llvm-project/clang/utils/TableGen/ClangDiagnosticsEmitter.cpp

//=- ClangDiagnosticsEmitter.cpp - Generate Clang diagnostics tables -*- C++ -*-
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// These tablegen backends emit Clang diagnostics tables.
//
//===----------------------------------------------------------------------===//

#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/PointerUnion.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/Twine.h"
#include "llvm/TableGen/Error.h"
#include "llvm/TableGen/Record.h"
#include "llvm/TableGen/StringToOffsetTable.h"
#include "llvm/TableGen/TableGenBackend.h"
#include <algorithm>
#include <cctype>
#include <functional>
#include <map>
#include <set>
using namespace llvm;

//===----------------------------------------------------------------------===//
// Diagnostic category computation code.
//===----------------------------------------------------------------------===//

namespace {
class DiagGroupParentMap {
  RecordKeeper &Records;
  std::map<const Record*, std::vector<Record*> > Mapping;
public:
  DiagGroupParentMap(RecordKeeper &records) : Records(records) {
    std::vector<Record*> DiagGroups
      = Records.getAllDerivedDefinitions("DiagGroup");
    for (unsigned i = 0, e = DiagGroups.size(); i != e; ++i) {
      std::vector<Record*> SubGroups =
        DiagGroups[i]->getValueAsListOfDefs("SubGroups");
      for (unsigned j = 0, e = SubGroups.size(); j != e; ++j)
        Mapping[SubGroups[j]].push_back(DiagGroups[i]);
    }
  }

  const std::vector<Record*> &getParents(const Record *Group) {
    return Mapping[Group];
  }
};
} // end anonymous namespace.

static std::string
getCategoryFromDiagGroup(const Record *Group,
                         DiagGroupParentMap &DiagGroupParents) {
  // If the DiagGroup has a category, return it.
  std::string CatName = Group->getValueAsString("CategoryName");
  if (!CatName.empty()) return CatName;

  // The diag group may the subgroup of one or more other diagnostic groups,
  // check these for a category as well.
  const std::vector<Record*> &Parents = DiagGroupParents.getParents(Group);
  for (unsigned i = 0, e = Parents.size(); i != e; ++i) {
    CatName = getCategoryFromDiagGroup(Parents[i], DiagGroupParents);
    if (!CatName.empty()) return CatName;
  }
  return "";
}

/// getDiagnosticCategory - Return the category that the specified diagnostic
/// lives in.
static std::string getDiagnosticCategory(const Record *R,
                                         DiagGroupParentMap &DiagGroupParents) {
  // If the diagnostic is in a group, and that group has a category, use it.
  if (DefInit *Group = dyn_cast<DefInit>(R->getValueInit("Group"))) {
    // Check the diagnostic's diag group for a category.
    std::string CatName = getCategoryFromDiagGroup(Group->getDef(),
                                                   DiagGroupParents);
    if (!CatName.empty()) return CatName;
  }

  // If the diagnostic itself has a category, get it.
  return R->getValueAsString("CategoryName");
}

namespace {
  class DiagCategoryIDMap {
    RecordKeeper &Records;
    StringMap<unsigned> CategoryIDs;
    std::vector<std::string> CategoryStrings;
  public:
    DiagCategoryIDMap(RecordKeeper &records) : Records(records) {
      DiagGroupParentMap ParentInfo(Records);

      // The zero'th category is "".
      CategoryStrings.push_back("");
      CategoryIDs[""] = 0;

      std::vector<Record*> Diags =
      Records.getAllDerivedDefinitions("Diagnostic");
      for (unsigned i = 0, e = Diags.size(); i != e; ++i) {
        std::string Category = getDiagnosticCategory(Diags[i], ParentInfo);
        if (Category.empty()) continue;  // Skip diags with no category.

        unsigned &ID = CategoryIDs[Category];
        if (ID != 0) continue;  // Already seen.

        ID = CategoryStrings.size();
        CategoryStrings.push_back(Category);
      }
    }

    unsigned getID(StringRef CategoryString) {
      return CategoryIDs[CategoryString];
    }

    typedef std::vector<std::string>::const_iterator const_iterator;
    const_iterator begin() const { return CategoryStrings.begin(); }
    const_iterator end() const { return CategoryStrings.end(); }
  };

  struct GroupInfo {
    std::vector<const Record*> DiagsInGroup;
    std::vector<std::string> SubGroups;
    unsigned IDNo;

    const Record *ExplicitDef;

    GroupInfo() : ExplicitDef(nullptr) {}
  };
} // end anonymous namespace.

static bool beforeThanCompare(const Record *LHS, const Record *RHS) {
  assert(!LHS->getLoc().empty() && !RHS->getLoc().empty());
  return
    LHS->getLoc().front().getPointer() < RHS->getLoc().front().getPointer();
}

static bool diagGroupBeforeByName(const Record *LHS, const Record *RHS) {
  return LHS->getValueAsString("GroupName") <
         RHS->getValueAsString("GroupName");
}

static bool beforeThanCompareGroups(const GroupInfo *LHS, const GroupInfo *RHS){
  assert(!LHS->DiagsInGroup.empty() && !RHS->DiagsInGroup.empty());
  return beforeThanCompare(LHS->DiagsInGroup.front(),
                           RHS->DiagsInGroup.front());
}

static SMRange findSuperClassRange(const Record *R, StringRef SuperName) {
  ArrayRef<std::pair<Record *, SMRange>> Supers = R->getSuperClasses();
  auto I = std::find_if(Supers.begin(), Supers.end(),
                        [&](const std::pair<Record *, SMRange> &SuperPair) {
                          return SuperPair.first->getName() == SuperName;
                        });
  return (I != Supers.end()) ? I->second : SMRange();
}

/// \brief Invert the 1-[0/1] mapping of diags to group into a one to many
/// mapping of groups to diags in the group.
static void groupDiagnostics(const std::vector<Record*> &Diags,
                             const std::vector<Record*> &DiagGroups,
                             std::map<std::string, GroupInfo> &DiagsInGroup) {

  for (unsigned i = 0, e = Diags.size(); i != e; ++i) {
    const Record *R = Diags[i];
    DefInit *DI = dyn_cast<DefInit>(R->getValueInit("Group"));
    if (!DI)
      continue;
    assert(R->getValueAsDef("Class")->getName() != "CLASS_NOTE" &&
           "Note can't be in a DiagGroup");
    std::string GroupName = DI->getDef()->getValueAsString("GroupName");
    DiagsInGroup[GroupName].DiagsInGroup.push_back(R);
  }

  typedef SmallPtrSet<GroupInfo *, 16> GroupSetTy;
  GroupSetTy ImplicitGroups;

  // Add all DiagGroup's to the DiagsInGroup list to make sure we pick up empty
  // groups (these are warnings that GCC supports that clang never produces).
  for (unsigned i = 0, e = DiagGroups.size(); i != e; ++i) {
    Record *Group = DiagGroups[i];
    GroupInfo &GI = DiagsInGroup[Group->getValueAsString("GroupName")];
    if (Group->isAnonymous()) {
      if (GI.DiagsInGroup.size() > 1)
        ImplicitGroups.insert(&GI);
    } else {
      if (GI.ExplicitDef)
        assert(GI.ExplicitDef == Group);
      else
        GI.ExplicitDef = Group;
    }

    std::vector<Record*> SubGroups = Group->getValueAsListOfDefs("SubGroups");
    for (unsigned j = 0, e = SubGroups.size(); j != e; ++j)
      GI.SubGroups.push_back(SubGroups[j]->getValueAsString("GroupName"));
  }

  // Assign unique ID numbers to the groups.
  unsigned IDNo = 0;
  for (std::map<std::string, GroupInfo>::iterator
       I = DiagsInGroup.begin(), E = DiagsInGroup.end(); I != E; ++I, ++IDNo)
    I->second.IDNo = IDNo;

  // Sort the implicit groups, so we can warn about them deterministically.
  SmallVector<GroupInfo *, 16> SortedGroups(ImplicitGroups.begin(),
                                            ImplicitGroups.end());
  for (SmallVectorImpl<GroupInfo *>::iterator I = SortedGroups.begin(),
                                              E = SortedGroups.end();
       I != E; ++I) {
    MutableArrayRef<const Record *> GroupDiags = (*I)->DiagsInGroup;
    std::sort(GroupDiags.begin(), GroupDiags.end(), beforeThanCompare);
  }
  std::sort(SortedGroups.begin(), SortedGroups.end(), beforeThanCompareGroups);

  // Warn about the same group being used anonymously in multiple places.
  for (SmallVectorImpl<GroupInfo *>::const_iterator I = SortedGroups.begin(),
                                                    E = SortedGroups.end();
       I != E; ++I) {
    ArrayRef<const Record *> GroupDiags = (*I)->DiagsInGroup;

    if ((*I)->ExplicitDef) {
      std::string Name = (*I)->ExplicitDef->getValueAsString("GroupName");
      for (ArrayRef<const Record *>::const_iterator DI = GroupDiags.begin(),
                                                    DE = GroupDiags.end();
           DI != DE; ++DI) {
        const DefInit *GroupInit = cast<DefInit>((*DI)->getValueInit("Group"));
        const Record *NextDiagGroup = GroupInit->getDef();
        if (NextDiagGroup == (*I)->ExplicitDef)
          continue;

        SMRange InGroupRange = findSuperClassRange(*DI, "InGroup");
        SmallString<64> Replacement;
        if (InGroupRange.isValid()) {
          Replacement += "InGroup<";
          Replacement += (*I)->ExplicitDef->getName();
          Replacement += ">";
        }
        SMFixIt FixIt(InGroupRange, Replacement);

        SrcMgr.PrintMessage(NextDiagGroup->getLoc().front(),
                            SourceMgr::DK_Error,
                            Twine("group '") + Name +
                              "' is referred to anonymously",
                            None,
                            InGroupRange.isValid() ? FixIt
                                                   : ArrayRef<SMFixIt>());
        SrcMgr.PrintMessage((*I)->ExplicitDef->getLoc().front(),
                            SourceMgr::DK_Note, "group defined here");
      }
    } else {
      // If there's no existing named group, we should just warn once and use
      // notes to list all the other cases.
      ArrayRef<const Record *>::const_iterator DI = GroupDiags.begin(),
                                               DE = GroupDiags.end();
      assert(DI != DE && "We only care about groups with multiple uses!");

      const DefInit *GroupInit = cast<DefInit>((*DI)->getValueInit("Group"));
      const Record *NextDiagGroup = GroupInit->getDef();
      std::string Name = NextDiagGroup->getValueAsString("GroupName");

      SMRange InGroupRange = findSuperClassRange(*DI, "InGroup");
      SrcMgr.PrintMessage(NextDiagGroup->getLoc().front(),
                          SourceMgr::DK_Error,
                          Twine("group '") + Name +
                            "' is referred to anonymously",
                          InGroupRange);

      for (++DI; DI != DE; ++DI) {
        GroupInit = cast<DefInit>((*DI)->getValueInit("Group"));
        InGroupRange = findSuperClassRange(*DI, "InGroup");
        SrcMgr.PrintMessage(GroupInit->getDef()->getLoc().front(),
                            SourceMgr::DK_Note, "also referenced here",
                            InGroupRange);
      }
    }
  }
}

//===----------------------------------------------------------------------===//
// Infer members of -Wpedantic.
//===----------------------------------------------------------------------===//

typedef std::vector<const Record *> RecordVec;
typedef llvm::DenseSet<const Record *> RecordSet;
typedef llvm::PointerUnion<RecordVec*, RecordSet*> VecOrSet;

namespace {
class InferPedantic {
  typedef llvm::DenseMap<const Record*,
                         std::pair<unsigned, Optional<unsigned> > > GMap;

  DiagGroupParentMap &DiagGroupParents;
  const std::vector<Record*> &Diags;
  const std::vector<Record*> DiagGroups;
  std::map<std::string, GroupInfo> &DiagsInGroup;
  llvm::DenseSet<const Record*> DiagsSet;
  GMap GroupCount;
public:
  InferPedantic(DiagGroupParentMap &DiagGroupParents,
                const std::vector<Record*> &Diags,
                const std::vector<Record*> &DiagGroups,
                std::map<std::string, GroupInfo> &DiagsInGroup)
  : DiagGroupParents(DiagGroupParents),
  Diags(Diags),
  DiagGroups(DiagGroups),
  DiagsInGroup(DiagsInGroup) {}

  /// Compute the set of diagnostics and groups that are immediately
  /// in -Wpedantic.
  void compute(VecOrSet DiagsInPedantic,
               VecOrSet GroupsInPedantic);

private:
  /// Determine whether a group is a subgroup of another group.
  bool isSubGroupOfGroup(const Record *Group,
                         llvm::StringRef RootGroupName);

  /// Determine if the diagnostic is an extension.
  bool isExtension(const Record *Diag);

  /// Determine if the diagnostic is off by default.
  bool isOffByDefault(const Record *Diag);

  /// Increment the count for a group, and transitively marked
  /// parent groups when appropriate.
  void markGroup(const Record *Group);

  /// Return true if the diagnostic is in a pedantic group.
  bool groupInPedantic(const Record *Group, bool increment = false);
};
} // end anonymous namespace

bool InferPedantic::isSubGroupOfGroup(const Record *Group,
                                      llvm::StringRef GName) {

  const std::string &GroupName = Group->getValueAsString("GroupName");
  if (GName == GroupName)
    return true;

  const std::vector<Record*> &Parents = DiagGroupParents.getParents(Group);
  for (unsigned i = 0, e = Parents.size(); i != e; ++i)
    if (isSubGroupOfGroup(Parents[i], GName))
      return true;

  return false;
}

/// Determine if the diagnostic is an extension.
bool InferPedantic::isExtension(const Record *Diag) {
  const std::string &ClsName = Diag->getValueAsDef("Class")->getName();
  return ClsName == "CLASS_EXTENSION";
}

bool InferPedantic::isOffByDefault(const Record *Diag) {
  const std::string &DefSeverity =
      Diag->getValueAsDef("DefaultSeverity")->getValueAsString("Name");
  return DefSeverity == "Ignored";
}

bool InferPedantic::groupInPedantic(const Record *Group, bool increment) {
  GMap::mapped_type &V = GroupCount[Group];
  // Lazily compute the threshold value for the group count.
  if (!V.second.hasValue()) {
    const GroupInfo &GI = DiagsInGroup[Group->getValueAsString("GroupName")];
    V.second = GI.SubGroups.size() + GI.DiagsInGroup.size();
  }

  if (increment)
    ++V.first;

  // Consider a group in -Wpendatic IFF if has at least one diagnostic
  // or subgroup AND all of those diagnostics and subgroups are covered
  // by -Wpedantic via our computation.
  return V.first != 0 && V.first == V.second.getValue();
}

void InferPedantic::markGroup(const Record *Group) {
  // If all the diagnostics and subgroups have been marked as being
  // covered by -Wpedantic, increment the count of parent groups.  Once the
  // group's count is equal to the number of subgroups and diagnostics in
  // that group, we can safely add this group to -Wpedantic.
  if (groupInPedantic(Group, /* increment */ true)) {
    const std::vector<Record*> &Parents = DiagGroupParents.getParents(Group);
    for (unsigned i = 0, e = Parents.size(); i != e; ++i)
      markGroup(Parents[i]);
  }
}

void InferPedantic::compute(VecOrSet DiagsInPedantic,
                            VecOrSet GroupsInPedantic) {
  // All extensions that are not on by default are implicitly in the
  // "pedantic" group.  For those that aren't explicitly included in -Wpedantic,
  // mark them for consideration to be included in -Wpedantic directly.
  for (unsigned i = 0, e = Diags.size(); i != e; ++i) {
    Record *R = Diags[i];
    if (isExtension(R) && isOffByDefault(R)) {
      DiagsSet.insert(R);
      if (DefInit *Group = dyn_cast<DefInit>(R->getValueInit("Group"))) {
        const Record *GroupRec = Group->getDef();
        if (!isSubGroupOfGroup(GroupRec, "pedantic")) {
          markGroup(GroupRec);
        }
      }
    }
  }

  // Compute the set of diagnostics that are directly in -Wpedantic.  We
  // march through Diags a second time to ensure the results are emitted
  // in deterministic order.
  for (unsigned i = 0, e = Diags.size(); i != e; ++i) {
    Record *R = Diags[i];
    if (!DiagsSet.count(R))
      continue;
    // Check if the group is implicitly in -Wpedantic.  If so,
    // the diagnostic should not be directly included in the -Wpedantic
    // diagnostic group.
    if (DefInit *Group = dyn_cast<DefInit>(R->getValueInit("Group")))
      if (groupInPedantic(Group->getDef()))
        continue;

    // The diagnostic is not included in a group that is (transitively) in
    // -Wpedantic.  Include it in -Wpedantic directly.
    if (RecordVec *V = DiagsInPedantic.dyn_cast<RecordVec*>())
      V->push_back(R);
    else {
      DiagsInPedantic.get<RecordSet*>()->insert(R);
    }
  }

  if (!GroupsInPedantic)
    return;

  // Compute the set of groups that are directly in -Wpedantic.  We
  // march through the groups to ensure the results are emitted
  /// in a deterministc order.
  for (unsigned i = 0, ei = DiagGroups.size(); i != ei; ++i) {
    Record *Group = DiagGroups[i];
    if (!groupInPedantic(Group))
      continue;

    unsigned ParentsInPedantic = 0;
    const std::vector<Record*> &Parents = DiagGroupParents.getParents(Group);
    for (unsigned j = 0, ej = Parents.size(); j != ej; ++j) {
      if (groupInPedantic(Parents[j]))
        ++ParentsInPedantic;
    }
    // If all the parents are in -Wpedantic, this means that this diagnostic
    // group will be indirectly included by -Wpedantic already.  In that
    // case, do not add it directly to -Wpedantic.  If the group has no
    // parents, obviously it should go into -Wpedantic.
    if (Parents.size() > 0 && ParentsInPedantic == Parents.size())
      continue;

    if (RecordVec *V = GroupsInPedantic.dyn_cast<RecordVec*>())
      V->push_back(Group);
    else {
      GroupsInPedantic.get<RecordSet*>()->insert(Group);
    }
  }
}

//===----------------------------------------------------------------------===//
// Warning Tables (.inc file) generation.
//===----------------------------------------------------------------------===//

static bool isError(const Record &Diag) {
  const std::string &ClsName = Diag.getValueAsDef("Class")->getName();
  return ClsName == "CLASS_ERROR";
}

static bool isRemark(const Record &Diag) {
  const std::string &ClsName = Diag.getValueAsDef("Class")->getName();
  return ClsName == "CLASS_REMARK";
}

/// ClangDiagsDefsEmitter - The top-level class emits .def files containing
/// declarations of Clang diagnostics.
namespace clang {
void EmitClangDiagsDefs(RecordKeeper &Records, raw_ostream &OS,
                        const std::string &Component) {
  // Write the #if guard
  if (!Component.empty()) {
    std::string ComponentName = StringRef(Component).upper();
    OS << "#ifdef " << ComponentName << "START\n";
    OS << "__" << ComponentName << "START = DIAG_START_" << ComponentName
       << ",\n";
    OS << "#undef " << ComponentName << "START\n";
    OS << "#endif\n\n";
  }

  const std::vector<Record*> &Diags =
    Records.getAllDerivedDefinitions("Diagnostic");

  std::vector<Record*> DiagGroups
    = Records.getAllDerivedDefinitions("DiagGroup");

  std::map<std::string, GroupInfo> DiagsInGroup;
  groupDiagnostics(Diags, DiagGroups, DiagsInGroup);

  DiagCategoryIDMap CategoryIDs(Records);
  DiagGroupParentMap DGParentMap(Records);

  // Compute the set of diagnostics that are in -Wpedantic.
  RecordSet DiagsInPedantic;
  InferPedantic inferPedantic(DGParentMap, Diags, DiagGroups, DiagsInGroup);
  inferPedantic.compute(&DiagsInPedantic, (RecordVec*)nullptr);

  for (unsigned i = 0, e = Diags.size(); i != e; ++i) {
    const Record &R = *Diags[i];

    // Check if this is an error that is accidentally in a warning
    // group.
    if (isError(R)) {
      if (DefInit *Group = dyn_cast<DefInit>(R.getValueInit("Group"))) {
        const Record *GroupRec = Group->getDef();
        const std::string &GroupName = GroupRec->getValueAsString("GroupName");
        PrintFatalError(R.getLoc(), "Error " + R.getName() +
                      " cannot be in a warning group [" + GroupName + "]");
      }
    }

    // Check that all remarks have an associated diagnostic group.
    if (isRemark(R)) {
      if (!isa<DefInit>(R.getValueInit("Group"))) {
        PrintFatalError(R.getLoc(), "Error " + R.getName() +
                                        " not in any diagnostic group");
      }
    }

    // Filter by component.
    if (!Component.empty() && Component != R.getValueAsString("Component"))
      continue;

    OS << "DIAG(" << R.getName() << ", ";
    OS << R.getValueAsDef("Class")->getName();
    OS << ", (unsigned)diag::Severity::"
       << R.getValueAsDef("DefaultSeverity")->getValueAsString("Name");

    // Description string.
    OS << ", \"";
    OS.write_escaped(R.getValueAsString("Text")) << '"';

    // Warning associated with the diagnostic. This is stored as an index into
    // the alphabetically sorted warning table.
    if (DefInit *DI = dyn_cast<DefInit>(R.getValueInit("Group"))) {
      std::map<std::string, GroupInfo>::iterator I =
          DiagsInGroup.find(DI->getDef()->getValueAsString("GroupName"));
      assert(I != DiagsInGroup.end());
      OS << ", " << I->second.IDNo;
    } else if (DiagsInPedantic.count(&R)) {
      std::map<std::string, GroupInfo>::iterator I =
        DiagsInGroup.find("pedantic");
      assert(I != DiagsInGroup.end() && "pedantic group not defined");
      OS << ", " << I->second.IDNo;
    } else {
      OS << ", 0";
    }

    // SFINAE response.
    OS << ", " << R.getValueAsDef("SFINAE")->getName();

    // Default warning has no Werror bit.
    if (R.getValueAsBit("WarningNoWerror"))
      OS << ", true";
    else
      OS << ", false";

    if (R.getValueAsBit("ShowInSystemHeader"))
      OS << ", true";
    else
      OS << ", false";

    // Category number.
    OS << ", " << CategoryIDs.getID(getDiagnosticCategory(&R, DGParentMap));
    OS << ")\n";
  }
}
} // end namespace clang

//===----------------------------------------------------------------------===//
// Warning Group Tables generation
//===----------------------------------------------------------------------===//

static std::string getDiagCategoryEnum(llvm::StringRef name) {
  if (name.empty())
    return "DiagCat_None";
  SmallString<256> enumName = llvm::StringRef("DiagCat_");
  for (llvm::StringRef::iterator I = name.begin(), E = name.end(); I != E; ++I)
    enumName += isalnum(*I) ? *I : '_';
  return enumName.str();
}

/// \brief Emit the array of diagnostic subgroups.
///
/// The array of diagnostic subgroups contains for each group a list of its
/// subgroups. The individual lists are separated by '-1'. Groups with no
/// subgroups are skipped.
///
/// \code
///   static const int16_t DiagSubGroups[] = {
///     /* Empty */ -1,
///     /* DiagSubGroup0 */ 142, -1,
///     /* DiagSubGroup13 */ 265, 322, 399, -1
///   }
/// \endcode
///
static void emitDiagSubGroups(std::map<std::string, GroupInfo> &DiagsInGroup,
                              RecordVec &GroupsInPedantic, raw_ostream &OS) {
  OS << "static const int16_t DiagSubGroups[] = {\n"
     << "  /* Empty */ -1,\n";
  for (auto const &I : DiagsInGroup) {
    const bool IsPedantic = I.first == "pedantic";

    const std::vector<std::string> &SubGroups = I.second.SubGroups;
    if (!SubGroups.empty() || (IsPedantic && !GroupsInPedantic.empty())) {
      OS << "  /* DiagSubGroup" << I.second.IDNo << " */ ";
      for (auto const &SubGroup : SubGroups) {
        std::map<std::string, GroupInfo>::const_iterator RI =
            DiagsInGroup.find(SubGroup);
        assert(RI != DiagsInGroup.end() && "Referenced without existing?");
        OS << RI->second.IDNo << ", ";
      }
      // Emit the groups implicitly in "pedantic".
      if (IsPedantic) {
        for (auto const &Group : GroupsInPedantic) {
          const std::string &GroupName = Group->getValueAsString("GroupName");
          std::map<std::string, GroupInfo>::const_iterator RI =
              DiagsInGroup.find(GroupName);
          assert(RI != DiagsInGroup.end() && "Referenced without existing?");
          OS << RI->second.IDNo << ", ";
        }
      }

      OS << "-1,\n";
    }
  }
  OS << "};\n\n";
}

/// \brief Emit the list of diagnostic arrays.
///
/// This data structure is a large array that contains itself arrays of varying
/// size. Each array represents a list of diagnostics. The different arrays are
/// separated by the value '-1'.
///
/// \code
///   static const int16_t DiagArrays[] = {
///     /* Empty */ -1,
///     /* DiagArray1 */ diag::warn_pragma_message,
///                      -1,
///     /* DiagArray2 */ diag::warn_abs_too_small,
///                      diag::warn_unsigned_abs,
///                      diag::warn_wrong_absolute_value_type,
///                      -1
///   };
/// \endcode
///
static void emitDiagArrays(std::map<std::string, GroupInfo> &DiagsInGroup,
                           RecordVec &DiagsInPedantic, raw_ostream &OS) {
  OS << "static const int16_t DiagArrays[] = {\n"
     << "  /* Empty */ -1,\n";
  for (auto const &I : DiagsInGroup) {
    const bool IsPedantic = I.first == "pedantic";

    const std::vector<const Record *> &V = I.second.DiagsInGroup;
    if (!V.empty() || (IsPedantic && !DiagsInPedantic.empty())) {
      OS << "  /* DiagArray" << I.second.IDNo << " */ ";
      for (auto *Record : V)
        OS << "diag::" << Record->getName() << ", ";
      // Emit the diagnostics implicitly in "pedantic".
      if (IsPedantic) {
        for (auto const &Diag : DiagsInPedantic)
          OS << "diag::" << Diag->getName() << ", ";
      }
      OS << "-1,\n";
    }
  }
  OS << "};\n\n";
}

/// \brief Emit a list of group names.
///
/// This creates a long string which by itself contains a list of pascal style
/// strings, which consist of a length byte directly followed by the string.
///
/// \code
///   static const char DiagGroupNames[] = {
///     \000\020#pragma-messages\t#warnings\020CFString-literal"
///   };
/// \endcode
static void emitDiagGroupNames(StringToOffsetTable &GroupNames,
                               raw_ostream &OS) {
  OS << "static const char DiagGroupNames[] = {\n";
  GroupNames.EmitString(OS);
  OS << "};\n\n";
}

/// \brief Emit diagnostic arrays and related data structures.
///
/// This creates the actual diagnostic array, an array of diagnostic subgroups
/// and an array of subgroup names.
///
/// \code
///  #ifdef GET_DIAG_ARRAYS
///     static const int16_t DiagArrays[];
///     static const int16_t DiagSubGroups[];
///     static const char DiagGroupNames[];
///  #endif
///  \endcode
static void emitAllDiagArrays(std::map<std::string, GroupInfo> &DiagsInGroup,
                              RecordVec &DiagsInPedantic,
                              RecordVec &GroupsInPedantic,
                              StringToOffsetTable &GroupNames,
                              raw_ostream &OS) {
  OS << "\n#ifdef GET_DIAG_ARRAYS\n";
  emitDiagArrays(DiagsInGroup, DiagsInPedantic, OS);
  emitDiagSubGroups(DiagsInGroup, GroupsInPedantic, OS);
  emitDiagGroupNames(GroupNames, OS);
  OS << "#endif // GET_DIAG_ARRAYS\n\n";
}

/// \brief Emit diagnostic table.
///
/// The table is sorted by the name of the diagnostic group. Each element
/// consists of the name of the diagnostic group (given as offset in the
/// group name table), a reference to a list of diagnostics (optional) and a
/// reference to a set of subgroups (optional).
///
/// \code
/// #ifdef GET_DIAG_TABLE
///  {/* abi */              159, /* DiagArray11 */ 19, /* Empty */          0},
///  {/* aggregate-return */ 180, /* Empty */        0, /* Empty */          0},
///  {/* all */              197, /* Empty */        0, /* DiagSubGroup13 */ 3},
///  {/* deprecated */       1981,/* DiagArray1 */ 348, /* DiagSubGroup3 */  9},
/// #endif
/// \endcode
static void emitDiagTable(std::map<std::string, GroupInfo> &DiagsInGroup,
                          RecordVec &DiagsInPedantic,
                          RecordVec &GroupsInPedantic,
                          StringToOffsetTable &GroupNames, raw_ostream &OS) {
  unsigned MaxLen = 0;

  for (auto const &I: DiagsInGroup)
    MaxLen = std::max(MaxLen, (unsigned)I.first.size());

  OS << "\n#ifdef GET_DIAG_TABLE\n";
  unsigned SubGroupIndex = 1, DiagArrayIndex = 1;
  for (auto const &I: DiagsInGroup) {
    // Group option string.
    OS << "  { /* ";
    if (I.first.find_first_not_of("abcdefghijklmnopqrstuvwxyz"
                                   "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
                                   "0123456789!@#$%^*-+=:?") !=
        std::string::npos)
      PrintFatalError("Invalid character in diagnostic group '" + I.first +
                      "'");
    OS << I.first << " */ " << std::string(MaxLen - I.first.size(), ' ');
    // Store a pascal-style length byte at the beginning of the string.
    std::string Name = char(I.first.size()) + I.first;
    OS << GroupNames.GetOrAddStringOffset(Name, false) << ", ";

    // Special handling for 'pedantic'.
    const bool IsPedantic = I.first == "pedantic";

    // Diagnostics in the group.
    const std::vector<const Record *> &V = I.second.DiagsInGroup;
    const bool hasDiags =
        !V.empty() || (IsPedantic && !DiagsInPedantic.empty());
    if (hasDiags) {
      OS << "/* DiagArray" << I.second.IDNo << " */ " << DiagArrayIndex
         << ", ";
      if (IsPedantic)
        DiagArrayIndex += DiagsInPedantic.size();
      DiagArrayIndex += V.size() + 1;
    } else {
      OS << "/* Empty */     0, ";
    }

    // Subgroups.
    const std::vector<std::string> &SubGroups = I.second.SubGroups;
    const bool hasSubGroups =
        !SubGroups.empty() || (IsPedantic && !GroupsInPedantic.empty());
    if (hasSubGroups) {
      OS << "/* DiagSubGroup" << I.second.IDNo << " */ " << SubGroupIndex;
      if (IsPedantic)
        SubGroupIndex += GroupsInPedantic.size();
      SubGroupIndex += SubGroups.size() + 1;
    } else {
      OS << "/* Empty */         0";
    }

    OS << " },\n";
  }
  OS << "#endif // GET_DIAG_TABLE\n\n";
}

/// \brief Emit the table of diagnostic categories.
///
/// The table has the form of macro calls that have two parameters. The
/// category's name as well as an enum that represents the category. The
/// table can be used by defining the macro 'CATEGORY' and including this
/// table right after.
///
/// \code
/// #ifdef GET_CATEGORY_TABLE
///   CATEGORY("Semantic Issue", DiagCat_Semantic_Issue)
///   CATEGORY("Lambda Issue", DiagCat_Lambda_Issue)
/// #endif
/// \endcode
static void emitCategoryTable(RecordKeeper &Records, raw_ostream &OS) {
  DiagCategoryIDMap CategoriesByID(Records);
  OS << "\n#ifdef GET_CATEGORY_TABLE\n";
  for (auto const &C : CategoriesByID)
    OS << "CATEGORY(\"" << C << "\", " << getDiagCategoryEnum(C) << ")\n";
  OS << "#endif // GET_CATEGORY_TABLE\n\n";
}

namespace clang {
void EmitClangDiagGroups(RecordKeeper &Records, raw_ostream &OS) {
  // Compute a mapping from a DiagGroup to all of its parents.
  DiagGroupParentMap DGParentMap(Records);

  std::vector<Record *> Diags = Records.getAllDerivedDefinitions("Diagnostic");

  std::vector<Record *> DiagGroups =
      Records.getAllDerivedDefinitions("DiagGroup");

  std::map<std::string, GroupInfo> DiagsInGroup;
  groupDiagnostics(Diags, DiagGroups, DiagsInGroup);

  // All extensions are implicitly in the "pedantic" group.  Record the
  // implicit set of groups in the "pedantic" group, and use this information
  // later when emitting the group information for Pedantic.
  RecordVec DiagsInPedantic;
  RecordVec GroupsInPedantic;
  InferPedantic inferPedantic(DGParentMap, Diags, DiagGroups, DiagsInGroup);
  inferPedantic.compute(&DiagsInPedantic, &GroupsInPedantic);

  StringToOffsetTable GroupNames;
  for (std::map<std::string, GroupInfo>::const_iterator
           I = DiagsInGroup.begin(),
           E = DiagsInGroup.end();
       I != E; ++I) {
    // Store a pascal-style length byte at the beginning of the string.
    std::string Name = char(I->first.size()) + I->first;
    GroupNames.GetOrAddStringOffset(Name, false);
  }

  emitAllDiagArrays(DiagsInGroup, DiagsInPedantic, GroupsInPedantic, GroupNames,
                    OS);
  emitDiagTable(DiagsInGroup, DiagsInPedantic, GroupsInPedantic, GroupNames,
                OS);
  emitCategoryTable(Records, OS);
}
} // end namespace clang

//===----------------------------------------------------------------------===//
// Diagnostic name index generation
//===----------------------------------------------------------------------===//

namespace {
struct RecordIndexElement
{
  RecordIndexElement() {}
  explicit RecordIndexElement(Record const &R):
    Name(R.getName()) {}

  std::string Name;
};
} // end anonymous namespace.

namespace clang {
void EmitClangDiagsIndexName(RecordKeeper &Records, raw_ostream &OS) {
  const std::vector<Record*> &Diags =
    Records.getAllDerivedDefinitions("Diagnostic");

  std::vector<RecordIndexElement> Index;
  Index.reserve(Diags.size());
  for (unsigned i = 0, e = Diags.size(); i != e; ++i) {
    const Record &R = *(Diags[i]);
    Index.push_back(RecordIndexElement(R));
  }

  std::sort(Index.begin(), Index.end(),
            [](const RecordIndexElement &Lhs,
               const RecordIndexElement &Rhs) { return Lhs.Name < Rhs.Name; });

  for (unsigned i = 0, e = Index.size(); i != e; ++i) {
    const RecordIndexElement &R = Index[i];

    OS << "DIAG_NAME_INDEX(" << R.Name << ")\n";
  }
}

//===----------------------------------------------------------------------===//
// Diagnostic documentation generation
//===----------------------------------------------------------------------===//

namespace docs {
namespace {

/// Diagnostic text, parsed into pieces.
struct DiagText {
  struct Piece {
    // This type and its derived classes are move-only.
    Piece() {}
    Piece(Piece &&O) {}
    Piece &operator=(Piece &&O) { return *this; }

    virtual void print(std::vector<std::string> &RST) = 0;
    virtual ~Piece() {}
  };
  struct TextPiece : Piece {
    StringRef Role;
    std::string Text;
    void print(std::vector<std::string> &RST) override;
  };
  struct PlaceholderPiece : Piece {
    int Index;
    void print(std::vector<std::string> &RST) override;
  };
  struct SelectPiece : Piece {
    SelectPiece() {}
    SelectPiece(SelectPiece &&O) noexcept : Options(std::move(O.Options)) {}
    std::vector<DiagText> Options;
    void print(std::vector<std::string> &RST) override;
  };

  std::vector<std::unique_ptr<Piece>> Pieces;

  DiagText();
  DiagText(DiagText &&O) noexcept : Pieces(std::move(O.Pieces)) {}

  DiagText(StringRef Text);
  DiagText(StringRef Kind, StringRef Text);

  template<typename P> void add(P Piece) {
    Pieces.push_back(llvm::make_unique<P>(std::move(Piece)));
  }
  void print(std::vector<std::string> &RST);
};

DiagText parseDiagText(StringRef &Text, bool Nested = false) {
  DiagText Parsed;

  while (!Text.empty()) {
    size_t End = (size_t)-2;
    do
      End = Nested ? Text.find_first_of("%|}", End + 2)
                   : Text.find_first_of('%', End + 2);
    while (End < Text.size() - 1 && Text[End] == '%' && Text[End + 1] == '%');

    if (End) {
      DiagText::TextPiece Piece;
      Piece.Role = "diagtext";
      Piece.Text = Text.slice(0, End);
      Parsed.add(std::move(Piece));
      Text = Text.slice(End, StringRef::npos);
      if (Text.empty()) break;
    }

    if (Text[0] == '|' || Text[0] == '}')
      break;

    // Drop the '%'.
    Text = Text.drop_front();

    // Extract the (optional) modifier.
    size_t ModLength = Text.find_first_of("0123456789{");
    StringRef Modifier = Text.slice(0, ModLength);
    Text = Text.slice(ModLength, StringRef::npos);

    // FIXME: Handle %ordinal here.
    if (Modifier == "select" || Modifier == "plural") {
      DiagText::SelectPiece Select;
      do {
        Text = Text.drop_front();
        if (Modifier == "plural")
          while (Text[0] != ':')
            Text = Text.drop_front();
        Select.Options.push_back(parseDiagText(Text, true));
        assert(!Text.empty() && "malformed %select");
      } while (Text.front() == '|');
      Parsed.add(std::move(Select));

      // Drop the trailing '}n'.
      Text = Text.drop_front(2);
      continue;
    }

    // For %diff, just take the second alternative (tree diagnostic). It would
    // be preferable to take the first one, and replace the $ with the suitable
    // placeholders.
    if (Modifier == "diff") {
      Text = Text.drop_front(); // '{'
      parseDiagText(Text, true);
      Text = Text.drop_front(); // '|'

      DiagText D = parseDiagText(Text, true);
      for (auto &P : D.Pieces)
        Parsed.Pieces.push_back(std::move(P));

      Text = Text.drop_front(4); // '}n,m'
      continue;
    }

    if (Modifier == "s") {
      Text = Text.drop_front();
      DiagText::SelectPiece Select;
      Select.Options.push_back(DiagText(""));
      Select.Options.push_back(DiagText("s"));
      Parsed.add(std::move(Select));
      continue;
    }

    assert(!Text.empty() && isdigit(Text[0]) && "malformed placeholder");
    DiagText::PlaceholderPiece Placeholder;
    Placeholder.Index = Text[0] - '0';
    Parsed.add(std::move(Placeholder));
    Text = Text.drop_front();
    continue;
  }
  return Parsed;
}

DiagText::DiagText() {}

DiagText::DiagText(StringRef Text) : DiagText(parseDiagText(Text, false)) {}

DiagText::DiagText(StringRef Kind, StringRef Text) : DiagText(parseDiagText(Text, false)) {
  TextPiece Prefix;
  Prefix.Role = Kind;
  Prefix.Text = Kind;
  Prefix.Text += ": ";
  Pieces.insert(Pieces.begin(),
                llvm::make_unique<TextPiece>(std::move(Prefix)));
}

void escapeRST(StringRef Str, std::string &Out) {
  for (auto K : Str) {
    if (StringRef("`*|_[]\\").count(K))
      Out.push_back('\\');
    Out.push_back(K);
  }
}

template<typename It> void padToSameLength(It Begin, It End) {
  size_t Width = 0;
  for (It I = Begin; I != End; ++I)
    Width = std::max(Width, I->size());
  for (It I = Begin; I != End; ++I)
    (*I) += std::string(Width - I->size(), ' ');
}

template<typename It> void makeTableRows(It Begin, It End) {
  if (Begin == End) return;
  padToSameLength(Begin, End);
  for (It I = Begin; I != End; ++I)
    *I = "|" + *I + "|";
}

void makeRowSeparator(std::string &Str) {
  for (char &K : Str)
    K = (K == '|' ? '+' : '-');
}

void DiagText::print(std::vector<std::string> &RST) {
  if (Pieces.empty()) {
    RST.push_back("");
    return;
  }

  if (Pieces.size() == 1)
    return Pieces[0]->print(RST);

  std::string EmptyLinePrefix;
  size_t Start = RST.size();
  bool HasMultipleLines = true;
  for (auto &P : Pieces) {
    std::vector<std::string> Lines;
    P->print(Lines);
    if (Lines.empty())
      continue;

    // We need a vertical separator if either this or the previous piece is a
    // multi-line piece, or this is the last piece.
    const char *Separator = (Lines.size() > 1 || HasMultipleLines) ? "|" : "";
    HasMultipleLines = Lines.size() > 1;

    if (Start + Lines.size() > RST.size())
      RST.resize(Start + Lines.size(), EmptyLinePrefix);

    padToSameLength(Lines.begin(), Lines.end());
    for (size_t I = 0; I != Lines.size(); ++I)
      RST[Start + I] += Separator + Lines[I];
    std::string Empty(Lines[0].size(), ' ');
    for (size_t I = Start + Lines.size(); I != RST.size(); ++I)
      RST[I] += Separator + Empty;
    EmptyLinePrefix += Separator + Empty;
  }
  for (size_t I = Start; I != RST.size(); ++I)
    RST[I] += "|";
  EmptyLinePrefix += "|";

  makeRowSeparator(EmptyLinePrefix);
  RST.insert(RST.begin() + Start, EmptyLinePrefix);
  RST.insert(RST.end(), EmptyLinePrefix);
}

void DiagText::TextPiece::print(std::vector<std::string> &RST) {
  RST.push_back("");
  auto &S = RST.back();

  StringRef T = Text;
  while (!T.empty() && T.front() == ' ') {
    RST.back() += " |nbsp| ";
    T = T.drop_front();
  }

  std::string Suffix;
  while (!T.empty() && T.back() == ' ') {
    Suffix += " |nbsp| ";
    T = T.drop_back();
  }

  if (!T.empty()) {
    S += ':';
    S += Role;
    S += ":`";
    escapeRST(T, S);
    S += '`';
  }
  
  S += Suffix;
}

void DiagText::PlaceholderPiece::print(std::vector<std::string> &RST) {
  RST.push_back(std::string(":placeholder:`") + char('A' + Index) + "`");
}

void DiagText::SelectPiece::print(std::vector<std::string> &RST) {
  std::vector<size_t> SeparatorIndexes;
  SeparatorIndexes.push_back(RST.size());
  RST.emplace_back();
  for (auto &O : Options) {
    O.print(RST);
    SeparatorIndexes.push_back(RST.size());
    RST.emplace_back();
  }

  makeTableRows(RST.begin() + SeparatorIndexes.front(),
                RST.begin() + SeparatorIndexes.back() + 1);
  for (size_t I : SeparatorIndexes)
    makeRowSeparator(RST[I]);
}

bool isRemarkGroup(const Record *DiagGroup,
                   const std::map<std::string, GroupInfo> &DiagsInGroup) {
  bool AnyRemarks = false, AnyNonRemarks = false;

  std::function<void(StringRef)> Visit = [&](StringRef GroupName) {
    auto &GroupInfo = DiagsInGroup.find(GroupName)->second;
    for (const Record *Diag : GroupInfo.DiagsInGroup)
      (isRemark(*Diag) ? AnyRemarks : AnyNonRemarks) = true;
    for (const auto &Name : GroupInfo.SubGroups)
      Visit(Name);
  };
  Visit(DiagGroup->getValueAsString("GroupName"));

  if (AnyRemarks && AnyNonRemarks)
    PrintFatalError(
        DiagGroup->getLoc(),
        "Diagnostic group contains both remark and non-remark diagnostics");
  return AnyRemarks;
}

std::string getDefaultSeverity(const Record *Diag) {
  return Diag->getValueAsDef("DefaultSeverity")->getValueAsString("Name");
}

std::set<std::string>
getDefaultSeverities(const Record *DiagGroup,
                     const std::map<std::string, GroupInfo> &DiagsInGroup) {
  std::set<std::string> States;

  std::function<void(StringRef)> Visit = [&](StringRef GroupName) {
    auto &GroupInfo = DiagsInGroup.find(GroupName)->second;
    for (const Record *Diag : GroupInfo.DiagsInGroup)
      States.insert(getDefaultSeverity(Diag));
    for (const auto &Name : GroupInfo.SubGroups)
      Visit(Name);
  };
  Visit(DiagGroup->getValueAsString("GroupName"));
  return States;
}

void writeHeader(StringRef Str, raw_ostream &OS, char Kind = '-') {
  OS << Str << "\n" << std::string(Str.size(), Kind) << "\n";
}

void writeDiagnosticText(StringRef Role, StringRef Text, raw_ostream &OS) {
  if (Text == "%0")
    OS << "The text of this diagnostic is not controlled by Clang.\n\n";
  else {
    std::vector<std::string> Out;
    DiagText(Role, Text).print(Out);
    for (auto &Line : Out)
      OS << Line << "\n";
    OS << "\n";
  }
}

}  // namespace
}  // namespace docs

void EmitClangDiagDocs(RecordKeeper &Records, raw_ostream &OS) {
  using namespace docs;

  // Get the documentation introduction paragraph.
  const Record *Documentation = Records.getDef("GlobalDocumentation");
  if (!Documentation) {
    PrintFatalError("The Documentation top-level definition is missing, "
                    "no documentation will be generated.");
    return;
  }

  OS << Documentation->getValueAsString("Intro") << "\n";

  std::vector<Record*> Diags =
      Records.getAllDerivedDefinitions("Diagnostic");
  std::vector<Record*> DiagGroups =
      Records.getAllDerivedDefinitions("DiagGroup");
  std::sort(DiagGroups.begin(), DiagGroups.end(), diagGroupBeforeByName);

  DiagGroupParentMap DGParentMap(Records);

  std::map<std::string, GroupInfo> DiagsInGroup;
  groupDiagnostics(Diags, DiagGroups, DiagsInGroup);

  // Compute the set of diagnostics that are in -Wpedantic.
  {
    RecordSet DiagsInPedanticSet;
    RecordSet GroupsInPedanticSet;
    InferPedantic inferPedantic(DGParentMap, Diags, DiagGroups, DiagsInGroup);
    inferPedantic.compute(&DiagsInPedanticSet, &GroupsInPedanticSet);
    auto &PedDiags = DiagsInGroup["pedantic"];
    // Put the diagnostics into a deterministic order.
    RecordVec DiagsInPedantic(DiagsInPedanticSet.begin(),
                              DiagsInPedanticSet.end());
    RecordVec GroupsInPedantic(GroupsInPedanticSet.begin(),
                               GroupsInPedanticSet.end());
    std::sort(DiagsInPedantic.begin(), DiagsInPedantic.end(),
              beforeThanCompare);
    std::sort(GroupsInPedantic.begin(), GroupsInPedantic.end(),
              beforeThanCompare);
    PedDiags.DiagsInGroup.insert(PedDiags.DiagsInGroup.end(),
                                 DiagsInPedantic.begin(),
                                 DiagsInPedantic.end());
    for (auto *Group : GroupsInPedantic)
      PedDiags.SubGroups.push_back(Group->getValueAsString("GroupName"));
  }

  // FIXME: Write diagnostic categories and link to diagnostic groups in each.

  // Write out the diagnostic groups.
  for (const Record *G : DiagGroups) {
    bool IsRemarkGroup = isRemarkGroup(G, DiagsInGroup);
    auto &GroupInfo = DiagsInGroup[G->getValueAsString("GroupName")];
    bool IsSynonym = GroupInfo.DiagsInGroup.empty() &&
                     GroupInfo.SubGroups.size() == 1;

    writeHeader(((IsRemarkGroup ? "-R" : "-W") +
                    G->getValueAsString("GroupName")).str(),
                OS);

    if (!IsSynonym) {
      // FIXME: Ideally, all the diagnostics in a group should have the same
      // default state, but that is not currently the case.
      auto DefaultSeverities = getDefaultSeverities(G, DiagsInGroup);
      if (!DefaultSeverities.empty() && !DefaultSeverities.count("Ignored")) {
        bool AnyNonErrors = DefaultSeverities.count("Warning") ||
                            DefaultSeverities.count("Remark");
        if (!AnyNonErrors)
          OS << "This diagnostic is an error by default, but the flag ``-Wno-"
             << G->getValueAsString("GroupName") << "`` can be used to disable "
             << "the error.\n\n";
        else
          OS << "This diagnostic is enabled by default.\n\n";
      } else if (DefaultSeverities.size() > 1) {
        OS << "Some of the diagnostics controlled by this flag are enabled "
           << "by default.\n\n";
      }
    }

    if (!GroupInfo.SubGroups.empty()) {
      if (IsSynonym)
        OS << "Synonym for ";
      else if (GroupInfo.DiagsInGroup.empty())
        OS << "Controls ";
      else
        OS << "Also controls ";

      bool First = true;
      std::sort(GroupInfo.SubGroups.begin(), GroupInfo.SubGroups.end());
      for (const auto &Name : GroupInfo.SubGroups) {
        if (!First) OS << ", ";
        OS << "`" << (IsRemarkGroup ? "-R" : "-W") << Name << "`_";
        First = false;
      }
      OS << ".\n\n";
    }

    if (!GroupInfo.DiagsInGroup.empty()) {
      OS << "**Diagnostic text:**\n\n";
      for (const Record *D : GroupInfo.DiagsInGroup) {
        auto Severity = getDefaultSeverity(D);
        Severity[0] = tolower(Severity[0]);
        if (Severity == "ignored")
          Severity = IsRemarkGroup ? "remark" : "warning";
        writeDiagnosticText(Severity, D->getValueAsString("Text"), OS);
      }
    }

    auto Doc = G->getValueAsString("Documentation");
    if (!Doc.empty())
      OS << Doc;
    else if (GroupInfo.SubGroups.empty() && GroupInfo.DiagsInGroup.empty())
      OS << "This diagnostic flag exists for GCC compatibility, and has no "
            "effect in Clang.\n";
    OS << "\n";
  }
}

} // end namespace clang