SemaDecl.cpp

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//===--- SemaDecl.cpp - Semantic Analysis for Declarations ----------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
//  This file implements semantic analysis for declarations.
//
//===----------------------------------------------------------------------===//

#include "TypeLocBuilder.h"
#include "clang/AST/ASTConsumer.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/ASTLambda.h"
#include "clang/AST/CXXInheritance.h"
#include "clang/AST/CharUnits.h"
#include "clang/AST/CommentDiagnostic.h"
#include "clang/AST/DeclCXX.h"
#include "clang/AST/DeclObjC.h"
#include "clang/AST/DeclTemplate.h"
#include "clang/AST/EvaluatedExprVisitor.h"
#include "clang/AST/ExprCXX.h"
#include "clang/AST/StmtCXX.h"
#include "clang/Basic/Builtins.h"
#include "clang/Basic/PartialDiagnostic.h"
#include "clang/Basic/SourceManager.h"
#include "clang/Basic/TargetInfo.h"
#include "clang/Lex/HeaderSearch.h" // TODO: Sema shouldn't depend on Lex
#include "clang/Lex/Lexer.h" // TODO: Extract static functions to fix layering.
#include "clang/Lex/ModuleLoader.h" // TODO: Sema shouldn't depend on Lex
#include "clang/Lex/Preprocessor.h" // Included for isCodeCompletionEnabled()
#include "clang/Sema/CXXFieldCollector.h"
#include "clang/Sema/DeclSpec.h"
#include "clang/Sema/DelayedDiagnostic.h"
#include "clang/Sema/Initialization.h"
#include "clang/Sema/Lookup.h"
#include "clang/Sema/ParsedTemplate.h"
#include "clang/Sema/Scope.h"
#include "clang/Sema/ScopeInfo.h"
#include "clang/Sema/SemaInternal.h"
#include "clang/Sema/Template.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/Triple.h"
#include <algorithm>
#include <cstring>
#include <functional>

using namespace clang;
using namespace sema;

Sema::DeclGroupPtrTy Sema::ConvertDeclToDeclGroup(Decl *Ptr, Decl *OwnedType) {
  if (OwnedType) {
    Decl *Group[2] = { OwnedType, Ptr };
    return DeclGroupPtrTy::make(DeclGroupRef::Create(Context, Group, 2));
  }

  return DeclGroupPtrTy::make(DeclGroupRef(Ptr));
}

namespace {

class TypeNameValidatorCCC : public CorrectionCandidateCallback {
 public:
   TypeNameValidatorCCC(bool AllowInvalid, bool WantClass = false,
                        bool AllowTemplates = false,
                        bool AllowNonTemplates = true)
       : AllowInvalidDecl(AllowInvalid), WantClassName(WantClass),
         AllowTemplates(AllowTemplates), AllowNonTemplates(AllowNonTemplates) {
     WantExpressionKeywords = false;
     WantCXXNamedCasts = false;
     WantRemainingKeywords = false;
  }

  bool ValidateCandidate(const TypoCorrection &candidate) override {
    if (NamedDecl *ND = candidate.getCorrectionDecl()) {
      if (!AllowInvalidDecl && ND->isInvalidDecl())
        return false;

      if (getAsTypeTemplateDecl(ND))
        return AllowTemplates;

      bool IsType = isa<TypeDecl>(ND) || isa<ObjCInterfaceDecl>(ND);
      if (!IsType)
        return false;

      if (AllowNonTemplates)
        return true;

      // An injected-class-name of a class template (specialization) is valid
      // as a template or as a non-template.
      if (AllowTemplates) {
        auto *RD = dyn_cast<CXXRecordDecl>(ND);
        if (!RD || !RD->isInjectedClassName())
          return false;
        RD = cast<CXXRecordDecl>(RD->getDeclContext());
        return RD->getDescribedClassTemplate() ||
               isa<ClassTemplateSpecializationDecl>(RD);
      }

      return false;
    }

    return !WantClassName && candidate.isKeyword();
  }

 private:
  bool AllowInvalidDecl;
  bool WantClassName;
  bool AllowTemplates;
  bool AllowNonTemplates;
};

} // end anonymous namespace

/// Determine whether the token kind starts a simple-type-specifier.
bool Sema::isSimpleTypeSpecifier(tok::TokenKind Kind) const {
  switch (Kind) {
  // FIXME: Take into account the current language when deciding whether a
  // token kind is a valid type specifier
  case tok::kw_short:
  case tok::kw_long:
  case tok::kw___int64:
  case tok::kw___int128:
  case tok::kw_signed:
  case tok::kw_unsigned:
  case tok::kw_void:
  case tok::kw_char:
  case tok::kw_int:
  case tok::kw_half:
  case tok::kw_float:
  case tok::kw_double:
  case tok::kw__Float16:
  case tok::kw___float128:
  case tok::kw_wchar_t:
  case tok::kw_bool:
  case tok::kw___underlying_type:
  case tok::kw___auto_type:
    return true;

  case tok::annot_typename:
  case tok::kw_char16_t:
  case tok::kw_char32_t:
  case tok::kw_typeof:
  case tok::annot_decltype:
  case tok::kw_decltype:
    return getLangOpts().CPlusPlus;

  case tok::kw_char8_t:
    return getLangOpts().Char8;

  default:
    break;
  }

  return false;
}

namespace {
enum class UnqualifiedTypeNameLookupResult {
  NotFound,
  FoundNonType,
  FoundType
};
} // end anonymous namespace

/// Tries to perform unqualified lookup of the type decls in bases for
/// dependent class.
/// \return \a NotFound if no any decls is found, \a FoundNotType if found not a
/// type decl, \a FoundType if only type decls are found.
static UnqualifiedTypeNameLookupResult
lookupUnqualifiedTypeNameInBase(Sema &S, const IdentifierInfo &II,
                                SourceLocation NameLoc,
                                const CXXRecordDecl *RD) {
  if (!RD->hasDefinition())
    return UnqualifiedTypeNameLookupResult::NotFound;
  // Look for type decls in base classes.
  UnqualifiedTypeNameLookupResult FoundTypeDecl =
      UnqualifiedTypeNameLookupResult::NotFound;
  for (const auto &Base : RD->bases()) {
    const CXXRecordDecl *BaseRD = nullptr;
    if (auto *BaseTT = Base.getType()->getAs<TagType>())
      BaseRD = BaseTT->getAsCXXRecordDecl();
    else if (auto *TST = Base.getType()->getAs<TemplateSpecializationType>()) {
      // Look for type decls in dependent base classes that have known primary
      // templates.
      if (!TST || !TST->isDependentType())
        continue;
      auto *TD = TST->getTemplateName().getAsTemplateDecl();
      if (!TD)
        continue;
      if (auto *BasePrimaryTemplate =
          dyn_cast_or_null<CXXRecordDecl>(TD->getTemplatedDecl())) {
        if (BasePrimaryTemplate->getCanonicalDecl() != RD->getCanonicalDecl())
          BaseRD = BasePrimaryTemplate;
        else if (auto *CTD = dyn_cast<ClassTemplateDecl>(TD)) {
          if (const ClassTemplatePartialSpecializationDecl *PS =
                  CTD->findPartialSpecialization(Base.getType()))
            if (PS->getCanonicalDecl() != RD->getCanonicalDecl())
              BaseRD = PS;
        }
      }
    }
    if (BaseRD) {
      for (NamedDecl *ND : BaseRD->lookup(&II)) {
        if (!isa<TypeDecl>(ND))
          return UnqualifiedTypeNameLookupResult::FoundNonType;
        FoundTypeDecl = UnqualifiedTypeNameLookupResult::FoundType;
      }
      if (FoundTypeDecl == UnqualifiedTypeNameLookupResult::NotFound) {
        switch (lookupUnqualifiedTypeNameInBase(S, II, NameLoc, BaseRD)) {
        case UnqualifiedTypeNameLookupResult::FoundNonType:
          return UnqualifiedTypeNameLookupResult::FoundNonType;
        case UnqualifiedTypeNameLookupResult::FoundType:
          FoundTypeDecl = UnqualifiedTypeNameLookupResult::FoundType;
          break;
        case UnqualifiedTypeNameLookupResult::NotFound:
          break;
        }
      }
    }
  }

  return FoundTypeDecl;
}

static ParsedType recoverFromTypeInKnownDependentBase(Sema &S,
                                                      const IdentifierInfo &II,
                                                      SourceLocation NameLoc) {
  // Lookup in the parent class template context, if any.
  const CXXRecordDecl *RD = nullptr;
  UnqualifiedTypeNameLookupResult FoundTypeDecl =
      UnqualifiedTypeNameLookupResult::NotFound;
  for (DeclContext *DC = S.CurContext;
       DC && FoundTypeDecl == UnqualifiedTypeNameLookupResult::NotFound;
       DC = DC->getParent()) {
    // Look for type decls in dependent base classes that have known primary
    // templates.
    RD = dyn_cast<CXXRecordDecl>(DC);
    if (RD && RD->getDescribedClassTemplate())
      FoundTypeDecl = lookupUnqualifiedTypeNameInBase(S, II, NameLoc, RD);
  }
  if (FoundTypeDecl != UnqualifiedTypeNameLookupResult::FoundType)
    return nullptr;

  // We found some types in dependent base classes.  Recover as if the user
  // wrote 'typename MyClass::II' instead of 'II'.  We'll fully resolve the
  // lookup during template instantiation.
  S.Diag(NameLoc, diag::ext_found_via_dependent_bases_lookup) << &II;

  ASTContext &Context = S.Context;
  auto *NNS = NestedNameSpecifier::Create(Context, nullptr, false,
                                          cast<Type>(Context.getRecordType(RD)));
  QualType T = Context.getDependentNameType(ETK_Typename, NNS, &II);

  CXXScopeSpec SS;
  SS.MakeTrivial(Context, NNS, SourceRange(NameLoc));

  TypeLocBuilder Builder;
  DependentNameTypeLoc DepTL = Builder.push<DependentNameTypeLoc>(T);
  DepTL.setNameLoc(NameLoc);
  DepTL.setElaboratedKeywordLoc(SourceLocation());
  DepTL.setQualifierLoc(SS.getWithLocInContext(Context));
  return S.CreateParsedType(T, Builder.getTypeSourceInfo(Context, T));
}

/// If the identifier refers to a type name within this scope,
/// return the declaration of that type.
///
/// This routine performs ordinary name lookup of the identifier II
/// within the given scope, with optional C++ scope specifier SS, to
/// determine whether the name refers to a type. If so, returns an
/// opaque pointer (actually a QualType) corresponding to that
/// type. Otherwise, returns NULL.
ParsedType Sema::getTypeName(const IdentifierInfo &II, SourceLocation NameLoc,
                             Scope *S, CXXScopeSpec *SS,
                             bool isClassName, bool HasTrailingDot,
                             ParsedType ObjectTypePtr,
                             bool IsCtorOrDtorName,
                             bool WantNontrivialTypeSourceInfo,
                             bool IsClassTemplateDeductionContext,
                             IdentifierInfo **CorrectedII) {
  // FIXME: Consider allowing this outside C++1z mode as an extension.
  bool AllowDeducedTemplate = IsClassTemplateDeductionContext &&
                              getLangOpts().CPlusPlus17 && !IsCtorOrDtorName &&
                              !isClassName && !HasTrailingDot;

  // Determine where we will perform name lookup.
  DeclContext *LookupCtx = nullptr;
  if (ObjectTypePtr) {
    QualType ObjectType = ObjectTypePtr.get();
    if (ObjectType->isRecordType())
      LookupCtx = computeDeclContext(ObjectType);
  } else if (SS && SS->isNotEmpty()) {
    LookupCtx = computeDeclContext(*SS, false);

    if (!LookupCtx) {
      if (isDependentScopeSpecifier(*SS)) {
        // C++ [temp.res]p3:
        //   A qualified-id that refers to a type and in which the
        //   nested-name-specifier depends on a template-parameter (14.6.2)
        //   shall be prefixed by the keyword typename to indicate that the
        //   qualified-id denotes a type, forming an
        //   elaborated-type-specifier (7.1.5.3).
        //
        // We therefore do not perform any name lookup if the result would
        // refer to a member of an unknown specialization.
        if (!isClassName && !IsCtorOrDtorName)
          return nullptr;

        // We know from the grammar that this name refers to a type,
        // so build a dependent node to describe the type.
        if (WantNontrivialTypeSourceInfo)
          return ActOnTypenameType(S, SourceLocation(), *SS, II, NameLoc).get();

        NestedNameSpecifierLoc QualifierLoc = SS->getWithLocInContext(Context);
        QualType T = CheckTypenameType(ETK_None, SourceLocation(), QualifierLoc,
                                       II, NameLoc);
        return ParsedType::make(T);
      }

      return nullptr;
    }

    if (!LookupCtx->isDependentContext() &&
        RequireCompleteDeclContext(*SS, LookupCtx))
      return nullptr;
  }

  // FIXME: LookupNestedNameSpecifierName isn't the right kind of
  // lookup for class-names.
  LookupNameKind Kind = isClassName ? LookupNestedNameSpecifierName :
                                      LookupOrdinaryName;
  LookupResult Result(*this, &II, NameLoc, Kind);
  if (LookupCtx) {
    // Perform "qualified" name lookup into the declaration context we
    // computed, which is either the type of the base of a member access
    // expression or the declaration context associated with a prior
    // nested-name-specifier.
    LookupQualifiedName(Result, LookupCtx);

    if (ObjectTypePtr && Result.empty()) {
      // C++ [basic.lookup.classref]p3:
      //   If the unqualified-id is ~type-name, the type-name is looked up
      //   in the context of the entire postfix-expression. If the type T of
      //   the object expression is of a class type C, the type-name is also
      //   looked up in the scope of class C. At least one of the lookups shall
      //   find a name that refers to (possibly cv-qualified) T.
      LookupName(Result, S);
    }
  } else {
    // Perform unqualified name lookup.
    LookupName(Result, S);

    // For unqualified lookup in a class template in MSVC mode, look into
    // dependent base classes where the primary class template is known.
    if (Result.empty() && getLangOpts().MSVCCompat && (!SS || SS->isEmpty())) {
      if (ParsedType TypeInBase =
              recoverFromTypeInKnownDependentBase(*this, II, NameLoc))
        return TypeInBase;
    }
  }

  NamedDecl *IIDecl = nullptr;
  switch (Result.getResultKind()) {
  case LookupResult::NotFound:
  case LookupResult::NotFoundInCurrentInstantiation:
    if (CorrectedII) {
      TypoCorrection Correction =
          CorrectTypo(Result.getLookupNameInfo(), Kind, S, SS,
                      llvm::make_unique<TypeNameValidatorCCC>(
                          true, isClassName, AllowDeducedTemplate),
                      CTK_ErrorRecovery);
      IdentifierInfo *NewII = Correction.getCorrectionAsIdentifierInfo();
      TemplateTy Template;
      bool MemberOfUnknownSpecialization;
      UnqualifiedId TemplateName;
      TemplateName.setIdentifier(NewII, NameLoc);
      NestedNameSpecifier *NNS = Correction.getCorrectionSpecifier();
      CXXScopeSpec NewSS, *NewSSPtr = SS;
      if (SS && NNS) {
        NewSS.MakeTrivial(Context, NNS, SourceRange(NameLoc));
        NewSSPtr = &NewSS;
      }
      if (Correction && (NNS || NewII != &II) &&
          // Ignore a correction to a template type as the to-be-corrected
          // identifier is not a template (typo correction for template names
          // is handled elsewhere).
          !(getLangOpts().CPlusPlus && NewSSPtr &&
            isTemplateName(S, *NewSSPtr, false, TemplateName, nullptr, false,
                           Template, MemberOfUnknownSpecialization))) {
        ParsedType Ty = getTypeName(*NewII, NameLoc, S, NewSSPtr,
                                    isClassName, HasTrailingDot, ObjectTypePtr,
                                    IsCtorOrDtorName,
                                    WantNontrivialTypeSourceInfo,
                                    IsClassTemplateDeductionContext);
        if (Ty) {
          diagnoseTypo(Correction,
                       PDiag(diag::err_unknown_type_or_class_name_suggest)
                         << Result.getLookupName() << isClassName);
          if (SS && NNS)
            SS->MakeTrivial(Context, NNS, SourceRange(NameLoc));
          *CorrectedII = NewII;
          return Ty;
        }
      }
    }
    // If typo correction failed or was not performed, fall through
    LLVM_FALLTHROUGH;
  case LookupResult::FoundOverloaded:
  case LookupResult::FoundUnresolvedValue:
    Result.suppressDiagnostics();
    return nullptr;

  case LookupResult::Ambiguous:
    // Recover from type-hiding ambiguities by hiding the type.  We'll
    // do the lookup again when looking for an object, and we can
    // diagnose the error then.  If we don't do this, then the error
    // about hiding the type will be immediately followed by an error
    // that only makes sense if the identifier was treated like a type.
    if (Result.getAmbiguityKind() == LookupResult::AmbiguousTagHiding) {
      Result.suppressDiagnostics();
      return nullptr;
    }

    // Look to see if we have a type anywhere in the list of results.
    for (LookupResult::iterator Res = Result.begin(), ResEnd = Result.end();
         Res != ResEnd; ++Res) {
      if (isa<TypeDecl>(*Res) || isa<ObjCInterfaceDecl>(*Res) ||
          (AllowDeducedTemplate && getAsTypeTemplateDecl(*Res))) {
        if (!IIDecl ||
            (*Res)->getLocation().getRawEncoding() <
              IIDecl->getLocation().getRawEncoding())
          IIDecl = *Res;
      }
    }

    if (!IIDecl) {
      // None of the entities we found is a type, so there is no way
      // to even assume that the result is a type. In this case, don't
      // complain about the ambiguity. The parser will either try to
      // perform this lookup again (e.g., as an object name), which
      // will produce the ambiguity, or will complain that it expected
      // a type name.
      Result.suppressDiagnostics();
      return nullptr;
    }

    // We found a type within the ambiguous lookup; diagnose the
    // ambiguity and then return that type. This might be the right
    // answer, or it might not be, but it suppresses any attempt to
    // perform the name lookup again.
    break;

  case LookupResult::Found:
    IIDecl = Result.getFoundDecl();
    break;
  }

  assert(IIDecl && "Didn't find decl");

  QualType T;
  if (TypeDecl *TD = dyn_cast<TypeDecl>(IIDecl)) {
    // C++ [class.qual]p2: A lookup that would find the injected-class-name
    // instead names the constructors of the class, except when naming a class.
    // This is ill-formed when we're not actually forming a ctor or dtor name.
    auto *LookupRD = dyn_cast_or_null<CXXRecordDecl>(LookupCtx);
    auto *FoundRD = dyn_cast<CXXRecordDecl>(TD);
    if (!isClassName && !IsCtorOrDtorName && LookupRD && FoundRD &&
        FoundRD->isInjectedClassName() &&
        declaresSameEntity(LookupRD, cast<Decl>(FoundRD->getParent())))
      Diag(NameLoc, diag::err_out_of_line_qualified_id_type_names_constructor)
          << &II << /*Type*/1;

    DiagnoseUseOfDecl(IIDecl, NameLoc);

    T = Context.getTypeDeclType(TD);
    MarkAnyDeclReferenced(TD->getLocation(), TD, /*OdrUse=*/false);
  } else if (ObjCInterfaceDecl *IDecl = dyn_cast<ObjCInterfaceDecl>(IIDecl)) {
    (void)DiagnoseUseOfDecl(IDecl, NameLoc);
    if (!HasTrailingDot)
      T = Context.getObjCInterfaceType(IDecl);
  } else if (AllowDeducedTemplate) {
    if (auto *TD = getAsTypeTemplateDecl(IIDecl))
      T = Context.getDeducedTemplateSpecializationType(TemplateName(TD),
                                                       QualType(), false);
  }

  if (T.isNull()) {
    // If it's not plausibly a type, suppress diagnostics.
    Result.suppressDiagnostics();
    return nullptr;
  }

  // NOTE: avoid constructing an ElaboratedType(Loc) if this is a
  // constructor or destructor name (in such a case, the scope specifier
  // will be attached to the enclosing Expr or Decl node).
  if (SS && SS->isNotEmpty() && !IsCtorOrDtorName &&
      !isa<ObjCInterfaceDecl>(IIDecl)) {
    if (WantNontrivialTypeSourceInfo) {
      // Construct a type with type-source information.
      TypeLocBuilder Builder;
      Builder.pushTypeSpec(T).setNameLoc(NameLoc);

      T = getElaboratedType(ETK_None, *SS, T);
      ElaboratedTypeLoc ElabTL = Builder.push<ElaboratedTypeLoc>(T);
      ElabTL.setElaboratedKeywordLoc(SourceLocation());
      ElabTL.setQualifierLoc(SS->getWithLocInContext(Context));
      return CreateParsedType(T, Builder.getTypeSourceInfo(Context, T));
    } else {
      T = getElaboratedType(ETK_None, *SS, T);
    }
  }

  return ParsedType::make(T);
}

// Builds a fake NNS for the given decl context.
static NestedNameSpecifier *
synthesizeCurrentNestedNameSpecifier(ASTContext &Context, DeclContext *DC) {
  for (;; DC = DC->getLookupParent()) {
    DC = DC->getPrimaryContext();
    auto *ND = dyn_cast<NamespaceDecl>(DC);
    if (ND && !ND->isInline() && !ND->isAnonymousNamespace())
      return NestedNameSpecifier::Create(Context, nullptr, ND);
    else if (auto *RD = dyn_cast<CXXRecordDecl>(DC))
      return NestedNameSpecifier::Create(Context, nullptr, RD->isTemplateDecl(),
                                         RD->getTypeForDecl());
    else if (isa<TranslationUnitDecl>(DC))
      return NestedNameSpecifier::GlobalSpecifier(Context);
  }
  llvm_unreachable("something isn't in TU scope?");
}

/// Find the parent class with dependent bases of the innermost enclosing method
/// context. Do not look for enclosing CXXRecordDecls directly, or we will end
/// up allowing unqualified dependent type names at class-level, which MSVC
/// correctly rejects.
static const CXXRecordDecl *
findRecordWithDependentBasesOfEnclosingMethod(const DeclContext *DC) {
  for (; DC && DC->isDependentContext(); DC = DC->getLookupParent()) {
    DC = DC->getPrimaryContext();
    if (const auto *MD = dyn_cast<CXXMethodDecl>(DC))
      if (MD->getParent()->hasAnyDependentBases())
        return MD->getParent();
  }
  return nullptr;
}

ParsedType Sema::ActOnMSVCUnknownTypeName(const IdentifierInfo &II,
                                          SourceLocation NameLoc,
                                          bool IsTemplateTypeArg) {
  assert(getLangOpts().MSVCCompat && "shouldn't be called in non-MSVC mode");

  NestedNameSpecifier *NNS = nullptr;
  if (IsTemplateTypeArg && getCurScope()->isTemplateParamScope()) {
    // If we weren't able to parse a default template argument, delay lookup
    // until instantiation time by making a non-dependent DependentTypeName. We
    // pretend we saw a NestedNameSpecifier referring to the current scope, and
    // lookup is retried.
    // FIXME: This hurts our diagnostic quality, since we get errors like "no
    // type named 'Foo' in 'current_namespace'" when the user didn't write any
    // name specifiers.
    NNS = synthesizeCurrentNestedNameSpecifier(Context, CurContext);
    Diag(NameLoc, diag::ext_ms_delayed_template_argument) << &II;
  } else if (const CXXRecordDecl *RD =
                 findRecordWithDependentBasesOfEnclosingMethod(CurContext)) {
    // Build a DependentNameType that will perform lookup into RD at
    // instantiation time.
    NNS = NestedNameSpecifier::Create(Context, nullptr, RD->isTemplateDecl(),
                                      RD->getTypeForDecl());

    // Diagnose that this identifier was undeclared, and retry the lookup during
    // template instantiation.
    Diag(NameLoc, diag::ext_undeclared_unqual_id_with_dependent_base) << &II
                                                                      << RD;
  } else {
    // This is not a situation that we should recover from.
    return ParsedType();
  }

  QualType T = Context.getDependentNameType(ETK_None, NNS, &II);

  // Build type location information.  We synthesized the qualifier, so we have
  // to build a fake NestedNameSpecifierLoc.
  NestedNameSpecifierLocBuilder NNSLocBuilder;
  NNSLocBuilder.MakeTrivial(Context, NNS, SourceRange(NameLoc));
  NestedNameSpecifierLoc QualifierLoc = NNSLocBuilder.getWithLocInContext(Context);

  TypeLocBuilder Builder;
  DependentNameTypeLoc DepTL = Builder.push<DependentNameTypeLoc>(T);
  DepTL.setNameLoc(NameLoc);
  DepTL.setElaboratedKeywordLoc(SourceLocation());
  DepTL.setQualifierLoc(QualifierLoc);
  return CreateParsedType(T, Builder.getTypeSourceInfo(Context, T));
}

/// isTagName() - This method is called *for error recovery purposes only*
/// to determine if the specified name is a valid tag name ("struct foo").  If
/// so, this returns the TST for the tag corresponding to it (TST_enum,
/// TST_union, TST_struct, TST_interface, TST_class).  This is used to diagnose
/// cases in C where the user forgot to specify the tag.
DeclSpec::TST Sema::isTagName(IdentifierInfo &II, Scope *S) {
  // Do a tag name lookup in this scope.
  LookupResult R(*this, &II, SourceLocation(), LookupTagName);
  LookupName(R, S, false);
  R.suppressDiagnostics();
  if (R.getResultKind() == LookupResult::Found)
    if (const TagDecl *TD = R.getAsSingle<TagDecl>()) {
      switch (TD->getTagKind()) {
      case TTK_Struct: return DeclSpec::TST_struct;
      case TTK_Interface: return DeclSpec::TST_interface;
      case TTK_Union:  return DeclSpec::TST_union;
      case TTK_Class:  return DeclSpec::TST_class;
      case TTK_Enum:   return DeclSpec::TST_enum;
      }
    }

  return DeclSpec::TST_unspecified;
}

/// isMicrosoftMissingTypename - In Microsoft mode, within class scope,
/// if a CXXScopeSpec's type is equal to the type of one of the base classes
/// then downgrade the missing typename error to a warning.
/// This is needed for MSVC compatibility; Example:
/// @code
/// template<class T> class A {
/// public:
///   typedef int TYPE;
/// };
/// template<class T> class B : public A<T> {
/// public:
///   A<T>::TYPE a; // no typename required because A<T> is a base class.
/// };
/// @endcode
bool Sema::isMicrosoftMissingTypename(const CXXScopeSpec *SS, Scope *S) {
  if (CurContext->isRecord()) {
    if (SS->getScopeRep()->getKind() == NestedNameSpecifier::Super)
      return true;

    const Type *Ty = SS->getScopeRep()->getAsType();

    CXXRecordDecl *RD = cast<CXXRecordDecl>(CurContext);
    for (const auto &Base : RD->bases())
      if (Ty && Context.hasSameUnqualifiedType(QualType(Ty, 1), Base.getType()))
        return true;
    return S->isFunctionPrototypeScope();
  }
  return CurContext->isFunctionOrMethod() || S->isFunctionPrototypeScope();
}

void Sema::DiagnoseUnknownTypeName(IdentifierInfo *&II,
                                   SourceLocation IILoc,
                                   Scope *S,
                                   CXXScopeSpec *SS,
                                   ParsedType &SuggestedType,
                                   bool IsTemplateName) {
  // Don't report typename errors for editor placeholders.
  if (II->isEditorPlaceholder())
    return;
  // We don't have anything to suggest (yet).
  SuggestedType = nullptr;

  // There may have been a typo in the name of the type. Look up typo
  // results, in case we have something that we can suggest.
  if (TypoCorrection Corrected =
          CorrectTypo(DeclarationNameInfo(II, IILoc), LookupOrdinaryName, S, SS,
                      llvm::make_unique<TypeNameValidatorCCC>(
                          false, false, IsTemplateName, !IsTemplateName),
                      CTK_ErrorRecovery)) {
    // FIXME: Support error recovery for the template-name case.
    bool CanRecover = !IsTemplateName;
    if (Corrected.isKeyword()) {
      // We corrected to a keyword.
      diagnoseTypo(Corrected,
                   PDiag(IsTemplateName ? diag::err_no_template_suggest
                                        : diag::err_unknown_typename_suggest)
                       << II);
      II = Corrected.getCorrectionAsIdentifierInfo();
    } else {
      // We found a similarly-named type or interface; suggest that.
      if (!SS || !SS->isSet()) {
        diagnoseTypo(Corrected,
                     PDiag(IsTemplateName ? diag::err_no_template_suggest
                                          : diag::err_unknown_typename_suggest)
                         << II, CanRecover);
      } else if (DeclContext *DC = computeDeclContext(*SS, false)) {
        std::string CorrectedStr(Corrected.getAsString(getLangOpts()));
        bool DroppedSpecifier = Corrected.WillReplaceSpecifier() &&
                                II->getName().equals(CorrectedStr);
        diagnoseTypo(Corrected,
                     PDiag(IsTemplateName
                               ? diag::err_no_member_template_suggest
                               : diag::err_unknown_nested_typename_suggest)
                         << II << DC << DroppedSpecifier << SS->getRange(),
                     CanRecover);
      } else {
        llvm_unreachable("could not have corrected a typo here");
      }

      if (!CanRecover)
        return;

      CXXScopeSpec tmpSS;
      if (Corrected.getCorrectionSpecifier())
        tmpSS.MakeTrivial(Context, Corrected.getCorrectionSpecifier(),
                          SourceRange(IILoc));
      // FIXME: Support class template argument deduction here.
      SuggestedType =
          getTypeName(*Corrected.getCorrectionAsIdentifierInfo(), IILoc, S,
                      tmpSS.isSet() ? &tmpSS : SS, false, false, nullptr,
                      /*IsCtorOrDtorName=*/false,
                      /*NonTrivialTypeSourceInfo=*/true);
    }
    return;
  }

  if (getLangOpts().CPlusPlus && !IsTemplateName) {
    // See if II is a class template that the user forgot to pass arguments to.
    UnqualifiedId Name;
    Name.setIdentifier(II, IILoc);
    CXXScopeSpec EmptySS;
    TemplateTy TemplateResult;
    bool MemberOfUnknownSpecialization;
    if (isTemplateName(S, SS ? *SS : EmptySS, /*hasTemplateKeyword=*/false,
                       Name, nullptr, true, TemplateResult,
                       MemberOfUnknownSpecialization) == TNK_Type_template) {
      diagnoseMissingTemplateArguments(TemplateResult.get(), IILoc);
      return;
    }
  }

  // FIXME: Should we move the logic that tries to recover from a missing tag
  // (struct, union, enum) from Parser::ParseImplicitInt here, instead?

  if (!SS || (!SS->isSet() && !SS->isInvalid()))
    Diag(IILoc, IsTemplateName ? diag::err_no_template
                               : diag::err_unknown_typename)
        << II;
  else if (DeclContext *DC = computeDeclContext(*SS, false))
    Diag(IILoc, IsTemplateName ? diag::err_no_member_template
                               : diag::err_typename_nested_not_found)
        << II << DC << SS->getRange();
  else if (isDependentScopeSpecifier(*SS)) {
    unsigned DiagID = diag::err_typename_missing;
    if (getLangOpts().MSVCCompat && isMicrosoftMissingTypename(SS, S))
      DiagID = diag::ext_typename_missing;

    Diag(SS->getRange().getBegin(), DiagID)
      << SS->getScopeRep() << II->getName()
      << SourceRange(SS->getRange().getBegin(), IILoc)
      << FixItHint::CreateInsertion(SS->getRange().getBegin(), "typename ");
    SuggestedType = ActOnTypenameType(S, SourceLocation(),
                                      *SS, *II, IILoc).get();
  } else {
    assert(SS && SS->isInvalid() &&
           "Invalid scope specifier has already been diagnosed");
  }
}

/// Determine whether the given result set contains either a type name
/// or
static bool isResultTypeOrTemplate(LookupResult &R, const Token &NextToken) {
  bool CheckTemplate = R.getSema().getLangOpts().CPlusPlus &&
                       NextToken.is(tok::less);

  for (LookupResult::iterator I = R.begin(), IEnd = R.end(); I != IEnd; ++I) {
    if (isa<TypeDecl>(*I) || isa<ObjCInterfaceDecl>(*I))
      return true;

    if (CheckTemplate && isa<TemplateDecl>(*I))
      return true;
  }

  return false;
}

static bool isTagTypeWithMissingTag(Sema &SemaRef, LookupResult &Result,
                                    Scope *S, CXXScopeSpec &SS,
                                    IdentifierInfo *&Name,
                                    SourceLocation NameLoc) {
  LookupResult R(SemaRef, Name, NameLoc, Sema::LookupTagName);
  SemaRef.LookupParsedName(R, S, &SS);
  if (TagDecl *Tag = R.getAsSingle<TagDecl>()) {
    StringRef FixItTagName;
    switch (Tag->getTagKind()) {
      case TTK_Class:
        FixItTagName = "class ";
        break;

      case TTK_Enum:
        FixItTagName = "enum ";
        break;

      case TTK_Struct:
        FixItTagName = "struct ";
        break;

      case TTK_Interface:
        FixItTagName = "__interface ";
        break;

      case TTK_Union:
        FixItTagName = "union ";
        break;
    }

    StringRef TagName = FixItTagName.drop_back();
    SemaRef.Diag(NameLoc, diag::err_use_of_tag_name_without_tag)
      << Name << TagName << SemaRef.getLangOpts().CPlusPlus
      << FixItHint::CreateInsertion(NameLoc, FixItTagName);

    for (LookupResult::iterator I = Result.begin(), IEnd = Result.end();
         I != IEnd; ++I)
      SemaRef.Diag((*I)->getLocation(), diag::note_decl_hiding_tag_type)
        << Name << TagName;

    // Replace lookup results with just the tag decl.
    Result.clear(Sema::LookupTagName);
    SemaRef.LookupParsedName(Result, S, &SS);
    return true;
  }

  return false;
}

/// Build a ParsedType for a simple-type-specifier with a nested-name-specifier.
static ParsedType buildNestedType(Sema &S, CXXScopeSpec &SS,
                                  QualType T, SourceLocation NameLoc) {
  ASTContext &Context = S.Context;

  TypeLocBuilder Builder;
  Builder.pushTypeSpec(T).setNameLoc(NameLoc);

  T = S.getElaboratedType(ETK_None, SS, T);
  ElaboratedTypeLoc ElabTL = Builder.push<ElaboratedTypeLoc>(T);
  ElabTL.setElaboratedKeywordLoc(SourceLocation());
  ElabTL.setQualifierLoc(SS.getWithLocInContext(Context));
  return S.CreateParsedType(T, Builder.getTypeSourceInfo(Context, T));
}

Sema::NameClassification
Sema::ClassifyName(Scope *S, CXXScopeSpec &SS, IdentifierInfo *&Name,
                   SourceLocation NameLoc, const Token &NextToken,
                   bool IsAddressOfOperand,
                   std::unique_ptr<CorrectionCandidateCallback> CCC) {
  DeclarationNameInfo NameInfo(Name, NameLoc);
  ObjCMethodDecl *CurMethod = getCurMethodDecl();

  if (NextToken.is(tok::coloncolon)) {
    NestedNameSpecInfo IdInfo(Name, NameLoc, NextToken.getLocation());
    BuildCXXNestedNameSpecifier(S, IdInfo, false, SS, nullptr, false);
  } else if (getLangOpts().CPlusPlus && SS.isSet() &&
             isCurrentClassName(*Name, S, &SS)) {
    // Per [class.qual]p2, this names the constructors of SS, not the
    // injected-class-name. We don't have a classification for that.
    // There's not much point caching this result, since the parser
    // will reject it later.
    return NameClassification::Unknown();
  }

  LookupResult Result(*this, Name, NameLoc, LookupOrdinaryName);
  LookupParsedName(Result, S, &SS, !CurMethod);

  // For unqualified lookup in a class template in MSVC mode, look into
  // dependent base classes where the primary class template is known.
  if (Result.empty() && SS.isEmpty() && getLangOpts().MSVCCompat) {
    if (ParsedType TypeInBase =
            recoverFromTypeInKnownDependentBase(*this, *Name, NameLoc))
      return TypeInBase;
  }

  // Perform lookup for Objective-C instance variables (including automatically
  // synthesized instance variables), if we're in an Objective-C method.
  // FIXME: This lookup really, really needs to be folded in to the normal
  // unqualified lookup mechanism.
  if (!SS.isSet() && CurMethod && !isResultTypeOrTemplate(Result, NextToken)) {
    ExprResult E = LookupInObjCMethod(Result, S, Name, true);
    if (E.get() || E.isInvalid())
      return E;
  }

  bool SecondTry = false;
  bool IsFilteredTemplateName = false;

Corrected:
  switch (Result.getResultKind()) {
  case LookupResult::NotFound:
    // If an unqualified-id is followed by a '(', then we have a function
    // call.
    if (!SS.isSet() && NextToken.is(tok::l_paren)) {
      // In C++, this is an ADL-only call.
      // FIXME: Reference?
      if (getLangOpts().CPlusPlus)
        return BuildDeclarationNameExpr(SS, Result, /*ADL=*/true);

      // C90 6.3.2.2:
      //   If the expression that precedes the parenthesized argument list in a
      //   function call consists solely of an identifier, and if no
      //   declaration is visible for this identifier, the identifier is
      //   implicitly declared exactly as if, in the innermost block containing
      //   the function call, the declaration
      //
      //     extern int identifier ();
      //
      //   appeared.
      //
      // We also allow this in C99 as an extension.
      if (NamedDecl *D = ImplicitlyDefineFunction(NameLoc, *Name, S)) {
        Result.addDecl(D);
        Result.resolveKind();
        return BuildDeclarationNameExpr(SS, Result, /*ADL=*/false);
      }
    }

    // In C, we first see whether there is a tag type by the same name, in
    // which case it's likely that the user just forgot to write "enum",
    // "struct", or "union".
    if (!getLangOpts().CPlusPlus && !SecondTry &&
        isTagTypeWithMissingTag(*this, Result, S, SS, Name, NameLoc)) {
      break;
    }

    // Perform typo correction to determine if there is another name that is
    // close to this name.
    if (!SecondTry && CCC) {
      SecondTry = true;
      if (TypoCorrection Corrected = CorrectTypo(Result.getLookupNameInfo(),
                                                 Result.getLookupKind(), S,
                                                 &SS, std::move(CCC),
                                                 CTK_ErrorRecovery)) {
        unsigned UnqualifiedDiag = diag::err_undeclared_var_use_suggest;
        unsigned QualifiedDiag = diag::err_no_member_suggest;

        NamedDecl *FirstDecl = Corrected.getFoundDecl();
        NamedDecl *UnderlyingFirstDecl = Corrected.getCorrectionDecl();
        if (getLangOpts().CPlusPlus && NextToken.is(tok::less) &&
            UnderlyingFirstDecl && isa<TemplateDecl>(UnderlyingFirstDecl)) {
          UnqualifiedDiag = diag::err_no_template_suggest;
          QualifiedDiag = diag::err_no_member_template_suggest;
        } else if (UnderlyingFirstDecl &&
                   (isa<TypeDecl>(UnderlyingFirstDecl) ||
                    isa<ObjCInterfaceDecl>(UnderlyingFirstDecl) ||
                    isa<ObjCCompatibleAliasDecl>(UnderlyingFirstDecl))) {
          UnqualifiedDiag = diag::err_unknown_typename_suggest;
          QualifiedDiag = diag::err_unknown_nested_typename_suggest;
        }

        if (SS.isEmpty()) {
          diagnoseTypo(Corrected, PDiag(UnqualifiedDiag) << Name);
        } else {// FIXME: is this even reachable? Test it.
          std::string CorrectedStr(Corrected.getAsString(getLangOpts()));
          bool DroppedSpecifier = Corrected.WillReplaceSpecifier() &&
                                  Name->getName().equals(CorrectedStr);
          diagnoseTypo(Corrected, PDiag(QualifiedDiag)
                                    << Name << computeDeclContext(SS, false)
                                    << DroppedSpecifier << SS.getRange());
        }

        // Update the name, so that the caller has the new name.
        Name = Corrected.getCorrectionAsIdentifierInfo();

        // Typo correction corrected to a keyword.
        if (Corrected.isKeyword())
          return Name;

        // Also update the LookupResult...
        // FIXME: This should probably go away at some point
        Result.clear();
        Result.setLookupName(Corrected.getCorrection());
        if (FirstDecl)
          Result.addDecl(FirstDecl);

        // If we found an Objective-C instance variable, let
        // LookupInObjCMethod build the appropriate expression to
        // reference the ivar.
        // FIXME: This is a gross hack.
        if (ObjCIvarDecl *Ivar = Result.getAsSingle<ObjCIvarDecl>()) {
          Result.clear();
          ExprResult E(LookupInObjCMethod(Result, S, Ivar->getIdentifier()));
          return E;
        }

        goto Corrected;
      }
    }

    // We failed to correct; just fall through and let the parser deal with it.
    Result.suppressDiagnostics();
    return NameClassification::Unknown();

  case LookupResult::NotFoundInCurrentInstantiation: {
    // We performed name lookup into the current instantiation, and there were
    // dependent bases, so we treat this result the same way as any other
    // dependent nested-name-specifier.

    // C++ [temp.res]p2:
    //   A name used in a template declaration or definition and that is
    //   dependent on a template-parameter is assumed not to name a type
    //   unless the applicable name lookup finds a type name or the name is
    //   qualified by the keyword typename.
    //
    // FIXME: If the next token is '<', we might want to ask the parser to
    // perform some heroics to see if we actually have a
    // template-argument-list, which would indicate a missing 'template'
    // keyword here.
    return ActOnDependentIdExpression(SS, /*TemplateKWLoc=*/SourceLocation(),
                                      NameInfo, IsAddressOfOperand,
                                      /*TemplateArgs=*/nullptr);
  }

  case LookupResult::Found:
  case LookupResult::FoundOverloaded:
  case LookupResult::FoundUnresolvedValue:
    break;

  case LookupResult::Ambiguous:
    if (getLangOpts().CPlusPlus && NextToken.is(tok::less) &&
        hasAnyAcceptableTemplateNames(Result)) {
      // C++ [temp.local]p3:
      //   A lookup that finds an injected-class-name (10.2) can result in an
      //   ambiguity in certain cases (for example, if it is found in more than
      //   one base class). If all of the injected-class-names that are found
      //   refer to specializations of the same class template, and if the name
      //   is followed by a template-argument-list, the reference refers to the
      //   class template itself and not a specialization thereof, and is not
      //   ambiguous.
      //
      // This filtering can make an ambiguous result into an unambiguous one,
      // so try again after filtering out template names.
      FilterAcceptableTemplateNames(Result);
      if (!Result.isAmbiguous()) {
        IsFilteredTemplateName = true;
        break;
      }
    }

    // Diagnose the ambiguity and return an error.
    return NameClassification::Error();
  }

  if (getLangOpts().CPlusPlus && NextToken.is(tok::less) &&
      (IsFilteredTemplateName || hasAnyAcceptableTemplateNames(Result))) {
    // C++ [temp.names]p3:
    //   After name lookup (3.4) finds that a name is a template-name or that
    //   an operator-function-id or a literal- operator-id refers to a set of
    //   overloaded functions any member of which is a function template if
    //   this is followed by a <, the < is always taken as the delimiter of a
    //   template-argument-list and never as the less-than operator.
    if (!IsFilteredTemplateName)
      FilterAcceptableTemplateNames(Result);

    if (!Result.empty()) {
      bool IsFunctionTemplate;
      bool IsVarTemplate;
      TemplateName Template;
      if (Result.end() - Result.begin() > 1) {
        IsFunctionTemplate = true;
        Template = Context.getOverloadedTemplateName(Result.begin(),
                                                     Result.end());
      } else {
        TemplateDecl *TD
          = cast<TemplateDecl>((*Result.begin())->getUnderlyingDecl());
        IsFunctionTemplate = isa<FunctionTemplateDecl>(TD);
        IsVarTemplate = isa<VarTemplateDecl>(TD);

        if (SS.isSet() && !SS.isInvalid())
          Template = Context.getQualifiedTemplateName(SS.getScopeRep(),
                                                    /*TemplateKeyword=*/false,
                                                      TD);
        else
          Template = TemplateName(TD);
      }

      if (IsFunctionTemplate) {
        // Function templates always go through overload resolution, at which
        // point we'll perform the various checks (e.g., accessibility) we need
        // to based on which function we selected.
        Result.suppressDiagnostics();

        return NameClassification::FunctionTemplate(Template);
      }

      return IsVarTemplate ? NameClassification::VarTemplate(Template)
                           : NameClassification::TypeTemplate(Template);
    }
  }

  NamedDecl *FirstDecl = (*Result.begin())->getUnderlyingDecl();
  if (TypeDecl *Type = dyn_cast<TypeDecl>(FirstDecl)) {
    DiagnoseUseOfDecl(Type, NameLoc);
    MarkAnyDeclReferenced(Type->getLocation(), Type, /*OdrUse=*/false);
    QualType T = Context.getTypeDeclType(Type);
    if (SS.isNotEmpty())
      return buildNestedType(*this, SS, T, NameLoc);
    return ParsedType::make(T);
  }

  ObjCInterfaceDecl *Class = dyn_cast<ObjCInterfaceDecl>(FirstDecl);
  if (!Class) {
    // FIXME: It's unfortunate that we don't have a Type node for handling this.
    if (ObjCCompatibleAliasDecl *Alias =
            dyn_cast<ObjCCompatibleAliasDecl>(FirstDecl))
      Class = Alias->getClassInterface();
  }

  if (Class) {
    DiagnoseUseOfDecl(Class, NameLoc);

    if (NextToken.is(tok::period)) {
      // Interface. <something> is parsed as a property reference expression.
      // Just return "unknown" as a fall-through for now.
      Result.suppressDiagnostics();
      return NameClassification::Unknown();
    }

    QualType T = Context.getObjCInterfaceType(Class);
    return ParsedType::make(T);
  }

  // We can have a type template here if we're classifying a template argument.
  if (isa<TemplateDecl>(FirstDecl) && !isa<FunctionTemplateDecl>(FirstDecl) &&
      !isa<VarTemplateDecl>(FirstDecl))
    return NameClassification::TypeTemplate(
        TemplateName(cast<TemplateDecl>(FirstDecl)));

  // Check for a tag type hidden by a non-type decl in a few cases where it
  // seems likely a type is wanted instead of the non-type that was found.
  bool NextIsOp = NextToken.isOneOf(tok::amp, tok::star);
  if ((NextToken.is(tok::identifier) ||
       (NextIsOp &&
        FirstDecl->getUnderlyingDecl()->isFunctionOrFunctionTemplate())) &&
      isTagTypeWithMissingTag(*this, Result, S, SS, Name, NameLoc)) {
    TypeDecl *Type = Result.getAsSingle<TypeDecl>();
    DiagnoseUseOfDecl(Type, NameLoc);
    QualType T = Context.getTypeDeclType(Type);
    if (SS.isNotEmpty())
      return buildNestedType(*this, SS, T, NameLoc);
    return ParsedType::make(T);
  }

  if (FirstDecl->isCXXClassMember())
    return BuildPossibleImplicitMemberExpr(SS, SourceLocation(), Result,
                                           nullptr, S);

  bool ADL = UseArgumentDependentLookup(SS, Result, NextToken.is(tok::l_paren));
  return BuildDeclarationNameExpr(SS, Result, ADL);
}

Sema::TemplateNameKindForDiagnostics
Sema::getTemplateNameKindForDiagnostics(TemplateName Name) {
  auto *TD = Name.getAsTemplateDecl();
  if (!TD)
    return TemplateNameKindForDiagnostics::DependentTemplate;
  if (isa<ClassTemplateDecl>(TD))
    return TemplateNameKindForDiagnostics::ClassTemplate;
  if (isa<FunctionTemplateDecl>(TD))
    return TemplateNameKindForDiagnostics::FunctionTemplate;
  if (isa<VarTemplateDecl>(TD))
    return TemplateNameKindForDiagnostics::VarTemplate;
  if (isa<TypeAliasTemplateDecl>(TD))
    return TemplateNameKindForDiagnostics::AliasTemplate;
  if (isa<TemplateTemplateParmDecl>(TD))
    return TemplateNameKindForDiagnostics::TemplateTemplateParam;
  return TemplateNameKindForDiagnostics::DependentTemplate;
}

// Determines the context to return to after temporarily entering a
// context.  This depends in an unnecessarily complicated way on the
// exact ordering of callbacks from the parser.
DeclContext *Sema::getContainingDC(DeclContext *DC) {

  // Functions defined inline within classes aren't parsed until we've
  // finished parsing the top-level class, so the top-level class is
  // the context we'll need to return to.
  // A Lambda call operator whose parent is a class must not be treated
  // as an inline member function.  A Lambda can be used legally
  // either as an in-class member initializer or a default argument.  These
  // are parsed once the class has been marked complete and so the containing
  // context would be the nested class (when the lambda is defined in one);
  // If the class is not complete, then the lambda is being used in an
  // ill-formed fashion (such as to specify the width of a bit-field, or
  // in an array-bound) - in which case we still want to return the
  // lexically containing DC (which could be a nested class).
  if (isa<FunctionDecl>(DC) && !isLambdaCallOperator(DC)) {
    DC = DC->getLexicalParent();

    // A function not defined within a class will always return to its
    // lexical context.
    if (!isa<CXXRecordDecl>(DC))
      return DC;

    // A C++ inline method/friend is parsed *after* the topmost class
    // it was declared in is fully parsed ("complete");  the topmost
    // class is the context we need to return to.
    while (CXXRecordDecl *RD = dyn_cast<CXXRecordDecl>(DC->getLexicalParent()))
      DC = RD;

    // Return the declaration context of the topmost class the inline method is
    // declared in.
    return DC;
  }

  return DC->getLexicalParent();
}

void Sema::PushDeclContext(Scope *S, DeclContext *DC) {
  assert(getContainingDC(DC) == CurContext &&
      "The next DeclContext should be lexically contained in the current one.");
  CurContext = DC;
  S->setEntity(DC);
}

void Sema::PopDeclContext() {
  assert(CurContext && "DeclContext imbalance!");

  CurContext = getContainingDC(CurContext);
  assert(CurContext && "Popped translation unit!");
}

Sema::SkippedDefinitionContext Sema::ActOnTagStartSkippedDefinition(Scope *S,
                                                                    Decl *D) {
  // Unlike PushDeclContext, the context to which we return is not necessarily
  // the containing DC of TD, because the new context will be some pre-existing
  // TagDecl definition instead of a fresh one.
  auto Result = static_cast<SkippedDefinitionContext>(CurContext);
  CurContext = cast<TagDecl>(D)->getDefinition();
  assert(CurContext && "skipping definition of undefined tag");
  // Start lookups from the parent of the current context; we don't want to look
  // into the pre-existing complete definition.
  S->setEntity(CurContext->getLookupParent());
  return Result;
}

void Sema::ActOnTagFinishSkippedDefinition(SkippedDefinitionContext Context) {
  CurContext = static_cast<decltype(CurContext)>(Context);
}

/// EnterDeclaratorContext - Used when we must lookup names in the context
/// of a declarator's nested name specifier.
///
void Sema::EnterDeclaratorContext(Scope *S, DeclContext *DC) {
  // C++0x [basic.lookup.unqual]p13:
  //   A name used in the definition of a static data member of class
  //   X (after the qualified-id of the static member) is looked up as
  //   if the name was used in a member function of X.
  // C++0x [basic.lookup.unqual]p14:
  //   If a variable member of a namespace is defined outside of the
  //   scope of its namespace then any name used in the definition of
  //   the variable member (after the declarator-id) is looked up as
  //   if the definition of the variable member occurred in its
  //   namespace.
  // Both of these imply that we should push a scope whose context
  // is the semantic context of the declaration.  We can't use
  // PushDeclContext here because that context is not necessarily
  // lexically contained in the current context.  Fortunately,
  // the containing scope should have the appropriate information.

  assert(!S->getEntity() && "scope already has entity");

#ifndef NDEBUG
  Scope *Ancestor = S->getParent();
  while (!Ancestor->getEntity()) Ancestor = Ancestor->getParent();
  assert(Ancestor->getEntity() == CurContext && "ancestor context mismatch");
#endif

  CurContext = DC;
  S->setEntity(DC);
}

void Sema::ExitDeclaratorContext(Scope *S) {
  assert(S->getEntity() == CurContext && "Context imbalance!");

  // Switch back to the lexical context.  The safety of this is
  // enforced by an assert in EnterDeclaratorContext.
  Scope *Ancestor = S->getParent();
  while (!Ancestor->getEntity()) Ancestor = Ancestor->getParent();
  CurContext = Ancestor->getEntity();

  // We don't need to do anything with the scope, which is going to
  // disappear.
}

void Sema::ActOnReenterFunctionContext(Scope* S, Decl *D) {
  // We assume that the caller has already called
  // ActOnReenterTemplateScope so getTemplatedDecl() works.
  FunctionDecl *FD = D->getAsFunction();
  if (!FD)
    return;

  // Same implementation as PushDeclContext, but enters the context
  // from the lexical parent, rather than the top-level class.
  assert(CurContext == FD->getLexicalParent() &&
    "The next DeclContext should be lexically contained in the current one.");
  CurContext = FD;
  S->setEntity(CurContext);

  for (unsigned P = 0, NumParams = FD->getNumParams(); P < NumParams; ++P) {
    ParmVarDecl *Param = FD->getParamDecl(P);
    // If the parameter has an identifier, then add it to the scope
    if (Param->getIdentifier()) {
      S->AddDecl(Param);
      IdResolver.AddDecl(Param);
    }
  }
}

void Sema::ActOnExitFunctionContext() {
  // Same implementation as PopDeclContext, but returns to the lexical parent,
  // rather than the top-level class.
  assert(CurContext && "DeclContext imbalance!");
  CurContext = CurContext->getLexicalParent();
  assert(CurContext && "Popped translation unit!");
}

/// Determine whether we allow overloading of the function
/// PrevDecl with another declaration.
///
/// This routine determines whether overloading is possible, not
/// whether some new function is actually an overload. It will return
/// true in C++ (where we can always provide overloads) or, as an
/// extension, in C when the previous function is already an
/// overloaded function declaration or has the "overloadable"
/// attribute.
static bool AllowOverloadingOfFunction(LookupResult &Previous,
                                       ASTContext &Context,
                                       const FunctionDecl *New) {
  if (Context.getLangOpts().CPlusPlus)
    return true;

  if (Previous.getResultKind() == LookupResult::FoundOverloaded)
    return true;

  return Previous.getResultKind() == LookupResult::Found &&
         (Previous.getFoundDecl()->hasAttr<OverloadableAttr>() ||
          New->hasAttr<OverloadableAttr>());
}

/// Add this decl to the scope shadowed decl chains.
void Sema::PushOnScopeChains(NamedDecl *D, Scope *S, bool AddToContext) {
  // Move up the scope chain until we find the nearest enclosing
  // non-transparent context. The declaration will be introduced into this
  // scope.
  while (S->getEntity() && S->getEntity()->isTransparentContext())
    S = S->getParent();

  // Add scoped declarations into their context, so that they can be
  // found later. Declarations without a context won't be inserted
  // into any context.
  if (AddToContext)
    CurContext->addDecl(D);

  // Out-of-line definitions shouldn't be pushed into scope in C++, unless they
  // are function-local declarations.
  if (getLangOpts().CPlusPlus && D->isOutOfLine() &&
      !D->getDeclContext()->getRedeclContext()->Equals(
        D->getLexicalDeclContext()->getRedeclContext()) &&
      !D->getLexicalDeclContext()->isFunctionOrMethod())
    return;

  // Template instantiations should also not be pushed into scope.
  if (isa<FunctionDecl>(D) &&
      cast<FunctionDecl>(D)->isFunctionTemplateSpecialization())
    return;

  // If this replaces anything in the current scope,
  IdentifierResolver::iterator I = IdResolver.begin(D->getDeclName()),
                               IEnd = IdResolver.end();
  for (; I != IEnd; ++I) {
    if (S->isDeclScope(*I) && D->declarationReplaces(*I)) {
      S->RemoveDecl(*I);
      IdResolver.RemoveDecl(*I);

      // Should only need to replace one decl.
      break;
    }
  }

  S->AddDecl(D);

  if (isa<LabelDecl>(D) && !cast<LabelDecl>(D)->isGnuLocal()) {
    // Implicitly-generated labels may end up getting generated in an order that
    // isn't strictly lexical, which breaks name lookup. Be careful to insert
    // the label at the appropriate place in the identifier chain.
    for (I = IdResolver.begin(D->getDeclName()); I != IEnd; ++I) {
      DeclContext *IDC = (*I)->getLexicalDeclContext()->getRedeclContext();
      if (IDC == CurContext) {
        if (!S->isDeclScope(*I))
          continue;
      } else if (IDC->Encloses(CurContext))
        break;
    }

    IdResolver.InsertDeclAfter(I, D);
  } else {
    IdResolver.AddDecl(D);
  }
}

void Sema::pushExternalDeclIntoScope(NamedDecl *D, DeclarationName Name) {
  if (IdResolver.tryAddTopLevelDecl(D, Name) && TUScope)
    TUScope->AddDecl(D);
}

bool Sema::isDeclInScope(NamedDecl *D, DeclContext *Ctx, Scope *S,
                         bool AllowInlineNamespace) {
  return IdResolver.isDeclInScope(D, Ctx, S, AllowInlineNamespace);
}

Scope *Sema::getScopeForDeclContext(Scope *S, DeclContext *DC) {
  DeclContext *TargetDC = DC->getPrimaryContext();
  do {
    if (DeclContext *ScopeDC = S->getEntity())
      if (ScopeDC->getPrimaryContext() == TargetDC)
        return S;
  } while ((S = S->getParent()));

  return nullptr;
}

static bool isOutOfScopePreviousDeclaration(NamedDecl *,
                                            DeclContext*,
                                            ASTContext&);

/// Filters out lookup results that don't fall within the given scope
/// as determined by isDeclInScope.
void Sema::FilterLookupForScope(LookupResult &R, DeclContext *Ctx, Scope *S,
                                bool ConsiderLinkage,
                                bool AllowInlineNamespace) {
  LookupResult::Filter F = R.makeFilter();
  while (F.hasNext()) {
    NamedDecl *D = F.next();

    if (isDeclInScope(D, Ctx, S, AllowInlineNamespace))
      continue;

    if (ConsiderLinkage && isOutOfScopePreviousDeclaration(D, Ctx, Context))
      continue;

    F.erase();
  }

  F.done();
}

/// We've determined that \p New is a redeclaration of \p Old. Check that they
/// have compatible owning modules.
bool Sema::CheckRedeclarationModuleOwnership(NamedDecl *New, NamedDecl *Old) {
  // FIXME: The Modules TS is not clear about how friend declarations are
  // to be treated. It's not meaningful to have different owning modules for
  // linkage in redeclarations of the same entity, so for now allow the
  // redeclaration and change the owning modules to match.
  if (New->getFriendObjectKind() &&
      Old->getOwningModuleForLinkage() != New->getOwningModuleForLinkage()) {
    New->setLocalOwningModule(Old->getOwningModule());
    makeMergedDefinitionVisible(New);
    return false;
  }

  Module *NewM = New->getOwningModule();
  Module *OldM = Old->getOwningModule();
  if (NewM == OldM)
    return false;

  // FIXME: Check proclaimed-ownership-declarations here too.
  bool NewIsModuleInterface = NewM && NewM->Kind == Module::ModuleInterfaceUnit;
  bool OldIsModuleInterface = OldM && OldM->Kind == Module::ModuleInterfaceUnit;
  if (NewIsModuleInterface || OldIsModuleInterface) {
    // C++ Modules TS [basic.def.odr] 6.2/6.7 [sic]:
    //   if a declaration of D [...] appears in the purview of a module, all
    //   other such declarations shall appear in the purview of the same module
    Diag(New->getLocation(), diag::err_mismatched_owning_module)
      << New
      << NewIsModuleInterface
      << (NewIsModuleInterface ? NewM->getFullModuleName() : "")
      << OldIsModuleInterface
      << (OldIsModuleInterface ? OldM->getFullModuleName() : "");
    Diag(Old->getLocation(), diag::note_previous_declaration);
    New->setInvalidDecl();
    return true;
  }

  return false;
}

static bool isUsingDecl(NamedDecl *D) {
  return isa<UsingShadowDecl>(D) ||
         isa<UnresolvedUsingTypenameDecl>(D) ||
         isa<UnresolvedUsingValueDecl>(D);
}

/// Removes using shadow declarations from the lookup results.
static void RemoveUsingDecls(LookupResult &R) {
  LookupResult::Filter F = R.makeFilter();
  while (F.hasNext())
    if (isUsingDecl(F.next()))
      F.erase();

  F.done();
}

/// Check for this common pattern:
/// @code
/// class S {
///   S(const S&); // DO NOT IMPLEMENT
///   void operator=(const S&); // DO NOT IMPLEMENT
/// };
/// @endcode
static bool IsDisallowedCopyOrAssign(const CXXMethodDecl *D) {
  // FIXME: Should check for private access too but access is set after we get
  // the decl here.
  if (D->doesThisDeclarationHaveABody())
    return false;

  if (const CXXConstructorDecl *CD = dyn_cast<CXXConstructorDecl>(D))
    return CD->isCopyConstructor();
  return D->isCopyAssignmentOperator();
}

// We need this to handle
//
// typedef struct {
//   void *foo() { return 0; }
// } A;
//
// When we see foo we don't know if after the typedef we will get 'A' or '*A'
// for example. If 'A', foo will have external linkage. If we have '*A',
// foo will have no linkage. Since we can't know until we get to the end
// of the typedef, this function finds out if D might have non-external linkage.
// Callers should verify at the end of the TU if it D has external linkage or
// not.
bool Sema::mightHaveNonExternalLinkage(const DeclaratorDecl *D) {
  const DeclContext *DC = D->getDeclContext();
  while (!DC->isTranslationUnit()) {
    if (const RecordDecl *RD = dyn_cast<RecordDecl>(DC)){
      if (!RD->hasNameForLinkage())
        return true;
    }
    DC = DC->getParent();
  }

  return !D->isExternallyVisible();
}

// FIXME: This needs to be refactored; some other isInMainFile users want
// these semantics.
static bool isMainFileLoc(const Sema &S, SourceLocation Loc) {
  if (S.TUKind != TU_Complete)
    return false;
  return S.SourceMgr.isInMainFile(Loc);
}

bool Sema::ShouldWarnIfUnusedFileScopedDecl(const DeclaratorDecl *D) const {
  assert(D);

  if (D->isInvalidDecl() || D->isUsed() || D->hasAttr<UnusedAttr>())
    return false;

  // Ignore all entities declared within templates, and out-of-line definitions
  // of members of class templates.
  if (D->getDeclContext()->isDependentContext() ||
      D->getLexicalDeclContext()->isDependentContext())
    return false;

  if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(D)) {
    if (FD->getTemplateSpecializationKind() == TSK_ImplicitInstantiation)
      return false;
    // A non-out-of-line declaration of a member specialization was implicitly
    // instantiated; it's the out-of-line declaration that we're interested in.
    if (FD->getTemplateSpecializationKind() == TSK_ExplicitSpecialization &&
        FD->getMemberSpecializationInfo() && !FD->isOutOfLine())
      return false;

    if (const CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(FD)) {
      if (MD->isVirtual() || IsDisallowedCopyOrAssign(MD))
        return false;
    } else {
      // 'static inline' functions are defined in headers; don't warn.
      if (FD->isInlined() && !isMainFileLoc(*this, FD->getLocation()))
        return false;
    }

    if (FD->doesThisDeclarationHaveABody() &&
        Context.DeclMustBeEmitted(FD))
      return false;
  } else if (const VarDecl *VD = dyn_cast<VarDecl>(D)) {
    // Constants and utility variables are defined in headers with internal
    // linkage; don't warn.  (Unlike functions, there isn't a convenient marker
    // like "inline".)
    if (!isMainFileLoc(*this, VD->getLocation()))
      return false;

    if (Context.DeclMustBeEmitted(VD))
      return false;

    if (VD->isStaticDataMember() &&
        VD->getTemplateSpecializationKind() == TSK_ImplicitInstantiation)
      return false;
    if (VD->isStaticDataMember() &&
        VD->getTemplateSpecializationKind() == TSK_ExplicitSpecialization &&
        VD->getMemberSpecializationInfo() && !VD->isOutOfLine())
      return false;

    if (VD->isInline() && !isMainFileLoc(*this, VD->getLocation()))
      return false;
  } else {
    return false;
  }

  // Only warn for unused decls internal to the translation unit.
  // FIXME: This seems like a bogus check; it suppresses -Wunused-function
  // for inline functions defined in the main source file, for instance.
  return mightHaveNonExternalLinkage(D);
}

void Sema::MarkUnusedFileScopedDecl(const DeclaratorDecl *D) {
  if (!D)
    return;

  if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(D)) {
    const FunctionDecl *First = FD->getFirstDecl();
    if (FD != First && ShouldWarnIfUnusedFileScopedDecl(First))
      return; // First should already be in the vector.
  }

  if (const VarDecl *VD = dyn_cast<VarDecl>(D)) {
    const VarDecl *First = VD->getFirstDecl();
    if (VD != First && ShouldWarnIfUnusedFileScopedDecl(First))
      return; // First should already be in the vector.
  }

  if (ShouldWarnIfUnusedFileScopedDecl(D))
    UnusedFileScopedDecls.push_back(D);
}

static bool ShouldDiagnoseUnusedDecl(const NamedDecl *D) {
  if (D->isInvalidDecl())
    return false;

  bool Referenced = false;
  if (auto *DD = dyn_cast<DecompositionDecl>(D)) {
    // For a decomposition declaration, warn if none of the bindings are
    // referenced, instead of if the variable itself is referenced (which
    // it is, by the bindings' expressions).
    for (auto *BD : DD->bindings()) {
      if (BD->isReferenced()) {
        Referenced = true;
        break;
      }
    }
  } else if (!D->getDeclName()) {
    return false;
  } else if (D->isReferenced() || D->isUsed()) {
    Referenced = true;
  }

  if (Referenced || D->hasAttr<UnusedAttr>() ||
      D->hasAttr<ObjCPreciseLifetimeAttr>())
    return false;

  if (isa<LabelDecl>(D))
    return true;

  // Except for labels, we only care about unused decls that are local to
  // functions.
  bool WithinFunction = D->getDeclContext()->isFunctionOrMethod();
  if (const auto *R = dyn_cast<CXXRecordDecl>(D->getDeclContext()))
    // For dependent types, the diagnostic is deferred.
    WithinFunction =
        WithinFunction || (R->isLocalClass() && !R->isDependentType());
  if (!WithinFunction)
    return false;

  if (isa<TypedefNameDecl>(D))
    return true;

  // White-list anything that isn't a local variable.
  if (!isa<VarDecl>(D) || isa<ParmVarDecl>(D) || isa<ImplicitParamDecl>(D))
    return false;

  // Types of valid local variables should be complete, so this should succeed.
  if (const VarDecl *VD = dyn_cast<VarDecl>(D)) {

    // White-list anything with an __attribute__((unused)) type.
    const auto *Ty = VD->getType().getTypePtr();

    // Only look at the outermost level of typedef.
    if (const TypedefType *TT = Ty->getAs<TypedefType>()) {
      if (TT->getDecl()->hasAttr<UnusedAttr>())
        return false;
    }

    // If we failed to complete the type for some reason, or if the type is
    // dependent, don't diagnose the variable.
    if (Ty->isIncompleteType() || Ty->isDependentType())
      return false;

    // Look at the element type to ensure that the warning behaviour is
    // consistent for both scalars and arrays.
    Ty = Ty->getBaseElementTypeUnsafe();

    if (const TagType *TT = Ty->getAs<TagType>()) {
      const TagDecl *Tag = TT->getDecl();
      if (Tag->hasAttr<UnusedAttr>())
        return false;

      if (const CXXRecordDecl *RD = dyn_cast<CXXRecordDecl>(Tag)) {
        if (!RD->hasTrivialDestructor() && !RD->hasAttr<WarnUnusedAttr>())
          return false;

        if (const Expr *Init = VD->getInit()) {
          if (const ExprWithCleanups *Cleanups =
                  dyn_cast<ExprWithCleanups>(Init))
            Init = Cleanups->getSubExpr();
          const CXXConstructExpr *Construct =
            dyn_cast<CXXConstructExpr>(Init);
          if (Construct && !Construct->isElidable()) {
            CXXConstructorDecl *CD = Construct->getConstructor();
            if (!CD->isTrivial() && !RD->hasAttr<WarnUnusedAttr>() &&
                (VD->getInit()->isValueDependent() || !VD->evaluateValue()))
              return false;
          }
        }
      }
    }

    // TODO: __attribute__((unused)) templates?
  }

  return true;
}

static void GenerateFixForUnusedDecl(const NamedDecl *D, ASTContext &Ctx,
                                     FixItHint &Hint) {
  if (isa<LabelDecl>(D)) {
    SourceLocation AfterColon = Lexer::findLocationAfterToken(
        D->getEndLoc(), tok::colon, Ctx.getSourceManager(), Ctx.getLangOpts(),
        true);
    if (AfterColon.isInvalid())
      return;
    Hint = FixItHint::CreateRemoval(
        CharSourceRange::getCharRange(D->getBeginLoc(), AfterColon));
  }
}

void Sema::DiagnoseUnusedNestedTypedefs(const RecordDecl *D) {
  if (D->getTypeForDecl()->isDependentType())
    return;

  for (auto *TmpD : D->decls()) {
    if (const auto *T = dyn_cast<TypedefNameDecl>(TmpD))
      DiagnoseUnusedDecl(T);
    else if(const auto *R = dyn_cast<RecordDecl>(TmpD))
      DiagnoseUnusedNestedTypedefs(R);
  }
}

/// DiagnoseUnusedDecl - Emit warnings about declarations that are not used
/// unless they are marked attr(unused).
void Sema::DiagnoseUnusedDecl(const NamedDecl *D) {
  if (!ShouldDiagnoseUnusedDecl(D))
    return;

  if (auto *TD = dyn_cast<TypedefNameDecl>(D)) {
    // typedefs can be referenced later on, so the diagnostics are emitted
    // at end-of-translation-unit.
    UnusedLocalTypedefNameCandidates.insert(TD);
    return;
  }

  FixItHint Hint;
  GenerateFixForUnusedDecl(D, Context, Hint);

  unsigned DiagID;
  if (isa<VarDecl>(D) && cast<VarDecl>(D)->isExceptionVariable())
    DiagID = diag::warn_unused_exception_param;
  else if (isa<LabelDecl>(D))
    DiagID = diag::warn_unused_label;
  else
    DiagID = diag::warn_unused_variable;

  Diag(D->getLocation(), DiagID) << D << Hint;
}

static void CheckPoppedLabel(LabelDecl *L, Sema &S) {
  // Verify that we have no forward references left.  If so, there was a goto
  // or address of a label taken, but no definition of it.  Label fwd
  // definitions are indicated with a null substmt which is also not a resolved
  // MS inline assembly label name.
  bool Diagnose = false;
  if (L->isMSAsmLabel())
    Diagnose = !L->isResolvedMSAsmLabel();
  else
    Diagnose = L->getStmt() == nullptr;
  if (Diagnose)
    S.Diag(L->getLocation(), diag::err_undeclared_label_use) <<L->getDeclName();
}

void Sema::ActOnPopScope(SourceLocation Loc, Scope *S) {
  S->mergeNRVOIntoParent();

  if (S->decl_empty()) return;
  assert((S->getFlags() & (Scope::DeclScope | Scope::TemplateParamScope)) &&
         "Scope shouldn't contain decls!");

  for (auto *TmpD : S->decls()) {
    assert(TmpD && "This decl didn't get pushed??");

    assert(isa<NamedDecl>(TmpD) && "Decl isn't NamedDecl?");
    NamedDecl *D = cast<NamedDecl>(TmpD);

    // Diagnose unused variables in this scope.
    if (!S->hasUnrecoverableErrorOccurred()) {
      DiagnoseUnusedDecl(D);
      if (const auto *RD = dyn_cast<RecordDecl>(D))
        DiagnoseUnusedNestedTypedefs(RD);
    }

    if (!D->getDeclName()) continue;

    // If this was a forward reference to a label, verify it was defined.
    if (LabelDecl *LD = dyn_cast<LabelDecl>(D))
      CheckPoppedLabel(LD, *this);

    // Remove this name from our lexical scope, and warn on it if we haven't
    // already.
    IdResolver.RemoveDecl(D);
    auto ShadowI = ShadowingDecls.find(D);
    if (ShadowI != ShadowingDecls.end()) {
      if (const auto *FD = dyn_cast<FieldDecl>(ShadowI->second)) {
        Diag(D->getLocation(), diag::warn_ctor_parm_shadows_field)
            << D << FD << FD->getParent();
        Diag(FD->getLocation(), diag::note_previous_declaration);
      }
      ShadowingDecls.erase(ShadowI);
    }
  }
}

/// Look for an Objective-C class in the translation unit.
///
/// \param Id The name of the Objective-C class we're looking for. If
/// typo-correction fixes this name, the Id will be updated
/// to the fixed name.
///
/// \param IdLoc The location of the name in the translation unit.
///
/// \param DoTypoCorrection If true, this routine will attempt typo correction
/// if there is no class with the given name.
///
/// \returns The declaration of the named Objective-C class, or NULL if the
/// class could not be found.
ObjCInterfaceDecl *Sema::getObjCInterfaceDecl(IdentifierInfo *&Id,
                                              SourceLocation IdLoc,
                                              bool DoTypoCorrection) {
  // The third "scope" argument is 0 since we aren't enabling lazy built-in
  // creation from this context.
  NamedDecl *IDecl = LookupSingleName(TUScope, Id, IdLoc, LookupOrdinaryName);

  if (!IDecl && DoTypoCorrection) {
    // Perform typo correction at the given location, but only if we
    // find an Objective-C class name.
    if (TypoCorrection C = CorrectTypo(
            DeclarationNameInfo(Id, IdLoc), LookupOrdinaryName, TUScope, nullptr,
            llvm::make_unique<DeclFilterCCC<ObjCInterfaceDecl>>(),
            CTK_ErrorRecovery)) {
      diagnoseTypo(C, PDiag(diag::err_undef_interface_suggest) << Id);
      IDecl = C.getCorrectionDeclAs<ObjCInterfaceDecl>();
      Id = IDecl->getIdentifier();
    }
  }
  ObjCInterfaceDecl *Def = dyn_cast_or_null<ObjCInterfaceDecl>(IDecl);
  // This routine must always return a class definition, if any.
  if (Def && Def->getDefinition())
      Def = Def->getDefinition();
  return Def;
}

/// getNonFieldDeclScope - Retrieves the innermost scope, starting
/// from S, where a non-field would be declared. This routine copes
/// with the difference between C and C++ scoping rules in structs and
/// unions. For example, the following code is well-formed in C but
/// ill-formed in C++:
/// @code
/// struct S6 {
///   enum { BAR } e;
/// };
///
/// void test_S6() {
///   struct S6 a;
///   a.e = BAR;
/// }
/// @endcode
/// For the declaration of BAR, this routine will return a different
/// scope. The scope S will be the scope of the unnamed enumeration
/// within S6. In C++, this routine will return the scope associated
/// with S6, because the enumeration's scope is a transparent
/// context but structures can contain non-field names. In C, this
/// routine will return the translation unit scope, since the
/// enumeration's scope is a transparent context and structures cannot
/// contain non-field names.
Scope *Sema::getNonFieldDeclScope(Scope *S) {
  while (((S->getFlags() & Scope::DeclScope) == 0) ||
         (S->getEntity() && S->getEntity()->isTransparentContext()) ||
         (S->isClassScope() && !getLangOpts().CPlusPlus))
    S = S->getParent();
  return S;
}

/// Looks up the declaration of "struct objc_super" and
/// saves it for later use in building builtin declaration of
/// objc_msgSendSuper and objc_msgSendSuper_stret. If no such
/// pre-existing declaration exists no action takes place.
static void LookupPredefedObjCSuperType(Sema &ThisSema, Scope *S,
                                        IdentifierInfo *II) {
  if (!II->isStr("objc_msgSendSuper"))
    return;
  ASTContext &Context = ThisSema.Context;

  LookupResult Result(ThisSema, &Context.Idents.get("objc_super"),
                      SourceLocation(), Sema::LookupTagName);
  ThisSema.LookupName(Result, S);
  if (Result.getResultKind() == LookupResult::Found)
    if (const TagDecl *TD = Result.getAsSingle<TagDecl>())
      Context.setObjCSuperType(Context.getTagDeclType(TD));
}

static StringRef getHeaderName(ASTContext::GetBuiltinTypeError Error) {
  switch (Error) {
  case ASTContext::GE_None:
    return "";
  case ASTContext::GE_Missing_stdio:
    return "stdio.h";
  case ASTContext::GE_Missing_setjmp:
    return "setjmp.h";
  case ASTContext::GE_Missing_ucontext:
    return "ucontext.h";
  }
  llvm_unreachable("unhandled error kind");
}

/// LazilyCreateBuiltin - The specified Builtin-ID was first used at
/// file scope.  lazily create a decl for it. ForRedeclaration is true
/// if we're creating this built-in in anticipation of redeclaring the
/// built-in.
NamedDecl *Sema::LazilyCreateBuiltin(IdentifierInfo *II, unsigned ID,
                                     Scope *S, bool ForRedeclaration,
                                     SourceLocation Loc) {
  LookupPredefedObjCSuperType(*this, S, II);

  ASTContext::GetBuiltinTypeError Error;
  QualType R = Context.GetBuiltinType(ID, Error);
  if (Error) {
    if (ForRedeclaration)
      Diag(Loc, diag::warn_implicit_decl_requires_sysheader)
          << getHeaderName(Error) << Context.BuiltinInfo.getName(ID);
    return nullptr;
  }

  if (!ForRedeclaration &&
      (Context.BuiltinInfo.isPredefinedLibFunction(ID) ||
       Context.BuiltinInfo.isHeaderDependentFunction(ID))) {
    Diag(Loc, diag::ext_implicit_lib_function_decl)
        << Context.BuiltinInfo.getName(ID) << R;
    if (Context.BuiltinInfo.getHeaderName(ID) &&
        !Diags.isIgnored(diag::ext_implicit_lib_function_decl, Loc))
      Diag(Loc, diag::note_include_header_or_declare)
          << Context.BuiltinInfo.getHeaderName(ID)
          << Context.BuiltinInfo.getName(ID);
  }

  if (R.isNull())
    return nullptr;

  DeclContext *Parent = Context.getTranslationUnitDecl();
  if (getLangOpts().CPlusPlus) {
    LinkageSpecDecl *CLinkageDecl =
        LinkageSpecDecl::Create(Context, Parent, Loc, Loc,
                                LinkageSpecDecl::lang_c, false);
    CLinkageDecl->setImplicit();
    Parent->addDecl(CLinkageDecl);
    Parent = CLinkageDecl;
  }

  FunctionDecl *New = FunctionDecl::Create(Context,
                                           Parent,
                                           Loc, Loc, II, R, /*TInfo=*/nullptr,
                                           SC_Extern,
                                           false,
                                           R->isFunctionProtoType());
  New->setImplicit();

  // Create Decl objects for each parameter, adding them to the
  // FunctionDecl.
  if (const FunctionProtoType *FT = dyn_cast<FunctionProtoType>(R)) {
    SmallVector<ParmVarDecl*, 16> Params;
    for (unsigned i = 0, e = FT->getNumParams(); i != e; ++i) {
      ParmVarDecl *parm =
          ParmVarDecl::Create(Context, New, SourceLocation(), SourceLocation(),
                              nullptr, FT->getParamType(i), /*TInfo=*/nullptr,
                              SC_None, nullptr);
      parm->setScopeInfo(0, i);
      Params.push_back(parm);
    }
    New->setParams(Params);
  }

  AddKnownFunctionAttributes(New);
  RegisterLocallyScopedExternCDecl(New, S);

  // TUScope is the translation-unit scope to insert this function into.
  // FIXME: This is hideous. We need to teach PushOnScopeChains to
  // relate Scopes to DeclContexts, and probably eliminate CurContext
  // entirely, but we're not there yet.
  DeclContext *SavedContext = CurContext;
  CurContext = Parent;
  PushOnScopeChains(New, TUScope);
  CurContext = SavedContext;
  return New;
}

/// Typedef declarations don't have linkage, but they still denote the same
/// entity if their types are the same.
/// FIXME: This is notionally doing the same thing as ASTReaderDecl's
/// isSameEntity.
static void filterNonConflictingPreviousTypedefDecls(Sema &S,
                                                     TypedefNameDecl *Decl,
                                                     LookupResult &Previous) {
  // This is only interesting when modules are enabled.
  if (!S.getLangOpts().Modules && !S.getLangOpts().ModulesLocalVisibility)
    return;

  // Empty sets are uninteresting.
  if (Previous.empty())
    return;

  LookupResult::Filter Filter = Previous.makeFilter();
  while (Filter.hasNext()) {
    NamedDecl *Old = Filter.next();

    // Non-hidden declarations are never ignored.
    if (S.isVisible(Old))
      continue;

    // Declarations of the same entity are not ignored, even if they have
    // different linkages.
    if (auto *OldTD = dyn_cast<TypedefNameDecl>(Old)) {
      if (S.Context.hasSameType(OldTD->getUnderlyingType(),
                                Decl->getUnderlyingType()))
        continue;

      // If both declarations give a tag declaration a typedef name for linkage
      // purposes, then they declare the same entity.
      if (OldTD->getAnonDeclWithTypedefName(/*AnyRedecl*/true) &&
          Decl->getAnonDeclWithTypedefName())
        continue;
    }

    Filter.erase();
  }

  Filter.done();
}

bool Sema::isIncompatibleTypedef(TypeDecl *Old, TypedefNameDecl *New) {
  QualType OldType;
  if (TypedefNameDecl *OldTypedef = dyn_cast<TypedefNameDecl>(Old))
    OldType = OldTypedef->getUnderlyingType();
  else
    OldType = Context.getTypeDeclType(Old);
  QualType NewType = New->getUnderlyingType();

  if (NewType->isVariablyModifiedType()) {
    // Must not redefine a typedef with a variably-modified type.
    int Kind = isa<TypeAliasDecl>(Old) ? 1 : 0;
    Diag(New->getLocation(), diag::err_redefinition_variably_modified_typedef)
      << Kind << NewType;
    if (Old->getLocation().isValid())
      notePreviousDefinition(Old, New->getLocation());
    New->setInvalidDecl();
    return true;
  }

  if (OldType != NewType &&
      !OldType->isDependentType() &&
      !NewType->isDependentType() &&
      !Context.hasSameType(OldType, NewType)) {
    int Kind = isa<TypeAliasDecl>(Old) ? 1 : 0;
    Diag(New->getLocation(), diag::err_redefinition_different_typedef)
      << Kind << NewType << OldType;
    if (Old->getLocation().isValid())
      notePreviousDefinition(Old, New->getLocation());
    New->setInvalidDecl();
    return true;
  }
  return false;
}

/// MergeTypedefNameDecl - We just parsed a typedef 'New' which has the
/// same name and scope as a previous declaration 'Old'.  Figure out
/// how to resolve this situation, merging decls or emitting
/// diagnostics as appropriate. If there was an error, set New to be invalid.
///
void Sema::MergeTypedefNameDecl(Scope *S, TypedefNameDecl *New,
                                LookupResult &OldDecls) {
  // If the new decl is known invalid already, don't bother doing any
  // merging checks.
  if (New->isInvalidDecl()) return;

  // Allow multiple definitions for ObjC built-in typedefs.
  // FIXME: Verify the underlying types are equivalent!
  if (getLangOpts().ObjC1) {
    const IdentifierInfo *TypeID = New->getIdentifier();
    switch (TypeID->getLength()) {
    default: break;
    case 2:
      {
        if (!TypeID->isStr("id"))
          break;
        QualType T = New->getUnderlyingType();
        if (!T->isPointerType())
          break;
        if (!T->isVoidPointerType()) {
          QualType PT = T->getAs<PointerType>()->getPointeeType();
          if (!PT->isStructureType())
            break;
        }
        Context.setObjCIdRedefinitionType(T);
        // Install the built-in type for 'id', ignoring the current definition.
        New->setTypeForDecl(Context.getObjCIdType().getTypePtr());
        return;
      }
    case 5:
      if (!TypeID->isStr("Class"))
        break;
      Context.setObjCClassRedefinitionType(New->getUnderlyingType());
      // Install the built-in type for 'Class', ignoring the current definition.
      New->setTypeForDecl(Context.getObjCClassType().getTypePtr());
      return;
    case 3:
      if (!TypeID->isStr("SEL"))
        break;
      Context.setObjCSelRedefinitionType(New->getUnderlyingType());
      // Install the built-in type for 'SEL', ignoring the current definition.
      New->setTypeForDecl(Context.getObjCSelType().getTypePtr());
      return;
    }
    // Fall through - the typedef name was not a builtin type.
  }

  // Verify the old decl was also a type.
  TypeDecl *Old = OldDecls.getAsSingle<TypeDecl>();
  if (!Old) {
    Diag(New->getLocation(), diag::err_redefinition_different_kind)
      << New->getDeclName();

    NamedDecl *OldD = OldDecls.getRepresentativeDecl();
    if (OldD->getLocation().isValid())
      notePreviousDefinition(OldD, New->getLocation());

    return New->setInvalidDecl();
  }

  // If the old declaration is invalid, just give up here.
  if (Old->isInvalidDecl())
    return New->setInvalidDecl();

  if (auto *OldTD = dyn_cast<TypedefNameDecl>(Old)) {
    auto *OldTag = OldTD->getAnonDeclWithTypedefName(/*AnyRedecl*/true);
    auto *NewTag = New->getAnonDeclWithTypedefName();
    NamedDecl *Hidden = nullptr;
    if (OldTag && NewTag &&
        OldTag->getCanonicalDecl() != NewTag->getCanonicalDecl() &&
        !hasVisibleDefinition(OldTag, &Hidden)) {
      // There is a definition of this tag, but it is not visible. Use it
      // instead of our tag.
      New->setTypeForDecl(OldTD->getTypeForDecl());
      if (OldTD->isModed())
        New->setModedTypeSourceInfo(OldTD->getTypeSourceInfo(),
                                    OldTD->getUnderlyingType());
      else
        New->setTypeSourceInfo(OldTD->getTypeSourceInfo());

      // Make the old tag definition visible.
      makeMergedDefinitionVisible(Hidden);

      // If this was an unscoped enumeration, yank all of its enumerators
      // out of the scope.
      if (isa<EnumDecl>(NewTag)) {
        Scope *EnumScope = getNonFieldDeclScope(S);
        for (auto *D : NewTag->decls()) {
          auto *ED = cast<EnumConstantDecl>(D);
          assert(EnumScope->isDeclScope(ED));
          EnumScope->RemoveDecl(ED);
          IdResolver.RemoveDecl(ED);
          ED->getLexicalDeclContext()->removeDecl(ED);
        }
      }
    }
  }

  // If the typedef types are not identical, reject them in all languages and
  // with any extensions enabled.
  if (isIncompatibleTypedef(Old, New))
    return;

  // The types match.  Link up the redeclaration chain and merge attributes if
  // the old declaration was a typedef.
  if (TypedefNameDecl *Typedef = dyn_cast<TypedefNameDecl>(Old)) {
    New->setPreviousDecl(Typedef);
    mergeDeclAttributes(New, Old);
  }

  if (getLangOpts().MicrosoftExt)
    return;

  if (getLangOpts().CPlusPlus) {
    // C++ [dcl.typedef]p2:
    //   In a given non-class scope, a typedef specifier can be used to
    //   redefine the name of any type declared in that scope to refer
    //   to the type to which it already refers.
    if (!isa<CXXRecordDecl>(CurContext))
      return;

    // C++0x [dcl.typedef]p4:
    //   In a given class scope, a typedef specifier can be used to redefine
    //   any class-name declared in that scope that is not also a typedef-name
    //   to refer to the type to which it already refers.
    //
    // This wording came in via DR424, which was a correction to the
    // wording in DR56, which accidentally banned code like:
    //
    //   struct S {
    //     typedef struct A { } A;
    //   };
    //
    // in the C++03 standard. We implement the C++0x semantics, which
    // allow the above but disallow
    //
    //   struct S {
    //     typedef int I;
    //     typedef int I;
    //   };
    //
    // since that was the intent of DR56.
    if (!isa<TypedefNameDecl>(Old))
      return;

    Diag(New->getLocation(), diag::err_redefinition)
      << New->getDeclName();
    notePreviousDefinition(Old, New->getLocation());
    return New->setInvalidDecl();
  }

  // Modules always permit redefinition of typedefs, as does C11.
  if (getLangOpts().Modules || getLangOpts().C11)
    return;

  // If we have a redefinition of a typedef in C, emit a warning.  This warning
  // is normally mapped to an error, but can be controlled with
  // -Wtypedef-redefinition.  If either the original or the redefinition is
  // in a system header, don't emit this for compatibility with GCC.
  if (getDiagnostics().getSuppressSystemWarnings() &&
      // Some standard types are defined implicitly in Clang (e.g. OpenCL).
      (Old->isImplicit() ||
       Context.getSourceManager().isInSystemHeader(Old->getLocation()) ||
       Context.getSourceManager().isInSystemHeader(New->getLocation())))
    return;

  Diag(New->getLocation(), diag::ext_redefinition_of_typedef)
    << New->getDeclName();
  notePreviousDefinition(Old, New->getLocation());
}

/// DeclhasAttr - returns true if decl Declaration already has the target
/// attribute.
static bool DeclHasAttr(const Decl *D, const Attr *A) {
  const OwnershipAttr *OA = dyn_cast<OwnershipAttr>(A);
  const AnnotateAttr *Ann = dyn_cast<AnnotateAttr>(A);
  for (const auto *i : D->attrs())
    if (i->getKind() == A->getKind()) {
      if (Ann) {
        if (Ann->getAnnotation() == cast<AnnotateAttr>(i)->getAnnotation())
          return true;
        continue;
      }
      // FIXME: Don't hardcode this check
      if (OA && isa<OwnershipAttr>(i))
        return OA->getOwnKind() == cast<OwnershipAttr>(i)->getOwnKind();
      return true;
    }

  return false;
}

static bool isAttributeTargetADefinition(Decl *D) {
  if (VarDecl *VD = dyn_cast<VarDecl>(D))
    return VD->isThisDeclarationADefinition();
  if (TagDecl *TD = dyn_cast<TagDecl>(D))
    return TD->isCompleteDefinition() || TD->isBeingDefined();
  return true;
}

/// Merge alignment attributes from \p Old to \p New, taking into account the
/// special semantics of C11's _Alignas specifier and C++11's alignas attribute.
///
/// \return \c true if any attributes were added to \p New.
static bool mergeAlignedAttrs(Sema &S, NamedDecl *New, Decl *Old) {
  // Look for alignas attributes on Old, and pick out whichever attribute
  // specifies the strictest alignment requirement.
  AlignedAttr *OldAlignasAttr = nullptr;
  AlignedAttr *OldStrictestAlignAttr = nullptr;
  unsigned OldAlign = 0;
  for (auto *I : Old->specific_attrs<AlignedAttr>()) {
    // FIXME: We have no way of representing inherited dependent alignments
    // in a case like:
    //   template<int A, int B> struct alignas(A) X;
    //   template<int A, int B> struct alignas(B) X {};
    // For now, we just ignore any alignas attributes which are not on the
    // definition in such a case.
    if (I->isAlignmentDependent())
      return false;

    if (I->isAlignas())
      OldAlignasAttr = I;

    unsigned Align = I->getAlignment(S.Context);
    if (Align > OldAlign) {
      OldAlign = Align;
      OldStrictestAlignAttr = I;
    }
  }

  // Look for alignas attributes on New.
  AlignedAttr *NewAlignasAttr = nullptr;
  unsigned NewAlign = 0;
  for (auto *I : New->specific_attrs<AlignedAttr>()) {
    if (I->isAlignmentDependent())
      return false;

    if (I->isAlignas())
      NewAlignasAttr = I;

    unsigned Align = I->getAlignment(S.Context);
    if (Align > NewAlign)
      NewAlign = Align;
  }

  if (OldAlignasAttr && NewAlignasAttr && OldAlign != NewAlign) {
    // Both declarations have 'alignas' attributes. We require them to match.
    // C++11 [dcl.align]p6 and C11 6.7.5/7 both come close to saying this, but
    // fall short. (If two declarations both have alignas, they must both match
    // every definition, and so must match each other if there is a definition.)

    // If either declaration only contains 'alignas(0)' specifiers, then it
    // specifies the natural alignment for the type.
    if (OldAlign == 0 || NewAlign == 0) {
      QualType Ty;
      if (ValueDecl *VD = dyn_cast<ValueDecl>(New))
        Ty = VD->getType();
      else
        Ty = S.Context.getTagDeclType(cast<TagDecl>(New));

      if (OldAlign == 0)
        OldAlign = S.Context.getTypeAlign(Ty);
      if (NewAlign == 0)
        NewAlign = S.Context.getTypeAlign(Ty);
    }

    if (OldAlign != NewAlign) {
      S.Diag(NewAlignasAttr->getLocation(), diag::err_alignas_mismatch)
        << (unsigned)S.Context.toCharUnitsFromBits(OldAlign).getQuantity()
        << (unsigned)S.Context.toCharUnitsFromBits(NewAlign).getQuantity();
      S.Diag(OldAlignasAttr->getLocation(), diag::note_previous_declaration);
    }
  }

  if (OldAlignasAttr && !NewAlignasAttr && isAttributeTargetADefinition(New)) {
    // C++11 [dcl.align]p6:
    //   if any declaration of an entity has an alignment-specifier,
    //   every defining declaration of that entity shall specify an
    //   equivalent alignment.
    // C11 6.7.5/7:
    //   If the definition of an object does not have an alignment
    //   specifier, any other declaration of that object shall also
    //   have no alignment specifier.
    S.Diag(New->getLocation(), diag::err_alignas_missing_on_definition)
      << OldAlignasAttr;
    S.Diag(OldAlignasAttr->getLocation(), diag::note_alignas_on_declaration)
      << OldAlignasAttr;
  }

  bool AnyAdded = false;

  // Ensure we have an attribute representing the strictest alignment.
  if (OldAlign > NewAlign) {
    AlignedAttr *Clone = OldStrictestAlignAttr->clone(S.Context);
    Clone->setInherited(true);
    New->addAttr(Clone);
    AnyAdded = true;
  }

  // Ensure we have an alignas attribute if the old declaration had one.
  if (OldAlignasAttr && !NewAlignasAttr &&
      !(AnyAdded && OldStrictestAlignAttr->isAlignas())) {
    AlignedAttr *Clone = OldAlignasAttr->clone(S.Context);
    Clone->setInherited(true);
    New->addAttr(Clone);
    AnyAdded = true;
  }

  return AnyAdded;
}

static bool mergeDeclAttribute(Sema &S, NamedDecl *D,
                               const InheritableAttr *Attr,
                               Sema::AvailabilityMergeKind AMK) {
  // This function copies an attribute Attr from a previous declaration to the
  // new declaration D if the new declaration doesn't itself have that attribute
  // yet or if that attribute allows duplicates.
  // If you're adding a new attribute that requires logic different from
  // "use explicit attribute on decl if present, else use attribute from
  // previous decl", for example if the attribute needs to be consistent
  // between redeclarations, you need to call a custom merge function here.
  InheritableAttr *NewAttr = nullptr;
  unsigned AttrSpellingListIndex = Attr->getSpellingListIndex();
  if (const auto *AA = dyn_cast<AvailabilityAttr>(Attr))
    NewAttr = S.mergeAvailabilityAttr(D, AA->getRange(), AA->getPlatform(),
                                      AA->isImplicit(), AA->getIntroduced(),
                                      AA->getDeprecated(),
                                      AA->getObsoleted(), AA->getUnavailable(),
                                      AA->getMessage(), AA->getStrict(),
                                      AA->getReplacement(), AMK,
                                      AttrSpellingListIndex);
  else if (const auto *VA = dyn_cast<VisibilityAttr>(Attr))
    NewAttr = S.mergeVisibilityAttr(D, VA->getRange(), VA->getVisibility(),
                                    AttrSpellingListIndex);
  else if (const auto *VA = dyn_cast<TypeVisibilityAttr>(Attr))
    NewAttr = S.mergeTypeVisibilityAttr(D, VA->getRange(), VA->getVisibility(),
                                        AttrSpellingListIndex);
  else if (const auto *ImportA = dyn_cast<DLLImportAttr>(Attr))
    NewAttr = S.mergeDLLImportAttr(D, ImportA->getRange(),
                                   AttrSpellingListIndex);
  else if (const auto *ExportA = dyn_cast<DLLExportAttr>(Attr))
    NewAttr = S.mergeDLLExportAttr(D, ExportA->getRange(),
                                   AttrSpellingListIndex);
  else if (const auto *FA = dyn_cast<FormatAttr>(Attr))
    NewAttr = S.mergeFormatAttr(D, FA->getRange(), FA->getType(),
                                FA->getFormatIdx(), FA->getFirstArg(),
                                AttrSpellingListIndex);
  else if (const auto *SA = dyn_cast<SectionAttr>(Attr))
    NewAttr = S.mergeSectionAttr(D, SA->getRange(), SA->getName(),
                                 AttrSpellingListIndex);
  else if (const auto *CSA = dyn_cast<CodeSegAttr>(Attr))
    NewAttr = S.mergeCodeSegAttr(D, CSA->getRange(), CSA->getName(),
                                 AttrSpellingListIndex);
  else if (const auto *IA = dyn_cast<MSInheritanceAttr>(Attr))
    NewAttr = S.mergeMSInheritanceAttr(D, IA->getRange(), IA->getBestCase(),
                                       AttrSpellingListIndex,
                                       IA->getSemanticSpelling());
  else if (const auto *AA = dyn_cast<AlwaysInlineAttr>(Attr))
    NewAttr = S.mergeAlwaysInlineAttr(D, AA->getRange(),
                                      &S.Context.Idents.get(AA->getSpelling()),
                                      AttrSpellingListIndex);
  else if (S.getLangOpts().CUDA && isa<FunctionDecl>(D) &&
           (isa<CUDAHostAttr>(Attr) || isa<CUDADeviceAttr>(Attr) ||
            isa<CUDAGlobalAttr>(Attr))) {
    // CUDA target attributes are part of function signature for
    // overloading purposes and must not be merged.
    return false;
  } else if (const auto *MA = dyn_cast<MinSizeAttr>(Attr))
    NewAttr = S.mergeMinSizeAttr(D, MA->getRange(), AttrSpellingListIndex);
  else if (const auto *OA = dyn_cast<OptimizeNoneAttr>(Attr))
    NewAttr = S.mergeOptimizeNoneAttr(D, OA->getRange(), AttrSpellingListIndex);
  else if (const auto *InternalLinkageA = dyn_cast<InternalLinkageAttr>(Attr))
    NewAttr = S.mergeInternalLinkageAttr(D, *InternalLinkageA);
  else if (const auto *CommonA = dyn_cast<CommonAttr>(Attr))
    NewAttr = S.mergeCommonAttr(D, *CommonA);
  else if (isa<AlignedAttr>(Attr))
    // AlignedAttrs are handled separately, because we need to handle all
    // such attributes on a declaration at the same time.
    NewAttr = nullptr;
  else if ((isa<DeprecatedAttr>(Attr) || isa<UnavailableAttr>(Attr)) &&
           (AMK == Sema::AMK_Override ||
            AMK == Sema::AMK_ProtocolImplementation))
    NewAttr = nullptr;
  else if (const auto *UA = dyn_cast<UuidAttr>(Attr))
    NewAttr = S.mergeUuidAttr(D, UA->getRange(), AttrSpellingListIndex,
                              UA->getGuid());
  else if (Attr->shouldInheritEvenIfAlreadyPresent() || !DeclHasAttr(D, Attr))
    NewAttr = cast<InheritableAttr>(Attr->clone(S.Context));

  if (NewAttr) {
    NewAttr->setInherited(true);
    D->addAttr(NewAttr);
    if (isa<MSInheritanceAttr>(NewAttr))
      S.Consumer.AssignInheritanceModel(cast<CXXRecordDecl>(D));
    return true;
  }

  return false;
}

static const NamedDecl *getDefinition(const Decl *D) {
  if (const TagDecl *TD = dyn_cast<TagDecl>(D))
    return TD->getDefinition();
  if (const VarDecl *VD = dyn_cast<VarDecl>(D)) {
    const VarDecl *Def = VD->getDefinition();
    if (Def)
      return Def;
    return VD->getActingDefinition();
  }
  if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(D))
    return FD->getDefinition();
  return nullptr;
}

static bool hasAttribute(const Decl *D, attr::Kind Kind) {
  for (const auto *Attribute : D->attrs())
    if (Attribute->getKind() == Kind)
      return true;
  return false;
}

/// checkNewAttributesAfterDef - If we already have a definition, check that
/// there are no new attributes in this declaration.
static void checkNewAttributesAfterDef(Sema &S, Decl *New, const Decl *Old) {
  if (!New->hasAttrs())
    return;

  const NamedDecl *Def = getDefinition(Old);
  if (!Def || Def == New)
    return;

  AttrVec &NewAttributes = New->getAttrs();
  for (unsigned I = 0, E = NewAttributes.size(); I != E;) {
    const Attr *NewAttribute = NewAttributes[I];

    if (isa<AliasAttr>(NewAttribute) || isa<IFuncAttr>(NewAttribute)) {
      if (FunctionDecl *FD = dyn_cast<FunctionDecl>(New)) {
        Sema::SkipBodyInfo SkipBody;
        S.CheckForFunctionRedefinition(FD, cast<FunctionDecl>(Def), &SkipBody);

        // If we're skipping this definition, drop the "alias" attribute.
        if (SkipBody.ShouldSkip) {
          NewAttributes.erase(NewAttributes.begin() + I);
          --E;
          continue;
        }
      } else {
        VarDecl *VD = cast<VarDecl>(New);
        unsigned Diag = cast<VarDecl>(Def)->isThisDeclarationADefinition() ==
                                VarDecl::TentativeDefinition
                            ? diag::err_alias_after_tentative
                            : diag::err_redefinition;
        S.Diag(VD->getLocation(), Diag) << VD->getDeclName();
        if (Diag == diag::err_redefinition)
          S.notePreviousDefinition(Def, VD->getLocation());
        else
          S.Diag(Def->getLocation(), diag::note_previous_definition);
        VD->setInvalidDecl();
      }
      ++I;
      continue;
    }

    if (const VarDecl *VD = dyn_cast<VarDecl>(Def)) {
      // Tentative definitions are only interesting for the alias check above.
      if (VD->isThisDeclarationADefinition() != VarDecl::Definition) {
        ++I;
        continue;
      }
    }

    if (hasAttribute(Def, NewAttribute->getKind())) {
      ++I;
      continue; // regular attr merging will take care of validating this.
    }

    if (isa<C11NoReturnAttr>(NewAttribute)) {
      // C's _Noreturn is allowed to be added to a function after it is defined.
      ++I;
      continue;
    } else if (const AlignedAttr *AA = dyn_cast<AlignedAttr>(NewAttribute)) {
      if (AA->isAlignas()) {
        // C++11 [dcl.align]p6:
        //   if any declaration of an entity has an alignment-specifier,
        //   every defining declaration of that entity shall specify an
        //   equivalent alignment.
        // C11 6.7.5/7:
        //   If the definition of an object does not have an alignment
        //   specifier, any other declaration of that object shall also
        //   have no alignment specifier.
        S.Diag(Def->getLocation(), diag::err_alignas_missing_on_definition)
          << AA;
        S.Diag(NewAttribute->getLocation(), diag::note_alignas_on_declaration)
          << AA;
        NewAttributes.erase(NewAttributes.begin() + I);
        --E;
        continue;
      }
    }

    S.Diag(NewAttribute->getLocation(),
           diag::warn_attribute_precede_definition);
    S.Diag(Def->getLocation(), diag::note_previous_definition);
    NewAttributes.erase(NewAttributes.begin() + I);
    --E;
  }
}

/// mergeDeclAttributes - Copy attributes from the Old decl to the New one.
void Sema::mergeDeclAttributes(NamedDecl *New, Decl *Old,
                               AvailabilityMergeKind AMK) {
  if (UsedAttr *OldAttr = Old->getMostRecentDecl()->getAttr<UsedAttr>()) {
    UsedAttr *NewAttr = OldAttr->clone(Context);
    NewAttr->setInherited(true);
    New->addAttr(NewAttr);
  }

  if (!Old->hasAttrs() && !New->hasAttrs())
    return;

  // Attributes declared post-definition are currently ignored.
  checkNewAttributesAfterDef(*this, New, Old);

  if (AsmLabelAttr *NewA = New->getAttr<AsmLabelAttr>()) {
    if (AsmLabelAttr *OldA = Old->getAttr<AsmLabelAttr>()) {
      if (OldA->getLabel() != NewA->getLabel()) {
        // This redeclaration changes __asm__ label.
        Diag(New->getLocation(), diag::err_different_asm_label);
        Diag(OldA->getLocation(), diag::note_previous_declaration);
      }
    } else if (Old->isUsed()) {
      // This redeclaration adds an __asm__ label to a declaration that has
      // already been ODR-used.
      Diag(New->getLocation(), diag::err_late_asm_label_name)
        << isa<FunctionDecl>(Old) << New->getAttr<AsmLabelAttr>()->getRange();
    }
  }

  // Re-declaration cannot add abi_tag's.
  if (const auto *NewAbiTagAttr = New->getAttr<AbiTagAttr>()) {
    if (const auto *OldAbiTagAttr = Old->getAttr<AbiTagAttr>()) {
      for (const auto &NewTag : NewAbiTagAttr->tags()) {
        if (std::find(OldAbiTagAttr->tags_begin(), OldAbiTagAttr->tags_end(),
                      NewTag) == OldAbiTagAttr->tags_end()) {
          Diag(NewAbiTagAttr->getLocation(),
               diag::err_new_abi_tag_on_redeclaration)
              << NewTag;
          Diag(OldAbiTagAttr->getLocation(), diag::note_previous_declaration);
        }
      }
    } else {
      Diag(NewAbiTagAttr->getLocation(), diag::err_abi_tag_on_redeclaration);
      Diag(Old->getLocation(), diag::note_previous_declaration);
    }
  }

  // This redeclaration adds a section attribute.
  if (New->hasAttr<SectionAttr>() && !Old->hasAttr<SectionAttr>()) {
    if (auto *VD = dyn_cast<VarDecl>(New)) {
      if (VD->isThisDeclarationADefinition() == VarDecl::DeclarationOnly) {
        Diag(New->getLocation(), diag::warn_attribute_section_on_redeclaration);
        Diag(Old->getLocation(), diag::note_previous_declaration);
      }
    }
  }

  // Redeclaration adds code-seg attribute.
  const auto *NewCSA = New->getAttr<CodeSegAttr>();
  if (NewCSA && !Old->hasAttr<CodeSegAttr>() &&
      !NewCSA->isImplicit() && isa<CXXMethodDecl>(New)) {
    Diag(New->getLocation(), diag::warn_mismatched_section)
         << 0 /*codeseg*/;
    Diag(Old->getLocation(), diag::note_previous_declaration);
  }

  if (!Old->hasAttrs())
    return;

  bool foundAny = New->hasAttrs();

  // Ensure that any moving of objects within the allocated map is done before
  // we process them.
  if (!foundAny) New->setAttrs(AttrVec());

  for (auto *I : Old->specific_attrs<InheritableAttr>()) {
    // Ignore deprecated/unavailable/availability attributes if requested.
    AvailabilityMergeKind LocalAMK = AMK_None;
    if (isa<DeprecatedAttr>(I) ||
        isa<UnavailableAttr>(I) ||
        isa<AvailabilityAttr>(I)) {
      switch (AMK) {
      case AMK_None:
        continue;

      case AMK_Redeclaration:
      case AMK_Override:
      case AMK_ProtocolImplementation:
        LocalAMK = AMK;
        break;
      }
    }

    // Already handled.
    if (isa<UsedAttr>(I))
      continue;

    if (mergeDeclAttribute(*this, New, I, LocalAMK))
      foundAny = true;
  }

  if (mergeAlignedAttrs(*this, New, Old))
    foundAny = true;

  if (!foundAny) New->dropAttrs();
}

/// mergeParamDeclAttributes - Copy attributes from the old parameter
/// to the new one.
static void mergeParamDeclAttributes(ParmVarDecl *newDecl,
                                     const ParmVarDecl *oldDecl,
                                     Sema &S) {
  // C++11 [dcl.attr.depend]p2:
  //   The first declaration of a function shall specify the
  //   carries_dependency attribute for its declarator-id if any declaration
  //   of the function specifies the carries_dependency attribute.
  const CarriesDependencyAttr *CDA = newDecl->getAttr<CarriesDependencyAttr>();
  if (CDA && !oldDecl->hasAttr<CarriesDependencyAttr>()) {
    S.Diag(CDA->getLocation(),
           diag::err_carries_dependency_missing_on_first_decl) << 1/*Param*/;
    // Find the first declaration of the parameter.
    // FIXME: Should we build redeclaration chains for function parameters?
    const FunctionDecl *FirstFD =
      cast<FunctionDecl>(oldDecl->getDeclContext())->getFirstDecl();
    const ParmVarDecl *FirstVD =
      FirstFD->getParamDecl(oldDecl->getFunctionScopeIndex());
    S.Diag(FirstVD->getLocation(),
           diag::note_carries_dependency_missing_first_decl) << 1/*Param*/;
  }

  if (!oldDecl->hasAttrs())
    return;

  bool foundAny = newDecl->hasAttrs();

  // Ensure that any moving of objects within the allocated map is
  // done before we process them.
  if (!foundAny) newDecl->setAttrs(AttrVec());

  for (const auto *I : oldDecl->specific_attrs<InheritableParamAttr>()) {
    if (!DeclHasAttr(newDecl, I)) {
      InheritableAttr *newAttr =
        cast<InheritableParamAttr>(I->clone(S.Context));
      newAttr->setInherited(true);
      newDecl->addAttr(newAttr);
      foundAny = true;
    }
  }

  if (!foundAny) newDecl->dropAttrs();
}

static void mergeParamDeclTypes(ParmVarDecl *NewParam,
                                const ParmVarDecl *OldParam,
                                Sema &S) {
  if (auto Oldnullability = OldParam->getType()->getNullability(S.Context)) {
    if (auto Newnullability = NewParam->getType()->getNullability(S.Context)) {
      if (*Oldnullability != *Newnullability) {
        S.Diag(NewParam->getLocation(), diag::warn_mismatched_nullability_attr)
          << DiagNullabilityKind(
               *Newnullability,
               ((NewParam->getObjCDeclQualifier() & Decl::OBJC_TQ_CSNullability)
                != 0))
          << DiagNullabilityKind(
               *Oldnullability,
               ((OldParam->getObjCDeclQualifier() & Decl::OBJC_TQ_CSNullability)
                != 0));
        S.Diag(OldParam->getLocation(), diag::note_previous_declaration);
      }
    } else {
      QualType NewT = NewParam->getType();
      NewT = S.Context.getAttributedType(
                         AttributedType::getNullabilityAttrKind(*Oldnullability),
                         NewT, NewT);
      NewParam->setType(NewT);
    }
  }
}

namespace {

/// Used in MergeFunctionDecl to keep track of function parameters in
/// C.
struct GNUCompatibleParamWarning {
  ParmVarDecl *OldParm;
  ParmVarDecl *NewParm;
  QualType PromotedType;
};

} // end anonymous namespace

/// getSpecialMember - get the special member enum for a method.
Sema::CXXSpecialMember Sema::getSpecialMember(const CXXMethodDecl *MD) {
  if (const CXXConstructorDecl *Ctor = dyn_cast<CXXConstructorDecl>(MD)) {
    if (Ctor->isDefaultConstructor())
      return Sema::CXXDefaultConstructor;

    if (Ctor->isCopyConstructor())
      return Sema::CXXCopyConstructor;

    if (Ctor->isMoveConstructor())
      return Sema::CXXMoveConstructor;
  } else if (isa<CXXDestructorDecl>(MD)) {
    return Sema::CXXDestructor;
  } else if (MD->isCopyAssignmentOperator()) {
    return Sema::CXXCopyAssignment;
  } else if (MD->isMoveAssignmentOperator()) {
    return Sema::CXXMoveAssignment;
  }

  return Sema::CXXInvalid;
}

// Determine whether the previous declaration was a definition, implicit
// declaration, or a declaration.
template <typename T>
static std::pair<diag::kind, SourceLocation>
getNoteDiagForInvalidRedeclaration(const T *Old, const T *New) {
  diag::kind PrevDiag;
  SourceLocation OldLocation = Old->getLocation();
  if (Old->isThisDeclarationADefinition())
    PrevDiag = diag::note_previous_definition;
  else if (Old->isImplicit()) {
    PrevDiag = diag::note_previous_implicit_declaration;
    if (OldLocation.isInvalid())
      OldLocation = New->getLocation();
  } else
    PrevDiag = diag::note_previous_declaration;
  return std::make_pair(PrevDiag, OldLocation);
}

/// canRedefineFunction - checks if a function can be redefined. Currently,
/// only extern inline functions can be redefined, and even then only in
/// GNU89 mode.
static bool canRedefineFunction(const FunctionDecl *FD,
                                const LangOptions& LangOpts) {
  return ((FD->hasAttr<GNUInlineAttr>() || LangOpts.GNUInline) &&
          !LangOpts.CPlusPlus &&
          FD->isInlineSpecified() &&
          FD->getStorageClass() == SC_Extern);
}

const AttributedType *Sema::getCallingConvAttributedType(QualType T) const {
  const AttributedType *AT = T->getAs<AttributedType>();
  while (AT && !AT->isCallingConv())
    AT = AT->getModifiedType()->getAs<AttributedType>();
  return AT;
}

template <typename T>
static bool haveIncompatibleLanguageLinkages(const T *Old, const T *New) {
  const DeclContext *DC = Old->getDeclContext();
  if (DC->isRecord())
    return false;

  LanguageLinkage OldLinkage = Old->getLanguageLinkage();
  if (OldLinkage == CXXLanguageLinkage && New->isInExternCContext())
    return true;
  if (OldLinkage == CLanguageLinkage && New->isInExternCXXContext())
    return true;
  return false;
}

template<typename T> static bool isExternC(T *D) { return D->isExternC(); }
static bool isExternC(VarTemplateDecl *) { return false; }

/// Check whether a redeclaration of an entity introduced by a
/// using-declaration is valid, given that we know it's not an overload
/// (nor a hidden tag declaration).
template<typename ExpectedDecl>
static bool checkUsingShadowRedecl(Sema &S, UsingShadowDecl *OldS,
                                   ExpectedDecl *New) {
  // C++11 [basic.scope.declarative]p4:
  //   Given a set of declarations in a single declarative region, each of
  //   which specifies the same unqualified name,
  //   -- they shall all refer to the same entity, or all refer to functions
  //      and function templates; or
  //   -- exactly one declaration shall declare a class name or enumeration
  //      name that is not a typedef name and the other declarations shall all
  //      refer to the same variable or enumerator, or all refer to functions
  //      and function templates; in this case the class name or enumeration
  //      name is hidden (3.3.10).

  // C++11 [namespace.udecl]p14:
  //   If a function declaration in namespace scope or block scope has the
  //   same name and the same parameter-type-list as a function introduced
  //   by a using-declaration, and the declarations do not declare the same
  //   function, the program is ill-formed.

  auto *Old = dyn_cast<ExpectedDecl>(OldS->getTargetDecl());
  if (Old &&
      !Old->getDeclContext()->getRedeclContext()->Equals(
          New->getDeclContext()->getRedeclContext()) &&
      !(isExternC(Old) && isExternC(New)))
    Old = nullptr;

  if (!Old) {
    S.Diag(New->getLocation(), diag::err_using_decl_conflict_reverse);
    S.Diag(OldS->getTargetDecl()->getLocation(), diag::note_using_decl_target);
    S.Diag(OldS->getUsingDecl()->getLocation(), diag::note_using_decl) << 0;
    return true;
  }
  return false;
}

static bool hasIdenticalPassObjectSizeAttrs(const FunctionDecl *A,
                                            const FunctionDecl *B) {
  assert(A->getNumParams() == B->getNumParams());

  auto AttrEq = [](const ParmVarDecl *A, const ParmVarDecl *B) {
    const auto *AttrA = A->getAttr<PassObjectSizeAttr>();
    const auto *AttrB = B->getAttr<PassObjectSizeAttr>();
    if (AttrA == AttrB)
      return true;
    return AttrA && AttrB && AttrA->getType() == AttrB->getType();
  };

  return std::equal(A->param_begin(), A->param_end(), B->param_begin(), AttrEq);
}

/// If necessary, adjust the semantic declaration context for a qualified
/// declaration to name the correct inline namespace within the qualifier.
static void adjustDeclContextForDeclaratorDecl(DeclaratorDecl *NewD,
                                               DeclaratorDecl *OldD) {
  // The only case where we need to update the DeclContext is when
  // redeclaration lookup for a qualified name finds a declaration
  // in an inline namespace within the context named by the qualifier:
  //
  //   inline namespace N { int f(); }
  //   int ::f(); // Sema DC needs adjusting from :: to N::.
  //
  // For unqualified declarations, the semantic context *can* change
  // along the redeclaration chain (for local extern declarations,
  // extern "C" declarations, and friend declarations in particular).
  if (!NewD->getQualifier())
    return;

  // NewD is probably already in the right context.
  auto *NamedDC = NewD->getDeclContext()->getRedeclContext();
  auto *SemaDC = OldD->getDeclContext()->getRedeclContext();
  if (NamedDC->Equals(SemaDC))
    return;

  assert((NamedDC->InEnclosingNamespaceSetOf(SemaDC) ||
          NewD->isInvalidDecl() || OldD->isInvalidDecl()) &&
         "unexpected context for redeclaration");

  auto *LexDC = NewD->getLexicalDeclContext();
  auto FixSemaDC = [=](NamedDecl *D) {
    if (!D)
      return;
    D->setDeclContext(SemaDC);
    D->setLexicalDeclContext(LexDC);
  };

  FixSemaDC(NewD);
  if (auto *FD = dyn_cast<FunctionDecl>(NewD))
    FixSemaDC(FD->getDescribedFunctionTemplate());
  else if (auto *VD = dyn_cast<VarDecl>(NewD))
    FixSemaDC(VD->getDescribedVarTemplate());
}

/// MergeFunctionDecl - We just parsed a function 'New' from
/// declarator D which has the same name and scope as a previous
/// declaration 'Old'.  Figure out how to resolve this situation,
/// merging decls or emitting diagnostics as appropriate.
///
/// In C++, New and Old must be declarations that are not
/// overloaded. Use IsOverload to determine whether New and Old are
/// overloaded, and to select the Old declaration that New should be
/// merged with.
///
/// Returns true if there was an error, false otherwise.
bool Sema::MergeFunctionDecl(FunctionDecl *New, NamedDecl *&OldD,
                             Scope *S, bool MergeTypeWithOld) {
  // Verify the old decl was also a function.
  FunctionDecl *Old = OldD->getAsFunction();
  if (!Old) {
    if (UsingShadowDecl *Shadow = dyn_cast<UsingShadowDecl>(OldD)) {
      if (New->getFriendObjectKind()) {
        Diag(New->getLocation(), diag::err_using_decl_friend);
        Diag(Shadow->getTargetDecl()->getLocation(),
             diag::note_using_decl_target);
        Diag(Shadow->getUsingDecl()->getLocation(),
             diag::note_using_decl) << 0;
        return true;
      }

      // Check whether the two declarations might declare the same function.
      if (checkUsingShadowRedecl<FunctionDecl>(*this, Shadow, New))
        return true;
      OldD = Old = cast<FunctionDecl>(Shadow->getTargetDecl());
    } else {
      Diag(New->getLocation(), diag::err_redefinition_different_kind)
        << New->getDeclName();
      notePreviousDefinition(OldD, New->getLocation());
      return true;
    }
  }

  // If the old declaration is invalid, just give up here.
  if (Old->isInvalidDecl())
    return true;

  // Disallow redeclaration of some builtins.
  if (!getASTContext().canBuiltinBeRedeclared(Old)) {
    Diag(New->getLocation(), diag::err_builtin_redeclare) << Old->getDeclName();
    Diag(Old->getLocation(), diag::note_previous_builtin_declaration)
        << Old << Old->getType();
    return true;
  }

  diag::kind PrevDiag;
  SourceLocation OldLocation;
  std::tie(PrevDiag, OldLocation) =
      getNoteDiagForInvalidRedeclaration(Old, New);

  // Don't complain about this if we're in GNU89 mode and the old function
  // is an extern inline function.
  // Don't complain about specializations. They are not supposed to have
  // storage classes.
  if (!isa<CXXMethodDecl>(New) && !isa<CXXMethodDecl>(Old) &&
      New->getStorageClass() == SC_Static &&
      Old->hasExternalFormalLinkage() &&
      !New->getTemplateSpecializationInfo() &&
      !canRedefineFunction(Old, getLangOpts())) {
    if (getLangOpts().MicrosoftExt) {
      Diag(New->getLocation(), diag::ext_static_non_static) << New;
      Diag(OldLocation, PrevDiag);
    } else {
      Diag(New->getLocation(), diag::err_static_non_static) << New;
      Diag(OldLocation, PrevDiag);
      return true;
    }
  }

  if (New->hasAttr<InternalLinkageAttr>() &&
      !Old->hasAttr<InternalLinkageAttr>()) {
    Diag(New->getLocation(), diag::err_internal_linkage_redeclaration)
        << New->getDeclName();
    notePreviousDefinition(Old, New->getLocation());
    New->dropAttr<InternalLinkageAttr>();
  }

  if (CheckRedeclarationModuleOwnership(New, Old))
    return true;

  if (!getLangOpts().CPlusPlus) {
    bool OldOvl = Old->hasAttr<OverloadableAttr>();
    if (OldOvl != New->hasAttr<OverloadableAttr>() && !Old->isImplicit()) {
      Diag(New->getLocation(), diag::err_attribute_overloadable_mismatch)
        << New << OldOvl;

      // Try our best to find a decl that actually has the overloadable
      // attribute for the note. In most cases (e.g. programs with only one
      // broken declaration/definition), this won't matter.
      //
      // FIXME: We could do this if we juggled some extra state in
      // OverloadableAttr, rather than just removing it.
      const Decl *DiagOld = Old;
      if (OldOvl) {
        auto OldIter = llvm::find_if(Old->redecls(), [](const Decl *D) {
          const auto *A = D->getAttr<OverloadableAttr>();
          return A && !A->isImplicit();
        });
        // If we've implicitly added *all* of the overloadable attrs to this
        // chain, emitting a "previous redecl" note is pointless.
        DiagOld = OldIter == Old->redecls_end() ? nullptr : *OldIter;
      }

      if (DiagOld)
        Diag(DiagOld->getLocation(),
             diag::note_attribute_overloadable_prev_overload)
          << OldOvl;

      if (OldOvl)
        New->addAttr(OverloadableAttr::CreateImplicit(Context));
      else
        New->dropAttr<OverloadableAttr>();
    }
  }

  // If a function is first declared with a calling convention, but is later
  // declared or defined without one, all following decls assume the calling
  // convention of the first.
  //
  // It's OK if a function is first declared without a calling convention,
  // but is later declared or defined with the default calling convention.
  //
  // To test if either decl has an explicit calling convention, we look for
  // AttributedType sugar nodes on the type as written.  If they are missing or
  // were canonicalized away, we assume the calling convention was implicit.
  //
  // Note also that we DO NOT return at this point, because we still have
  // other tests to run.
  QualType OldQType = Context.getCanonicalType(Old->getType());
  QualType NewQType = Context.getCanonicalType(New->getType());
  const FunctionType *OldType = cast<FunctionType>(OldQType);
  const FunctionType *NewType = cast<FunctionType>(NewQType);
  FunctionType::ExtInfo OldTypeInfo = OldType->getExtInfo();
  FunctionType::ExtInfo NewTypeInfo = NewType->getExtInfo();
  bool RequiresAdjustment = false;

  if (OldTypeInfo.getCC() != NewTypeInfo.getCC()) {
    FunctionDecl *First = Old->getFirstDecl();
    const FunctionType *FT =
        First->getType().getCanonicalType()->castAs<FunctionType>();
    FunctionType::ExtInfo FI = FT->getExtInfo();
    bool NewCCExplicit = getCallingConvAttributedType(New->getType());
    if (!NewCCExplicit) {
      // Inherit the CC from the previous declaration if it was specified
      // there but not here.
      NewTypeInfo = NewTypeInfo.withCallingConv(OldTypeInfo.getCC());
      RequiresAdjustment = true;
    } else {
      // Calling conventions aren't compatible, so complain.
      bool FirstCCExplicit = getCallingConvAttributedType(First->getType());
      Diag(New->getLocation(), diag::err_cconv_change)
        << FunctionType::getNameForCallConv(NewTypeInfo.getCC())
        << !FirstCCExplicit
        << (!FirstCCExplicit ? "" :
            FunctionType::getNameForCallConv(FI.getCC()));

      // Put the note on the first decl, since it is the one that matters.
      Diag(First->getLocation(), diag::note_previous_declaration);
      return true;
    }
  }

  // FIXME: diagnose the other way around?
  if (OldTypeInfo.getNoReturn() && !NewTypeInfo.getNoReturn()) {
    NewTypeInfo = NewTypeInfo.withNoReturn(true);
    RequiresAdjustment = true;
  }

  // Merge regparm attribute.
  if (OldTypeInfo.getHasRegParm() != NewTypeInfo.getHasRegParm() ||
      OldTypeInfo.getRegParm() != NewTypeInfo.getRegParm()) {
    if (NewTypeInfo.getHasRegParm()) {
      Diag(New->getLocation(), diag::err_regparm_mismatch)
        << NewType->getRegParmType()
        << OldType->getRegParmType();
      Diag(OldLocation, diag::note_previous_declaration);
      return true;
    }

    NewTypeInfo = NewTypeInfo.withRegParm(OldTypeInfo.getRegParm());
    RequiresAdjustment = true;
  }

  // Merge ns_returns_retained attribute.
  if (OldTypeInfo.getProducesResult() != NewTypeInfo.getProducesResult()) {
    if (NewTypeInfo.getProducesResult()) {
      Diag(New->getLocation(), diag::err_function_attribute_mismatch)
          << "'ns_returns_retained'";
      Diag(OldLocation, diag::note_previous_declaration);
      return true;
    }

    NewTypeInfo = NewTypeInfo.withProducesResult(true);
    RequiresAdjustment = true;
  }

  if (OldTypeInfo.getNoCallerSavedRegs() !=
      NewTypeInfo.getNoCallerSavedRegs()) {
    if (NewTypeInfo.getNoCallerSavedRegs()) {
      AnyX86NoCallerSavedRegistersAttr *Attr =
        New->getAttr<AnyX86NoCallerSavedRegistersAttr>();
      Diag(New->getLocation(), diag::err_function_attribute_mismatch) << Attr;
      Diag(OldLocation, diag::note_previous_declaration);
      return true;
    }

    NewTypeInfo = NewTypeInfo.withNoCallerSavedRegs(true);
    RequiresAdjustment = true;
  }

  if (RequiresAdjustment) {
    const FunctionType *AdjustedType = New->getType()->getAs<FunctionType>();
    AdjustedType = Context.adjustFunctionType(AdjustedType, NewTypeInfo);
    New->setType(QualType(AdjustedType, 0));
    NewQType = Context.getCanonicalType(New->getType());
    NewType = cast<FunctionType>(NewQType);
  }

  // If this redeclaration makes the function inline, we may need to add it to
  // UndefinedButUsed.
  if (!Old->isInlined() && New->isInlined() &&
      !New->hasAttr<GNUInlineAttr>() &&
      !getLangOpts().GNUInline &&
      Old->isUsed(false) &&
      !Old->isDefined() && !New->isThisDeclarationADefinition())
    UndefinedButUsed.insert(std::make_pair(Old->getCanonicalDecl(),
                                           SourceLocation()));

  // If this redeclaration makes it newly gnu_inline, we don't want to warn
  // about it.
  if (New->hasAttr<GNUInlineAttr>() &&
      Old->isInlined() && !Old->hasAttr<GNUInlineAttr>()) {
    UndefinedButUsed.erase(Old->getCanonicalDecl());
  }

  // If pass_object_size params don't match up perfectly, this isn't a valid
  // redeclaration.
  if (Old->getNumParams() > 0 && Old->getNumParams() == New->getNumParams() &&
      !hasIdenticalPassObjectSizeAttrs(Old, New)) {
    Diag(New->getLocation(), diag::err_different_pass_object_size_params)
        << New->getDeclName();
    Diag(OldLocation, PrevDiag) << Old << Old->getType();
    return true;
  }

  if (getLangOpts().CPlusPlus) {
    // C++1z [over.load]p2
    //   Certain function declarations cannot be overloaded:
    //     -- Function declarations that differ only in the return type,
    //        the exception specification, or both cannot be overloaded.

    // Check the exception specifications match. This may recompute the type of
    // both Old and New if it resolved exception specifications, so grab the
    // types again after this. Because this updates the type, we do this before
    // any of the other checks below, which may update the "de facto" NewQType
    // but do not necessarily update the type of New.
    if (CheckEquivalentExceptionSpec(Old, New))
      return true;
    OldQType = Context.getCanonicalType(Old->getType());
    NewQType = Context.getCanonicalType(New->getType());

    // Go back to the type source info to compare the declared return types,
    // per C++1y [dcl.type.auto]p13:
    //   Redeclarations or specializations of a function or function template
    //   with a declared return type that uses a placeholder type shall also
    //   use that placeholder, not a deduced type.
    QualType OldDeclaredReturnType = Old->getDeclaredReturnType();
    QualType NewDeclaredReturnType = New->getDeclaredReturnType();
    if (!Context.hasSameType(OldDeclaredReturnType, NewDeclaredReturnType) &&
        canFullyTypeCheckRedeclaration(New, Old, NewDeclaredReturnType,
                                       OldDeclaredReturnType)) {
      QualType ResQT;
      if (NewDeclaredReturnType->isObjCObjectPointerType() &&
          OldDeclaredReturnType->isObjCObjectPointerType())
        // FIXME: This does the wrong thing for a deduced return type.
        ResQT = Context.mergeObjCGCQualifiers(NewQType, OldQType);
      if (ResQT.isNull()) {
        if (New->isCXXClassMember() && New->isOutOfLine())
          Diag(New->getLocation(), diag::err_member_def_does_not_match_ret_type)
              << New << New->getReturnTypeSourceRange();
        else
          Diag(New->getLocation(), diag::err_ovl_diff_return_type)
              << New->getReturnTypeSourceRange();
        Diag(OldLocation, PrevDiag) << Old << Old->getType()
                                    << Old->getReturnTypeSourceRange();
        return true;
      }
      else
        NewQType = ResQT;
    }

    QualType OldReturnType = OldType->getReturnType();
    QualType NewReturnType = cast<FunctionType>(NewQType)->getReturnType();
    if (OldReturnType != NewReturnType) {
      // If this function has a deduced return type and has already been
      // defined, copy the deduced value from the old declaration.
      AutoType *OldAT = Old->getReturnType()->getContainedAutoType();
      if (OldAT && OldAT->isDeduced()) {
        New->setType(
            SubstAutoType(New->getType(),
                          OldAT->isDependentType() ? Context.DependentTy
                                                   : OldAT->getDeducedType()));
        NewQType = Context.getCanonicalType(
            SubstAutoType(NewQType,
                          OldAT->isDependentType() ? Context.DependentTy
                                                   : OldAT->getDeducedType()));
      }
    }

    const CXXMethodDecl *OldMethod = dyn_cast<CXXMethodDecl>(Old);
    CXXMethodDecl *NewMethod = dyn_cast<CXXMethodDecl>(New);
    if (OldMethod && NewMethod) {
      // Preserve triviality.
      NewMethod->setTrivial(OldMethod->isTrivial());

      // MSVC allows explicit template specialization at class scope:
      // 2 CXXMethodDecls referring to the same function will be injected.
      // We don't want a redeclaration error.
      bool IsClassScopeExplicitSpecialization =
                              OldMethod->isFunctionTemplateSpecialization() &&
                              NewMethod->isFunctionTemplateSpecialization();
      bool isFriend = NewMethod->getFriendObjectKind();

      if (!isFriend && NewMethod->getLexicalDeclContext()->isRecord() &&
          !IsClassScopeExplicitSpecialization) {
        //    -- Member function declarations with the same name and the
        //       same parameter types cannot be overloaded if any of them
        //       is a static member function declaration.
        if (OldMethod->isStatic() != NewMethod->isStatic()) {
          Diag(New->getLocation(), diag::err_ovl_static_nonstatic_member);
          Diag(OldLocation, PrevDiag) << Old << Old->getType();
          return true;
        }

        // C++ [class.mem]p1:
        //   [...] A member shall not be declared twice in the
        //   member-specification, except that a nested class or member
        //   class template can be declared and then later defined.
        if (!inTemplateInstantiation()) {
          unsigned NewDiag;
          if (isa<CXXConstructorDecl>(OldMethod))
            NewDiag = diag::err_constructor_redeclared;
          else if (isa<CXXDestructorDecl>(NewMethod))
            NewDiag = diag::err_destructor_redeclared;
          else if (isa<CXXConversionDecl>(NewMethod))
            NewDiag = diag::err_conv_function_redeclared;
          else
            NewDiag = diag::err_member_redeclared;

          Diag(New->getLocation(), NewDiag);
        } else {
          Diag(New->getLocation(), diag::err_member_redeclared_in_instantiation)
            << New << New->getType();
        }
        Diag(OldLocation, PrevDiag) << Old << Old->getType();
        return true;

      // Complain if this is an explicit declaration of a special
      // member that was initially declared implicitly.
      //
      // As an exception, it's okay to befriend such methods in order
      // to permit the implicit constructor/destructor/operator calls.
      } else if (OldMethod->isImplicit()) {
        if (isFriend) {
          NewMethod->setImplicit();
        } else {
          Diag(NewMethod->getLocation(),
               diag::err_definition_of_implicitly_declared_member)
            << New << getSpecialMember(OldMethod);
          return true;
        }
      } else if (OldMethod->getFirstDecl()->isExplicitlyDefaulted() && !isFriend) {
        Diag(NewMethod->getLocation(),
             diag::err_definition_of_explicitly_defaulted_member)
          << getSpecialMember(OldMethod);
        return true;
      }
    }

    // C++11 [dcl.attr.noreturn]p1:
    //   The first declaration of a function shall specify the noreturn
    //   attribute if any declaration of that function specifies the noreturn
    //   attribute.
    const CXX11NoReturnAttr *NRA = New->getAttr<CXX11NoReturnAttr>();
    if (NRA && !Old->hasAttr<CXX11NoReturnAttr>()) {
      Diag(NRA->getLocation(), diag::err_noreturn_missing_on_first_decl);
      Diag(Old->getFirstDecl()->getLocation(),
           diag::note_noreturn_missing_first_decl);
    }

    // C++11 [dcl.attr.depend]p2:
    //   The first declaration of a function shall specify the
    //   carries_dependency attribute for its declarator-id if any declaration
    //   of the function specifies the carries_dependency attribute.
    const CarriesDependencyAttr *CDA = New->getAttr<CarriesDependencyAttr>();
    if (CDA && !Old->hasAttr<CarriesDependencyAttr>()) {
      Diag(CDA->getLocation(),
           diag::err_carries_dependency_missing_on_first_decl) << 0/*Function*/;
      Diag(Old->getFirstDecl()->getLocation(),
           diag::note_carries_dependency_missing_first_decl) << 0/*Function*/;
    }

    // (C++98 8.3.5p3):
    //   All declarations for a function shall agree exactly in both the
    //   return type and the parameter-type-list.
    // We also want to respect all the extended bits except noreturn.

    // noreturn should now match unless the old type info didn't have it.
    QualType OldQTypeForComparison = OldQType;
    if (!OldTypeInfo.getNoReturn() && NewTypeInfo.getNoReturn()) {
      auto *OldType = OldQType->castAs<FunctionProtoType>();
      const FunctionType *OldTypeForComparison
        = Context.adjustFunctionType(OldType, OldTypeInfo.withNoReturn(true));
      OldQTypeForComparison = QualType(OldTypeForComparison, 0);
      assert(OldQTypeForComparison.isCanonical());
    }

    if (haveIncompatibleLanguageLinkages(Old, New)) {
      // As a special case, retain the language linkage from previous
      // declarations of a friend function as an extension.
      //
      // This liberal interpretation of C++ [class.friend]p3 matches GCC/MSVC
      // and is useful because there's otherwise no way to specify language
      // linkage within class scope.
      //
      // Check cautiously as the friend object kind isn't yet complete.
      if (New->getFriendObjectKind() != Decl::FOK_None) {
        Diag(New->getLocation(), diag::ext_retained_language_linkage) << New;
        Diag(OldLocation, PrevDiag);
      } else {
        Diag(New->getLocation(), diag::err_different_language_linkage) << New;
        Diag(OldLocation, PrevDiag);
        return true;
      }
    }

    if (OldQTypeForComparison == NewQType)
      return MergeCompatibleFunctionDecls(New, Old, S, MergeTypeWithOld);

    // If the types are imprecise (due to dependent constructs in friends or
    // local extern declarations), it's OK if they differ. We'll check again
    // during instantiation.
    if (!canFullyTypeCheckRedeclaration(New, Old, NewQType, OldQType))
      return false;

    // Fall through for conflicting redeclarations and redefinitions.
  }

  // C: Function types need to be compatible, not identical. This handles
  // duplicate function decls like "void f(int); void f(enum X);" properly.
  if (!getLangOpts().CPlusPlus &&
      Context.typesAreCompatible(OldQType, NewQType)) {
    const FunctionType *OldFuncType = OldQType->getAs<FunctionType>();
    const FunctionType *NewFuncType = NewQType->getAs<FunctionType>();
    const FunctionProtoType *OldProto = nullptr;
    if (MergeTypeWithOld && isa<FunctionNoProtoType>(NewFuncType) &&
        (OldProto = dyn_cast<FunctionProtoType>(OldFuncType))) {
      // The old declaration provided a function prototype, but the
      // new declaration does not. Merge in the prototype.
      assert(!OldProto->hasExceptionSpec() && "Exception spec in C");
      SmallVector<QualType, 16> ParamTypes(OldProto->param_types());
      NewQType =
          Context.getFunctionType(NewFuncType->getReturnType(), ParamTypes,
                                  OldProto->getExtProtoInfo());
      New->setType(NewQType);
      New->setHasInheritedPrototype();

      // Synthesize parameters with the same types.
      SmallVector<ParmVarDecl*, 16> Params;
      for (const auto &ParamType : OldProto->param_types()) {
        ParmVarDecl *Param = ParmVarDecl::Create(Context, New, SourceLocation(),
                                                 SourceLocation(), nullptr,
                                                 ParamType, /*TInfo=*/nullptr,
                                                 SC_None, nullptr);
        Param->setScopeInfo(0, Params.size());
        Param->setImplicit();
        Params.push_back(Param);
      }

      New->setParams(Params);
    }

    return MergeCompatibleFunctionDecls(New, Old, S, MergeTypeWithOld);
  }

  // GNU C permits a K&R definition to follow a prototype declaration
  // if the declared types of the parameters in the K&R definition
  // match the types in the prototype declaration, even when the
  // promoted types of the parameters from the K&R definition differ
  // from the types in the prototype. GCC then keeps the types from
  // the prototype.
  //
  // If a variadic prototype is followed by a non-variadic K&R definition,
  // the K&R definition becomes variadic.  This is sort of an edge case, but
  // it's legal per the standard depending on how you read C99 6.7.5.3p15 and
  // C99 6.9.1p8.
  if (!getLangOpts().CPlusPlus &&
      Old->hasPrototype() && !New->hasPrototype() &&
      New->getType()->getAs<FunctionProtoType>() &&
      Old->getNumParams() == New->getNumParams()) {
    SmallVector<QualType, 16> ArgTypes;
    SmallVector<GNUCompatibleParamWarning, 16> Warnings;
    const FunctionProtoType *OldProto
      = Old->getType()->getAs<FunctionProtoType>();
    const FunctionProtoType *NewProto
      = New->getType()->getAs<FunctionProtoType>();

    // Determine whether this is the GNU C extension.
    QualType MergedReturn = Context.mergeTypes(OldProto->getReturnType(),
                                               NewProto->getReturnType());
    bool LooseCompatible = !MergedReturn.isNull();
    for (unsigned Idx = 0, End = Old->getNumParams();
         LooseCompatible && Idx != End; ++Idx) {
      ParmVarDecl *OldParm = Old->getParamDecl(Idx);
      ParmVarDecl *NewParm = New->getParamDecl(Idx);
      if (Context.typesAreCompatible(OldParm->getType(),
                                     NewProto->getParamType(Idx))) {
        ArgTypes.push_back(NewParm->getType());
      } else if (Context.typesAreCompatible(OldParm->getType(),
                                            NewParm->getType(),
                                            /*CompareUnqualified=*/true)) {
        GNUCompatibleParamWarning Warn = { OldParm, NewParm,
                                           NewProto->getParamType(Idx) };
        Warnings.push_back(Warn);
        ArgTypes.push_back(NewParm->getType());
      } else
        LooseCompatible = false;
    }

    if (LooseCompatible) {
      for (unsigned Warn = 0; Warn < Warnings.size(); ++Warn) {
        Diag(Warnings[Warn].NewParm->getLocation(),
             diag::ext_param_promoted_not_compatible_with_prototype)
          << Warnings[Warn].PromotedType
          << Warnings[Warn].OldParm->getType();
        if (Warnings[Warn].OldParm->getLocation().isValid())
          Diag(Warnings[Warn].OldParm->getLocation(),
               diag::note_previous_declaration);
      }

      if (MergeTypeWithOld)
        New->setType(Context.getFunctionType(MergedReturn, ArgTypes,
                                             OldProto->getExtProtoInfo()));
      return MergeCompatibleFunctionDecls(New, Old, S, MergeTypeWithOld);
    }

    // Fall through to diagnose conflicting types.
  }

  // A function that has already been declared has been redeclared or
  // defined with a different type; show an appropriate diagnostic.

  // If the previous declaration was an implicitly-generated builtin
  // declaration, then at the very least we should use a specialized note.
  unsigned BuiltinID;
  if (Old->isImplicit() && (BuiltinID = Old->getBuiltinID())) {
    // If it's actually a library-defined builtin function like 'malloc'
    // or 'printf', just warn about the incompatible redeclaration.
    if (Context.BuiltinInfo.isPredefinedLibFunction(BuiltinID)) {
      Diag(New->getLocation(), diag::warn_redecl_library_builtin) << New;
      Diag(OldLocation, diag::note_previous_builtin_declaration)
        << Old << Old->getType();

      // If this is a global redeclaration, just forget hereafter
      // about the "builtin-ness" of the function.
      //
      // Doing this for local extern declarations is problematic.  If
      // the builtin declaration remains visible, a second invalid
      // local declaration will produce a hard error; if it doesn't
      // remain visible, a single bogus local redeclaration (which is
      // actually only a warning) could break all the downstream code.
      if (!New->getLexicalDeclContext()->isFunctionOrMethod())
        New->getIdentifier()->revertBuiltin();

      return false;
    }

    PrevDiag = diag::note_previous_builtin_declaration;
  }

  Diag(New->getLocation(), diag::err_conflicting_types) << New->getDeclName();
  Diag(OldLocation, PrevDiag) << Old << Old->getType();
  return true;
}

/// Completes the merge of two function declarations that are
/// known to be compatible.
///
/// This routine handles the merging of attributes and other
/// properties of function declarations from the old declaration to
/// the new declaration, once we know that New is in fact a
/// redeclaration of Old.
///
/// \returns false
bool Sema::MergeCompatibleFunctionDecls(FunctionDecl *New, FunctionDecl *Old,
                                        Scope *S, bool MergeTypeWithOld) {
  // Merge the attributes
  mergeDeclAttributes(New, Old);

  // Merge "pure" flag.
  if (Old->isPure())
    New->setPure();

  // Merge "used" flag.
  if (Old->getMostRecentDecl()->isUsed(false))
    New->setIsUsed();

  // Merge attributes from the parameters.  These can mismatch with K&R
  // declarations.
  if (New->getNumParams() == Old->getNumParams())
      for (unsigned i = 0, e = New->getNumParams(); i != e; ++i) {
        ParmVarDecl *NewParam = New->getParamDecl(i);
        ParmVarDecl *OldParam = Old->getParamDecl(i);
        mergeParamDeclAttributes(NewParam, OldParam, *this);
        mergeParamDeclTypes(NewParam, OldParam, *this);
      }

  if (getLangOpts().CPlusPlus)
    return MergeCXXFunctionDecl(New, Old, S);

  // Merge the function types so the we get the composite types for the return
  // and argument types. Per C11 6.2.7/4, only update the type if the old decl
  // was visible.
  QualType Merged = Context.mergeTypes(Old->getType(), New->getType());
  if (!Merged.isNull() && MergeTypeWithOld)
    New->setType(Merged);

  return false;
}

void Sema::mergeObjCMethodDecls(ObjCMethodDecl *newMethod,
                                ObjCMethodDecl *oldMethod) {
  // Merge the attributes, including deprecated/unavailable
  AvailabilityMergeKind MergeKind =
    isa<ObjCProtocolDecl>(oldMethod->getDeclContext())
      ? AMK_ProtocolImplementation
      : isa<ObjCImplDecl>(newMethod->getDeclContext()) ? AMK_Redeclaration
                                                       : AMK_Override;

  mergeDeclAttributes(newMethod, oldMethod, MergeKind);

  // Merge attributes from the parameters.
  ObjCMethodDecl::param_const_iterator oi = oldMethod->param_begin(),
                                       oe = oldMethod->param_end();
  for (ObjCMethodDecl::param_iterator
         ni = newMethod->param_begin(), ne = newMethod->param_end();
       ni != ne && oi != oe; ++ni, ++oi)
    mergeParamDeclAttributes(*ni, *oi, *this);

  CheckObjCMethodOverride(newMethod, oldMethod);
}

static void diagnoseVarDeclTypeMismatch(Sema &S, VarDecl *New, VarDecl* Old) {
  assert(!S.Context.hasSameType(New->getType(), Old->getType()));

  S.Diag(New->getLocation(), New->isThisDeclarationADefinition()
         ? diag::err_redefinition_different_type
         : diag::err_redeclaration_different_type)
    << New->getDeclName() << New->getType() << Old->getType();

  diag::kind PrevDiag;
  SourceLocation OldLocation;
  std::tie(PrevDiag, OldLocation)
    = getNoteDiagForInvalidRedeclaration(Old, New);
  S.Diag(OldLocation, PrevDiag);
  New->setInvalidDecl();
}

/// MergeVarDeclTypes - We parsed a variable 'New' which has the same name and
/// scope as a previous declaration 'Old'.  Figure out how to merge their types,
/// emitting diagnostics as appropriate.
///
/// Declarations using the auto type specifier (C++ [decl.spec.auto]) call back
/// to here in AddInitializerToDecl. We can't check them before the initializer
/// is attached.
void Sema::MergeVarDeclTypes(VarDecl *New, VarDecl *Old,
                             bool MergeTypeWithOld) {
  if (New->isInvalidDecl() || Old->isInvalidDecl())
    return;

  QualType MergedT;
  if (getLangOpts().CPlusPlus) {
    if (New->getType()->isUndeducedType()) {
      // We don't know what the new type is until the initializer is attached.
      return;
    } else if (Context.hasSameType(New->getType(), Old->getType())) {
      // These could still be something that needs exception specs checked.
      return MergeVarDeclExceptionSpecs(New, Old);
    }
    // C++ [basic.link]p10:
    //   [...] the types specified by all declarations referring to a given
    //   object or function shall be identical, except that declarations for an
    //   array object can specify array types that differ by the presence or
    //   absence of a major array bound (8.3.4).
    else if (Old->getType()->isArrayType() && New->getType()->isArrayType()) {
      const ArrayType *OldArray = Context.getAsArrayType(Old->getType());
      const ArrayType *NewArray = Context.getAsArrayType(New->getType());

      // We are merging a variable declaration New into Old. If it has an array
      // bound, and that bound differs from Old's bound, we should diagnose the
      // mismatch.
      if (!NewArray->isIncompleteArrayType() && !NewArray->isDependentType()) {
        for (VarDecl *PrevVD = Old->getMostRecentDecl(); PrevVD;
             PrevVD = PrevVD->getPreviousDecl()) {
          const ArrayType *PrevVDTy = Context.getAsArrayType(PrevVD->getType());
          if (PrevVDTy->isIncompleteArrayType() || PrevVDTy->isDependentType())
            continue;

          if (!Context.hasSameType(NewArray, PrevVDTy))
            return diagnoseVarDeclTypeMismatch(*this, New, PrevVD);
        }
      }

      if (OldArray->isIncompleteArrayType() && NewArray->isArrayType()) {
        if (Context.hasSameType(OldArray->getElementType(),
                                NewArray->getElementType()))
          MergedT = New->getType();
      }
      // FIXME: Check visibility. New is hidden but has a complete type. If New
      // has no array bound, it should not inherit one from Old, if Old is not
      // visible.
      else if (OldArray->isArrayType() && NewArray->isIncompleteArrayType()) {
        if (Context.hasSameType(OldArray->getElementType(),
                                NewArray->getElementType()))
          MergedT = Old->getType();
      }
    }
    else if (New->getType()->isObjCObjectPointerType() &&
               Old->getType()->isObjCObjectPointerType()) {
      MergedT = Context.mergeObjCGCQualifiers(New->getType(),
                                              Old->getType());
    }
  } else {
    // C 6.2.7p2:
    //   All declarations that refer to the same object or function shall have
    //   compatible type.
    MergedT = Context.mergeTypes(New->getType(), Old->getType());
  }
  if (MergedT.isNull()) {
    // It's OK if we couldn't merge types if either type is dependent, for a
    // block-scope variable. In other cases (static data members of class
    // templates, variable templates, ...), we require the types to be
    // equivalent.
    // FIXME: The C++ standard doesn't say anything about this.
    if ((New->getType()->isDependentType() ||
         Old->getType()->isDependentType()) && New->isLocalVarDecl()) {
      // If the old type was dependent, we can't merge with it, so the new type
      // becomes dependent for now. We'll reproduce the original type when we
      // instantiate the TypeSourceInfo for the variable.
      if (!New->getType()->isDependentType() && MergeTypeWithOld)
        New->setType(Context.DependentTy);
      return;
    }
    return diagnoseVarDeclTypeMismatch(*this, New, Old);
  }

  // Don't actually update the type on the new declaration if the old
  // declaration was an extern declaration in a different scope.
  if (MergeTypeWithOld)
    New->setType(MergedT);
}

static bool mergeTypeWithPrevious(Sema &S, VarDecl *NewVD, VarDecl *OldVD,
                                  LookupResult &Previous) {
  // C11 6.2.7p4:
  //   For an identifier with internal or external linkage declared
  //   in a scope in which a prior declaration of that identifier is
  //   visible, if the prior declaration specifies internal or
  //   external linkage, the type of the identifier at the later
  //   declaration becomes the composite type.
  //
  // If the variable isn't visible, we do not merge with its type.
  if (Previous.isShadowed())
    return false;

  if (S.getLangOpts().CPlusPlus) {
    // C++11 [dcl.array]p3:
    //   If there is a preceding declaration of the entity in the same
    //   scope in which the bound was specified, an omitted array bound
    //   is taken to be the same as in that earlier declaration.
    return NewVD->isPreviousDeclInSameBlockScope() ||
           (!OldVD->getLexicalDeclContext()->isFunctionOrMethod() &&
            !NewVD->getLexicalDeclContext()->isFunctionOrMethod());
  } else {
    // If the old declaration was function-local, don't merge with its
    // type unless we're in the same function.
    return !OldVD->getLexicalDeclContext()->isFunctionOrMethod() ||
           OldVD->getLexicalDeclContext() == NewVD->getLexicalDeclContext();
  }
}

/// MergeVarDecl - We just parsed a variable 'New' which has the same name
/// and scope as a previous declaration 'Old'.  Figure out how to resolve this
/// situation, merging decls or emitting diagnostics as appropriate.
///
/// Tentative definition rules (C99 6.9.2p2) are checked by
/// FinalizeDeclaratorGroup. Unfortunately, we can't analyze tentative
/// definitions here, since the initializer hasn't been attached.
///
void Sema::MergeVarDecl(VarDecl *New, LookupResult &Previous) {
  // If the new decl is already invalid, don't do any other checking.
  if (New->isInvalidDecl())
    return;

  if (!shouldLinkPossiblyHiddenDecl(Previous, New))
    return;

  VarTemplateDecl *NewTemplate = New->getDescribedVarTemplate();

  // Verify the old decl was also a variable or variable template.
  VarDecl *Old = nullptr;
  VarTemplateDecl *OldTemplate = nullptr;
  if (Previous.isSingleResult()) {
    if (NewTemplate) {
      OldTemplate = dyn_cast<VarTemplateDecl>(Previous.getFoundDecl());
      Old = OldTemplate ? OldTemplate->getTemplatedDecl() : nullptr;

      if (auto *Shadow =
              dyn_cast<UsingShadowDecl>(Previous.getRepresentativeDecl()))
        if (checkUsingShadowRedecl<VarTemplateDecl>(*this, Shadow, NewTemplate))
          return New->setInvalidDecl();
    } else {
      Old = dyn_cast<VarDecl>(Previous.getFoundDecl());

      if (auto *Shadow =
              dyn_cast<UsingShadowDecl>(Previous.getRepresentativeDecl()))
        if (checkUsingShadowRedecl<VarDecl>(*this, Shadow, New))
          return New->setInvalidDecl();
    }
  }
  if (!Old) {
    Diag(New->getLocation(), diag::err_redefinition_different_kind)
        << New->getDeclName();
    notePreviousDefinition(Previous.getRepresentativeDecl(),
                           New->getLocation());
    return New->setInvalidDecl();
  }

  // Ensure the template parameters are compatible.
  if (NewTemplate &&
      !TemplateParameterListsAreEqual(NewTemplate->getTemplateParameters(),
                                      OldTemplate->getTemplateParameters(),
                                      /*Complain=*/true, TPL_TemplateMatch))
    return New->setInvalidDecl();

  // C++ [class.mem]p1:
  //   A member shall not be declared twice in the member-specification [...]
  //
  // Here, we need only consider static data members.
  if (Old->isStaticDataMember() && !New->isOutOfLine()) {
    Diag(New->getLocation(), diag::err_duplicate_member)
      << New->getIdentifier();
    Diag(Old->getLocation(), diag::note_previous_declaration);
    New->setInvalidDecl();
  }

  mergeDeclAttributes(New, Old);
  // Warn if an already-declared variable is made a weak_import in a subsequent
  // declaration
  if (New->hasAttr<WeakImportAttr>() &&
      Old->getStorageClass() == SC_None &&
      !Old->hasAttr<WeakImportAttr>()) {
    Diag(New->getLocation(), diag::warn_weak_import) << New->getDeclName();
    notePreviousDefinition(Old, New->getLocation());
    // Remove weak_import attribute on new declaration.
    New->dropAttr<WeakImportAttr>();
  }

  if (New->hasAttr<InternalLinkageAttr>() &&
      !Old->hasAttr<InternalLinkageAttr>()) {
    Diag(New->getLocation(), diag::err_internal_linkage_redeclaration)
        << New->getDeclName();
    notePreviousDefinition(Old, New->getLocation());
    New->dropAttr<InternalLinkageAttr>();
  }

  // Merge the types.
  VarDecl *MostRecent = Old->getMostRecentDecl();
  if (MostRecent != Old) {
    MergeVarDeclTypes(New, MostRecent,
                      mergeTypeWithPrevious(*this, New, MostRecent, Previous));
    if (New->isInvalidDecl())
      return;
  }

  MergeVarDeclTypes(New, Old, mergeTypeWithPrevious(*this, New, Old, Previous));
  if (New->isInvalidDecl())
    return;

  diag::kind PrevDiag;
  SourceLocation OldLocation;
  std::tie(PrevDiag, OldLocation) =
      getNoteDiagForInvalidRedeclaration(Old, New);

  // [dcl.stc]p8: Check if we have a non-static decl followed by a static.
  if (New->getStorageClass() == SC_Static &&
      !New->isStaticDataMember() &&
      Old->hasExternalFormalLinkage()) {
    if (getLangOpts().MicrosoftExt) {
      Diag(New->getLocation(), diag::ext_static_non_static)
          << New->getDeclName();
      Diag(OldLocation, PrevDiag);
    } else {
      Diag(New->getLocation(), diag::err_static_non_static)
          << New->getDeclName();
      Diag(OldLocation, PrevDiag);
      return New->setInvalidDecl();
    }
  }
  // C99 6.2.2p4:
  //   For an identifier declared with the storage-class specifier
  //   extern in a scope in which a prior declaration of that
  //   identifier is visible,23) if the prior declaration specifies
  //   internal or external linkage, the linkage of the identifier at
  //   the later declaration is the same as the linkage specified at
  //   the prior declaration. If no prior declaration is visible, or
  //   if the prior declaration specifies no linkage, then the
  //   identifier has external linkage.
  if (New->hasExternalStorage() && Old->hasLinkage())
    /* Okay */;
  else if (New->getCanonicalDecl()->getStorageClass() != SC_Static &&
           !New->isStaticDataMember() &&
           Old->getCanonicalDecl()->getStorageClass() == SC_Static) {
    Diag(New->getLocation(), diag::err_non_static_static) << New->getDeclName();
    Diag(OldLocation, PrevDiag);
    return New->setInvalidDecl();
  }

  // Check if extern is followed by non-extern and vice-versa.
  if (New->hasExternalStorage() &&
      !Old->hasLinkage() && Old->isLocalVarDeclOrParm()) {
    Diag(New->getLocation(), diag::err_extern_non_extern) << New->getDeclName();
    Diag(OldLocation, PrevDiag);
    return New->setInvalidDecl();
  }
  if (Old->hasLinkage() && New->isLocalVarDeclOrParm() &&
      !New->hasExternalStorage()) {
    Diag(New->getLocation(), diag::err_non_extern_extern) << New->getDeclName();
    Diag(OldLocation, PrevDiag);
    return New->setInvalidDecl();
  }

  if (CheckRedeclarationModuleOwnership(New, Old))
    return;

  // Variables with external linkage are analyzed in FinalizeDeclaratorGroup.

  // FIXME: The test for external storage here seems wrong? We still
  // need to check for mismatches.
  if (!New->hasExternalStorage() && !New->isFileVarDecl() &&
      // Don't complain about out-of-line definitions of static members.
      !(Old->getLexicalDeclContext()->isRecord() &&
        !New->getLexicalDeclContext()->isRecord())) {
    Diag(New->getLocation(), diag::err_redefinition) << New->getDeclName();
    Diag(OldLocation, PrevDiag);
    return New->setInvalidDecl();
  }

  if (New->isInline() && !Old->getMostRecentDecl()->isInline()) {
    if (VarDecl *Def = Old->getDefinition()) {
      // C++1z [dcl.fcn.spec]p4:
      //   If the definition of a variable appears in a translation unit before
      //   its first declaration as inline, the program is ill-formed.
      Diag(New->getLocation(), diag::err_inline_decl_follows_def) << New;
      Diag(Def->getLocation(), diag::note_previous_definition);
    }
  }

  // If this redeclaration makes the variable inline, we may need to add it to
  // UndefinedButUsed.
  if (!Old->isInline() && New->isInline() && Old->isUsed(false) &&
      !Old->getDefinition() && !New->isThisDeclarationADefinition())
    UndefinedButUsed.insert(std::make_pair(Old->getCanonicalDecl(),
                                           SourceLocation()));

  if (New->getTLSKind() != Old->getTLSKind()) {
    if (!Old->getTLSKind()) {
      Diag(New->getLocation(), diag::err_thread_non_thread) << New->getDeclName();
      Diag(OldLocation, PrevDiag);
    } else if (!New->getTLSKind()) {
      Diag(New->getLocation(), diag::err_non_thread_thread) << New->getDeclName();
      Diag(OldLocation, PrevDiag);
    } else {
      // Do not allow redeclaration to change the variable between requiring
      // static and dynamic initialization.
      // FIXME: GCC allows this, but uses the TLS keyword on the first
      // declaration to determine the kind. Do we need to be compatible here?
      Diag(New->getLocation(), diag::err_thread_thread_different_kind)
        << New->getDeclName() << (New->getTLSKind() == VarDecl::TLS_Dynamic);
      Diag(OldLocation, PrevDiag);
    }
  }

  // C++ doesn't have tentative definitions, so go right ahead and check here.
  if (getLangOpts().CPlusPlus &&
      New->isThisDeclarationADefinition() == VarDecl::Definition) {
    if (Old->isStaticDataMember() && Old->getCanonicalDecl()->isInline() &&
        Old->getCanonicalDecl()->isConstexpr()) {
      // This definition won't be a definition any more once it's been merged.
      Diag(New->getLocation(),
           diag::warn_deprecated_redundant_constexpr_static_def);
    } else if (VarDecl *Def = Old->getDefinition()) {
      if (checkVarDeclRedefinition(Def, New))
        return;
    }
  }

  if (haveIncompatibleLanguageLinkages(Old, New)) {
    Diag(New->getLocation(), diag::err_different_language_linkage) << New;
    Diag(OldLocation, PrevDiag);
    New->setInvalidDecl();
    return;
  }

  // Merge "used" flag.
  if (Old->getMostRecentDecl()->isUsed(false))
    New->setIsUsed();

  // Keep a chain of previous declarations.
  New->setPreviousDecl(Old);
  if (NewTemplate)
    NewTemplate->setPreviousDecl(OldTemplate);
  adjustDeclContextForDeclaratorDecl(New, Old);

  // Inherit access appropriately.
  New->setAccess(Old->getAccess());
  if (NewTemplate)
    NewTemplate->setAccess(New->getAccess());

  if (Old->isInline())
    New->setImplicitlyInline();
}

void Sema::notePreviousDefinition(const NamedDecl *Old, SourceLocation New) {
  SourceManager &SrcMgr = getSourceManager();
  auto FNewDecLoc = SrcMgr.getDecomposedLoc(New);
  auto FOldDecLoc = SrcMgr.getDecomposedLoc(Old->getLocation());
  auto *FNew = SrcMgr.getFileEntryForID(FNewDecLoc.first);
  auto *FOld = SrcMgr.getFileEntryForID(FOldDecLoc.first);
  auto &HSI = PP.getHeaderSearchInfo();
  StringRef HdrFilename =
      SrcMgr.getFilename(SrcMgr.getSpellingLoc(Old->getLocation()));

  auto noteFromModuleOrInclude = [&](Module *Mod,
                                     SourceLocation IncLoc) -> bool {
    // Redefinition errors with modules are common with non modular mapped
    // headers, example: a non-modular header H in module A that also gets
    // included directly in a TU. Pointing twice to the same header/definition
    // is confusing, try to get better diagnostics when modules is on.
    if (IncLoc.isValid()) {
      if (Mod) {
        Diag(IncLoc, diag::note_redefinition_modules_same_file)
            << HdrFilename.str() << Mod->getFullModuleName();
        if (!Mod->DefinitionLoc.isInvalid())
          Diag(Mod->DefinitionLoc, diag::note_defined_here)
              << Mod->getFullModuleName();
      } else {
        Diag(IncLoc, diag::note_redefinition_include_same_file)
            << HdrFilename.str();
      }
      return true;
    }

    return false;
  };

  // Is it the same file and same offset? Provide more information on why
  // this leads to a redefinition error.
  bool EmittedDiag = false;
  if (FNew == FOld && FNewDecLoc.second == FOldDecLoc.second) {
    SourceLocation OldIncLoc = SrcMgr.getIncludeLoc(FOldDecLoc.first);
    SourceLocation NewIncLoc = SrcMgr.getIncludeLoc(FNewDecLoc.first);
    EmittedDiag = noteFromModuleOrInclude(Old->getOwningModule(), OldIncLoc);
    EmittedDiag |= noteFromModuleOrInclude(getCurrentModule(), NewIncLoc);

    // If the header has no guards, emit a note suggesting one.
    if (FOld && !HSI.isFileMultipleIncludeGuarded(FOld))
      Diag(Old->getLocation(), diag::note_use_ifdef_guards);

    if (EmittedDiag)
      return;
  }

  // Redefinition coming from different files or couldn't do better above.
  if (Old->getLocation().isValid())
    Diag(Old->getLocation(), diag::note_previous_definition);
}

/// We've just determined that \p Old and \p New both appear to be definitions
/// of the same variable. Either diagnose or fix the problem.
bool Sema::checkVarDeclRedefinition(VarDecl *Old, VarDecl *New) {
  if (!hasVisibleDefinition(Old) &&
      (New->getFormalLinkage() == InternalLinkage ||
       New->isInline() ||
       New->getDescribedVarTemplate() ||
       New->getNumTemplateParameterLists() ||
       New->getDeclContext()->isDependentContext())) {
    // The previous definition is hidden, and multiple definitions are
    // permitted (in separate TUs). Demote this to a declaration.
    New->demoteThisDefinitionToDeclaration();

    // Make the canonical definition visible.
    if (auto *OldTD = Old->getDescribedVarTemplate())
      makeMergedDefinitionVisible(OldTD);
    makeMergedDefinitionVisible(Old);
    return false;
  } else {
    Diag(New->getLocation(), diag::err_redefinition) << New;
    notePreviousDefinition(Old, New->getLocation());
    New->setInvalidDecl();
    return true;
  }
}

/// ParsedFreeStandingDeclSpec - This method is invoked when a declspec with
/// no declarator (e.g. "struct foo;") is parsed.
Decl *
Sema::ParsedFreeStandingDeclSpec(Scope *S, AccessSpecifier AS, DeclSpec &DS,
                                 RecordDecl *&AnonRecord) {
  return ParsedFreeStandingDeclSpec(S, AS, DS, MultiTemplateParamsArg(), false,
                                    AnonRecord);
}

// The MS ABI changed between VS2013 and VS2015 with regard to numbers used to
// disambiguate entities defined in different scopes.
// While the VS2015 ABI fixes potential miscompiles, it is also breaks
// compatibility.
// We will pick our mangling number depending on which version of MSVC is being
// targeted.
static unsigned getMSManglingNumber(const LangOptions &LO, Scope *S) {
  return LO.isCompatibleWithMSVC(LangOptions::MSVC2015)
             ? S->getMSCurManglingNumber()
             : S->getMSLastManglingNumber();
}

void Sema::handleTagNumbering(const TagDecl *Tag, Scope *TagScope) {
  if (!Context.getLangOpts().CPlusPlus)
    return;

  if (isa<CXXRecordDecl>(Tag->getParent())) {
    // If this tag is the direct child of a class, number it if
    // it is anonymous.
    if (!Tag->getName().empty() || Tag->getTypedefNameForAnonDecl())
      return;
    MangleNumberingContext &MCtx =
        Context.getManglingNumberContext(Tag->getParent());
    Context.setManglingNumber(
        Tag, MCtx.getManglingNumber(
                 Tag, getMSManglingNumber(getLangOpts(), TagScope)));
    return;
  }

  // If this tag isn't a direct child of a class, number it if it is local.
  Decl *ManglingContextDecl;
  if (MangleNumberingContext *MCtx = getCurrentMangleNumberContext(
          Tag->getDeclContext(), ManglingContextDecl)) {
    Context.setManglingNumber(
        Tag, MCtx->getManglingNumber(
                 Tag, getMSManglingNumber(getLangOpts(), TagScope)));
  }
}

void Sema::setTagNameForLinkagePurposes(TagDecl *TagFromDeclSpec,
                                        TypedefNameDecl *NewTD) {
  if (TagFromDeclSpec->isInvalidDecl())
    return;

  // Do nothing if the tag already has a name for linkage purposes.
  if (TagFromDeclSpec->hasNameForLinkage())
    return;

  // A well-formed anonymous tag must always be a TUK_Definition.
  assert(TagFromDeclSpec->isThisDeclarationADefinition());

  // The type must match the tag exactly;  no qualifiers allowed.
  if (!Context.hasSameType(NewTD->getUnderlyingType(),
                           Context.getTagDeclType(TagFromDeclSpec))) {
    if (getLangOpts().CPlusPlus)
      Context.addTypedefNameForUnnamedTagDecl(TagFromDeclSpec, NewTD);
    return;
  }

  // If we've already computed linkage for the anonymous tag, then
  // adding a typedef name for the anonymous decl can change that
  // linkage, which might be a serious problem.  Diagnose this as
  // unsupported and ignore the typedef name.  TODO: we should
  // pursue this as a language defect and establish a formal rule
  // for how to handle it.
  if (TagFromDeclSpec->hasLinkageBeenComputed()) {
    Diag(NewTD->getLocation(), diag::err_typedef_changes_linkage);

    SourceLocation tagLoc = TagFromDeclSpec->getInnerLocStart();
    tagLoc = getLocForEndOfToken(tagLoc);

    llvm::SmallString<40> textToInsert;
    textToInsert += ' ';
    textToInsert += NewTD->getIdentifier()->getName();
    Diag(tagLoc, diag::note_typedef_changes_linkage)
        << FixItHint::CreateInsertion(tagLoc, textToInsert);
    return;
  }

  // Otherwise, set this is the anon-decl typedef for the tag.
  TagFromDeclSpec->setTypedefNameForAnonDecl(NewTD);
}

static unsigned GetDiagnosticTypeSpecifierID(DeclSpec::TST T) {
  switch (T) {
  case DeclSpec::TST_class:
    return 0;
  case DeclSpec::TST_struct:
    return 1;
  case DeclSpec::TST_interface:
    return 2;
  case DeclSpec::TST_union:
    return 3;
  case DeclSpec::TST_enum:
    return 4;
  default:
    llvm_unreachable("unexpected type specifier");
  }
}

/// ParsedFreeStandingDeclSpec - This method is invoked when a declspec with
/// no declarator (e.g. "struct foo;") is parsed. It also accepts template
/// parameters to cope with template friend declarations.
Decl *
Sema::ParsedFreeStandingDeclSpec(Scope *S, AccessSpecifier AS, DeclSpec &DS,
                                 MultiTemplateParamsArg TemplateParams,
                                 bool IsExplicitInstantiation,
                                 RecordDecl *&AnonRecord) {
  Decl *TagD = nullptr;
  TagDecl *Tag = nullptr;
  if (DS.getTypeSpecType() == DeclSpec::TST_class ||
      DS.getTypeSpecType() == DeclSpec::TST_struct ||
      DS.getTypeSpecType() == DeclSpec::TST_interface ||
      DS.getTypeSpecType() == DeclSpec::TST_union ||
      DS.getTypeSpecType() == DeclSpec::TST_enum) {
    TagD = DS.getRepAsDecl();

    if (!TagD) // We probably had an error
      return nullptr;

    // Note that the above type specs guarantee that the
    // type rep is a Decl, whereas in many of the others
    // it's a Type.
    if (isa<TagDecl>(TagD))
      Tag = cast<TagDecl>(TagD);
    else if (ClassTemplateDecl *CTD = dyn_cast<ClassTemplateDecl>(TagD))
      Tag = CTD->getTemplatedDecl();
  }

  if (Tag) {
    handleTagNumbering(Tag, S);
    Tag->setFreeStanding();
    if (Tag->isInvalidDecl())
      return Tag;
  }

  if (unsigned TypeQuals = DS.getTypeQualifiers()) {
    // Enforce C99 6.7.3p2: "Types other than pointer types derived from object
    // or incomplete types shall not be restrict-qualified."
    if (TypeQuals & DeclSpec::TQ_restrict)
      Diag(DS.getRestrictSpecLoc(),
           diag::err_typecheck_invalid_restrict_not_pointer_noarg)
           << DS.getSourceRange();
  }

  if (DS.isInlineSpecified())
    Diag(DS.getInlineSpecLoc(), diag::err_inline_non_function)
        << getLangOpts().CPlusPlus17;

  if (DS.isConstexprSpecified()) {
    // C++0x [dcl.constexpr]p1: constexpr can only be applied to declarations
    // and definitions of functions and variables.
    if (Tag)
      Diag(DS.getConstexprSpecLoc(), diag::err_constexpr_tag)
          << GetDiagnosticTypeSpecifierID(DS.getTypeSpecType());
    else
      Diag(DS.getConstexprSpecLoc(), diag::err_constexpr_no_declarators);
    // Don't emit warnings after this error.
    return TagD;
  }

  DiagnoseFunctionSpecifiers(DS);

  if (DS.isFriendSpecified()) {
    // If we're dealing with a decl but not a TagDecl, assume that
    // whatever routines created it handled the friendship aspect.
    if (TagD && !Tag)
      return nullptr;
    return ActOnFriendTypeDecl(S, DS, TemplateParams);
  }

  const CXXScopeSpec &SS = DS.getTypeSpecScope();
  bool IsExplicitSpecialization =
    !TemplateParams.empty() && TemplateParams.back()->size() == 0;
  if (Tag && SS.isNotEmpty() && !Tag->isCompleteDefinition() &&
      !IsExplicitInstantiation && !IsExplicitSpecialization &&
      !isa<ClassTemplatePartialSpecializationDecl>(Tag)) {
    // Per C++ [dcl.type.elab]p1, a class declaration cannot have a
    // nested-name-specifier unless it is an explicit instantiation
    // or an explicit specialization.
    //
    // FIXME: We allow class template partial specializations here too, per the
    // obvious intent of DR1819.
    //
    // Per C++ [dcl.enum]p1, an opaque-enum-declaration can't either.
    Diag(SS.getBeginLoc(), diag::err_standalone_class_nested_name_specifier)
        << GetDiagnosticTypeSpecifierID(DS.getTypeSpecType()) << SS.getRange();
    return nullptr;
  }

  // Track whether this decl-specifier declares anything.
  bool DeclaresAnything = true;

  // Handle anonymous struct definitions.
  if (RecordDecl *Record = dyn_cast_or_null<RecordDecl>(Tag)) {
    if (!Record->getDeclName() && Record->isCompleteDefinition() &&
        DS.getStorageClassSpec() != DeclSpec::SCS_typedef) {
      if (getLangOpts().CPlusPlus ||
          Record->getDeclContext()->isRecord()) {
        // If CurContext is a DeclContext that can contain statements,
        // RecursiveASTVisitor won't visit the decls that
        // BuildAnonymousStructOrUnion() will put into CurContext.
        // Also store them here so that they can be part of the
        // DeclStmt that gets created in this case.
        // FIXME: Also return the IndirectFieldDecls created by
        // BuildAnonymousStructOr union, for the same reason?
        if (CurContext->isFunctionOrMethod())
          AnonRecord = Record;
        return BuildAnonymousStructOrUnion(S, DS, AS, Record,
                                           Context.getPrintingPolicy());
      }

      DeclaresAnything = false;
    }
  }

  // C11 6.7.2.1p2:
  //   A struct-declaration that does not declare an anonymous structure or
  //   anonymous union shall contain a struct-declarator-list.
  //
  // This rule also existed in C89 and C99; the grammar for struct-declaration
  // did not permit a struct-declaration without a struct-declarator-list.
  if (!getLangOpts().CPlusPlus && CurContext->isRecord() &&
      DS.getStorageClassSpec() == DeclSpec::SCS_unspecified) {
    // Check for Microsoft C extension: anonymous struct/union member.
    // Handle 2 kinds of anonymous struct/union:
    //   struct STRUCT;
    //   union UNION;
    // and
    //   STRUCT_TYPE;  <- where STRUCT_TYPE is a typedef struct.
    //   UNION_TYPE;   <- where UNION_TYPE is a typedef union.
    if ((Tag && Tag->getDeclName()) ||
        DS.getTypeSpecType() == DeclSpec::TST_typename) {
      RecordDecl *Record = nullptr;
      if (Tag)
        Record = dyn_cast<RecordDecl>(Tag);
      else if (const RecordType *RT =
                   DS.getRepAsType().get()->getAsStructureType())
        Record = RT->getDecl();
      else if (const RecordType *UT = DS.getRepAsType().get()->getAsUnionType())
        Record = UT->getDecl();

      if (Record && getLangOpts().MicrosoftExt) {
        Diag(DS.getBeginLoc(), diag::ext_ms_anonymous_record)
            << Record->isUnion() << DS.getSourceRange();
        return BuildMicrosoftCAnonymousStruct(S, DS, Record);
      }

      DeclaresAnything = false;
    }
  }

  // Skip all the checks below if we have a type error.
  if (DS.getTypeSpecType() == DeclSpec::TST_error ||
      (TagD && TagD->isInvalidDecl()))
    return TagD;

  if (getLangOpts().CPlusPlus &&
      DS.getStorageClassSpec() != DeclSpec::SCS_typedef)
    if (EnumDecl *Enum = dyn_cast_or_null<EnumDecl>(Tag))
      if (Enum->enumerator_begin() == Enum->enumerator_end() &&
          !Enum->getIdentifier() && !Enum->isInvalidDecl())
        DeclaresAnything = false;

  if (!DS.isMissingDeclaratorOk()) {
    // Customize diagnostic for a typedef missing a name.
    if (DS.getStorageClassSpec() == DeclSpec::SCS_typedef)
      Diag(DS.getBeginLoc(), diag::ext_typedef_without_a_name)
          << DS.getSourceRange();
    else
      DeclaresAnything = false;
  }

  if (DS.isModulePrivateSpecified() &&
      Tag && Tag->getDeclContext()->isFunctionOrMethod())
    Diag(DS.getModulePrivateSpecLoc(), diag::err_module_private_local_class)
      << Tag->getTagKind()
      << FixItHint::CreateRemoval(DS.getModulePrivateSpecLoc());

  ActOnDocumentableDecl(TagD);

  // C 6.7/2:
  //   A declaration [...] shall declare at least a declarator [...], a tag,
  //   or the members of an enumeration.
  // C++ [dcl.dcl]p3:
  //   [If there are no declarators], and except for the declaration of an
  //   unnamed bit-field, the decl-specifier-seq shall introduce one or more
  //   names into the program, or shall redeclare a name introduced by a
  //   previous declaration.
  if (!DeclaresAnything) {
    // In C, we allow this as a (popular) extension / bug. Don't bother
    // producing further diagnostics for redundant qualifiers after this.
    Diag(DS.getBeginLoc(), diag::ext_no_declarators) << DS.getSourceRange();
    return TagD;
  }

  // C++ [dcl.stc]p1:
  //   If a storage-class-specifier appears in a decl-specifier-seq, [...] the
  //   init-declarator-list of the declaration shall not be empty.
  // C++ [dcl.fct.spec]p1:
  //   If a cv-qualifier appears in a decl-specifier-seq, the
  //   init-declarator-list of the declaration shall not be empty.
  //
  // Spurious qualifiers here appear to be valid in C.
  unsigned DiagID = diag::warn_standalone_specifier;
  if (getLangOpts().CPlusPlus)
    DiagID = diag::ext_standalone_specifier;

  // Note that a linkage-specification sets a storage class, but
  // 'extern "C" struct foo;' is actually valid and not theoretically
  // useless.
  if (DeclSpec::SCS SCS = DS.getStorageClassSpec()) {
    if (SCS == DeclSpec::SCS_mutable)
      // Since mutable is not a viable storage class specifier in C, there is
      // no reason to treat it as an extension. Instead, diagnose as an error.
      Diag(DS.getStorageClassSpecLoc(), diag::err_mutable_nonmember);
    else if (!DS.isExternInLinkageSpec() && SCS != DeclSpec::SCS_typedef)
      Diag(DS.getStorageClassSpecLoc(), DiagID)
        << DeclSpec::getSpecifierName(SCS);
  }

  if (DeclSpec::TSCS TSCS = DS.getThreadStorageClassSpec())
    Diag(DS.getThreadStorageClassSpecLoc(), DiagID)
      << DeclSpec::getSpecifierName(TSCS);
  if (DS.getTypeQualifiers()) {
    if (DS.getTypeQualifiers() & DeclSpec::TQ_const)
      Diag(DS.getConstSpecLoc(), DiagID) << "const";
    if (DS.getTypeQualifiers() & DeclSpec::TQ_volatile)
      Diag(DS.getConstSpecLoc(), DiagID) << "volatile";
    // Restrict is covered above.
    if (DS.getTypeQualifiers() & DeclSpec::TQ_atomic)
      Diag(DS.getAtomicSpecLoc(), DiagID) << "_Atomic";
    if (DS.getTypeQualifiers() & DeclSpec::TQ_unaligned)
      Diag(DS.getUnalignedSpecLoc(), DiagID) << "__unaligned";
  }

  // Warn about ignored type attributes, for example:
  // __attribute__((aligned)) struct A;
  // Attributes should be placed after tag to apply to type declaration.
  if (!DS.getAttributes().empty()) {
    DeclSpec::TST TypeSpecType = DS.getTypeSpecType();
    if (TypeSpecType == DeclSpec::TST_class ||
        TypeSpecType == DeclSpec::TST_struct ||
        TypeSpecType == DeclSpec::TST_interface ||
        TypeSpecType == DeclSpec::TST_union ||
        TypeSpecType == DeclSpec::TST_enum) {
      for (const ParsedAttr &AL : DS.getAttributes())
        Diag(AL.getLoc(), diag::warn_declspec_attribute_ignored)
            << AL.getName() << GetDiagnosticTypeSpecifierID(TypeSpecType);
    }
  }

  return TagD;
}

/// We are trying to inject an anonymous member into the given scope;
/// check if there's an existing declaration that can't be overloaded.
///
/// \return true if this is a forbidden redeclaration
static bool CheckAnonMemberRedeclaration(Sema &SemaRef,
                                         Scope *S,
                                         DeclContext *Owner,
                                         DeclarationName Name,
                                         SourceLocation NameLoc,
                                         bool IsUnion) {
  LookupResult R(SemaRef, Name, NameLoc, Sema::LookupMemberName,
                 Sema::ForVisibleRedeclaration);
  if (!SemaRef.LookupName(R, S)) return false;

  // Pick a representative declaration.
  NamedDecl *PrevDecl = R.getRepresentativeDecl()->getUnderlyingDecl();
  assert(PrevDecl && "Expected a non-null Decl");

  if (!SemaRef.isDeclInScope(PrevDecl, Owner, S))
    return false;

  SemaRef.Diag(NameLoc, diag::err_anonymous_record_member_redecl)
    << IsUnion << Name;
  SemaRef.Diag(PrevDecl->getLocation(), diag::note_previous_declaration);

  return true;
}

/// InjectAnonymousStructOrUnionMembers - Inject the members of the
/// anonymous struct or union AnonRecord into the owning context Owner
/// and scope S. This routine will be invoked just after we realize
/// that an unnamed union or struct is actually an anonymous union or
/// struct, e.g.,
///
/// @code
/// union {
///   int i;
///   float f;
/// }; // InjectAnonymousStructOrUnionMembers called here to inject i and
///    // f into the surrounding scope.x
/// @endcode
///
/// This routine is recursive, injecting the names of nested anonymous
/// structs/unions into the owning context and scope as well.
static bool
InjectAnonymousStructOrUnionMembers(Sema &SemaRef, Scope *S, DeclContext *Owner,
                                    RecordDecl *AnonRecord, AccessSpecifier AS,
                                    SmallVectorImpl<NamedDecl *> &Chaining) {
  bool Invalid = false;

  // Look every FieldDecl and IndirectFieldDecl with a name.
  for (auto *D : AnonRecord->decls()) {
    if ((isa<FieldDecl>(D) || isa<IndirectFieldDecl>(D)) &&
        cast<NamedDecl>(D)->getDeclName()) {
      ValueDecl *VD = cast<ValueDecl>(D);
      if (CheckAnonMemberRedeclaration(SemaRef, S, Owner, VD->getDeclName(),
                                       VD->getLocation(),
                                       AnonRecord->isUnion())) {
        // C++ [class.union]p2:
        //   The names of the members of an anonymous union shall be
        //   distinct from the names of any other entity in the
        //   scope in which the anonymous union is declared.
        Invalid = true;
      } else {
        // C++ [class.union]p2:
        //   For the purpose of name lookup, after the anonymous union
        //   definition, the members of the anonymous union are
        //   considered to have been defined in the scope in which the
        //   anonymous union is declared.
        unsigned OldChainingSize = Chaining.size();
        if (IndirectFieldDecl *IF = dyn_cast<IndirectFieldDecl>(VD))
          Chaining.append(IF->chain_begin(), IF->chain_end());
        else
          Chaining.push_back(VD);

        assert(Chaining.size() >= 2);
        NamedDecl **NamedChain =
          new (SemaRef.Context)NamedDecl*[Chaining.size()];
        for (unsigned i = 0; i < Chaining.size(); i++)
          NamedChain[i] = Chaining[i];

        IndirectFieldDecl *IndirectField = IndirectFieldDecl::Create(
            SemaRef.Context, Owner, VD->getLocation(), VD->getIdentifier(),
            VD->getType(), {NamedChain, Chaining.size()});

        for (const auto *Attr : VD->attrs())
          IndirectField->addAttr(Attr->clone(SemaRef.Context));

        IndirectField->setAccess(AS);
        IndirectField->setImplicit();
        SemaRef.PushOnScopeChains(IndirectField, S);

        // That includes picking up the appropriate access specifier.
        if (AS != AS_none) IndirectField->setAccess(AS);

        Chaining.resize(OldChainingSize);
      }
    }
  }

  return Invalid;
}

/// StorageClassSpecToVarDeclStorageClass - Maps a DeclSpec::SCS to
/// a VarDecl::StorageClass. Any error reporting is up to the caller:
/// illegal input values are mapped to SC_None.
static StorageClass
StorageClassSpecToVarDeclStorageClass(const DeclSpec &DS) {
  DeclSpec::SCS StorageClassSpec = DS.getStorageClassSpec();
  assert(StorageClassSpec != DeclSpec::SCS_typedef &&
         "Parser allowed 'typedef' as storage class VarDecl.");
  switch (StorageClassSpec) {
  case DeclSpec::SCS_unspecified:    return SC_None;
  case DeclSpec::SCS_extern:
    if (DS.isExternInLinkageSpec())
      return SC_None;
    return SC_Extern;
  case DeclSpec::SCS_static:         return SC_Static;
  case DeclSpec::SCS_auto:           return SC_Auto;
  case DeclSpec::SCS_register:       return SC_Register;
  case DeclSpec::SCS_private_extern: return SC_PrivateExtern;
    // Illegal SCSs map to None: error reporting is up to the caller.
  case DeclSpec::SCS_mutable:        // Fall through.
  case DeclSpec::SCS_typedef:        return SC_None;
  }
  llvm_unreachable("unknown storage class specifier");
}

static SourceLocation findDefaultInitializer(const CXXRecordDecl *Record) {
  assert(Record->hasInClassInitializer());

  for (const auto *I : Record->decls()) {
    const auto *FD = dyn_cast<FieldDecl>(I);
    if (const auto *IFD = dyn_cast<IndirectFieldDecl>(I))
      FD = IFD->getAnonField();
    if (FD && FD->hasInClassInitializer())
      return FD->getLocation();
  }

  llvm_unreachable("couldn't find in-class initializer");
}

static void checkDuplicateDefaultInit(Sema &S, CXXRecordDecl *Parent,
                                      SourceLocation DefaultInitLoc) {
  if (!Parent->isUnion() || !Parent->hasInClassInitializer())
    return;

  S.Diag(DefaultInitLoc, diag::err_multiple_mem_union_initialization);
  S.Diag(findDefaultInitializer(Parent), diag::note_previous_initializer) << 0;
}

static void checkDuplicateDefaultInit(Sema &S, CXXRecordDecl *Parent,
                                      CXXRecordDecl *AnonUnion) {
  if (!Parent->isUnion() || !Parent->hasInClassInitializer())
    return;

  checkDuplicateDefaultInit(S, Parent, findDefaultInitializer(AnonUnion));
}

/// BuildAnonymousStructOrUnion - Handle the declaration of an
/// anonymous structure or union. Anonymous unions are a C++ feature
/// (C++ [class.union]) and a C11 feature; anonymous structures
/// are a C11 feature and GNU C++ extension.
Decl *Sema::BuildAnonymousStructOrUnion(Scope *S, DeclSpec &DS,
                                        AccessSpecifier AS,
                                        RecordDecl *Record,
                                        const PrintingPolicy &Policy) {
  DeclContext *Owner = Record->getDeclContext();

  // Diagnose whether this anonymous struct/union is an extension.
  if (Record->isUnion() && !getLangOpts().CPlusPlus && !getLangOpts().C11)
    Diag(Record->getLocation(), diag::ext_anonymous_union);
  else if (!Record->isUnion() && getLangOpts().CPlusPlus)
    Diag(Record->getLocation(), diag::ext_gnu_anonymous_struct);
  else if (!Record->isUnion() && !getLangOpts().C11)
    Diag(Record->getLocation(), diag::ext_c11_anonymous_struct);

  // C and C++ require different kinds of checks for anonymous
  // structs/unions.
  bool Invalid = false;
  if (getLangOpts().CPlusPlus) {
    const char *PrevSpec = nullptr;
    unsigned DiagID;
    if (Record->isUnion()) {
      // C++ [class.union]p6:
      // C++17 [class.union.anon]p2:
      //   Anonymous unions declared in a named namespace or in the
      //   global namespace shall be declared static.
      DeclContext *OwnerScope = Owner->getRedeclContext();
      if (DS.getStorageClassSpec() != DeclSpec::SCS_static &&
          (OwnerScope->isTranslationUnit() ||
           (OwnerScope->isNamespace() &&
            !cast<NamespaceDecl>(OwnerScope)->isAnonymousNamespace()))) {
        Diag(Record->getLocation(), diag::err_anonymous_union_not_static)
          << FixItHint::CreateInsertion(Record->getLocation(), "static ");

        // Recover by adding 'static'.
        DS.SetStorageClassSpec(*this, DeclSpec::SCS_static, SourceLocation(),
                               PrevSpec, DiagID, Policy);
      }
      // C++ [class.union]p6:
      //   A storage class is not allowed in a declaration of an
      //   anonymous union in a class scope.
      else if (DS.getStorageClassSpec() != DeclSpec::SCS_unspecified &&
               isa<RecordDecl>(Owner)) {
        Diag(DS.getStorageClassSpecLoc(),
             diag::err_anonymous_union_with_storage_spec)
          << FixItHint::CreateRemoval(DS.getStorageClassSpecLoc());

        // Recover by removing the storage specifier.
        DS.SetStorageClassSpec(*this, DeclSpec::SCS_unspecified,
                               SourceLocation(),
                               PrevSpec, DiagID, Context.getPrintingPolicy());
      }
    }

    // Ignore const/volatile/restrict qualifiers.
    if (DS.getTypeQualifiers()) {
      if (DS.getTypeQualifiers() & DeclSpec::TQ_const)
        Diag(DS.getConstSpecLoc(), diag::ext_anonymous_struct_union_qualified)
          << Record->isUnion() << "const"
          << FixItHint::CreateRemoval(DS.getConstSpecLoc());
      if (DS.getTypeQualifiers() & DeclSpec::TQ_volatile)
        Diag(DS.getVolatileSpecLoc(),
             diag::ext_anonymous_struct_union_qualified)
          << Record->isUnion() << "volatile"
          << FixItHint::CreateRemoval(DS.getVolatileSpecLoc());
      if (DS.getTypeQualifiers() & DeclSpec::TQ_restrict)
        Diag(DS.getRestrictSpecLoc(),
             diag::ext_anonymous_struct_union_qualified)
          << Record->isUnion() << "restrict"
          << FixItHint::CreateRemoval(DS.getRestrictSpecLoc());
      if (DS.getTypeQualifiers() & DeclSpec::TQ_atomic)
        Diag(DS.getAtomicSpecLoc(),
             diag::ext_anonymous_struct_union_qualified)
          << Record->isUnion() << "_Atomic"
          << FixItHint::CreateRemoval(DS.getAtomicSpecLoc());
      if (DS.getTypeQualifiers() & DeclSpec::TQ_unaligned)
        Diag(DS.getUnalignedSpecLoc(),
             diag::ext_anonymous_struct_union_qualified)
          << Record->isUnion() << "__unaligned"
          << FixItHint::CreateRemoval(DS.getUnalignedSpecLoc());

      DS.ClearTypeQualifiers();
    }

    // C++ [class.union]p2:
    //   The member-specification of an anonymous union shall only
    //   define non-static data members. [Note: nested types and
    //   functions cannot be declared within an anonymous union. ]
    for (auto *Mem : Record->decls()) {
      if (auto *FD = dyn_cast<FieldDecl>(Mem)) {
        // C++ [class.union]p3:
        //   An anonymous union shall not have private or protected
        //   members (clause 11).
        assert(FD->getAccess() != AS_none);
        if (FD->getAccess() != AS_public) {
          Diag(FD->getLocation(), diag::err_anonymous_record_nonpublic_member)
            << Record->isUnion() << (FD->getAccess() == AS_protected);
          Invalid = true;
        }

        // C++ [class.union]p1
        //   An object of a class with a non-trivial constructor, a non-trivial
        //   copy constructor, a non-trivial destructor, or a non-trivial copy
        //   assignment operator cannot be a member of a union, nor can an
        //   array of such objects.
        if (CheckNontrivialField(FD))
          Invalid = true;
      } else if (Mem->isImplicit()) {
        // Any implicit members are fine.
      } else if (isa<TagDecl>(Mem) && Mem->getDeclContext() != Record) {
        // This is a type that showed up in an
        // elaborated-type-specifier inside the anonymous struct or
        // union, but which actually declares a type outside of the
        // anonymous struct or union. It's okay.
      } else if (auto *MemRecord = dyn_cast<RecordDecl>(Mem)) {
        if (!MemRecord->isAnonymousStructOrUnion() &&
            MemRecord->getDeclName()) {
          // Visual C++ allows type definition in anonymous struct or union.
          if (getLangOpts().MicrosoftExt)
            Diag(MemRecord->getLocation(), diag::ext_anonymous_record_with_type)
              << Record->isUnion();
          else {
            // This is a nested type declaration.
            Diag(MemRecord->getLocation(), diag::err_anonymous_record_with_type)
              << Record->isUnion();
            Invalid = true;
          }
        } else {
          // This is an anonymous type definition within another anonymous type.
          // This is a popular extension, provided by Plan9, MSVC and GCC, but
          // not part of standard C++.
          Diag(MemRecord->getLocation(),
               diag::ext_anonymous_record_with_anonymous_type)
            << Record->isUnion();
        }
      } else if (isa<AccessSpecDecl>(Mem)) {
        // Any access specifier is fine.
      } else if (isa<StaticAssertDecl>(Mem)) {
        // In C++1z, static_assert declarations are also fine.
      } else {
        // We have something that isn't a non-static data
        // member. Complain about it.
        unsigned DK = diag::err_anonymous_record_bad_member;
        if (isa<TypeDecl>(Mem))
          DK = diag::err_anonymous_record_with_type;
        else if (isa<FunctionDecl>(Mem))
          DK = diag::err_anonymous_record_with_function;
        else if (isa<VarDecl>(Mem))
          DK = diag::err_anonymous_record_with_static;

        // Visual C++ allows type definition in anonymous struct or union.
        if (getLangOpts().MicrosoftExt &&
            DK == diag::err_anonymous_record_with_type)
          Diag(Mem->getLocation(), diag::ext_anonymous_record_with_type)
            << Record->isUnion();
        else {
          Diag(Mem->getLocation(), DK) << Record->isUnion();
          Invalid = true;
        }
      }
    }

    // C++11 [class.union]p8 (DR1460):
    //   At most one variant member of a union may have a
    //   brace-or-equal-initializer.
    if (cast<CXXRecordDecl>(Record)->hasInClassInitializer() &&
        Owner->isRecord())
      checkDuplicateDefaultInit(*this, cast<CXXRecordDecl>(Owner),
                                cast<CXXRecordDecl>(Record));
  }

  if (!Record->isUnion() && !Owner->isRecord()) {
    Diag(Record->getLocation(), diag::err_anonymous_struct_not_member)
      << getLangOpts().CPlusPlus;
    Invalid = true;
  }

  // Mock up a declarator.
  Declarator Dc(DS, DeclaratorContext::MemberContext);
  TypeSourceInfo *TInfo = GetTypeForDeclarator(Dc, S);
  assert(TInfo && "couldn't build declarator info for anonymous struct/union");

  // Create a declaration for this anonymous struct/union.
  NamedDecl *Anon = nullptr;
  if (RecordDecl *OwningClass = dyn_cast<RecordDecl>(Owner)) {
    Anon = FieldDecl::Create(
        Context, OwningClass, DS.getBeginLoc(), Record->getLocation(),
        /*IdentifierInfo=*/nullptr, Context.getTypeDeclType(Record), TInfo,
        /*BitWidth=*/nullptr, /*Mutable=*/false,
        /*InitStyle=*/ICIS_NoInit);
    Anon->setAccess(AS);
    if (getLangOpts().CPlusPlus)
      FieldCollector->Add(cast<FieldDecl>(Anon));
  } else {
    DeclSpec::SCS SCSpec = DS.getStorageClassSpec();
    StorageClass SC = StorageClassSpecToVarDeclStorageClass(DS);
    if (SCSpec == DeclSpec::SCS_mutable) {
      // mutable can only appear on non-static class members, so it's always
      // an error here
      Diag(Record->getLocation(), diag::err_mutable_nonmember);
      Invalid = true;
      SC = SC_None;
    }

    Anon = VarDecl::Create(Context, Owner, DS.getBeginLoc(),
                           Record->getLocation(), /*IdentifierInfo=*/nullptr,
                           Context.getTypeDeclType(Record), TInfo, SC);

    // Default-initialize the implicit variable. This initialization will be
    // trivial in almost all cases, except if a union member has an in-class
    // initializer:
    //   union { int n = 0; };
    ActOnUninitializedDecl(Anon);
  }
  Anon->setImplicit();

  // Mark this as an anonymous struct/union type.
  Record->setAnonymousStructOrUnion(true);

  // Add the anonymous struct/union object to the current
  // context. We'll be referencing this object when we refer to one of
  // its members.
  Owner->addDecl(Anon);

  // Inject the members of the anonymous struct/union into the owning
  // context and into the identifier resolver chain for name lookup
  // purposes.
  SmallVector<NamedDecl*, 2> Chain;
  Chain.push_back(Anon);

  if (InjectAnonymousStructOrUnionMembers(*this, S, Owner, Record, AS, Chain))
    Invalid = true;

  if (VarDecl *NewVD = dyn_cast<VarDecl>(Anon)) {
    if (getLangOpts().CPlusPlus && NewVD->isStaticLocal()) {
      Decl *ManglingContextDecl;
      if (MangleNumberingContext *MCtx = getCurrentMangleNumberContext(
              NewVD->getDeclContext(), ManglingContextDecl)) {
        Context.setManglingNumber(
            NewVD, MCtx->getManglingNumber(
                       NewVD, getMSManglingNumber(getLangOpts(), S)));
        Context.setStaticLocalNumber(NewVD, MCtx->getStaticLocalNumber(NewVD));
      }
    }
  }

  if (Invalid)
    Anon->setInvalidDecl();

  return Anon;
}

/// BuildMicrosoftCAnonymousStruct - Handle the declaration of an
/// Microsoft C anonymous structure.
/// Ref: http://msdn.microsoft.com/en-us/library/z2cx9y4f.aspx
/// Example:
///
/// struct A { int a; };
/// struct B { struct A; int b; };
///
/// void foo() {
///   B var;
///   var.a = 3;
/// }
///
Decl *Sema::BuildMicrosoftCAnonymousStruct(Scope *S, DeclSpec &DS,
                                           RecordDecl *Record) {
  assert(Record && "expected a record!");

  // Mock up a declarator.
  Declarator Dc(DS, DeclaratorContext::TypeNameContext);
  TypeSourceInfo *TInfo = GetTypeForDeclarator(Dc, S);
  assert(TInfo && "couldn't build declarator info for anonymous struct");

  auto *ParentDecl = cast<RecordDecl>(CurContext);
  QualType RecTy = Context.getTypeDeclType(Record);

  // Create a declaration for this anonymous struct.
  NamedDecl *Anon =
      FieldDecl::Create(Context, ParentDecl, DS.getBeginLoc(), DS.getBeginLoc(),
                        /*IdentifierInfo=*/nullptr, RecTy, TInfo,
                        /*BitWidth=*/nullptr, /*Mutable=*/false,
                        /*InitStyle=*/ICIS_NoInit);
  Anon->setImplicit();

  // Add the anonymous struct object to the current context.
  CurContext->addDecl(Anon);

  // Inject the members of the anonymous struct into the current
  // context and into the identifier resolver chain for name lookup
  // purposes.
  SmallVector<NamedDecl*, 2> Chain;
  Chain.push_back(Anon);

  RecordDecl *RecordDef = Record->getDefinition();
  if (RequireCompleteType(Anon->getLocation(), RecTy,
                          diag::err_field_incomplete) ||
      InjectAnonymousStructOrUnionMembers(*this, S, CurContext, RecordDef,
                                          AS_none, Chain)) {
    Anon->setInvalidDecl();
    ParentDecl->setInvalidDecl();
  }

  return Anon;
}

/// GetNameForDeclarator - Determine the full declaration name for the
/// given Declarator.
DeclarationNameInfo Sema::GetNameForDeclarator(Declarator &D) {
  return GetNameFromUnqualifiedId(D.getName());
}

/// Retrieves the declaration name from a parsed unqualified-id.
DeclarationNameInfo
Sema::GetNameFromUnqualifiedId(const UnqualifiedId &Name) {
  DeclarationNameInfo NameInfo;
  NameInfo.setLoc(Name.StartLocation);

  switch (Name.getKind()) {

  case UnqualifiedIdKind::IK_ImplicitSelfParam:
  case UnqualifiedIdKind::IK_Identifier:
    NameInfo.setName(Name.Identifier);
    return NameInfo;

  case UnqualifiedIdKind::IK_DeductionGuideName: {
    // C++ [temp.deduct.guide]p3:
    //   The simple-template-id shall name a class template specialization.
    //   The template-name shall be the same identifier as the template-name
    //   of the simple-template-id.
    // These together intend to imply that the template-name shall name a
    // class template.
    // FIXME: template<typename T> struct X {};
    //        template<typename T> using Y = X<T>;
    //        Y(int) -> Y<int>;
    //   satisfies these rules but does not name a class template.
    TemplateName TN = Name.TemplateName.get().get();
    auto *Template = TN.getAsTemplateDecl();
    if (!Template || !isa<ClassTemplateDecl>(Template)) {
      Diag(Name.StartLocation,
           diag::err_deduction_guide_name_not_class_template)
        << (int)getTemplateNameKindForDiagnostics(TN) << TN;
      if (Template)
        Diag(Template->getLocation(), diag::note_template_decl_here);
      return DeclarationNameInfo();
    }

    NameInfo.setName(
        Context.DeclarationNames.getCXXDeductionGuideName(Template));
    return NameInfo;
  }

  case UnqualifiedIdKind::IK_OperatorFunctionId:
    NameInfo.setName(Context.DeclarationNames.getCXXOperatorName(
                                           Name.OperatorFunctionId.Operator));
    NameInfo.getInfo().CXXOperatorName.BeginOpNameLoc
      = Name.OperatorFunctionId.SymbolLocations[0];
    NameInfo.getInfo().CXXOperatorName.EndOpNameLoc
      = Name.EndLocation.getRawEncoding();
    return NameInfo;

  case UnqualifiedIdKind::IK_LiteralOperatorId:
    NameInfo.setName(Context.DeclarationNames.getCXXLiteralOperatorName(
                                                           Name.Identifier));
    NameInfo.setCXXLiteralOperatorNameLoc(Name.EndLocation);
    return NameInfo;

  case UnqualifiedIdKind::IK_ConversionFunctionId: {
    TypeSourceInfo *TInfo;
    QualType Ty = GetTypeFromParser(Name.ConversionFunctionId, &TInfo);
    if (Ty.isNull())
      return DeclarationNameInfo();
    NameInfo.setName(Context.DeclarationNames.getCXXConversionFunctionName(
                                               Context.getCanonicalType(Ty)));
    NameInfo.setNamedTypeInfo(TInfo);
    return NameInfo;
  }

  case UnqualifiedIdKind::IK_ConstructorName: {
    TypeSourceInfo *TInfo;
    QualType Ty = GetTypeFromParser(Name.ConstructorName, &TInfo);
    if (Ty.isNull())
      return DeclarationNameInfo();
    NameInfo.setName(Context.DeclarationNames.getCXXConstructorName(
                                              Context.getCanonicalType(Ty)));
    NameInfo.setNamedTypeInfo(TInfo);
    return NameInfo;
  }

  case UnqualifiedIdKind::IK_ConstructorTemplateId: {
    // In well-formed code, we can only have a constructor
    // template-id that refers to the current context, so go there
    // to find the actual type being constructed.
    CXXRecordDecl *CurClass = dyn_cast<CXXRecordDecl>(CurContext);
    if (!CurClass || CurClass->getIdentifier() != Name.TemplateId->Name)
      return DeclarationNameInfo();

    // Determine the type of the class being constructed.
    QualType CurClassType = Context.getTypeDeclType(CurClass);

    // FIXME: Check two things: that the template-id names the same type as
    // CurClassType, and that the template-id does not occur when the name
    // was qualified.

    NameInfo.setName(Context.DeclarationNames.getCXXConstructorName(
                                    Context.getCanonicalType(CurClassType)));
    // FIXME: should we retrieve TypeSourceInfo?
    NameInfo.setNamedTypeInfo(nullptr);
    return NameInfo;
  }

  case UnqualifiedIdKind::IK_DestructorName: {
    TypeSourceInfo *TInfo;
    QualType Ty = GetTypeFromParser(Name.DestructorName, &TInfo);
    if (Ty.isNull())
      return DeclarationNameInfo();
    NameInfo.setName(Context.DeclarationNames.getCXXDestructorName(
                                              Context.getCanonicalType(Ty)));
    NameInfo.setNamedTypeInfo(TInfo);
    return NameInfo;
  }

  case UnqualifiedIdKind::IK_TemplateId: {
    TemplateName TName = Name.TemplateId->Template.get();
    SourceLocation TNameLoc = Name.TemplateId->TemplateNameLoc;
    return Context.getNameForTemplate(TName, TNameLoc);
  }

  } // switch (Name.getKind())

  llvm_unreachable("Unknown name kind");
}

static QualType getCoreType(QualType Ty) {
  do {
    if (Ty->isPointerType() || Ty->isReferenceType())
      Ty = Ty->getPointeeType();
    else if (Ty->isArrayType())
      Ty = Ty->castAsArrayTypeUnsafe()->getElementType();
    else
      return Ty.withoutLocalFastQualifiers();
  } while (true);
}

/// hasSimilarParameters - Determine whether the C++ functions Declaration
/// and Definition have "nearly" matching parameters. This heuristic is
/// used to improve diagnostics in the case where an out-of-line function
/// definition doesn't match any declaration within the class or namespace.
/// Also sets Params to the list of indices to the parameters that differ
/// between the declaration and the definition. If hasSimilarParameters
/// returns true and Params is empty, then all of the parameters match.
static bool hasSimilarParameters(ASTContext &Context,
                                     FunctionDecl *Declaration,
                                     FunctionDecl *Definition,
                                     SmallVectorImpl<unsigned> &Params) {
  Params.clear();
  if (Declaration->param_size() != Definition->param_size())
    return false;
  for (unsigned Idx = 0; Idx < Declaration->param_size(); ++Idx) {
    QualType DeclParamTy = Declaration->getParamDecl(Idx)->getType();
    QualType DefParamTy = Definition->getParamDecl(Idx)->getType();

    // The parameter types are identical
    if (Context.hasSameType(DefParamTy, DeclParamTy))
      continue;

    QualType DeclParamBaseTy = getCoreType(DeclParamTy);
    QualType DefParamBaseTy = getCoreType(DefParamTy);
    const IdentifierInfo *DeclTyName = DeclParamBaseTy.getBaseTypeIdentifier();
    const IdentifierInfo *DefTyName = DefParamBaseTy.getBaseTypeIdentifier();

    if (Context.hasSameUnqualifiedType(DeclParamBaseTy, DefParamBaseTy) ||
        (DeclTyName && DeclTyName == DefTyName))
      Params.push_back(Idx);
    else  // The two parameters aren't even close
      return false;
  }

  return true;
}

/// NeedsRebuildingInCurrentInstantiation - Checks whether the given
/// declarator needs to be rebuilt in the current instantiation.
/// Any bits of declarator which appear before the name are valid for
/// consideration here.  That's specifically the type in the decl spec
/// and the base type in any member-pointer chunks.
static bool RebuildDeclaratorInCurrentInstantiation(Sema &S, Declarator &D,
                                                    DeclarationName Name) {
  // The types we specifically need to rebuild are:
  //   - typenames, typeofs, and decltypes
  //   - types which will become injected class names
  // Of course, we also need to rebuild any type referencing such a
  // type.  It's safest to just say "dependent", but we call out a
  // few cases here.

  DeclSpec &DS = D.getMutableDeclSpec();
  switch (DS.getTypeSpecType()) {
  case DeclSpec::TST_typename:
  case DeclSpec::TST_typeofType:
  case DeclSpec::TST_underlyingType:
  case DeclSpec::TST_atomic: {
    // Grab the type from the parser.
    TypeSourceInfo *TSI = nullptr;
    QualType T = S.GetTypeFromParser(DS.getRepAsType(), &TSI);
    if (T.isNull() || !T->isDependentType()) break;

    // Make sure there's a type source info.  This isn't really much
    // of a waste; most dependent types should have type source info
    // attached already.
    if (!TSI)
      TSI = S.Context.getTrivialTypeSourceInfo(T, DS.getTypeSpecTypeLoc());

    // Rebuild the type in the current instantiation.
    TSI = S.RebuildTypeInCurrentInstantiation(TSI, D.getIdentifierLoc(), Name);
    if (!TSI) return true;

    // Store the new type back in the decl spec.
    ParsedType LocType = S.CreateParsedType(TSI->getType(), TSI);
    DS.UpdateTypeRep(LocType);
    break;
  }

  case DeclSpec::TST_decltype:
  case DeclSpec::TST_typeofExpr: {
    Expr *E = DS.getRepAsExpr();
    ExprResult Result = S.RebuildExprInCurrentInstantiation(E);
    if (Result.isInvalid()) return true;
    DS.UpdateExprRep(Result.get());
    break;
  }

  default:
    // Nothing to do for these decl specs.
    break;
  }

  // It doesn't matter what order we do this in.
  for (unsigned I = 0, E = D.getNumTypeObjects(); I != E; ++I) {
    DeclaratorChunk &Chunk = D.getTypeObject(I);

    // The only type information in the declarator which can come
    // before the declaration name is the base type of a member
    // pointer.
    if (Chunk.Kind != DeclaratorChunk::MemberPointer)
      continue;

    // Rebuild the scope specifier in-place.
    CXXScopeSpec &SS = Chunk.Mem.Scope();
    if (S.RebuildNestedNameSpecifierInCurrentInstantiation(SS))
      return true;
  }

  return false;
}

Decl *Sema::ActOnDeclarator(Scope *S, Declarator &D) {
  D.setFunctionDefinitionKind(FDK_Declaration);
  Decl *Dcl = HandleDeclarator(S, D, MultiTemplateParamsArg());

  if (OriginalLexicalContext && OriginalLexicalContext->isObjCContainer() &&
      Dcl && Dcl->getDeclContext()->isFileContext())
    Dcl->setTopLevelDeclInObjCContainer();

  if (getLangOpts().OpenCL)
    setCurrentOpenCLExtensionForDecl(Dcl);

  return Dcl;
}

/// DiagnoseClassNameShadow - Implement C++ [class.mem]p13:
///   If T is the name of a class, then each of the following shall have a
///   name different from T:
///     - every static data member of class T;
///     - every member function of class T
///     - every member of class T that is itself a type;
/// \returns true if the declaration name violates these rules.
bool Sema::DiagnoseClassNameShadow(DeclContext *DC,
                                   DeclarationNameInfo NameInfo) {
  DeclarationName Name = NameInfo.getName();

  CXXRecordDecl *Record = dyn_cast<CXXRecordDecl>(DC);
  while (Record && Record->isAnonymousStructOrUnion())
    Record = dyn_cast<CXXRecordDecl>(Record->getParent());
  if (Record && Record->getIdentifier() && Record->getDeclName() == Name) {
    Diag(NameInfo.getLoc(), diag::err_member_name_of_class) << Name;
    return true;
  }

  return false;
}

/// Diagnose a declaration whose declarator-id has the given
/// nested-name-specifier.
///
/// \param SS The nested-name-specifier of the declarator-id.
///
/// \param DC The declaration context to which the nested-name-specifier
/// resolves.
///
/// \param Name The name of the entity being declared.
///
/// \param Loc The location of the name of the entity being declared.
///
/// \param IsTemplateId Whether the name is a (simple-)template-id, and thus
/// we're declaring an explicit / partial specialization / instantiation.
///
/// \returns true if we cannot safely recover from this error, false otherwise.
bool Sema::diagnoseQualifiedDeclaration(CXXScopeSpec &SS, DeclContext *DC,
                                        DeclarationName Name,
                                        SourceLocation Loc, bool IsTemplateId) {
  DeclContext *Cur = CurContext;
  while (isa<LinkageSpecDecl>(Cur) || isa<CapturedDecl>(Cur))
    Cur = Cur->getParent();

  // If the user provided a superfluous scope specifier that refers back to the
  // class in which the entity is already declared, diagnose and ignore it.
  //
  // class X {
  //   void X::f();
  // };
  //
  // Note, it was once ill-formed to give redundant qualification in all
  // contexts, but that rule was removed by DR482.
  if (Cur->Equals(DC)) {
    if (Cur->isRecord()) {
      Diag(Loc, LangOpts.MicrosoftExt ? diag::warn_member_extra_qualification
                                      : diag::err_member_extra_qualification)
        << Name << FixItHint::CreateRemoval(SS.getRange());
      SS.clear();
    } else {
      Diag(Loc, diag::warn_namespace_member_extra_qualification) << Name;
    }
    return false;
  }

  // Check whether the qualifying scope encloses the scope of the original
  // declaration. For a template-id, we perform the checks in
  // CheckTemplateSpecializationScope.
  if (!Cur->Encloses(DC) && !IsTemplateId) {
    if (Cur->isRecord())
      Diag(Loc, diag::err_member_qualification)
        << Name << SS.getRange();
    else if (isa<TranslationUnitDecl>(DC))
      Diag(Loc, diag::err_invalid_declarator_global_scope)
        << Name << SS.getRange();
    else if (isa<FunctionDecl>(Cur))
      Diag(Loc, diag::err_invalid_declarator_in_function)
        << Name << SS.getRange();
    else if (isa<BlockDecl>(Cur))
      Diag(Loc, diag::err_invalid_declarator_in_block)
        << Name << SS.getRange();
    else
      Diag(Loc, diag::err_invalid_declarator_scope)
      << Name << cast<NamedDecl>(Cur) << cast<NamedDecl>(DC) << SS.getRange();

    return true;
  }

  if (Cur->isRecord()) {
    // Cannot qualify members within a class.
    Diag(Loc, diag::err_member_qualification)
      << Name << SS.getRange();
    SS.clear();

    // C++ constructors and destructors with incorrect scopes can break
    // our AST invariants by having the wrong underlying types. If
    // that's the case, then drop this declaration entirely.
    if ((Name.getNameKind() == DeclarationName::CXXConstructorName ||
         Name.getNameKind() == DeclarationName::CXXDestructorName) &&
        !Context.hasSameType(Name.getCXXNameType(),
                             Context.getTypeDeclType(cast<CXXRecordDecl>(Cur))))
      return true;

    return false;
  }

  // C++11 [dcl.meaning]p1:
  //   [...] "The nested-name-specifier of the qualified declarator-id shall
  //   not begin with a decltype-specifer"
  NestedNameSpecifierLoc SpecLoc(SS.getScopeRep(), SS.location_data());
  while (SpecLoc.getPrefix())
    SpecLoc = SpecLoc.getPrefix();
  if (dyn_cast_or_null<DecltypeType>(
        SpecLoc.getNestedNameSpecifier()->getAsType()))
    Diag(Loc, diag::err_decltype_in_declarator)
      << SpecLoc.getTypeLoc().getSourceRange();

  return false;
}

NamedDecl *Sema::HandleDeclarator(Scope *S, Declarator &D,
                                  MultiTemplateParamsArg TemplateParamLists) {
  // TODO: consider using NameInfo for diagnostic.
  DeclarationNameInfo NameInfo = GetNameForDeclarator(D);
  DeclarationName Name = NameInfo.getName();

  // All of these full declarators require an identifier.  If it doesn't have
  // one, the ParsedFreeStandingDeclSpec action should be used.
  if (D.isDecompositionDeclarator()) {
    return ActOnDecompositionDeclarator(S, D, TemplateParamLists);
  } else if (!Name) {
    if (!D.isInvalidType())  // Reject this if we think it is valid.
      Diag(D.getDeclSpec().getBeginLoc(), diag::err_declarator_need_ident)
          << D.getDeclSpec().getSourceRange() << D.getSourceRange();
    return nullptr;
  } else if (DiagnoseUnexpandedParameterPack(NameInfo, UPPC_DeclarationType))
    return nullptr;

  // The scope passed in may not be a decl scope.  Zip up the scope tree until
  // we find one that is.
  while ((S->getFlags() & Scope::DeclScope) == 0 ||
         (S->getFlags() & Scope::TemplateParamScope) != 0)
    S = S->getParent();

  DeclContext *DC = CurContext;
  if (D.getCXXScopeSpec().isInvalid())
    D.setInvalidType();
  else if (D.getCXXScopeSpec().isSet()) {
    if (DiagnoseUnexpandedParameterPack(D.getCXXScopeSpec(),
                                        UPPC_DeclarationQualifier))
      return nullptr;

    bool EnteringContext = !D.getDeclSpec().isFriendSpecified();
    DC = computeDeclContext(D.getCXXScopeSpec(), EnteringContext);
    if (!DC || isa<EnumDecl>(DC)) {
      // If we could not compute the declaration context, it's because the
      // declaration context is dependent but does not refer to a class,
      // class template, or class template partial specialization. Complain
      // and return early, to avoid the coming semantic disaster.
      Diag(D.getIdentifierLoc(),
           diag::err_template_qualified_declarator_no_match)
        << D.getCXXScopeSpec().getScopeRep()
        << D.getCXXScopeSpec().getRange();
      return nullptr;
    }
    bool IsDependentContext = DC->isDependentContext();

    if (!IsDependentContext &&
        RequireCompleteDeclContext(D.getCXXScopeSpec(), DC))
      return nullptr;

    // If a class is incomplete, do not parse entities inside it.
    if (isa<CXXRecordDecl>(DC) && !cast<CXXRecordDecl>(DC)->hasDefinition()) {
      Diag(D.getIdentifierLoc(),
           diag::err_member_def_undefined_record)
        << Name << DC << D.getCXXScopeSpec().getRange();
      return nullptr;
    }
    if (!D.getDeclSpec().isFriendSpecified()) {
      if (diagnoseQualifiedDeclaration(
              D.getCXXScopeSpec(), DC, Name, D.getIdentifierLoc(),
              D.getName().getKind() == UnqualifiedIdKind::IK_TemplateId)) {
        if (DC->isRecord())
          return nullptr;

        D.setInvalidType();
      }
    }

    // Check whether we need to rebuild the type of the given
    // declaration in the current instantiation.
    if (EnteringContext && IsDependentContext &&
        TemplateParamLists.size() != 0) {
      ContextRAII SavedContext(*this, DC);
      if (RebuildDeclaratorInCurrentInstantiation(*this, D, Name))
        D.setInvalidType();
    }
  }

  TypeSourceInfo *TInfo = GetTypeForDeclarator(D, S);
  QualType R = TInfo->getType();

  if (DiagnoseUnexpandedParameterPack(D.getIdentifierLoc(), TInfo,
                                      UPPC_DeclarationType))
    D.setInvalidType();

  LookupResult Previous(*this, NameInfo, LookupOrdinaryName,
                        forRedeclarationInCurContext());

  // See if this is a redefinition of a variable in the same scope.
  if (!D.getCXXScopeSpec().isSet()) {
    bool IsLinkageLookup = false;
    bool CreateBuiltins = false;

    // If the declaration we're planning to build will be a function
    // or object with linkage, then look for another declaration with
    // linkage (C99 6.2.2p4-5 and C++ [basic.link]p6).
    //
    // If the declaration we're planning to build will be declared with
    // external linkage in the translation unit, create any builtin with
    // the same name.
    if (D.getDeclSpec().getStorageClassSpec() == DeclSpec::SCS_typedef)
      /* Do nothing*/;
    else if (CurContext->isFunctionOrMethod() &&
             (D.getDeclSpec().getStorageClassSpec() == DeclSpec::SCS_extern ||
              R->isFunctionType())) {
      IsLinkageLookup = true;
      CreateBuiltins =
          CurContext->getEnclosingNamespaceContext()->isTranslationUnit();
    } else if (CurContext->getRedeclContext()->isTranslationUnit() &&
               D.getDeclSpec().getStorageClassSpec() != DeclSpec::SCS_static)
      CreateBuiltins = true;

    if (IsLinkageLookup) {
      Previous.clear(LookupRedeclarationWithLinkage);
      Previous.setRedeclarationKind(ForExternalRedeclaration);
    }

    LookupName(Previous, S, CreateBuiltins);
  } else { // Something like "int foo::x;"
    LookupQualifiedName(Previous, DC);

    // C++ [dcl.meaning]p1:
    //   When the declarator-id is qualified, the declaration shall refer to a
    //  previously declared member of the class or namespace to which the
    //  qualifier refers (or, in the case of a namespace, of an element of the
    //  inline namespace set of that namespace (7.3.1)) or to a specialization
    //  thereof; [...]
    //
    // Note that we already checked the context above, and that we do not have
    // enough information to make sure that Previous contains the declaration
    // we want to match. For example, given:
    //
    //   class X {
    //     void f();
    //     void f(float);
    //   };
    //
    //   void X::f(int) { } // ill-formed
    //
    // In this case, Previous will point to the overload set
    // containing the two f's declared in X, but neither of them
    // matches.

    // C++ [dcl.meaning]p1:
    //   [...] the member shall not merely have been introduced by a
    //   using-declaration in the scope of the class or namespace nominated by
    //   the nested-name-specifier of the declarator-id.
    RemoveUsingDecls(Previous);
  }

  if (Previous.isSingleResult() &&
      Previous.getFoundDecl()->isTemplateParameter()) {
    // Maybe we will complain about the shadowed template parameter.
    if (!D.isInvalidType())
      DiagnoseTemplateParameterShadow(D.getIdentifierLoc(),
                                      Previous.getFoundDecl());

    // Just pretend that we didn't see the previous declaration.
    Previous.clear();
  }

  if (!R->isFunctionType() && DiagnoseClassNameShadow(DC, NameInfo))
    // Forget that the previous declaration is the injected-class-name.
    Previous.clear();

  // In C++, the previous declaration we find might be a tag type
  // (class or enum). In this case, the new declaration will hide the
  // tag type. Note that this applies to functions, function templates, and
  // variables, but not to typedefs (C++ [dcl.typedef]p4) or variable templates.
  if (Previous.isSingleTagDecl() &&
      D.getDeclSpec().getStorageClassSpec() != DeclSpec::SCS_typedef &&
      (TemplateParamLists.size() == 0 || R->isFunctionType()))
    Previous.clear();

  // Check that there are no default arguments other than in the parameters
  // of a function declaration (C++ only).
  if (getLangOpts().CPlusPlus)
    CheckExtraCXXDefaultArguments(D);

  NamedDecl *New;

  bool AddToScope = true;
  if (D.getDeclSpec().getStorageClassSpec() == DeclSpec::SCS_typedef) {
    if (TemplateParamLists.size()) {
      Diag(D.getIdentifierLoc(), diag::err_template_typedef);
      return nullptr;
    }

    New = ActOnTypedefDeclarator(S, D, DC, TInfo, Previous);
  } else if (R->isFunctionType()) {
    New = ActOnFunctionDeclarator(S, D, DC, TInfo, Previous,
                                  TemplateParamLists,
                                  AddToScope);
  } else {
    New = ActOnVariableDeclarator(S, D, DC, TInfo, Previous, TemplateParamLists,
                                  AddToScope);
  }

  if (!New)
    return