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!");
}