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(), DS.getTypeSpecTypeLoc());
  if (T.isNull())
    return true;

  if (!T->isDependentType() && !T->getAs<TagType>()) {
    Diag(DS.getTypeSpecTypeLoc(), diag::err_expected_class_or_namespace)
      << T << getLangOpts().CPlusPlus;
    return true;
  }

  TypeLocBuilder TLB;
  DecltypeTypeLoc DecltypeTL = TLB.push<DecltypeTypeLoc>(T);
  DecltypeTL.setNameLoc(DS.getTypeSpecTypeLoc());
  SS.Extend(Context, SourceLocation(), TLB.getTypeLocInContext(Context, T),
            ColonColonLoc);
  return false;
}

TemplateArgumentLoc
Sema::getTemplateArgumentPackExpansionPattern(
      TemplateArgumentLoc OrigLoc,
      SourceLocation &Ellipsis, Optional<unsigned> &NumExpansions) const {
  const TemplateArgument &Argument = OrigLoc.getArgument();
  assert(Argument.isPackExpansion());
  switch (Argument.getKind()) {
  case TemplateArgument::Type: {
    // FIXME: We shouldn't ever have to worry about missing
    // type-source info!
    TypeSourceInfo *ExpansionTSInfo = OrigLoc.getTypeSourceInfo();
    if (!ExpansionTSInfo)
      ExpansionTSInfo = Context.getTrivialTypeSourceInfo(Argument.getAsType(),
                                                         Ellipsis);
    PackExpansionTypeLoc Expansion =
        ExpansionTSInfo->getTypeLoc().castAs<PackExpansionTypeLoc>();
    Ellipsis = Expansion.getEllipsisLoc();

    TypeLoc Pattern = Expansion.getPatternLoc();
    NumExpansions = Expansion.getTypePtr()->getNumExpansions();

    // We need to copy the TypeLoc because TemplateArgumentLocs store a
    // TypeSourceInfo.
    // FIXME: Find some way to avoid the copy?
    TypeLocBuilder TLB;
    TLB.pushFullCopy(Pattern);
    TypeSourceInfo *PatternTSInfo =
        TLB.getTypeSourceInfo(Context, Pattern.getType());
    return TemplateArgumentLoc(TemplateArgument(Pattern.getType()),
                               PatternTSInfo);
  }

  case TemplateArgument::Expression: {
    PackExpansionExpr *Expansion
      = cast<PackExpansionExpr>(Argument.getAsExpr());
    Expr *Pattern = Expansion->getPattern();
    Ellipsis = Expansion->getEllipsisLoc();
    NumExpansions = Expansion->getNumExpansions();
    return TemplateArgumentLoc(Pattern, Pattern);
  }

  case TemplateArgument::TemplateExpansion:
    Ellipsis = OrigLoc.getTemplateEllipsisLoc();
    NumExpansions = Argument.getNumTemplateExpansions();
    return TemplateArgumentLoc(Argument.getPackExpansionPattern(),
                               OrigLoc.getTemplateQualifierLoc(),
                               OrigLoc.getTemplateNameLoc());

  case TemplateArgument::Declaration:
  case TemplateArgument::NullPtr:
  case TemplateArgument::Template:
  case TemplateArgument::Integral:
  case TemplateArgument::Pack:
  case TemplateArgument::Null:
    return TemplateArgumentLoc();
  }

  llvm_unreachable("Invalid TemplateArgument Kind!");
}

TypeSourceInfo *
Sema::CheckPackExpansion(TypeSourceInfo *Pattern, SourceLocation EllipsisLoc,
                         Optional<unsigned> NumExpansions) {
  // Create the pack expansion type and source-location information.
  QualType Result = CheckPackExpansion(Pattern->getType(),
                                       Pattern->getTypeLoc().getSourceRange(),
                                       EllipsisLoc, NumExpansions);
  if (Result.isNull())
    return nullptr;

  TypeLocBuilder TLB;
  TLB.pushFullCopy(Pattern->getTypeLoc());
  PackExpansionTypeLoc TL = TLB.push<PackExpansionTypeLoc>(Result);
  TL.setEllipsisLoc(EllipsisLoc);

  return TLB.getTypeSourceInfo(Context, Result);
}

bool Sema::ActOnCXXNestedNameSpecifier(Scope *S,
                                       SourceLocation TemplateLoc, 
                                       CXXScopeSpec &SS, 
                                       TemplateTy Template,
                                       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);

  if (DependentTemplateName *DTN = Template.get().getAsDependentTemplateName()){
    // Handle a dependent template specialization for which we cannot resolve
    // the template name.
    assert(DTN->getQualifier()
             == static_cast<NestedNameSpecifier*>(SS.getScopeRep()));
    QualType T = Context.getDependentTemplateSpecializationType(ETK_None,
                                                          DTN->getQualifier(),
                                                          DTN->getIdentifier(),
                                                                TemplateArgs);
    
    // Create source-location information for this type.
    TypeLocBuilder Builder;
    DependentTemplateSpecializationTypeLoc SpecTL 
      = Builder.push<DependentTemplateSpecializationTypeLoc>(T);
    SpecTL.setLAngleLoc(LAngleLoc);
    SpecTL.setRAngleLoc(RAngleLoc);
    SpecTL.setKeywordLoc(SourceLocation());
    SpecTL.setNameLoc(TemplateNameLoc);
    SpecTL.setQualifierLoc(SS.getWithLocInContext(Context));
    for (unsigned I = 0, N = TemplateArgs.size(); I != N; ++I)
      SpecTL.setArgLocInfo(I, TemplateArgs[I].getLocInfo());
    
    SS.Extend(Context, TemplateLoc, Builder.getTypeLocInContext(Context, T), 
              CCLoc);
    return false;
  }
  
  
  if (Template.get().getAsOverloadedTemplate() ||
      isa<FunctionTemplateDecl>(Template.get().getAsTemplateDecl())) {
    SourceRange R(TemplateNameLoc, RAngleLoc);
    if (SS.getRange().isValid())
      R.setBegin(SS.getRange().getBegin());
      
    Diag(CCLoc, diag::err_non_type_template_in_nested_name_specifier)
      << Template.get() << R;
    NoteAllFoundTemplates(Template.get());
    return true;
  }
                                
  // We were able to resolve the template name to an actual template. 
  // Build an appropriate nested-name-specifier.
  QualType T = CheckTemplateIdType(Template.get(), TemplateNameLoc, 
                                   TemplateArgs);
  if (T.isNull())
    return true;

  // Alias template specializations can produce types which are not valid
  // nested name specifiers.
  if (!T->isDependentType() && !T->getAs<TagType>()) {
    Diag(TemplateNameLoc, diag::err_nested_name_spec_non_tag) << T;
    NoteAllFoundTemplates(Template.get());
    return true;
  }

  // Provide source-location information for the template specialization 
  // type.
  TypeLocBuilder Builder;
  TemplateSpecializationTypeLoc SpecTL 
    = Builder.push<TemplateSpecializationTypeLoc>(T);
  
  SpecTL.setLAngleLoc(LAngleLoc);
  SpecTL.setRAngleLoc(RAngleLoc);
  SpecTL.setTemplateNameLoc(TemplateNameLoc);
  for (unsigned I = 0, N = TemplateArgs.size(); I != N; ++I)
    SpecTL.setArgLocInfo(I, TemplateArgs[I].getLocInfo());


  SS.Extend(Context, TemplateLoc, Builder.getTypeLocInContext(Context, T), 
            CCLoc);
  return false;
}

//.........这里部分代码省略.........
                            Context.getTypeDeclType(cast<TypeDecl>(OuterDecl)),
                               Context.getTypeDeclType(cast<TypeDecl>(SD))))) {
         if (ErrorRecoveryLookup)
           return true;

         Diag(IdentifierLoc, 
              diag::err_nested_name_member_ref_lookup_ambiguous)
           << &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 we're just performing this lookup for error-recovery purposes, 
    // don't extend the nested-name-specifier. Just return now.
    if (ErrorRecoveryLookup)
      return false;
    
    if (NamespaceDecl *Namespace = dyn_cast<NamespaceDecl>(SD)) {
      SS.Extend(Context, Namespace, IdentifierLoc, CCLoc);
      return false;
    }

    if (NamespaceAliasDecl *Alias = dyn_cast<NamespaceAliasDecl>(SD)) {
      SS.Extend(Context, Alias, IdentifierLoc, CCLoc);
      return false;
    }

    QualType T = Context.getTypeDeclType(cast<TypeDecl>(SD));
    TypeLocBuilder TLB;
    if (isa<InjectedClassNameType>(T)) {
      InjectedClassNameTypeLoc InjectedTL
        = TLB.push<InjectedClassNameTypeLoc>(T);
      InjectedTL.setNameLoc(IdentifierLoc);
    } else if (isa<RecordType>(T)) {
      RecordTypeLoc RecordTL = TLB.push<RecordTypeLoc>(T);
      RecordTL.setNameLoc(IdentifierLoc);
    } else if (isa<TypedefType>(T)) {
      TypedefTypeLoc TypedefTL = TLB.push<TypedefTypeLoc>(T);
      TypedefTL.setNameLoc(IdentifierLoc);
    } else if (isa<EnumType>(T)) {
      EnumTypeLoc EnumTL = TLB.push<EnumTypeLoc>(T);
      EnumTL.setNameLoc(IdentifierLoc);
    } else if (isa<TemplateTypeParmType>(T)) {
      TemplateTypeParmTypeLoc TemplateTypeTL
        = TLB.push<TemplateTypeParmTypeLoc>(T);
      TemplateTypeTL.setNameLoc(IdentifierLoc);
    } else if (isa<UnresolvedUsingType>(T)) {
      UnresolvedUsingTypeLoc UnresolvedTL
        = TLB.push<UnresolvedUsingTypeLoc>(T);
      UnresolvedTL.setNameLoc(IdentifierLoc);
    } else if (isa<SubstTemplateTypeParmType>(T)) {
      SubstTemplateTypeParmTypeLoc TL 
        = TLB.push<SubstTemplateTypeParmTypeLoc>(T);
      TL.setNameLoc(IdentifierLoc);
    } else if (isa<SubstTemplateTypeParmPackType>(T)) {
      SubstTemplateTypeParmPackTypeLoc TL
        = TLB.push<SubstTemplateTypeParmPackTypeLoc>(T);
      TL.setNameLoc(IdentifierLoc);
    } else {
      llvm_unreachable("Unhandled TypeDecl node in nested-name-specifier");
    }

//.........这里部分代码省略.........
           << 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;
    }

    QualType T =
        Context.getTypeDeclType(cast<TypeDecl>(SD->getUnderlyingDecl()));
    TypeLocBuilder TLB;
    if (isa<InjectedClassNameType>(T)) {
      InjectedClassNameTypeLoc InjectedTL
        = TLB.push<InjectedClassNameTypeLoc>(T);
      InjectedTL.setNameLoc(IdInfo.IdentifierLoc);
    } else if (isa<RecordType>(T)) {
      RecordTypeLoc RecordTL = TLB.push<RecordTypeLoc>(T);
      RecordTL.setNameLoc(IdInfo.IdentifierLoc);
    } else if (isa<TypedefType>(T)) {
      TypedefTypeLoc TypedefTL = TLB.push<TypedefTypeLoc>(T);
      TypedefTL.setNameLoc(IdInfo.IdentifierLoc);
    } else if (isa<EnumType>(T)) {
      EnumTypeLoc EnumTL = TLB.push<EnumTypeLoc>(T);
      EnumTL.setNameLoc(IdInfo.IdentifierLoc);
    } else if (isa<TemplateTypeParmType>(T)) {
      TemplateTypeParmTypeLoc TemplateTypeTL
        = TLB.push<TemplateTypeParmTypeLoc>(T);
      TemplateTypeTL.setNameLoc(IdInfo.IdentifierLoc);
    } else if (isa<UnresolvedUsingType>(T)) {
      UnresolvedUsingTypeLoc UnresolvedTL
        = TLB.push<UnresolvedUsingTypeLoc>(T);
      UnresolvedTL.setNameLoc(IdInfo.IdentifierLoc);
    } else if (isa<SubstTemplateTypeParmType>(T)) {
      SubstTemplateTypeParmTypeLoc TL
        = TLB.push<SubstTemplateTypeParmTypeLoc>(T);
      TL.setNameLoc(IdInfo.IdentifierLoc);
    } else if (isa<SubstTemplateTypeParmPackType>(T)) {
      SubstTemplateTypeParmPackTypeLoc TL
        = TLB.push<SubstTemplateTypeParmPackTypeLoc>(T);
      TL.setNameLoc(IdInfo.IdentifierLoc);
    } else {
      llvm_unreachable("Unhandled TypeDecl node in nested-name-specifier");
    }