->addDeclInternal(ToD);
  return ToD;
}

ExpectedDecl ASTNodeImporter::VisitNamespaceDecl(NamespaceDecl *D) {
  // Import the major distinguishing characteristics of this namespace.
  DeclContext *DC, *LexicalDC;
  DeclarationName Name;
  SourceLocation Loc;
  NamedDecl *ToD;
  if (Error Err = ImportDeclParts(D, DC, LexicalDC, Name, ToD, Loc))
    return std::move(Err);
  if (ToD)
    return ToD;

  NamespaceDecl *MergeWithNamespace = nullptr;
  if (!Name) {
    // This is an anonymous namespace. Adopt an existing anonymous
    // namespace if we can.
    // FIXME: Not testable.
    if (auto *TU = dyn_cast<TranslationUnitDecl>(DC))
      MergeWithNamespace = TU->getAnonymousNamespace();
    else
      MergeWithNamespace = cast<NamespaceDecl>(DC)->getAnonymousNamespace();
  } else {
    SmallVector<NamedDecl *, 4> ConflictingDecls;
    auto FoundDecls = Importer.findDeclsInToCtx(DC, Name);
    for (auto *FoundDecl : FoundDecls) {
      if (!FoundDecl->isInIdentifierNamespace(Decl::IDNS_Namespace))
        continue;

      if (auto *FoundNS = dyn_cast<NamespaceDecl>(FoundDecl)) {
        MergeWithNamespace = FoundNS;
        ConflictingDecls.clear();
        break;
      }

      ConflictingDecls.push_back(FoundDecl);
    }

    if (!ConflictingDecls.empty()) {
      Name = Importer.HandleNameConflict(Name, DC, Decl::IDNS_Namespace,
                                         ConflictingDecls.data(),
                                         ConflictingDecls.size());
      if (!Name)
        return make_error<ImportError>(ImportError::NameConflict);
    }
  }

  ExpectedSLoc BeginLocOrErr = import(D->getBeginLoc());
  if (!BeginLocOrErr)
    return BeginLocOrErr.takeError();

  // Create the "to" namespace, if needed.
  NamespaceDecl *ToNamespace = MergeWithNamespace;
  if (!ToNamespace) {
    if (GetImportedOrCreateDecl(
            ToNamespace, D, Importer.getToContext(), DC, D->isInline(),
            *BeginLocOrErr, Loc, Name.getAsIdentifierInfo(),
            /*PrevDecl=*/nullptr))
      return ToNamespace;
    ToNamespace->setLexicalDeclContext(LexicalDC);
    LexicalDC->addDeclInternal(ToNamespace);

    // If this is an anonymous namespace, register it as the anonymous
    // namespace within its context.
    if (!Name) {
      if (auto *TU = dyn_cast<TranslationUnitDecl>(DC))
        TU->setAnonymousNamespace(ToNamespace);
      else
        cast<NamespaceDecl>(DC)->setAnonymousNamespace(ToNamespace);
    }
  }
  Importer.MapImported(D, ToNamespace);

  if (Error Err = ImportDeclContext(D))
    return std::move(Err);

  return ToNamespace;
}

ExpectedDecl ASTNodeImporter::VisitNamespaceAliasDecl(NamespaceAliasDecl *D) {
  // Import the major distinguishing characteristics of this namespace.
  DeclContext *DC, *LexicalDC;
  DeclarationName Name;
  SourceLocation Loc;
  NamedDecl *LookupD;
  if (Error Err = ImportDeclParts(D, DC, LexicalDC, Name, LookupD, Loc))
    return std::move(Err);
  if (LookupD)
    return LookupD;

  // NOTE: No conflict resolution is done for namespace aliases now.

  SourceLocation ToNamespaceLoc, ToAliasLoc, ToTargetNameLoc;
  NestedNameSpecifierLoc ToQualifierLoc;
  NamespaceDecl *ToNamespace;
  if (auto Imp = importSeq(
      D->getNamespaceLoc(), D->getAliasLoc(), D->getQualifierLoc(),
      D->getTargetNameLoc(), D->getNamespace()))
    std::tie(
        ToNamespaceLoc, ToAliasLoc, ToQualifierLoc, ToTargetNameLoc,
        ToNamespace) = *Imp;
  else
    return Imp.takeError();
  IdentifierInfo *ToIdentifier = Importer.Import(D->getIdentifier());

  NamespaceAliasDecl *ToD;
  if (GetImportedOrCreateDecl(
      ToD, D, Importer.getToContext(), DC, ToNamespaceLoc, ToAliasLoc,
      ToIdentifier, ToQualifierLoc, ToTargetNameLoc, ToNamespace))
    return ToD;

  ToD->setLexicalDeclContext(LexicalDC);
  LexicalDC->addDeclInternal(ToD);

  return ToD;
}

ExpectedDecl
ASTNodeImporter::VisitTypedefNameDecl(TypedefNameDecl *D, bool IsAlias) {
  // Import the major distinguishing characteristics of this typedef.
  DeclContext *DC, *LexicalDC;
  DeclarationName Name;
  SourceLocation Loc;
  NamedDecl *ToD;
  if (Error Err = ImportDeclParts(D, DC, LexicalDC, Name, ToD, Loc))
    return std::move(Err);
  if (ToD)
    return ToD;

  // If this typedef is not in block scope, determine whether we've
  // seen a typedef with the same name (that we can merge with) or any
  // other entity by that name (which name lookup could conflict with).
  if (!DC->isFunctionOrMethod()) {
    SmallVector<NamedDecl *, 4> ConflictingDecls;
    unsigned IDNS = Decl::IDNS_Ordinary;
    auto FoundDecls = Importer.findDeclsInToCtx(DC, Name);
    for (auto *FoundDecl : FoundDecls) {
      if (!FoundDecl->isInIdentifierNamespace(IDNS))
        continue;
      if (auto *FoundTypedef = dyn_cast<TypedefNameDecl>(FoundDecl)) {
        QualType FromUT = D->getUnderlyingType();
        QualType FoundUT = FoundTypedef->getUnderlyingType();
        if (Importer.IsStructurallyEquivalent(FromUT, FoundUT)) {
          // If the "From" context has a complete underlying type but we
          // already have a complete underlying type then return with that.
          if (!FromUT->isIncompleteType() && !FoundUT->isIncompleteType())
            return Importer.MapImported(D, FoundTypedef);
        }
        // FIXME Handle redecl chain.
        break;
      }

      ConflictingDecls.push_back(FoundDecl);
    }

    if (!ConflictingDecls.empty()) {
      Name = Importer.HandleNameConflict(Name, DC, IDNS,
                                         ConflictingDecls.data(),
                                         ConflictingDecls.size());
      if (!Name)
        return make_error<ImportError>(ImportError::NameConflict);
    }
  }

  QualType ToUnderlyingType;
  TypeSourceInfo *ToTypeSourceInfo;
  SourceLocation ToBeginLoc;
  if (auto Imp = importSeq(
      D->getUnderlyingType(), D->getTypeSourceInfo(), D->getBeginLoc()))
    std::tie(ToUnderlyingType, ToTypeSourceInfo, ToBeginLoc) = *Imp;
  else
    return Imp.takeError();

  // Create the new typedef node.
  // FIXME: ToUnderlyingType is not used.
  TypedefNameDecl *ToTypedef;
  if (IsAlias) {
    if (GetImportedOrCreateDecl<TypeAliasDecl>(
        ToTypedef, D, Importer.getToContext(), DC, ToBeginLoc, Loc,
        Name.getAsIdentifierInfo(), ToTypeSourceInfo))
      return ToTypedef;
  } else if (GetImportedOrCreateDecl<TypedefDecl>(
      ToTypedef, D, Importer.getToContext(), DC, ToBeginLoc, Loc,
      Name.getAsIdentifierInfo(), ToTypeSourceInfo))
    return ToTypedef;

  ToTypedef->setAccess(D->getAccess());
  ToTypedef->setLexicalDeclContext(LexicalDC);

  // Templated declarations should not appear in DeclContext.
  TypeAliasDecl *FromAlias = IsAlias ? cast<TypeAliasDecl>(D) : nullptr;
  if (!FromAlias || !FromAlias->getDescribedAliasTemplate())
    LexicalDC->addDeclInternal(ToTypedef);

  return ToTypedef;
}

ExpectedDecl ASTNodeImporter::VisitTypedefDecl(TypedefDecl *D) {
  return VisitTypedefNameDecl(D, /*IsAlias=*/false);
}

ExpectedDecl ASTNodeImporter::VisitTypeAliasDecl(TypeAliasDecl *D) {
  return VisitTypedefNameDecl(D, /*IsAlias=*/true);
}

ExpectedDecl
ASTNodeImporter::VisitTypeAliasTemplateDecl(TypeAliasTemplateDecl *D) {
  // Import the major distinguishing characteristics of this typedef.
  DeclContext *DC, *LexicalDC;
  DeclarationName Name;
  SourceLocation Loc;
  NamedDecl *FoundD;
  if (Error Err = ImportDeclParts(D, DC, LexicalDC, Name, FoundD, Loc))
    return std::move(Err);
  if (FoundD)
    return FoundD;

  // If this typedef is not in block scope, determine whether we've
  // seen a typedef with the same name (that we can merge with) or any
  // other entity by that name (which name lookup could conflict with).
  if (!DC->isFunctionOrMethod()) {
    SmallVector<NamedDecl *, 4> ConflictingDecls;
    unsigned IDNS = Decl::IDNS_Ordinary;
    auto FoundDecls = Importer.findDeclsInToCtx(DC, Name);
    for (auto *FoundDecl : FoundDecls) {
      if (!FoundDecl->isInIdentifierNamespace(IDNS))
        continue;
      if (auto *FoundAlias = dyn_cast<TypeAliasTemplateDecl>(FoundDecl))
        return Importer.MapImported(D, FoundAlias);
      ConflictingDecls.push_back(FoundDecl);
    }

    if (!ConflictingDecls.empty()) {
      Name = Importer.HandleNameConflict(Name, DC, IDNS,
                                         ConflictingDecls.data(),
                                         ConflictingDecls.size());
      if (!Name)
        return make_error<ImportError>(ImportError::NameConflict);
    }
  }

  TemplateParameterList *ToTemplateParameters;
  TypeAliasDecl *ToTemplatedDecl;
  if (auto Imp = importSeq(D->getTemplateParameters(), D->getTemplatedDecl()))
    std::tie(ToTemplateParameters, ToTemplatedDecl) = *Imp;
  else
    return Imp.takeError();

  TypeAliasTemplateDecl *ToAlias;
  if (GetImportedOrCreateDecl(ToAlias, D, Importer.getToContext(), DC, Loc,
                              Name, ToTemplateParameters, ToTemplatedDecl))
    return ToAlias;

  ToTemplatedDecl->setDescribedAliasTemplate(ToAlias);

  ToAlias->setAccess(D->getAccess());
  ToAlias->setLexicalDeclContext(LexicalDC);
  LexicalDC->addDeclInternal(ToAlias);
  return ToAlias;
}

ExpectedDecl ASTNodeImporter::VisitLabelDecl(LabelDecl *D) {
  // Import the major distinguishing characteristics of this label.
  DeclContext *DC, *LexicalDC;
  DeclarationName Name;
  SourceLocation Loc;
  NamedDecl *ToD;
  if (Error Err = ImportDeclParts(D, DC, LexicalDC, Name, ToD, Loc))
    return std::move(Err);
  if (ToD)
    return ToD;

  assert(LexicalDC->isFunctionOrMethod());

  LabelDecl *ToLabel;
  if (D->isGnuLocal()) {
    ExpectedSLoc BeginLocOrErr = import(D->getBeginLoc());
    if (!BeginLocOrErr)
      return BeginLocOrErr.takeError();
    if (GetImportedOrCreateDecl(ToLabel, D, Importer.getToContext(), DC, Loc,
                                Name.getAsIdentifierInfo(), *BeginLocOrErr))
      return ToLabel;

  } else {
    if (GetImportedOrCreateDecl(ToLabel, D, Importer.getToContext(), DC, Loc,
                                Name.getAsIdentifierInfo()))
      return ToLabel;

  }

  Expected<LabelStmt *> ToStmtOrErr = import(D->getStmt());
  if (!ToStmtOrErr)
    return ToStmtOrErr.takeError();

  ToLabel->setStmt(*ToStmtOrErr);
  ToLabel->setLexicalDeclContext(LexicalDC);
  LexicalDC->addDeclInternal(ToLabel);
  return ToLabel;
}

ExpectedDecl ASTNodeImporter::VisitEnumDecl(EnumDecl *D) {
  // Import the major distinguishing characteristics of this enum.
  DeclContext *DC, *LexicalDC;
  DeclarationName Name;
  SourceLocation Loc;
  NamedDecl *ToD;
  if (Error Err = ImportDeclParts(D, DC, LexicalDC, Name, ToD, Loc))
    return std::move(Err);
  if (ToD)
    return ToD;

  // Figure out what enum name we're looking for.
  unsigned IDNS = Decl::IDNS_Tag;
  DeclarationName SearchName = Name;
  if (!SearchName && D->getTypedefNameForAnonDecl()) {
    if (Error Err = importInto(
        SearchName, D->getTypedefNameForAnonDecl()->getDeclName()))
      return std::move(Err);
    IDNS = Decl::IDNS_Ordinary;
  } else if (Importer.getToContext().getLangOpts().CPlusPlus)
    IDNS |= Decl::IDNS_Ordinary;

  // We may already have an enum of the same name; try to find and match it.
  if (!DC->isFunctionOrMethod() && SearchName) {
    SmallVector<NamedDecl *, 4> ConflictingDecls;
    auto FoundDecls =
        Importer.findDeclsInToCtx(DC, SearchName);
    for (auto *FoundDecl : FoundDecls) {
      if (!FoundDecl->isInIdentifierNamespace(IDNS))
        continue;

      if (auto *Typedef = dyn_cast<TypedefNameDecl>(FoundDecl)) {
        if (const auto *Tag = Typedef->getUnderlyingType()->getAs<TagType>())
          FoundDecl = Tag->getDecl();
      }

      if (auto *FoundEnum = dyn_cast<EnumDecl>(FoundDecl)) {
        if (IsStructuralMatch(D, FoundEnum))
          return Importer.MapImported(D, FoundEnum);
      }

      ConflictingDecls.push_back(FoundDecl);
    }

    if (!ConflictingDecls.empty()) {
      Name = Importer.HandleNameConflict(Name, DC, IDNS,
                                         ConflictingDecls.data(),
                                         ConflictingDecls.size());
      if (!Name)
        return make_error<ImportError>(ImportError::NameConflict);
    }
  }

  SourceLocation ToBeginLoc;
  NestedNameSpecifierLoc ToQualifierLoc;
  QualType ToIntegerType;
  if (auto Imp = importSeq(
      D->getBeginLoc(), D->getQualifierLoc(), D->getIntegerType()))
    std::tie(ToBeginLoc, ToQualifierLoc, ToIntegerType) = *Imp;
  else
    return Imp.takeError();

  // Create the enum declaration.
  EnumDecl *D2;
  if (GetImportedOrCreateDecl(
          D2, D, Importer.getToContext(), DC, ToBeginLoc,
          Loc, Name.getAsIdentifierInfo(), nullptr, D->isScoped(),
          D->isScopedUsingClassTag(), D->isFixed()))
    return D2;

  D2->setQualifierInfo(ToQualifierLoc);
  D2->setIntegerType(ToIntegerType);
  D2->setAccess(D->getAccess());
  D2->setLexicalDeclContext(LexicalDC);
  LexicalDC->addDeclInternal(D2);

  // Import the definition
  if (D->isCompleteDefinition())
    if (Error Err = ImportDefinition(D, D2))
      return std::move(Err);

  return D2;
}

ExpectedDecl ASTNodeImporter::VisitRecordDecl(RecordDecl *D) {
  bool IsFriendTemplate = false;
  if (auto *DCXX = dyn_cast<CXXRecordDecl>(D)) {
    IsFriendTemplate =
        DCXX->getDescribedClassTemplate() &&
        DCXX->getDescribedClassTemplate()->getFriendObjectKind() !=
            Decl::FOK_None;
  }

  // If this record has a definition in the translation unit we're coming from,
  // but this particular declaration is not that definition, import the
  // definition and map to that.
  TagDecl *Definition = D->getDefinition();
  if (Definition && Definition != D &&
      // Friend template declaration must be imported on its own.
      !IsFriendTemplate &&
      // In contrast to a normal CXXRecordDecl, the implicit
      // CXXRecordDecl of ClassTemplateSpecializationDecl is its redeclaration.
      // The definition of the implicit CXXRecordDecl in this case is the
      // ClassTemplateSpecializationDecl itself. Thus, we start with an extra
      // condition in order to be able to import the implict Decl.
      !D->isImplicit()) {
    ExpectedDecl ImportedDefOrErr = import(Definition);
    if (!ImportedDefOrErr)
      return ImportedDefOrErr.takeError();

    return Importer.MapImported(D, *ImportedDefOrErr);
  }

  // Import the major distinguishing characteristics of this record.
  DeclContext *DC, *LexicalDC;
  DeclarationName Name;
  SourceLocation Loc;
  NamedDecl *ToD;
  if (Error Err = ImportDeclParts(D, DC, LexicalDC, Name, ToD, Loc))
    return std::move(Err);
  if (ToD)
    return ToD;

  // Figure out what structure name we're looking for.
  unsigned IDNS = Decl::IDNS_Tag;
  DeclarationName SearchName = Name;
  if (!SearchName && D->getTypedefNameForAnonDecl()) {
    if (Error Err = importInto(
        SearchName, D->getTypedefNameForAnonDecl()->getDeclName()))
      return std::move(Err);
    IDNS = Decl::IDNS_Ordinary;
  } else if (Importer.getToContext().getLangOpts().CPlusPlus)
    IDNS |= Decl::IDNS_Ordinary | Decl::IDNS_TagFriend;

  // We may already have a record of the same name; try to find and match it.
  RecordDecl *PrevDecl = nullptr;
  if (!DC->isFunctionOrMethod()) {
    SmallVector<NamedDecl *, 4> ConflictingDecls;
    auto FoundDecls =
        Importer.findDeclsInToCtx(DC, SearchName);
    if (!FoundDecls.empty()) {
      // We're going to have to compare D against potentially conflicting Decls, so complete it.
      if (D->hasExternalLexicalStorage() && !D->isCompleteDefinition())
        D->getASTContext().getExternalSource()->CompleteType(D);
    }

    for (auto *FoundDecl : FoundDecls) {
      if (!FoundDecl->isInIdentifierNamespace(IDNS))
        continue;

      Decl *Found = FoundDecl;
      if (auto *Typedef = dyn_cast<TypedefNameDecl>(Found)) {
        if (const auto *Tag = Typedef->getUnderlyingType()->getAs<TagType>())
          Found = Tag->getDecl();
      }

      if (auto *FoundRecord = dyn_cast<RecordDecl>(Found)) {
        // Do not emit false positive diagnostic in case of unnamed
        // struct/union and in case of anonymous structs.  Would be false
        // because there may be several anonymous/unnamed structs in a class.
        // E.g. these are both valid:
        //  struct A { // unnamed structs
        //    struct { struct A *next; } entry0;
        //    struct { struct A *next; } entry1;
        //  };
        //  struct X { struct { int a; }; struct { int b; }; }; // anon structs
        if (!SearchName)
          if (!IsStructuralMatch(D, FoundRecord, false))
            continue;

        if (IsStructuralMatch(D, FoundRecord)) {
          RecordDecl *FoundDef = FoundRecord->getDefinition();
          if (D->isThisDeclarationADefinition() && FoundDef) {
            // FIXME: Structural equivalence check should check for same
            // user-defined methods.
            Importer.MapImported(D, FoundDef);
            if (const auto *DCXX = dyn_cast<CXXRecordDecl>(D)) {
              auto *FoundCXX = dyn_cast<CXXRecordDecl>(FoundDef);
              assert(FoundCXX && "Record type mismatch");

              if (!Importer.isMinimalImport())
                // FoundDef may not have every implicit method that D has
                // because implicit methods are created only if they are used.
                if (Error Err = ImportImplicitMethods(DCXX, FoundCXX))
                  return std::move(Err);
            }
          }
          PrevDecl = FoundRecord->getMostRecentDecl();
          break;
        }
      }

      ConflictingDecls.push_back(FoundDecl);
    } // for

    if (!ConflictingDecls.empty() && SearchName) {
      Name = Importer.HandleNameConflict(Name, DC, IDNS,
                                         ConflictingDecls.data(),
                                         ConflictingDecls.size());
      if (!Name)
        return make_error<ImportError>(ImportError::NameConflict);
    }
  }

  ExpectedSLoc BeginLocOrErr = import(D->getBeginLoc());
  if (!BeginLocOrErr)
    return BeginLocOrErr.takeError();

  // Create the record declaration.
  RecordDecl *D2 = nullptr;
  CXXRecordDecl *D2CXX = nullptr;
  if (auto *DCXX = dyn_cast<CXXRecordDecl>(D)) {
    if (DCXX->isLambda()) {
      auto TInfoOrErr = import(DCXX->getLambdaTypeInfo());
      if (!TInfoOrErr)
        return TInfoOrErr.takeError();
      if (GetImportedOrCreateSpecialDecl(
              D2CXX, CXXRecordDecl::CreateLambda, D, Importer.getToContext(),
              DC, *TInfoOrErr, Loc, DCXX->isDependentLambda(),
              DCXX->isGenericLambda(), DCXX->getLambdaCaptureDefault()))
        return D2CXX;
      ExpectedDecl CDeclOrErr = import(DCXX->getLambdaContextDecl());
      if (!CDeclOrErr)
        return CDeclOrErr.takeError();
      D2CXX->setLambdaMangling(DCXX->getLambdaManglingNumber(), *CDeclOrErr);
    } else if (DCXX->isInjectedClassName()) {
      // We have to be careful to do a similar dance to the one in
      // Sema::ActOnStartCXXMemberDeclarations
      const bool DelayTypeCreation = true;
      if (GetImportedOrCreateDecl(
              D2CXX, D, Importer.getToContext(), D->getTagKind(), DC,
              *BeginLocOrErr, Loc, Name.getAsIdentifierInfo(),
              cast_or_null<CXXRecordDecl>(PrevDecl), DelayTypeCreation))
        return D2CXX;
      Importer.getToContext().getTypeDeclType(
          D2CXX, dyn_cast<CXXRecordDecl>(DC));
    } else {
      if (GetImportedOrCreateDecl(D2CXX, D, Importer.getToContext(),
                                  D->getTagKind(), DC, *BeginLocOrErr, Loc,
                                  Name.getAsIdentifierInfo(),
                                  cast_or_null<CXXRecordDecl>(PrevDecl)))
        return D2CXX;
    }

    D2 = D2CXX;
    D2->setAccess(D->getAccess());
    D2->setLexicalDeclContext(LexicalDC);
    if (!DCXX->getDescribedClassTemplate() || DCXX->isImplicit())
      LexicalDC->addDeclInternal(D2);

    if (LexicalDC != DC && D->isInIdentifierNamespace(Decl::IDNS_TagFriend))
      DC->makeDeclVisibleInContext(D2);

    if (ClassTemplateDecl *FromDescribed =
        DCXX->getDescribedClassTemplate()) {
      ClassTemplateDecl *ToDescribed;
      if (Error Err = importInto(ToDescribed, FromDescribed))
        return std::move(Err);
      D2CXX->setDescribedClassTemplate(ToDescribed);
      if (!DCXX->isInjectedClassName() && !IsFriendTemplate) {
        // In a record describing a template the type should be an
        // InjectedClassNameType (see Sema::CheckClassTemplate). Update the
        // previously set type to the correct value here (ToDescribed is not
        // available at record create).
        // FIXME: The previous type is cleared but not removed from
        // ASTContext's internal storage.
        CXXRecordDecl *Injected = nullptr;
        for (NamedDecl *Found : D2CXX->noload_lookup(Name)) {
          auto *Record = dyn_cast<CXXRecordDecl>(Found);
          if (Record && Record->isInjectedClassName()) {
            Injected = Record;
            break;
          }
        }
        // Create an injected type for the whole redecl chain.
        SmallVector<Decl *, 2> Redecls =
            getCanonicalForwardRedeclChain(D2CXX);
        for (auto *R : Redecls) {
          auto *RI = cast<CXXRecordDecl>(R);
          RI->setTypeForDecl(nullptr);
          // Below we create a new injected type and assign that to the
          // canonical decl, subsequent declarations in the chain will reuse
          // that type.
          Importer.getToContext().getInjectedClassNameType(
              RI, ToDescribed->getInjectedClassNameSpecialization());
        }
        // Set the new type for the previous injected decl too.
        if (Injected) {
          Injected->setTypeForDecl(nullptr);
          Importer.getToContext().getTypeDeclType(Injected, D2CXX);
        }
      }
    } else if (MemberSpecializationInfo *MemberInfo =
                   DCXX->getMemberSpecializationInfo()) {
        TemplateSpecializationKind SK =
            MemberInfo->getTemplateSpecializationKind();
        CXXRecordDecl *FromInst = DCXX->getInstantiatedFromMemberClass();

        if (Expected<CXXRecordDecl *> ToInstOrErr = import(FromInst))
          D2CXX->setInstantiationOfMemberClass(*ToInstOrErr, SK);
        else
          return ToInstOrErr.takeError();

        if (ExpectedSLoc POIOrErr =
            import(MemberInfo->getPointOfInstantiation()))
          D2CXX->getMemberSpecializationInfo()->setPointOfInstantiation(
            *POIOrErr);
        else
          return POIOrErr.takeError();
    }

  } else {
    if (GetImportedOrCreateDecl(D2, D, Importer.getToContext(),
                                D->getTagKind(), DC, *BeginLocOrErr, Loc,
                                Name.getAsIdentifierInfo(), PrevDecl))
      return D2;
    D2->setLexicalDeclContext(LexicalDC);
    LexicalDC->addDeclInternal(D2);
  }

  if (auto QualifierLocOrErr = import(D->getQualifierLoc()))
    D2->setQualifierInfo(*QualifierLocOrErr);
  else
    return QualifierLocOrErr.takeError();

  if (D->isAnonymousStructOrUnion())
    D2->setAnonymousStructOrUnion(true);

  if (D->isCompleteDefinition())
    if (Error Err = ImportDefinition(D, D2, IDK_Default))
      return std::move(Err);

  return D2;
}

ExpectedDecl ASTNodeImporter::VisitEnumConstantDecl(EnumConstantDecl *D) {
  // Import the major distinguishing characteristics of this enumerator.
  DeclContext *DC, *LexicalDC;
  DeclarationName Name;
  SourceLocation Loc;
  NamedDecl *ToD;
  if (Error Err = ImportDeclParts(D, DC, LexicalDC, Name, ToD, Loc))
    return std::move(Err);
  if (ToD)
    return ToD;

  // Determine whether there are any other declarations with the same name and
  // in the same context.
  if (!LexicalDC->isFunctionOrMethod()) {
    SmallVector<NamedDecl *, 4> ConflictingDecls;
    unsigned IDNS = Decl::IDNS_Ordinary;
    auto FoundDecls = Importer.findDeclsInToCtx(DC, Name);
    for (auto *FoundDecl : FoundDecls) {
      if (!FoundDecl->isInIdentifierNamespace(IDNS))
        continue;

      if (auto *FoundEnumConstant = dyn_cast<EnumConstantDecl>(FoundDecl)) {
        if (IsStructuralMatch(D, FoundEnumConstant))
          return Importer.MapImported(D, FoundEnumConstant);
      }

      ConflictingDecls.push_back(FoundDecl);
    }

    if (!ConflictingDecls.empty()) {
      Name = Importer.HandleNameConflict(Name, DC, IDNS,
                                         ConflictingDecls.data(),
                                         ConflictingDecls.size());
      if (!Name)
        return make_error<ImportError>(ImportError::NameConflict);
    }
  }

  ExpectedType TypeOrErr = import(D->getType());
  if (!TypeOrErr)
    return TypeOrErr.takeError();

  ExpectedExpr InitOrErr = import(D->getInitExpr());
  if (!InitOrErr)
    return InitOrErr.takeError();

  EnumConstantDecl *ToEnumerator;
  if (GetImportedOrCreateDecl(
          ToEnumerator, D, Importer.getToContext(), cast<EnumDecl>(DC), Loc,
          Name.getAsIdentifierInfo(), *TypeOrErr, *InitOrErr, D->getInitVal()))
    return ToEnumerator;

  ToEnumerator->setAccess(D->getAccess());
  ToEnumerator->setLexicalDeclContext(LexicalDC);
  LexicalDC->addDeclInternal(ToEnumerator);
  return ToEnumerator;
}

Error ASTNodeImporter::ImportTemplateInformation(
    FunctionDecl *FromFD, FunctionDecl *ToFD) {
  switch (FromFD->getTemplatedKind()) {
  case FunctionDecl::TK_NonTemplate:
  case FunctionDecl::TK_FunctionTemplate:
    return Error::success();

  case FunctionDecl::TK_MemberSpecialization: {
    TemplateSpecializationKind TSK = FromFD->getTemplateSpecializationKind();

    if (Expected<FunctionDecl *> InstFDOrErr =
        import(FromFD->getInstantiatedFromMemberFunction()))
      ToFD->setInstantiationOfMemberFunction(*InstFDOrErr, TSK);
    else
      return InstFDOrErr.takeError();

    if (ExpectedSLoc POIOrErr = import(
        FromFD->getMemberSpecializationInfo()->getPointOfInstantiation()))
      ToFD->getMemberSpecializationInfo()->setPointOfInstantiation(*POIOrErr);
    else
      return POIOrErr.takeError();

    return Error::success();
  }

  case FunctionDecl::TK_FunctionTemplateSpecialization: {
    auto FunctionAndArgsOrErr =
        ImportFunctionTemplateWithTemplateArgsFromSpecialization(FromFD);
    if (!FunctionAndArgsOrErr)
      return FunctionAndArgsOrErr.takeError();

    TemplateArgumentList *ToTAList = TemplateArgumentList::CreateCopy(
          Importer.getToContext(), std::get<1>(*FunctionAndArgsOrErr));

    auto *FTSInfo = FromFD->getTemplateSpecializationInfo();
    TemplateArgumentListInfo ToTAInfo;
    const auto *FromTAArgsAsWritten = FTSInfo->TemplateArgumentsAsWritten;
    if (FromTAArgsAsWritten)
      if (Error Err = ImportTemplateArgumentListInfo(
          *FromTAArgsAsWritten, ToTAInfo))
        return Err;

    ExpectedSLoc POIOrErr = import(FTSInfo->getPointOfInstantiation());
    if (!POIOrErr)
      return POIOrErr.takeError();

    TemplateSpecializationKind TSK = FTSInfo->getTemplateSpecializationKind();
    ToFD->setFunctionTemplateSpecialization(
        std::get<0>(*FunctionAndArgsOrErr), ToTAList, /* InsertPos= */ nullptr,
        TSK, FromTAArgsAsWritten ? &ToTAInfo : nullptr, *POIOrErr);
    return Error::success();
  }

  case FunctionDecl::TK_DependentFunctionTemplateSpecialization: {
    auto *FromInfo = FromFD->getDependentSpecializationInfo();
    UnresolvedSet<8> TemplDecls;
    unsigned NumTemplates = FromInfo->getNumTemplates();
    for (unsigned I = 0; I < NumTemplates; I++) {
      if (Expected<FunctionTemplateDecl *> ToFTDOrErr =
          import(FromInfo->getTemplate(I)))
        TemplDecls.addDecl(*ToFTDOrErr);
      else
        return ToFTDOrErr.takeError();
    }

    // Import TemplateArgumentListInfo.
    TemplateArgumentListInfo ToTAInfo;
    if (Error Err = ImportTemplateArgumentListInfo(
        FromInfo->getLAngleLoc(), FromInfo->getRAngleLoc(),
        llvm::makeArrayRef(
            FromInfo->getTemplateArgs(), FromInfo->getNumTemplateArgs()),
        ToTAInfo))
      return Err;

    ToFD->setDependentTemplateSpecialization(Importer.getToContext(),
                                             TemplDecls, ToTAInfo);
    return Error::success();
  }
  }
  llvm_unreachable("All cases should be covered!");
}

Expected<FunctionDecl *>
ASTNodeImporter::FindFunctionTemplateSpecialization(FunctionDecl *FromFD) {
  auto FunctionAndArgsOrErr =
      ImportFunctionTemplateWithTemplateArgsFromSpecialization(FromFD);
  if (!FunctionAndArgsOrErr)
    return FunctionAndArgsOrErr.takeError();

  FunctionTemplateDecl *Template;
  TemplateArgsTy ToTemplArgs;
  std::tie(Template, ToTemplArgs) = *FunctionAndArgsOrErr;
  void *InsertPos = nullptr;
  auto *FoundSpec = Template->findSpecialization(ToTemplArgs, InsertPos);
  return FoundSpec;
}

ExpectedDecl ASTNodeImporter::VisitFunctionDecl(FunctionDecl *D) {

  SmallVector<Decl *, 2> Redecls = getCanonicalForwardRedeclChain(D);
  auto RedeclIt = Redecls.begin();
  // Import the first part of the decl chain. I.e. import all previous
  // declarations starting from the canonical decl.
  for (; RedeclIt != Redecls.end() && *RedeclIt != D; ++RedeclIt) {
    ExpectedDecl ToRedeclOrErr = import(*RedeclIt);
    if (!ToRedeclOrErr)
      return ToRedeclOrErr.takeError();
  }
  assert(*RedeclIt == D);

  // Import the major distinguishing characteristics of this function.
  DeclContext *DC, *LexicalDC;
  DeclarationName Name;
  SourceLocation Loc;
  NamedDecl *ToD;
  if (Error Err = ImportDeclParts(D, DC, LexicalDC, Name, ToD, Loc))
    return std::move(Err);
  if (ToD)
    return ToD;

  const FunctionDecl *FoundByLookup = nullptr;
  FunctionTemplateDecl *FromFT = D->getDescribedFunctionTemplate();

  // If this is a function template specialization, then try to find the same
  // existing specialization in the "to" context. The lookup below will not
  // find any specialization, but would find the primary template; thus, we
  // have to skip normal lookup in case of specializations.
  // FIXME handle member function templates (TK_MemberSpecialization) similarly?
  if (D->getTemplatedKind() ==
      FunctionDecl::TK_FunctionTemplateSpecialization) {
    auto FoundFunctionOrErr = FindFunctionTemplateSpecialization(D);
    if (!FoundFunctionOrErr)
      return FoundFunctionOrErr.takeError();
    if (FunctionDecl *FoundFunction = *FoundFunctionOrErr) {
      if (D->doesThisDeclarationHaveABody() && FoundFunction->hasBody())
        return Importer.MapImported(D, FoundFunction);
      FoundByLookup = FoundFunction;
    }
  }
  // Try to find a function in our own ("to") context with the same name, same
  // type, and in the same context as the function we're importing.
  else if (!LexicalDC->isFunctionOrMethod()) {
    SmallVector<NamedDecl *, 4> ConflictingDecls;
    unsigned IDNS = Decl::IDNS_Ordinary | Decl::IDNS_OrdinaryFriend;
    auto FoundDecls = Importer.findDeclsInToCtx(DC, Name);
    for (auto *FoundDecl : FoundDecls) {
      if (!FoundDecl->isInIdentifierNamespace(IDNS))
        continue;

      if (auto *FoundFunction = dyn_cast<FunctionDecl>(FoundDecl)) {
        if (FoundFunction->hasExternalFormalLinkage() &&
            D->hasExternalFormalLinkage()) {
          if (IsStructuralMatch(D, FoundFunction)) {
            const FunctionDecl *Definition = nullptr;
            if (D->doesThisDeclarationHaveABody() &&
                FoundFunction->hasBody(Definition)) {
              return Importer.MapImported(
                  D, const_cast<FunctionDecl *>(Definition));
            }
            FoundByLookup = FoundFunction;
            break;
          }

          // FIXME: Check for overloading more carefully, e.g., by boosting
          // Sema::IsOverload out to the AST library.

          // Function overloading is okay in C++.
          if (Importer.getToContext().getLangOpts().CPlusPlus)
            continue;

          // Complain about inconsistent function types.
          Importer.ToDiag(Loc, diag::err_odr_function_type_inconsistent)
            << Name << D->getType() << FoundFunction->getType();
          Importer.ToDiag(FoundFunction->getLocation(),
                          diag::note_odr_value_here)
            << FoundFunction->getType();
        }
      }

      ConflictingDecls.push_back(FoundDecl);
    }

    if (!ConflictingDecls.empty()) {
      Name = Importer.HandleNameConflict(Name, DC, IDNS,
                                         ConflictingDecls.data(),
                                         ConflictingDecls.size());
      if (!Name)
        return make_error<ImportError>(ImportError::NameConflict);
    }
  }

  DeclarationNameInfo NameInfo(Name, Loc);
  // Import additional name location/type info.
  if (Error Err = ImportDeclarationNameLoc(D->getNameInfo(), NameInfo))
    return std::move(Err);

  QualType FromTy = D->getType();
  bool usedDifferentExceptionSpec = false;

  if (const auto *FromFPT = D->getType()->getAs<FunctionProtoType>()) {
    FunctionProtoType::ExtProtoInfo FromEPI = FromFPT->getExtProtoInfo();
    // FunctionProtoType::ExtProtoInfo's ExceptionSpecDecl can point to the
    // FunctionDecl that we are importing the FunctionProtoType for.
    // To avoid an infinite recursion when importing, create the FunctionDecl
    // with a simplified function type and update it afterwards.
    if (FromEPI.ExceptionSpec.SourceDecl ||
        FromEPI.ExceptionSpec.SourceTemplate ||
        FromEPI.ExceptionSpec.NoexceptExpr) {
      FunctionProtoType::ExtProtoInfo DefaultEPI;
      FromTy = Importer.getFromContext().getFunctionType(
          FromFPT->getReturnType(), FromFPT->getParamTypes(), DefaultEPI);
      usedDifferentExceptionSpec = true;
    }
  }

  QualType T;
  TypeSourceInfo *TInfo;
  SourceLocation ToInnerLocStart, ToEndLoc;
  NestedNameSpecifierLoc ToQualifierLoc;
  if (auto Imp = importSeq(
      FromTy, D->getTypeSourceInfo(), D->getInnerLocStart(),
      D->getQualifierLoc(), D->getEndLoc()))
    std::tie(T, TInfo, ToInnerLocStart, ToQualifierLoc, ToEndLoc) = *Imp;
  else
    return Imp.takeError();

  // Import the function parameters.
  SmallVector<ParmVarDecl *, 8> Parameters;
  for (auto P : D->parameters()) {
    if (Expected<ParmVarDecl *> ToPOrErr = import(P))
      Parameters.push_back(*ToPOrErr);
    else
      return ToPOrErr.takeError();
  }

  // Create the imported function.
  FunctionDecl *ToFunction = nullptr;
  if (auto *FromConstructor = dyn_cast<CXXConstructorDecl>(D)) {
    if (GetImportedOrCreateDecl<CXXConstructorDecl>(
        ToFunction, D, Importer.getToContext(), cast<CXXRecordDecl>(DC),
        ToInnerLocStart, NameInfo, T, TInfo,
        FromConstructor->isExplicit(),
        D->isInlineSpecified(), D->isImplicit(), D->isConstexpr()))
      return ToFunction;
  } else if (isa<CXXDestructorDecl>(D)) {
    if (GetImportedOrCreateDecl<CXXDestructorDecl>(
        ToFunction, D, Importer.getToContext(), cast<CXXRecordDecl>(DC),
        ToInnerLocStart, NameInfo, T, TInfo, D->isInlineSpecified(),
        D->isImplicit()))
      return ToFunction;
  } else if (CXXConversionDecl *FromConversion =
                 dyn_cast<CXXConversionDecl>(D)) {
    if (GetImportedOrCreateDecl<CXXConversionDecl>(
            ToFunction, D, Importer.getToContext(), cast<CXXRecordDecl>(DC),
            ToInnerLocStart, NameInfo, T, TInfo, D->isInlineSpecified(),
            FromConversion->isExplicit(), D->isConstexpr(), SourceLocation()))
      return ToFunction;
  } else if (auto *Method = dyn_cast<CXXMethodDecl>(D)) {
    if (GetImportedOrCreateDecl<CXXMethodDecl>(
            ToFunction, D, Importer.getToContext(), cast<CXXRecordDecl>(DC),
            ToInnerLocStart, NameInfo, T, TInfo, Method->getStorageClass(),
            Method->isInlineSpecified(), D->isConstexpr(), SourceLocation()))
      return ToFunction;
  } else {
    if (GetImportedOrCreateDecl(ToFunction, D, Importer.getToContext(), DC,
                                ToInnerLocStart, NameInfo, T, TInfo,
                                D->getStorageClass(), D->isInlineSpecified(),
                                D->hasWrittenPrototype(), D->isConstexpr()))
      return ToFunction;
  }

  // Connect the redecl chain.
  if (FoundByLookup) {
    auto *Recent = const_cast<FunctionDecl *>(
          FoundByLookup->getMostRecentDecl());
    ToFunction->setPreviousDecl(Recent);
  }

  // Import Ctor initializers.
  if (auto *FromConstructor = dyn_cast<CXXConstructorDecl>(D)) {
    if (unsigned NumInitializers = FromConstructor->getNumCtorInitializers()) {
      SmallVector<CXXCtorInitializer *, 4> CtorInitializers(NumInitializers);
      // Import first, then allocate memory and copy if there was no error.
      if (Error Err = ImportContainerChecked(
          FromConstructor->inits(), CtorInitializers))
        return std::move(Err);
      auto **Memory =
          new (Importer.getToContext()) CXXCtorInitializer *[NumInitializers];
      std::copy(CtorInitializers.begin(), CtorInitializers.end(), Memory);
      auto *ToCtor = cast<CXXConstructorDecl>(ToFunction);
      ToCtor->setCtorInitializers(Memory);
      ToCtor->setNumCtorInitializers(NumInitializers);
    }
  }

  ToFunction->setQualifierInfo(ToQualifierLoc);
  ToFunction->setAccess(D->getAccess());
  ToFunction->setLexicalDeclContext(LexicalDC);
  ToFunction->setVirtualAsWritten(D->isVirtualAsWritten());
  ToFunction->setTrivial(D->isTrivial());
  ToFunction->setPure(D->isPure());
  ToFunction->setRangeEnd(ToEndLoc);

  // Set the parameters.
  for (auto *Param : Parameters) {
    Param->setOwningFunction(ToFunction);
    ToFunction->addDeclInternal(Param);
  }
  ToFunction->setParams(Parameters);

  // We need to complete creation of FunctionProtoTypeLoc manually with setting
  // params it refers to.
  if (TInfo) {
    if (auto ProtoLoc =
        TInfo->getTypeLoc().IgnoreParens().getAs<FunctionProtoTypeLoc>()) {
      for (unsigned I = 0, N = Parameters.size(); I != N; ++I)
        ProtoLoc.setParam(I, Parameters[I]);
    }
  }

  if (usedDifferentExceptionSpec) {
    // Update FunctionProtoType::ExtProtoInfo.
    if (ExpectedType TyOrErr = import(D->getType()))
      ToFunction->setType(*TyOrErr);
    else
      return TyOrErr.takeError();
  }

  // Import the describing template function, if any.
  if (FromFT) {
    auto ToFTOrErr = import(FromFT);
    if (!ToFTOrErr)
      return ToFTOrErr.takeError();
  }

  if (D->doesThisDeclarationHaveABody()) {
    if (Stmt *FromBody = D->getBody()) {
      if (ExpectedStmt ToBodyOrErr = import(FromBody))
        ToFunction->setBody(*ToBodyOrErr);
      else
        return ToBodyOrErr.takeError();
    }
  }

  // FIXME: Other bits to merge?

  // If it is a template, import all related things.
  if (Error Err = ImportTemplateInformation(D, ToFunction))
    return std::move(Err);

  bool IsFriend = D->isInIdentifierNamespace(Decl::IDNS_OrdinaryFriend);

  // TODO Can we generalize this approach to other AST nodes as well?
  if (D->getDeclContext()->containsDeclAndLoad(D))
    DC->addDeclInternal(ToFunction);
  if (DC != LexicalDC && D->getLexicalDeclContext()->containsDeclAndLoad(D))
    LexicalDC->addDeclInternal(ToFunction);

  // Friend declaration's lexical context is the befriending class, but the
  // semantic context is the enclosing scope of the befriending class.
  // We want the friend functions to be found in the semantic context by lookup.
  // FIXME should we handle this generically in VisitFriendDecl?
  // In Other cases when LexicalDC != DC we don't want it to be added,
  // e.g out-of-class definitions like void B::f() {} .
  if (LexicalDC != DC && IsFriend) {
    DC->makeDeclVisibleInContext(ToFunction);
  }

  if (auto *FromCXXMethod = dyn_cast<CXXMethodDecl>(D))
    ImportOverrides(cast<CXXMethodDecl>(ToFunction), FromCXXMethod);

  // Import the rest of the chain. I.e. import all subsequent declarations.
  for (++RedeclIt; RedeclIt != Redecls.end(); ++RedeclIt) {
    ExpectedDecl ToRedeclOrErr = import(*RedeclIt);
    if (!ToRedeclOrErr)
      return ToRedeclOrErr.takeError();
  }

  return ToFunction;
}

ExpectedDecl ASTNodeImporter::VisitCXXMethodDecl(CXXMethodDecl *D) {
  return VisitFunctionDecl(D);
}

ExpectedDecl ASTNodeImporter::VisitCXXConstructorDecl(CXXConstructorDecl *D) {
  return VisitCXXMethodDecl(D);
}

ExpectedDecl ASTNodeImporter::VisitCXXDestructorDecl(CXXDestructorDecl *D) {
  return VisitCXXMethodDecl(D);
}

ExpectedDecl ASTNodeImporter::VisitCXXConversionDecl(CXXConversionDecl *D) {
  return VisitCXXMethodDecl(D);
}

ExpectedDecl ASTNodeImporter::VisitFieldDecl(FieldDecl *D) {
  // Import the major distinguishing characteristics of a variable.
  DeclContext *DC, *LexicalDC;
  DeclarationName Name;
  SourceLocation Loc;
  NamedDecl *ToD;
  if (Error Err = ImportDeclParts(D, DC, LexicalDC, Name, ToD, Loc))
    return std::move(Err);
  if (ToD)
    return ToD;

  // Determine whether we've already imported this field.
  auto FoundDecls = Importer.findDeclsInToCtx(DC, Name);
  for (auto *FoundDecl : FoundDecls) {
    if (FieldDecl *FoundField = dyn_cast<FieldDecl>(FoundDecl)) {
      // For anonymous fields, match up by index.
      if (!Name &&
          ASTImporter::getFieldIndex(D) !=
          ASTImporter::getFieldIndex(FoundField))
        continue;

      if (Importer.IsStructurallyEquivalent(D->getType(),
                                            FoundField->getType())) {
        Importer.MapImported(D, FoundField);
        // In case of a FieldDecl of a ClassTemplateSpecializationDecl, the
        // initializer of a FieldDecl might not had been instantiated in the
        // "To" context.  However, the "From" context might instantiated that,
        // thus we have to merge that.
        if (Expr *FromInitializer = D->getInClassInitializer()) {
          // We don't have yet the initializer set.
          if (FoundField->hasInClassInitializer() &&
              !FoundField->getInClassInitializer()) {
            if (ExpectedExpr ToInitializerOrErr = import(FromInitializer))
              FoundField->setInClassInitializer(*ToInitializerOrErr);
            else {
              // We can't return error here,
              // since we already mapped D as imported.
              // FIXME: warning message?
              consumeError(ToInitializerOrErr.takeError());
              return FoundField;
            }
          }
        }
        return FoundField;
      }

      // FIXME: Why is this case not handled with calling HandleNameConflict?
      Importer.ToDiag(Loc, diag::err_odr_field_type_inconsistent)
        << Name << D->getType() << FoundField->getType();
      Importer.ToDiag(FoundField->getLocation(), diag::note_odr_value_here)
        << FoundField->getType();

      return make_error<ImportError>(ImportError::NameConflict);
    }
  }

  QualType ToType;
  TypeSourceInfo *ToTInfo;
  Expr *ToBitWidth;
  SourceLocation ToInnerLocStart;
  Expr *ToInitializer;
  if (auto Imp = importSeq(
      D->getType(), D->getTypeSourceInfo(), D->getBitWidth(),
      D->getInnerLocStart(), D->getInClassInitializer()))
    std::tie(
        ToType, ToTInfo, ToBitWidth, ToInnerLocStart, ToInitializer) = *Imp;
  else
    return Imp.takeError();

  FieldDecl *ToField;
  if (GetImportedOrCreateDecl(ToField, D, Importer.getToContext(), DC,
                              ToInnerLocStart, Loc, Name.getAsIdentifierInfo(),
                              ToType, ToTInfo, ToBitWidth, D->isMutable(),
                              D->getInClassInitStyle()))
    return ToField;

  ToField->setAccess(D->getAccess());
  ToField->setLexicalDeclContext(LexicalDC);
  if (ToInitializer)
    ToField->setInClassInitializer(ToInitializer);
  ToField->setImplicit(D->isImplicit());
  LexicalDC->addDeclInternal(ToField);
  return ToField;
}

ExpectedDecl ASTNodeImporter::VisitIndirectFieldDecl(IndirectFieldDecl *D) {
  // Import the major distinguishing characteristics of a variable.
  DeclContext *DC, *LexicalDC;
  DeclarationName Name;
  SourceLocation Loc;
  NamedDecl *ToD;
  if (Error Err = ImportDeclParts(D, DC, LexicalDC, Name, ToD, Loc))
    return std::move(Err);
  if (ToD)
    return ToD;

  // Determine whether we've already imported this field.
  auto FoundDecls = Importer.findDeclsInToCtx(DC, Name);
  for (unsigned I = 0, N = FoundDecls.size(); I != N; ++I) {
    if (auto *FoundField = dyn_cast<IndirectFieldDecl>(FoundDecls[I])) {
      // For anonymous indirect fields, match up by index.
      if (!Name &&
          ASTImporter::getFieldIndex(D) !=
          ASTImporter::getFieldIndex(FoundField))
        continue;

      if (Importer.IsStructurallyEquivalent(D->getType(),
                                            FoundField->getType(),
                                            !Name.isEmpty())) {
        Importer.MapImported(D, FoundField);
        return FoundField;
      }

      // If there are more anonymous fields to check, continue.
      if (!Name && I < N-1)
        continue;

      // FIXME: Why is this case not handled with calling HandleNameConflict?
      Importer.ToDiag(Loc, diag::err_odr_field_type_inconsistent)
        << Name << D->getType() << FoundField->getType();
      Importer.ToDiag(FoundField->getLocation(), diag::note_odr_value_here)
        << FoundField->getType();

      return make_error<ImportError>(ImportError::NameConflict);
    }
  }

  // Import the type.
  auto TypeOrErr = import(D->getType());
  if (!TypeOrErr)
    return TypeOrErr.takeError();

  auto **NamedChain =
    new (Importer.getToContext()) NamedDecl*[D->getChainingSize()];

  unsigned i = 0;
  for (auto *PI : D->chain())
    if (Expected<NamedDecl *> ToD = import(PI))
      NamedChain[i++] = *ToD;
    else
      return ToD.takeError();

  llvm::MutableArrayRef<NamedDecl *> CH = {NamedChain, D->getChainingSize()};
  IndirectFieldDecl *ToIndirectField;
  if (GetImportedOrCreateDecl(ToIndirectField, D, Importer.getToContext(), DC,
                              Loc, Name.getAsIdentifierInfo(), *TypeOrErr, CH))
    // FIXME here we leak `NamedChain` which is allocated before
    return ToIndirectField;

  for (const auto *Attr : D->attrs())
    ToIndirectField->addAttr(Importer.Import(Attr));

  ToIndirectField->setAccess(D->getAccess());
  ToIndirectField->setLexicalDeclContext(LexicalDC);
  LexicalDC->addDeclInternal(ToIndirectField);
  return ToIndirectField;
}

ExpectedDecl ASTNodeImporter::VisitFriendDecl(FriendDecl *D) {
  // Import the major distinguishing characteristics of a declaration.
  DeclContext *DC, *LexicalDC;
  if (Error Err = ImportDeclContext(D, DC, LexicalDC))
    return std::move(Err);

  // Determine whether we've already imported this decl.
  // FriendDecl is not a NamedDecl so we cannot use lookup.
  auto *RD = cast<CXXRecordDecl>(DC);
  FriendDecl *ImportedFriend = RD->getFirstFriend();

  while (ImportedFriend) {
    if (D->getFriendDecl() && ImportedFriend->getFriendDecl()) {
      if (IsStructuralMatch(D->getFriendDecl(), ImportedFriend->getFriendDecl(),
                            /*Complain=*/false))
        return Importer.MapImported(D, ImportedFriend);

    } else if (D->getFriendType() && ImportedFriend->getFriendType()) {
      if (Importer.IsStructurallyEquivalent(
            D->getFriendType()->getType(),
            ImportedFriend->getFriendType()->getType(), true))
        return Importer.MapImported(D, ImportedFriend);
    }
    ImportedFriend = ImportedFriend->getNextFriend();
  }

  // Not found. Create it.
  FriendDecl::FriendUnion ToFU;
  if (NamedDecl *FriendD = D->getFriendDecl()) {
    NamedDecl *ToFriendD;
    if (Error Err = importInto(ToFriendD, FriendD))
      return std::move(Err);

    if (FriendD->getFriendObjectKind() != Decl::FOK_None &&
        !(FriendD->isInIdentifierNamespace(Decl::IDNS_NonMemberOperator)))
      ToFriendD->setObjectOfFriendDecl(false);

    ToFU = ToFriendD;
  } else { // The friend is a type, not a decl.
    if (auto TSIOrErr = import(D->getFriendType()))
      ToFU = *TSIOrErr;
    else
      return TSIOrErr.takeError();
  }

  SmallVector<TemplateParameterList *, 1> ToTPLists(D->NumTPLists);
  auto **FromTPLists = D->getTrailingObjects<TemplateParameterList *>();
  for (unsigned I = 0; I < D->NumTPLists; I++) {
    if (auto ListOrErr = ImportTemplateParameterList(FromTPLists[I]))
      ToTPLists[I] = *ListOrErr;
    else
      return ListOrErr.takeError();
  }

  auto LocationOrErr = import(D->getLocation());
  if (!LocationOrErr)
    return LocationOrErr.takeError();
  auto FriendLocOrErr = import(D->getFriendLoc());
  if (!FriendLocOrErr)
    return FriendLocOrErr.takeError();

  FriendDecl *FrD;
  if (GetImportedOrCreateDecl(FrD, D, Importer.getToContext(), DC,
                              *LocationOrErr, ToFU,
                              *FriendLocOrErr, ToTPLists))
    return FrD;

  FrD->setAccess(D->getAccess());
  FrD->setLexicalDeclContext(LexicalDC);
  LexicalDC->addDeclInternal(FrD);
  return FrD;
}

ExpectedDecl ASTNodeImporter::VisitObjCIvarDecl(ObjCIvarDecl *D) {
  // Import the major distinguishing characteristics of an ivar.
  DeclContext *DC, *LexicalDC;
  DeclarationName Name;
  SourceLocation Loc;
  NamedDecl *ToD;
  if (Error Err = ImportDeclParts(D, DC, LexicalDC, Name, ToD, Loc))
    return std::move(Err);
  if (ToD)
    return ToD;

  // Determine whether we've already imported this ivar
  auto FoundDecls = Importer.findDeclsInToCtx(DC, Name);
  for (auto *FoundDecl : FoundDecls) {
    if (ObjCIvarDecl *FoundIvar = dyn_cast<ObjCIvarDecl>(FoundDecl)) {
      if (Importer.IsStructurallyEquivalent(D->getType(),
                                            FoundIvar->getType())) {
        Importer.MapImported(D, FoundIvar);
        return FoundIvar;
      }

      Importer.ToDiag(Loc, diag::err_odr_ivar_type_inconsistent)
        << Name << D->getType() << FoundIvar->getType();
      Importer.ToDiag(FoundIvar->getLocation(), diag::note_odr_value_here)
        << FoundIvar->getType();

      return make_error<ImportError>(ImportError::NameConflict);
    }
  }

  QualType ToType;
  TypeSourceInfo *ToTypeSourceInfo;
  Expr *ToBitWidth;
  SourceLocation ToInnerLocStart;
  if (auto Imp = importSeq(
      D->getType(), D->getTypeSourceInfo(), D->getBitWidth(), D->getInnerLocStart()))
    std::tie(ToType, ToTypeSourceInfo, ToBitWidth, ToInnerLocStart) = *Imp;
  else
    return Imp.takeError();

  ObjCIvarDecl *ToIvar;
  if (GetImportedOrCreateDecl(
          ToIvar, D, Importer.getToContext(), cast<ObjCContainerDecl>(DC),
          ToInnerLocStart, Loc, Name.getAsIdentifierInfo(),
          ToType, ToTypeSourceInfo,
          D->getAccessControl(),ToBitWidth, D->getSynthesize()))
    return ToIvar;

  ToIvar->setLexicalDeclContext(LexicalDC);
  LexicalDC->addDeclInternal(ToIvar);
  return ToIvar;
}

ExpectedDecl ASTNodeImporter::VisitVarDecl(VarDecl *D) {

  SmallVector<Decl*, 2> Redecls = getCanonicalForwardRedeclChain(D);
  auto RedeclIt = Redecls.begin();
  // Import the first part of the decl chain. I.e. import all previous
  // declarations starting from the canonical decl.
  for (; RedeclIt != Redecls.end() && *RedeclIt != D; ++RedeclIt) {
    ExpectedDecl RedeclOrErr = import(*RedeclIt);
    if (!RedeclOrErr)
      return RedeclOrErr.takeError();
  }
  assert(*RedeclIt == D);

  // Import the major distinguishing characteristics of a variable.
  DeclContext *DC, *LexicalDC;
  DeclarationName Name;
  SourceLocation Loc;
  NamedDecl *ToD;
  if (Error Err = ImportDeclParts(D, DC, LexicalDC, Name, ToD, Loc))
    return std::move(Err);
  if (ToD)
    return ToD;

  // Try to find a variable in our own ("to") context with the same name and
  // in the same context as the variable we're importing.
  VarDecl *FoundByLookup = nullptr;
  if (D->isFileVarDecl()) {
    SmallVector<NamedDecl *, 4> ConflictingDecls;
    unsigned IDNS = Decl::IDNS_Ordinary;
    auto FoundDecls = Importer.findDeclsInToCtx(DC, Name);
    for (auto *FoundDecl : FoundDecls) {
      if (!FoundDecl->isInIdentifierNamespace(IDNS))
        continue;

      if (auto *FoundVar = dyn_cast<VarDecl>(FoundDecl)) {
        // We have found a variable that we may need to merge with. Check it.
        if (FoundVar->hasExternalFormalLinkage() &&
            D->hasExternalFormalLinkage()) {
          if (Importer.IsStructurallyEquivalent(D->getType(),
                                                FoundVar->getType())) {

            // The VarDecl in the "From" context has a definition, but in the
            // "To" context we already have a definition.
            VarDecl *FoundDef = FoundVar->getDefinition();
            if (D->isThisDeclarationADefinition() && FoundDef)
              // FIXME Check for ODR error if the two definitions have
              // different initializers?
              return Importer.MapImported(D, FoundDef);

            // The VarDecl in the "From" context has an initializer, but in the
            // "To" context we already have an initializer.
            const VarDecl *FoundDInit = nullptr;
            if (D->getInit() && FoundVar->getAnyInitializer(FoundDInit))
              // FIXME Diagnose ODR error if the two initializers are different?
              return Importer.MapImported(D, const_cast<VarDecl*>(FoundDInit));

            FoundByLookup = FoundVar;
            break;
          }

          const ArrayType *FoundArray
            = Importer.getToContext().getAsArrayType(FoundVar->getType());
          const ArrayType *TArray
            = Importer.getToContext().getAsArrayType(D->getType());
          if (FoundArray && TArray) {
            if (isa<IncompleteArrayType>(FoundArray) &&
                isa<ConstantArrayType>(TArray)) {
              // Import the type.
              if (auto TyOrErr = import(D->getType()))
                FoundVar->setType(*TyOrErr);
              else
                return TyOrErr.takeError();

              FoundByLookup = FoundVar;
              break;
            } else if (isa<IncompleteArrayType>(TArray) &&
                       isa<ConstantArrayType>(FoundArray)) {
              FoundByLookup = FoundVar;
              break;
            }
          }

          Importer.ToDiag(Loc, diag::err_odr_variable_type_inconsistent)
            << Name << D->getType() << FoundVar->getType();
          Importer.ToDiag(FoundVar->getLocation(), diag::note_odr_value_here)
            << FoundVar->getType();
        }
      }

      ConflictingDecls.push_back(FoundDecl);
    }

    if (!ConflictingDecls.empty()) {
      Name = Importer.HandleNameConflict(Name, DC, IDNS,
                                         ConflictingDecls.data(),
                                         ConflictingDecls.size());
      if (!Name)
        return make_error<ImportError>(ImportError::NameConflict);
    }
  }

  QualType ToType;
  TypeSourceInfo *ToTypeSourceInfo;
  SourceLocation ToInnerLocStart;
  NestedNameSpecifierLoc ToQualifierLoc;
  if (auto Imp = importSeq(
      D->getType(), D->getTypeSourceInfo(), D->getInnerLocStart(),
      D->getQualifierLoc()))
    std::tie(ToType, ToTypeSourceInfo, ToInnerLocStart, ToQualifierLoc) = *Imp;
  else
    return Imp.takeError();

  // Create the imported variable.
  VarDecl *ToVar;
  if (GetImportedOrCreateDecl(ToVar, D, Importer.getToContext(), DC,
                              ToInnerLocStart, Loc,
                              Name.getAsIdentifierInfo(),
                              ToType, ToTypeSourceInfo,
                              D->getStorageClass()))
    return ToVar;

  ToVar->setQualifierInfo(ToQualifierLoc);
  ToVar->setAccess(D->getAccess());
  ToVar->setLexicalDeclContext(LexicalDC);

  if (FoundByLookup) {
    auto *Recent = const_cast<VarDecl *>(FoundByLookup->getMostRecentDecl());
    ToVar->setPreviousDecl(Recent);
  }

  if (Error Err = ImportInitializer(D, ToVar))
    return std::move(Err);

  if (D->isConstexpr())
    ToVar->setConstexpr(true);

  if (D->getDeclContext()->containsDeclAndLoad(D))
    DC->addDeclInternal(ToVar);
  if (DC != LexicalDC && D->getLexicalDeclContext()->containsDeclAndLoad(D))
    LexicalDC->addDeclInternal(ToVar);

  // Import the rest of the chain. I.e. import all subsequent declarations.
  for (++RedeclIt; RedeclIt != Redecls.end(); ++RedeclIt) {
    ExpectedDecl RedeclOrErr = import(*RedeclIt);
    if (!RedeclOrErr)
      return RedeclOrErr.takeError();
  }

  return ToVar;
}

ExpectedDecl ASTNodeImporter::VisitImplicitParamDecl(ImplicitParamDecl *D) {
  // Parameters are created in the translation unit's context, then moved
  // into the function declaration's context afterward.
  DeclContext *DC = Importer.getToContext().getTranslationUnitDecl();

  DeclarationName ToDeclName;
  SourceLocation ToLocation;
  QualType ToType;
  if (auto Imp = importSeq(D->getDeclName(), D->getLocation(), D->getType()))
    std::tie(ToDeclName, ToLocation, ToType) = *Imp;
  else
    return Imp.takeError();

  // Create the imported parameter.
  ImplicitParamDecl *ToParm = nullptr;
  if (GetImportedOrCreateDecl(ToParm, D, Importer.getToContext(), DC,
                              ToLocation, ToDeclName.getAsIdentifierInfo(),
                              ToType, D->getParameterKind()))
    return ToParm;
  return ToParm;
}

ExpectedDecl ASTNodeImporter::VisitParmVarDecl(ParmVarDecl *D) {
  // Parameters are created in the translation unit's context, then moved
  // into the function declaration's context afterward.
  DeclContext *DC = Importer.getToContext().getTranslationUnitDecl();

  DeclarationName ToDeclName;
  SourceLocation ToLocation, ToInnerLocStart;
  QualType ToType;
  TypeSourceInfo *ToTypeSourceInfo;
  if (auto Imp = importSeq(
      D->getDeclName(), D->getLocation(), D->getType(), D->getInnerLocStart(),
      D->getTypeSourceInfo()))
    std::tie(
        ToDeclName, ToLocation, ToType, ToInnerLocStart,
        ToTypeSourceInfo) = *Imp;
  else
    return Imp.takeError();

  ParmVarDecl *ToParm;
  if (GetImportedOrCreateDecl(ToParm, D, Importer.getToContext(), DC,
                              ToInnerLocStart, ToLocation,
                              ToDeclName.getAsIdentifierInfo(), ToType,
                              ToTypeSourceInfo, D->getStorageClass(),
                              /*DefaultArg*/ nullptr))
    return ToParm;

  // Set the default argument.
  ToParm->setHasInheritedDefaultArg(D->hasInheritedDefaultArg());
  ToParm->setKNRPromoted(D->isKNRPromoted());

  if (D->hasUninstantiatedDefaultArg()) {
    if (auto ToDefArgOrErr = import(D->getUninstantiatedDefaultArg()))
      ToParm->setUninstantiatedDefaultArg(*ToDefArgOrErr);
    else
      return ToDefArgOrErr.takeError();
  } else if (D->hasUnparsedDefaultArg()) {
    ToParm->setUnparsedDefaultArg();
  } else if (D->hasDefaultArg()) {
    if (auto ToDefArgOrErr = import(D->getDefaultArg()))
      ToParm->setDefaultArg(*ToDefArgOrErr);
    else
      return ToDefArgOrErr.takeError();
  }

  if (D->isObjCMethodParameter()) {
    ToParm->setObjCMethodScopeInfo(D->getFunctionScopeIndex());
    ToParm->setObjCDeclQualifier(D->getObjCDeclQualifier());
  } else {
    ToParm->setScopeInfo(D->getFunctionScopeDepth(),
                         D->getFunctionScopeIndex());
  }

  return ToParm;
}

ExpectedDecl ASTNodeImporter::VisitObjCMethodDecl(ObjCMethodDecl *D) {
  // Import the major distinguishing characteristics of a method.
  DeclContext *DC, *LexicalDC;
  DeclarationName Name;
  SourceLocation Loc;
  NamedDecl *ToD;
  if (Error Err = ImportDeclParts(D, DC, LexicalDC, Name, ToD, Loc))
    return std::move(Err);
  if (ToD)
    return ToD;

  auto FoundDecls = Importer.findDeclsInToCtx(DC, Name);
  for (auto *FoundDecl : FoundDecls) {
    if (auto *FoundMethod = dyn_cast<ObjCMethodDecl>(FoundDecl)) {
      if (FoundMethod->isInstanceMethod() != D->isInstanceMethod())
        continue;

      // Check return types.
      if (!Importer.IsStructurallyEquivalent(D->getReturnType(),
                                             FoundMethod->getReturnType())) {
        Importer.ToDiag(Loc, diag::err_odr_objc_method_result_type_inconsistent)
            << D->isInstanceMethod() << Name << D->getReturnType()
            << FoundMethod->getReturnType();
        Importer.ToDiag(FoundMethod->getLocation(),
                        diag::note_odr_objc_method_here)
          << D->isInstanceMethod() << Name;

        return make_error<ImportError>(ImportError::NameConflict);
      }

      // Check the number of parameters.
      if (D->param_size() != FoundMethod->param_size()) {
        Importer.ToDiag(Loc, diag::err_odr_objc_method_num_params_inconsistent)
          << D->isInstanceMethod() << Name
          << D->param_size() << FoundMethod->param_size();
        Importer.ToDiag(FoundMethod->getLocation(),
                        diag::note_odr_objc_method_here)
          << D->isInstanceMethod() << Name;

        return make_error<ImportError>(ImportError::NameConflict);
      }

      // Check parameter types.
      for (ObjCMethodDecl::param_iterator P = D->param_begin(),
             PEnd = D->param_end(), FoundP = FoundMethod->param_begin();
           P != PEnd; ++P, ++FoundP) {
        if (!Importer.IsStructurallyEquivalent((*P)->getType(),
                                               (*FoundP)->getType())) {
          Importer.FromDiag((*P)->getLocation(),
                            diag::err_odr_objc_method_param_type_inconsistent)
            << D->isInstanceMethod() << Name
            << (*P)->getType() << (*FoundP)->getType();
          Importer.ToDiag((*FoundP)->getLocation(), diag::note_odr_value_here)
            << (*FoundP)->getType();

          return make_error<ImportError>(ImportError::NameConflict);
        }
      }

      // Check variadic/non-variadic.
      // Check the number of parameters.
      if (D->isVariadic() != FoundMethod->isVariadic()) {
        Importer.ToDiag(Loc, diag::err_odr_objc_method_variadic_inconsistent)
          << D->isInstanceMethod() << Name;
        Importer.ToDiag(FoundMethod->getLocation(),
                        diag::note_odr_objc_method_here)
          << D->isInstanceMethod() << Name;

        return make_error<ImportError>(ImportError::NameConflict);
      }

      // FIXME: Any other bits we need to merge?
      return Importer.MapImported(D, FoundMethod);
    }
  }

  SourceLocation ToEndLoc;
  QualType ToReturnType;
  TypeSourceInfo *ToReturnTypeSourceInfo;
  if (auto Imp = importSeq(
      D->getEndLoc(), D->getReturnType(), D->getReturnTypeSourceInfo()))
    std::tie(ToEndLoc, ToReturnType, ToReturnTypeSourceInfo) = *Imp;
  else
    return Imp.takeError();

  ObjCMethodDecl *ToMethod;
  if (GetImportedOrCreateDecl(
          ToMethod, D, Importer.getToContext(), Loc,
          ToEndLoc, Name.getObjCSelector(), ToReturnType,
          ToReturnTypeSourceInfo, DC, D->isInstanceMethod(), D->isVariadic(),
          D->isPropertyAccessor(), D->isImplicit(), D->isDefined(),
          D->getImplementationControl(), D->hasRelatedResultType()))
    return ToMethod;

  // FIXME: When we decide to merge method definitions, we'll need to
  // deal with implicit parameters.

  // Import the parameters
  SmallVector<ParmVarDecl *, 5> ToParams;
  for (auto *FromP : D->parameters()) {
    if (Expected<ParmVarDecl *> ToPOrErr = import(FromP))
      ToParams.push_back(*ToPOrErr);
    else
      return ToPOrErr.takeError();
  }

  // Set the parameters.
  for (auto *ToParam : ToParams) {
    ToParam->setOwningFunction(ToMethod);
    ToMethod->addDeclInternal(ToParam);
  }

  SmallVector<SourceLocation, 12> FromSelLocs;
  D->getSelectorLocs(FromSelLocs);
  SmallVector<SourceLocation, 12> ToSelLocs(FromSelLocs.size());
  if (Error Err = ImportContainerChecked(FromSelLocs, ToSelLocs))
    return std::move(Err);

  ToMethod->setMethodParams(Importer.getToContext(), ToParams, ToSelLocs);

  ToMethod->setLexicalDeclContext(LexicalDC);
  LexicalDC->addDeclInternal(ToMethod);
  return ToMethod;
}

ExpectedDecl ASTNodeImporter::VisitObjCTypeParamDecl(ObjCTypeParamDecl *D) {
  // Import the major distinguishing characteristics of a category.
  DeclContext *DC, *LexicalDC;
  DeclarationName Name;
  SourceLocation Loc;
  NamedDecl *ToD;
  if (Error Err = ImportDeclParts(D, DC, LexicalDC, Name, ToD, Loc))
    return std::move(Err);
  if (ToD)
    return ToD;

  SourceLocation ToVarianceLoc, ToLocation, ToColonLoc;
  TypeSourceInfo *ToTypeSourceInfo;
  if (auto Imp = importSeq(
      D->getVarianceLoc(), D->getLocation(), D->getColonLoc(),
      D->getTypeSourceInfo()))
    std::tie(ToVarianceLoc, ToLocation, ToColonLoc, ToTypeSourceInfo) = *Imp;
  else
    return Imp.takeError();

  ObjCTypeParamDecl *Result;
  if (GetImportedOrCreateDecl(
          Result, D, Importer.getToContext(), DC, D->getVariance(),
          ToVarianceLoc, D->getIndex(),
          ToLocation, Name.getAsIdentifierInfo(),
          ToColonLoc, ToTypeSourceInfo))
    return Result;

  Result->setLexicalDeclContext(LexicalDC);
  return Result;
}

ExpectedDecl ASTNodeImporter::VisitObjCCategoryDecl(ObjCCategoryDecl *D) {
  // Import the major distinguishing characteristics of a category.
  DeclContext *DC, *LexicalDC;
  DeclarationName Name;
  SourceLocation Loc;
  NamedDecl *ToD;
  if (Error Err = ImportDeclParts(D, DC, LexicalDC, Name, ToD, Loc))
    return std::move(Err);
  if (ToD)
    return ToD;

  ObjCInterfaceDecl *ToInterface;
  if (Error Err = importInto(ToInterface, D->getClassInterface()))
    return std::move(Err);

  // Determine if we've already encountered this category.
  ObjCCategoryDecl *MergeWithCategory
    = ToInterface->FindCategoryDeclaration(Name.getAsIdentifierInfo());
  ObjCCategoryDecl *ToCategory = MergeWithCategory;
  if (!ToCategory) {
    SourceLocation ToAtStartLoc, ToCategoryNameLoc;
    SourceLocation ToIvarLBraceLoc, ToIvarRBraceLoc;
    if (auto Imp = importSeq(
        D->getAtStartLoc(), D->getCategoryNameLoc(),
        D->getIvarLBraceLoc(), D->getIvarRBraceLoc()))
      std::tie(
          ToAtStartLoc, ToCategoryNameLoc,
          ToIvarLBraceLoc, ToIvarRBraceLoc) = *Imp;
    else
      return Imp.takeError();

    if (GetImportedOrCreateDecl(ToCategory, D, Importer.getToContext(), DC,
                                ToAtStartLoc, Loc,
                                ToCategoryNameLoc,
                                Name.getAsIdentifierInfo(), ToInterface,
                                /*TypeParamList=*/nullptr,
                                ToIvarLBraceLoc,
                                ToIvarRBraceLoc))
      return ToCategory;

    ToCategory->setLexicalDeclContext(LexicalDC);
    LexicalDC->addDeclInternal(ToCategory);
    // Import the type parameter list after MapImported, to avoid
    // loops when bringing in their DeclContext.
    if (auto PListOrErr = ImportObjCTypeParamList(D->getTypeParamList()))
      ToCategory->setTypeParamList(*PListOrErr);
    else
      return PListOrErr.takeError();

    // Import protocols
    SmallVector<ObjCProtocolDecl *, 4> Protocols;
    SmallVector<SourceLocation, 4> ProtocolLocs;
    ObjCCategoryDecl::protocol_loc_iterator FromProtoLoc
      = D->protocol_loc_begin();
    for (ObjCCategoryDecl::protocol_iterator FromProto = D->protocol_begin(),
                                          FromProtoEnd = D->protocol_end();
         FromProto != FromProtoEnd;
         ++FromProto, ++FromProtoLoc) {
      if (Expected<ObjCProtocolDecl *> ToProtoOrErr = import(*FromProto))
        Protocols.push_back(*ToProtoOrErr);
      else
        return ToProtoOrErr.takeError();

      if (ExpectedSLoc ToProtoLocOrErr = import(*FromProtoLoc))
        ProtocolLocs.push_back(*ToProtoLocOrErr);
      else
        return ToProtoLocOrErr.takeError();
    }

    // FIXME: If we're merging, make sure that the protocol list is the same.
    ToCategory->setProtocolList(Protocols.data(), Protocols.size(),
                                ProtocolLocs.data(), Importer.getToContext());

  } else {
    Importer.MapImported(D, ToCategory);
  }

  // Import all of the members of this category.
  if (Error Err = ImportDeclContext(D))
    return std::move(Err);

  // If we have an implementation, import it as well.
  if (D->getImplementation()) {
    if (Expected<ObjCCategoryImplDecl *> ToImplOrErr =
        import(D->getImplementation()))
      ToCategory->setImplementation(*ToImplOrErr);
    else
      return ToImplOrErr.takeError();
  }

  return ToCategory;
}

Error ASTNodeImporter::ImportDefinition(
    ObjCProtocolDecl *From, ObjCProtocolDecl *To, ImportDefinitionKind Kind) {
  if (To->getDefinition()) {
    if (shouldForceImportDeclContext(Kind))
      if (Error Err = ImportDeclContext(From))
        return Err;
    return Error::success();
  }

  // Start the protocol definition
  To->startDefinition();

  // Import protocols
  SmallVector<ObjCProtocolDecl *, 4> Protocols;
  SmallVector<SourceLocation, 4> ProtocolLocs;
  ObjCProtocolDecl::protocol_loc_iterator FromProtoLoc =
      From->protocol_loc_begin();
  for (ObjCProtocolDecl::protocol_iterator FromProto = From->protocol_begin(),
                                        FromProtoEnd = From->protocol_end();
       FromProto != FromProtoEnd;
       ++FromProto, ++FromProtoLoc) {
    if (Expected<ObjCProtocolDecl *> ToProtoOrErr = import(*FromProto))
      Protocols.push_back(*ToProtoOrErr);
    else
      return ToProtoOrErr.takeError();

    if (ExpectedSLoc ToProtoLocOrErr = import(*FromProtoLoc))
      ProtocolLocs.push_back(*ToProtoLocOrErr);
    else
      return ToProtoLocOrErr.takeError();

  }

  // FIXME: If we're merging, make sure that the protocol list is the same.
  To->setProtocolList(Protocols.data(), Protocols.size(),
                      ProtocolLocs.data(), Importer.getToContext());

  if (shouldForceImportDeclContext(Kind)) {
    // Import all of the members of this protocol.
    if (Error Err = ImportDeclContext(From, /*ForceImport=*/true))
      return Err;
  }
  return Error::success();
}

ExpectedDecl ASTNodeImporter::VisitObjCProtocolDecl(ObjCProtocolDecl *D) {
  // If this protocol has a definition in the translation unit we're coming
  // from, but this particular declaration is not that definition, import the
  // definition and map to that.
  ObjCProtocolDecl *Definition = D->getDefinition();
  if (Definition && Definition != D) {
    if (ExpectedDecl ImportedDefOrErr = import(Definition))
      return Importer.MapImported(D, *ImportedDefOrErr);
    else
      return ImportedDefOrErr.takeError();
  }

  // Import the major distinguishing characteristics of a protocol.
  DeclContext *DC, *LexicalDC;
  DeclarationName Name;
  SourceLocation Loc;
  NamedDecl *ToD;
  if (Error Err = ImportDeclParts(D, DC, LexicalDC, Name, ToD, Loc))
    return std::move(Err);
  if (ToD)
    return ToD;

  ObjCProtocolDecl *MergeWithProtocol = nullptr;
  auto FoundDecls = Importer.findDeclsInToCtx(DC, Name);
  for (auto *FoundDecl : FoundDecls) {
    if (!FoundDecl->isInIdentifierNamespace(Decl::IDNS_ObjCProtocol))
      continue;

    if ((MergeWithProtocol = dyn_cast<ObjCProtocolDecl>(FoundDecl)))
      break;
  }

  ObjCProtocolDecl *ToProto = MergeWithProtocol;
  if (!ToProto) {
    auto ToAtBeginLocOrErr = import(D->getAtStartLoc());
    if (!ToAtBeginLocOrErr)
      return ToAtBeginLocOrErr.takeError();

    if (GetImportedOrCreateDecl(ToProto, D, Importer.getToContext(), DC,
                                Name.getAsIdentifierInfo(), Loc,
                                *ToAtBeginLocOrErr,
                                /*PrevDecl=*/nullptr))
      return ToProto;
    ToProto->setLexicalDeclContext(LexicalDC);
    LexicalDC->addDeclInternal(ToProto);
  }

  Importer.MapImported(D, ToProto);

  if (D->isThisDeclarationADefinition())
    if (Error Err = ImportDefinition(D, ToProto))
      return std::move(Err);

  return ToProto;
}

ExpectedDecl ASTNodeImporter::VisitLinkageSpecDecl(LinkageSpecDecl *D) {
  DeclContext *DC, *LexicalDC;
  if (Error Err = ImportDeclContext(D, DC, LexicalDC))
    return std::move(Err);

  ExpectedSLoc ExternLocOrErr = import(D->getExternLoc());
  if (!ExternLocOrErr)
    return ExternLocOrErr.takeError();

  ExpectedSLoc LangLocOrErr = import(D->getLocation());
  if (!LangLocOrErr)
    return LangLocOrErr.takeError();

  bool HasBraces = D->hasBraces();

  LinkageSpecDecl *ToLinkageSpec;
  if (GetImportedOrCreateDecl(ToLinkageSpec, D, Importer.getToContext(), DC,
                              *ExternLocOrErr, *LangLocOrErr,
                              D->getLanguage(), HasBraces))
    return ToLinkageSpec;

  if (HasBraces) {
    ExpectedSLoc RBraceLocOrErr = import(D->getRBraceLoc());
    if (!RBraceLocOrErr)
      return RBraceLocOrErr.takeError();
    ToLinkageSpec->setRBraceLoc(*RBraceLocOrErr);
  }

  ToLinkageSpec->setLexicalDeclContext(LexicalDC);
  LexicalDC->addDeclInternal(ToLinkageSpec);

  return ToLinkageSpec;
}

ExpectedDecl ASTNodeImporter::VisitUsingDecl(UsingDecl *D) {
  DeclContext *DC, *LexicalDC;
  DeclarationName Name;
  SourceLocation Loc;
  NamedDecl *ToD = nullptr;
  if (Error Err = ImportDeclParts(D, DC, LexicalDC, Name, ToD, Loc))
    return std::move(Err);
  if (ToD)
    return ToD;

  SourceLocation ToLoc, ToUsingLoc;
  NestedNameSpecifierLoc ToQualifierLoc;
  if (auto Imp = importSeq(
      D->getNameInfo().getLoc(), D->getUsingLoc(), D->getQualifierLoc()))
    std::tie(ToLoc, ToUsingLoc, ToQualifierLoc) = *Imp;
  else
    return Imp.takeError();

  DeclarationNameInfo NameInfo(Name, ToLoc);
  if (Error Err = ImportDeclarationNameLoc(D->getNameInfo(), NameInfo))
    return std::move(Err);

  UsingDecl *ToUsing;
  if (GetImportedOrCreateDecl(ToUsing, D, Importer.getToContext(), DC,
                              ToUsingLoc, ToQualifierLoc, NameInfo,
                              D->hasTypename()))
    return ToUsing;

  ToUsing->setLexicalDeclContext(LexicalDC);
  LexicalDC->addDeclInternal(ToUsing);

  if (NamedDecl *FromPattern =
      Importer.getFromContext().getInstantiatedFromUsingDecl(D)) {
    if (Expected<NamedDecl *> ToPatternOrErr = import(FromPattern))
      Importer.getToContext().setInstantiatedFromUsingDecl(
          ToUsing, *ToPatternOrErr);
    else
      return ToPatternOrErr.takeError();
  }

  for (UsingShadowDecl *FromShadow : D->shadows()) {
    if (Expected<UsingShadowDecl *> ToShadowOrErr = import(FromShadow))
      ToUsing->addShadowDecl(*ToShadowOrErr);
    else
      // FIXME: We return error here but the definition is already created
      // and available with lookups. How to fix this?..
      return ToShadowOrErr.takeError();
  }
  return ToUsing;
}

ExpectedDecl ASTNodeImporter::VisitUsingShadowDecl(UsingShadowDecl *D) {
  DeclContext *DC, *LexicalDC;
  DeclarationName Name;
  SourceLocation Loc;
  NamedDecl *ToD = nullptr;
  if (Error Err = ImportDeclParts(D, DC, LexicalDC, Name, ToD, Loc))
    return std::move(Err);
  if (ToD)
    return ToD;

  Expected<UsingDecl *> ToUsingOrErr = import(D->getUsingDecl());
  if (!ToUsingOrErr)
    return ToUsingOrErr.takeError();

  Expected<NamedDecl *> ToTargetOrErr = import(D->getTargetDecl());
  if (!ToTargetOrErr)
    return ToTargetOrErr.takeError();

  UsingShadowDecl *ToShadow;
  if (GetImportedOrCreateDecl(ToShadow, D, Importer.getToContext(), DC, Loc,
                              *ToUsingOrErr, *ToTargetOrErr))
    return ToShadow;

  ToShadow->setLexicalDeclContext(LexicalDC);
  ToShadow->setAccess(D->getAccess());

  if (UsingShadowDecl *FromPattern =
      Importer.getFromContext().getInstantiatedFromUsingShadowDecl(D)) {
    if (Expected<UsingShadowDecl *> ToPatternOrErr = import(FromPattern))
      Importer.getToContext().setInstantiatedFromUsingShadowDecl(
          ToShadow, *ToPatternOrErr);
    else
      // FIXME: We return error here but the definition is already created
      // and available with lookups. How to fix this?..
      return ToPatternOrErr.takeError();
  }

  LexicalDC->addDeclInternal(ToShadow);

  return ToShadow;
}

ExpectedDecl ASTNodeImporter::VisitUsingDirectiveDecl(UsingDirectiveDecl *D) {
  DeclContext *DC, *LexicalDC;
  DeclarationName Name;
  SourceLocation Loc;
  NamedDecl *ToD = nullptr;
  if (Error Err = ImportDeclParts(D, DC, LexicalDC, Name, ToD, Loc))
    return std::move(Err);
  if (ToD)
    return ToD;

  auto ToComAncestorOrErr = Importer.ImportContext(D->getCommonAncestor());
  if (!ToComAncestorOrErr)
    return ToComAncestorOrErr.takeError();

  NamespaceDecl *ToNominatedNamespace;
  SourceLocation ToUsingLoc, ToNamespaceKeyLocation, ToIdentLocation;
  NestedNameSpecifierLoc ToQualifierLoc;
  if (auto Imp = importSeq(
      D->getNominatedNamespace(), D->getUsingLoc(),
      D->getNamespaceKeyLocation(), D->getQualifierLoc(),
      D->getIdentLocation()))
    std::tie(
        ToNominatedNamespace, ToUsingLoc, ToNamespaceKeyLocation,
        ToQualifierLoc, ToIdentLocation) = *Imp;
  else
    return Imp.takeError();

  UsingDirectiveDecl *ToUsingDir;
  if (GetImportedOrCreateDecl(ToUsingDir, D, Importer.getToContext(), DC,
                              ToUsingLoc,
                              ToNamespaceKeyLocation,
                              ToQualifierLoc,
                              ToIdentLocation,
                              ToNominatedNamespace, *ToComAncestorOrErr))
    return ToUsingDir;

  ToUsingDir->setLexicalDeclContext(LexicalDC);
  LexicalDC->addDeclInternal(ToUsingDir);

  return ToUsingDir;
}

ExpectedDecl ASTNodeImporter::VisitUnresolvedUsingValueDecl(
    UnresolvedUsingValueDecl *D) {
  DeclContext *DC, *LexicalDC;
  DeclarationName Name;
  SourceLocation Loc;
  NamedDecl *ToD = nullptr;
  if (Error Err = ImportDeclParts(D, DC, LexicalDC, Name, ToD, Loc))
    return std::move(Err);
  if (ToD)
    return ToD;

  SourceLocation ToLoc, ToUsingLoc, ToEllipsisLoc;
  NestedNameSpecifierLoc ToQualifierLoc;
  if (auto Imp = importSeq(
      D->getNameInfo().getLoc(), D->getUsingLoc(), D->getQualifierLoc(),
      D->getEllipsisLoc()))
    std::tie(ToLoc, ToUsingLoc, ToQualifierLoc, ToEllipsisLoc) = *Imp;
  else
    return Imp.takeError();

  DeclarationNameInfo NameInfo(Name, ToLoc);
  if (Error Err = ImportDeclarationNameLoc(D->getNameInfo(), NameInfo))
    return std::move(Err);

  UnresolvedUsingValueDecl *ToUsingValue;
  if (GetImportedOrCreateDecl(ToUsingValue, D, Importer.getToContext(), DC,
                              ToUsingLoc, ToQualifierLoc, NameInfo,
                              ToEllipsisLoc))
    return ToUsingValue;

  ToUsingValue->setAccess(D->getAccess());
  ToUsingValue->setLexicalDeclContext(LexicalDC);
  LexicalDC->addDeclInternal(ToUsingValue);

  return ToUsingValue;
}

ExpectedDecl ASTNodeImporter::VisitUnresolvedUsingTypenameDecl(
    UnresolvedUsingTypenameDecl *D) {
  DeclContext *DC, *LexicalDC;
  DeclarationName Name;
  SourceLocation Loc;
  NamedDecl *ToD = nullptr;
  if (Error Err = ImportDeclParts(D, DC, LexicalDC, Name, ToD, Loc))
    return std::move(Err);
  if (ToD)
    return ToD;

  SourceLocation ToUsingLoc, ToTypenameLoc, ToEllipsisLoc;
  NestedNameSpecifierLoc ToQualifierLoc;
  if (auto Imp = importSeq(
      D->getUsingLoc(), D->getTypenameLoc(), D->getQualifierLoc(),
      D->getEllipsisLoc()))
    std::tie(ToUsingLoc, ToTypenameLoc, ToQualifierLoc, ToEllipsisLoc) = *Imp;
  else
    return Imp.takeError();

  UnresolvedUsingTypenameDecl *ToUsing;
  if (GetImportedOrCreateDecl(ToUsing, D, Importer.getToContext(), DC,
                              ToUsingLoc, ToTypenameLoc,
                              ToQualifierLoc, Loc, Name, ToEllipsisLoc))
    return ToUsing;

  ToUsing->setAccess(D->getAccess());
  ToUsing->setLexicalDeclContext(LexicalDC);
  LexicalDC->addDeclInternal(ToUsing);

  return ToUsing;
}


Error ASTNodeImporter::ImportDefinition(
    ObjCInterfaceDecl *From, ObjCInterfaceDecl *To, ImportDefinitionKind Kind) {
  if (To->getDefinition()) {
    // Check consistency of superclass.
    ObjCInterfaceDecl *FromSuper = From->getSuperClass();
    if (FromSuper) {
      if (auto FromSuperOrErr = import(FromSuper))
        FromSuper = *FromSuperOrErr;
      else
        return FromSuperOrErr.takeError();
    }

    ObjCInterfaceDecl *ToSuper = To->getSuperClass();
    if ((bool)FromSuper != (bool)ToSuper ||
        (FromSuper && !declaresSameEntity(FromSuper, ToSuper))) {
      Importer.ToDiag(To->getLocation(),
                      diag::err_odr_objc_superclass_inconsistent)
        << To->getDeclName();
      if (ToSuper)
        Importer.ToDiag(To->getSuperClassLoc(), diag::note_odr_objc_superclass)
          << To->getSuperClass()->getDeclName();
      else
        Importer.ToDiag(To->getLocation(),
                        diag::note_odr_objc_missing_superclass);
      if (From->getSuperClass())
        Importer.FromDiag(From->getSuperClassLoc(),
                          diag::note_odr_objc_superclass)
        << From->getSuperClass()->getDeclName();
      else
        Importer.FromDiag(From->getLocation(),
                          diag::note_odr_objc_missing_superclass);
    }

    if (shouldForceImportDeclContext(Kind))
      if (Error Err = ImportDeclContext(From))
        return Err;
    return Error::success();
  }

  // Start the definition.
  To->startDefinition();

  // If this class has a superclass, import it.
  if (From->getSuperClass()) {
    if (auto SuperTInfoOrErr = import(From->getSuperClassTInfo()))
      To->setSuperClass(*SuperTInfoOrErr);
    else
      return SuperTInfoOrErr.takeError();
  }

  // Import protocols
  SmallVector<ObjCProtocolDecl *, 4> Protocols;
  SmallVector<SourceLocation, 4> ProtocolLocs;
  ObjCInterfaceDecl::protocol_loc_iterator FromProtoLoc =
      From->protocol_loc_begin();

  for (ObjCInterfaceDecl::protocol_iterator FromProto = From->protocol_begin(),
                                         FromProtoEnd = From->protocol_end();
       FromProto != FromProtoEnd;
       ++FromProto, ++FromProtoLoc) {
    if (Expected<ObjCProtocolDecl *> ToProtoOrErr = import(*FromProto))
      Protocols.push_back(*ToProtoOrErr);
    else
      return ToProtoOrErr.takeError();

    if (ExpectedSLoc ToProtoLocOrErr = import(*FromProtoLoc))
      ProtocolLocs.push_back(*ToProtoLocOrErr);
    else
      return ToProtoLocOrErr.takeError();

  }

  // FIXME: If we're merging, make sure that the protocol list is the same.
  To->setProtocolList(Protocols.data(), Protocols.size(),
                      ProtocolLocs.data(), Importer.getToContext());

  // Import categories. When the categories themselves are imported, they'll
  // hook themselves into this interface.
  for (auto *Cat : From->known_categories()) {
    auto ToCatOrErr = import(Cat);
    if (!ToCatOrErr)
      return ToCatOrErr.takeError();
  }

  // If we have an @implementation, import it as well.
  if (From->getImplementation()) {
    if (Expected<ObjCImplementationDecl *> ToImplOrErr =
        import(From->getImplementation()))
      To->setImplementation(*ToImplOrErr);
    else
      return ToImplOrErr.takeError();
  }

  if (shouldForceImportDeclContext(Kind)) {
    // Import all of the members of this class.
    if (Error Err = ImportDeclContext(From, /*ForceImport=*/true))
      return Err;
  }
  return Error::success();
}

Expected<ObjCTypeParamList *>
ASTNodeImporter::ImportObjCTypeParamList(ObjCTypeParamList *list) {
  if (!list)
    return nullptr;

  SmallVector<ObjCTypeParamDecl *, 4> toTypeParams;
  for (auto *fromTypeParam : *list) {
    if (auto toTypeParamOrErr = import(fromTypeParam))
      toTypeParams.push_back(*toTypeParamOrErr);
    else
      return toTypeParamOrErr.takeError();
  }

  auto LAngleLocOrErr = import(list->getLAngleLoc());
  if (!LAngleLocOrErr)
    return LAngleLocOrErr.takeError();

  auto RAngleLocOrErr = import(list->getRAngleLoc());
  if (!RAngleLocOrErr)
    return RAngleLocOrErr.takeError();

  return ObjCTypeParamList::create(Importer.getToContext(),
                                   *LAngleLocOrErr,
                                   toTypeParams,
                                   *RAngleLocOrErr);
}

ExpectedDecl ASTNodeImporter::VisitObjCInterfaceDecl(ObjCInterfaceDecl *D) {
  // If this class has a definition in the translation unit we're coming from,
  // but this particular declaration is not that definition, import the
  // definition and map to that.
  ObjCInterfaceDecl *Definition = D->getDefinition();
  if (Definition && Definition != D) {
    if (ExpectedDecl ImportedDefOrErr = import(Definition))
      return Importer.MapImported(D, *ImportedDefOrErr);
    else
      return ImportedDefOrErr.takeError();
  }

  // Import the major distinguishing characteristics of an @interface.
  DeclContext *DC, *LexicalDC;
  DeclarationName Name;
  SourceLocation Loc;
  NamedDecl *ToD;
  if (Error Err = ImportDeclParts(D, DC, LexicalDC, Name, ToD, Loc))
    return std::move(Err);
  if (ToD)
    return ToD;

  // Look for an existing interface with the same name.
  ObjCInterfaceDecl *MergeWithIface = nullptr;
  auto FoundDecls = Importer.findDeclsInToCtx(DC, Name);
  for (auto *FoundDecl : FoundDecls) {
    if (!FoundDecl->isInIdentifierNamespace(Decl::IDNS_Ordinary))
      continue;

    if ((MergeWithIface = dyn_cast<ObjCInterfaceDecl>(FoundDecl)))
      break;
  }

  // Create an interface declaration, if one does not already exist.
  ObjCInterfaceDecl *ToIface = MergeWithIface;
  if (!ToIface) {
    ExpectedSLoc AtBeginLocOrErr = import(D->getAtStartLoc());
    if (!AtBeginLocOrErr)
      return AtBeginLocOrErr.takeError();

    if (GetImportedOrCreateDecl(
            ToIface, D, Importer.getToContext(), DC,
            *AtBeginLocOrErr, Name.getAsIdentifierInfo(),
            /*TypeParamList=*/nullptr,
            /*PrevDecl=*/nullptr, Loc, D->isImplicitInterfaceDecl()))
      return ToIface;
    ToIface->setLexicalDeclContext(LexicalDC);
    LexicalDC->addDeclInternal(ToIface);
  }
  Importer.MapImported(D, ToIface);
  // Import the type parameter list after MapImported, to avoid
  // loops when bringing in their DeclContext.
  if (auto ToPListOrErr =
      ImportObjCTypeParamList(D->getTypeParamListAsWritten()))
    ToIface->setTypeParamList(*ToPListOrErr);
  else
    return ToPListOrErr.takeError();

  if (D->isThisDeclarationADefinition())
    if (Error Err = ImportDefinition(D, ToIface))
      return std::move(Err);

  return ToIface;
}

ExpectedDecl
ASTNodeImporter::VisitObjCCategoryImplDecl(ObjCCategoryImplDecl *D) {
  ObjCCategoryDecl *Category;
  if (Error Err = importInto(Category, D->getCategoryDecl()))
    return std::move(Err);

  ObjCCategoryImplDecl *ToImpl = Category->getImplementation();
  if (!ToImpl) {
    DeclContext *DC, *LexicalDC;
    if (Error Err = ImportDeclContext(D, DC, LexicalDC))
      return std::move(Err);

    SourceLocation ToLocation, ToAtStartLoc, ToCategoryNameLoc;
    if (auto Imp = importSeq(
        D->getLocation(), D->getAtStartLoc(), D->getCategoryNameLoc()))
      std::tie(ToLocation, ToAtStartLoc, ToCategoryNameLoc) = *Imp;
    else
      return Imp.takeError();

    if (GetImportedOrCreateDecl(
            ToImpl, D, Importer.getToContext(), DC,
            Importer.Import(D->getIdentifier()), Category->getClassInterface(),
            ToLocation, ToAtStartLoc, ToCategoryNameLoc))
      return ToImpl;

    ToImpl->setLexicalDeclContext(LexicalDC);
    LexicalDC->addDeclInternal(ToImpl);
    Category->setImplementation(ToImpl);
  }

  Importer.MapImported(D, ToImpl);
  if (Error Err = ImportDeclContext(D))
    return std::move(Err);

  return ToImpl;
}

ExpectedDecl
ASTNodeImporter::VisitObjCImplementationDecl(ObjCImplementationDecl *D) {
  // Find the corresponding interface.
  ObjCInterfaceDecl *Iface;
  if (Error Err = importInto(Iface, D->getClassInterface()))
    return std::move(Err);

  // Import the superclass, if any.
  ObjCInterfaceDecl *Super;
  if (Error Err = importInto(Super, D->getSuperClass()))
    return std::move(Err);

  ObjCImplementationDecl *Impl = Iface->getImplementation();
  if (!Impl) {
    // We haven't imported an implementation yet. Create a new @implementation
    // now.
    DeclContext *DC, *LexicalDC;
    if (Error Err = ImportDeclContext(D, DC, LexicalDC))
      return std::move(Err);

    SourceLocation ToLocation, ToAtStartLoc, ToSuperClassLoc;
    SourceLocation ToIvarLBraceLoc, ToIvarRBraceLoc;
    if (auto Imp = importSeq(
        D->getLocation(), D->getAtStartLoc(), D->getSuperClassLoc(),
        D->getIvarLBraceLoc(), D->getIvarRBraceLoc()))
      std::tie(
          ToLocation, ToAtStartLoc, ToSuperClassLoc,
          ToIvarLBraceLoc, ToIvarRBraceLoc) = *Imp;
    else
      return Imp.takeError();

    if (GetImportedOrCreateDecl(Impl, D, Importer.getToContext(),
                                DC, Iface, Super,
                                ToLocation,
                                ToAtStartLoc,
                                ToSuperClassLoc,
                                ToIvarLBraceLoc,
                                ToIvarRBraceLoc))
      return Impl;

    Impl->setLexicalDeclContext(LexicalDC);

    // Associate the implementation with the class it implements.
    Iface->setImplementation(Impl);
    Importer.MapImported(D, Iface->getImplementation());
  } else {
    Importer.MapImported(D, Iface->getImplementation());

    // Verify that the existing @implementation has the same superclass.
    if ((Super && !Impl->getSuperClass()) ||
        (!Super && Impl->getSuperClass()) ||
        (Super && Impl->getSuperClass() &&
         !declaresSameEntity(Super->getCanonicalDecl(),
                             Impl->getSuperClass()))) {
      Importer.ToDiag(Impl->getLocation(),
                      diag::err_odr_objc_superclass_inconsistent)
        << Iface->getDeclName();
      // FIXME: It would be nice to have the location of the superclass
      // below.
      if (Impl->getSuperClass())
        Importer.ToDiag(Impl->getLocation(),
                        diag::note_odr_objc_superclass)
        << Impl->getSuperClass()->getDeclName();
      else
        Importer.ToDiag(Impl->getLocation(),
                        diag::note_odr_objc_missing_superclass);
      if (D->getSuperClass())
        Importer.FromDiag(D->getLocation(),
                          diag::note_odr_objc_superclass)
        << D->getSuperClass()->getDeclName();
      else
        Importer.FromDiag(D->getLocation(),
                          diag::note_odr_objc_missing_superclass);

      return make_error<ImportError>(ImportError::NameConflict);
    }
  }

  // Import all of the members of this @implementation.
  if (Error Err = ImportDeclContext(D))
    return std::move(Err);

  return Impl;
}

ExpectedDecl ASTNodeImporter::VisitObjCPropertyDecl(ObjCPropertyDecl *D) {
  // Import the major distinguishing characteristics of an @property.
  DeclContext *DC, *LexicalDC;
  DeclarationName Name;
  SourceLocation Loc;
  NamedDecl *ToD;
  if (Error Err = ImportDeclParts(D, DC, LexicalDC, Name, ToD, Loc))
    return std::move(Err);
  if (ToD)
    return ToD;

  // Check whether we have already imported this property.
  auto FoundDecls = Importer.findDeclsInToCtx(DC, Name);
  for (auto *FoundDecl : FoundDecls) {
    if (auto *FoundProp = dyn_cast<ObjCPropertyDecl>(FoundDecl)) {
      // Check property types.
      if (!Importer.IsStructurallyEquivalent(D->getType(),
                                             FoundProp->getType())) {
        Importer.ToDiag(Loc, diag::err_odr_objc_property_type_inconsistent)
          << Name << D->getType() << FoundProp->getType();
        Importer.ToDiag(FoundProp->getLocation(), diag::note_odr_value_here)
          << FoundProp->getType();

        return make_error<ImportError>(ImportError::NameConflict);
      }

      // FIXME: Check property attributes, getters, setters, etc.?

      // Consider these properties to be equivalent.
      Importer.MapImported(D, FoundProp);
      return FoundProp;
    }
  }

  QualType ToType;
  TypeSourceInfo *ToTypeSourceInfo;
  SourceLocation ToAtLoc, ToLParenLoc;
  if (auto Imp = importSeq(
      D->getType(), D->getTypeSourceInfo(), D->getAtLoc(), D->getLParenLoc()))
    std::tie(ToType, ToTypeSourceInfo, ToAtLoc, ToLParenLoc) = *Imp;
  else
    return Imp.takeError();

  // Create the new property.
  ObjCPropertyDecl *ToProperty;
  if (GetImportedOrCreateDecl(
          ToProperty, D, Importer.getToContext(), DC, Loc,
          Name.getAsIdentifierInfo(), ToAtLoc,
          ToLParenLoc, ToType,
          ToTypeSourceInfo, D->getPropertyImplementation()))
    return ToProperty;

  Selector ToGetterName, ToSetterName;
  SourceLocation ToGetterNameLoc, ToSetterNameLoc;
  ObjCMethodDecl *ToGetterMethodDecl, *ToSetterMethodDecl;
  ObjCIvarDecl *ToPropertyIvarDecl;
  if (auto Imp = importSeq(
      D->getGetterName(), D->getSetterName(),
      D->getGetterNameLoc(), D->getSetterNameLoc(),
      D->getGetterMethodDecl(), D->getSetterMethodDecl(),
      D->getPropertyIvarDecl()))
    std::tie(
        ToGetterName, ToSetterName,
        ToGetterNameLoc, ToSetterNameLoc,
        ToGetterMethodDecl, ToSetterMethodDecl,
        ToPropertyIvarDecl) = *Imp;
  else
    return Imp.takeError();

  ToProperty->setLexicalDeclContext(LexicalDC);
  LexicalDC->addDeclInternal(ToProperty);

  ToProperty->setPropertyAttributes(D->getPropertyAttributes());
  ToProperty->setPropertyAttributesAsWritten(
                                      D->getPropertyAttributesAsWritten());
  ToProperty->setGetterName(ToGetterName, ToGetterNameLoc);
  ToProperty->setSetterName(ToSetterName, ToSetterNameLoc);
  ToProperty->setGetterMethodDecl(ToGetterMethodDecl);
  ToProperty->setSetterMethodDecl(ToSetterMethodDecl);
  ToProperty->setPropertyIvarDecl(ToPropertyIvarDecl);
  return ToProperty;
}

ExpectedDecl
ASTNodeImporter::VisitObjCPropertyImplDecl(ObjCPropertyImplDecl *D) {
  ObjCPropertyDecl *Property;
  if (Error Err = importInto(Property, D->getPropertyDecl()))
    return std::move(Err);

  DeclContext *DC, *LexicalDC;
  if (Error Err = ImportDeclContext(D, DC, LexicalDC))
    return std::move(Err);

  auto *InImpl = cast<ObjCImplDecl>(LexicalDC);

  // Import the ivar (for an @synthesize).
  ObjCIvarDecl *Ivar = nullptr;
  if (Error Err = importInto(Ivar, D->getPropertyIvarDecl()))
    return std::move(Err);

  ObjCPropertyImplDecl *ToImpl
    = InImpl->FindPropertyImplDecl(Property->getIdentifier(),
                                   Property->getQueryKind());
  if (!ToImpl) {
    SourceLocation ToBeginLoc, ToLocation, ToPropertyIvarDeclLoc;
    if (auto Imp = importSeq(
        D->getBeginLoc(), D->getLocation(), D->getPropertyIvarDeclLoc()))
      std::tie(ToBeginLoc, ToLocation, ToPropertyIvarDeclLoc) = *Imp;
    else
      return Imp.takeError();

    if (GetImportedOrCreateDecl(ToImpl, D, Importer.getToContext(), DC,
                                ToBeginLoc,
                                ToLocation, Property,
                                D->getPropertyImplementation(), Ivar,
                                ToPropertyIvarDeclLoc))
      return ToImpl;

    ToImpl->setLexicalDeclContext(LexicalDC);
    LexicalDC->addDeclInternal(ToImpl);
  } else {
    // Check that we have the same kind of property implementation (@synthesize
    // vs. @dynamic).
    if (D->getPropertyImplementation() != ToImpl->getPropertyImplementation()) {
      Importer.ToDiag(ToImpl->getLocation(),
                      diag::err_odr_objc_property_impl_kind_inconsistent)
        << Property->getDeclName()
        << (ToImpl->getPropertyImplementation()
                                              == ObjCPropertyImplDecl::Dynamic);
      Importer.FromDiag(D->getLocation(),
                        diag::note_odr_objc_property_impl_kind)
        << D->getPropertyDecl()->getDeclName()
        << (D->getPropertyImplementation() == ObjCPropertyImplDecl::Dynamic);

      return make_error<ImportError>(ImportError::NameConflict);
    }

    // For @synthesize, check that we have the same
    if (D->getPropertyImplementation() == ObjCPropertyImplDecl::Synthesize &&
        Ivar != ToImpl->getPropertyIvarDecl()) {
      Importer.ToDiag(ToImpl->getPropertyIvarDeclLoc(),
                      diag::err_odr_objc_synthesize_ivar_inconsistent)
        << Property->getDeclName()
        << ToImpl->getPropertyIvarDecl()->getDeclName()
        << Ivar->getDeclName();
      Importer.FromDiag(D->getPropertyIvarDeclLoc(),
                        diag::note_odr_objc_synthesize_ivar_here)
        << D->getPropertyIvarDecl()->getDeclName();

      return make_error<ImportError>(ImportError::NameConflict);
    }

    // Merge the existing implementation with the new implementation.
    Importer.MapImported(D, ToImpl);
  }

  return ToImpl;
}

ExpectedDecl
ASTNodeImporter::VisitTemplateTypeParmDecl(TemplateTypeParmDecl *D) {
  // For template arguments, we adopt the translation unit as our declaration
  // context. This context will be fixed when the actual template declaration
  // is created.

  // FIXME: Import default argument.

  ExpectedSLoc BeginLocOrErr = import(D->getBeginLoc());
  if (!BeginLocOrErr)
    return BeginLocOrErr.takeError();

  ExpectedSLoc LocationOrErr = import(D->getLocation());
  if (!LocationOrErr)
    return LocationOrErr.takeError();

  TemplateTypeParmDecl *ToD = nullptr;
  (void)GetImportedOrCreateDecl(
      ToD, D, Importer.getToContext(),
      Importer.getToContext().getTranslationUnitDecl(),
      *BeginLocOrErr, *LocationOrErr,
      D->getDepth(), D->getIndex(), Importer.Import(D->getIdentifier()),
      D->wasDeclaredWithTypename(), D->isParameterPack());
  return ToD;
}

ExpectedDecl
ASTNodeImporter::VisitNonTypeTemplateParmDecl(NonTypeTemplateParmDecl *D) {
  DeclarationName ToDeclName;
  SourceLocation ToLocation, ToInnerLocStart;
  QualType ToType;
  TypeSourceInfo *ToTypeSourceInfo;
  if (auto Imp = importSeq(
      D->getDeclName(), D->getLocation(), D->getType(), D->getTypeSourceInfo(),
      D->getInnerLocStart()))
    std::tie(
        ToDeclName, ToLocation, ToType, ToTypeSourceInfo,
        ToInnerLocStart) = *Imp;
  else
    return Imp.takeError();

  // FIXME: Import default argument.

  NonTypeTemplateParmDecl *ToD = nullptr;
  (void)GetImportedOrCreateDecl(
      ToD, D, Importer.getToContext(),
      Importer.getToContext().getTranslationUnitDecl(),
      ToInnerLocStart, ToLocation, D->getDepth(),
      D->getPosition(), ToDeclName.getAsIdentifierInfo(), ToType,
      D->isParameterPack(), ToTypeSourceInfo);
  return ToD;
}

ExpectedDecl
ASTNodeImporter::VisitTemplateTemplateParmDecl(TemplateTemplateParmDecl *D) {
  // Import the name of this declaration.
  auto NameOrErr = import(D->getDeclName());
  if (!NameOrErr)
    return NameOrErr.takeError();

  // Import the location of this declaration.
  ExpectedSLoc LocationOrErr = import(D->getLocation());
  if (!LocationOrErr)
    return LocationOrErr.takeError();

  // Import template parameters.
  auto TemplateParamsOrErr = ImportTemplateParameterList(
      D->getTemplateParameters());
  if (!TemplateParamsOrErr)
    return TemplateParamsOrErr.takeError();

  // FIXME: Import default argument.

  TemplateTemplateParmDecl *ToD = nullptr;
  (void)GetImportedOrCreateDecl(
      ToD, D, Importer.getToContext(),
      Importer.getToContext().getTranslationUnitDecl(), *LocationOrErr,
      D->getDepth(), D->getPosition(), D->isParameterPack(),
      (*NameOrErr).getAsIdentifierInfo(),
      *TemplateParamsOrErr);
  return ToD;
}

// Returns the definition for a (forward) declaration of a ClassTemplateDecl, if
// it has any definition in the redecl chain.
static ClassTemplateDecl *getDefinition(ClassTemplateDecl *D) {
  CXXRecordDecl *ToTemplatedDef = D->getTemplatedDecl()->getDefinition();
  if (!ToTemplatedDef)
    return nullptr;
  ClassTemplateDecl *TemplateWithDef =
      ToTemplatedDef->getDescribedClassTemplate();
  return TemplateWithDef;
}

ExpectedDecl ASTNodeImporter::VisitClassTemplateDecl(ClassTemplateDecl *D) {
  bool IsFriend = D->getFriendObjectKind() != Decl::FOK_None;

  // If this template has a definition in the translation unit we're coming
  // from, but this particular declaration is not that definition, import the
  // definition and map to that.
  ClassTemplateDecl *Definition = getDefinition(D);
  if (Definition && Definition != D && !IsFriend) {
    if (ExpectedDecl ImportedDefOrErr = import(Definition))
      return Importer.MapImported(D, *ImportedDefOrErr);
    else
      return ImportedDefOrErr.takeError();
  }

  // Import the major distinguishing characteristics of this class template.
  DeclContext *DC, *LexicalDC;
  DeclarationName Name;
  SourceLocation Loc;
  NamedDecl *ToD;
  if (Error Err = ImportDeclParts(D, DC, LexicalDC, Name, ToD, Loc))
    return std::move(Err);
  if (ToD)
    return ToD;

  ClassTemplateDecl *FoundByLookup = nullptr;

  // We may already have a template of the same name; try to find and match it.
  if (!DC->isFunctionOrMethod()) {
    SmallVector<NamedDecl *, 4> ConflictingDecls;
    auto FoundDecls = Importer.findDeclsInToCtx(DC, Name);
    for (auto *FoundDecl : FoundDecls) {
      if (!FoundDecl->isInIdentifierNamespace(Decl::IDNS_Ordinary |
                                              Decl::IDNS_TagFriend))
        continue;

      Decl *Found = FoundDecl;
      auto *FoundTemplate = dyn_cast<ClassTemplateDecl>(Found);
      if (FoundTemplate) {

        if (IsStructuralMatch(D, FoundTemplate)) {
          ClassTemplateDecl *TemplateWithDef = getDefinition(FoundTemplate);
          if (D->isThisDeclarationADefinition() && TemplateWithDef) {
            return Importer.MapImported(D, TemplateWithDef);
          }
          FoundByLookup = FoundTemplate;
          break;
        }
      }

      ConflictingDecls.push_back(FoundDecl);
    }

    if (!ConflictingDecls.empty()) {
      Name = Importer.HandleNameConflict(Name, DC, Decl::IDNS_Ordinary,
                                         ConflictingDecls.data(),
                                         ConflictingDecls.size());
    }

    if (!Name)
      return make_error<ImportError>(ImportError::NameConflict);
  }

  CXXRecordDecl *FromTemplated = D->getTemplatedDecl();

  // Create the declaration that is being templated.
  CXXRecordDecl *ToTemplated;
  if (Error Err = importInto(ToTemplated, FromTemplated))
    return std::move(Err);

  // Create the class template declaration itself.
  auto TemplateParamsOrErr = ImportTemplateParameterList(
      D->getTemplateParameters());
  if (!TemplateParamsOrErr)
    return TemplateParamsOrErr.takeError();

  ClassTemplateDecl *D2;
  if (GetImportedOrCreateDecl(D2, D, Importer.getToContext(), DC, Loc, Name,
                              *TemplateParamsOrErr, ToTemplated))
    return D2;

  ToTemplated->setDescribedClassTemplate(D2);

  D2->setAccess(D->getAccess());
  D2->setLexicalDeclContext(LexicalDC);

  if (D->getDeclContext()->containsDeclAndLoad(D))
    DC->addDeclInternal(D2);
  if (DC != LexicalDC && D->getLexicalDeclContext()->containsDeclAndLoad(D))
    LexicalDC->addDeclInternal(D2);

  if (FoundByLookup) {
    auto *Recent =
        const_cast<ClassTemplateDecl *>(FoundByLookup->getMostRecentDecl());

    // It is possible that during the import of the class template definition
    // we start the import of a fwd friend decl of the very same class template
    // and we add the fwd friend decl to the lookup table. But the ToTemplated
    // had been created earlier and by that time the lookup could not find
    // anything existing, so it has no previous decl. Later, (still during the
    // import of the fwd friend decl) we start to import the definition again
    // and this time the lookup finds the previous fwd friend class template.
    // In this case we must set up the previous decl for the templated decl.
    if (!ToTemplated->getPreviousDecl()) {
      CXXRecordDecl *PrevTemplated =
          FoundByLookup->getTemplatedDecl()->getMostRecentDecl();
      if (ToTemplated != PrevTemplated)
        ToTemplated->setPreviousDecl(PrevTemplated);
    }

    D2->setPreviousDecl(Recent);
  }

  if (LexicalDC != DC && IsFriend)
    DC->makeDeclVisibleInContext(D2);

  if (FromTemplated->isCompleteDefinition() &&
      !ToTemplated->isCompleteDefinition()) {
    // FIXME: Import definition!
  }

  return D2;
}

ExpectedDecl ASTNodeImporter::VisitClassTemplateSpecializationDecl(
                                          ClassTemplateSpecializationDecl *D) {
  // If this record has a definition in the translation unit we're coming from,
  // but this particular declaration is not that definition, import the
  // definition and map to that.
  TagDecl *Definition = D->getDefinition();
  if (Definition && Definition != D) {
    if (ExpectedDecl ImportedDefOrErr = import(Definition))
      return Importer.MapImported(D, *ImportedDefOrErr);
    else
      return ImportedDefOrErr.takeError();
  }

  ClassTemplateDecl *ClassTemplate;
  if (Error Err = importInto(ClassTemplate, D->getSpecializedTemplate()))
    return std::move(Err);

  // Import the context of this declaration.
  DeclContext *DC, *LexicalDC;
  if (Error Err = ImportDeclContext(D, DC, LexicalDC))
    return std::move(Err);

  // Import template arguments.
  SmallVector<TemplateArgument, 2> TemplateArgs;
  if (Error Err = ImportTemplateArguments(
      D->getTemplateArgs().data(), D->getTemplateArgs().size(), TemplateArgs))
    return std::move(Err);

  // Try to find an existing specialization with these template arguments.
  void *InsertPos = nullptr;
  ClassTemplateSpecializationDecl *D2 = nullptr;
  ClassTemplatePartialSpecializationDecl *PartialSpec =
            dyn_cast<ClassTemplatePartialSpecializationDecl>(D);
  if (PartialSpec)
    D2 = ClassTemplate->findPartialSpecialization(TemplateArgs, InsertPos);
  else
    D2 = ClassTemplate->findSpecialization(TemplateArgs, InsertPos);
  ClassTemplateSpecializationDecl * const PrevDecl = D2;
  RecordDecl *FoundDef = D2 ? D2->getDefinition() : nullptr;
  if (FoundDef) {
    if (!D->isCompleteDefinition()) {
      // The "From" translation unit only had a forward declaration; call it
      // the same declaration.
      // TODO Handle the redecl chain properly!
      return Importer.MapImported(D, FoundDef);
    }

    if (IsStructuralMatch(D, FoundDef)) {

      Importer.MapImported(D, FoundDef);

      // Import those those default field initializers which have been
      // instantiated in the "From" context, but not in the "To" context.
      for (auto *FromField : D->fields()) {
        auto ToOrErr = import(FromField);
        if (!ToOrErr)
          // FIXME: return the error?
          consumeError(ToOrErr.takeError());
      }

      // Import those methods which have been instantiated in the
      // "From" context, but not in the "To" context.
      for (CXXMethodDecl *FromM : D->methods()) {
        auto ToOrErr = import(FromM);
        if (!ToOrErr)
          // FIXME: return the error?
          consumeError(ToOrErr.takeError());
      }

      // TODO Import instantiated default arguments.
      // TODO Import instantiated exception specifications.
      //
      // Generally, ASTCommon.h/DeclUpdateKind enum gives a very good hint what
      // else could be fused during an AST merge.

      return FoundDef;
    }
  } else { // We either couldn't find any previous specialization in the "To"
           // context,  or we found one but without definition.  Let's create a
           // new specialization and register that at the class template.

    // Import the location of this declaration.
    ExpectedSLoc BeginLocOrErr = import(D->getBeginLoc());
    if (!BeginLocOrErr)
      return BeginLocOrErr.takeError();
    ExpectedSLoc IdLocOrErr = import(D->getLocation());
    if (!IdLocOrErr)
      return IdLocOrErr.takeError();

    if (PartialSpec) {
      // Import TemplateArgumentListInfo.
      TemplateArgumentListInfo ToTAInfo;
      const auto &ASTTemplateArgs = *PartialSpec->getTemplateArgsAsWritten();
      if (Error Err = ImportTemplateArgumentListInfo(ASTTemplateArgs, ToTAInfo))
        return std::move(Err);

      QualType CanonInjType;
      if (Error Err = importInto(
          CanonInjType, PartialSpec->getInjectedSpecializationType()))
        return std::move(Err);
      CanonInjType = CanonInjType.getCanonicalType();

      auto ToTPListOrErr = ImportTemplateParameterList(
          PartialSpec->getTemplateParameters());
      if (!ToTPListOrErr)
        return ToTPListOrErr.takeError();

      if (GetImportedOrCreateDecl<ClassTemplatePartialSpecializationDecl>(
              D2, D, Importer.getToContext(), D->getTagKind(), DC,
              *BeginLocOrErr, *IdLocOrErr, *ToTPListOrErr, ClassTemplate,
              llvm::makeArrayRef(TemplateArgs.data(), TemplateArgs.size()),
              ToTAInfo, CanonInjType,
              cast_or_null<ClassTemplatePartialSpecializationDecl>(PrevDecl)))
        return D2;

      // Update InsertPos, because preceding import calls may have invalidated
      // it by adding new specializations.
      if (!ClassTemplate->findPartialSpecialization(TemplateArgs, InsertPos))
        // Add this partial specialization to the class template.
        ClassTemplate->AddPartialSpecialization(
            cast<ClassTemplatePartialSpecializationDecl>(D2), InsertPos);

    } else { // Not a partial specialization.
      if (GetImportedOrCreateDecl(
              D2, D, Importer.getToContext(), D->getTagKind(), DC,
              *BeginLocOrErr, *IdLocOrErr, ClassTemplate, TemplateArgs,
              PrevDecl))
        return D2;

      // Update InsertPos, because preceding import calls may have invalidated
      // it by adding new specializations.
      if (!ClassTemplate->findSpecialization(TemplateArgs, InsertPos))
        // Add this specialization to the class template.
        ClassTemplate->AddSpecialization(D2, InsertPos);
    }

    D2->setSpecializationKind(D->getSpecializationKind());

    // Import the qualifier, if any.
    if (auto LocOrErr = import(D->getQualifierLoc()))
      D2->setQualifierInfo(*LocOrErr);
    else
      return LocOrErr.takeError();

    if (auto *TSI = D->getTypeAsWritten()) {
      if (auto TInfoOrErr = import(TSI))
        D2->setTypeAsWritten(*TInfoOrErr);
      else
        return TInfoOrErr.takeError();

      if (auto LocOrErr = import(D->getTemplateKeywordLoc()))
        D2->setTemplateKeywordLoc(*LocOrErr);
      else
        return LocOrErr.takeError();

      if (auto LocOrErr = import(D->getExternLoc()))
        D2->setExternLoc(*LocOrErr);
      else
        return LocOrErr.takeError();
    }

    if (D->getPointOfInstantiation().isValid()) {
      if (auto POIOrErr = import(D->getPointOfInstantiation()))
        D2->setPointOfInstantiation(*POIOrErr);
      else
        return POIOrErr.takeError();
    }

    D2->setTemplateSpecializationKind(D->getTemplateSpecializationKind());

    // Set the context of this specialization/instantiation.
    D2->setLexicalDeclContext(LexicalDC);

    // Add to the DC only if it was an explicit specialization/instantiation.
    if (D2->isExplicitInstantiationOrSpecialization()) {
      LexicalDC->addDeclInternal(D2);
    }
  }
  if (D->isCompleteDefinition())
    if (Error Err = ImportDefinition(D, D2))
      return std::move(Err);

  return D2;
}

ExpectedDecl ASTNodeImporter::VisitVarTemplateDecl(VarTemplateDecl *D) {
  // If this variable has a definition in the translation unit we're coming
  // from,
  // but this particular declaration is not that definition, import the
  // definition and map to that.
  auto *Definition =
      cast_or_null<VarDecl>(D->getTemplatedDecl()->getDefinition());
  if (Definition && Definition != D->getTemplatedDecl()) {
    if (ExpectedDecl ImportedDefOrErr = import(
        Definition->getDescribedVarTemplate()))
      return Importer.MapImported(D, *ImportedDefOrErr);
    else
      return ImportedDefOrErr.takeError();
  }

  // Import the major distinguishing characteristics of this variable template.
  DeclContext *DC, *LexicalDC;
  DeclarationName Name;
  SourceLocation Loc;
  NamedDecl *ToD;
  if (Error Err = ImportDeclParts(D, DC, LexicalDC, Name, ToD, Loc))
    return std::move(Err);
  if (ToD)
    return ToD;

  // We may already have a template of the same name; try to find and match it.
  assert(!DC->isFunctionOrMethod() &&
         "Variable templates cannot be declared at function scope");
  SmallVector<NamedDecl *, 4> ConflictingDecls;
  auto FoundDecls = Importer.findDeclsInToCtx(DC, Name);
  for (auto *FoundDecl : FoundDecls) {
    if (!FoundDecl->isInIdentifierNamespace(Decl::IDNS_Ordinary))
      continue;

    Decl *Found = FoundDecl;
    if (VarTemplateDecl *FoundTemplate = dyn_cast<VarTemplateDecl>(Found)) {
      if (IsStructuralMatch(D, FoundTemplate)) {
        // The variable templates structurally match; call it the same template.
        Importer.MapImported(D->getTemplatedDecl(),
                             FoundTemplate->getTemplatedDecl());
        return Importer.MapImported(D, FoundTemplate);
      }
    }

    ConflictingDecls.push_back(FoundDecl);
  }

  if (!ConflictingDecls.empty()) {
    Name = Importer.HandleNameConflict(Name, DC, Decl::IDNS_Ordinary,
                                       ConflictingDecls.data(),
                                       ConflictingDecls.size());
  }

  if (!Name)
    // FIXME: Is it possible to get other error than name conflict?
    // (Put this `if` into the previous `if`?)
    return make_error<ImportError>(ImportError::NameConflict);

  VarDecl *DTemplated = D->getTemplatedDecl();

  // Import the type.
  // FIXME: Value not used?
  ExpectedType TypeOrErr = import(DTemplated->getType());
  if (!TypeOrErr)
    return TypeOrErr.takeError();

  // Create the declaration that is being templated.
  VarDecl *ToTemplated;
  if (Error Err = importInto(ToTemplated, DTemplated))
    return std::move(Err);

  // Create the variable template declaration itself.
  auto TemplateParamsOrErr = ImportTemplateParameterList(
      D->getTemplateParameters());
  if (!TemplateParamsOrErr)
    return TemplateParamsOrErr.takeError();

  VarTemplateDecl *ToVarTD;
  if (GetImportedOrCreateDecl(ToVarTD, D, Importer.getToContext(), DC, Loc,
                              Name, *TemplateParamsOrErr, ToTemplated))
    return ToVarTD;

  ToTemplated->setDescribedVarTemplate(ToVarTD);

  ToVarTD->setAccess(D->getAccess());
  ToVarTD->setLexicalDeclContext(LexicalDC);
  LexicalDC->addDeclInternal(ToVarTD);

  if (DTemplated->isThisDeclarationADefinition() &&
      !ToTemplated->isThisDeclarationADefinition()) {
    // FIXME: Import definition!
  }

  return ToVarTD;
}

ExpectedDecl ASTNodeImporter::VisitVarTemplateSpecializationDecl(
    VarTemplateSpecializationDecl *D) {
  // If this record has a definition in the translation unit we're coming from,
  // but this particular declaration is not that definition, import the
  // definition and map to that.
  VarDecl *Definition = D->getDefinition();
  if (Definition && Definition != D) {
    if (ExpectedDecl ImportedDefOrErr = import(Definition))
      return Importer.MapImported(D, *ImportedDefOrErr);
    else
      return ImportedDefOrErr.takeError();
  }

  VarTemplateDecl *VarTemplate;
  if (Error Err = importInto(VarTemplate, D->getSpecializedTemplate()))
    return std::move(Err);

  // Import the context of this declaration.
  DeclContext *DC, *LexicalDC;
  if (Error Err = ImportDeclContext(D, DC, LexicalDC))
    return std::move(Err);

  // Import the location of this declaration.
  ExpectedSLoc BeginLocOrErr = import(D->getBeginLoc());
  if (!BeginLocOrErr)
    return BeginLocOrErr.takeError();

  auto IdLocOrErr = import(D->getLocation());
  if (!IdLocOrErr)
    return IdLocOrErr.takeError();

  // Import template arguments.
  SmallVector<TemplateArgument, 2> TemplateArgs;
  if (Error Err = ImportTemplateArguments(
      D->getTemplateArgs().data(), D->getTemplateArgs().size(), TemplateArgs))
    return std::move(Err);

  // Try to find an existing specialization with these template arguments.
  void *InsertPos = nullptr;
  VarTemplateSpecializationDecl *D2 = VarTemplate->findSpecialization(
      TemplateArgs, InsertPos);
  if (D2) {
    // We already have a variable template specialization with these template
    // arguments.

    // FIXME: Check for specialization vs. instantiation errors.

    if (VarDecl *FoundDef = D2->getDefinition()) {
      if (!D->isThisDeclarationADefinition() ||
          IsStructuralMatch(D, FoundDef)) {
        // The record types structurally match, or the "from" translation
        // unit only had a forward declaration anyway; call it the same
        // variable.
        return Importer.MapImported(D, FoundDef);
      }
    }
  } else {
    // Import the type.
    QualType T;
    if (Error Err = importInto(T, D->getType()))
      return std::move(Err);

    auto TInfoOrErr = import(D->getTypeSourceInfo());
    if (!TInfoOrErr)
      return TInfoOrErr.takeError();

    TemplateArgumentListInfo ToTAInfo;
    if (Error Err = ImportTemplateArgumentListInfo(
        D->getTemplateArgsInfo(), ToTAInfo))
      return std::move(Err);

    using PartVarSpecDecl = VarTemplatePartialSpecializationDecl;
    // Create a new specialization.
    if (auto *FromPartial = dyn_cast<PartVarSpecDecl>(D)) {
      // Import TemplateArgumentListInfo
      TemplateArgumentListInfo ArgInfos;
      const auto *FromTAArgsAsWritten = FromPartial->getTemplateArgsAsWritten();
      // NOTE: FromTAArgsAsWritten and template parameter list are non-null.
      if (Error Err = ImportTemplateArgumentListInfo(
          *FromTAArgsAsWritten, ArgInfos))
        return std::move(Err);

      auto ToTPListOrErr = ImportTemplateParameterList(
          FromPartial->getTemplateParameters());
      if (!ToTPListOrErr)
        return ToTPListOrErr.takeError();

      PartVarSpecDecl *ToPartial;
      if (GetImportedOrCreateDecl(ToPartial, D, Importer.getToContext(), DC,
                                  *BeginLocOrErr, *IdLocOrErr, *ToTPListOrErr,
                                  VarTemplate, T, *TInfoOrErr,
                                  D->getStorageClass(), TemplateArgs, ArgInfos))
        return ToPartial;

      if (Expected<PartVarSpecDecl *> ToInstOrErr = import(
          FromPartial->getInstantiatedFromMember()))
        ToPartial->setInstantiatedFromMember(*ToInstOrErr);
      else
        return ToInstOrErr.takeError();

      if (FromPartial->isMemberSpecialization())
        ToPartial->setMemberSpecialization();

      D2 = ToPartial;

    } else { // Full specialization
      if (GetImportedOrCreateDecl(D2, D, Importer.getToContext(), DC,
                                  *BeginLocOrErr, *IdLocOrErr, VarTemplate,
                                  T, *TInfoOrErr,
                                  D->getStorageClass(), TemplateArgs))
        return D2;
    }

    if (D->getPointOfInstantiation().isValid()) {
      if (ExpectedSLoc POIOrErr = import(D->getPointOfInstantiation()))
        D2->setPointOfInstantiation(*POIOrErr);
      else
        return POIOrErr.takeError();
    }

    D2->setSpecializationKind(D->getSpecializationKind());
    D2->setTemplateArgsInfo(ToTAInfo);

    // Add this specialization to the class template.
    VarTemplate->AddSpecialization(D2, InsertPos);

    // Import the qualifier, if any.
    if (auto LocOrErr = import(D->getQualifierLoc()))
      D2->setQualifierInfo(*LocOrErr);
    else
      return LocOrErr.takeError();

    if (D->isConstexpr())
      D2->setConstexpr(true);

    // Add the specialization to this context.
    D2->setLexicalDeclContext(LexicalDC);
    LexicalDC->addDeclInternal(D2);

    D2->setAccess(D->getAccess());
  }

  if (Error Err = ImportInitializer(D, D2))
    return std::move(Err);

  return D2;
}

ExpectedDecl
ASTNodeImporter::VisitFunctionTemplateDecl(FunctionTemplateDecl *D) {
  DeclContext *DC, *LexicalDC;
  DeclarationName Name;
  SourceLocation Loc;
  NamedDecl *ToD;

  if (Error Err = ImportDeclParts(D, DC, LexicalDC, Name, ToD, Loc))
    return std::move(Err);

  if (ToD)
    return ToD;

  // Try to find a function in our own ("to") context with the same name, same
  // type, and in the same context as the function we're importing.
  if (!LexicalDC->isFunctionOrMethod()) {
    unsigned IDNS = Decl::IDNS_Ordinary;
    auto FoundDecls = Importer.findDeclsInToCtx(DC, Name);
    for (auto *FoundDecl : FoundDecls) {
      if (!FoundDecl->isInIdentifierNamespace(IDNS))
        continue;

      if (auto *FoundFunction =
          dyn_cast<FunctionTemplateDecl>(FoundDecl)) {
        if (FoundFunction->hasExternalFormalLinkage() &&
            D->hasExternalFormalLinkage()) {
          if (IsStructuralMatch(D, FoundFunction)) {
            Importer.MapImported(D, FoundFunction);
            // FIXME: Actually try to merge the body and other attributes.
            return FoundFunction;
          }
        }
      }
      // TODO: handle conflicting names
    }
  }

  auto ParamsOrErr = ImportTemplateParameterList(
      D->getTemplateParameters());
  if (!ParamsOrErr)
    return ParamsOrErr.takeError();

  FunctionDecl *TemplatedFD;
  if (Error Err = importInto(TemplatedFD, D->getTemplatedDecl()))
    return std::move(Err);

  FunctionTemplateDecl *ToFunc;
  if (GetImportedOrCreateDecl(ToFunc, D, Importer.getToContext(), DC, Loc, Name,
                              *ParamsOrErr, TemplatedFD))
    return ToFunc;

  TemplatedFD->setDescribedFunctionTemplate(ToFunc);
  ToFunc->setAccess(D->getAccess());
  ToFunc->setLexicalDeclContext(LexicalDC);

  LexicalDC->addDeclInternal(ToFunc);
  return ToFunc;
}

//----------------------------------------------------------------------------
// Import Statements
//----------------------------------------------------------------------------

ExpectedStmt ASTNodeImporter::VisitStmt(Stmt *S) {
  Importer.FromDiag(S->getBeginLoc(), diag::err_unsupported_ast_node)
      << S->getStmtClassName();
  return make_error<ImportError>(ImportError::UnsupportedConstruct);
}


ExpectedStmt ASTNodeImporter::VisitGCCAsmStmt(GCCAsmStmt *S) {
  SmallVector<IdentifierInfo *, 4> Names;
  for (unsigned I = 0, E = S->getNumOutputs(); I != E; I++) {
    IdentifierInfo *ToII = Importer.Import(S->getOutputIdentifier(I));
    // ToII is nullptr when no symbolic name is given for output operand
    // see ParseStmtAsm::ParseAsmOperandsOpt
    Names.push_back(ToII);
  }

  for (unsigned I = 0, E = S->getNumInputs(); I != E; I++) {
    IdentifierInfo *ToII = Importer.Import(S->getInputIdentifier(I));
    // ToII is nullptr when no symbolic name is given for input operand
    // see ParseStmtAsm::ParseAsmOperandsOpt
    Names.push_back(ToII);
  }

  SmallVector<StringLiteral *, 4> Clobbers;
  for (unsigned I = 0, E = S->getNumClobbers(); I != E; I++) {
    if (auto ClobberOrErr = import(S->getClobberStringLiteral(I)))
      Clobbers.push_back(*ClobberOrErr);
    else
      return ClobberOrErr.takeError();

  }

  SmallVector<StringLiteral *, 4> Constraints;
  for (unsigned I = 0, E = S->getNumOutputs(); I != E; I++) {
    if (auto OutputOrErr = import(S->getOutputConstraintLiteral(I)))
      Constraints.push_back(*OutputOrErr);
    else
      return OutputOrErr.takeError();
  }

  for (unsigned I = 0, E = S->getNumInputs(); I != E; I++) {
    if (auto InputOrErr = import(S->getInputConstraintLiteral(I)))
      Constraints.push_back(*InputOrErr);
    else
      return InputOrErr.takeError();
  }

  SmallVector<Expr *, 4> Exprs(S->getNumOutputs() + S->getNumInputs());
  if (Error Err = ImportContainerChecked(S->outputs(), Exprs))
    return std::move(Err);

  if (Error Err = ImportArrayChecked(
      S->inputs(), Exprs.begin() + S->getNumOutputs()))
    return std::move(Err);

  ExpectedSLoc AsmLocOrErr = import(S->getAsmLoc());
  if (!AsmLocOrErr)
    return AsmLocOrErr.takeError();
  auto AsmStrOrErr = import(S->getAsmString());
  if (!AsmStrOrErr)
    return AsmStrOrErr.takeError();
  ExpectedSLoc RParenLocOrErr = import(S->getRParenLoc());
  if (!RParenLocOrErr)
    return RParenLocOrErr.takeError();

  return new (Importer.getToContext()) GCCAsmStmt(
      Importer.getToContext(),
      *AsmLocOrErr,
      S->isSimple(),
      S->isVolatile(),
      S->getNumOutputs(),
      S->getNumInputs(),
      Names.data(),
      Constraints.data(),
      Exprs.data(),
      *AsmStrOrErr,
      S->getNumClobbers(),
      Clobbers.data(),
      *RParenLocOrErr);
}

ExpectedStmt ASTNodeImporter::VisitDeclStmt(DeclStmt *S) {
  auto Imp = importSeq(S->getDeclGroup(), S->getBeginLoc(), S->getEndLoc());
  if (!Imp)
    return Imp.takeError();

  DeclGroupRef ToDG;
  SourceLocation ToBeginLoc, ToEndLoc;
  std::tie(ToDG, ToBeginLoc, ToEndLoc) = *Imp;

  return new (Importer.getToContext()) DeclStmt(ToDG, ToBeginLoc, ToEndLoc);
}

ExpectedStmt ASTNodeImporter::VisitNullStmt(NullStmt *S) {
  ExpectedSLoc ToSemiLocOrErr = import(S->getSemiLoc());
  if (!ToSemiLocOrErr)
    return ToSemiLocOrErr.takeError();
  return new (Importer.getToContext()) NullStmt(
      *ToSemiLocOrErr, S->hasLeadingEmptyMacro());
}

ExpectedStmt ASTNodeImporter::VisitCompoundStmt(CompoundStmt *S) {
  SmallVector<Stmt *, 8> ToStmts(S->size());

  if (Error Err = ImportContainerChecked(S->body(), ToStmts))
    return std::move(Err);

  ExpectedSLoc ToLBracLocOrErr = import(S->getLBracLoc());
  if (!ToLBracLocOrErr)
    return ToLBracLocOrErr.takeError();

  ExpectedSLoc ToRBracLocOrErr = import(S->getRBracLoc());
  if (!ToRBracLocOrErr)
    return ToRBracLocOrErr.takeError();

  return CompoundStmt::Create(
      Importer.getToContext(), ToStmts,
      *ToLBracLocOrErr, *ToRBracLocOrErr);
}

ExpectedStmt ASTNodeImporter::VisitCaseStmt(CaseStmt *S) {
  auto Imp = importSeq(
      S->getLHS(), S->getRHS(), S->getSubStmt(), S->getCaseLoc(),
      S->getEllipsisLoc(), S->getColonLoc());
  if (!Imp)
    return Imp.takeError();

  Expr *ToLHS, *ToRHS;
  Stmt *ToSubStmt;
  SourceLocation ToCaseLoc, ToEllipsisLoc, ToColonLoc;
  std::tie(ToLHS, ToRHS, ToSubStmt, ToCaseLoc, ToEllipsisLoc, ToColonLoc) =
      *Imp;

  auto *ToStmt = CaseStmt::Create(Importer.getToContext(), ToLHS, ToRHS,
                                  ToCaseLoc, ToEllipsisLoc, ToColonLoc);
  ToStmt->setSubStmt(ToSubStmt);

  return ToStmt;
}

ExpectedStmt ASTNodeImporter::VisitDefaultStmt(DefaultStmt *S) {
  auto Imp = importSeq(S->getDefaultLoc(), S->getColonLoc(), S->getSubStmt());
  if (!Imp)
    return Imp.takeError();

  SourceLocation ToDefaultLoc, ToColonLoc;
  Stmt *ToSubStmt;
  std::tie(ToDefaultLoc, ToColonLoc, ToSubStmt) = *Imp;

  return new (Importer.getToContext()) DefaultStmt(
    ToDefaultLoc, ToColonLoc, ToSubStmt);
}

ExpectedStmt ASTNodeImporter::VisitLabelStmt(LabelStmt *S) {
  auto Imp = importSeq(S->getIdentLoc(), S->getDecl(), S->getSubStmt());
  if (!Imp)
    return Imp.takeError();

  SourceLocation ToIdentLoc;
  LabelDecl *ToLabelDecl;
  Stmt *ToSubStmt;
  std::tie(ToIdentLoc, ToLabelDecl, ToSubStmt) = *Imp;

  return new (Importer.getToContext()) LabelStmt(
      ToIdentLoc, ToLabelDecl, ToSubStmt);
}

ExpectedStmt ASTNodeImporter::VisitAttributedStmt(AttributedStmt *S) {
  ExpectedSLoc ToAttrLocOrErr = import(S->getAttrLoc());
  if (!ToAttrLocOrErr)
    return ToAttrLocOrErr.takeError();
  ArrayRef<const Attr*> FromAttrs(S->getAttrs());
  SmallVector<const Attr *, 1> ToAttrs(FromAttrs.size());
  if (Error Err = ImportContainerChecked(FromAttrs, ToAttrs))
    return std::move(Err);
  ExpectedStmt ToSubStmtOrErr = import(S->getSubStmt());
  if (!ToSubStmtOrErr)
    return ToSubStmtOrErr.takeError();

  return AttributedStmt::Create(
      Importer.getToContext(), *ToAttrLocOrErr, ToAttrs, *ToSubStmtOrErr);
}

ExpectedStmt ASTNodeImporter::VisitIfStmt(IfStmt *S) {
  auto Imp = importSeq(
      S->getIfLoc(), S->getInit(), S->getConditionVariable(), S->getCond(),
      S->getThen(), S->getElseLoc(), S->getElse());
  if (!Imp)
    return Imp.takeError();

  SourceLocation ToIfLoc, ToElseLoc;
  Stmt *ToInit, *ToThen, *ToElse;
  VarDecl *ToConditionVariable;
  Expr *ToCond;
  std::tie(
      ToIfLoc, ToInit, ToConditionVariable, ToCond, ToThen, ToElseLoc, ToElse) =
          *Imp;

  return IfStmt::Create(Importer.getToContext(), ToIfLoc, S->isConstexpr(),
                        ToInit, ToConditionVariable, ToCond, ToThen, ToElseLoc,
                        ToElse);
}

ExpectedStmt ASTNodeImporter::VisitSwitchStmt(SwitchStmt *S) {
  auto Imp = importSeq(
      S->getInit(), S->getConditionVariable(), S->getCond(),
      S->getBody(), S->getSwitchLoc());
  if (!Imp)
    return Imp.takeError();

  Stmt *ToInit, *ToBody;
  VarDecl *ToConditionVariable;
  Expr *ToCond;
  SourceLocation ToSwitchLoc;
  std::tie(ToInit, ToConditionVariable, ToCond, ToBody, ToSwitchLoc) = *Imp;

  auto *ToStmt = SwitchStmt::Create(Importer.getToContext(), ToInit,
                                    ToConditionVariable, ToCond);
  ToStmt->setBody(ToBody);
  ToStmt->setSwitchLoc(ToSwitchLoc);

  // Now we have to re-chain the cases.
  SwitchCase *LastChainedSwitchCase = nullptr;
  for (SwitchCase *SC = S->getSwitchCaseList(); SC != nullptr;
       SC = SC->getNextSwitchCase()) {
    Expected<SwitchCase *> ToSCOrErr = import(SC);
    if (!ToSCOrErr)
      return ToSCOrErr.takeError();
    if (LastChainedSwitchCase)
      LastChainedSwitchCase->setNextSwitchCase(*ToSCOrErr);
    else
      ToStmt->setSwitchCaseList(*ToSCOrErr);
    LastChainedSwitchCase = *ToSCOrErr;
  }

  return ToStmt;
}

ExpectedStmt ASTNodeImporter::VisitWhileStmt(WhileStmt *S) {
  auto Imp = importSeq(
      S->getConditionVar