src/demangle/ItaniumDemangle.h

//===------------------------- ItaniumDemangle.h ----------------*- C++ -*-===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// Generic itanium demangler library.
// There are two copies of this file in the source tree.  The one under
// libcxxabi is the original and the one under llvm is the copy.  Use
// cp-to-llvm.sh to update the copy.  See README.txt for more details.
//
//===----------------------------------------------------------------------===//

#ifndef DEMANGLE_ITANIUMDEMANGLE_H
#define DEMANGLE_ITANIUMDEMANGLE_H

#include "DemangleConfig.h"
#include "StringViewExtras.h"
#include "Utility.h"
#include <__cxxabi_config.h>
#include <algorithm>
#include <cctype>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <limits>
#include <new>
#include <string_view>
#include <type_traits>
#include <utility>

#ifdef _LIBCXXABI_COMPILER_CLANG
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wunused-template"
#endif

DEMANGLE_NAMESPACE_BEGIN

template <class T, size_t N> class PODSmallVector {
  static_assert(std::is_trivial<T>::value,
                "T is required to be a trivial type");
  T *First = nullptr;
  T *Last = nullptr;
  T *Cap = nullptr;
  T Inline[N] = {};

  bool isInline() const { return First == Inline; }

  void clearInline() {
    First = Inline;
    Last = Inline;
    Cap = Inline + N;
  }

  void reserve(size_t NewCap) {
    size_t S = size();
    if (isInline()) {
      auto *Tmp = static_cast<T *>(std::malloc(NewCap * sizeof(T)));
      if (Tmp == nullptr)
        std::abort();
      std::copy(First, Last, Tmp);
      First = Tmp;
    } else {
      First = static_cast<T *>(std::realloc(First, NewCap * sizeof(T)));
      if (First == nullptr)
        std::abort();
    }
    Last = First + S;
    Cap = First + NewCap;
  }

public:
  PODSmallVector() : First(Inline), Last(First), Cap(Inline + N) {}

  PODSmallVector(const PODSmallVector &) = delete;
  PODSmallVector &operator=(const PODSmallVector &) = delete;

  PODSmallVector(PODSmallVector &&Other) : PODSmallVector() {
    if (Other.isInline()) {
      std::copy(Other.begin(), Other.end(), First);
      Last = First + Other.size();
      Other.clear();
      return;
    }

    First = Other.First;
    Last = Other.Last;
    Cap = Other.Cap;
    Other.clearInline();
  }

  PODSmallVector &operator=(PODSmallVector &&Other) {
    if (Other.isInline()) {
      if (!isInline()) {
        std::free(First);
        clearInline();
      }
      std::copy(Other.begin(), Other.end(), First);
      Last = First + Other.size();
      Other.clear();
      return *this;
    }

    if (isInline()) {
      First = Other.First;
      Last = Other.Last;
      Cap = Other.Cap;
      Other.clearInline();
      return *this;
    }

    std::swap(First, Other.First);
    std::swap(Last, Other.Last);
    std::swap(Cap, Other.Cap);
    Other.clear();
    return *this;
  }

  // NOLINTNEXTLINE(readability-identifier-naming)
  void push_back(const T &Elem) {
    if (Last == Cap)
      reserve(size() * 2);
    *Last++ = Elem;
  }

  // NOLINTNEXTLINE(readability-identifier-naming)
  void pop_back() {
    DEMANGLE_ASSERT(Last != First, "Popping empty vector!");
    --Last;
  }

  void shrinkToSize(size_t Index) {
    DEMANGLE_ASSERT(Index <= size(), "shrinkToSize() can't expand!");
    Last = First + Index;
  }

  T *begin() { return First; }
  T *end() { return Last; }

  bool empty() const { return First == Last; }
  size_t size() const { return static_cast<size_t>(Last - First); }
  T &back() {
    DEMANGLE_ASSERT(Last != First, "Calling back() on empty vector!");
    return *(Last - 1);
  }
  T &operator[](size_t Index) {
    DEMANGLE_ASSERT(Index < size(), "Invalid access!");
    return *(begin() + Index);
  }
  void clear() { Last = First; }

  ~PODSmallVector() {
    if (!isInline())
      std::free(First);
  }
};

// Base class of all AST nodes. The AST is built by the parser, then is
// traversed by the printLeft/Right functions to produce a demangled string.
class Node {
public:
  enum Kind : unsigned char {
#define NODE(NodeKind) K##NodeKind,
#include "ItaniumNodes.def"
  };

  /// Three-way bool to track a cached value. Unknown is possible if this node
  /// has an unexpanded parameter pack below it that may affect this cache.
  enum class Cache : unsigned char { Yes, No, Unknown, };

  /// Operator precedence for expression nodes. Used to determine required
  /// parens in expression emission.
  enum class Prec {
    Primary,
    Postfix,
    Unary,
    Cast,
    PtrMem,
    Multiplicative,
    Additive,
    Shift,
    Spaceship,
    Relational,
    Equality,
    And,
    Xor,
    Ior,
    AndIf,
    OrIf,
    Conditional,
    Assign,
    Comma,
    Default,
  };

private:
  Kind K;

  Prec Precedence : 6;

protected:
  /// Tracks if this node has a component on its right side, in which case we
  /// need to call printRight.
  Cache RHSComponentCache : 2;

  /// Track if this node is a (possibly qualified) array type. This can affect
  /// how we format the output string.
  Cache ArrayCache : 2;

  /// Track if this node is a (possibly qualified) function type. This can
  /// affect how we format the output string.
  Cache FunctionCache : 2;

public:
  Node(Kind K_, Prec Precedence_ = Prec::Primary,
       Cache RHSComponentCache_ = Cache::No, Cache ArrayCache_ = Cache::No,
       Cache FunctionCache_ = Cache::No)
      : K(K_), Precedence(Precedence_), RHSComponentCache(RHSComponentCache_),
        ArrayCache(ArrayCache_), FunctionCache(FunctionCache_) {}
  Node(Kind K_, Cache RHSComponentCache_, Cache ArrayCache_ = Cache::No,
       Cache FunctionCache_ = Cache::No)
      : Node(K_, Prec::Primary, RHSComponentCache_, ArrayCache_,
             FunctionCache_) {}

  /// Visit the most-derived object corresponding to this object.
  template<typename Fn> void visit(Fn F) const;

  // The following function is provided by all derived classes:
  //
  // Call F with arguments that, when passed to the constructor of this node,
  // would construct an equivalent node.
  //template<typename Fn> void match(Fn F) const;

  bool hasRHSComponent(OutputBuffer &OB) const {
    if (RHSComponentCache != Cache::Unknown)
      return RHSComponentCache == Cache::Yes;
    return hasRHSComponentSlow(OB);
  }

  bool hasArray(OutputBuffer &OB) const {
    if (ArrayCache != Cache::Unknown)
      return ArrayCache == Cache::Yes;
    return hasArraySlow(OB);
  }

  bool hasFunction(OutputBuffer &OB) const {
    if (FunctionCache != Cache::Unknown)
      return FunctionCache == Cache::Yes;
    return hasFunctionSlow(OB);
  }

  Kind getKind() const { return K; }

  Prec getPrecedence() const { return Precedence; }
  Cache getRHSComponentCache() const { return RHSComponentCache; }
  Cache getArrayCache() const { return ArrayCache; }
  Cache getFunctionCache() const { return FunctionCache; }

  virtual bool hasRHSComponentSlow(OutputBuffer &) const { return false; }
  virtual bool hasArraySlow(OutputBuffer &) const { return false; }
  virtual bool hasFunctionSlow(OutputBuffer &) const { return false; }

  // Dig through "glue" nodes like ParameterPack and ForwardTemplateReference to
  // get at a node that actually represents some concrete syntax.
  virtual const Node *getSyntaxNode(OutputBuffer &) const { return this; }

  // Print this node as an expression operand, surrounding it in parentheses if
  // its precedence is [Strictly] weaker than P.
  void printAsOperand(OutputBuffer &OB, Prec P = Prec::Default,
                      bool StrictlyWorse = false) const {
    bool Paren =
        unsigned(getPrecedence()) >= unsigned(P) + unsigned(StrictlyWorse);
    if (Paren)
      OB.printOpen();
    print(OB);
    if (Paren)
      OB.printClose();
  }

  void print(OutputBuffer &OB) const {
    printLeft(OB);
    if (RHSComponentCache != Cache::No)
      printRight(OB);
  }

  // Print the "left" side of this Node into OutputBuffer.
  virtual void printLeft(OutputBuffer &) const = 0;

  // Print the "right". This distinction is necessary to represent C++ types
  // that appear on the RHS of their subtype, such as arrays or functions.
  // Since most types don't have such a component, provide a default
  // implementation.
  virtual void printRight(OutputBuffer &) const {}

  virtual std::string_view getBaseName() const { return {}; }

  // Silence compiler warnings, this dtor will never be called.
  virtual ~Node() = default;

#ifndef NDEBUG
  DEMANGLE_DUMP_METHOD void dump() const;
#endif
};

class NodeArray {
  Node **Elements;
  size_t NumElements;

public:
  NodeArray() : Elements(nullptr), NumElements(0) {}
  NodeArray(Node **Elements_, size_t NumElements_)
      : Elements(Elements_), NumElements(NumElements_) {}

  bool empty() const { return NumElements == 0; }
  size_t size() const { return NumElements; }

  Node **begin() const { return Elements; }
  Node **end() const { return Elements + NumElements; }

  Node *operator[](size_t Idx) const { return Elements[Idx]; }

  void printWithComma(OutputBuffer &OB) const {
    bool FirstElement = true;
    for (size_t Idx = 0; Idx != NumElements; ++Idx) {
      size_t BeforeComma = OB.getCurrentPosition();
      if (!FirstElement)
        OB += ", ";
      size_t AfterComma = OB.getCurrentPosition();
      Elements[Idx]->printAsOperand(OB, Node::Prec::Comma);

      // Elements[Idx] is an empty parameter pack expansion, we should erase the
      // comma we just printed.
      if (AfterComma == OB.getCurrentPosition()) {
        OB.setCurrentPosition(BeforeComma);
        continue;
      }

      FirstElement = false;
    }
  }
};

struct NodeArrayNode : Node {
  NodeArray Array;
  NodeArrayNode(NodeArray Array_) : Node(KNodeArrayNode), Array(Array_) {}

  template<typename Fn> void match(Fn F) const { F(Array); }

  void printLeft(OutputBuffer &OB) const override { Array.printWithComma(OB); }
};

class DotSuffix final : public Node {
  const Node *Prefix;
  const std::string_view Suffix;

public:
  DotSuffix(const Node *Prefix_, std::string_view Suffix_)
      : Node(KDotSuffix), Prefix(Prefix_), Suffix(Suffix_) {}

  template<typename Fn> void match(Fn F) const { F(Prefix, Suffix); }

  void printLeft(OutputBuffer &OB) const override {
    Prefix->print(OB);
    OB += " (";
    OB += Suffix;
    OB += ")";
  }
};

class VendorExtQualType final : public Node {
  const Node *Ty;
  std::string_view Ext;
  const Node *TA;

public:
  VendorExtQualType(const Node *Ty_, std::string_view Ext_, const Node *TA_)
      : Node(KVendorExtQualType), Ty(Ty_), Ext(Ext_), TA(TA_) {}

  const Node *getTy() const { return Ty; }
  std::string_view getExt() const { return Ext; }
  const Node *getTA() const { return TA; }

  template <typename Fn> void match(Fn F) const { F(Ty, Ext, TA); }

  void printLeft(OutputBuffer &OB) const override {
    Ty->print(OB);
    OB += " ";
    OB += Ext;
    if (TA != nullptr)
      TA->print(OB);
  }
};

enum FunctionRefQual : unsigned char {
  FrefQualNone,
  FrefQualLValue,
  FrefQualRValue,
};

enum Qualifiers {
  QualNone = 0,
  QualConst = 0x1,
  QualVolatile = 0x2,
  QualRestrict = 0x4,
};

inline Qualifiers operator|=(Qualifiers &Q1, Qualifiers Q2) {
  return Q1 = static_cast<Qualifiers>(Q1 | Q2);
}

class QualType final : public Node {
protected:
  const Qualifiers Quals;
  const Node *Child;

  void printQuals(OutputBuffer &OB) const {
    if (Quals & QualConst)
      OB += " const";
    if (Quals & QualVolatile)
      OB += " volatile";
    if (Quals & QualRestrict)
      OB += " restrict";
  }

public:
  QualType(const Node *Child_, Qualifiers Quals_)
      : Node(KQualType, Child_->getRHSComponentCache(), Child_->getArrayCache(),
             Child_->getFunctionCache()),
        Quals(Quals_), Child(Child_) {}

  Qualifiers getQuals() const { return Quals; }
  const Node *getChild() const { return Child; }

  template<typename Fn> void match(Fn F) const { F(Child, Quals); }

  bool hasRHSComponentSlow(OutputBuffer &OB) const override {
    return Child->hasRHSComponent(OB);
  }
  bool hasArraySlow(OutputBuffer &OB) const override {
    return Child->hasArray(OB);
  }
  bool hasFunctionSlow(OutputBuffer &OB) const override {
    return Child->hasFunction(OB);
  }

  void printLeft(OutputBuffer &OB) const override {
    Child->printLeft(OB);
    printQuals(OB);
  }

  void printRight(OutputBuffer &OB) const override { Child->printRight(OB); }
};

class ConversionOperatorType final : public Node {
  const Node *Ty;

public:
  ConversionOperatorType(const Node *Ty_)
      : Node(KConversionOperatorType), Ty(Ty_) {}

  template<typename Fn> void match(Fn F) const { F(Ty); }

  void printLeft(OutputBuffer &OB) const override {
    OB += "operator ";
    Ty->print(OB);
  }
};

class PostfixQualifiedType final : public Node {
  const Node *Ty;
  const std::string_view Postfix;

public:
  PostfixQualifiedType(const Node *Ty_, std::string_view Postfix_)
      : Node(KPostfixQualifiedType), Ty(Ty_), Postfix(Postfix_) {}

  template<typename Fn> void match(Fn F) const { F(Ty, Postfix); }

  void printLeft(OutputBuffer &OB) const override {
    Ty->printLeft(OB);
    OB += Postfix;
  }
};

class NameType final : public Node {
  const std::string_view Name;

public:
  NameType(std::string_view Name_) : Node(KNameType), Name(Name_) {}

  template<typename Fn> void match(Fn F) const { F(Name); }

  std::string_view getName() const { return Name; }
  std::string_view getBaseName() const override { return Name; }

  void printLeft(OutputBuffer &OB) const override { OB += Name; }
};

class BitIntType final : public Node {
  const Node *Size;
  bool Signed;

public:
  BitIntType(const Node *Size_, bool Signed_)
      : Node(KBitIntType), Size(Size_), Signed(Signed_) {}

  template <typename Fn> void match(Fn F) const { F(Size, Signed); }

  void printLeft(OutputBuffer &OB) const override {
    if (!Signed)
      OB += "unsigned ";
    OB += "_BitInt";
    OB.printOpen();
    Size->printAsOperand(OB);
    OB.printClose();
  }
};

class ElaboratedTypeSpefType : public Node {
  std::string_view Kind;
  Node *Child;
public:
  ElaboratedTypeSpefType(std::string_view Kind_, Node *Child_)
      : Node(KElaboratedTypeSpefType), Kind(Kind_), Child(Child_) {}

  template<typename Fn> void match(Fn F) const { F(Kind, Child); }

  void printLeft(OutputBuffer &OB) const override {
    OB += Kind;
    OB += ' ';
    Child->print(OB);
  }
};

class TransformedType : public Node {
  std::string_view Transform;
  Node *BaseType;
public:
  TransformedType(std::string_view Transform_, Node *BaseType_)
      : Node(KTransformedType), Transform(Transform_), BaseType(BaseType_) {}

  template<typename Fn> void match(Fn F) const { F(Transform, BaseType); }

  void printLeft(OutputBuffer &OB) const override {
    OB += Transform;
    OB += '(';
    BaseType->print(OB);
    OB += ')';
  }
};

struct AbiTagAttr : Node {
  Node *Base;
  std::string_view Tag;

  AbiTagAttr(Node *Base_, std::string_view Tag_)
      : Node(KAbiTagAttr, Base_->getRHSComponentCache(), Base_->getArrayCache(),
             Base_->getFunctionCache()),
        Base(Base_), Tag(Tag_) {}

  template<typename Fn> void match(Fn F) const { F(Base, Tag); }

  std::string_view getBaseName() const override { return Base->getBaseName(); }

  void printLeft(OutputBuffer &OB) const override {
    Base->printLeft(OB);
    OB += "[abi:";
    OB += Tag;
    OB += "]";
  }
};

class EnableIfAttr : public Node {
  NodeArray Conditions;
public:
  EnableIfAttr(NodeArray Conditions_)
      : Node(KEnableIfAttr), Conditions(Conditions_) {}

  template<typename Fn> void match(Fn F) const { F(Conditions); }

  void printLeft(OutputBuffer &OB) const override {
    OB += " [enable_if:";
    Conditions.printWithComma(OB);
    OB += ']';
  }
};

class ObjCProtoName : public Node {
  const Node *Ty;
  std::string_view Protocol;

  friend class PointerType;

public:
  ObjCProtoName(const Node *Ty_, std::string_view Protocol_)
      : Node(KObjCProtoName), Ty(Ty_), Protocol(Protocol_) {}

  template<typename Fn> void match(Fn F) const { F(Ty, Protocol); }

  bool isObjCObject() const {
    return Ty->getKind() == KNameType &&
           static_cast<const NameType *>(Ty)->getName() == "objc_object";
  }

  void printLeft(OutputBuffer &OB) const override {
    Ty->print(OB);
    OB += "<";
    OB += Protocol;
    OB += ">";
  }
};

class PointerType final : public Node {
  const Node *Pointee;

public:
  PointerType(const Node *Pointee_)
      : Node(KPointerType, Pointee_->getRHSComponentCache()),
        Pointee(Pointee_) {}

  const Node *getPointee() const { return Pointee; }

  template<typename Fn> void match(Fn F) const { F(Pointee); }

  bool hasRHSComponentSlow(OutputBuffer &OB) const override {
    return Pointee->hasRHSComponent(OB);
  }

  void printLeft(OutputBuffer &OB) const override {
    // We rewrite objc_object<SomeProtocol>* into id<SomeProtocol>.
    if (Pointee->getKind() != KObjCProtoName ||
        !static_cast<const ObjCProtoName *>(Pointee)->isObjCObject()) {
      Pointee->printLeft(OB);
      if (Pointee->hasArray(OB))
        OB += " ";
      if (Pointee->hasArray(OB) || Pointee->hasFunction(OB))
        OB += "(";
      OB += "*";
    } else {
      const auto *objcProto = static_cast<const ObjCProtoName *>(Pointee);
      OB += "id<";
      OB += objcProto->Protocol;
      OB += ">";
    }
  }

  void printRight(OutputBuffer &OB) const override {
    if (Pointee->getKind() != KObjCProtoName ||
        !static_cast<const ObjCProtoName *>(Pointee)->isObjCObject()) {
      if (Pointee->hasArray(OB) || Pointee->hasFunction(OB))
        OB += ")";
      Pointee->printRight(OB);
    }
  }
};

enum class ReferenceKind {
  LValue,
  RValue,
};

// Represents either a LValue or an RValue reference type.
class ReferenceType : public Node {
  const Node *Pointee;
  ReferenceKind RK;

  mutable bool Printing = false;

  // Dig through any refs to refs, collapsing the ReferenceTypes as we go. The
  // rule here is rvalue ref to rvalue ref collapses to a rvalue ref, and any
  // other combination collapses to a lvalue ref.
  //
  // A combination of a TemplateForwardReference and a back-ref Substitution
  // from an ill-formed string may have created a cycle; use cycle detection to
  // avoid looping forever.
  std::pair<ReferenceKind, const Node *> collapse(OutputBuffer &OB) const {
    auto SoFar = std::make_pair(RK, Pointee);
    // Track the chain of nodes for the Floyd's 'tortoise and hare'
    // cycle-detection algorithm, since getSyntaxNode(S) is impure
    PODSmallVector<const Node *, 8> Prev;
    for (;;) {
      const Node *SN = SoFar.second->getSyntaxNode(OB);
      if (SN->getKind() != KReferenceType)
        break;
      auto *RT = static_cast<const ReferenceType *>(SN);
      SoFar.second = RT->Pointee;
      SoFar.first = std::min(SoFar.first, RT->RK);

      // The middle of Prev is the 'slow' pointer moving at half speed
      Prev.push_back(SoFar.second);
      if (Prev.size() > 1 && SoFar.second == Prev[(Prev.size() - 1) / 2]) {
        // Cycle detected
        SoFar.second = nullptr;
        break;
      }
    }
    return SoFar;
  }

public:
  ReferenceType(const Node *Pointee_, ReferenceKind RK_)
      : Node(KReferenceType, Pointee_->getRHSComponentCache()),
        Pointee(Pointee_), RK(RK_) {}

  template<typename Fn> void match(Fn F) const { F(Pointee, RK); }

  bool hasRHSComponentSlow(OutputBuffer &OB) const override {
    return Pointee->hasRHSComponent(OB);
  }

  void printLeft(OutputBuffer &OB) const override {
    if (Printing)
      return;
    ScopedOverride<bool> SavePrinting(Printing, true);
    std::pair<ReferenceKind, const Node *> Collapsed = collapse(OB);
    if (!Collapsed.second)
      return;
    Collapsed.second->printLeft(OB);
    if (Collapsed.second->hasArray(OB))
      OB += " ";
    if (Collapsed.second->hasArray(OB) || Collapsed.second->hasFunction(OB))
      OB += "(";

    OB += (Collapsed.first == ReferenceKind::LValue ? "&" : "&&");
  }
  void printRight(OutputBuffer &OB) const override {
    if (Printing)
      return;
    ScopedOverride<bool> SavePrinting(Printing, true);
    std::pair<ReferenceKind, const Node *> Collapsed = collapse(OB);
    if (!Collapsed.second)
      return;
    if (Collapsed.second->hasArray(OB) || Collapsed.second->hasFunction(OB))
      OB += ")";
    Collapsed.second->printRight(OB);
  }
};

class PointerToMemberType final : public Node {
  const Node *ClassType;
  const Node *MemberType;

public:
  PointerToMemberType(const Node *ClassType_, const Node *MemberType_)
      : Node(KPointerToMemberType, MemberType_->getRHSComponentCache()),
        ClassType(ClassType_), MemberType(MemberType_) {}

  template<typename Fn> void match(Fn F) const { F(ClassType, MemberType); }

  bool hasRHSComponentSlow(OutputBuffer &OB) const override {
    return MemberType->hasRHSComponent(OB);
  }

  void printLeft(OutputBuffer &OB) const override {
    MemberType->printLeft(OB);
    if (MemberType->hasArray(OB) || MemberType->hasFunction(OB))
      OB += "(";
    else
      OB += " ";
    ClassType->print(OB);
    OB += "::*";
  }

  void printRight(OutputBuffer &OB) const override {
    if (MemberType->hasArray(OB) || MemberType->hasFunction(OB))
      OB += ")";
    MemberType->printRight(OB);
  }
};

class ArrayType final : public Node {
  const Node *Base;
  Node *Dimension;

public:
  ArrayType(const Node *Base_, Node *Dimension_)
      : Node(KArrayType,
             /*RHSComponentCache=*/Cache::Yes,
             /*ArrayCache=*/Cache::Yes),
        Base(Base_), Dimension(Dimension_) {}

  template<typename Fn> void match(Fn F) const { F(Base, Dimension); }

  bool hasRHSComponentSlow(OutputBuffer &) const override { return true; }
  bool hasArraySlow(OutputBuffer &) const override { return true; }

  void printLeft(OutputBuffer &OB) const override { Base->printLeft(OB); }

  void printRight(OutputBuffer &OB) const override {
    if (OB.back() != ']')
      OB += " ";
    OB += "[";
    if (Dimension)
      Dimension->print(OB);
    OB += "]";
    Base->printRight(OB);
  }
};

class FunctionType final : public Node {
  const Node *Ret;
  NodeArray Params;
  Qualifiers CVQuals;
  FunctionRefQual RefQual;
  const Node *ExceptionSpec;

public:
  FunctionType(const Node *Ret_, NodeArray Params_, Qualifiers CVQuals_,
               FunctionRefQual RefQual_, const Node *ExceptionSpec_)
      : Node(KFunctionType,
             /*RHSComponentCache=*/Cache::Yes, /*ArrayCache=*/Cache::No,
             /*FunctionCache=*/Cache::Yes),
        Ret(Ret_), Params(Params_), CVQuals(CVQuals_), RefQual(RefQual_),
        ExceptionSpec(ExceptionSpec_) {}

  template<typename Fn> void match(Fn F) const {
    F(Ret, Params, CVQuals, RefQual, ExceptionSpec);
  }

  bool hasRHSComponentSlow(OutputBuffer &) const override { return true; }
  bool hasFunctionSlow(OutputBuffer &) const override { return true; }

  // Handle C++'s ... quirky decl grammar by using the left & right
  // distinction. Consider:
  //   int (*f(float))(char) {}
  // f is a function that takes a float and returns a pointer to a function
  // that takes a char and returns an int. If we're trying to print f, start
  // by printing out the return types's left, then print our parameters, then
  // finally print right of the return type.
  void printLeft(OutputBuffer &OB) const override {
    Ret->printLeft(OB);
    OB += " ";
  }

  void printRight(OutputBuffer &OB) const override {
    OB.printOpen();
    Params.printWithComma(OB);
    OB.printClose();
    Ret->printRight(OB);

    if (CVQuals & QualConst)
      OB += " const";
    if (CVQuals & QualVolatile)
      OB += " volatile";
    if (CVQuals & QualRestrict)
      OB += " restrict";

    if (RefQual == FrefQualLValue)
      OB += " &";
    else if (RefQual == FrefQualRValue)
      OB += " &&";

    if (ExceptionSpec != nullptr) {
      OB += ' ';
      ExceptionSpec->print(OB);
    }
  }
};

class NoexceptSpec : public Node {
  const Node *E;
public:
  NoexceptSpec(const Node *E_) : Node(KNoexceptSpec), E(E_) {}

  template<typename Fn> void match(Fn F) const { F(E); }

  void printLeft(OutputBuffer &OB) const override {
    OB += "noexcept";
    OB.printOpen();
    E->printAsOperand(OB);
    OB.printClose();
  }
};

class DynamicExceptionSpec : public Node {
  NodeArray Types;
public:
  DynamicExceptionSpec(NodeArray Types_)
      : Node(KDynamicExceptionSpec), Types(Types_) {}

  template<typename Fn> void match(Fn F) const { F(Types); }

  void printLeft(OutputBuffer &OB) const override {
    OB += "throw";
    OB.printOpen();
    Types.printWithComma(OB);
    OB.printClose();
  }
};

/// Represents the explicitly named object parameter.
/// E.g.,
/// \code{.cpp}
///   struct Foo {
///     void bar(this Foo && self);
///   };
/// \endcode
class ExplicitObjectParameter final : public Node {
  Node *Base;

public:
  ExplicitObjectParameter(Node *Base_)
      : Node(KExplicitObjectParameter), Base(Base_) {
    DEMANGLE_ASSERT(
        Base != nullptr,
        "Creating an ExplicitObjectParameter without a valid Base Node.");
  }

  template <typename Fn> void match(Fn F) const { F(Base); }

  void printLeft(OutputBuffer &OB) const override {
    OB += "this ";
    Base->print(OB);
  }
};

class FunctionEncoding final : public Node {
  const Node *Ret;
  const Node *Name;
  NodeArray Params;
  const Node *Attrs;
  const Node *Requires;
  Qualifiers CVQuals;
  FunctionRefQual RefQual;

public:
  FunctionEncoding(const Node *Ret_, const Node *Name_, NodeArray Params_,
                   const Node *Attrs_, const Node *Requires_,
                   Qualifiers CVQuals_, FunctionRefQual RefQual_)
      : Node(KFunctionEncoding,
             /*RHSComponentCache=*/Cache::Yes, /*ArrayCache=*/Cache::No,
             /*FunctionCache=*/Cache::Yes),
        Ret(Ret_), Name(Name_), Params(Params_), Attrs(Attrs_),
        Requires(Requires_), CVQuals(CVQuals_), RefQual(RefQual_) {}

  template<typename Fn> void match(Fn F) const {
    F(Ret, Name, Params, Attrs, Requires, CVQuals, RefQual);
  }

  Qualifiers getCVQuals() const { return CVQuals; }
  FunctionRefQual getRefQual() const { return RefQual; }
  NodeArray getParams() const { return Params; }
  const Node *getReturnType() const { return Ret; }

  bool hasRHSComponentSlow(OutputBuffer &) const override { return true; }
  bool hasFunctionSlow(OutputBuffer &) const override { return true; }

  const Node *getName() const { return Name; }

  void printLeft(OutputBuffer &OB) const override {
    if (Ret) {
      Ret->printLeft(OB);
      if (!Ret->hasRHSComponent(OB))
        OB += " ";
    }
    Name->print(OB);
  }

  void printRight(OutputBuffer &OB) const override {
    OB.printOpen();
    Params.printWithComma(OB);
    OB.printClose();
    if (Ret)
      Ret->printRight(OB);

    if (CVQuals & QualConst)
      OB += " const";
    if (CVQuals & QualVolatile)
      OB += " volatile";
    if (CVQuals & QualRestrict)
      OB += " restrict";

    if (RefQual == FrefQualLValue)
      OB += " &";
    else if (RefQual == FrefQualRValue)
      OB += " &&";

    if (Attrs != nullptr)
      Attrs->print(OB);

    if (Requires != nullptr) {
      OB += " requires ";
      Requires->print(OB);
    }
  }
};

class LiteralOperator : public Node {
  const Node *OpName;

public:
  LiteralOperator(const Node *OpName_)
      : Node(KLiteralOperator), OpName(OpName_) {}

  template<typename Fn> void match(Fn F) const { F(OpName); }

  void printLeft(OutputBuffer &OB) const override {
    OB += "operator\"\" ";
    OpName->print(OB);
  }
};

class SpecialName final : public Node {
  const std::string_view Special;
  const Node *Child;

public:
  SpecialName(std::string_view Special_, const Node *Child_)
      : Node(KSpecialName), Special(Special_), Child(Child_) {}

  template<typename Fn> void match(Fn F) const { F(Special, Child); }

  void printLeft(OutputBuffer &OB) const override {
    OB += Special;
    Child->print(OB);
  }
};

class CtorVtableSpecialName final : public Node {
  const Node *FirstType;
  const Node *SecondType;

public:
  CtorVtableSpecialName(const Node *FirstType_, const Node *SecondType_)
      : Node(KCtorVtableSpecialName),
        FirstType(FirstType_), SecondType(SecondType_) {}

  template<typename Fn> void match(Fn F) const { F(FirstType, SecondType); }

  void printLeft(OutputBuffer &OB) const override {
    OB += "construction vtable for ";
    FirstType->print(OB);
    OB += "-in-";
    SecondType->print(OB);
  }
};

struct NestedName : Node {
  Node *Qual;
  Node *Name;

  NestedName(Node *Qual_, Node *Name_)
      : Node(KNestedName), Qual(Qual_), Name(Name_) {}

  template<typename Fn> void match(Fn F) const { F(Qual, Name); }

  std::string_view getBaseName() const override { return Name->getBaseName(); }

  void printLeft(OutputBuffer &OB) const override {
    Qual->print(OB);
    OB += "::";
    Name->print(OB);
  }
};

struct MemberLikeFriendName : Node {
  Node *Qual;
  Node *Name;

  MemberLikeFriendName(Node *Qual_, Node *Name_)
      : Node(KMemberLikeFriendName), Qual(Qual_), Name(Name_) {}

  template<typename Fn> void match(Fn F) const { F(Qual, Name); }

  std::string_view getBaseName() const override { return Name->getBaseName(); }

  void printLeft(OutputBuffer &OB) const override {
    Qual->print(OB);
    OB += "::friend ";
    Name->print(OB);
  }
};

struct ModuleName : Node {
  ModuleName *Parent;
  Node *Name;
  bool IsPartition;

  ModuleName(ModuleName *Parent_, Node *Name_, bool IsPartition_ = false)
      : Node(KModuleName), Parent(Parent_), Name(Name_),
        IsPartition(IsPartition_) {}

  template <typename Fn> void match(Fn F) const {
    F(Parent, Name, IsPartition);
  }

  void printLeft(OutputBuffer &OB) const override {
    if (Parent)
      Parent->print(OB);
    if (Parent || IsPartition)
      OB += IsPartition ? ':' : '.';
    Name->print(OB);
  }
};

struct ModuleEntity : Node {
  ModuleName *Module;
  Node *Name;

  ModuleEntity(ModuleName *Module_, Node *Name_)
      : Node(KModuleEntity), Module(Module_), Name(Name_) {}

  template <typename Fn> void match(Fn F) const { F(Module, Name); }

  std::string_view getBaseName() const override { return Name->getBaseName(); }

  void printLeft(OutputBuffer &OB) const override {
    Name->print(OB);
    OB += '@';
    Module->print(OB);
  }
};

struct LocalName : Node {
  Node *Encoding;
  Node *Entity;

  LocalName(Node *Encoding_, Node *Entity_)
      : Node(KLocalName), Encoding(Encoding_), Entity(Entity_) {}

  template<typename Fn> void match(Fn F) const { F(Encoding, Entity); }

  void printLeft(OutputBuffer &OB) const override {
    Encoding->print(OB);
    OB += "::";
    Entity->print(OB);
  }
};

class QualifiedName final : public Node {
  // qualifier::name
  const Node *Qualifier;
  const Node *Name;

public:
  QualifiedName(const Node *Qualifier_, const Node *Name_)
      : Node(KQualifiedName), Qualifier(Qualifier_), Name(Name_) {}

  template<typename Fn> void match(Fn F) const { F(Qualifier, Name); }

  std::string_view getBaseName() const override { return Name->getBaseName(); }

  void printLeft(OutputBuffer &OB) const override {
    Qualifier->print(OB);
    OB += "::";
    Name->print(OB);
  }
};

class VectorType final : public Node {
  const Node *BaseType;
  const Node *Dimension;

public:
  VectorType(const Node *BaseType_, const Node *Dimension_)
      : Node(KVectorType), BaseType(BaseType_), Dimension(Dimension_) {}

  const Node *getBaseType() const { return BaseType; }
  const Node *getDimension() const { return Dimension; }

  template<typename Fn> void match(Fn F) const { F(BaseType, Dimension); }

  void printLeft(OutputBuffer &OB) const override {
    BaseType->print(OB);
    OB += " vector[";
    if (Dimension)
      Dimension->print(OB);
    OB += "]";
  }
};

class PixelVectorType final : public Node {
  const Node *Dimension;

public:
  PixelVectorType(const Node *Dimension_)
      : Node(KPixelVectorType), Dimension(Dimension_) {}

  template<typename Fn> void match(Fn F) const { F(Dimension); }

  void printLeft(OutputBuffer &OB) const override {
    // FIXME: This should demangle as "vector pixel".
    OB += "pixel vector[";
    Dimension->print(OB);
    OB += "]";
  }
};

class BinaryFPType final : public Node {
  const Node *Dimension;

public:
  BinaryFPType(const Node *Dimension_)
      : Node(KBinaryFPType), Dimension(Dimension_) {}

  template<typename Fn> void match(Fn F) const { F(Dimension); }

  void printLeft(OutputBuffer &OB) const override {
    OB += "_Float";
    Dimension->print(OB);
  }
};

enum class TemplateParamKind { Type, NonType, Template };

/// An invented name for a template parameter for which we don't have a
/// corresponding template argument.
///
/// This node is created when parsing the <lambda-sig> for a lambda with
/// explicit template arguments, which might be referenced in the parameter
/// types appearing later in the <lambda-sig>.
class SyntheticTemplateParamName final : public Node {
  TemplateParamKind Kind;
  unsigned Index;

public:
  SyntheticTemplateParamName(TemplateParamKind Kind_, unsigned Index_)
      : Node(KSyntheticTemplateParamName), Kind(Kind_), Index(Index_) {}

  template<typename Fn> void match(Fn F) const { F(Kind, Index); }

  void printLeft(OutputBuffer &OB) const override {
    switch (Kind) {
    case TemplateParamKind::Type:
      OB += "$T";
      break;
    case TemplateParamKind::NonType:
      OB += "$N";
      break;
    case TemplateParamKind::Template:
      OB += "$TT";
      break;
    }
    if (Index > 0)
      OB << Index - 1;
  }
};

class TemplateParamQualifiedArg final : public Node {
  Node *Param;
  Node *Arg;

public:
  TemplateParamQualifiedArg(Node *Param_, Node *Arg_)
      : Node(KTemplateParamQualifiedArg), Param(Param_), Arg(Arg_) {}

  template <typename Fn> void match(Fn F) const { F(Param, Arg); }

  Node *getArg() { return Arg; }

  void printLeft(OutputBuffer &OB) const override {
    // Don't print Param to keep the output consistent.
    Arg->print(OB);
  }
};

/// A template type parameter declaration, 'typename T'.
class TypeTemplateParamDecl final : public Node {
  Node *Name;

public:
  TypeTemplateParamDecl(Node *Name_)
      : Node(KTypeTemplateParamDecl, Cache::Yes), Name(Name_) {}

  template<typename Fn> void match(Fn F) const { F(Name); }

  void printLeft(OutputBuffer &OB) const override { OB += "typename "; }

  void printRight(OutputBuffer &OB) const override { Name->print(OB); }
};

/// A constrained template type parameter declaration, 'C<U> T'.
class ConstrainedTypeTemplateParamDecl final : public Node {
  Node *Constraint;
  Node *Name;

public:
  ConstrainedTypeTemplateParamDecl(Node *Constraint_, Node *Name_)
      : Node(KConstrainedTypeTemplateParamDecl, Cache::Yes),
        Constraint(Constraint_), Name(Name_) {}

  template<typename Fn> void match(Fn F) const { F(Constraint, Name); }

  void printLeft(OutputBuffer &OB) const override {
    Constraint->print(OB);
    OB += " ";
  }

  void printRight(OutputBuffer &OB) const override { Name->print(OB); }
};

/// A non-type template parameter declaration, 'int N'.
class NonTypeTemplateParamDecl final : public Node {
  Node *Name;
  Node *Type;

public:
  NonTypeTemplateParamDecl(Node *Name_, Node *Type_)
      : Node(KNonTypeTemplateParamDecl, Cache::Yes), Name(Name_), Type(Type_) {}

  template<typename Fn> void match(Fn F) const { F(Name, Type); }

  void printLeft(OutputBuffer &OB) const override {
    Type->printLeft(OB);
    if (!Type->hasRHSComponent(OB))
      OB += " ";
  }

  void printRight(OutputBuffer &OB) const override {
    Name->print(OB);
    Type->printRight(OB);
  }
};

/// A template template parameter declaration,
/// 'template<typename T> typename N'.
class TemplateTemplateParamDecl final : public Node {
  Node *Name;
  NodeArray Params;
  Node *Requires;

public:
  TemplateTemplateParamDecl(Node *Name_, NodeArray Params_, Node *Requires_)
      : Node(KTemplateTemplateParamDecl, Cache::Yes), Name(Name_),
        Params(Params_), Requires(Requires_) {}

  template <typename Fn> void match(Fn F) const { F(Name, Params, Requires); }

  void printLeft(OutputBuffer &OB) const override {
    ScopedOverride<unsigned> LT(OB.GtIsGt, 0);
    OB += "template<";
    Params.printWithComma(OB);
    OB += "> typename ";
  }

  void printRight(OutputBuffer &OB) const override {
    Name->print(OB);
    if (Requires != nullptr) {
      OB += " requires ";
      Requires->print(OB);
    }
  }
};

/// A template parameter pack declaration, 'typename ...T'.
class TemplateParamPackDecl final : public Node {
  Node *Param;

public:
  TemplateParamPackDecl(Node *Param_)
      : Node(KTemplateParamPackDecl, Cache::Yes), Param(Param_) {}

  template<typename Fn> void match(Fn F) const { F(Param); }

  void printLeft(OutputBuffer &OB) const override {
    Param->printLeft(OB);
    OB += "...";
  }

  void printRight(OutputBuffer &OB) const override { Param->printRight(OB); }
};

/// An unexpanded parameter pack (either in the expression or type context). If
/// this AST is correct, this node will have a ParameterPackExpansion node above
/// it.
///
/// This node is created when some <template-args> are found that apply to an
/// <encoding>, and is stored in the TemplateParams table. In order for this to
/// appear in the final AST, it has to referenced via a <template-param> (ie,
/// T_).
class ParameterPack final : public Node {
  NodeArray Data;

  // Setup OutputBuffer for a pack expansion, unless we're already expanding
  // one.
  void initializePackExpansion(OutputBuffer &OB) const {
    if (OB.CurrentPackMax == std::numeric_limits<unsigned>::max()) {
      OB.CurrentPackMax = static_cast<unsigned>(Data.size());
      OB.CurrentPackIndex = 0;
    }
  }

public:
  ParameterPack(NodeArray Data_) : Node(KParameterPack), Data(Data_) {
    ArrayCache = FunctionCache = RHSComponentCache = Cache::Unknown;
    if (std::all_of(Data.begin(), Data.end(),
                    [](Node *P) { return P->getArrayCache() == Cache::No; }))
      ArrayCache = Cache::No;
    if (std::all_of(Data.begin(), Data.end(),
                    [](Node *P) { return P->getFunctionCache() == Cache::No; }))
      FunctionCache = Cache::No;
    if (std::all_of(Data.begin(), Data.end(), [](Node *P) {
          return P->getRHSComponentCache() == Cache::No;
        }))
      RHSComponentCache = Cache::No;
  }

  template<typename Fn> void match(Fn F) const { F(Data); }

  bool hasRHSComponentSlow(OutputBuffer &OB) const override {
    initializePackExpansion(OB);
    size_t Idx = OB.CurrentPackIndex;
    return Idx < Data.size() && Data[Idx]->hasRHSComponent(OB);
  }
  bool hasArraySlow(OutputBuffer &OB) const override {
    initializePackExpansion(OB);
    size_t Idx = OB.CurrentPackIndex;
    return Idx < Data.size() && Data[Idx]->hasArray(OB);
  }
  bool hasFunctionSlow(OutputBuffer &OB) const override {
    initializePackExpansion(OB);
    size_t Idx = OB.CurrentPackIndex;
    return Idx < Data.size() && Data[Idx]->hasFunction(OB);
  }
  const Node *getSyntaxNode(OutputBuffer &OB) const override {
    initializePackExpansion(OB);
    size_t Idx = OB.CurrentPackIndex;
    return Idx < Data.size() ? Data[Idx]->getSyntaxNode(OB) : this;
  }

  void printLeft(OutputBuffer &OB) const override {
    initializePackExpansion(OB);
    size_t Idx = OB.CurrentPackIndex;
    if (Idx < Data.size())
      Data[Idx]->printLeft(OB);
  }
  void printRight(OutputBuffer &OB) const override {
    initializePackExpansion(OB);
    size_t Idx = OB.CurrentPackIndex;
    if (Idx < Data.size())
      Data[Idx]->printRight(OB);
  }
};

/// A variadic template argument. This node represents an occurrence of
/// J<something>E in some <template-args>. It isn't itself unexpanded, unless
/// one of its Elements is. The parser inserts a ParameterPack into the
/// TemplateParams table if the <template-args> this pack belongs to apply to an
/// <encoding>.
class TemplateArgumentPack final : public Node {
  NodeArray Elements;
public:
  TemplateArgumentPack(NodeArray Elements_)
      : Node(KTemplateArgumentPack), Elements(Elements_) {}

  template<typename Fn> void match(Fn F) const { F(Elements); }

  NodeArray getElements() const { return Elements; }

  void printLeft(OutputBuffer &OB) const override {
    Elements.printWithComma(OB);
  }
};

/// A pack expansion. Below this node, there are some unexpanded ParameterPacks
/// which each have Child->ParameterPackSize elements.
class ParameterPackExpansion final : public Node {
  const Node *Child;

public:
  ParameterPackExpansion(const Node *Child_)
      : Node(KParameterPackExpansion), Child(Child_) {}

  template<typename Fn> void match(Fn F) const { F(Child); }

  const Node *getChild() const { return Child; }

  void printLeft(OutputBuffer &OB) const override {
    constexpr unsigned Max = std::numeric_limits<unsigned>::max();
    ScopedOverride<unsigned> SavePackIdx(OB.CurrentPackIndex, Max);
    ScopedOverride<unsigned> SavePackMax(OB.CurrentPackMax, Max);
    size_t StreamPos = OB.getCurrentPosition();

    // Print the first element in the pack. If Child contains a ParameterPack,
    // it will set up S.CurrentPackMax and print the first element.
    Child->print(OB);

    // No ParameterPack was found in Child. This can occur if we've found a pack
    // expansion on a <function-param>.
    if (OB.CurrentPackMax == Max) {
      OB += "...";
      return;
    }

    // We found a ParameterPack, but it has no elements. Erase whatever we may
    // of printed.
    if (OB.CurrentPackMax == 0) {
      OB.setCurrentPosition(StreamPos);
      return;
    }

    // Else, iterate through the rest of the elements in the pack.
    for (unsigned I = 1, E = OB.CurrentPackMax; I < E; ++I) {
      OB += ", ";
      OB.CurrentPackIndex = I;
      Child->print(OB);
    }
  }
};

class TemplateArgs final : public Node {
  NodeArray Params;
  Node *Requires;

public:
  TemplateArgs(NodeArray Params_, Node *Requires_)
      : Node(KTemplateArgs), Params(Params_), Requires(Requires_) {}

  template<typename Fn> void match(Fn F) const { F(Params, Requires); }

  NodeArray getParams() { return Params; }

  void printLeft(OutputBuffer &OB) const override {
    ScopedOverride<unsigned> LT(OB.GtIsGt, 0);
    OB += "<";
    Params.printWithComma(OB);
    OB += ">";
    // Don't print the requires clause to keep the output simple.
  }
};

/// A forward-reference to a template argument that was not known at the point
/// where the template parameter name was parsed in a mangling.
///
/// This is created when demangling the name of a specialization of a
/// conversion function template:
///
/// \code
/// struct A {
///   template<typename T> operator T*();
/// };
/// \endcode
///
/// When demangling a specialization of the conversion function template, we
/// encounter the name of the template (including the \c T) before we reach
/// the template argument list, so we cannot substitute the parameter name
/// for the corresponding argument while parsing. Instead, we create a
/// \c ForwardTemplateReference node that is resolved after we parse the
/// template arguments.
struct ForwardTemplateReference : Node {
  size_t Index;
  Node *Ref = nullptr;

  // If we're currently printing this node. It is possible (though invalid) for
  // a forward template reference to refer to itself via a substitution. This
  // creates a cyclic AST, which will stack overflow printing. To fix this, bail
  // out if more than one print* function is active.
  mutable bool Printing = false;

  ForwardTemplateReference(size_t Index_)
      : Node(KForwardTemplateReference, Cache::Unknown, Cache::Unknown,
             Cache::Unknown),
        Index(Index_) {}

  // We don't provide a matcher for these, because the value of the node is
  // not determined by its construction parameters, and it generally needs
  // special handling.
  template<typename Fn> void match(Fn F) const = delete;

  bool hasRHSComponentSlow(OutputBuffer &OB) const override {
    if (Printing)
      return false;
    ScopedOverride<bool> SavePrinting(Printing, true);
    return Ref->hasRHSComponent(OB);
  }
  bool hasArraySlow(OutputBuffer &OB) const override {
    if (Printing)
      return false;
    ScopedOverride<bool> SavePrinting(Printing, true);
    return Ref->hasArray(OB);
  }
  bool hasFunctionSlow(OutputBuffer &OB) const override {
    if (Printing)
      return false;
    ScopedOverride<bool> SavePrinting(Printing, true);
    return Ref->hasFunction(OB);
  }
  const Node *getSyntaxNode(OutputBuffer &OB) const override {
    if (Printing)
      return this;
    ScopedOverride<bool> SavePrinting(Printing, true);
    return Ref->getSyntaxNode(OB);
  }

  void printLeft(OutputBuffer &OB) const override {
    if (Printing)
      return;
    ScopedOverride<bool> SavePrinting(Printing, true);
    Ref->printLeft(OB);
  }
  void printRight(OutputBuffer &OB) const override {
    if (Printing)
      return;
    ScopedOverride<bool> SavePrinting(Printing, true);
    Ref->printRight(OB);
  }
};

struct NameWithTemplateArgs : Node {
  // name<template_args>
  Node *Name;
  Node *TemplateArgs;

  NameWithTemplateArgs(Node *Name_, Node *TemplateArgs_)
      : Node(KNameWithTemplateArgs), Name(Name_), TemplateArgs(TemplateArgs_) {}

  template<typename Fn> void match(Fn F) const { F(Name, TemplateArgs); }

  std::string_view getBaseName() const override { return Name->getBaseName(); }

  void printLeft(OutputBuffer &OB) const override {
    Name->print(OB);
    TemplateArgs->print(OB);
  }
};

class GlobalQualifiedName final : public Node {
  Node *Child;

public:
  GlobalQualifiedName(Node* Child_)
      : Node(KGlobalQualifiedName), Child(Child_) {}

  template<typename Fn> void match(Fn F) const { F(Child); }

  std::string_view getBaseName() const override { return Child->getBaseName(); }

  void printLeft(OutputBuffer &OB) const override {
    OB += "::";
    Child->print(OB);
  }
};

enum class SpecialSubKind {
  allocator,
  basic_string,
  string,
  istream,
  ostream,
  iostream,
};

class SpecialSubstitution;
class ExpandedSpecialSubstitution : public Node {
protected:
  SpecialSubKind SSK;

  ExpandedSpecialSubstitution(SpecialSubKind SSK_, Kind K_)
      : Node(K_), SSK(SSK_) {}
public:
  ExpandedSpecialSubstitution(SpecialSubKind SSK_)
      : ExpandedSpecialSubstitution(SSK_, KExpandedSpecialSubstitution) {}
  inline ExpandedSpecialSubstitution(SpecialSubstitution const *);

  template<typename Fn> void match(Fn F) const { F(SSK); }

protected:
  bool isInstantiation() const {
    return unsigned(SSK) >= unsigned(SpecialSubKind::string);
  }

  std::string_view getBaseName() const override {
    switch (SSK) {
    case SpecialSubKind::allocator:
      return {"allocator"};
    case SpecialSubKind::basic_string:
      return {"basic_string"};
    case SpecialSubKind::string:
      return {"basic_string"};
    case SpecialSubKind::istream:
      return {"basic_istream"};
    case SpecialSubKind::ostream:
      return {"basic_ostream"};
    case SpecialSubKind::iostream:
      return {"basic_iostream"};
    }
    DEMANGLE_UNREACHABLE;
  }

private:
  void printLeft(OutputBuffer &OB) const override {
    OB << "std::" << getBaseName();
    if (isInstantiation()) {
      OB << "<char, std::char_traits<char>";
      if (SSK == SpecialSubKind::string)
        OB << ", std::allocator<char>";
      OB << ">";
    }
  }
};

class SpecialSubstitution final : public ExpandedSpecialSubstitution {
public:
  SpecialSubstitution(SpecialSubKind SSK_)
      : ExpandedSpecialSubstitution(SSK_, KSpecialSubstitution) {}

  template<typename Fn> void match(Fn F) const { F(SSK); }

  std::string_view getBaseName() const override {
    std::string_view SV = ExpandedSpecialSubstitution::getBaseName();
    if (isInstantiation()) {
      // The instantiations are typedefs that drop the "basic_" prefix.
      DEMANGLE_ASSERT(starts_with(SV, "basic_"), "");
      SV.remove_prefix(sizeof("basic_") - 1);
    }
    return SV;
  }

  void printLeft(OutputBuffer &OB) const override {
    OB << "std::" << getBaseName();
  }
};

inline ExpandedSpecialSubstitution::ExpandedSpecialSubstitution(
    SpecialSubstitution const *SS)
    : ExpandedSpecialSubstitution(SS->SSK) {}

class CtorDtorName final : public Node {
  const Node *Basename;
  const bool IsDtor;
  const int Variant;

public:
  CtorDtorName(const Node *Basename_, bool IsDtor_, int Variant_)
      : Node(KCtorDtorName), Basename(Basename_), IsDtor(IsDtor_),
        Variant(Variant_) {}

  template<typename Fn> void match(Fn F) const { F(Basename, IsDtor, Variant); }

  void printLeft(OutputBuffer &OB) const override {
    if (IsDtor)
      OB += "~";
    OB += Basename->getBaseName();
  }
};

class DtorName : public Node {
  const Node *Base;

public:
  DtorName(const Node *Base_) : Node(KDtorName), Base(Base_) {}

  template<typename Fn> void match(Fn F) const { F(Base); }

  void printLeft(OutputBuffer &OB) const override {
    OB += "~";
    Base->printLeft(OB);
  }
};

class UnnamedTypeName : public Node {
  const std::string_view Count;

public:
  UnnamedTypeName(std::string_view Count_)
      : Node(KUnnamedTypeName), Count(Count_) {}

  template<typename Fn> void match(Fn F) const { F(Count); }

  void printLeft(OutputBuffer &OB) const override {
    OB += "'unnamed";
    OB += Count;
    OB += "\'";
  }
};

class ClosureTypeName : public Node {
  NodeArray TemplateParams;
  const Node *Requires1;
  NodeArray Params;
  const Node *Requires2;
  std::string_view Count;

public:
  ClosureTypeName(NodeArray TemplateParams_, const Node *Requires1_,
                  NodeArray Params_, const Node *Requires2_,
                  std::string_view Count_)
      : Node(KClosureTypeName), TemplateParams(TemplateParams_),
        Requires1(Requires1_), Params(Params_), Requires2(Requires2_),
        Count(Count_) {}

  template<typename Fn> void match(Fn F) const {
    F(TemplateParams, Requires1, Params, Requires2, Count);
  }

  void printDeclarator(OutputBuffer &OB) const {
    if (!TemplateParams.empty()) {
      ScopedOverride<unsigned> LT(OB.GtIsGt, 0);
      OB += "<";
      TemplateParams.printWithComma(OB);
      OB += ">";
    }
    if (Requires1 != nullptr) {
      OB += " requires ";
      Requires1->print(OB);
      OB += " ";
    }
    OB.printOpen();
    Params.printWithComma(OB);
    OB.printClose();
    if (Requires2 != nullptr) {
      OB += " requires ";
      Requires2->print(OB);
    }
  }

  void printLeft(OutputBuffer &OB) const override {
    // FIXME: This demangling is not particularly readable.
    OB += "\'lambda";
    OB += Count;
    OB += "\'";
    printDeclarator(OB);
  }
};

class StructuredBindingName : public Node {
  NodeArray Bindings;
public:
  StructuredBindingName(NodeArray Bindings_)
      : Node(KStructuredBindingName), Bindings(Bindings_) {}

  template<typename Fn> void match(Fn F) const { F(Bindings); }

  void printLeft(OutputBuffer &OB) const override {
    OB.printOpen('[');
    Bindings.printWithComma(OB);
    OB.printClose(']');
  }
};

// -- Expression Nodes --

class BinaryExpr : public Node {
  const Node *LHS;
  const std::string_view InfixOperator;
  const Node *RHS;

public:
  BinaryExpr(const Node *LHS_, std::string_view InfixOperator_,
             const Node *RHS_, Prec Prec_)
      : Node(KBinaryExpr, Prec_), LHS(LHS_), InfixOperator(InfixOperator_),
        RHS(RHS_) {}

  template <typename Fn> void match(Fn F) const {
    F(LHS, InfixOperator, RHS, getPrecedence());
  }

  void printLeft(OutputBuffer &OB) const override {
    bool ParenAll = OB.isGtInsideTemplateArgs() &&
                    (InfixOperator == ">" || InfixOperator == ">>");
    if (ParenAll)
      OB.printOpen();
    // Assignment is right associative, with special LHS precedence.
    bool IsAssign = getPrecedence() == Prec::Assign;
    LHS->printAsOperand(OB, IsAssign ? Prec::OrIf : getPrecedence(), !IsAssign);
    // No space before comma operator
    if (!(InfixOperator == ","))
      OB += " ";
    OB += InfixOperator;
    OB += " ";
    RHS->printAsOperand(OB, getPrecedence(), IsAssign);
    if (ParenAll)
      OB.printClose();
  }
};

class ArraySubscriptExpr : public Node {
  const Node *Op1;
  const Node *Op2;

public:
  ArraySubscriptExpr(const Node *Op1_, const Node *Op2_, Prec Prec_)
      : Node(KArraySubscriptExpr, Prec_), Op1(Op1_), Op2(Op2_) {}

  template <typename Fn> void match(Fn F) const {
    F(Op1, Op2, getPrecedence());
  }

  void printLeft(OutputBuffer &OB) const override {
    Op1->printAsOperand(OB, getPrecedence());
    OB.printOpen('[');
    Op2->printAsOperand(OB);
    OB.printClose(']');
  }
};

class PostfixExpr : public Node {
  const Node *Child;
  const std::string_view Operator;

public:
  PostfixExpr(const Node *Child_, std::string_view Operator_, Prec Prec_)
      : Node(KPostfixExpr, Prec_), Child(Child_), Operator(Operator_) {}

  template <typename Fn> void match(Fn F) const {
    F(Child, Operator, getPrecedence());
  }

  void printLeft(OutputBuffer &OB) const override {
    Child->printAsOperand(OB, getPrecedence(), true);
    OB += Operator;
  }
};

class ConditionalExpr : public Node {
  const Node *Cond;
  const Node *Then;
  const Node *Else;

public:
  ConditionalExpr(const Node *Cond_, const Node *Then_, const Node *Else_,
                  Prec Prec_)
      : Node(KConditionalExpr, Prec_), Cond(Cond_), Then(Then_), Else(Else_) {}

  template <typename Fn> void match(Fn F) const {
    F(Cond, Then, Else, getPrecedence());
  }

  void printLeft(OutputBuffer &OB) const override {
    Cond->printAsOperand(OB, getPrecedence());
    OB += " ? ";
    Then->printAsOperand(OB);
    OB += " : ";
    Else->printAsOperand(OB, Prec::Assign, true);
  }
};

class MemberExpr : public Node {
  const Node *LHS;
  const std::string_view Kind;
  const Node *RHS;

public:
  MemberExpr(const Node *LHS_, std::string_view Kind_, const Node *RHS_,
             Prec Prec_)
      : Node(KMemberExpr, Prec_), LHS(LHS_), Kind(Kind_), RHS(RHS_) {}

  template <typename Fn> void match(Fn F) const {
    F(LHS, Kind, RHS, getPrecedence());
  }

  void printLeft(OutputBuffer &OB) const override {
    LHS->printAsOperand(OB, getPrecedence(), true);
    OB += Kind;
    RHS->printAsOperand(OB, getPrecedence(), false);
  }
};

class SubobjectExpr : public Node {
  const Node *Type;
  const Node *SubExpr;
  std::string_view Offset;
  NodeArray UnionSelectors;
  bool OnePastTheEnd;

public:
  SubobjectExpr(const Node *Type_, const Node *SubExpr_,
                std::string_view Offset_, NodeArray UnionSelectors_,
                bool OnePastTheEnd_)
      : Node(KSubobjectExpr), Type(Type_), SubExpr(SubExpr_), Offset(Offset_),
        UnionSelectors(UnionSelectors_), OnePastTheEnd(OnePastTheEnd_) {}

  template<typename Fn> void match(Fn F) const {
    F(Type, SubExpr, Offset, UnionSelectors, OnePastTheEnd);
  }

  void printLeft(OutputBuffer &OB) const override {
    SubExpr->print(OB);
    OB += ".<";
    Type->print(OB);
    OB += " at offset ";
    if (Offset.empty()) {
      OB += "0";
    } else if (Offset[0] == 'n') {
      OB += "-";
      OB += std::string_view(Offset.data() + 1, Offset.size() - 1);
    } else {
      OB += Offset;
    }
    OB += ">";
  }
};

class EnclosingExpr : public Node {
  const std::string_view Prefix;
  const Node *Infix;
  const std::string_view Postfix;

public:
  EnclosingExpr(std::string_view Prefix_, const Node *Infix_,
                Prec Prec_ = Prec::Primary)
      : Node(KEnclosingExpr, Prec_), Prefix(Prefix_), Infix(Infix_) {}

  template <typename Fn> void match(Fn F) const {
    F(Prefix, Infix, getPrecedence());
  }

  void printLeft(OutputBuffer &OB) const override {
    OB += Prefix;
    OB.printOpen();
    Infix->print(OB);
    OB.printClose();
    OB += Postfix;
  }
};

class CastExpr : public Node {
  // cast_kind<to>(from)
  const std::string_view CastKind;
  const Node *To;
  const Node *From;

public:
  CastExpr(std::string_view CastKind_, const Node *To_, const Node *From_,
           Prec Prec_)
      : Node(KCastExpr, Prec_), CastKind(CastKind_), To(To_), From(From_) {}

  template <typename Fn> void match(Fn F) const {
    F(CastKind, To, From, getPrecedence());
  }

  void printLeft(OutputBuffer &OB) const override {
    OB += CastKind;
    {
      ScopedOverride<unsigned> LT(OB.GtIsGt, 0);
      OB += "<";
      To->printLeft(OB);
      OB += ">";
    }
    OB.printOpen();
    From->printAsOperand(OB);
    OB.printClose();
  }
};

class SizeofParamPackExpr : public Node {
  const Node *Pack;

public:
  SizeofParamPackExpr(const Node *Pack_)
      : Node(KSizeofParamPackExpr), Pack(Pack_) {}

  template<typename Fn> void match(Fn F) const { F(Pack); }

  void printLeft(OutputBuffer &OB) const override {
    OB += "sizeof...";
    OB.printOpen();
    ParameterPackExpansion PPE(Pack);
    PPE.printLeft(OB);
    OB.printClose();
  }
};

class CallExpr : public Node {
  const Node *Callee;
  NodeArray Args;

public:
  CallExpr(const Node *Callee_, NodeArray Args_, Prec Prec_)
      : Node(KCallExpr, Prec_), Callee(Callee_), Args(Args_) {}

  template <typename Fn> void match(Fn F) const {
    F(Callee, Args, getPrecedence());
  }

  void printLeft(OutputBuffer &OB) const override {
    Callee->print(OB);
    OB.printOpen();
    Args.printWithComma(OB);
    OB.printClose();
  }
};

class NewExpr : public Node {
  // new (expr_list) type(init_list)
  NodeArray ExprList;
  Node *Type;
  NodeArray InitList;
  bool IsGlobal; // ::operator new ?
  bool IsArray;  // new[] ?
public:
  NewExpr(NodeArray ExprList_, Node *Type_, NodeArray InitList_, bool IsGlobal_,
          bool IsArray_, Prec Prec_)
      : Node(KNewExpr, Prec_), ExprList(ExprList_), Type(Type_),
        InitList(InitList_), IsGlobal(IsGlobal_), IsArray(IsArray_) {}

  template<typename Fn> void match(Fn F) const {
    F(ExprList, Type, InitList, IsGlobal, IsArray, getPrecedence());
  }

  void printLeft(OutputBuffer &OB) const override {
    if (IsGlobal)
      OB += "::";
    OB += "new";
    if (IsArray)
      OB += "[]";
    if (!ExprList.empty()) {
      OB.printOpen();
      ExprList.printWithComma(OB);
      OB.printClose();
    }
    OB += " ";
    Type->print(OB);
    if (!InitList.empty()) {
      OB.printOpen();
      InitList.printWithComma(OB);
      OB.printClose();
    }
  }
};

class DeleteExpr : public Node {
  Node *Op;
  bool IsGlobal;
  bool IsArray;

public:
  DeleteExpr(Node *Op_, bool IsGlobal_, bool IsArray_, Prec Prec_)
      : Node(KDeleteExpr, Prec_), Op(Op_), IsGlobal(IsGlobal_),
        IsArray(IsArray_) {}

  template <typename Fn> void match(Fn F) const {
    F(Op, IsGlobal, IsArray, getPrecedence());
  }

  void printLeft(OutputBuffer &OB) const override {
    if (IsGlobal)
      OB += "::";
    OB += "delete";
    if (IsArray)
      OB += "[]";
    OB += ' ';
    Op->print(OB);
  }
};

class PrefixExpr : public Node {
  std::string_view Prefix;
  Node *Child;

public:
  PrefixExpr(std::string_view Prefix_, Node *Child_, Prec Prec_)
      : Node(KPrefixExpr, Prec_), Prefix(Prefix_), Child(Child_) {}

  template <typename Fn> void match(Fn F) const {
    F(Prefix, Child, getPrecedence());
  }

  void printLeft(OutputBuffer &OB) const override {
    OB += Prefix;
    Child->printAsOperand(OB, getPrecedence());
  }
};

class FunctionParam : public Node {
  std::string_view Number;

public:
  FunctionParam(std::string_view Number_)
      : Node(KFunctionParam), Number(Number_) {}

  template<typename Fn> void match(Fn F) const { F(Number); }

  void printLeft(OutputBuffer &OB) const override {
    OB += "fp";
    OB += Number;
  }
};

class ConversionExpr : public Node {
  const Node *Type;
  NodeArray Expressions;

public:
  ConversionExpr(const Node *Type_, NodeArray Expressions_, Prec Prec_)
      : Node(KConversionExpr, Prec_), Type(Type_), Expressions(Expressions_) {}

  template <typename Fn> void match(Fn F) const {
    F(Type, Expressions, getPrecedence());
  }

  void printLeft(OutputBuffer &OB) const override {
    OB.printOpen();
    Type->print(OB);
    OB.printClose();
    OB.printOpen();
    Expressions.printWithComma(OB);
    OB.printClose();
  }
};

class PointerToMemberConversionExpr : public Node {
  const Node *Type;
  const Node *SubExpr;
  std::string_view Offset;

public:
  PointerToMemberConversionExpr(const Node *Type_, const Node *SubExpr_,
                                std::string_view Offset_, Prec Prec_)
      : Node(KPointerToMemberConversionExpr, Prec_), Type(Type_),
        SubExpr(SubExpr_), Offset(Offset_) {}

  template <typename Fn> void match(Fn F) const {
    F(Type, SubExpr, Offset, getPrecedence());
  }

  void printLeft(OutputBuffer &OB) const override {
    OB.printOpen();
    Type->print(OB);
    OB.printClose();
    OB.printOpen();
    SubExpr->print(OB);
    OB.printClose();
  }
};

class InitListExpr : public Node {
  const Node *Ty;
  NodeArray Inits;
public:
  InitListExpr(const Node *Ty_, NodeArray Inits_)
      : Node(KInitListExpr), Ty(Ty_), Inits(Inits_) {}

  template<typename Fn> void match(Fn F) const { F(Ty, Inits); }

  void printLeft(OutputBuffer &OB) const override {
    if (Ty)
      Ty->print(OB);
    OB += '{';
    Inits.printWithComma(OB);
    OB += '}';
  }
};

class BracedExpr : public Node {
  const Node *Elem;
  const Node *Init;
  bool IsArray;
public:
  BracedExpr(const Node *Elem_, const Node *Init_, bool IsArray_)
      : Node(KBracedExpr), Elem(Elem_), Init(Init_), IsArray(IsArray_) {}

  template<typename Fn> void match(Fn F) const { F(Elem, Init, IsArray); }

  void printLeft(OutputBuffer &OB) const override {
    if (IsArray) {
      OB += '[';
      Elem->print(OB);
      OB += ']';
    } else {
      OB += '.';
      Elem->print(OB);
    }
    if (Init->getKind() != KBracedExpr && Init->getKind() != KBracedRangeExpr)
      OB += " = ";
    Init->print(OB);
  }
};

class BracedRangeExpr : public Node {
  const Node *First;
  const Node *Last;
  const Node *Init;
public:
  BracedRangeExpr(const Node *First_, const Node *Last_, const Node *Init_)
      : Node(KBracedRangeExpr), First(First_), Last(Last_), Init(Init_) {}

  template<typename Fn> void match(Fn F) const { F(First, Last, Init); }

  void printLeft(OutputBuffer &OB) const override {
    OB += '[';
    First->print(OB);
    OB += " ... ";
    Last->print(OB);
    OB += ']';
    if (Init->getKind() != KBracedExpr && Init->getKind() != KBracedRangeExpr)
      OB += " = ";
    Init->print(OB);
  }
};

class FoldExpr : public Node {
  const Node *Pack, *Init;
  std::string_view OperatorName;
  bool IsLeftFold;

public:
  FoldExpr(bool IsLeftFold_, std::string_view OperatorName_, const Node *Pack_,
           const Node *Init_)
      : Node(KFoldExpr), Pack(Pack_), Init(Init_), OperatorName(OperatorName_),
        IsLeftFold(IsLeftFold_) {}

  template<typename Fn> void match(Fn F) const {
    F(IsLeftFold, OperatorName, Pack, Init);
  }

  void printLeft(OutputBuffer &OB) const override {
    auto PrintPack = [&] {
      OB.printOpen();
      ParameterPackExpansion(Pack).print(OB);
      OB.printClose();
    };

    OB.printOpen();
    // Either '[init op ]... op pack' or 'pack op ...[ op init]'
    // Refactored to '[(init|pack) op ]...[ op (pack|init)]'
    // Fold expr operands are cast-expressions
    if (!IsLeftFold || Init != nullptr) {
      // '(init|pack) op '
      if (IsLeftFold)
        Init->printAsOperand(OB, Prec::Cast, true);
      else
        PrintPack();
      OB << " " << OperatorName << " ";
    }
    OB << "...";
    if (IsLeftFold || Init != nullptr) {
      // ' op (init|pack)'
      OB << " " << OperatorName << " ";
      if (IsLeftFold)
        PrintPack();
      else
        Init->printAsOperand(OB, Prec::Cast, true);
    }
    OB.printClose();
  }
};

class ThrowExpr : public Node {
  const Node *Op;

public:
  ThrowExpr(const Node *Op_) : Node(KThrowExpr), Op(Op_) {}

  template<typename Fn> void match(Fn F) const { F(Op); }

  void printLeft(OutputBuffer &OB) const override {
    OB += "throw ";
    Op->print(OB);
  }
};

class BoolExpr : public Node {
  bool Value;

public:
  BoolExpr(bool Value_) : Node(KBoolExpr), Value(Value_) {}

  template<typename Fn> void match(Fn F) const { F(Value); }

  void printLeft(OutputBuffer &OB) const override {
    OB += Value ? std::string_view("true") : std::string_view("false");
  }
};

class StringLiteral : public Node {
  const Node *Type;

public:
  StringLiteral(const Node *Type_) : Node(KStringLiteral), Type(Type_) {}

  template<typename Fn> void match(Fn F) const { F(Type); }

  void printLeft(OutputBuffer &OB) const override {
    OB += "\"<";
    Type->print(OB);
    OB += ">\"";
  }
};

class LambdaExpr : public Node {
  const Node *Type;

public:
  LambdaExpr(const Node *Type_) : Node(KLambdaExpr), Type(Type_) {}

  template<typename Fn> void match(Fn F) const { F(Type); }

  void printLeft(OutputBuffer &OB) const override {
    OB += "[]";
    if (Type->getKind() == KClosureTypeName)
      static_cast<const ClosureTypeName *>(Type)->printDeclarator(OB);
    OB += "{...}";
  }
};

class EnumLiteral : public Node {
  // ty(integer)
  const Node *Ty;
  std::string_view Integer;

public:
  EnumLiteral(const Node *Ty_, std::string_view Integer_)
      : Node(KEnumLiteral), Ty(Ty_), Integer(Integer_) {}

  template<typename Fn> void match(Fn F) const { F(Ty, Integer); }

  void printLeft(OutputBuffer &OB) const override {
    OB.printOpen();
    Ty->print(OB);
    OB.printClose();

    if (Integer[0] == 'n')
      OB << '-' << std::string_view(Integer.data() + 1, Integer.size() - 1);
    else
      OB << Integer;
  }
};

class IntegerLiteral : public Node {
  std::string_view Type;
  std::string_view Value;

public:
  IntegerLiteral(std::string_view Type_, std::string_view Value_)
      : Node(KIntegerLiteral), Type(Type_), Value(Value_) {}

  template<typename Fn> void match(Fn F) const { F(Type, Value); }

  void printLeft(OutputBuffer &OB) const override {
    if (Type.size() > 3) {
      OB.printOpen();
      OB += Type;
      OB.printClose();
    }

    if (Value[0] == 'n')
      OB << '-' << std::string_view(Value.data() + 1, Value.size() - 1);
    else
      OB += Value;

    if (Type.size() <= 3)
      OB += Type;
  }
};

class RequiresExpr : public Node {
  NodeArray Parameters;
  NodeArray Requirements;
public:
  RequiresExpr(NodeArray Parameters_, NodeArray Requirements_)
      : Node(KRequiresExpr), Parameters(Parameters_),
        Requirements(Requirements_) {}

  template<typename Fn> void match(Fn F) const { F(Parameters, Requirements); }

  void printLeft(OutputBuffer &OB) const override {
    OB += "requires";
    if (!Parameters.empty()) {
      OB += ' ';
      OB.printOpen();
      Parameters.printWithComma(OB);
      OB.printClose();
    }
    OB += ' ';
    OB.printOpen('{');
    for (const Node *Req : Requirements) {
      Req->print(OB);
    }
    OB += ' ';
    OB.printClose('}');
  }
};

class ExprRequirement : public Node {
  const Node *Expr;
  bool IsNoexcept;
  const Node *TypeConstraint;
public:
  ExprRequirement(const Node *Expr_, bool IsNoexcept_,
                  const Node *TypeConstraint_)
      : Node(KExprRequirement), Expr(Expr_), IsNoexcept(IsNoexcept_),
        TypeConstraint(TypeConstraint_) {}

  template <typename Fn> void match(Fn F) const {
    F(Expr, IsNoexcept, TypeConstraint);
  }

  void printLeft(OutputBuffer &OB) const override {
    OB += " ";
    if (IsNoexcept || TypeConstraint)
      OB.printOpen('{');
    Expr->print(OB);
    if (IsNoexcept || TypeConstraint)
      OB.printClose('}');
    if (IsNoexcept)
      OB += " noexcept";
    if (TypeConstraint) {
      OB += " -> ";
      TypeConstraint->print(OB);
    }
    OB += ';';
  }
};

class TypeRequirement : public Node {
  const Node *Type;
public:
  TypeRequirement(const Node *Type_)
      : Node(KTypeRequirement), Type(Type_) {}

  template <typename Fn> void match(Fn F) const { F(Type); }

  void printLeft(OutputBuffer &OB) const override {
    OB += " typename ";
    Type->print(OB);
    OB += ';';
  }
};

class NestedRequirement : public Node {
  const Node *Constraint;
public:
  NestedRequirement(const Node *Constraint_)
      : Node(KNestedRequirement), Constraint(Constraint_) {}

  template <typename Fn> void match(Fn F) const { F(Constraint); }

  void printLeft(OutputBuffer &OB) const override {
    OB += " requires ";
    Constraint->print(OB);
    OB += ';';
  }
};

template <class Float> struct FloatData;

namespace float_literal_impl {
constexpr Node::Kind getFloatLiteralKind(float *) {
  return Node::KFloatLiteral;
}
constexpr Node::Kind getFloatLiteralKind(double *) {
  return Node::KDoubleLiteral;
}
constexpr Node::Kind getFloatLiteralKind(long double *) {
  return Node::KLongDoubleLiteral;
}
}

template <class Float> class FloatLiteralImpl : public Node {
  const std::string_view Contents;

  static constexpr Kind KindForClass =
      float_literal_impl::getFloatLiteralKind((Float *)nullptr);

public:
  FloatLiteralImpl(std::string_view Contents_)
      : Node(KindForClass), Contents(Contents_) {}

  template<typename Fn> void match(Fn F) const { F(Contents); }

  void printLeft(OutputBuffer &OB) const override {
    const size_t N = FloatData<Float>::mangled_size;
    if (Contents.size() >= N) {
      union {
        Float value;
        char buf[sizeof(Float)];
      };
      const char *t = Contents.data();
      const char *last = t + N;
      char *e = buf;
      for (; t != last; ++t, ++e) {
        unsigned d1 = isdigit(*t) ? static_cast<unsigned>(*t - '0')
                                  : static_cast<unsigned>(*t - 'a' + 10);
        ++t;
        unsigned d0 = isdigit(*t) ? static_cast<unsigned>(*t - '0')
                                  : static_cast<unsigned>(*t - 'a' + 10);
        *e = static_cast<char>((d1 << 4) + d0);
      }
#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
      std::reverse(buf, e);
#endif
      char num[FloatData<Float>::max_demangled_size] = {0};
      int n = snprintf(num, sizeof(num), FloatData<Float>::spec, value);
      OB += std::string_view(num, n);
    }
  }
};

using FloatLiteral = FloatLiteralImpl<float>;
using DoubleLiteral = FloatLiteralImpl<double>;
using LongDoubleLiteral = FloatLiteralImpl<long double>;

/// Visit the node. Calls \c F(P), where \c P is the node cast to the
/// appropriate derived class.
template<typename Fn>
void Node::visit(Fn F) const {
  switch (K) {
#define NODE(X)                                                                \
  case K##X:                                                                   \
    return F(static_cast<const X *>(this));
#include "ItaniumNodes.def"
  }
  DEMANGLE_ASSERT(0, "unknown mangling node kind");
}

/// Determine the kind of a node from its type.
template<typename NodeT> struct NodeKind;
#define NODE(X)                                                                \
  template <> struct NodeKind<X> {                                             \
    static constexpr Node::Kind Kind = Node::K##X;                             \
    static constexpr const char *name() { return #X; }                         \
  };
#include "ItaniumNodes.def"

template <typename Derived, typename Alloc> struct AbstractManglingParser {
  const char *First;
  const char *Last;

  // Name stack, this is used by the parser to hold temporary names that were
  // parsed. The parser collapses multiple names into new nodes to construct
  // the AST. Once the parser is finished, names.size() == 1.
  PODSmallVector<Node *, 32> Names;

  // Substitution table. Itanium supports name substitutions as a means of
  // compression. The string "S42_" refers to the 44nd entry (base-36) in this
  // table.
  PODSmallVector<Node *, 32> Subs;

  // A list of template argument values corresponding to a template parameter
  // list.
  using TemplateParamList = PODSmallVector<Node *, 8>;

  class ScopedTemplateParamList {
    AbstractManglingParser *Parser;
    size_t OldNumTemplateParamLists;
    TemplateParamList Params;

  public:
    ScopedTemplateParamList(AbstractManglingParser *TheParser)
        : Parser(TheParser),
          OldNumTemplateParamLists(TheParser->TemplateParams.size()) {
      Parser->TemplateParams.push_back(&Params);
    }
    ~ScopedTemplateParamList() {
      DEMANGLE_ASSERT(Parser->TemplateParams.size() >= OldNumTemplateParamLists,
                      "");
      Parser->TemplateParams.shrinkToSize(OldNumTemplateParamLists);
    }
    TemplateParamList *params() { return &Params; }
  };

  // Template parameter table. Like the above, but referenced like "T42_".
  // This has a smaller size compared to Subs and Names because it can be
  // stored on the stack.
  TemplateParamList OuterTemplateParams;

  // Lists of template parameters indexed by template parameter depth,
  // referenced like "TL2_4_". If nonempty, element 0 is always
  // OuterTemplateParams; inner elements are always template parameter lists of
  // lambda expressions. For a generic lambda with no explicit template
  // parameter list, the corresponding parameter list pointer will be null.
  PODSmallVector<TemplateParamList *, 4> TemplateParams;

  class SaveTemplateParams {
    AbstractManglingParser *Parser;
    decltype(TemplateParams) OldParams;
    decltype(OuterTemplateParams) OldOuterParams;

  public:
    SaveTemplateParams(AbstractManglingParser *TheParser) : Parser(TheParser) {
      OldParams = std::move(Parser->TemplateParams);
      OldOuterParams = std::move(Parser->OuterTemplateParams);
      Parser->TemplateParams.clear();
      Parser->OuterTemplateParams.clear();
    }
    ~SaveTemplateParams() {
      Parser->TemplateParams = std::move(OldParams);
      Parser->OuterTemplateParams = std::move(OldOuterParams);
    }
  };

  // Set of unresolved forward <template-param> references. These can occur in a
  // conversion operator's type, and are resolved in the enclosing <encoding>.
  PODSmallVector<ForwardTemplateReference *, 4> ForwardTemplateRefs;

  bool TryToParseTemplateArgs = true;
  bool PermitForwardTemplateReferences = false;
  bool InConstraintExpr = false;
  size_t ParsingLambdaParamsAtLevel = (size_t)-1;

  u