src/third_party/llvm-project/llvm/lib/Demangle/ItaniumDemangle.cpp

//===------------------------- ItaniumDemangle.cpp ------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is dual licensed under the MIT and the University of Illinois Open
// Source Licenses. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

// FIXME: (possibly) incomplete list of features that clang mangles that this
// file does not yet support:
//   - C++ modules TS

#include "Compiler.h"
#include "StringView.h"
#include "Utility.h"
#include "llvm/Demangle/Demangle.h"

#include <cassert>
#include <cctype>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <numeric>
#include <utility>
#include <vector>

namespace {
// 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 {
    KNodeArrayNode,
    KDotSuffix,
    KVendorExtQualType,
    KQualType,
    KConversionOperatorType,
    KPostfixQualifiedType,
    KElaboratedTypeSpefType,
    KNameType,
    KAbiTagAttr,
    KEnableIfAttr,
    KObjCProtoName,
    KPointerType,
    KReferenceType,
    KPointerToMemberType,
    KArrayType,
    KFunctionType,
    KNoexceptSpec,
    KDynamicExceptionSpec,
    KFunctionEncoding,
    KLiteralOperator,
    KSpecialName,
    KCtorVtableSpecialName,
    KQualifiedName,
    KNestedName,
    KLocalName,
    KVectorType,
    KParameterPack,
    KTemplateArgumentPack,
    KParameterPackExpansion,
    KTemplateArgs,
    KForwardTemplateReference,
    KNameWithTemplateArgs,
    KGlobalQualifiedName,
    KStdQualifiedName,
    KExpandedSpecialSubstitution,
    KSpecialSubstitution,
    KCtorDtorName,
    KDtorName,
    KUnnamedTypeName,
    KClosureTypeName,
    KStructuredBindingName,
    KExpr,
    KBracedExpr,
    KBracedRangeExpr,
  };

  Kind K;

  /// 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, };

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

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

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

  Node(Kind K_, Cache RHSComponentCache_ = Cache::No,
       Cache ArrayCache_ = Cache::No, Cache FunctionCache_ = Cache::No)
      : K(K_), RHSComponentCache(RHSComponentCache_), ArrayCache(ArrayCache_),
        FunctionCache(FunctionCache_) {}

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

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

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

  Kind getKind() const { return K; }

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

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

  // Print the "left" side of this Node into OutputStream.
  virtual void printLeft(OutputStream &) 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(OutputStream &) const {}

  virtual StringView getBaseName() const { return StringView(); }

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

#ifndef NDEBUG
  LLVM_DUMP_METHOD void dump() const {
    char *Buffer = static_cast<char*>(std::malloc(1024));
    OutputStream S(Buffer, 1024);
    print(S);
    S += '\0';
    printf("Symbol dump for %p: %s\n", (const void*)this, S.getBuffer());
    std::free(S.getBuffer());
  }
#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(OutputStream &S) const {
    bool FirstElement = true;
    for (size_t Idx = 0; Idx != NumElements; ++Idx) {
      size_t BeforeComma = S.getCurrentPosition();
      if (!FirstElement)
        S += ", ";
      size_t AfterComma = S.getCurrentPosition();
      Elements[Idx]->print(S);

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

      FirstElement = false;
    }
  }
};

struct NodeArrayNode : Node {
  NodeArray Array;
  NodeArrayNode(NodeArray Array_) : Node(KNodeArrayNode), Array(Array_) {}
  void printLeft(OutputStream &S) const override {
    Array.printWithComma(S);
  }
};

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

public:
  DotSuffix(Node *Prefix_, StringView Suffix_)
      : Node(KDotSuffix), Prefix(Prefix_), Suffix(Suffix_) {}

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

class VendorExtQualType final : public Node {
  const Node *Ty;
  StringView Ext;

public:
  VendorExtQualType(Node *Ty_, StringView Ext_)
      : Node(KVendorExtQualType), Ty(Ty_), Ext(Ext_) {}

  void printLeft(OutputStream &S) const override {
    Ty->print(S);
    S += " ";
    S += Ext;
  }
};

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

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

void addQualifiers(Qualifiers &Q1, Qualifiers Q2) {
  Q1 = static_cast<Qualifiers>(Q1 | Q2);
}

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

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

public:
  QualType(Node *Child_, Qualifiers Quals_)
      : Node(KQualType, Child_->RHSComponentCache,
             Child_->ArrayCache, Child_->FunctionCache),
        Quals(Quals_), Child(Child_) {}

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

  void printLeft(OutputStream &S) const override {
    Child->printLeft(S);
    printQuals(S);
  }

  void printRight(OutputStream &S) const override { Child->printRight(S); }
};

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

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

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

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

public:
  PostfixQualifiedType(Node *Ty_, StringView Postfix_)
      : Node(KPostfixQualifiedType), Ty(Ty_), Postfix(Postfix_) {}

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

class NameType final : public Node {
  const StringView Name;

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

  StringView getName() const { return Name; }
  StringView getBaseName() const override { return Name; }

  void printLeft(OutputStream &s) const override { s += Name; }
};

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

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

struct AbiTagAttr : Node {
  Node *Base;
  StringView Tag;

  AbiTagAttr(Node* Base_, StringView Tag_)
      : Node(KAbiTagAttr, Base_->RHSComponentCache,
             Base_->ArrayCache, Base_->FunctionCache),
        Base(Base_), Tag(Tag_) {}

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

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

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

class ObjCProtoName : public Node {
  Node *Ty;
  StringView Protocol;

  friend class PointerType;

public:
  ObjCProtoName(Node *Ty_, StringView Protocol_)
      : Node(KObjCProtoName), Ty(Ty_), Protocol(Protocol_) {}

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

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

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

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

  bool hasRHSComponentSlow(OutputStream &S) const override {
    return Pointee->hasRHSComponent(S);
  }

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

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

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.
  std::pair<ReferenceKind, const Node *> collapse(OutputStream &S) const {
    auto SoFar = std::make_pair(RK, Pointee);
    for (;;) {
      const Node *SN = SoFar.second->getSyntaxNode(S);
      if (SN->getKind() != KReferenceType)
        break;
      auto *RT = static_cast<const ReferenceType *>(SN);
      SoFar.second = RT->Pointee;
      SoFar.first = std::min(SoFar.first, RT->RK);
    }
    return SoFar;
  }

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

  bool hasRHSComponentSlow(OutputStream &S) const override {
    return Pointee->hasRHSComponent(S);
  }

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

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

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

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

  bool hasRHSComponentSlow(OutputStream &S) const override {
    return MemberType->hasRHSComponent(S);
  }

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

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

class NodeOrString {
  const void *First;
  const void *Second;

public:
  /* implicit */ NodeOrString(StringView Str) {
    const char *FirstChar = Str.begin();
    const char *SecondChar = Str.end();
    if (SecondChar == nullptr) {
      assert(FirstChar == SecondChar);
      ++FirstChar, ++SecondChar;
    }
    First = static_cast<const void *>(FirstChar);
    Second = static_cast<const void *>(SecondChar);
  }

  /* implicit */ NodeOrString(Node *N)
      : First(static_cast<const void *>(N)), Second(nullptr) {}
  NodeOrString() : First(nullptr), Second(nullptr) {}

  bool isString() const { return Second && First; }
  bool isNode() const { return First && !Second; }
  bool isEmpty() const { return !First && !Second; }

  StringView asString() const {
    assert(isString());
    return StringView(static_cast<const char *>(First),
                      static_cast<const char *>(Second));
  }

  const Node *asNode() const {
    assert(isNode());
    return static_cast<const Node *>(First);
  }
};

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

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

  // Incomplete array type.
  ArrayType(Node *Base_)
      : Node(KArrayType,
             /*RHSComponentCache=*/Cache::Yes,
             /*ArrayCache=*/Cache::Yes),
        Base(Base_) {}

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

  void printLeft(OutputStream &S) const override { Base->printLeft(S); }

  void printRight(OutputStream &S) const override {
    if (S.back() != ']')
      S += " ";
    S += "[";
    if (Dimension.isString())
      S += Dimension.asString();
    else if (Dimension.isNode())
      Dimension.asNode()->print(S);
    S += "]";
    Base->printRight(S);
  }
};

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

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

  bool hasRHSComponentSlow(OutputStream &) const override { return true; }
  bool hasFunctionSlow(OutputStream &) 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(OutputStream &S) const override {
    Ret->printLeft(S);
    S += " ";
  }

  void printRight(OutputStream &S) const override {
    S += "(";
    Params.printWithComma(S);
    S += ")";
    Ret->printRight(S);

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

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

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

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

  void printLeft(OutputStream &S) const override {
    S += "noexcept(";
    E->print(S);
    S += ")";
  }
};

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

  void printLeft(OutputStream &S) const override {
    S += "throw(";
    Types.printWithComma(S);
    S += ')';
  }
};

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

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

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

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

  Node *getName() { return const_cast<Node *>(Name); }

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

  void printRight(OutputStream &S) const override {
    S += "(";
    Params.printWithComma(S);
    S += ")";
    if (Ret)
      Ret->printRight(S);

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

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

    if (Attrs != nullptr)
      Attrs->print(S);
  }
};

class LiteralOperator : public Node {
  const Node *OpName;

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

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

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

public:
  SpecialName(StringView Special_, Node* Child_)
      : Node(KSpecialName), Special(Special_), Child(Child_) {}

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

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

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

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

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

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

  StringView getBaseName() const override { return Name->getBaseName(); }

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

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

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

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

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

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

  StringView getBaseName() const override { return Name->getBaseName(); }

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

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

public:
  VectorType(NodeOrString Dimension_)
      : Node(KVectorType), BaseType(nullptr), Dimension(Dimension_),
        IsPixel(true) {}
  VectorType(Node *BaseType_, NodeOrString Dimension_)
      : Node(KVectorType), BaseType(BaseType_),
        Dimension(Dimension_), IsPixel(false) {}

  void printLeft(OutputStream &S) const override {
    if (IsPixel) {
      S += "pixel vector[";
      S += Dimension.asString();
      S += "]";
    } else {
      BaseType->print(S);
      S += " vector[";
      if (Dimension.isNode())
        Dimension.asNode()->print(S);
      else if (Dimension.isString())
        S += Dimension.asString();
      S += "]";
    }
  }
};

/// 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 OutputStream for a pack expansion unless we're already expanding one.
  void initializePackExpansion(OutputStream &S) const {
    if (S.CurrentPackMax == std::numeric_limits<unsigned>::max()) {
      S.CurrentPackMax = static_cast<unsigned>(Data.size());
      S.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->ArrayCache == Cache::No;
        }))
      ArrayCache = Cache::No;
    if (std::all_of(Data.begin(), Data.end(), [](Node* P) {
          return P->FunctionCache == Cache::No;
        }))
      FunctionCache = Cache::No;
    if (std::all_of(Data.begin(), Data.end(), [](Node* P) {
          return P->RHSComponentCache == Cache::No;
        }))
      RHSComponentCache = Cache::No;
  }

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

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

/// 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 it's 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_) {}

  NodeArray getElements() const { return Elements; }

  void printLeft(OutputStream &S) const override {
    Elements.printWithComma(S);
  }
};

/// 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(Node* Child_)
      : Node(KParameterPackExpansion), Child(Child_) {}

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

  void printLeft(OutputStream &S) const override {
    constexpr unsigned Max = std::numeric_limits<unsigned>::max();
    SwapAndRestore<unsigned> SavePackIdx(S.CurrentPackIndex, Max);
    SwapAndRestore<unsigned> SavePackMax(S.CurrentPackMax, Max);
    size_t StreamPos = S.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(S);

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

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

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

class TemplateArgs final : public Node {
  NodeArray Params;

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

  NodeArray getParams() { return Params; }

  void printLeft(OutputStream &S) const override {
    S += "<";
    Params.printWithComma(S);
    if (S.back() == '>')
      S += " ";
    S += ">";
  }
};

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_) {}

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

  void printLeft(OutputStream &S) const override {
    if (Printing)
      return;
    SwapAndRestore<bool> SavePrinting(Printing, true);
    Ref->printLeft(S);
  }
  void printRight(OutputStream &S) const override {
    if (Printing)
      return;
    SwapAndRestore<bool> SavePrinting(Printing, true);
    Ref->printRight(S);
  }
};

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

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

  StringView getBaseName() const override { return Name->getBaseName(); }

  void printLeft(OutputStream &S) const override {
    Name->print(S);
    TemplateArgs->print(S);
  }
};

class GlobalQualifiedName final : public Node {
  Node *Child;

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

  StringView getBaseName() const override { return Child->getBaseName(); }

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

struct StdQualifiedName : Node {
  Node *Child;

  StdQualifiedName(Node *Child_) : Node(KStdQualifiedName), Child(Child_) {}

  StringView getBaseName() const override { return Child->getBaseName(); }

  void printLeft(OutputStream &S) const override {
    S += "std::";
    Child->print(S);
  }
};

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

class ExpandedSpecialSubstitution final : public Node {
  SpecialSubKind SSK;

public:
  ExpandedSpecialSubstitution(SpecialSubKind SSK_)
      : Node(KExpandedSpecialSubstitution), SSK(SSK_) {}

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

  void printLeft(OutputStream &S) const override {
    switch (SSK) {
    case SpecialSubKind::allocator:
      S += "std::basic_string<char, std::char_traits<char>, "
           "std::allocator<char> >";
      break;
    case SpecialSubKind::basic_string:
    case SpecialSubKind::string:
      S += "std::basic_string<char, std::char_traits<char>, "
           "std::allocator<char> >";
      break;
    case SpecialSubKind::istream:
      S += "std::basic_istream<char, std::char_traits<char> >";
      break;
    case SpecialSubKind::ostream:
      S += "std::basic_ostream<char, std::char_traits<char> >";
      break;
    case SpecialSubKind::iostream:
      S += "std::basic_iostream<char, std::char_traits<char> >";
      break;
    }
  }
};

class SpecialSubstitution final : public Node {
public:
  SpecialSubKind SSK;

  SpecialSubstitution(SpecialSubKind SSK_)
      : Node(KSpecialSubstitution), SSK(SSK_) {}

  StringView getBaseName() const override {
    switch (SSK) {
    case SpecialSubKind::allocator:
      return StringView("allocator");
    case SpecialSubKind::basic_string:
      return StringView("basic_string");
    case SpecialSubKind::string:
      return StringView("string");
    case SpecialSubKind::istream:
      return StringView("istream");
    case SpecialSubKind::ostream:
      return StringView("ostream");
    case SpecialSubKind::iostream:
      return StringView("iostream");
    }
    LLVM_BUILTIN_UNREACHABLE;
  }

  void printLeft(OutputStream &S) const override {
    switch (SSK) {
    case SpecialSubKind::allocator:
      S += "std::allocator";
      break;
    case SpecialSubKind::basic_string:
      S += "std::basic_string";
      break;
    case SpecialSubKind::string:
      S += "std::string";
      break;
    case SpecialSubKind::istream:
      S += "std::istream";
      break;
    case SpecialSubKind::ostream:
      S += "std::ostream";
      break;
    case SpecialSubKind::iostream:
      S += "std::iostream";
      break;
    }
  }
};

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

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

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

class DtorName : public Node {
  const Node *Base;

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

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

class UnnamedTypeName : public Node {
  const StringView Count;

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

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

class ClosureTypeName : public Node {
  NodeArray Params;
  StringView Count;

public:
  ClosureTypeName(NodeArray Params_, StringView Count_)
      : Node(KClosureTypeName), Params(Params_), Count(Count_) {}

  void printLeft(OutputStream &S) const override {
    S += "\'lambda";
    S += Count;
    S += "\'(";
    Params.printWithComma(S);
    S += ")";
  }
};

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

  void printLeft(OutputStream &S) const override {
    S += '[';
    Bindings.printWithComma(S);
    S += ']';
  }
};

// -- Expression Nodes --

struct Expr : public Node {
  Expr(Kind K = KExpr) : Node(K) {}
};

class BinaryExpr : public Expr {
  const Node *LHS;
  const StringView InfixOperator;
  const Node *RHS;

public:
  BinaryExpr(Node *LHS_, StringView InfixOperator_, Node *RHS_)
      : LHS(LHS_), InfixOperator(InfixOperator_), RHS(RHS_) {}

  void printLeft(OutputStream &S) const override {
    // might be a template argument expression, then we need to disambiguate
    // with parens.
    if (InfixOperator == ">")
      S += "(";

    S += "(";
    LHS->print(S);
    S += ") ";
    S += InfixOperator;
    S += " (";
    RHS->print(S);
    S += ")";

    if (InfixOperator == ">")
      S += ")";
  }
};

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

public:
  ArraySubscriptExpr(Node *Op1_, Node *Op2_) : Op1(Op1_), Op2(Op2_) {}

  void printLeft(OutputStream &S) const override {
    S += "(";
    Op1->print(S);
    S += ")[";
    Op2->print(S);
    S += "]";
  }
};

class PostfixExpr : public Expr {
  const Node *Child;
  const StringView Operand;

public:
  PostfixExpr(Node *Child_, StringView Operand_)
      : Child(Child_), Operand(Operand_) {}

  void printLeft(OutputStream &S) const override {
    S += "(";
    Child->print(S);
    S += ")";
    S += Operand;
  }
};

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

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

  void printLeft(OutputStream &S) const override {
    S += "(";
    Cond->print(S);
    S += ") ? (";
    Then->print(S);
    S += ") : (";
    Else->print(S);
    S += ")";
  }
};

class MemberExpr : public Expr {
  const Node *LHS;
  const StringView Kind;
  const Node *RHS;

public:
  MemberExpr(Node *LHS_, StringView Kind_, Node *RHS_)
      : LHS(LHS_), Kind(Kind_), RHS(RHS_) {}

  void printLeft(OutputStream &S) const override {
    LHS->print(S);
    S += Kind;
    RHS->print(S);
  }
};

class EnclosingExpr : public Expr {
  const StringView Prefix;
  const Node *Infix;
  const StringView Postfix;

public:
  EnclosingExpr(StringView Prefix_, Node *Infix_, StringView Postfix_)
      : Prefix(Prefix_), Infix(Infix_), Postfix(Postfix_) {}

  void printLeft(OutputStream &S) const override {
    S += Prefix;
    Infix->print(S);
    S += Postfix;
  }
};

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

public:
  CastExpr(StringView CastKind_, Node *To_, Node *From_)
      : CastKind(CastKind_), To(To_), From(From_) {}

  void printLeft(OutputStream &S) const override {
    S += CastKind;
    S += "<";
    To->printLeft(S);
    S += ">(";
    From->printLeft(S);
    S += ")";
  }
};

class SizeofParamPackExpr : public Expr {
  Node *Pack;

public:
  SizeofParamPackExpr(Node *Pack_) : Pack(Pack_) {}

  void printLeft(OutputStream &S) const override {
    S += "sizeof...(";
    ParameterPackExpansion PPE(Pack);
    PPE.printLeft(S);
    S += ")";
  }
};

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

public:
  CallExpr(Node *Callee_, NodeArray Args_) : Callee(Callee_), Args(Args_) {}

  void printLeft(OutputStream &S) const override {
    Callee->print(S);
    S += "(";
    Args.printWithComma(S);
    S += ")";
  }
};

class NewExpr : public Expr {
  // 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_)
      : ExprList(ExprList_), Type(Type_), InitList(InitList_),
        IsGlobal(IsGlobal_), IsArray(IsArray_) {}

  void printLeft(OutputStream &S) const override {
    if (IsGlobal)
      S += "::operator ";
    S += "new";
    if (IsArray)
      S += "[]";
    S += ' ';
    if (!ExprList.empty()) {
      S += "(";
      ExprList.printWithComma(S);
      S += ")";
    }
    Type->print(S);
    if (!InitList.empty()) {
      S += "(";
      InitList.printWithComma(S);
      S += ")";
    }

  }
};

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

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

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

class PrefixExpr : public Expr {
  StringView Prefix;
  Node *Child;

public:
  PrefixExpr(StringView Prefix_, Node *Child_) : Prefix(Prefix_), Child(Child_) {}

  void printLeft(OutputStream &S) const override {
    S += Prefix;
    S += "(";
    Child->print(S);
    S += ")";
  }
};

class FunctionParam : public Expr {
  StringView Number;

public:
  FunctionParam(StringView Number_) : Number(Number_) {}

  void printLeft(OutputStream &S) const override {
    S += "fp";
    S += Number;
  }
};

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

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

  void printLeft(OutputStream &S) const override {
    S += "(";
    Type->print(S);
    S += ")(";
    Expressions.printWithComma(S);
    S += ")";
  }
};

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

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

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

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

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

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

struct FoldExpr : Expr {
  Node *Pack, *Init;
  StringView OperatorName;
  bool IsLeftFold;

  FoldExpr(bool IsLeftFold_, StringView OperatorName_, Node *Pack_, Node *Init_)
      : Pack(Pack_), Init(Init_), OperatorName(OperatorName_),
        IsLeftFold(IsLeftFold_) {}

  void printLeft(OutputStream &S) const override {
    auto PrintPack = [&] {
      S += '(';
      ParameterPackExpansion(Pack).print(S);
      S += ')';
    };

    S += '(';

    if (IsLeftFold) {
      // init op ... op pack
      if (Init != nullptr) {
        Init->print(S);
        S += ' ';
        S += OperatorName;
        S += ' ';
      }
      // ... op pack
      S += "... ";
      S += OperatorName;
      S += ' ';
      PrintPack();
    } else { // !IsLeftFold
      // pack op ...
      PrintPack();
      S += ' ';
      S += OperatorName;
      S += " ...";
      // pack op ... op init
      if (Init != nullptr) {
        S += ' ';
        S += OperatorName;
        S += ' ';
        Init->print(S);
      }
    }
    S += ')';
  }
};

class ThrowExpr : public Expr {
  const Node *Op;

public:
  ThrowExpr(Node *Op_) : Op(Op_) {}

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

class BoolExpr : public Expr {
  bool Value;

public:
  BoolExpr(bool Value_) : Value(Value_) {}

  void printLeft(OutputStream &S) const override {
    S += Value ? StringView("true") : StringView("false");
  }
};

class IntegerCastExpr : public Expr {
  // ty(integer)
  Node *Ty;
  StringView Integer;

public:
  IntegerCastExpr(Node *Ty_, StringView Integer_)
      : Ty(Ty_), Integer(Integer_) {}

  void printLeft(OutputStream &S) const override {
    S += "(";
    Ty->print(S);
    S += ")";
    S += Integer;
  }
};

class IntegerExpr : public Expr {
  StringView Type;
  StringView Value;

public:
  IntegerExpr(StringView Type_, StringView Value_) : Type(Type_), Value(Value_) {}

  void printLeft(OutputStream &S) const override {
    if (Type.size() > 3) {
      S += "(";
      S += Type;
      S += ")";
    }

    if (Value[0] == 'n') {
      S += "-";
      S += Value.dropFront(1);
    } else
      S += Value;

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

template <class Float> struct FloatData;

template <class Float> class FloatExpr : public Expr {
  const StringView Contents;

public:
  FloatExpr(StringView Contents_) : Contents(Contents_) {}

  void printLeft(OutputStream &s) const override {
    const char *first = Contents.begin();
    const char *last = Contents.end() + 1;

    const size_t N = FloatData<Float>::mangled_size;
    if (static_cast<std::size_t>(last - first) > N) {
      last = first + N;
      union {
        Float value;
        char buf[sizeof(Float)];
      };
      const char *t = first;
      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);
      s += StringView(num, num + n);
    }
  }
};

class BumpPointerAllocator {
  struct BlockMeta {
    BlockMeta* Next;
    size_t Current;
  };

  static constexpr size_t AllocSize = 4096;
  static constexpr size_t UsableAllocSize = AllocSize - sizeof(BlockMeta);

  alignas(long double) char InitialBuffer[AllocSize];
  BlockMeta* BlockList = nullptr;

  void grow() {
    char* NewMeta = static_cast<char *>(std::malloc(AllocSize));
    if (NewMeta == nullptr)
      std::terminate();
    BlockList = new (NewMeta) BlockMeta{BlockList, 0};
  }

  void* allocateMassive(size_t NBytes) {
    NBytes += sizeof(BlockMeta);
    BlockMeta* NewMeta = reinterpret_cast<BlockMeta*>(std::malloc(NBytes));
    if (NewMeta == nullptr)
      std::terminate();
    BlockList->Next = new (NewMeta) BlockMeta{BlockList->Next, 0};
    return static_cast<void*>(NewMeta + 1);
  }

public:
  BumpPointerAllocator()
      : BlockList(new (InitialBuffer) BlockMeta{nullptr, 0}) {}

  void* allocate(size_t N) {
    N = (N + 15u) & ~15u;
    if (N + BlockList->Current >= UsableAllocSize) {
      if (N > UsableAllocSize)
        return allocateMassive(N);
      grow();
    }
    BlockList->Current += N;
    return static_cast<void*>(reinterpret_cast<char*>(BlockList + 1) +
                              BlockList->Current - N);
  }

  void reset() {
    while (BlockList) {
      BlockMeta* Tmp = BlockList;
      BlockList = BlockList->Next;
      if (reinterpret_cast<char*>(Tmp) != InitialBuffer)
        std::free(Tmp);
    }
    BlockList = new (InitialBuffer) BlockMeta{nullptr, 0};
  }

  ~BumpPointerAllocator() { reset(); }
};

template <class T, size_t N>
class PODSmallVector {
  static_assert(std::is_pod<T>::value,
                "T is required to be a plain old data type");

  T* First;
  T* Last;
  T* Cap;
  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::terminate();
      std::copy(First, Last, Tmp);
      First = Tmp;
    } else {
      First = static_cast<T*>(std::realloc(First, NewCap * sizeof(T)));
      if (First == nullptr)
        std::terminate();
    }
    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;
  }

  void push_back(const T& Elem) {
    if (Last == Cap)
      reserve(size() * 2);
    *Last++ = Elem;
  }

  void pop_back() {
    assert(Last != First && "Popping empty vector!");
    --Last;
  }

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

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

struct Db {
  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;

  // 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.
  PODSmallVector<Node *, 8> TemplateParams;

  // 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 ParsingLambdaParams = false;

  BumpPointerAllocator ASTAllocator;

  Db(const char *First_, const char *Last_) : First(First_), Last(Last_) {}

  void reset(const char *First_, const char *Last_) {
    First = First_;
    Last = Last_;
    Names.clear();
    Subs.clear();
    TemplateParams.clear();
    ParsingLambdaParams = false;
    TryToParseTemplateArgs = true;
    PermitForwardTemplateReferences = false;
    ASTAllocator.reset();
  }

  template <class T, class... Args> T *make(Args &&... args) {
    return new (ASTAllocator.allocate(sizeof(T)))
        T(std::forward<Args>(args)...);
  }

  template <class It> NodeArray makeNodeArray(It begin, It end) {
    size_t sz = static_cast<size_t>(end - begin);
    void *mem = ASTAllocator.allocate(sizeof(Node *) * sz);
    Node **data = new (mem) Node *[sz];
    std::copy(begin, end, data);
    return NodeArray(data, sz);
  }

  NodeArray popTrailingNodeArray(size_t FromPosition) {
    assert(FromPosition <= Names.size());
    NodeArray res =
        makeNodeArray(Names.begin() + (long)FromPosition, Names.end());
    Names.dropBack(FromPosition);
    return res;
  }

  bool consumeIf(StringView S) {
    if (StringView(First, Last).startsWith(S)) {
      First += S.size();
      return true;
    }
    return false;
  }

  bool consumeIf(char C) {
    if (First != Last && *First == C) {
      ++First;
      return true;
    }
    return false;
  }

  char consume() { return First != Last ? *First++ : '\0'; }

  char look(unsigned Lookahead = 0) {
    if (static_cast<size_t>(Last - First) <= Lookahead)
      return '\0';
    return First[Lookahead];
  }

  size_t numLeft() const { return static_cast<size_t>(Last - First); }

  StringView parseNumber(bool AllowNegative = false);
  Qualifiers parseCVQualifiers();
  bool parsePositiveInteger(size_t *Out);
  StringView parseBareSourceName();

  bool parseSeqId(size_t *Out);
  Node *parseSubstitution();
  Node *parseTemplateParam();
  Node *parseTemplateArgs(bool TagTemplates = false);
  Node *parseTemplateArg();

  /// Parse the <expr> production.
  Node *parseExpr();
  Node *parsePrefixExpr(StringView Kind);
  Node *parseBinaryExpr(StringView Kind);
  Node *parseIntegerLiteral(StringView Lit);
  Node *parseExprPrimary();
  template <class Float> Node *parseFloatingLiteral();
  Node *parseFunctionParam();
  Node *parseNewExpr();
  Node *parseConversionExpr();
  Node *parseBracedExpr();
  Node *parseFoldExpr();

  /// Parse the <type> production.
  Node *parseType();
  Node *parseFunctionType();
  Node *parseVectorType();
  Node *parseDecltype();
  Node *parseArrayType();
  Node *parsePointerToMemberType();
  Node *parseClassEnumType();
  Node *parseQualifiedType();

  Node *parseEncoding();
  bool parseCallOffset();
  Node *parseSpecialName();

  /// Holds some extra information about a <name> that is being parsed. This
  /// information is only pertinent if the <name> refers to an <encoding>.
  struct NameState {
    bool CtorDtorConversion = false;
    bool EndsWithTemplateArgs = false;
    Qualifiers CVQualifiers = QualNone;
    FunctionRefQual ReferenceQualifier = FrefQualNone;
    size_t ForwardTemplateRefsBegin;

    NameState(Db *Enclosing)
        : ForwardTemplateRefsBegin(Enclosing->ForwardTemplateRefs.size()) {}
  };

  bool resolveForwardTemplateRefs(NameState &State) {
    size_t I = State.ForwardTemplateRefsBegin;
    size_t E = ForwardTemplateRefs.size();
    for (; I < E; ++I) {
      size_t Idx = ForwardTemplateRefs[I]->Index;
      if (Idx >= TemplateParams.size())
        return true;
      ForwardTemplateRefs[I]->Ref = TemplateParams[Idx];
    }
    ForwardTemplateRefs.dropBack(State.ForwardTemplateRefsBegin);
    return false;
  }

  /// Parse the <name> production>
  Node *parseName(NameState *State = nullptr);
  Node *parseLocalName(NameState *State);
  Node *parseOperatorName(NameState *State);
  Node *parseUnqualifiedName(NameState *State);
  Node *parseUnnamedTypeName(NameState *State);
  Node *parseSourceName(NameState *State);
  Node *parseUnscopedName(NameState *State);
  Node *parseNestedName(NameState *State);
  Node *parseCtorDtorName(Node *&SoFar, NameState *State);

  Node *parseAbiTags(Node *N);

  /// Parse the <unresolved-name> production.
  Node *parseUnresolvedName();
  Node *parseSimpleId();
  Node *parseBaseUnresolvedName();
  Node *parseUnresolvedType();
  Node *parseDestructorName();

  /// Top-level entry point into the parser.
  Node *parse();
};

const char* parse_discriminator(const char* first, const char* last);

// <name> ::= <nested-name> // N
//        ::= <local-name> # See Scope Encoding below  // Z
//        ::= <unscoped-template-name> <template-args>
//        ::= <unscoped-name>
//
// <unscoped-template-name> ::= <unscoped-name>
//                          ::= <substitution>
Node *Db::parseName(NameState *State) {
  consumeIf('L'); // extension

  if (look() == 'N')
    return parseNestedName(State);
  if (look() == 'Z')
    return parseLocalName(State);

  //        ::= <unscoped-template-name> <template-args>
  if (look() == 'S' && look(1) != 't') {
    Node *S = parseSubstitution();
    if (S == nullptr)
      return nullptr;
    if (look() != 'I')
      return nullptr;
    Node *TA = parseTemplateArgs(State != nullptr);
    if (TA == nullptr)
      return nullptr;
    if (State) State->EndsWithTemplateArgs = true;
    return make<NameWithTemplateArgs>(S, TA);
  }

  Node *N = parseUnscopedName(State);
  if (N == nullptr)
    return nullptr;
  //        ::= <unscoped-template-name> <template-args>
  if (look() == 'I') {
    Subs.push_back(N);
    Node *TA = parseTemplateArgs(State != nullptr);
    if (TA == nullptr)
      return nullptr;
    if (State) State->EndsWithTemplateArgs = true;
    return make<NameWithTemplateArgs>(N, TA);
  }
  //        ::= <unscoped-name>
  return N;
}

// <local-name> := Z <function encoding> E <entity name> [<discriminator>]
//              := Z <function encoding> E s [<discriminator>]
//              := Z <function encoding> Ed [ <parameter number> ] _ <entity name>
Node *Db::parseLocalName(NameState *State) {
  if (!consumeIf('Z'))
    return nullptr;
  Node *Encoding = parseEncoding();
  if (Encoding == nullptr || !consumeIf('E'))
    return nullptr;

  if (consumeIf('s')) {
    First = parse_discriminator(First, Last);
    return make<LocalName>(Encoding, make<NameType>("string literal"));
  }

  if (consumeIf('d')) {
    parseNumber(true);
    if (!consumeIf('_'))
      return nullptr;
    Node *N = parseName(State);
    if (N == nullptr)
      return nullptr;
    return make<LocalName>(Encoding, N);
  }

  Node *Entity = parseName(State);
  if (Entity == nullptr)
    return nullptr;
  First = parse_discriminator(First, Last);
  return make<LocalName>(Encoding, Entity);
}

// <unscoped-name> ::= <unqualified-name>
//                 ::= St <unqualified-name>   # ::std::
// extension       ::= StL<unqualified-name>
Node *Db::parseUnscopedName(NameState *State) {
 if (consumeIf("StL") || consumeIf("St")) {
   Node *R = parseUnqualifiedName(State);
   if (R == nullptr)
     return nullptr;
   return make<StdQualifiedName>(R);
 }
 return parseUnqualifiedName(State);
}

// <unqualified-name> ::= <operator-name> [abi-tags]
//                    ::= <ctor-dtor-name>
//                    ::= <source-name>
//                    ::= <unnamed-type-name>
//                    ::= DC <source-name>+ E      # structured binding declaration
Node *Db::parseUnqualifiedName(NameState *State) {
 // <ctor-dtor-name>s are special-cased in parseNestedName().
 Node *Result;
 if (look() == 'U')
   Result = parseUnnamedTypeName(State);
 else if (look() >= '1' && look() <= '9')
   Result = parseSourceName(State);
 else if (consumeIf("DC")) {
   size_t BindingsBegin = Names.size();
   do {
     Node *Binding = parseSourceName(State);
     if (Binding == nullptr)
       return nullptr;
     Names.push_back(Binding);
   } while (!consumeIf('E'));
   Result = make<StructuredBindingName>(popTrailingNodeArray(BindingsBegin));
 } else
   Result = parseOperatorName(State);
 if (Result != nullptr)
   Result = parseAbiTags(Result);
 return Result;
}

// <unnamed-type-name> ::= Ut [<nonnegative number>] _
//                     ::= <closure-type-name>
//
// <closure-type-name> ::= Ul <lambda-sig> E [ <nonnegative number> ] _
//
// <lambda-sig> ::= <parameter type>+  # Parameter types or "v" if the lambda has no parameters
Node *Db::parseUnnamedTypeName(NameState *) {
  if (consumeIf("Ut")) {
    StringView Count = parseNumber();
    if (!consumeIf('_'))
      return nullptr;
    return make<UnnamedTypeName>(Count);
  }
  if (consumeIf("Ul")) {
    NodeArray Params;
    SwapAndRestore<bool> SwapParams(ParsingLambdaParams, true);
    if (!consumeIf("vE")) {
      size_t ParamsBegin = Names.size();
      do {
        Node *P = parseType();
        if (P == nullptr)
          return nullptr;
        Names.push_back(P);
      } while (!consumeIf('E'));
      Params = popTrailingNodeArray(ParamsBegin);
    }
    StringView Count = parseNumber();
    if (!consumeIf('_'))
      return nullptr;
    return make<ClosureTypeName>(Params, Count);
  }
  return nullptr;
}

// <source-name> ::= <positive length number> <identifier>
Node *Db::parseSourceName(NameState *) {
  size_t Length = 0;
  if (parsePositiveInteger(&Length))
    return nullptr;
  if (numLeft() < Length || Length == 0)
    return nullptr;
  StringView Name(First, First + Length);
  First += Length;
  if (Name.startsWith("_GLOBAL__N"))
    return make<NameType>("(anonymous namespace)");
  return make<NameType>(Name);
}

//   <operator-name> ::= aa    # &&
//                   ::= ad    # & (unary)
//                   ::= an    # &
//                   ::= aN    # &=
//                   ::= aS    # =
//                   ::= cl    # ()
//                   ::= cm    # ,
//                   ::= co    # ~
//                   ::= cv <type>    # (cast)
//                   ::= da    # delete[]
//                   ::= de    # * (unary)
//                   ::= dl    # delete
//                   ::= dv    # /
//                   ::= dV    # /=
//                   ::= eo    # ^
//                   ::= eO    # ^=
//                   ::= eq    # ==
//                   ::= ge    # >=
//                   ::= gt    # >
//                   ::= ix    # []
//                   ::= le    # <=
//                   ::= li <source-name>  # operator ""
//                   ::= ls    # <<
//                   ::= lS    # <<=
//                   ::= lt    # <
//                   ::= mi    # -
//                   ::= mI    # -=
//                   ::= ml    # *
//                   ::= mL    # *=
//                   ::= mm    # -- (postfix in <expression> context)
//                   ::= na    # new[]
//                   ::= ne    # !=
//                   ::= ng    # - (unary)
//                   ::= nt    # !
//                   ::= nw    # new
//                   ::= oo    # ||
//                   ::= or    # |
//                   ::= oR    # |=
//                   ::= pm    # ->*
//                   ::= pl    # +
//                   ::= pL    # +=
//                   ::= pp    # ++ (postfix in <expression> context)
//                   ::= ps    # + (unary)
//                   ::= pt    # ->
//                   ::= qu    # ?
//                   ::= rm    # %
//                   ::= rM    # %=
//                   ::= rs    # >>
//                   ::= rS    # >>=
//                   ::= ss    # <=> C++2a
//                   ::= v <digit> <source-name>        # vendor extended operator
Node *Db::parseOperatorName(NameState *State) {
  switch (look()) {
  case 'a':
    switch (look(1)) {
    case 'a':
      First += 2;
      return make<NameType>("operator&&");
    case 'd':
    case 'n':
      First += 2;
      return make<NameType>("operator&");
    case 'N':
      First += 2;
      return make<NameType>("operator&=");
    case 'S':
      First += 2;
      return make<NameType>("operator=");
    }
    return nullptr;
  case 'c':
    switch (look(1)) {
    case 'l':
      First += 2;
      return make<NameType>("operator()");
    case 'm':
      First += 2;
      return make<NameType>("operator,");
    case 'o':
      First += 2;
      return make<NameType>("operator~");
    //                   ::= cv <type>    # (cast)
    case 'v': {
      First += 2;
      SwapAndRestore<bool> SaveTemplate(TryToParseTemplateArgs, false);
      // If we're parsing an encoding, State != nullptr and the conversion
      // operators' <type> could have a <template-param> that refers to some
      // <template-arg>s further ahead in the mangled name.
      SwapAndRestore<bool> SavePermit(PermitForwardTemplateReferences,
                                      PermitForwardTemplateReferences ||
                                          State != nullptr);
      Node* Ty = parseType();
      if (Ty == nullptr)
        return nullptr;
      if (State) State->CtorDtorConversion = true;
      return make<ConversionOperatorType>(Ty);
    }
    }
    return nullptr;
  case 'd':
    switch (look(1)) {
    case 'a':
      First += 2;
      return make<NameType>("operator delete[]");
    case 'e':
      First += 2;
      return make<NameType>("operator*");
    case 'l':
      First += 2;
      return make<NameType>("operator delete");
    case 'v':
      First += 2;
      return make<NameType>("operator/");
    case 'V':
      First += 2;
      return make<NameType>("operator/=");
    }
    return nullptr;
  case 'e':
    switch (look(1)) {
    case 'o':
      First += 2;
      return make<NameType>("operator^");
    case 'O':
      First += 2;
      return make<NameType>("operator^=");
    case 'q':
      First += 2;
      return make<NameType>("operator==");
    }
    return nullptr;
  case 'g':
    switch (look(1)) {
    case 'e':
      First += 2;
      return make<NameType>("operator>=");
    case 't':
      First += 2;
      return make<NameType>("operator>");
    }
    return nullptr;
  case 'i':
    if (look(1) == 'x') {
      First += 2;
      return make<NameType>("operator[]");
    }
    return nullptr;
  case 'l':
    switch (look(1)) {
    case 'e':
      First += 2;
      return make<NameType>("operator<=");
    //                   ::= li <source-name>  # operator ""
    case 'i': {
      First += 2;
      Node *SN = parseSourceName(State);
      if (SN == nullptr)
        return nullptr;
      return make<LiteralOperator>(SN);
    }
    case 's':
      First += 2;
      return make<NameType>("operator<<");
    case 'S':
      First += 2;
      return make<NameType>("operator<<=");
    case 't':
      First += 2;
      return make<NameType>("operator<");
    }
    return nullptr;
  case 'm':
    switch (look(1)) {
    case 'i':
      First += 2;
      return make<NameType>("operator-");
    case 'I':
      First += 2;
      return make<NameType>("operator-=");
    case 'l':
      First += 2;
      return make<NameType>("operator*");
    case 'L':
      First += 2;
      return make<NameType>("operator*=");
    case 'm':
      First += 2;
      return make<NameType>("operator--");
    }
    return nullptr;
  case 'n':
    switch (look(1)) {
    case 'a':
      First += 2;
      return make<NameType>("operator new[]");
    case 'e':
      First += 2;
      return make<NameType>("operator!=");
    case 'g':
      First += 2;
      return make<NameType>("operator-");
    case 't':
      First += 2;
      return make<NameType>("operator!");
    case 'w':
      First += 2;
      return make<NameType>("operator new");
    }
    return nullptr;
  case 'o':
    switch (look(1)) {
    case 'o':
      First += 2;
      return make<NameType>("operator||");
    case 'r':
      First += 2;
      return make<NameType>("operator|");
    case 'R':
      First += 2;
      return make<NameType>("operator|=");
    }
    return nullptr;
  case 'p':
    switch (look(1)) {
    case 'm':
      First += 2;
      return make<NameType>("operator->*");
    case 'l':
      First += 2;
      return make<NameType>("operator+");
    case 'L':
      First += 2;
      return make<NameType>("operator+=");
    case 'p':
      First += 2;
      return make<NameType>("operator++");
    case 's':
      First += 2;
      return make<NameType>("operator+");
    case 't':
      First += 2;
      return make<NameType>("operator->");
    }
    return nullptr;
  case 'q':
    if (look(1) == 'u') {
      First += 2;
      return make<NameType>("operator?");
    }
    return nullptr;
  case 'r':
    switch (look(1)) {
    case 'm':
      First += 2;
      return make<NameType>("operator%");
    case 'M':
      First += 2;
      return make<NameType>("operator%=");
    case 's':
      First += 2;
      return make<NameType>("operator>>");
    case 'S':
      First += 2;
      return make<NameType>("operator>>=");
    }
    return nullptr;
  case 's':
    if (look(1) == 's') {
      First += 2;
      return make<NameType>("operator<=>");
    }
    return nullptr;
  // ::= v <digit> <source-name>        # vendor extended operator
  case 'v':
    if (std::isdigit(look(1))) {
      First += 2;
      Node *SN = parseSourceName(State);
      if (SN == nullptr)
        return nullptr;
      return make<ConversionOperatorType>(SN);
    }
    return nullptr;
  }
  return nullptr;
}

// <ctor-dtor-name> ::= C1  # complete object constructor
//                  ::= C2  # base object constructor
//                  ::= C3  # complete object allocating constructor
//   extension      ::= C5    # ?
//                  ::= D0  # deleting destructor
//                  ::= D1  # complete object destructor
//                  ::= D2  # base object destructor
//   extension      ::= D5    # ?
Node *Db::parseCtorDtorName(Node *&SoFar, NameState *State) {
  if (SoFar->K == Node::KSpecialSubstitution) {
    auto SSK = static_cast<SpecialSubstitution *>(SoFar)->SSK;
    switch (SSK) {
    case SpecialSubKind::string:
    case SpecialSubKind::istream:
    case SpecialSubKind::ostream:
    case SpecialSubKind::iostream:
      SoFar = make<ExpandedSpecialSubstitution>(SSK);
    default:
      break;
    }
  }

  if (consumeIf('C')) {
    bool IsInherited = consumeIf('I');
    if (look() != '1' && look() != '2' && look() != '3' && look() != '5')
      return nullptr;
    ++First;
    if (State) State->CtorDtorConversion = true;
    if (IsInherited) {
      if (parseName(State) == nullptr)
        return nullptr;
    }
    return make<CtorDtorName>(SoFar, false);
  }

  if (look() == 'D' &&
      (look(1) == '0' || look(1) == '1' || look(1) == '2' || look(1) == '5')) {
    First += 2;
    if (State) State->CtorDtorConversion = true;
    return make<CtorDtorName>(SoFar, true);
  }

  return nullptr;
}

// <nested-name> ::= N [<CV-Qualifiers>] [<ref-qualifier>] <prefix> <unqualified-name> E
//               ::= N [<CV-Qualifiers>] [<ref-qualifier>] <template-prefix> <template-args> E
//
// <prefix> ::= <prefix> <unqualified-name>
//          ::= <template-prefix> <template-args>
//          ::= <template-param>
//          ::= <decltype>
//          ::= # empty
//          ::= <substitution>
//          ::= <prefix> <data-member-prefix>
//  extension ::= L
//
// <data-member-prefix> := <member source-name> [<template-args>] M
//
// <template-prefix> ::= <prefix> <template unqualified-name>
//                   ::= <template-param>
//                   ::= <substitution>
Node *Db::parseNestedName(NameState *State) {
  if (!consumeIf('N'))
    return nullptr;

  Qualifiers CVTmp = parseCVQualifiers();
  if (State) State->CVQualifiers = CVTmp;

  if (consumeIf('O')) {
    if (State) State->ReferenceQualifier = FrefQualRValue;
  } else if (consumeIf('R')) {
    if (State) State->ReferenceQualifier = FrefQualLValue;
  } else
    if (State) State->ReferenceQualifier = FrefQualNone;

  Node *SoFar = nullptr;
  auto PushComponent = [&](Node *Comp) {
    if (SoFar) SoFar = make<NestedName>(SoFar, Comp);
    else       SoFar = Comp;
    if (State) State->EndsWithTemplateArgs = false;
  };

  if (consumeIf("St"))
    SoFar = make<NameType>("std");

  while (!consumeIf('E')) {
    consumeIf('L'); // extension

    // <data-member-prefix> := <member source-name> [<template-args>] M
    if (consumeIf('M')) {
      if (SoFar == nullptr)
        return nullptr;
      continue;
    }

    //          ::= <template-param>
    if (look() == 'T') {
      Node *TP = parseTemplateParam();
      if (TP == nullptr)
        return nullptr;
      PushComponent(TP);
      Subs.push_back(SoFar);
      continue;
    }

    //          ::= <template-prefix> <template-args>
    if (look() == 'I') {
      Node *TA = parseTemplateArgs(State != nullptr);
      if (TA == nullptr || SoFar == nullptr)
        return nullptr;
      SoFar = make<NameWithTemplateArgs>(SoFar, TA);
      if (State) State->EndsWithTemplateArgs = true;
      Subs.push_back(SoFar);
      continue;
    }

    //          ::= <decltype>
    if (look() == 'D' && (look(1) == 't' || look(1) == 'T')) {
      Node *DT = parseDecltype();
      if (DT == nullptr)
        return nullptr;
      PushComponent(DT);
      Subs.push_back(SoFar);
      continue;
    }

    //          ::= <substitution>
    if (look() == 'S' && look(1) != 't') {
      Node *S = parseSubstitution();
      if (S == nullptr)
        return nullptr;
      PushComponent(S);
      if (SoFar != S)
        Subs.push_back(S);
      continue;
    }

    // Parse an <unqualified-name> thats actually a <ctor-dtor-name>.
    if (look() == 'C' || (look() == 'D' && look(1) != 'C')) {
      if (SoFar == nullptr)
        return nullptr;
      Node *CtorDtor = parseCtorDtorName(SoFar, State);
      if (CtorDtor == nullptr)
        return nullptr;
      PushComponent(CtorDtor);
      SoFar = parseAbiTags(SoFar);
      if (SoFar == nullptr)
        return nullptr;
      Subs.push_back(SoFar);
      continue;
    }

    //          ::= <prefix> <unqualified-name>
    Node *N = parseUnqualifiedName(State);
    if (N == nullptr)
      return nullptr;
    PushComponent(N);
    Subs.push_back(SoFar);
  }

  if (SoFar == nullptr || Subs.empty())
    return nullptr;

  Subs.pop_back();
  return SoFar;
}

// <simple-id> ::= <source-name> [ <template-args> ]
Node *Db::parseSimpleId() {
  Node *SN = parseSourceName(/*NameState=*/nullptr);
  if (SN == nullptr)
    return nullptr;
  if (look() == 'I') {
    Node *TA = parseTemplateArgs();
    if (TA == nullptr)
      return nullptr;
    return make<NameWithTemplateArgs>(SN, TA);
  }
  return SN;
}

// <destructor-name> ::= <unresolved-type>  # e.g., ~T or ~decltype(f())
//                   ::= <simple-id>        # e.g., ~A<2*N>
Node *Db::parseDestructorName() {
  Node *Result;
  if (std::isdigit(look()))
    Result = parseSimpleId();
  else
    Result = parseUnresolvedType();
  if (Result == nullptr)
    return nullptr;
  return make<DtorName>(Result);
}

// <unresolved-type> ::= <template-param>
//                   ::= <decltype>
//                   ::= <substitution>
Node *Db::parseUnresolvedType() {
  if (look() == 'T') {
    Node *TP = parseTemplateParam();
    if (TP == nullptr)
      return nullptr;
    Subs.push_back(TP);
    return TP;
  }
  if (look() == 'D') {
    Node *DT = parseDecltype();
    if (DT == nullptr)
      return nullptr;
    Subs.push_back(DT);
    return DT;
  }
  return parseSubstitution();
}

// <base-unresolved-name> ::= <simple-id>                                # unresolved name
//          extension     ::= <operator-name>                            # unresolved operator-function-id
//          extension     ::= <operator-name> <template-args>            # unresolved operator template-id
//                        ::= on <operator-name>                         # unresolved operator-function-id
//                        ::= on <operator-name> <template-args>         # unresolved operator template-id
//                        ::= dn <destructor-name>                       # destructor or pseudo-destructor;
//                                                                         # e.g. ~X or ~X<N-1>
Node *Db::parseBaseUnresolvedName() {
  if (std::isdigit(look()))
    return parseSimpleId();