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/ASTContext.h"
#include "clang/AST/ASTDiagnostic.h"
#include "clang/AST/ASTImporterSharedState.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/Builtins.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/STLExtras.h"
#include "llvm/ADT/ScopeExit.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 <optional>
#include <type_traits>
#include <utility>
 
namespace clang {
 
  using llvm::make_error;
  using llvm::Error;
  using llvm::Expected;
  using ExpectedTypePtr = llvm::Expected<const Type *>;
  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>;
  using ExpectedName = llvm::Expected<DeclarationName>;
 
  std::string ASTImportError::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 ASTImportError::log(raw_ostream &OS) const { OS << toString(); }
 
  std::error_code ASTImportError::convertToErrorCode() const {
    llvm_unreachable("Function not implemented.");
  }
 
  char ASTImportError::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();
  }
 
  /// How to handle import errors that occur when import of a child declaration
  /// of a DeclContext fails.
  class ChildErrorHandlingStrategy {
    /// This context is imported (in the 'from' domain).
    /// It is nullptr if a non-DeclContext is imported.
    const DeclContext *const FromDC;
    /// Ignore import errors of the children.
    /// If true, the context can be imported successfully if a child
    /// of it failed to import. Otherwise the import errors of the child nodes
    /// are accumulated (joined) into the import error object of the parent.
    /// (Import of a parent can fail in other ways.)
    bool const IgnoreChildErrors;
 
  public:
    ChildErrorHandlingStrategy(const DeclContext *FromDC)
        : FromDC(FromDC), IgnoreChildErrors(!isa<TagDecl>(FromDC)) {}
    ChildErrorHandlingStrategy(const Decl *FromD)
        : FromDC(dyn_cast<DeclContext>(FromD)),
          IgnoreChildErrors(!isa<TagDecl>(FromD)) {}
 
    /// Process the import result of a child (of the current declaration).
    /// \param ResultErr The import error that can be used as result of
    /// importing the parent. This may be changed by the function.
    /// \param ChildErr Result of importing a child. Can be success or error.
    void handleChildImportResult(Error &ResultErr, Error &&ChildErr) {
      if (ChildErr && !IgnoreChildErrors)
        ResultErr = joinErrors(std::move(ResultErr), std::move(ChildErr));
      else
        consumeError(std::move(ChildErr));
    }
 
    /// Determine if import failure of a child does not cause import failure of
    /// its parent.
    bool ignoreChildErrorOnParent(Decl *FromChildD) const {
      if (!IgnoreChildErrors || !FromDC)
        return false;
      return FromDC->containsDecl(FromChildD);
    }
  };
 
  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>
    [[nodiscard]] Error importInto(ImportT &To, const ImportT &From) {
      return Importer.importInto(To, From);
    }
 
    // Use this to import pointers of specific type.
    template <typename ImportT>
    [[nodiscard]] Error importInto(ImportT *&To, ImportT *From) {
      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>
    auto import(T *From)
        -> std::conditional_t<std::is_base_of_v<Type, T>, Expected<const T *>,
                              Expected<T *>> {
      auto ToOrErr = Importer.Import(From);
      if (!ToOrErr)
        return ToOrErr.takeError();
      return cast_or_null<T>(*ToOrErr);
    }
 
    template <typename T>
    auto 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) {
      return Importer.Import(From);
    }
 
    // Import an std::optional<T> by importing the contained T, if any.
    template <typename T>
    Expected<std::optional<T>> import(std::optional<T> From) {
      if (!From)
        return std::nullopt;
      return import(*From);
    }
 
    ExplicitSpecifier importExplicitSpecifier(Error &Err,
                                              ExplicitSpecifier ESpec);
 
    // Wrapper for an overload set.
    template <typename ToDeclT> struct CallOverloadedCreateFun {
      template <typename... Args> decltype(auto) operator()(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>
    [[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>
    [[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>
    [[nodiscard]] bool
    GetImportedOrCreateSpecialDecl(ToDeclT *&ToD, CreateFunT CreateFun,
                                   FromDeclT *FromD, Args &&...args) {
      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.RegisterImportedDecl(FromD, ToD);
      Importer.SharedState->markAsNewDecl(ToD);
      InitializeImportedDecl(FromD, ToD);
      return false; // A new Decl is created.
    }
 
    void InitializeImportedDecl(Decl *FromD, Decl *ToD) {
      ToD->IdentifierNamespace = FromD->IdentifierNamespace;
      if (FromD->isUsed())
        ToD->setIsUsed();
      if (FromD->isImplicit())
        ToD->setImplicit();
    }
 
    // Check if we have found an existing definition.  Returns with that
    // definition if yes, otherwise returns null.
    Decl *FindAndMapDefinition(FunctionDecl *D, FunctionDecl *FoundFunction) {
      const FunctionDecl *Definition = nullptr;
      if (D->doesThisDeclarationHaveABody() &&
          FoundFunction->hasBody(Definition))
        return Importer.MapImported(D, const_cast<FunctionDecl *>(Definition));
      return nullptr;
    }
 
    void addDeclToContexts(Decl *FromD, Decl *ToD) {
      if (Importer.isMinimalImport()) {
        // In minimal import case the decl must be added even if it is not
        // contained in original context, for LLDB compatibility.
        // FIXME: Check if a better solution is possible.
        if (!FromD->getDescribedTemplate() &&
            FromD->getFriendObjectKind() == Decl::FOK_None)
          ToD->getLexicalDeclContext()->addDeclInternal(ToD);
        return;
      }
 
      DeclContext *FromDC = FromD->getDeclContext();
      DeclContext *FromLexicalDC = FromD->getLexicalDeclContext();
      DeclContext *ToDC = ToD->getDeclContext();
      DeclContext *ToLexicalDC = ToD->getLexicalDeclContext();
 
      bool Visible = false;
      if (FromDC->containsDeclAndLoad(FromD)) {
        ToDC->addDeclInternal(ToD);
        Visible = true;
      }
      if (ToDC != ToLexicalDC && FromLexicalDC->containsDeclAndLoad(FromD)) {
        ToLexicalDC->addDeclInternal(ToD);
        Visible = true;
      }
 
      // If the Decl was added to any context, it was made already visible.
      // Otherwise it is still possible that it should be visible.
      if (!Visible) {
        if (auto *FromNamed = dyn_cast<NamedDecl>(FromD)) {
          auto *ToNamed = cast<NamedDecl>(ToD);
          DeclContextLookupResult FromLookup =
              FromDC->lookup(FromNamed->getDeclName());
          if (llvm::is_contained(FromLookup, FromNamed))
            ToDC->makeDeclVisibleInContext(ToNamed);
        }
      }
    }
 
    void updateLookupTableForTemplateParameters(TemplateParameterList &Params,
                                                DeclContext *OldDC) {
      ASTImporterLookupTable *LT = Importer.SharedState->getLookupTable();
      if (!LT)
        return;
 
      for (NamedDecl *TP : Params)
        LT->update(TP, OldDC);
    }
 
    void updateLookupTableForTemplateParameters(TemplateParameterList &Params) {
      updateLookupTableForTemplateParameters(
          Params, Importer.getToContext().getTranslationUnitDecl());
    }
 
  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 VisitUsingType(const UsingType *T);
    ExpectedType VisitDecltypeType(const DecltypeType *T);
    ExpectedType VisitUnaryTransformType(const UnaryTransformType *T);
    ExpectedType VisitAutoType(const AutoType *T);
    ExpectedType VisitDeducedTemplateSpecializationType(
        const DeducedTemplateSpecializationType *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
    VisitSubstTemplateTypeParmPackType(const SubstTemplateTypeParmPackType *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, DeclarationName &Name, NamedDecl *&ToD,
                          SourceLocation &Loc);
    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);
    Expected<APValue> ImportAPValue(const APValue &FromValue);
 
    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);
    Error ImportTemplateArguments(ArrayRef<TemplateArgument> FromArgs,
                                  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 ImportTemplateParameterLists(const DeclaratorDecl *FromD,
                                       DeclaratorDecl *ToD);
 
    Error ImportTemplateInformation(FunctionDecl *FromFD, FunctionDecl *ToFD);
 
    Error ImportFunctionDeclBody(FunctionDecl *FromFD, FunctionDecl *ToFD);
 
    Error ImportDefaultArgOfParmVarDecl(const ParmVarDecl *FromParam,
                                        ParmVarDecl *ToParam);
 
    Expected<InheritedConstructor>
    ImportInheritedConstructor(const InheritedConstructor &From);
 
    template <typename T>
    bool hasSameVisibilityContextAndLinkage(T *Found, T *From);
 
    bool IsStructuralMatch(Decl *From, Decl *To, bool Complain = true);
    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 VisitBindingDecl(BindingDecl *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 VisitCXXDeductionGuideDecl(CXXDeductionGuideDecl *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 VisitUsingPackDecl(UsingPackDecl *D);
    ExpectedDecl ImportUsingShadowDecls(BaseUsingDecl *D, BaseUsingDecl *ToSI);
    ExpectedDecl VisitUsingEnumDecl(UsingEnumDecl *D);
    ExpectedDecl VisitUnresolvedUsingValueDecl(UnresolvedUsingValueDecl *D);
    ExpectedDecl VisitUnresolvedUsingTypenameDecl(UnresolvedUsingTypenameDecl *D);
    ExpectedDecl VisitBuiltinTemplateDecl(BuiltinTemplateDecl *D);
    ExpectedDecl
    VisitLifetimeExtendedTemporaryDecl(LifetimeExtendedTemporaryDecl *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 VisitSourceLocExpr(SourceLocExpr *E);
    ExpectedStmt VisitVAArgExpr(VAArgExpr *E);
    ExpectedStmt VisitChooseExpr(ChooseExpr *E);
    ExpectedStmt VisitShuffleVectorExpr(ShuffleVectorExpr *E);
    ExpectedStmt VisitGNUNullExpr(GNUNullExpr *E);
    ExpectedStmt VisitGenericSelectionExpr(GenericSelectionExpr *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 VisitFixedPointLiteral(FixedPointLiteral *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);
    ExpectedStmt VisitCXXFoldExpr(CXXFoldExpr *E);
 
    // Helper for chaining together multiple imports. If an error is detected,
    // subsequent imports will return default constructed nodes, so that failure
    // can be detected with a single conditional branch after a sequence of
    // imports.
    template <typename T> T importChecked(Error &Err, const T &From) {
      // Don't attempt to import nodes if we hit an error earlier.
      if (Err)
        return T{};
      Expected<T> MaybeVal = import(From);
      if (!MaybeVal) {
        Err = MaybeVal.takeError();
        return T{};
      }
      return *MaybeVal;
    }
 
    template<typename IIter, typename OIter>
    Error ImportArrayChecked(IIter Ibegin, IIter Iend, OIter Obegin) {
      using ItemT = std::remove_reference_t<decltype(*Obegin)>;
      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);
    }
 
    Error ImportOverriddenMethods(CXXMethodDecl *ToMethod,
                                  CXXMethodDecl *FromMethod);
 
    Expected<FunctionDecl *> FindFunctionTemplateSpecialization(
        FunctionDecl *FromFD);
 
    // Returns true if the given function has a placeholder return type and
    // that type is declared inside the body of the function.
    // E.g. auto f() { struct X{}; return X(); }
    bool hasAutoReturnTypeDeclaredInside(FunctionDecl *D);
  };
 
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.
  if (Error Err = ImportTemplateArguments(FTSInfo->TemplateArguments->asArray(),
                                          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, /*isNullPtr*/ false,
                            From.getIsDefaulted());
  }
 
  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, From.getIsDefaulted());
  }
 
  case TemplateArgument::NullPtr: {
    ExpectedType ToTypeOrErr = import(From.getNullPtrType());
    if (!ToTypeOrErr)
      return ToTypeOrErr.takeError();
    return TemplateArgument(*ToTypeOrErr, /*isNullPtr*/ true,
                            From.getIsDefaulted());
  }
 
  case TemplateArgument::Template: {
    Expected<TemplateName> ToTemplateOrErr = import(From.getAsTemplate());
    if (!ToTemplateOrErr)
      return ToTemplateOrErr.takeError();
 
    return TemplateArgument(*ToTemplateOrErr, From.getIsDefaulted());
  }
 
  case TemplateArgument::TemplateExpansion: {
    Expected<TemplateName> ToTemplateOrErr =
        import(From.getAsTemplateOrTemplatePattern());
    if (!ToTemplateOrErr)
      return ToTemplateOrErr.takeError();
 
    return TemplateArgument(*ToTemplateOrErr, From.getNumTemplateExpansions(),
                            From.getIsDefaulted());
  }
 
  case TemplateArgument::Expression:
    if (ExpectedExpr ToExpr = import(From.getAsExpr()))
      return TemplateArgument(*ToExpr, From.getIsDefaulted());
    else
      return ToExpr.takeError();
 
  case TemplateArgument::Pack: {
    SmallVector<TemplateArgument, 2> ToPack;
    ToPack.reserve(From.pack_size());
    if (Error Err = ImportTemplateArguments(From.pack_elements(), ToPack))
      return std::move(Err);
 
    return TemplateArgument(
        llvm::ArrayRef(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(
        Importer.getToContext(), *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 DesignatedInitExpr::Designator::CreateFieldDesignator(
        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::CreateArrayDesignator(D.getArrayIndex(),
                                             *ToLBracketLocOrErr,
                                             *ToRBracketLocOrErr);
 
  ExpectedSLoc ToEllipsisLocOrErr = import(D.getEllipsisLoc());
  if (!ToEllipsisLocOrErr)
    return ToEllipsisLocOrErr.takeError();
 
  assert(D.isArrayRangeDesignator());
  return Designator::CreateArrayRangeDesignator(
      D.getArrayIndex(), *ToLBracketLocOrErr, *ToEllipsisLocOrErr,
      *ToRBracketLocOrErr);
}
 
template <>
Expected<LambdaCapture> ASTNodeImporter::import(const LambdaCapture &From) {
  ValueDecl *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);
}
 
template <typename T>
bool ASTNodeImporter::hasSameVisibilityContextAndLinkage(T *Found, T *From) {
  if (Found->getLinkageInternal() != From->getLinkageInternal())
    return false;
 
  if (From->hasExternalFormalLinkage())
    return Found->hasExternalFormalLinkage();
  if (Importer.GetFromTU(Found) != From->getTranslationUnitDecl())
    return false;
  if (From->isInAnonymousNamespace())
    return Found->isInAnonymousNamespace();
  else
    return !Found->isInAnonymousNamespace() &&
           !Found->hasExternalFormalLinkage();
}
 
template <>
bool ASTNodeImporter::hasSameVisibilityContextAndLinkage(TypedefNameDecl *Found,
                                               TypedefNameDecl *From) {
  if (Found->getLinkageInternal() != From->getLinkageInternal())
    return false;
 
  if (From->isInAnonymousNamespace() && Found->isInAnonymousNamespace())
    return Importer.GetFromTU(Found) == From->getTranslationUnitDecl();
  return From->isInAnonymousNamespace() == Found->isInAnonymousNamespace();
}
 
} // 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<ASTImportError>(ASTImportError::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 SVE_TYPE(Name, Id, SingletonId) \
  case BuiltinType::Id: \
    return Importer.getToContext().SingletonId;
#include "clang/Basic/AArch64SVEACLETypes.def"
#define PPC_VECTOR_TYPE(Name, Id, Size) \
  case BuiltinType::Id: \
    return Importer.getToContext().Id##Ty;
#include "clang/Basic/PPCTypes.def"
#define RVV_TYPE(Name, Id, SingletonId)                                        \
  case BuiltinType::Id:                                                        \
    return Importer.getToContext().SingletonId;
#include "clang/Basic/RISCVVTypes.def"
#define WASM_TYPE(Name, Id, SingletonId)                                       \
  case BuiltinType::Id:                                                        \
    return Importer.getToContext().SingletonId;
#include "clang/Basic/WebAssemblyReferenceTypes.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();
 
  ExpectedTypePtr ClassTypeOrErr = import(T->getClass());
  if (!ClassTypeOrErr)
    return ClassTypeOrErr.takeError();
 
  return Importer.getToContext().getMemberPointerType(*ToPointeeTypeOrErr,
                                                      *ClassTypeOrErr);
}
 
ExpectedType
ASTNodeImporter::VisitConstantArrayType(const ConstantArrayType *T) {
  Error Err = Error::success();
  auto ToElementType = importChecked(Err, T->getElementType());
  auto ToSizeExpr = importChecked(Err, T->getSizeExpr());
  if (Err)
    return std::move(Err);
 
  return Importer.getToContext().getConstantArrayType(
      ToElementType, T->getSize(), ToSizeExpr, 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) {
  Error Err = Error::success();
  QualType ToElementType = importChecked(Err, T->getElementType());
  Expr *ToSizeExpr = importChecked(Err, T->getSizeExpr());
  SourceRange ToBracketsRange = importChecked(Err, T->getBracketsRange());
  if (Err)
    return std::move(Err);
  return Importer.getToContext().getVariableArrayType(
      ToElementType, ToSizeExpr, T->getSizeModifier(),
      T->getIndexTypeCVRQualifiers(), ToBracketsRange);
}
 
ExpectedType ASTNodeImporter::VisitDependentSizedArrayType(
    const DependentSizedArrayType *T) {
  Error Err = Error::success();
  QualType ToElementType = importChecked(Err, T->getElementType());
  Expr *ToSizeExpr = importChecked(Err, T->getSizeExpr());
  SourceRange ToBracketsRange = importChecked(Err, T->getBracketsRange());
  if (Err)
    return std::move(Err);
  // 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();
  Error Err = Error::success();
  FunctionProtoType::ExtProtoInfo ToEPI;
  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.NoexceptExpr =
      importChecked(Err, FromEPI.ExceptionSpec.NoexceptExpr);
  ToEPI.ExceptionSpec.SourceDecl =
      importChecked(Err, FromEPI.ExceptionSpec.SourceDecl);
  ToEPI.ExceptionSpec.SourceTemplate =
      importChecked(Err, FromEPI.ExceptionSpec.SourceTemplate);
  ToEPI.ExceptionSpec.Exceptions = ExceptionTypes;
 
  if (Err)
    return std::move(Err);
 
  return Importer.getToContext().getFunctionType(
      *ToReturnTypeOrErr, ArgTypes, ToEPI);
}
 
ExpectedType ASTNodeImporter::VisitUnresolvedUsingType(
    const UnresolvedUsingType *T) {
  Error Err = Error::success();
  auto ToD = importChecked(Err, T->getDecl());
  auto ToPrevD = importChecked(Err, T->getDecl()->getPreviousDecl());
  if (Err)
    return std::move(Err);
 
  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();
 
  TypedefNameDecl *ToDecl = *ToDeclOrErr;
  if (ToDecl->getTypeForDecl())
    return QualType(ToDecl->getTypeForDecl(), 0);
 
  ExpectedType ToUnderlyingTypeOrErr = import(T->desugar());
  if (!ToUnderlyingTypeOrErr)
    return ToUnderlyingTypeOrErr.takeError();
 
  return Importer.getToContext().getTypedefType(ToDecl, *ToUnderlyingTypeOrErr);
}
 
ExpectedType ASTNodeImporter::VisitTypeOfExprType(const TypeOfExprType *T) {
  ExpectedExpr ToExprOrErr = import(T->getUnderlyingExpr());
  if (!ToExprOrErr)
    return ToExprOrErr.takeError();
  return Importer.getToContext().getTypeOfExprType(*ToExprOrErr, T->getKind());
}
 
ExpectedType ASTNodeImporter::VisitTypeOfType(const TypeOfType *T) {
  ExpectedType ToUnderlyingTypeOrErr = import(T->getUnmodifiedType());
  if (!ToUnderlyingTypeOrErr)
    return ToUnderlyingTypeOrErr.takeError();
  return Importer.getToContext().getTypeOfType(*ToUnderlyingTypeOrErr,
                                               T->getKind());
}
 
ExpectedType ASTNodeImporter::VisitUsingType(const UsingType *T) {
  Expected<UsingShadowDecl *> FoundOrErr = import(T->getFoundDecl());
  if (!FoundOrErr)
    return FoundOrErr.takeError();
  Expected<QualType> UnderlyingOrErr = import(T->getUnderlyingType());
  if (!UnderlyingOrErr)
    return UnderlyingOrErr.takeError();
 
  return Importer.getToContext().getUsingType(*FoundOrErr, *UnderlyingOrErr);
}
 
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();
 
  ExpectedDecl ToTypeConstraintConcept = import(T->getTypeConstraintConcept());
  if (!ToTypeConstraintConcept)
    return ToTypeConstraintConcept.takeError();
 
  SmallVector<TemplateArgument, 2> ToTemplateArgs;
  if (Error Err = ImportTemplateArguments(T->getTypeConstraintArguments(),
                                          ToTemplateArgs))
    return std::move(Err);
 
  return Importer.getToContext().getAutoType(
      *ToDeducedTypeOrErr, T->getKeyword(), /*IsDependent*/false,
      /*IsPack=*/false, cast_or_null<ConceptDecl>(*ToTypeConstraintConcept),
      ToTemplateArgs);
}
 
ExpectedType ASTNodeImporter::VisitDeducedTemplateSpecializationType(
    const DeducedTemplateSpecializationType *T) {
  // FIXME: Make sure that the "to" context supports C++17!
  Expected<TemplateName> ToTemplateNameOrErr = import(T->getTemplateName());
  if (!ToTemplateNameOrErr)
    return ToTemplateNameOrErr.takeError();
  ExpectedType ToDeducedTypeOrErr = import(T->getDeducedType());
  if (!ToDeducedTypeOrErr)
    return ToDeducedTypeOrErr.takeError();
 
  return Importer.getToContext().getDeducedTemplateSpecializationType(
      *ToTemplateNameOrErr, *ToDeducedTypeOrErr, T->isDependentType());
}
 
ExpectedType ASTNodeImporter::VisitInjectedClassNameType(
    const InjectedClassNameType *T) {
  Expected<CXXRecordDecl *> ToDeclOrErr = import(T->getDecl());
  if (!ToDeclOrErr)
    return ToDeclOrErr.takeError();
 
  // The InjectedClassNameType is created in VisitRecordDecl when the
  // T->getDecl() is imported. Here we can return the existing type.
  const Type *Ty = (*ToDeclOrErr)->getTypeForDecl();
  assert(Ty && isa<InjectedClassNameType>(Ty));
  return QualType(Ty, 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) {
  Expected<Decl *> ReplacedOrErr = import(T->getAssociatedDecl());
  if (!ReplacedOrErr)
    return ReplacedOrErr.takeError();
 
  ExpectedType ToReplacementTypeOrErr = import(T->getReplacementType());
  if (!ToReplacementTypeOrErr)
    return ToReplacementTypeOrErr.takeError();
 
  return Importer.getToContext().getSubstTemplateTypeParmType(
      *ToReplacementTypeOrErr, *ReplacedOrErr, T->getIndex(),
      T->getPackIndex());
}
 
ExpectedType ASTNodeImporter::VisitSubstTemplateTypeParmPackType(
    const SubstTemplateTypeParmPackType *T) {
  Expected<Decl *> ReplacedOrErr = import(T->getAssociatedDecl());
  if (!ReplacedOrErr)
    return ReplacedOrErr.takeError();
 
  Expected<TemplateArgument> ToArgumentPack = import(T->getArgumentPack());
  if (!ToArgumentPack)
    return ToArgumentPack.takeError();
 
  return Importer.getToContext().getSubstTemplateTypeParmPackType(
      *ReplacedOrErr, T->getIndex(), T->getFinal(), *ToArgumentPack);
}
 
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->template_arguments(), ToTemplateArgs))
    return std::move(Err);
 
  QualType ToCanonType;
  if (!T->isCanonicalUnqualified()) {
    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(),
                                                      /*ExpactPack=*/false);
}
 
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->template_arguments().size());
  if (Error Err = ImportTemplateArguments(T->template_arguments(), 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);
  // FIXME: We could support these constructs by importing a different type of
  // this parameter and by importing the original type of the parameter only
  // after the FunctionDecl is created. See
  // VisitFunctionDecl::UsedDifferentProtoType.
  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<ASTImportError>(ASTImportError::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::ImportDeclParts(NamedDecl *D, DeclarationName &Name,
                                       NamedDecl *&ToD, SourceLocation &Loc) {
 
  // 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();
  }
 
  // We use strict error handling in case of records and enums, but not
  // with e.g. namespaces.
  //
  // FIXME Clients of the ASTImporter should be able to choose an
  // appropriate error handling strategy for their needs.  For instance,
  // they may not want to mark an entire namespace as erroneous merely
  // because there is an ODR error with two typedefs.  As another example,
  // the client may allow EnumConstantDecls with same names but with
  // different values in two distinct translation units.
  ChildErrorHandlingStrategy HandleChildErrors(FromDC);
 
  Error ChildErrors = Error::success();
  for (auto *From : FromDC->decls()) {
    ExpectedDecl ImportedOrErr = import(From);
 
    // If we are in the process of ImportDefinition(...) for a RecordDecl we
    // want to make sure that we are also completing each FieldDecl. There
    // are currently cases where this does not happen and this is correctness
    // fix since operations such as code generation will expect this to be so.
    if (ImportedOrErr) {
      FieldDecl *FieldFrom = dyn_cast_or_null<FieldDecl>(From);
      Decl *ImportedDecl = *ImportedOrErr;
      FieldDecl *FieldTo = dyn_cast_or_null<FieldDecl>(ImportedDecl);
      if (FieldFrom && FieldTo) {
        RecordDecl *FromRecordDecl = nullptr;
        RecordDecl *ToRecordDecl = nullptr;
        // If we have a field that is an ArrayType we need to check if the array
        // element is a RecordDecl and if so we need to import the definition.
        if (FieldFrom->getType()->isArrayType()) {
          // getBaseElementTypeUnsafe(...) handles multi-dimensonal arrays for us.
          FromRecordDecl = FieldFrom->getType()->getBaseElementTypeUnsafe()->getAsRecordDecl();
          ToRecordDecl = FieldTo->getType()->getBaseElementTypeUnsafe()->getAsRecordDecl();
        }
 
        if (!FromRecordDecl || !ToRecordDecl) {
          const RecordType *RecordFrom =
              FieldFrom->getType()->getAs<RecordType>();
          const RecordType *RecordTo = FieldTo->getType()->getAs<RecordType>();
 
          if (RecordFrom && RecordTo) {
            FromRecordDecl = RecordFrom->getDecl();
            ToRecordDecl = RecordTo->getDecl();
          }
        }
 
        if (FromRecordDecl && ToRecordDecl) {
          if (FromRecordDecl->isCompleteDefinition() &&
              !ToRecordDecl->isCompleteDefinition()) {
            Error Err = ImportDefinition(FromRecordDecl, ToRecordDecl);
            HandleChildErrors.handleChildImportResult(ChildErrors,
                                                      std::move(Err));
          }
        }
      }
    } else {
      HandleChildErrors.handleChildImportResult(ChildErrors,
                                                ImportedOrErr.takeError());
    }
  }
 
  // We reorder declarations in RecordDecls because they may have another order
  // in the "to" context than they have in the "from" context. This may happen
  // e.g when we import a class like this:
  //    struct declToImport {
  //        int a = c + b;
  //        int b = 1;
  //        int c = 2;
  //    };
  // During the import of `a` we import first the dependencies in sequence,
  // thus the order would be `c`, `b`, `a`. We will get the normal order by
  // first removing the already imported members and then adding them in the
  // order as they apper in the "from" context.
  //
  // Keeping field order is vital because it determines structure layout.
  //
  // Here and below, we cannot call field_begin() method and its callers on
  // ToDC if it has an external storage. Calling field_begin() will
  // automatically load all the fields by calling
  // LoadFieldsFromExternalStorage(). LoadFieldsFromExternalStorage() would
  // call ASTImporter::Import(). This is because the ExternalASTSource
  // interface in LLDB is implemented by the means of the ASTImporter. However,
  // calling an import at this point would result in an uncontrolled import, we
  // must avoid that.
  const auto *FromRD = dyn_cast<RecordDecl>(FromDC);
  if (!FromRD)
    return ChildErrors;
 
  auto ToDCOrErr = Importer.ImportContext(FromDC);
  if (!ToDCOrErr) {
    consumeError(std::move(ChildErrors));
    return ToDCOrErr.takeError();
  }
 
  DeclContext *ToDC = *ToDCOrErr;
  // Remove all declarations, which may be in wrong order in the
  // lexical DeclContext and then add them in the proper order.
  for (auto *D : FromRD->decls()) {
    if (isa<FieldDecl>(D) || isa<IndirectFieldDecl>(D) || isa<FriendDecl>(D)) {
      assert(D && "DC contains a null decl");
      Decl *ToD = Importer.GetAlreadyImportedOrNull(D);
      // Remove only the decls which we successfully imported.
      if (ToD) {
        assert(ToDC == ToD->getLexicalDeclContext() && ToDC->containsDecl(ToD));
        // Remove the decl from its wrong place in the linked list.
        ToDC->removeDecl(ToD);
        // Add the decl to the end of the linked list.
        // This time it will be at the proper place because the enclosing for
        // loop iterates in the original (good) order of the decls.
        ToDC->addDeclInternal(ToD);
      }
    }
  }
 
  return ChildErrors;
}
 
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()) {
    if (ExpectedDecl 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) {
  auto DefinitionCompleter = [To]() {
    // There are cases in LLDB when we first import a class without its
    // members. The class will have DefinitionData, but no members. Then,
    // importDefinition is called from LLDB, which tries to get the members, so
    // when we get here, the class already has the DefinitionData set, so we
    // must unset the CompleteDefinition here to be able to complete again the
    // definition.
    To->setCompleteDefinition(false);
    To->completeDefinition();
  };
 
  if (To->getDefinition() || To->isBeingDefined()) {
    if (Kind == IDK_Everything ||
        // In case of lambdas, the class already has a definition ptr set, but
        // the contained decls are not imported yet. Also, isBeingDefined was
        // set in CXXRecordDecl::CreateLambda.  We must import the contained
        // decls here and finish the definition.
        (To->isLambda() && shouldForceImportDeclContext(Kind))) {
      if (To->isLambda()) {
        auto *FromCXXRD = cast<CXXRecordDecl>(From);
        SmallVector<LambdaCapture, 8> ToCaptures;
        ToCaptures.reserve(FromCXXRD->capture_size());
        for (const auto &FromCapture : FromCXXRD->captures()) {
          if (auto ToCaptureOrErr = import(FromCapture))
            ToCaptures.push_back(*ToCaptureOrErr);
          else
            return ToCaptureOrErr.takeError();
        }
        cast<CXXRecordDecl>(To)->setCaptures(Importer.getToContext(),
                                             ToCaptures);
      }
 
      Error Result = ImportDeclContext(From, /*ForceImport=*/true);
      // Finish the definition of the lambda, set isBeingDefined to false.
      if (To->isLambda())
        DefinitionCompleter();
      return Result;
    }
 
    return Error::success();
  }
 
  To->startDefinition();
  // Set the definition to complete even if it is really not complete during
  // import. Some AST constructs (expressions) require the record layout
  // to be calculated (see 'clang::computeDependence') at the time they are
  // constructed. Import of such AST node is possible during import of the
  // same record, there is no way to have a completely defined record (all
  // fields imported) at that time without multiple AST import passes.
  if (!Importer.isMinimalImport())
    To->setCompleteDefinition(true);
  // Complete the definition even if error is returned.
  // The RecordDecl may be already part of the AST so it is better to
  // have it in complete state even if something is wrong with it.
  auto DefinitionCompleterScopeExit =
      llvm::make_scope_exit(DefinitionCompleter);
 
  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();
 
    #define FIELD(Name, Width, Merge) \
    ToData.Name = FromData.Name;
    #include "clang/AST/CXXRecordDeclDefinitionBits.def"
 
    // Copy over the data stored in RecordDeclBits
    ToCXX->setArgPassingRestrictions(FromCXX->getArgPassingRestrictions());
 
    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;
  }
 
  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 (EvaluatedStmt *FromEval = From->getEvaluatedStmt()) {
    EvaluatedStmt *ToEval = To->ensureEvaluatedStmt();
    ToEval->HasConstantInitialization = FromEval->HasConstantInitialization;
    ToEval->HasConstantDestruction = FromEval->HasConstantDestruction;
    // FIXME: Also import the initializer value.
  }
 
  // 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();
}
 
Error ASTNodeImporter::ImportTemplateArguments(
    ArrayRef<TemplateArgument> FromArgs,
    SmallVectorImpl<TemplateArgument> &ToArgs) {
  for (const auto &Arg : FromArgs) {
    if (auto ToOrErr = import(Arg))
      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) {
  // Eliminate a potential failure point where we attempt to re-import
  // something we're trying to import while completing ToRecord.
  Decl *ToOrigin = Importer.GetOriginalDecl(To);
  if (ToOrigin) {
    To = ToOrigin;
  }
 
  StructuralEquivalenceContext Ctx(
      Importer.getFromContext(), Importer.getToContext(),
      Importer.getNonEquivalentDecls(), getStructuralEquivalenceKind(Importer),
      false, Complain);
  return Ctx.IsEquivalent(From, To);
}
 
ExpectedDecl ASTNodeImporter::VisitDecl(Decl *D) {
  Importer.FromDiag(D->getLocation(), diag::err_unsupported_ast_node)
    << D->getDeclKindName();
  return make_error<ASTImportError>(ASTImportError::UnsupportedConstruct);
}
 
ExpectedDecl ASTNodeImporter::VisitImportDecl(ImportDecl *D) {
  Importer.FromDiag(D->getLocation(), diag::err_unsupported_ast_node)
      << D->getDeclKindName();
  return make_error<ASTImportError>(ASTImportError::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::VisitBindingDecl(BindingDecl *D) {
  DeclContext *DC, *LexicalDC;
  DeclarationName Name;
  SourceLocation Loc;
  NamedDecl *ToND;
  if (Error Err = ImportDeclParts(D, DC, LexicalDC, Name, ToND, Loc))
    return std::move(Err);
  if (ToND)
    return ToND;
 
  BindingDecl *ToD;
  if (GetImportedOrCreateDecl(ToD, D, Importer.getToContext(), DC, Loc,
                              Name.getAsIdentifierInfo()))
    return ToD;
 
  Error Err = Error::success();
  QualType ToType = importChecked(Err, D->getType());
  Expr *ToBinding = importChecked(Err, D->getBinding());
  ValueDecl *ToDecomposedDecl = importChecked(Err, D->getDecomposedDecl());
  if (Err)
    return std::move(Err);
 
  ToD->setBinding(ToType, ToBinding);
  ToD->setDecomposedDecl(ToDecomposedDecl);
  addDeclToContexts(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;
 
  Error Err = Error::success();
  auto ToLocation = importChecked(Err, D->getLocation());
  auto ToRParenLoc = importChecked(Err, D->getRParenLoc());
  auto ToAssertExpr = importChecked(Err, D->getAssertExpr());
  auto ToMessage = importChecked(Err, D->getMessage());
  if (Err)
    return std::move(Err);
 
  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()) {
      ExpectedName NameOrErr = Importer.HandleNameConflict(
          Name, DC, Decl::IDNS_Namespace, ConflictingDecls.data(),
          ConflictingDecls.size());
      if (NameOrErr)
        Name = NameOrErr.get();
      else
        return NameOrErr.takeError();
    }
  }
 
  ExpectedSLoc BeginLocOrErr = import(D->getBeginLoc());
  if (!BeginLocOrErr)
    return BeginLocOrErr.takeError();
  ExpectedSLoc RBraceLocOrErr = import(D->getRBraceLoc());
  if (!RBraceLocOrErr)
    return RBraceLocOrErr.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, D->isNested()))
      return ToNamespace;
    ToNamespace->setRBraceLoc(*RBraceLocOrErr);
    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.
 
  Error Err = Error::success();
  auto ToNamespaceLoc = importChecked(Err, D->getNamespaceLoc());
  auto ToAliasLoc = importChecked(Err, D->getAliasLoc());
  auto ToQualifierLoc = importChecked(Err, D->getQualifierLoc());
  auto ToTargetNameLoc = importChecked(Err, D->getTargetNameLoc());
  auto ToNamespace = importChecked(Err, D->getNamespace());
  if (Err)
    return std::move(Err);
 
  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.
  DeclarationName Name;
  SourceLocation Loc;
  NamedDecl *ToD;
  // Do not import the DeclContext, we will import it once the TypedefNameDecl
  // is created.
  if (Error Err = ImportDeclParts(D, Name, ToD, Loc))
    return std::move(Err);
  if (ToD)
    return ToD;
 
  DeclContext *DC = cast_or_null<DeclContext>(
      Importer.GetAlreadyImportedOrNull(cast<Decl>(D->getDeclContext())));
  DeclContext *LexicalDC =
      cast_or_null<DeclContext>(Importer.GetAlreadyImportedOrNull(
          cast<Decl>(D->getLexicalDeclContext())));
 
  // 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).
  // Note: Repeated typedefs are not valid in C99:
  // 'typedef int T; typedef int T;' is invalid
  // We do not care about this now.
  if (DC && !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)) {
        if (!hasSameVisibilityContextAndLinkage(FoundTypedef, D))
          continue;
 
        QualType FromUT = D->getUnderlyingType();
        QualType FoundUT = FoundTypedef->getUnderlyingType();
        if (Importer.IsStructurallyEquivalent(FromUT, FoundUT)) {
          // If the underlying declarations are unnamed records these can be
          // imported as different types. We should create a distinct typedef
          // node in this case.
          // If we found an existing underlying type with a record in a
          // different context (than the imported), this is already reason for
          // having distinct typedef nodes for these.
          // Again this can create situation like
          // 'typedef int T; typedef int T;' but this is hard to avoid without
          // a rename strategy at import.
          if (!FromUT.isNull() && !FoundUT.isNull()) {
            RecordDecl *FromR = FromUT->getAsRecordDecl();
            RecordDecl *FoundR = FoundUT->getAsRecordDecl();
            if (FromR && FoundR &&
                !hasSameVisibilityContextAndLinkage(FoundR, FromR))
              continue;
          }
          // 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. When you do that make consistent changes
          // in ASTImporterLookupTable too.
        } else {
          ConflictingDecls.push_back(FoundDecl);
        }
      }
    }
 
    if (!ConflictingDecls.empty()) {
      ExpectedName NameOrErr = Importer.HandleNameConflict(
          Name, DC, IDNS, ConflictingDecls.data(), ConflictingDecls.size());
      if (NameOrErr)
        Name = NameOrErr.get();
      else
        return NameOrErr.takeError();
    }
  }
 
  Error Err = Error::success();
  auto ToUnderlyingType = importChecked(Err, D->getUnderlyingType());
  auto ToTypeSourceInfo = importChecked(Err, D->getTypeSourceInfo());
  auto ToBeginLoc = importChecked(Err, D->getBeginLoc());
  if (Err)
    return std::move(Err);
 
  // Create the new typedef node.
  // FIXME: ToUnderlyingType is not used.
  (void)ToUnderlyingType;
  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;
 
  // Import the DeclContext and set it to the Typedef.
  if ((Err = ImportDeclContext(D, DC, LexicalDC)))
    return std::move(Err);
  ToTypedef->setDeclContext(DC);
  ToTypedef->setLexicalDeclContext(LexicalDC);
  // Add to the lookupTable because we could not do that in MapImported.
  Importer.AddToLookupTable(ToTypedef);
 
  ToTypedef->setAccess(D->getAccess());
 
  // 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()) {
      ExpectedName NameOrErr = Importer.HandleNameConflict(
          Name, DC, IDNS, ConflictingDecls.data(), ConflictingDecls.size());
      if (NameOrErr)
        Name = NameOrErr.get();
      else
        return NameOrErr.takeError();
    }
  }
 
  Error Err = Error::success();
  auto ToTemplateParameters = importChecked(Err, D->getTemplateParameters());
  auto ToTemplatedDecl = importChecked(Err, D->getTemplatedDecl());
  if (Err)
    return std::move(Err);
 
  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);
  if (DC != Importer.getToContext().getTranslationUnitDecl())
    updateLookupTableForTemplateParameters(*ToTemplateParameters);
  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.
  EnumDecl *PrevDecl = nullptr;
  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 (!hasSameVisibilityContextAndLinkage(FoundEnum, D))
          continue;
        if (IsStructuralMatch(D, FoundEnum)) {
          EnumDecl *FoundDef = FoundEnum->getDefinition();
          if (D->isThisDeclarationADefinition() && FoundDef)
            return Importer.MapImported(D, FoundDef);
          PrevDecl = FoundEnum->getMostRecentDecl();
          break;
        }
        ConflictingDecls.push_back(FoundDecl);
      }
    }
 
    if (!ConflictingDecls.empty()) {
      ExpectedName NameOrErr = Importer.HandleNameConflict(
          SearchName, DC, IDNS, ConflictingDecls.data(),
          ConflictingDecls.size());
      if (NameOrErr)
        Name = NameOrErr.get();
      else
        return NameOrErr.takeError();
    }
  }
 
  Error Err = Error::success();
  auto ToBeginLoc = importChecked(Err, D->getBeginLoc());
  auto ToQualifierLoc = importChecked(Err, D->getQualifierLoc());
  auto ToIntegerType = importChecked(Err, D->getIntegerType());
  auto ToBraceRange = importChecked(Err, D->getBraceRange());
  if (Err)
    return std::move(Err);
 
  // Create the enum declaration.
  EnumDecl *D2;
  if (GetImportedOrCreateDecl(
          D2, D, Importer.getToContext(), DC, ToBeginLoc,
          Loc, Name.getAsIdentifierInfo(), PrevDecl, D->isScoped(),
          D->isScopedUsingClassTag(), D->isFixed()))
    return D2;
 
  D2->setQualifierInfo(ToQualifierLoc);
  D2->setIntegerType(ToIntegerType);
  D2->setBraceRange(ToBraceRange);
  D2->setAccess(D->getAccess());
  D2->setLexicalDeclContext(LexicalDC);
  addDeclToContexts(D, D2);
 
  if (MemberSpecializationInfo *MemberInfo = D->getMemberSpecializationInfo()) {
    TemplateSpecializationKind SK = MemberInfo->getTemplateSpecializationKind();
    EnumDecl *FromInst = D->getInstantiatedFromMemberEnum();
    if (Expected<EnumDecl *> ToInstOrErr = import(FromInst))
      D2->setInstantiationOfMemberEnum(*ToInstOrErr, SK);
    else
      return ToInstOrErr.takeError();
    if (ExpectedSLoc POIOrErr = import(MemberInfo->getPointOfInstantiation()))
      D2->getMemberSpecializationInfo()->setPointOfInstantiation(*POIOrErr);
    else
      return POIOrErr.takeError();
  }
 
  // 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;
  }
 
  // Import the major distinguishing characteristics of this record.
  DeclContext *DC = nullptr, *LexicalDC = nullptr;
  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;
 
  // 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() && !D->isLambda()) {
    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 (!hasSameVisibilityContextAndLinkage(FoundRecord, D))
          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);
      } // kind is RecordDecl
    } // for
 
    if (!ConflictingDecls.empty() && SearchName) {
      ExpectedName NameOrErr = Importer.HandleNameConflict(
          SearchName, DC, IDNS, ConflictingDecls.data(),
          ConflictingDecls.size());
      if (NameOrErr)
        Name = NameOrErr.get();
      else
        return NameOrErr.takeError();
    }
  }
 
  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->getLambdaDependencyKind(),
              DCXX->isGenericLambda(), DCXX->getLambdaCaptureDefault()))
        return D2CXX;
      CXXRecordDecl::LambdaNumbering Numbering = DCXX->getLambdaNumbering();
      ExpectedDecl CDeclOrErr = import(Numbering.ContextDecl);
      if (!CDeclOrErr)
        return CDeclOrErr.takeError();
      Numbering.ContextDecl = *CDeclOrErr;
      D2CXX->setLambdaNumbering(Numbering);
   } 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);
    addDeclToContexts(D, 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).
        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.
        // The chain may contain an already existing injected type at the start,
        // if yes this should be reused. We must ensure that only one type
        // object exists for the injected type (including the injected record
        // declaration), ASTContext does not check it.
        SmallVector<Decl *, 2> Redecls =
            getCanonicalForwardRedeclChain(D2CXX);
        const Type *FrontTy =
            cast<CXXRecordDecl>(Redecls.front())->getTypeForDecl();
        QualType InjSpec;
        if (auto *InjTy = FrontTy->getAs<InjectedClassNameType>())
          InjSpec = InjTy->getInjectedSpecializationType();
        else
          InjSpec = ToDescribed->getInjectedClassNameSpecialization();
        for (auto *R : Redecls) {
          auto *RI = cast<CXXRecordDecl>(R);
          if (R != Redecls.front() ||
              !isa<InjectedClassNameType>(RI->getTypeForDecl()))
            RI->setTypeForDecl(nullptr);
          // This function tries to get the injected type from getTypeForDecl,
          // then from the previous declaration if possible. If not, it creates
          // a new type.
          Importer.getToContext().getInjectedClassNameType(RI, InjSpec);
        }
        // Set the new type for the injected decl too.
        if (Injected) {
          Injected->setTypeForDecl(nullptr);
          // This function will copy the injected type from D2CXX into Injected.
          // The injected decl does not have a previous decl to copy from.
          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);
    addDeclToContexts(D, D2);
  }
 
  if (auto BraceRangeOrErr = import(D->getBraceRange()))
    D2->setBraceRange(*BraceRangeOrErr);
  else
    return BraceRangeOrErr.takeError();
  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()) {
      ExpectedName NameOrErr = Importer.HandleNameConflict(
          Name, DC, IDNS, ConflictingDecls.data(), ConflictingDecls.size());
      if (NameOrErr)
        Name = NameOrErr.get();
      else
        return NameOrErr.takeError();
    }
  }
 
  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::ImportTemplateParameterLists(const DeclaratorDecl *FromD,
                                                    DeclaratorDecl *ToD) {
  unsigned int Num = FromD->getNumTemplateParameterLists();
  if (Num == 0)
    return Error::success();
  SmallVector<TemplateParameterList *, 2> ToTPLists(Num);
  for (unsigned int I = 0; I < Num; ++I)
    if (Expected<TemplateParameterList *> ToTPListOrErr =
            import(FromD->getTemplateParameterList(I)))
      ToTPLists[I] = *ToTPListOrErr;
    else
      return ToTPListOrErr.takeError();
  ToD->setTemplateParameterListsInfo(Importer.ToContext, ToTPLists);
  return Error::success();
}
 
Error ASTNodeImporter::ImportTemplateInformation(
    FunctionDecl *FromFD, FunctionDecl *ToFD) {
  switch (FromFD->getTemplatedKind()) {
  case FunctionDecl::TK_NonTemplate:
  case FunctionDecl::TK_FunctionTemplate:
    return Error::success();
 
  case FunctionDecl::TK_DependentNonTemplate:
    if (Expected<FunctionDecl *> InstFDOrErr =
            import(FromFD->getInstantiatedFromDecl()))
      ToFD->setInstantiatedFromDecl(*InstFDOrErr);
    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();
 
    if (Error Err = ImportTemplateParameterLists(FromFD, ToFD))
      return Err;
 
    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::ArrayRef(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;
}
 
Error ASTNodeImporter::ImportFunctionDeclBody(FunctionDecl *FromFD,
                                              FunctionDecl *ToFD) {
  if (Stmt *FromBody = FromFD->getBody()) {
    if (ExpectedStmt ToBodyOrErr = import(FromBody))
      ToFD->setBody(*ToBodyOrErr);
    else
      return ToBodyOrErr.takeError();
  }
  return Error::success();
}
 
// Returns true if the given D has a DeclContext up to the TranslationUnitDecl
// which is equal to the given DC, or D is equal to DC.
static bool isAncestorDeclContextOf(const DeclContext *DC, const Decl *D) {
  const DeclContext *DCi = dyn_cast<DeclContext>(D);
  if (!DCi)
    DCi = D->getDeclContext();
  assert(DCi && "Declaration should have a context");
  while (DCi != D->getTranslationUnitDecl()) {
    if (DCi == DC)
      return true;
    DCi = DCi->getParent();
  }
  return false;
}
 
// Check if there is a declaration that has 'DC' as parent context and is
// referenced from statement 'S' or one of its children. The search is done in
// BFS order through children of 'S'.
static bool isAncestorDeclContextOf(const DeclContext *DC, const Stmt *S) {
  SmallVector<const Stmt *> ToProcess;
  ToProcess.push_back(S);
  while (!ToProcess.empty()) {
    const Stmt *CurrentS = ToProcess.pop_back_val();
    ToProcess.append(CurrentS->child_begin(), CurrentS->child_end());
    if (const auto *DeclRef = dyn_cast<DeclRefExpr>(CurrentS))
      if (const Decl *D = DeclRef->getDecl())
        if (isAncestorDeclContextOf(DC, D))
          return true;
  }
  return false;
}
 
namespace {
/// Check if a type has any reference to a declaration that is inside the body
/// of a function.
/// The \c CheckType(QualType) function should be used to determine
/// this property.
///
/// The type visitor visits one type object only (not recursive).
/// To find all referenced declarations we must discover all type objects until
/// the canonical type is reached (walk over typedef and similar objects). This
/// is done by loop over all "sugar" type objects. For every such type we must
/// check all declarations that are referenced from it. For this check the
/// visitor is used. In the visit functions all referenced declarations except
/// the one that follows in the sugar chain (if any) must be checked. For this
/// check the same visitor is re-used (it has no state-dependent data).
///
/// The visit functions have 3 possible return values:
///  - True, found a declaration inside \c ParentDC.
///  - False, found declarations only outside \c ParentDC and it is not possible
///    to find more declarations (the "sugar" chain does not continue).
///  - Empty optional value, found no declarations or only outside \c ParentDC,
///    but it is possible to find more declarations in the type "sugar" chain.
/// The loop over the "sugar" types can be implemented by using type visit
/// functions only (call \c CheckType with the desugared type). With the current
/// solution no visit function is needed if the type has only a desugared type
/// as data.
class IsTypeDeclaredInsideVisitor
    : public TypeVisitor<IsTypeDeclaredInsideVisitor, std::optional<bool>> {
public:
  IsTypeDeclaredInsideVisitor(const FunctionDecl *ParentDC)
      : ParentDC(ParentDC) {}
 
  bool CheckType(QualType T) {
    // Check the chain of "sugar" types.
    // The "sugar" types are typedef or similar types that have the same
    // canonical type.
    if (std::optional<bool> Res = Visit(T.getTypePtr()))
      return *Res;
    QualType DsT =
        T.getSingleStepDesugaredType(ParentDC->getParentASTContext());
    while (DsT != T) {
      if (std::optional<bool> Res = Visit(DsT.getTypePtr()))
        return *Res;
      T = DsT;
      DsT = T.getSingleStepDesugaredType(ParentDC->getParentASTContext());
    }
    return false;
  }
 
  std::optional<bool> VisitTagType(const TagType *T) {
    if (auto *Spec = dyn_cast<ClassTemplateSpecializationDecl>(T->getDecl()))
      for (const auto &Arg : Spec->getTemplateArgs().asArray())
        if (checkTemplateArgument(Arg))
          return true;
    return isAncestorDeclContextOf(ParentDC, T->getDecl());
  }
 
  std::optional<bool> VisitPointerType(const PointerType *T) {
    return CheckType(T->getPointeeType());
  }
 
  std::optional<bool> VisitReferenceType(const ReferenceType *T) {
    return CheckType(T->getPointeeTypeAsWritten());
  }
 
  std::optional<bool> VisitTypedefType(const TypedefType *T) {
    const TypedefNameDecl *TD = T->getDecl();
    assert(TD);
    return isAncestorDeclContextOf(ParentDC, TD);
  }
 
  std::optional<bool> VisitUsingType(const UsingType *T) {
    if (T->getFoundDecl() &&
        isAncestorDeclContextOf(ParentDC, T->getFoundDecl()))
      return true;
 
    return {};
  }
 
  std::optional<bool>
  VisitTemplateSpecializationType(const TemplateSpecializationType *T) {
    for (const auto &Arg : T->template_arguments())
      if (checkTemplateArgument(Arg))
        return true;
    // This type is a "sugar" to a record type, it can have a desugared type.
    return {};
  }
 
  std::optional<bool> VisitConstantArrayType(const ConstantArrayType *T) {
    if (T->getSizeExpr() && isAncestorDeclContextOf(ParentDC, T->getSizeExpr()))
      return true;
 
    return CheckType(T->getElementType());
  }
 
  std::optional<bool> VisitVariableArrayType(const VariableArrayType *T) {
    llvm_unreachable(
        "Variable array should not occur in deduced return type of a function");
  }
 
  std::optional<bool> VisitIncompleteArrayType(const IncompleteArrayType *T) {
    llvm_unreachable("Incomplete array should not occur in deduced return type "
                     "of a function");
  }
 
  std::optional<bool> VisitDependentArrayType(const IncompleteArrayType *T) {
    llvm_unreachable("Dependent array should not occur in deduced return type "
                     "of a function");
  }
 
private:
  const DeclContext *const ParentDC;
 
  bool checkTemplateArgument(const TemplateArgument &Arg) {
    switch (Arg.getKind()) {
    case TemplateArgument::Null:
      return false;
    case TemplateArgument::Integral:
      return CheckType(Arg.getIntegralType());
    case TemplateArgument::Type:
      return CheckType(Arg.getAsType());
    case TemplateArgument::Expression:
      return isAncestorDeclContextOf(ParentDC, Arg.getAsExpr());
    case TemplateArgument::Declaration:
      // FIXME: The declaration in this case is not allowed to be in a function?
      return isAncestorDeclContextOf(ParentDC, Arg.getAsDecl());
    case TemplateArgument::NullPtr:
      // FIXME: The type is not allowed to be in the function?
      return CheckType(Arg.getNullPtrType());
    case TemplateArgument::Pack:
      for (const auto &PackArg : Arg.getPackAsArray())
        if (checkTemplateArgument(PackArg))
          return true;
      return false;
    case TemplateArgument::Template:
      // Templates can not be defined locally in functions.
      // A template passed as argument can be not in ParentDC.
      return false;
    case TemplateArgument::TemplateExpansion:
      // Templates can not be defined locally in functions.
      // A template passed as argument can be not in ParentDC.
      return false;
    }
    llvm_unreachable("Unknown TemplateArgument::ArgKind enum");
  };
};
} // namespace
 
bool ASTNodeImporter::hasAutoReturnTypeDeclaredInside(FunctionDecl *D) {
  QualType FromTy = D->getType();
  const auto *FromFPT = FromTy->getAs<FunctionProtoType>();
  assert(FromFPT && "Must be called on FunctionProtoType");
 
  QualType RetT = FromFPT->getReturnType();
  if (isa<AutoType>(RetT.getTypePtr())) {
    FunctionDecl *Def = D->getDefinition();
    IsTypeDeclaredInsideVisitor Visitor(Def ? Def : D);
    return Visitor.CheckType(RetT);
  }
 
  return false;
}
 
ExplicitSpecifier
ASTNodeImporter::importExplicitSpecifier(Error &Err, ExplicitSpecifier ESpec) {
  Expr *ExplicitExpr = ESpec.getExpr();
  if (ExplicitExpr)
    ExplicitExpr = importChecked(Err, ESpec.getExpr());
  return ExplicitSpecifier(ExplicitExpr, ESpec.getKind());
}
 
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;
 
  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 (Decl *Def = FindAndMapDefinition(D, FoundFunction))
        return Def;
      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 (!hasSameVisibilityContextAndLinkage(FoundFunction, D))
          continue;
 
        if (IsStructuralMatch(D, FoundFunction)) {
          if (Decl *Def = FindAndMapDefinition(D, FoundFunction))
            return Def;
          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::warn_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()) {
      ExpectedName NameOrErr = Importer.HandleNameConflict(
          Name, DC, IDNS, ConflictingDecls.data(), ConflictingDecls.size());
      if (NameOrErr)
        Name = NameOrErr.get();
      else
        return NameOrErr.takeError();
    }
  }
 
  // We do not allow more than one in-class declaration of a function. This is
  // because AST clients like VTableBuilder asserts on this. VTableBuilder
  // assumes there is only one in-class declaration. Building a redecl
  // chain would result in more than one in-class declaration for
  // overrides (even if they are part of the same redecl chain inside the
  // derived class.)
  if (FoundByLookup) {
    if (isa<CXXMethodDecl>(FoundByLookup)) {
      if (D->getLexicalDeclContext() == D->getDeclContext()) {
        if (!D->doesThisDeclarationHaveABody()) {
          if (FunctionTemplateDecl *DescribedD =
                  D->getDescribedFunctionTemplate()) {
            // Handle a "templated" function together with its described
            // template. This avoids need for a similar check at import of the
            // described template.
            assert(FoundByLookup->getDescribedFunctionTemplate() &&
                   "Templated function mapped to non-templated?");
            Importer.MapImported(DescribedD,
                                 FoundByLookup->getDescribedFunctionTemplate());
          }
          return Importer.MapImported(D, FoundByLookup);
        } else {
          // Let's continue and build up the redecl chain in this case.
          // FIXME Merge the functions into one decl.
        }
      }
    }
  }
 
  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();
  TypeSourceInfo *FromTSI = D->getTypeSourceInfo();
  // Set to true if we do not import the type of the function as is. There are
  // cases when the original type would result in an infinite recursion during
  // the import. To avoid an infinite recursion when importing, we create the
  // FunctionDecl with a simplified function type and update it only after the
  // relevant AST nodes are already imported.
  // The type is related to TypeSourceInfo (it references the type), so we must
  // do the same with TypeSourceInfo.
  bool UsedDifferentProtoType = false;
  if (const auto *FromFPT = FromTy->getAs<FunctionProtoType>()) {
    QualType FromReturnTy = FromFPT->getReturnType();
    // Functions with auto return type may define a struct inside their body
    // and the return type could refer to that struct.
    // E.g.: auto foo() { struct X{}; return X(); }
    // To avoid an infinite recursion when importing, create the FunctionDecl
    // with a simplified return type.
    if (hasAutoReturnTypeDeclaredInside(D)) {
      FromReturnTy = Importer.getFromContext().VoidTy;
      UsedDifferentProtoType = true;
    }
    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.
    if (FromEPI.ExceptionSpec.SourceDecl ||
        FromEPI.ExceptionSpec.SourceTemplate ||
        FromEPI.ExceptionSpec.NoexceptExpr) {
      FunctionProtoType::ExtProtoInfo DefaultEPI;
      FromEPI = DefaultEPI;
      UsedDifferentProtoType = true;
    }
    FromTy = Importer.getFromContext().getFunctionType(
        FromReturnTy, FromFPT->getParamTypes(), FromEPI);
    FromTSI = Importer.getFromContext().getTrivialTypeSourceInfo(
        FromTy, D->getBeginLoc());
  }
 
  Error Err = Error::success();
  auto T = importChecked(Err, FromTy);
  auto TInfo = importChecked(Err, FromTSI);
  auto ToInnerLocStart = importChecked(Err, D->getInnerLocStart());
  auto ToEndLoc = importChecked(Err, D->getEndLoc());
  auto ToDefaultLoc = importChecked(Err, D->getDefaultLoc());
  auto ToQualifierLoc = importChecked(Err, D->getQualifierLoc());
  auto TrailingRequiresClause =
      importChecked(Err, D->getTrailingRequiresClause());
  if (Err)
    return std::move(Err);
 
  // 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)) {
    ExplicitSpecifier ESpec =
        importExplicitSpecifier(Err, FromConstructor->getExplicitSpecifier());
    if (Err)
      return std::move(Err);
    auto ToInheritedConstructor = InheritedConstructor();
    if (FromConstructor->isInheritingConstructor()) {
      Expected<InheritedConstructor> ImportedInheritedCtor =
          import(FromConstructor->getInheritedConstructor());
      if (!ImportedInheritedCtor)
        return ImportedInheritedCtor.takeError();
      ToInheritedConstructor = *ImportedInheritedCtor;
    }
    if (GetImportedOrCreateDecl<CXXConstructorDecl>(
            ToFunction, D, Importer.getToContext(), cast<CXXRecordDecl>(DC),
            ToInnerLocStart, NameInfo, T, TInfo, ESpec, D->UsesFPIntrin(),
            D->isInlineSpecified(), D->isImplicit(), D->getConstexprKind(),
            ToInheritedConstructor, TrailingRequiresClause))
      return ToFunction;
  } else if (CXXDestructorDecl *FromDtor = dyn_cast<CXXDestructorDecl>(D)) {
 
    Error Err = Error::success();
    auto ToOperatorDelete = importChecked(
        Err, const_cast<FunctionDecl *>(FromDtor->getOperatorDelete()));
    auto ToThisArg = importChecked(Err, FromDtor->getOperatorDeleteThisArg());
    if (Err)
      return std::move(Err);
 
    if (GetImportedOrCreateDecl<CXXDestructorDecl>(
            ToFunction, D, Importer.getToContext(), cast<CXXRecordDecl>(DC),
            ToInnerLocStart, NameInfo, T, TInfo, D->UsesFPIntrin(),
            D->isInlineSpecified(), D->isImplicit(), D->getConstexprKind(),
            TrailingRequiresClause))
      return ToFunction;
 
    CXXDestructorDecl *ToDtor = cast<CXXDestructorDecl>(ToFunction);
 
    ToDtor->setOperatorDelete(ToOperatorDelete, ToThisArg);
  } else if (CXXConversionDecl *FromConversion =
                 dyn_cast<CXXConversionDecl>(D)) {
    ExplicitSpecifier ESpec =
        importExplicitSpecifier(Err, FromConversion->getExplicitSpecifier());
    if (Err)
      return std::move(Err);
    if (GetImportedOrCreateDecl<CXXConversionDecl>(
            ToFunction, D, Importer.getToContext(), cast<CXXRecordDecl>(DC),
            ToInnerLocStart, NameInfo, T, TInfo, D->UsesFPIntrin(),
            D->isInlineSpecified(), ESpec, D->getConstexprKind(),
            SourceLocation(), TrailingRequiresClause))
      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->UsesFPIntrin(), Method->isInlineSpecified(),
            D->getConstexprKind(), SourceLocation(), TrailingRequiresClause))
      return ToFunction;
  } else if (auto *Guide = dyn_cast<CXXDeductionGuideDecl>(D)) {
    ExplicitSpecifier ESpec =
        importExplicitSpecifier(Err, Guide->getExplicitSpecifier());
    CXXConstructorDecl *Ctor =
        importChecked(Err, Guide->getCorrespondingConstructor());
    if (Err)
      return std::move(Err);
    if (GetImportedOrCreateDecl<CXXDeductionGuideDecl>(
            ToFunction, D, Importer.getToContext(), DC, ToInnerLocStart, ESpec,
            NameInfo, T, TInfo, ToEndLoc, Ctor))
      return ToFunction;
    cast<CXXDeductionGuideDecl>(ToFunction)
        ->setIsCopyDeductionCandidate(Guide->isCopyDeductionCandidate());
  } else {
    if (GetImportedOrCreateDecl(
            ToFunction, D, Importer.getToContext(), DC, ToInnerLocStart,
            NameInfo, T, TInfo, D->getStorageClass(), D->UsesFPIntrin(),
            D->isInlineSpecified(), D->hasWrittenPrototype(),
            D->getConstexprKind(), TrailingRequiresClause))
      return ToFunction;
  }
 
  // Connect the redecl chain.
  if (FoundByLookup) {
    auto *Recent = const_cast<FunctionDecl *>(
          FoundByLookup->getMostRecentDecl());
    ToFunction->setPreviousDecl(Recent);
    // FIXME Probably we should merge exception specifications.  E.g. In the
    // "To" context the existing function may have exception specification with
    // noexcept-unevaluated, while the newly imported function may have an
    // evaluated noexcept.  A call to adjustExceptionSpec() on the imported
    // decl and its redeclarations may be required.
  }
 
  ToFunction->setQualifierInfo(ToQualifierLoc);
  ToFunction->setAccess(D->getAccess());
  ToFunction->setLexicalDeclContext(LexicalDC);
  ToFunction->setVirtualAsWritten(D->isVirtualAsWritten());
  ToFunction->setTrivial(D->isTrivial());
  ToFunction->setPure(D->isPure());
  ToFunction->setDefaulted(D->isDefaulted());
  ToFunction->setExplicitlyDefaulted(D->isExplicitlyDefaulted());
  ToFunction->setDeletedAsWritten(D->isDeletedAsWritten());
  ToFunction->setFriendConstraintRefersToEnclosingTemplate(
      D->FriendConstraintRefersToEnclosingTemplate());
  ToFunction->setRangeEnd(ToEndLoc);
  ToFunction->setDefaultLoc(ToDefaultLoc);
 
  // Set the parameters.
  for (auto *Param : Parameters) {
    Param->setOwningFunction(ToFunction);
    ToFunction->addDeclInternal(Param);
    if (ASTImporterLookupTable *LT = Importer.SharedState->getLookupTable())
      LT->update(Param, Importer.getToContext().getTranslationUnitDecl());
  }
  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]);
    }
  }
 
  // Import the describing template function, if any.
  if (FromFT) {
    auto ToFTOrErr = import(FromFT);
    if (!ToFTOrErr)
      return ToFTOrErr.takeError();
  }
 
  // 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);
    }
  }
 
  // If it is a template, import all related things.
  if (Error Err = ImportTemplateInformation(D, ToFunction))
    return std::move(Err);
 
  if (D->doesThisDeclarationHaveABody()) {
    Error Err = ImportFunctionDeclBody(D, ToFunction);
 
    if (Err)
      return std::move(Err);
  }
 
  // Import and set the original type in case we used another type.
  if (UsedDifferentProtoType) {
    if (ExpectedType TyOrErr = import(D->getType()))
      ToFunction->setType(*TyOrErr);
    else
      return TyOrErr.takeError();
    if (Expected<TypeSourceInfo *> TSIOrErr = import(D->getTypeSourceInfo()))
      ToFunction->setTypeSourceInfo(*TSIOrErr);
    else
      return TSIOrErr.takeError();
  }
 
  // FIXME: Other bits to merge?
 
  addDeclToContexts(D, ToFunction);
 
  if (auto *FromCXXMethod = dyn_cast<CXXMethodDecl>(D))
    if (Error Err = ImportOverriddenMethods(cast<CXXMethodDecl>(ToFunction),
                                            FromCXXMethod))
      return std::move(Err);
 
  // 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::VisitCXXDeductionGuideDecl(CXXDeductionGuideDecl *D) {
  return VisitFunctionDecl(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.
        // Note: `hasInClassInitializer()` is not the same as non-null
        // `getInClassInitializer()` value.
        if (Expr *FromInitializer = D->getInClassInitializer()) {
          if (ExpectedExpr ToInitializerOrErr = import(FromInitializer)) {
            // Import of the FromInitializer may result in the setting of
            // InClassInitializer. If not, set it here.
            assert(FoundField->hasInClassInitializer() &&
                   "Field should have an in-class initializer if it has an "
                   "expression for it.");
            if (!FoundField->getInClassInitializer())
              FoundField->setInClassInitializer(*ToInitializerOrErr);
          } else {
              return ToInitializerOrErr.takeError();
          }
        }
        return FoundField;
      }
 
      // FIXME: Why is this case not handled with calling HandleNameConflict?
      Importer.ToDiag(Loc, diag::warn_odr_field_type_inconsistent)
        << Name << D->getType() << FoundField->getType();
      Importer.ToDiag(FoundField->getLocation(), diag::note_odr_value_here)
        << FoundField->getType();
 
      return make_error<ASTImportError>(ASTImportError::NameConflict);
    }
  }
 
  Error Err = Error::success();
  auto ToType = importChecked(Err, D->getType());
  auto ToTInfo = importChecked(Err, D->getTypeSourceInfo());
  auto ToBitWidth = importChecked(Err, D->getBitWidth());
  auto ToInnerLocStart = importChecked(Err, D->getInnerLocStart());
  auto ToInitializer = importChecked(Err, D->getInClassInitializer());
  if (Err)
    return std::move(Err);
  const Type *ToCapturedVLAType = nullptr;
  if (Error Err = Importer.importInto(
          ToCapturedVLAType, cast_or_null<Type>(D->getCapturedVLAType())))
    return std::move(Err);
 
  FieldDecl *ToField;
  if (GetImportedOrCreateDecl(ToField, D, Importer.getToContext(), DC,
                              ToInnerLocStart, Loc, Name.getAsIdentifierInfo(),
                              ToType, ToTInfo, ToBitWidth, D->isMutable(),
                              D->getInClassInitStyle()))
    return ToField;
 
  // We need [[no_unqiue_address]] attributes to be added to FieldDecl, before
  // we add fields in CXXRecordDecl::addedMember, otherwise record will be
  // marked as having non-zero size.
  Err = Importer.ImportAttrs(ToField, D);
  if (Err)
    return std::move(Err);
  ToField->setAccess(D->getAccess());
  ToField->setLexicalDeclContext(LexicalDC);
  if (ToInitializer)
    ToField->setInClassInitializer(ToInitializer);
  ToField->setImplicit(D->isImplicit());
  if (ToCapturedVLAType)
    ToField->setCapturedVLAType(cast<VariableArrayType>(ToCapturedVLAType));
  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::warn_odr_field_type_inconsistent)
        << Name << D->getType() << FoundField->getType();
      Importer.ToDiag(FoundField->getLocation(), diag::note_odr_value_here)
        << FoundField->getType();
 
      return make_error<ASTImportError>(ASTImportError::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;
 
  ToIndirectField->setAccess(D->getAccess());
  ToIndirectField->setLexicalDeclContext(LexicalDC);
  LexicalDC->addDeclInternal(ToIndirectField);
  return ToIndirectField;
}
 
/// Used as return type of getFriendCountAndPosition.
struct FriendCountAndPosition {
  /// Number of similar looking friends.
  unsigned int TotalCount;
  /// Index of the specific FriendDecl.
  unsigned int IndexOfDecl;
};
 
template <class T>
static FriendCountAndPosition getFriendCountAndPosition(
    const FriendDecl *FD,
    llvm::function_ref<T(const FriendDecl *)> GetCanTypeOrDecl) {
  unsigned int FriendCount = 0;
  std::optional<unsigned int> FriendPosition;
  const auto *RD = cast<CXXRecordDecl>(FD->getLexicalDeclContext());
 
  T TypeOrDecl = GetCanTypeOrDecl(FD);
 
  for (const FriendDecl *FoundFriend : RD->friends()) {
    if (FoundFriend == FD) {
      FriendPosition = FriendCount;
      ++FriendCount;
    } else if (!FoundFriend->getFriendDecl() == !FD->getFriendDecl() &&
               GetCanTypeOrDecl(FoundFriend) == TypeOrDecl) {
      ++FriendCount;
    }
  }
 
  assert(FriendPosition && "Friend decl not found in own parent.");
 
  return {FriendCount, *FriendPosition};
}
 
static FriendCountAndPosition getFriendCountAndPosition(const FriendDecl *FD) {
  if (FD->getFriendType())
    return getFriendCountAndPosition<QualType>(FD, [](const FriendDecl *F) {
      if (TypeSourceInfo *TSI = F->getFriendType())
        return TSI->getType().getCanonicalType();
      llvm_unreachable("Wrong friend object type.");
    });
  else
    return getFriendCountAndPosition<Decl *>(FD, [](const FriendDecl *F) {
      if (Decl *D = F->getFriendDecl())
        return D->getCanonicalDecl();
      llvm_unreachable("Wrong friend object type.");
    });
}
 
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.
  // We try to maintain order and count of redundant friend declarations.
  const auto *RD = cast<CXXRecordDecl>(DC);
  FriendDecl *ImportedFriend = RD->getFirstFriend();
  SmallVector<FriendDecl *, 2> ImportedEquivalentFriends;
 
  while (ImportedFriend) {
    bool Match = false;
    if (D->getFriendDecl() && ImportedFriend->getFriendDecl()) {
      Match =
          IsStructuralMatch(D->getFriendDecl(), ImportedFriend->getFriendDecl(),
                            /*Complain=*/false);
    } else if (D->getFriendType() && ImportedFriend->getFriendType()) {
      Match = Importer.IsStructurallyEquivalent(
          D->getFriendType()->getType(),
          ImportedFriend->getFriendType()->getType(), /*Complain=*/false);
    }
    if (Match)
      ImportedEquivalentFriends.push_back(ImportedFriend);
 
    ImportedFriend = ImportedFriend->getNextFriend();
  }
  FriendCountAndPosition CountAndPosition = getFriendCountAndPosition(D);
 
  assert(ImportedEquivalentFriends.size() <= CountAndPosition.TotalCount &&
         "Class with non-matching friends is imported, ODR check wrong?");
  if (ImportedEquivalentFriends.size() == CountAndPosition.TotalCount)
    return Importer.MapImported(
        D, ImportedEquivalentFriends[CountAndPosition.IndexOfDecl]);
 
  // Not found. Create it.
  // The declarations will be put into order later by ImportDeclContext.
  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 = import(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::warn_odr_ivar_type_inconsistent)
        << Name << D->getType() << FoundIvar->getType();
      Importer.ToDiag(FoundIvar->getLocation(), diag::note_odr_value_here)
        << FoundIvar->getType();
 
      return make_error<ASTImportError>(ASTImportError::NameConflict);
    }
  }
 
  Error Err = Error::success();
  auto ToType = importChecked(Err, D->getType());
  auto ToTypeSourceInfo = importChecked(Err, D->getTypeSourceInfo());
  auto ToBitWidth = importChecked(Err, D->getBitWidth());
  auto ToInnerLocStart = importChecked(Err, D->getInnerLocStart());
  if (Err)
    return std::move(Err);
 
  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)) {
        if (!hasSameVisibilityContextAndLinkage(FoundVar, D))
          continue;
        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::warn_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()) {
      ExpectedName NameOrErr = Importer.HandleNameConflict(
          Name, DC, IDNS, ConflictingDecls.data(), ConflictingDecls.size());
      if (NameOrErr)
        Name = NameOrErr.get();
      else
        return NameOrErr.takeError();
    }
  }
 
  Error Err = Error::success();
  auto ToType = importChecked(Err, D->getType());
  auto ToTypeSourceInfo = importChecked(Err, D->getTypeSourceInfo());
  auto ToInnerLocStart = importChecked(Err, D->getInnerLocStart());
  auto ToQualifierLoc = importChecked(Err, D->getQualifierLoc());
  if (Err)
    return std::move(Err);
 
  VarDecl *ToVar;
  if (auto *FromDecomp = dyn_cast<DecompositionDecl>(D)) {
    SmallVector<BindingDecl *> Bindings(FromDecomp->bindings().size());
    if (Error Err =
            ImportArrayChecked(FromDecomp->bindings(), Bindings.begin()))
      return std::move(Err);
    DecompositionDecl *ToDecomp;
    if (GetImportedOrCreateDecl(
            ToDecomp, FromDecomp, Importer.getToContext(), DC, ToInnerLocStart,
            Loc, ToType, ToTypeSourceInfo, D->getStorageClass(), Bindings))
      return ToDecomp;
    ToVar = ToDecomp;
  } else {
    // Create the imported variable.
    if (GetImportedOrCreateDecl(ToVar, D, Importer.getToContext(), DC,
                                ToInnerLocStart, Loc,
                                Name.getAsIdentifierInfo(), ToType,
                                ToTypeSourceInfo, D->getStorageClass()))
      return ToVar;
  }
 
  ToVar->setTSCSpec(D->getTSCSpec());
  ToVar->setQualifierInfo(ToQualifierLoc);
  ToVar->setAccess(D->getAccess());
  ToVar->setLexicalDeclContext(LexicalDC);
 
  if (FoundByLookup) {
    auto *Recent = const_cast<VarDecl *>(FoundByLookup->getMostRecentDecl());
    ToVar->setPreviousDecl(Recent);
  }
 
  // Import the described template, if any.
  if (D->getDescribedVarTemplate()) {
    auto ToVTOrErr = import(D->getDescribedVarTemplate());
    if (!ToVTOrErr)
      return ToVTOrErr.takeError();
  }
 
  if (Error Err = ImportInitializer(D, ToVar))
    return std::move(Err);
 
  if (D->isConstexpr())
    ToVar->setConstexpr(true);
 
  addDeclToContexts(D, 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();
 
  Error Err = Error::success();
  auto ToDeclName = importChecked(Err, D->getDeclName());
  auto ToLocation = importChecked(Err, D->getLocation());
  auto ToType = importChecked(Err, D->getType());
  if (Err)
    return std::move(Err);
 
  // Create the imported parameter.
  ImplicitParamDecl *ToParm = nullptr;
  if (GetImportedOrCreateDecl(ToParm, D, Importer.getToContext(), DC,
                              ToLocation, ToDeclName.getAsIdentifierInfo(),
                              ToType, D->getParameterKind()))
    return ToParm;
  return ToParm;
}
 
Error ASTNodeImporter::ImportDefaultArgOfParmVarDecl(
    const ParmVarDecl *FromParam, ParmVarDecl *ToParam) {
  ToParam->setHasInheritedDefaultArg(FromParam->hasInheritedDefaultArg());
  ToParam->setKNRPromoted(FromParam->isKNRPromoted());
 
  if (FromParam->hasUninstantiatedDefaultArg()) {
    if (auto ToDefArgOrErr = import(FromParam->getUninstantiatedDefaultArg()))
      ToParam->setUninstantiatedDefaultArg(*ToDefArgOrErr);
    else
      return ToDefArgOrErr.takeError();
  } else if (FromParam->hasUnparsedDefaultArg()) {
    ToParam->setUnparsedDefaultArg();
  } else if (FromParam->hasDefaultArg()) {
    if (auto ToDefArgOrErr = import(FromParam->getDefaultArg()))
      ToParam->setDefaultArg(*ToDefArgOrErr);
    else
      return ToDefArgOrErr.takeError();
  }
 
  return Error::success();
}
 
Expected<InheritedConstructor>
ASTNodeImporter::ImportInheritedConstructor(const InheritedConstructor &From) {
  Error Err = Error::success();
  CXXConstructorDecl *ToBaseCtor = importChecked(Err, From.getConstructor());
  ConstructorUsingShadowDecl *ToShadow =
      importChecked(Err, From.getShadowDecl());
  if (Err)
    return std::move(Err);
  return InheritedConstructor(ToShadow, ToBaseCtor);
}
 
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();
 
  Error Err = Error::success();
  auto ToDeclName = importChecked(Err, D->getDeclName());
  auto ToLocation = importChecked(Err, D->getLocation());
  auto ToInnerLocStart = importChecked(Err, D->getInnerLocStart());
  auto ToType = importChecked(Err, D->getType());
  auto ToTypeSourceInfo = importChecked(Err, D->getTypeSourceInfo());
  if (Err)
    return std::move(Err);
 
  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. It should be no problem if it was already done.
  // Do not import the default expression before GetImportedOrCreateDecl call
  // to avoid possible infinite import loop because circular dependency.
  if (Error Err = ImportDefaultArgOfParmVarDecl(D, ToParm))
    return std::move(Err);
 
  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::warn_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<ASTImportError>(ASTImportError::NameConflict);
      }
 
      // Check the number of parameters.
      if (D->param_size() != FoundMethod->param_size()) {
        Importer.ToDiag(Loc, diag::warn_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<ASTImportError>(ASTImportError::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::warn_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<ASTImportError>(ASTImportError::NameConflict);
        }
      }
 
      // Check variadic/non-variadic.
      // Check the number of parameters.
      if (D->isVariadic() != FoundMethod->isVariadic()) {
        Importer.ToDiag(Loc, diag::warn_odr_objc_method_variadic_inconsistent)
          << D->isInstanceMethod() << Name;
        Importer.ToDiag(FoundMethod->getLocation(),
                        diag::note_odr_objc_method_here)
          << D->isInstanceMethod() << Name;
 
        return make_error<ASTImportError>(ASTImportError::NameConflict);
      }
 
      // FIXME: Any other bits we need to merge?
      return Importer.MapImported(D, FoundMethod);
    }
  }
 
  Error Err = Error::success();
  auto ToEndLoc = importChecked(Err, D->getEndLoc());
  auto ToReturnType = importChecked(Err, D->getReturnType());
  auto ToReturnTypeSourceInfo =
      importChecked(Err, D->getReturnTypeSourceInfo());
  if (Err)
    return std::move(Err);
 
  ObjCMethodDecl *ToMethod;
  if (GetImportedOrCreateDecl(
          ToMethod, D, Importer.getToContext(), Loc, ToEndLoc,
          Name.getObjCSelector(), ToReturnType, ToReturnTypeSourceInfo, DC,
          D->isInstanceMethod(), D->isVariadic(), D->isPropertyAccessor(),
          D->isSynthesizedAccessorStub(), 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);
 
  // Implicit params are declared when Sema encounters the definition but this
  // never happens when the method is imported. Manually declare the implicit
  // params now that the MethodDecl knows its class interface.
  if (D->getSelfDecl())
    ToMethod->createImplicitParams(Importer.getToContext(),
                                   ToMethod->getClassInterface());
 
  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;
 
  Error Err = Error::success();
  auto ToVarianceLoc = importChecked(Err, D->getVarianceLoc());
  auto ToLocation = importChecked(Err, D->getLocation());
  auto ToColonLoc = importChecked(Err, D->getColonLoc());
  auto ToTypeSourceInfo = importChecked(Err, D->getTypeSourceInfo());
  if (Err)
    return std::move(Err);
 
  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) {
 
    Error Err = Error::success();
    auto ToAtStartLoc = importChecked(Err, D->getAtStartLoc());
    auto ToCategoryNameLoc = importChecked(Err, D->getCategoryNameLoc());
    auto ToIvarLBraceLoc = importChecked(Err, D->getIvarLBraceLoc());
    auto ToIvarRBraceLoc = importChecked(Err, D->getIvarRBraceLoc());
    if (Err)
      return std::move(Err);
 
    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::ImportUsingShadowDecls(BaseUsingDecl *D,
                                                     BaseUsingDecl *ToSI) {
  for (UsingShadowDecl *FromShadow : D->shadows()) {
    if (Expected<UsingShadowDecl *> ToShadowOrErr = import(FromShadow))
      ToSI->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 ToSI;
}
 
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;
 
  Error Err = Error::success();
  auto ToLoc = importChecked(Err, D->getNameInfo().getLoc());
  auto ToUsingLoc = importChecked(Err, D->getUsingLoc());
  auto ToQualifierLoc = importChecked(Err, D->getQualifierLoc());
  if (Err)
    return std::move(Err);
 
  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();
  }
 
  return ImportUsingShadowDecls(D, ToUsing);
}
 
ExpectedDecl ASTNodeImporter::VisitUsingEnumDecl(UsingEnumDecl *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;
 
  Error Err = Error::success();
  auto ToUsingLoc = importChecked(Err, D->getUsingLoc());
  auto ToEnumLoc = importChecked(Err, D->getEnumLoc());
  auto ToNameLoc = importChecked(Err, D->getLocation());
  auto *ToEnumType = importChecked(Err, D->getEnumType());
  if (Err)
    return std::move(Err);
 
  UsingEnumDecl *ToUsingEnum;
  if (GetImportedOrCreateDecl(ToUsingEnum, D, Importer.getToContext(), DC,
                              ToUsingLoc, ToEnumLoc, ToNameLoc, ToEnumType))
    return ToUsingEnum;
 
  ToUsingEnum->setLexicalDeclContext(LexicalDC);
  LexicalDC->addDeclInternal(ToUsingEnum);
 
  if (UsingEnumDecl *FromPattern =
          Importer.getFromContext().getInstantiatedFromUsingEnumDecl(D)) {
    if (Expected<UsingEnumDecl *> ToPatternOrErr = import(FromPattern))
      Importer.getToContext().setInstantiatedFromUsingEnumDecl(ToUsingEnum,
                                                               *ToPatternOrErr);
    else
      return ToPatternOrErr.takeError();
  }
 
  return ImportUsingShadowDecls(D, ToUsingEnum);
}