SemaCXXScopeSpec.cpp

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//===--- SemaCXXScopeSpec.cpp - Semantic Analysis for C++ scope specifiers-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file implements C++ semantic analysis for scope specifiers.
//
//===----------------------------------------------------------------------===//
 
#include "TypeLocBuilder.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/DeclTemplate.h"
#include "clang/AST/ExprCXX.h"
#include "clang/AST/NestedNameSpecifier.h"
#include "clang/Basic/PartialDiagnostic.h"
#include "clang/Sema/DeclSpec.h"
#include "clang/Sema/Lookup.h"
#include "clang/Sema/Template.h"
#include "llvm/ADT/STLExtras.h"
using namespace clang;
 
/// Find the current instantiation that associated with the given type.
static CXXRecordDecl *getCurrentInstantiationOf(QualType T,
                                                DeclContext *CurContext) {
  if (T.isNull())
    return nullptr;
 
  const TagType *TagTy = dyn_cast<TagType>(T->getCanonicalTypeInternal());
  if (!isa_and_present<RecordType, InjectedClassNameType>(TagTy))
    return nullptr;
  auto *RD =
      cast<CXXRecordDecl>(TagTy->getOriginalDecl())->getDefinitionOrSelf();
  if (isa<InjectedClassNameType>(TagTy) ||
      RD->isCurrentInstantiation(CurContext))
    return RD;
  return nullptr;
}
 
DeclContext *Sema::computeDeclContext(QualType T) {
  if (!T->isDependentType())
    if (auto *D = T->getAsTagDecl())
      return D;
  return ::getCurrentInstantiationOf(T, CurContext);
}
 
DeclContext *Sema::computeDeclContext(const CXXScopeSpec &SS,
                                      bool EnteringContext) {
  if (!SS.isSet() || SS.isInvalid())
    return nullptr;
 
  NestedNameSpecifier NNS = SS.getScopeRep();
  if (NNS.isDependent()) {
    // If this nested-name-specifier refers to the current
    // instantiation, return its DeclContext.
    if (CXXRecordDecl *Record = getCurrentInstantiationOf(NNS))
      return Record;
 
    if (EnteringContext) {
      if (NNS.getKind() != NestedNameSpecifier::Kind::Type)
        return nullptr;
      const Type *NNSType = NNS.getAsType();
 
      // Look through type alias templates, per C++0x [temp.dep.type]p1.
      NNSType = Context.getCanonicalType(NNSType);
      if (const auto *SpecType =
              dyn_cast<TemplateSpecializationType>(NNSType)) {
        // We are entering the context of the nested name specifier, so try to
        // match the nested name specifier to either a primary class template
        // or a class template partial specialization.
        if (ClassTemplateDecl *ClassTemplate =
                dyn_cast_or_null<ClassTemplateDecl>(
                    SpecType->getTemplateName().getAsTemplateDecl())) {
          // FIXME: The fallback on the search of partial
          // specialization using ContextType should be eventually removed since
          // it doesn't handle the case of constrained template parameters
          // correctly. Currently removing this fallback would change the
          // diagnostic output for invalid code in a number of tests.
          ClassTemplatePartialSpecializationDecl *PartialSpec = nullptr;
          ArrayRef<TemplateParameterList *> TemplateParamLists =
              SS.getTemplateParamLists();
          if (!TemplateParamLists.empty()) {
            unsigned Depth = ClassTemplate->getTemplateParameters()->getDepth();
            auto L = find_if(TemplateParamLists,
                             [Depth](TemplateParameterList *TPL) {
                               return TPL->getDepth() == Depth;
                             });
            if (L != TemplateParamLists.end()) {
              void *Pos = nullptr;
              PartialSpec = ClassTemplate->findPartialSpecialization(
                  SpecType->template_arguments(), *L, Pos);
            }
          } else {
            PartialSpec =
                ClassTemplate->findPartialSpecialization(QualType(SpecType, 0));
          }
 
          if (PartialSpec) {
            // A declaration of the partial specialization must be visible.
            // We can always recover here, because this only happens when we're
            // entering the context, and that can't happen in a SFINAE context.
            assert(!isSFINAEContext() && "partial specialization scope "
                                         "specifier in SFINAE context?");
            if (PartialSpec->hasDefinition() &&
                !hasReachableDefinition(PartialSpec))
              diagnoseMissingImport(SS.getLastQualifierNameLoc(), PartialSpec,
                                    MissingImportKind::PartialSpecialization,
                                    true);
            return PartialSpec;
          }
 
          // If the type of the nested name specifier is the same as the
          // injected class name of the named class template, we're entering
          // into that class template definition.
          CanQualType Injected =
              ClassTemplate->getCanonicalInjectedSpecializationType(Context);
          if (Context.hasSameType(Injected, QualType(SpecType, 0)))
            return ClassTemplate->getTemplatedDecl();
        }
      } else if (const auto *RecordT = dyn_cast<RecordType>(NNSType)) {
        // The nested name specifier refers to a member of a class template.
        return RecordT->getOriginalDecl()->getDefinitionOrSelf();
      }
    }
 
    return nullptr;
  }
 
  switch (NNS.getKind()) {
  case NestedNameSpecifier::Kind::Namespace:
    return const_cast<NamespaceDecl *>(
        NNS.getAsNamespaceAndPrefix().Namespace->getNamespace());
 
  case NestedNameSpecifier::Kind::Type:
    return NNS.getAsType()->castAsTagDecl();
 
  case NestedNameSpecifier::Kind::Global:
    return Context.getTranslationUnitDecl();
 
  case NestedNameSpecifier::Kind::MicrosoftSuper:
    return NNS.getAsMicrosoftSuper();
 
  case NestedNameSpecifier::Kind::Null:
    llvm_unreachable("unexpected null nested name specifier");
  }
 
  llvm_unreachable("Invalid NestedNameSpecifier::Kind!");
}
 
bool Sema::isDependentScopeSpecifier(const CXXScopeSpec &SS) {
  if (!SS.isSet() || SS.isInvalid())
    return false;
 
  return SS.getScopeRep().isDependent();
}
 
CXXRecordDecl *Sema::getCurrentInstantiationOf(NestedNameSpecifier NNS) {
  assert(getLangOpts().CPlusPlus && "Only callable in C++");
  assert(NNS.isDependent() && "Only dependent nested-name-specifier allowed");
 
  if (NNS.getKind() != NestedNameSpecifier::Kind::Type)
    return nullptr;
 
  QualType T = QualType(NNS.getAsType(), 0);
  return ::getCurrentInstantiationOf(T, CurContext);
}
 
/// Require that the context specified by SS be complete.
///
/// If SS refers to a type, this routine checks whether the type is
/// complete enough (or can be made complete enough) for name lookup
/// into the DeclContext. A type that is not yet completed can be
/// considered "complete enough" if it is a class/struct/union/enum
/// that is currently being defined. Or, if we have a type that names
/// a class template specialization that is not a complete type, we
/// will attempt to instantiate that class template.
bool Sema::RequireCompleteDeclContext(CXXScopeSpec &SS,
                                      DeclContext *DC) {
  assert(DC && "given null context");
 
  TagDecl *tag = dyn_cast<TagDecl>(DC);
 
  // If this is a dependent type, then we consider it complete.
  // FIXME: This is wrong; we should require a (visible) definition to
  // exist in this case too.
  if (!tag || tag->isDependentContext())
    return false;
 
  // Grab the tag definition, if there is one.
  tag = tag->getDefinitionOrSelf();
 
  // If we're currently defining this type, then lookup into the
  // type is okay: don't complain that it isn't complete yet.
  if (tag->isBeingDefined())
    return false;
 
  SourceLocation loc = SS.getLastQualifierNameLoc();
  if (loc.isInvalid()) loc = SS.getRange().getBegin();
 
  // The type must be complete.
  if (RequireCompleteType(loc, Context.getCanonicalTagType(tag),
                          diag::err_incomplete_nested_name_spec,
                          SS.getRange())) {
    SS.SetInvalid(SS.getRange());
    return true;
  }
 
  if (auto *EnumD = dyn_cast<EnumDecl>(tag))
    // Fixed enum types and scoped enum instantiations are complete, but they
    // aren't valid as scopes until we see or instantiate their definition.
    return RequireCompleteEnumDecl(EnumD, loc, &SS);
 
  return false;
}
 
/// Require that the EnumDecl is completed with its enumerators defined or
/// instantiated. SS, if provided, is the ScopeRef parsed.
///
bool Sema::RequireCompleteEnumDecl(EnumDecl *EnumD, SourceLocation L,
                                   CXXScopeSpec *SS) {
  if (EnumD->isCompleteDefinition()) {
    // If we know about the definition but it is not visible, complain.
    NamedDecl *SuggestedDef = nullptr;
    if (!hasReachableDefinition(EnumD, &SuggestedDef,
                                /*OnlyNeedComplete*/ false)) {
      // If the user is going to see an error here, recover by making the
      // definition visible.
      bool TreatAsComplete = !isSFINAEContext();
      diagnoseMissingImport(L, SuggestedDef, MissingImportKind::Definition,
                            /*Recover*/ TreatAsComplete);
      return !TreatAsComplete;
    }
    return false;
  }
 
  // Try to instantiate the definition, if this is a specialization of an
  // enumeration temploid.
  if (EnumDecl *Pattern = EnumD->getInstantiatedFromMemberEnum()) {
    MemberSpecializationInfo *MSI = EnumD->getMemberSpecializationInfo();
    if (MSI->getTemplateSpecializationKind() != TSK_ExplicitSpecialization) {
      if (InstantiateEnum(L, EnumD, Pattern,
                          getTemplateInstantiationArgs(EnumD),
                          TSK_ImplicitInstantiation)) {
        if (SS)
          SS->SetInvalid(SS->getRange());
        return true;
      }
      return false;
    }
  }
 
  if (SS) {
    Diag(L, diag::err_incomplete_nested_name_spec)
        << Context.getCanonicalTagType(EnumD) << SS->getRange();
    SS->SetInvalid(SS->getRange());
  } else {
    Diag(L, diag::err_incomplete_enum) << Context.getCanonicalTagType(EnumD);
    Diag(EnumD->getLocation(), diag::note_declared_at);
  }
 
  return true;
}
 
bool Sema::ActOnCXXGlobalScopeSpecifier(SourceLocation CCLoc,
                                        CXXScopeSpec &SS) {
  SS.MakeGlobal(Context, CCLoc);
  return false;
}
 
bool Sema::ActOnSuperScopeSpecifier(SourceLocation SuperLoc,
                                    SourceLocation ColonColonLoc,
                                    CXXScopeSpec &SS) {
  if (getCurLambda()) {
    Diag(SuperLoc, diag::err_super_in_lambda_unsupported);
    return true;
  }
 
  CXXRecordDecl *RD = nullptr;
  for (Scope *S = getCurScope(); S; S = S->getParent()) {
    if (S->isFunctionScope()) {
      if (CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(S->getEntity()))
        RD = MD->getParent();
      break;
    }
    if (S->isClassScope()) {
      RD = cast<CXXRecordDecl>(S->getEntity());
      break;
    }
  }
 
  if (!RD) {
    Diag(SuperLoc, diag::err_invalid_super_scope);
    return true;
  } else if (RD->getNumBases() == 0) {
    Diag(SuperLoc, diag::err_no_base_classes) << RD->getName();
    return true;
  }
 
  SS.MakeMicrosoftSuper(Context, RD, SuperLoc, ColonColonLoc);
  return false;
}
 
bool Sema::isAcceptableNestedNameSpecifier(const NamedDecl *SD,
                                           bool *IsExtension) {
  if (!SD)
    return false;
 
  SD = SD->getUnderlyingDecl();
 
  // Namespace and namespace aliases are fine.
  if (isa<NamespaceDecl>(SD))
    return true;
 
  if (!isa<TypeDecl>(SD))
    return false;
 
  // Determine whether we have a class (or, in C++11, an enum) or
  // a typedef thereof. If so, build the nested-name-specifier.
  if (const TypedefNameDecl *TD = dyn_cast<TypedefNameDecl>(SD)) {
    if (TD->getUnderlyingType()->isRecordType())
      return true;
    if (TD->getUnderlyingType()->isEnumeralType()) {
      if (Context.getLangOpts().CPlusPlus11)
        return true;
      if (IsExtension)
        *IsExtension = true;
    }
  } else if (isa<RecordDecl>(SD)) {
    return true;
  } else if (isa<EnumDecl>(SD)) {
    if (Context.getLangOpts().CPlusPlus11)
      return true;
    if (IsExtension)
      *IsExtension = true;
  }
  if (auto *TD = dyn_cast<TagDecl>(SD)) {
    if (TD->isDependentType())
      return true;
  } else if (Context.getCanonicalTypeDeclType(cast<TypeDecl>(SD))
                 ->isDependentType()) {
    return true;
  }
 
  return false;
}
 
NamedDecl *Sema::FindFirstQualifierInScope(Scope *S, NestedNameSpecifier NNS) {
  if (!S)
    return nullptr;
 
  while (NNS.getKind() == NestedNameSpecifier::Kind::Type) {
    const Type *T = NNS.getAsType();
    if ((NNS = T->getPrefix()))
      continue;
 
    const auto *DNT = dyn_cast<DependentNameType>(T);
    if (!DNT)
      break;
 
    LookupResult Found(*this, DNT->getIdentifier(), SourceLocation(),
                       LookupNestedNameSpecifierName);
    LookupName(Found, S);
    assert(!Found.isAmbiguous() && "Cannot handle ambiguities here yet");
 
    if (!Found.isSingleResult())
      return nullptr;
 
    NamedDecl *Result = Found.getFoundDecl();
    if (isAcceptableNestedNameSpecifier(Result))
      return Result;
  }
  return nullptr;
}
 
namespace {
 
// Callback to only accept typo corrections that can be a valid C++ member
// initializer: either a non-static field member or a base class.
class NestedNameSpecifierValidatorCCC final
    : public CorrectionCandidateCallback {
public:
  explicit NestedNameSpecifierValidatorCCC(Sema &SRef)
      : SRef(SRef) {}
 
  bool ValidateCandidate(const TypoCorrection &candidate) override {
    return SRef.isAcceptableNestedNameSpecifier(candidate.getCorrectionDecl());
  }
 
  std::unique_ptr<CorrectionCandidateCallback> clone() override {
    return std::make_unique<NestedNameSpecifierValidatorCCC>(*this);
  }
 
 private:
  Sema &SRef;
};
 
}
 
[[nodiscard]] static bool ExtendNestedNameSpecifier(Sema &S, CXXScopeSpec &SS,
                                                    const NamedDecl *ND,
                                                    SourceLocation NameLoc,
                                                    SourceLocation CCLoc) {
  TypeLocBuilder TLB;
  QualType T;
  if (const auto *USD = dyn_cast<UsingShadowDecl>(ND)) {
    T = S.Context.getUsingType(ElaboratedTypeKeyword::None, SS.getScopeRep(),
                               USD);
    TLB.push<UsingTypeLoc>(T).set(/*ElaboratedKeywordLoc=*/SourceLocation(),
                                  SS.getWithLocInContext(S.Context), NameLoc);
  } else if (const auto *TD = dyn_cast<TypeDecl>(ND)) {
    T = S.Context.getTypeDeclType(ElaboratedTypeKeyword::None, SS.getScopeRep(),
                                  TD);
    switch (T->getTypeClass()) {
    case Type::Record:
    case Type::InjectedClassName:
    case Type::Enum: {
      auto TTL = TLB.push<TagTypeLoc>(T);
      TTL.setElaboratedKeywordLoc(SourceLocation());
      TTL.setQualifierLoc(SS.getWithLocInContext(S.Context));
      TTL.setNameLoc(NameLoc);
      break;
    }
    case Type::Typedef:
      TLB.push<TypedefTypeLoc>(T).set(/*ElaboratedKeywordLoc=*/SourceLocation(),
                                      SS.getWithLocInContext(S.Context),
                                      NameLoc);
      break;
    case Type::UnresolvedUsing:
      TLB.push<UnresolvedUsingTypeLoc>(T).set(
          /*ElaboratedKeywordLoc=*/SourceLocation(),
          SS.getWithLocInContext(S.Context), NameLoc);
      break;
    default:
      assert(SS.isEmpty());
      T = S.Context.getTypeDeclType(TD);
      TLB.pushTypeSpec(T).setNameLoc(NameLoc);
      break;
    }
  } else {
    return false;
  }
  SS.clear();
  SS.Make(S.Context, TLB.getTypeLocInContext(S.Context, T), CCLoc);
  return true;
}
 
bool Sema::BuildCXXNestedNameSpecifier(Scope *S, NestedNameSpecInfo &IdInfo,
                                       bool EnteringContext, CXXScopeSpec &SS,
                                       NamedDecl *ScopeLookupResult,
                                       bool ErrorRecoveryLookup,
                                       bool *IsCorrectedToColon,
                                       bool OnlyNamespace) {
  if (IdInfo.Identifier->isEditorPlaceholder())
    return true;
  LookupResult Found(*this, IdInfo.Identifier, IdInfo.IdentifierLoc,
                     OnlyNamespace ? LookupNamespaceName
                                   : LookupNestedNameSpecifierName);
  QualType ObjectType = GetTypeFromParser(IdInfo.ObjectType);
 
  // Determine where to perform name lookup
  DeclContext *LookupCtx = nullptr;
  bool isDependent = false;
  if (IsCorrectedToColon)
    *IsCorrectedToColon = false;
  if (!ObjectType.isNull()) {
    // This nested-name-specifier occurs in a member access expression, e.g.,
    // x->B::f, and we are looking into the type of the object.
    assert(!SS.isSet() && "ObjectType and scope specifier cannot coexist");
    LookupCtx = computeDeclContext(ObjectType);
    isDependent = ObjectType->isDependentType();
  } else if (SS.isSet()) {
    // This nested-name-specifier occurs after another nested-name-specifier,
    // so look into the context associated with the prior nested-name-specifier.
    LookupCtx = computeDeclContext(SS, EnteringContext);
    isDependent = isDependentScopeSpecifier(SS);
    Found.setContextRange(SS.getRange());
  }
 
  bool ObjectTypeSearchedInScope = false;
  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.
 
    // The declaration context must be complete.
    if (!LookupCtx->isDependentContext() &&
        RequireCompleteDeclContext(SS, LookupCtx))
      return true;
 
    LookupQualifiedName(Found, LookupCtx);
 
    if (!ObjectType.isNull() && Found.empty()) {
      // C++ [basic.lookup.classref]p4:
      //   If the id-expression in a class member access is a qualified-id of
      //   the form
      //
      //        class-name-or-namespace-name::...
      //
      //   the class-name-or-namespace-name following the . or -> operator is
      //   looked up both in the context of the entire postfix-expression and in
      //   the scope of the class of the object expression. If the name is found
      //   only in the scope of the class of the object expression, the name
      //   shall refer to a class-name. If the name is found only in the
      //   context of the entire postfix-expression, the name shall refer to a
      //   class-name or namespace-name. [...]
      //
      // Qualified name lookup into a class will not find a namespace-name,
      // so we do not need to diagnose that case specifically. However,
      // this qualified name lookup may find nothing. In that case, perform
      // unqualified name lookup in the given scope (if available) or
      // reconstruct the result from when name lookup was performed at template
      // definition time.
      if (S)
        LookupName(Found, S);
      else if (ScopeLookupResult)
        Found.addDecl(ScopeLookupResult);
 
      ObjectTypeSearchedInScope = true;
    }
  } else if (!isDependent) {
    // Perform unqualified name lookup in the current scope.
    LookupName(Found, S);
  }
 
  if (Found.isAmbiguous())
    return true;
 
  // If we performed lookup into a dependent context and did not find anything,
  // that's fine: just build a dependent nested-name-specifier.
  if (Found.empty() && isDependent &&
      !(LookupCtx && LookupCtx->isRecord() &&
        (!cast<CXXRecordDecl>(LookupCtx)->hasDefinition() ||
         !cast<CXXRecordDecl>(LookupCtx)->hasAnyDependentBases()))) {
    // Don't speculate if we're just trying to improve error recovery.
    if (ErrorRecoveryLookup)
      return true;
 
    // We were not able to compute the declaration context for a dependent
    // base object type or prior nested-name-specifier, so this
    // nested-name-specifier refers to an unknown specialization. Just build
    // a dependent nested-name-specifier.
 
    TypeLocBuilder TLB;
 
    QualType DTN = Context.getDependentNameType(
        ElaboratedTypeKeyword::None, SS.getScopeRep(), IdInfo.Identifier);
    auto DTNL = TLB.push<DependentNameTypeLoc>(DTN);
    DTNL.setElaboratedKeywordLoc(SourceLocation());
    DTNL.setNameLoc(IdInfo.IdentifierLoc);
    DTNL.setQualifierLoc(SS.getWithLocInContext(Context));
 
    SS.clear();
    SS.Make(Context, TLB.getTypeLocInContext(Context, DTN), IdInfo.CCLoc);
    return false;
  }
 
  if (Found.empty() && !ErrorRecoveryLookup) {
    // If identifier is not found as class-name-or-namespace-name, but is found
    // as other entity, don't look for typos.
    LookupResult R(*this, Found.getLookupNameInfo(), LookupOrdinaryName);
    if (LookupCtx)
      LookupQualifiedName(R, LookupCtx);
    else if (S && !isDependent)
      LookupName(R, S);
    if (!R.empty()) {
      // Don't diagnose problems with this speculative lookup.
      R.suppressDiagnostics();
      // The identifier is found in ordinary lookup. If correction to colon is
      // allowed, suggest replacement to ':'.
      if (IsCorrectedToColon) {
        *IsCorrectedToColon = true;
        Diag(IdInfo.CCLoc, diag::err_nested_name_spec_is_not_class)
            << IdInfo.Identifier << getLangOpts().CPlusPlus
            << FixItHint::CreateReplacement(IdInfo.CCLoc, ":");
        if (NamedDecl *ND = R.getAsSingle<NamedDecl>())
          Diag(ND->getLocation(), diag::note_declared_at);
        return true;
      }
      // Replacement '::' -> ':' is not allowed, just issue respective error.
      Diag(R.getNameLoc(), OnlyNamespace
                               ? unsigned(diag::err_expected_namespace_name)
                               : unsigned(diag::err_expected_class_or_namespace))
          << IdInfo.Identifier << getLangOpts().CPlusPlus;
      if (NamedDecl *ND = R.getAsSingle<NamedDecl>())
        Diag(ND->getLocation(), diag::note_entity_declared_at)
            << IdInfo.Identifier;
      return true;
    }
  }
 
  if (Found.empty() && !ErrorRecoveryLookup && !getLangOpts().MSVCCompat) {
    // We haven't found anything, and we're not recovering from a
    // different kind of error, so look for typos.
    DeclarationName Name = Found.getLookupName();
    Found.clear();
    NestedNameSpecifierValidatorCCC CCC(*this);
    if (TypoCorrection Corrected = CorrectTypo(
            Found.getLookupNameInfo(), Found.getLookupKind(), S, &SS, CCC,
            CorrectTypoKind::ErrorRecovery, LookupCtx, EnteringContext)) {
      if (LookupCtx) {
        bool DroppedSpecifier =
            Corrected.WillReplaceSpecifier() &&
            Name.getAsString() == Corrected.getAsString(getLangOpts());
        if (DroppedSpecifier)
          SS.clear();
        diagnoseTypo(Corrected, PDiag(diag::err_no_member_suggest)
                                  << Name << LookupCtx << DroppedSpecifier
                                  << SS.getRange());
      } else
        diagnoseTypo(Corrected, PDiag(diag::err_undeclared_var_use_suggest)
                                  << Name);
 
      if (Corrected.getCorrectionSpecifier())
        SS.MakeTrivial(Context, Corrected.getCorrectionSpecifier(),
                       SourceRange(Found.getNameLoc()));
 
      if (NamedDecl *ND = Corrected.getFoundDecl())
        Found.addDecl(ND);
      Found.setLookupName(Corrected.getCorrection());
    } else {
      Found.setLookupName(IdInfo.Identifier);
    }
  }
 
  NamedDecl *SD =
      Found.isSingleResult() ? Found.getRepresentativeDecl() : nullptr;
  bool IsExtension = false;
  bool AcceptSpec = isAcceptableNestedNameSpecifier(SD, &IsExtension);
  if (!AcceptSpec && IsExtension) {
    AcceptSpec = true;
    Diag(IdInfo.IdentifierLoc, diag::ext_nested_name_spec_is_enum);
  }
  if (AcceptSpec) {
    if (!ObjectType.isNull() && !ObjectTypeSearchedInScope &&
        !getLangOpts().CPlusPlus11) {
      // C++03 [basic.lookup.classref]p4:
      //   [...] If the name is found in both contexts, the
      //   class-name-or-namespace-name shall refer to the same entity.
      //
      // We already found the name in the scope of the object. Now, look
      // into the current scope (the scope of the postfix-expression) to
      // see if we can find the same name there. As above, if there is no
      // scope, reconstruct the result from the template instantiation itself.
      //
      // Note that C++11 does *not* perform this redundant lookup.
      NamedDecl *OuterDecl;
      if (S) {
        LookupResult FoundOuter(*this, IdInfo.Identifier, IdInfo.IdentifierLoc,
                                LookupNestedNameSpecifierName);
        LookupName(FoundOuter, S);
        OuterDecl = FoundOuter.getAsSingle<NamedDecl>();
      } else
        OuterDecl = ScopeLookupResult;
 
      if (isAcceptableNestedNameSpecifier(OuterDecl) &&
          OuterDecl->getCanonicalDecl() != SD->getCanonicalDecl() &&
          (!isa<TypeDecl>(OuterDecl) || !isa<TypeDecl>(SD) ||
           !Context.hasSameType(
               Context.getCanonicalTypeDeclType(cast<TypeDecl>(OuterDecl)),
               Context.getCanonicalTypeDeclType(cast<TypeDecl>(SD))))) {
        if (ErrorRecoveryLookup)
          return true;
 
         Diag(IdInfo.IdentifierLoc,
              diag::err_nested_name_member_ref_lookup_ambiguous)
           << IdInfo.Identifier;
         Diag(SD->getLocation(), diag::note_ambig_member_ref_object_type)
           << ObjectType;
         Diag(OuterDecl->getLocation(), diag::note_ambig_member_ref_scope);
 
         // Fall through so that we'll pick the name we found in the object
         // type, since that's probably what the user wanted anyway.
      }
    }
 
    if (auto *TD = dyn_cast_or_null<TypedefNameDecl>(SD))
      MarkAnyDeclReferenced(TD->getLocation(), TD, /*OdrUse=*/false);
 
    // If we're just performing this lookup for error-recovery purposes,
    // don't extend the nested-name-specifier. Just return now.
    if (ErrorRecoveryLookup)
      return false;
 
    // The use of a nested name specifier may trigger deprecation warnings.
    DiagnoseUseOfDecl(SD, IdInfo.CCLoc);
 
    if (NamespaceDecl *Namespace = dyn_cast<NamespaceDecl>(SD)) {
      SS.Extend(Context, Namespace, IdInfo.IdentifierLoc, IdInfo.CCLoc);
      return false;
    }
 
    if (NamespaceAliasDecl *Alias = dyn_cast<NamespaceAliasDecl>(SD)) {
      SS.Extend(Context, Alias, IdInfo.IdentifierLoc, IdInfo.CCLoc);
      return false;
    }
 
    const auto *TD = cast<TypeDecl>(SD->getUnderlyingDecl());
    if (isa<EnumDecl>(TD))
      Diag(IdInfo.IdentifierLoc, diag::warn_cxx98_compat_enum_nested_name_spec);
 
    [[maybe_unused]] bool IsType = ::ExtendNestedNameSpecifier(
        *this, SS, SD, IdInfo.IdentifierLoc, IdInfo.CCLoc);
    assert(IsType && "unhandled declaration kind");
    return false;
  }
 
  // Otherwise, we have an error case.  If we don't want diagnostics, just
  // return an error now.
  if (ErrorRecoveryLookup)
    return true;
 
  // If we didn't find anything during our lookup, try again with
  // ordinary name lookup, which can help us produce better error
  // messages.
  if (Found.empty()) {
    Found.clear(LookupOrdinaryName);
    LookupName(Found, S);
  }
 
  // In Microsoft mode, if we are within a templated function and we can't
  // resolve Identifier, then extend the SS with Identifier. This will have
  // the effect of resolving Identifier during template instantiation.
  // The goal is to be able to resolve a function call whose
  // nested-name-specifier is located inside a dependent base class.
  // Example:
  //
  // class C {
  // public:
  //    static void foo2() {  }
  // };
  // template <class T> class A { public: typedef C D; };
  //
  // template <class T> class B : public A<T> {
  // public:
  //   void foo() { D::foo2(); }
  // };
  if (getLangOpts().MSVCCompat) {
    DeclContext *DC = LookupCtx ? LookupCtx : CurContext;
    if (DC->isDependentContext() && DC->isFunctionOrMethod()) {
      CXXRecordDecl *ContainingClass = dyn_cast<CXXRecordDecl>(DC->getParent());
      if (ContainingClass && ContainingClass->hasAnyDependentBases()) {
        Diag(IdInfo.IdentifierLoc,
             diag::ext_undeclared_unqual_id_with_dependent_base)
            << IdInfo.Identifier << ContainingClass;
 
        TypeLocBuilder TLB;
 
        // Fake up a nested-name-specifier that starts with the
        // injected-class-name of the enclosing class.
        // FIXME: This should be done as part of an adjustment, so that this
        // doesn't get confused with something written in source.
        QualType Result =
            Context.getTagType(ElaboratedTypeKeyword::None, SS.getScopeRep(),
                               ContainingClass, /*OwnsTag=*/false);
        auto TTL = TLB.push<TagTypeLoc>(Result);
        TTL.setElaboratedKeywordLoc(SourceLocation());
        TTL.setQualifierLoc(SS.getWithLocInContext(Context));
        TTL.setNameLoc(IdInfo.IdentifierLoc);
        SS.Make(Context, TLB.getTypeLocInContext(Context, Result),
                SourceLocation());
 
        TLB.clear();
 
        // Form a DependentNameType.
        QualType DTN = Context.getDependentNameType(
            ElaboratedTypeKeyword::None, SS.getScopeRep(), IdInfo.Identifier);
        auto DTNL = TLB.push<DependentNameTypeLoc>(DTN);
        DTNL.setElaboratedKeywordLoc(SourceLocation());
        DTNL.setNameLoc(IdInfo.IdentifierLoc);
        DTNL.setQualifierLoc(SS.getWithLocInContext(Context));
        SS.clear();
        SS.Make(Context, TLB.getTypeLocInContext(Context, DTN), IdInfo.CCLoc);
        return false;
      }
    }
  }
 
  if (!Found.empty()) {
    const auto *ND = Found.getAsSingle<NamedDecl>();
    if (::ExtendNestedNameSpecifier(*this, SS, ND, IdInfo.IdentifierLoc,
                                    IdInfo.CCLoc)) {
      const Type *T = SS.getScopeRep().getAsType();
      Diag(IdInfo.IdentifierLoc, diag::err_expected_class_or_namespace)
          << QualType(T, 0) << getLangOpts().CPlusPlus;
      // Recover with this type if it would be a valid nested name specifier.
      return !T->getAsCanonical<TagType>();
    }
    if (isa<TemplateDecl>(ND)) {
      ParsedType SuggestedType;
      DiagnoseUnknownTypeName(IdInfo.Identifier, IdInfo.IdentifierLoc, S, &SS,
                              SuggestedType);
    } else {
      Diag(IdInfo.IdentifierLoc, diag::err_expected_class_or_namespace)
          << IdInfo.Identifier << getLangOpts().CPlusPlus;
      if (NamedDecl *ND = Found.getAsSingle<NamedDecl>())
        Diag(ND->getLocation(), diag::note_entity_declared_at)
            << IdInfo.Identifier;
    }
  } else if (SS.isSet())
    Diag(IdInfo.IdentifierLoc, diag::err_no_member) << IdInfo.Identifier
        << LookupCtx << SS.getRange();
  else
    Diag(IdInfo.IdentifierLoc, diag::err_undeclared_var_use)
        << IdInfo.Identifier;
 
  return true;
}
 
bool Sema::ActOnCXXNestedNameSpecifier(Scope *S, NestedNameSpecInfo &IdInfo,
                                       bool EnteringContext, CXXScopeSpec &SS,
                                       bool *IsCorrectedToColon,
                                       bool OnlyNamespace) {
  if (SS.isInvalid())
    return true;
 
  return BuildCXXNestedNameSpecifier(S, IdInfo, EnteringContext, SS,
                                     /*ScopeLookupResult=*/nullptr, false,
                                     IsCorrectedToColon, OnlyNamespace);
}
 
bool Sema::ActOnCXXNestedNameSpecifierDecltype(CXXScopeSpec &SS,
                                               const DeclSpec &DS,
                                               SourceLocation ColonColonLoc) {
  if (SS.isInvalid() || DS.getTypeSpecType() == DeclSpec::TST_error)
    return true;
 
  assert(DS.getTypeSpecType() == DeclSpec::TST_decltype);
 
  QualType T = BuildDecltypeType(DS.getRepAsExpr());
  if (T.isNull())
    return true;
 
  if (!T->isDependentType() && !isa<TagType>(T.getCanonicalType())) {
    Diag(DS.getTypeSpecTypeLoc(), diag::err_expected_class_or_namespace)
      << T << getLangOpts().CPlusPlus;
    return true;
  }
 
  assert(SS.isEmpty());
 
  TypeLocBuilder TLB;
  DecltypeTypeLoc DecltypeTL = TLB.push<DecltypeTypeLoc>(T);
  DecltypeTL.setDecltypeLoc(DS.getTypeSpecTypeLoc());
  DecltypeTL.setRParenLoc(DS.getTypeofParensRange().getEnd());
  SS.Make(Context, TLB.getTypeLocInContext(Context, T), ColonColonLoc);
  return false;
}
 
bool Sema::ActOnCXXNestedNameSpecifierIndexedPack(CXXScopeSpec &SS,
                                                  const DeclSpec &DS,
                                                  SourceLocation ColonColonLoc,
                                                  QualType Type) {
  if (SS.isInvalid() || DS.getTypeSpecType() == DeclSpec::TST_error)
    return true;
 
  assert(DS.getTypeSpecType() == DeclSpec::TST_typename_pack_indexing);
 
  if (Type.isNull())
    return true;
 
  assert(SS.isEmpty());
 
  TypeLocBuilder TLB;
  TLB.pushTrivial(getASTContext(),
                  cast<PackIndexingType>(Type.getTypePtr())->getPattern(),
                  DS.getBeginLoc());
  PackIndexingTypeLoc PIT = TLB.push<PackIndexingTypeLoc>(Type);
  PIT.setEllipsisLoc(DS.getEllipsisLoc());
  SS.Make(Context, TLB.getTypeLocInContext(Context, Type), ColonColonLoc);
  return false;
}
 
bool Sema::IsInvalidUnlessNestedName(Scope *S, CXXScopeSpec &SS,
                                     NestedNameSpecInfo &IdInfo,
                                     bool EnteringContext) {
  if (SS.isInvalid())
    return false;
 
  return !BuildCXXNestedNameSpecifier(S, IdInfo, EnteringContext, SS,
                                      /*ScopeLookupResult=*/nullptr, true);
}
 
bool Sema::ActOnCXXNestedNameSpecifier(Scope *S,
                                       CXXScopeSpec &SS,
                                       SourceLocation TemplateKWLoc,
                                       TemplateTy OpaqueTemplate,
                                       SourceLocation TemplateNameLoc,
                                       SourceLocation LAngleLoc,
                                       ASTTemplateArgsPtr TemplateArgsIn,
                                       SourceLocation RAngleLoc,
                                       SourceLocation CCLoc,
                                       bool EnteringContext) {
  if (SS.isInvalid())
    return true;
 
  // Translate the parser's template argument list in our AST format.
  TemplateArgumentListInfo TemplateArgs(LAngleLoc, RAngleLoc);
  translateTemplateArguments(TemplateArgsIn, TemplateArgs);
 
  // We were able to resolve the template name to an actual template.
  // Build an appropriate nested-name-specifier.
  QualType T = CheckTemplateIdType(
      ElaboratedTypeKeyword::None, OpaqueTemplate.get(), TemplateNameLoc,
      TemplateArgs, /*Scope=*/S, /*ForNestedNameSpecifier=*/true);
  if (T.isNull())
    return true;
 
  // Alias template specializations can produce types which are not valid
  // nested name specifiers.
  if (!T->isDependentType() && !isa<TagType>(T.getCanonicalType())) {
    Diag(TemplateNameLoc, diag::err_nested_name_spec_non_tag) << T;
    NoteAllFoundTemplates(OpaqueTemplate.get());
    return true;
  }
 
  // Provide source-location information for the template specialization type.
  TypeLocBuilder TLB;
  TLB.push<TemplateSpecializationTypeLoc>(T).set(
      /*ElaboratedKeywordLoc=*/SourceLocation(),
      SS.getWithLocInContext(Context), TemplateKWLoc, TemplateNameLoc,
      TemplateArgs);
 
  SS.clear();
  SS.Make(Context, TLB.getTypeLocInContext(Context, T), CCLoc);
  return false;
}
 
namespace {
  /// A structure that stores a nested-name-specifier annotation,
  /// including both the nested-name-specifier
  struct NestedNameSpecifierAnnotation {
    NestedNameSpecifier NNS = std::nullopt;
  };
}
 
void *Sema::SaveNestedNameSpecifierAnnotation(CXXScopeSpec &SS) {
  if (SS.isEmpty() || SS.isInvalid())
    return nullptr;
 
  void *Mem = Context.Allocate(
      (sizeof(NestedNameSpecifierAnnotation) + SS.location_size()),
      alignof(NestedNameSpecifierAnnotation));
  NestedNameSpecifierAnnotation *Annotation
    = new (Mem) NestedNameSpecifierAnnotation;
  Annotation->NNS = SS.getScopeRep();
  memcpy(Annotation + 1, SS.location_data(), SS.location_size());
  return Annotation;
}
 
void Sema::RestoreNestedNameSpecifierAnnotation(void *AnnotationPtr,
                                                SourceRange AnnotationRange,
                                                CXXScopeSpec &SS) {
  if (!AnnotationPtr) {
    SS.SetInvalid(AnnotationRange);
    return;
  }
 
  NestedNameSpecifierAnnotation *Annotation
    = static_cast<NestedNameSpecifierAnnotation *>(AnnotationPtr);
  SS.Adopt(NestedNameSpecifierLoc(Annotation->NNS, Annotation + 1));
}
 
bool Sema::ShouldEnterDeclaratorScope(Scope *S, const CXXScopeSpec &SS) {
  assert(SS.isSet() && "Parser passed invalid CXXScopeSpec.");
 
  // Don't enter a declarator context when the current context is an Objective-C
  // declaration.
  if (isa<ObjCContainerDecl>(CurContext) || isa<ObjCMethodDecl>(CurContext))
    return false;
 
  // There are only two places a well-formed program may qualify a
  // declarator: first, when defining a namespace or class member
  // out-of-line, and second, when naming an explicitly-qualified
  // friend function.  The latter case is governed by
  // C++03 [basic.lookup.unqual]p10:
  //   In a friend declaration naming a member function, a name used
  //   in the function declarator and not part of a template-argument
  //   in a template-id is first looked up in the scope of the member
  //   function's class. If it is not found, or if the name is part of
  //   a template-argument in a template-id, the look up is as
  //   described for unqualified names in the definition of the class
  //   granting friendship.
  // i.e. we don't push a scope unless it's a class member.
 
  switch (SS.getScopeRep().getKind()) {
  case NestedNameSpecifier::Kind::Global:
  case NestedNameSpecifier::Kind::Namespace:
    // These are always namespace scopes.  We never want to enter a
    // namespace scope from anything but a file context.
    return CurContext->getRedeclContext()->isFileContext();
 
  case NestedNameSpecifier::Kind::Type:
  case NestedNameSpecifier::Kind::MicrosoftSuper:
    // These are never namespace scopes.
    return true;
 
  case NestedNameSpecifier::Kind::Null:
    llvm_unreachable("unexpected null nested name specifier");
  }
 
  llvm_unreachable("Invalid NestedNameSpecifier::Kind!");
}
 
bool Sema::ActOnCXXEnterDeclaratorScope(Scope *S, CXXScopeSpec &SS) {
  assert(SS.isSet() && "Parser passed invalid CXXScopeSpec.");
 
  if (SS.isInvalid()) return true;
 
  DeclContext *DC = computeDeclContext(SS, true);
  if (!DC) return true;
 
  // Before we enter a declarator's context, we need to make sure that
  // it is a complete declaration context.
  if (!DC->isDependentContext() && RequireCompleteDeclContext(SS, DC))
    return true;
 
  EnterDeclaratorContext(S, DC);
 
  // Rebuild the nested name specifier for the new scope.
  if (DC->isDependentContext())
    RebuildNestedNameSpecifierInCurrentInstantiation(SS);
 
  return false;
}
 
void Sema::ActOnCXXExitDeclaratorScope(Scope *S, const CXXScopeSpec &SS) {
  assert(SS.isSet() && "Parser passed invalid CXXScopeSpec.");
  if (SS.isInvalid())
    return;
  assert(!SS.isInvalid() && computeDeclContext(SS, true) &&
         "exiting declarator scope we never really entered");
  ExitDeclaratorContext(S);
}