static DiagnosticMappingInfo GetDefaultDiagMappingInfo(unsigned DiagID) {
  DiagnosticMappingInfo Info = DiagnosticMappingInfo::Make(
    diag::MAP_FATAL, /*IsUser=*/false, /*IsPragma=*/false);

  if (const StaticDiagInfoRec *StaticInfo = GetDiagInfo(DiagID)) {
    Info.setMapping((diag::Mapping) StaticInfo->Mapping);

    if (StaticInfo->WarnNoWerror) {
      assert(Info.getMapping() == diag::MAP_WARNING &&
             "Unexpected mapping with no-Werror bit!");
      Info.setNoWarningAsError(true);
    }

    if (StaticInfo->WarnShowInSystemHeader) {
      assert(Info.getMapping() == diag::MAP_WARNING &&
             "Unexpected mapping with show-in-system-header bit!");
      Info.setShowInSystemHeader(true);
    }
  }

  return Info;
}
/// \brief This allows the client to specify that certain
/// warnings are ignored.  Notes can never be mapped, errors can only be
/// mapped to fatal, and WARNINGs and EXTENSIONs can be mapped arbitrarily.
///
/// \param The source location that this change of diagnostic state should
/// take affect. It can be null if we are setting the latest state.
void DiagnosticsEngine::setDiagnosticMapping(diag::kind Diag, diag::Mapping Map,
                                      SourceLocation L) {
  assert(Diag < diag::DIAG_UPPER_LIMIT &&
         "Can only map builtin diagnostics");
  assert((Diags->isBuiltinWarningOrExtension(Diag) ||
          (Map == diag::MAP_FATAL || Map == diag::MAP_ERROR)) &&
         "Cannot map errors into warnings!");
  assert(!DiagStatePoints.empty());

  bool isPragma = L.isValid();
  FullSourceLoc Loc(L, *SourceMgr);
  FullSourceLoc LastStateChangePos = DiagStatePoints.back().Loc;
  DiagnosticMappingInfo MappingInfo = DiagnosticMappingInfo::Make(
    Map, /*IsUser=*/true, isPragma);

  // If this is a pragma mapping, then set the diagnostic mapping flags so that
  // we override command line options.
  if (isPragma) {
    MappingInfo.setNoWarningAsError(true);
    MappingInfo.setNoErrorAsFatal(true);
  }

  // Common case; setting all the diagnostics of a group in one place.
  if (Loc.isInvalid() || Loc == LastStateChangePos) {
    GetCurDiagState()->setMappingInfo(Diag, MappingInfo);
    return;
  }

  // Another common case; modifying diagnostic state in a source location
  // after the previous one.
  if ((Loc.isValid() && LastStateChangePos.isInvalid()) ||
      LastStateChangePos.isBeforeInTranslationUnitThan(Loc)) {
    // A diagnostic pragma occurred, create a new DiagState initialized with
    // the current one and a new DiagStatePoint to record at which location
    // the new state became active.
    DiagStates.push_back(*GetCurDiagState());
    PushDiagStatePoint(&DiagStates.back(), Loc);
    GetCurDiagState()->setMappingInfo(Diag, MappingInfo);
    return;
  }

  // We allow setting the diagnostic state in random source order for
  // completeness but it should not be actually happening in normal practice.

  DiagStatePointsTy::iterator Pos = GetDiagStatePointForLoc(Loc);
  assert(Pos != DiagStatePoints.end());

  // Update all diagnostic states that are active after the given location.
  for (DiagStatePointsTy::iterator
         I = Pos+1, E = DiagStatePoints.end(); I != E; ++I) {
    GetCurDiagState()->setMappingInfo(Diag, MappingInfo);
  }

  // If the location corresponds to an existing point, just update its state.
  if (Pos->Loc == Loc) {
    GetCurDiagState()->setMappingInfo(Diag, MappingInfo);
    return;
  }

  // Create a new state/point and fit it into the vector of DiagStatePoints
  // so that the vector is always ordered according to location.
  Pos->Loc.isBeforeInTranslationUnitThan(Loc);
  DiagStates.push_back(*Pos->State);
  DiagState *NewState = &DiagStates.back();
  GetCurDiagState()->setMappingInfo(Diag, MappingInfo);
  DiagStatePoints.insert(Pos+1, DiagStatePoint(NewState,
                                               FullSourceLoc(Loc, *SourceMgr)));
}