YAMLTraits.h

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//===- llvm/Support/YAMLTraits.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
//
//===----------------------------------------------------------------------===//
 
#ifndef LLVM_SUPPORT_YAMLTRAITS_H
#define LLVM_SUPPORT_YAMLTRAITS_H
 
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/BitVector.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/Twine.h"
#include "llvm/Support/AlignOf.h"
#include "llvm/Support/Allocator.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Endian.h"
#include "llvm/Support/SMLoc.h"
#include "llvm/Support/SourceMgr.h"
#include "llvm/Support/YAMLParser.h"
#include "llvm/Support/raw_ostream.h"
#include <array>
#include <cassert>
#include <map>
#include <memory>
#include <new>
#include <optional>
#include <string>
#include <system_error>
#include <type_traits>
#include <vector>
 
namespace llvm {
 
class VersionTuple;
 
namespace yaml {
 
enum class NodeKind : uint8_t {
  Scalar,
  Map,
  Sequence,
};
 
struct EmptyContext {};
 
/// This class should be specialized by any type that needs to be converted
/// to/from a YAML mapping.  For example:
///
///     struct MappingTraits<MyStruct> {
///       static void mapping(IO &io, MyStruct &s) {
///         io.mapRequired("name", s.name);
///         io.mapRequired("size", s.size);
///         io.mapOptional("age",  s.age);
///       }
///     };
template <class T> struct MappingTraits {
  // Must provide:
  // static void mapping(IO &io, T &fields);
  // Optionally may provide:
  // static std::string validate(IO &io, T &fields);
  // static void enumInput(IO &io, T &value);
  //
  // The optional flow flag will cause generated YAML to use a flow mapping
  // (e.g. { a: 0, b: 1 }):
  // static const bool flow = true;
};
 
/// This class is similar to MappingTraits<T> but allows you to pass in
/// additional context for each map operation.  For example:
///
///     struct MappingContextTraits<MyStruct, MyContext> {
///       static void mapping(IO &io, MyStruct &s, MyContext &c) {
///         io.mapRequired("name", s.name);
///         io.mapRequired("size", s.size);
///         io.mapOptional("age",  s.age);
///         ++c.TimesMapped;
///       }
///     };
template <class T, class Context> struct MappingContextTraits {
  // Must provide:
  // static void mapping(IO &io, T &fields, Context &Ctx);
  // Optionally may provide:
  // static std::string validate(IO &io, T &fields, Context &Ctx);
  //
  // The optional flow flag will cause generated YAML to use a flow mapping
  // (e.g. { a: 0, b: 1 }):
  // static const bool flow = true;
};
 
/// This class should be specialized by any integral type that converts
/// to/from a YAML scalar where there is a one-to-one mapping between
/// in-memory values and a string in YAML.  For example:
///
///     struct ScalarEnumerationTraits<Colors> {
///         static void enumeration(IO &io, Colors &value) {
///           io.enumCase(value, "red",   cRed);
///           io.enumCase(value, "blue",  cBlue);
///           io.enumCase(value, "green", cGreen);
///         }
///       };
template <typename T, typename Enable = void> struct ScalarEnumerationTraits {
  // Must provide:
  // static void enumeration(IO &io, T &value);
};
 
/// This class should be specialized by any integer type that is a union
/// of bit values and the YAML representation is a flow sequence of
/// strings.  For example:
///
///      struct ScalarBitSetTraits<MyFlags> {
///        static void bitset(IO &io, MyFlags &value) {
///          io.bitSetCase(value, "big",   flagBig);
///          io.bitSetCase(value, "flat",  flagFlat);
///          io.bitSetCase(value, "round", flagRound);
///        }
///      };
template <typename T, typename Enable = void> struct ScalarBitSetTraits {
  // Must provide:
  // static void bitset(IO &io, T &value);
};
 
/// Describe which type of quotes should be used when quoting is necessary.
/// Some non-printable characters need to be double-quoted, while some others
/// are fine with simple-quoting, and some don't need any quoting.
enum class QuotingType { None, Single, Double };
 
/// This class should be specialized by type that requires custom conversion
/// to/from a yaml scalar.  For example:
///
///    template<>
///    struct ScalarTraits<MyType> {
///      static void output(const MyType &val, void*, llvm::raw_ostream &out) {
///        // stream out custom formatting
///        out << llvm::format("%x", val);
///      }
///      static StringRef input(StringRef scalar, void*, MyType &value) {
///        // parse scalar and set `value`
///        // return empty string on success, or error string
///        return StringRef();
///      }
///      static QuotingType mustQuote(StringRef) { return QuotingType::Single; }
///    };
template <typename T, typename Enable = void> struct ScalarTraits {
  // Must provide:
  //
  // Function to write the value as a string:
  // static void output(const T &value, void *ctxt, llvm::raw_ostream &out);
  //
  // Function to convert a string to a value.  Returns the empty
  // StringRef on success or an error string if string is malformed:
  // static StringRef input(StringRef scalar, void *ctxt, T &value);
  //
  // Function to determine if the value should be quoted.
  // static QuotingType mustQuote(StringRef);
};
 
/// This class should be specialized by type that requires custom conversion
/// to/from a YAML literal block scalar. For example:
///
///    template <>
///    struct BlockScalarTraits<MyType> {
///      static void output(const MyType &Value, void*, llvm::raw_ostream &Out)
///      {
///        // stream out custom formatting
///        Out << Value;
///      }
///      static StringRef input(StringRef Scalar, void*, MyType &Value) {
///        // parse scalar and set `value`
///        // return empty string on success, or error string
///        return StringRef();
///      }
///    };
template <typename T> struct BlockScalarTraits {
  // Must provide:
  //
  // Function to write the value as a string:
  // static void output(const T &Value, void *ctx, llvm::raw_ostream &Out);
  //
  // Function to convert a string to a value.  Returns the empty
  // StringRef on success or an error string if string is malformed:
  // static StringRef input(StringRef Scalar, void *ctxt, T &Value);
  //
  // Optional:
  // static StringRef inputTag(T &Val, std::string Tag)
  // static void outputTag(const T &Val, raw_ostream &Out)
};
 
/// This class should be specialized by type that requires custom conversion
/// to/from a YAML scalar with optional tags. For example:
///
///    template <>
///    struct TaggedScalarTraits<MyType> {
///      static void output(const MyType &Value, void*, llvm::raw_ostream
///      &ScalarOut, llvm::raw_ostream &TagOut)
///      {
///        // stream out custom formatting including optional Tag
///        Out << Value;
///      }
///      static StringRef input(StringRef Scalar, StringRef Tag, void*, MyType
///      &Value) {
///        // parse scalar and set `value`
///        // return empty string on success, or error string
///        return StringRef();
///      }
///      static QuotingType mustQuote(const MyType &Value, StringRef) {
///        return QuotingType::Single;
///      }
///    };
template <typename T> struct TaggedScalarTraits {
  // Must provide:
  //
  // Function to write the value and tag as strings:
  // static void output(const T &Value, void *ctx, llvm::raw_ostream &ScalarOut,
  // llvm::raw_ostream &TagOut);
  //
  // Function to convert a string to a value.  Returns the empty
  // StringRef on success or an error string if string is malformed:
  // static StringRef input(StringRef Scalar, StringRef Tag, void *ctxt, T
  // &Value);
  //
  // Function to determine if the value should be quoted.
  // static QuotingType mustQuote(const T &Value, StringRef Scalar);
};
 
/// This class should be specialized by any type that needs to be converted
/// to/from a YAML sequence.  For example:
///
///    template<>
///    struct SequenceTraits<MyContainer> {
///      static size_t size(IO &io, MyContainer &seq) {
///        return seq.size();
///      }
///      static MyType& element(IO &, MyContainer &seq, size_t index) {
///        if ( index >= seq.size() )
///          seq.resize(index+1);
///        return seq[index];
///      }
///    };
template <typename T, typename EnableIf = void> struct SequenceTraits {
  // Must provide:
  // static size_t size(IO &io, T &seq);
  // static T::value_type& element(IO &io, T &seq, size_t index);
  //
  // The following is option and will cause generated YAML to use
  // a flow sequence (e.g. [a,b,c]).
  // static const bool flow = true;
};
 
/// This class should be specialized by any type for which vectors of that
/// type need to be converted to/from a YAML sequence.
template <typename T, typename EnableIf = void> struct SequenceElementTraits {
  // Must provide:
  // static const bool flow;
};
 
/// This class should be specialized by any type that needs to be converted
/// to/from a list of YAML documents.
template <typename T> struct DocumentListTraits {
  // Must provide:
  // static size_t size(IO &io, T &seq);
  // static T::value_type& element(IO &io, T &seq, size_t index);
};
 
/// This class should be specialized by any type that needs to be converted
/// to/from a YAML mapping in the case where the names of the keys are not known
/// in advance, e.g. a string map.
template <typename T> struct CustomMappingTraits {
  // static void inputOne(IO &io, StringRef key, T &elem);
  // static void output(IO &io, T &elem);
};
 
/// This class should be specialized by any type that can be represented as
/// a scalar, map, or sequence, decided dynamically. For example:
///
///    typedef std::unique_ptr<MyBase> MyPoly;
///
///    template<>
///    struct PolymorphicTraits<MyPoly> {
///      static NodeKind getKind(const MyPoly &poly) {
///        return poly->getKind();
///      }
///      static MyScalar& getAsScalar(MyPoly &poly) {
///        if (!poly || !isa<MyScalar>(poly))
///          poly.reset(new MyScalar());
///        return *cast<MyScalar>(poly.get());
///      }
///      // ...
///    };
template <typename T> struct PolymorphicTraits {
  // Must provide:
  // static NodeKind getKind(const T &poly);
  // static scalar_type &getAsScalar(T &poly);
  // static map_type &getAsMap(T &poly);
  // static sequence_type &getAsSequence(T &poly);
};
 
// Only used for better diagnostics of missing traits
template <typename T> struct MissingTrait;
 
// Test if ScalarEnumerationTraits<T> is defined on type T.
template <class T> struct has_ScalarEnumerationTraits {
  using SignatureEnumeration = void (*)(class IO &, T &);
 
  template <class U>
  using check =
      SameType<SignatureEnumeration, &ScalarEnumerationTraits<U>::enumeration>;
 
  static constexpr bool value = is_detected<check, T>::value;
};
 
// Test if ScalarBitSetTraits<T> is defined on type T.
template <class T> struct has_ScalarBitSetTraits {
  using SignatureBitset = void (*)(class IO &, T &);
 
  template <class U>
  using check = SameType<SignatureBitset, &ScalarBitSetTraits<U>::bitset>;
 
  static constexpr bool value = is_detected<check, T>::value;
};
 
// Test if ScalarTraits<T> is defined on type T.
template <class T> struct has_ScalarTraits {
  using SignatureInput = StringRef (*)(StringRef, void *, T &);
  using SignatureOutput = void (*)(const T &, void *, raw_ostream &);
  using SignatureMustQuote = QuotingType (*)(StringRef);
 
  template <class U>
  using check = std::tuple<SameType<SignatureInput, &U::input>,
                           SameType<SignatureOutput, &U::output>,
                           SameType<SignatureMustQuote, &U::mustQuote>>;
 
  static constexpr bool value = is_detected<check, ScalarTraits<T>>::value;
};
 
// Test if BlockScalarTraits<T> is defined on type T.
template <class T> struct has_BlockScalarTraits {
  using SignatureInput = StringRef (*)(StringRef, void *, T &);
  using SignatureOutput = void (*)(const T &, void *, raw_ostream &);
 
  template <class U>
  using check = std::tuple<SameType<SignatureInput, &U::input>,
                           SameType<SignatureOutput, &U::output>>;
 
  static constexpr bool value = is_detected<check, BlockScalarTraits<T>>::value;
};
 
// Test if TaggedScalarTraits<T> is defined on type T.
template <class T> struct has_TaggedScalarTraits {
  using SignatureInput = StringRef (*)(StringRef, StringRef, void *, T &);
  using SignatureOutput = void (*)(const T &, void *, raw_ostream &,
                                   raw_ostream &);
  using SignatureMustQuote = QuotingType (*)(const T &, StringRef);
 
  template <class U>
  using check = std::tuple<SameType<SignatureInput, &U::input>,
                           SameType<SignatureOutput, &U::output>,
                           SameType<SignatureMustQuote, &U::mustQuote>>;
 
  static constexpr bool value =
      is_detected<check, TaggedScalarTraits<T>>::value;
};
 
// Test if MappingContextTraits<T> is defined on type T.
template <class T, class Context> struct has_MappingTraits {
  using SignatureMapping = void (*)(class IO &, T &, Context &);
 
  template <class U> using check = SameType<SignatureMapping, &U::mapping>;
 
  static constexpr bool value =
      is_detected<check, MappingContextTraits<T, Context>>::value;
};
 
// Test if MappingTraits<T> is defined on type T.
template <class T> struct has_MappingTraits<T, EmptyContext> {
  using SignatureMapping = void (*)(class IO &, T &);
 
  template <class U> using check = SameType<SignatureMapping, &U::mapping>;
 
  static constexpr bool value = is_detected<check, MappingTraits<T>>::value;
};
 
// Test if MappingContextTraits<T>::validate() is defined on type T.
template <class T, class Context> struct has_MappingValidateTraits {
  using SignatureValidate = std::string (*)(class IO &, T &, Context &);
 
  template <class U> using check = SameType<SignatureValidate, &U::validate>;
 
  static constexpr bool value =
      is_detected<check, MappingContextTraits<T, Context>>::value;
};
 
// Test if MappingTraits<T>::validate() is defined on type T.
template <class T> struct has_MappingValidateTraits<T, EmptyContext> {
  using SignatureValidate = std::string (*)(class IO &, T &);
 
  template <class U> using check = SameType<SignatureValidate, &U::validate>;
 
  static constexpr bool value = is_detected<check, MappingTraits<T>>::value;
};
 
// Test if MappingContextTraits<T>::enumInput() is defined on type T.
template <class T, class Context> struct has_MappingEnumInputTraits {
  using SignatureEnumInput = void (*)(class IO &, T &);
 
  template <class U> using check = SameType<SignatureEnumInput, &U::enumInput>;
 
  static constexpr bool value =
      is_detected<check, MappingContextTraits<T, Context>>::value;
};
 
// Test if MappingTraits<T>::enumInput() is defined on type T.
template <class T> struct has_MappingEnumInputTraits<T, EmptyContext> {
  using SignatureEnumInput = void (*)(class IO &, T &);
 
  template <class U> using check = SameType<SignatureEnumInput, &U::enumInput>;
 
  static constexpr bool value = is_detected<check, MappingTraits<T>>::value;
};
 
// Test if SequenceTraits<T> is defined on type T.
template <class T> struct has_SequenceMethodTraits {
  using SignatureSize = size_t (*)(class IO &, T &);
 
  template <class U> using check = SameType<SignatureSize, &U::size>;
 
  static constexpr bool value = is_detected<check, SequenceTraits<T>>::value;
};
 
// Test if CustomMappingTraits<T> is defined on type T.
template <class T> struct has_CustomMappingTraits {
  using SignatureInput = void (*)(IO &io, StringRef key, T &v);
 
  template <class U> using check = SameType<SignatureInput, &U::inputOne>;
 
  static constexpr bool value =
      is_detected<check, CustomMappingTraits<T>>::value;
};
 
// has_FlowTraits<int> will cause an error with some compilers because
// it subclasses int.  Using this wrapper only instantiates the
// real has_FlowTraits only if the template type is a class.
template <typename T, bool Enabled = std::is_class_v<T>> class has_FlowTraits {
public:
  static constexpr bool value = false;
};
 
template <class T> struct has_FlowTraits<T, true> {
  template <class U> using check = decltype(&U::flow);
 
  static constexpr bool value = is_detected<check, T>::value;
};
 
// Test if SequenceTraits<T> is defined on type T
template <typename T>
struct has_SequenceTraits
    : public std::bool_constant<has_SequenceMethodTraits<T>::value> {};
 
// Test if DocumentListTraits<T> is defined on type T
template <class T> struct has_DocumentListTraits {
  using SignatureSize = size_t (*)(class IO &, T &);
 
  template <class U> using check = SameType<SignatureSize, &U::size>;
 
  static constexpr bool value =
      is_detected<check, DocumentListTraits<T>>::value;
};
 
template <class T> struct has_PolymorphicTraits {
  using SignatureGetKind = NodeKind (*)(const T &);
 
  template <class U> using check = SameType<SignatureGetKind, &U::getKind>;
 
  static constexpr bool value = is_detected<check, PolymorphicTraits<T>>::value;
};
 
inline bool isNumeric(StringRef S) {
  const auto skipDigits = [](StringRef Input) {
    return Input.ltrim("0123456789");
  };
 
  // Make S.front() and S.drop_front().front() (if S.front() is [+-]) calls
  // safe.
  if (S.empty() || S == "+" || S == "-")
    return false;
 
  if (S == ".nan" || S == ".NaN" || S == ".NAN")
    return true;
 
  // Infinity and decimal numbers can be prefixed with sign.
  StringRef Tail = (S.front() == '-' || S.front() == '+') ? S.drop_front() : S;
 
  // Check for infinity first, because checking for hex and oct numbers is more
  // expensive.
  if (Tail == ".inf" || Tail == ".Inf" || Tail == ".INF")
    return true;
 
  // Section 10.3.2 Tag Resolution
  // YAML 1.2 Specification prohibits Base 8 and Base 16 numbers prefixed with
  // [-+], so S should be used instead of Tail.
  if (S.starts_with("0o"))
    return S.size() > 2 &&
           S.drop_front(2).find_first_not_of("01234567") == StringRef::npos;
 
  if (S.starts_with("0x"))
    return S.size() > 2 && S.drop_front(2).find_first_not_of(
                               "0123456789abcdefABCDEF") == StringRef::npos;
 
  // Parse float: [-+]? (\. [0-9]+ | [0-9]+ (\. [0-9]* )?) ([eE] [-+]? [0-9]+)?
  S = Tail;
 
  // Handle cases when the number starts with '.' and hence needs at least one
  // digit after dot (as opposed by number which has digits before the dot), but
  // doesn't have one.
  if (S.starts_with(".") &&
      (S == "." ||
       (S.size() > 1 && std::strchr("0123456789", S[1]) == nullptr)))
    return false;
 
  if (S.starts_with("E") || S.starts_with("e"))
    return false;
 
  enum ParseState {
    Default,
    FoundDot,
    FoundExponent,
  };
  ParseState State = Default;
 
  S = skipDigits(S);
 
  // Accept decimal integer.
  if (S.empty())
    return true;
 
  if (S.front() == '.') {
    State = FoundDot;
    S = S.drop_front();
  } else if (S.front() == 'e' || S.front() == 'E') {
    State = FoundExponent;
    S = S.drop_front();
  } else {
    return false;
  }
 
  if (State == FoundDot) {
    S = skipDigits(S);
    if (S.empty())
      return true;
 
    if (S.front() == 'e' || S.front() == 'E') {
      State = FoundExponent;
      S = S.drop_front();
    } else {
      return false;
    }
  }
 
  assert(State == FoundExponent && "Should have found exponent at this point.");
  if (S.empty())
    return false;
 
  if (S.front() == '+' || S.front() == '-') {
    S = S.drop_front();
    if (S.empty())
      return false;
  }
 
  return skipDigits(S).empty();
}
 
inline bool isNull(StringRef S) {
  return S == "null" || S == "Null" || S == "NULL" || S == "~";
}
 
inline bool isBool(StringRef S) {
  // FIXME: using parseBool is causing multiple tests to fail.
  return S == "true" || S == "True" || S == "TRUE" || S == "false" ||
         S == "False" || S == "FALSE";
}
 
// 5.1. Character Set
// The allowed character range explicitly excludes the C0 control block #x0-#x1F
// (except for TAB #x9, LF #xA, and CR #xD which are allowed), DEL #x7F, the C1
// control block #x80-#x9F (except for NEL #x85 which is allowed), the surrogate
// block #xD800-#xDFFF, #xFFFE, and #xFFFF.
//
// Some strings are valid YAML values even unquoted, but without quotes are
// interpreted as non-string type, for instance null, boolean or numeric values.
// If ForcePreserveAsString is set, such strings are quoted.
inline QuotingType needsQuotes(StringRef S, bool ForcePreserveAsString = true) {
  if (S.empty())
    return QuotingType::Single;
 
  QuotingType MaxQuotingNeeded = QuotingType::None;
  if (isSpace(static_cast<unsigned char>(S.front())) ||
      isSpace(static_cast<unsigned char>(S.back())))
    MaxQuotingNeeded = QuotingType::Single;
  if (ForcePreserveAsString) {
    if (isNull(S))
      MaxQuotingNeeded = QuotingType::Single;
    if (isBool(S))
      MaxQuotingNeeded = QuotingType::Single;
    if (isNumeric(S))
      MaxQuotingNeeded = QuotingType::Single;
  }
 
  // 7.3.3 Plain Style
  // Plain scalars must not begin with most indicators, as this would cause
  // ambiguity with other YAML constructs.
  if (std::strchr(R"(-?:\,[]{}#&*!|>'"%@`)", S[0]) != nullptr)
    MaxQuotingNeeded = QuotingType::Single;
 
  for (unsigned char C : S) {
    // Alphanum is safe.
    if (isAlnum(C))
      continue;
 
    switch (C) {
    // Safe scalar characters.
    case '_':
    case '-':
    case '^':
    case '.':
    case ',':
    case ' ':
    // TAB (0x9) is allowed in unquoted strings.
    case 0x9:
      continue;
    // LF(0xA) and CR(0xD) may delimit values and so require at least single
    // quotes. LLVM YAML parser cannot handle single quoted multiline so use
    // double quoting to produce valid YAML.
    case 0xA:
    case 0xD:
      return QuotingType::Double;
    // DEL (0x7F) are excluded from the allowed character range.
    case 0x7F:
      return QuotingType::Double;
    // Forward slash is allowed to be unquoted, but we quote it anyway.  We have
    // many tests that use FileCheck against YAML output, and this output often
    // contains paths.  If we quote backslashes but not forward slashes then
    // paths will come out either quoted or unquoted depending on which platform
    // the test is run on, making FileCheck comparisons difficult.
    case '/':
    default: {
      // C0 control block (0x0 - 0x1F) is excluded from the allowed character
      // range.
      if (C <= 0x1F)
        return QuotingType::Double;
 
      // Always double quote UTF-8.
      if ((C & 0x80) != 0)
        return QuotingType::Double;
 
      // The character is not safe, at least simple quoting needed.
      MaxQuotingNeeded = QuotingType::Single;
    }
    }
  }
 
  return MaxQuotingNeeded;
}
 
template <typename T, typename Context>
struct missingTraits
    : public std::bool_constant<
          !has_ScalarEnumerationTraits<T>::value &&
          !has_ScalarBitSetTraits<T>::value && !has_ScalarTraits<T>::value &&
          !has_BlockScalarTraits<T>::value &&
          !has_TaggedScalarTraits<T>::value &&
          !has_MappingTraits<T, Context>::value &&
          !has_SequenceTraits<T>::value && !has_CustomMappingTraits<T>::value &&
          !has_DocumentListTraits<T>::value &&
          !has_PolymorphicTraits<T>::value> {};
 
template <typename T, typename Context>
struct validatedMappingTraits
    : public std::bool_constant<has_MappingTraits<T, Context>::value &&
                                has_MappingValidateTraits<T, Context>::value> {
};
 
template <typename T, typename Context>
struct unvalidatedMappingTraits
    : public std::bool_constant<has_MappingTraits<T, Context>::value &&
                                !has_MappingValidateTraits<T, Context>::value> {
};
 
// Base class for Input and Output.
class LLVM_ABI IO {
public:
  IO(void *Ctxt = nullptr);
  virtual ~IO();
 
  virtual bool outputting() const = 0;
 
  virtual unsigned beginSequence() = 0;
  virtual bool preflightElement(unsigned, void *&) = 0;
  virtual void postflightElement(void *) = 0;
  virtual void endSequence() = 0;
  virtual bool canElideEmptySequence() = 0;
 
  virtual unsigned beginFlowSequence() = 0;
  virtual bool preflightFlowElement(unsigned, void *&) = 0;
  virtual void postflightFlowElement(void *) = 0;
  virtual void endFlowSequence() = 0;
 
  virtual bool mapTag(StringRef Tag, bool Default = false) = 0;
  virtual void beginMapping() = 0;
  virtual void endMapping() = 0;
  virtual bool preflightKey(const char *, bool, bool, bool &, void *&) = 0;
  virtual void postflightKey(void *) = 0;
  virtual std::vector<StringRef> keys() = 0;
 
  virtual void beginFlowMapping() = 0;
  virtual void endFlowMapping() = 0;
 
  virtual void beginEnumScalar() = 0;
  virtual bool matchEnumScalar(const char *, bool) = 0;
  virtual bool matchEnumFallback() = 0;
  virtual void endEnumScalar() = 0;
 
  virtual bool beginBitSetScalar(bool &) = 0;
  virtual bool bitSetMatch(const char *, bool) = 0;
  virtual void endBitSetScalar() = 0;
 
  virtual void scalarString(StringRef &, QuotingType) = 0;
  virtual void blockScalarString(StringRef &) = 0;
  virtual void scalarTag(std::string &) = 0;
 
  virtual NodeKind getNodeKind() = 0;
 
  virtual void setError(const Twine &) = 0;
  virtual std::error_code error() = 0;
  virtual void setAllowUnknownKeys(bool Allow);
 
  template <typename T>
  void enumCase(T &Val, const char *Str, const T ConstVal) {
    if (matchEnumScalar(Str, outputting() && Val == ConstVal)) {
      Val = ConstVal;
    }
  }
 
  // allow anonymous enum values to be used with LLVM_YAML_STRONG_TYPEDEF
  template <typename T>
  void enumCase(T &Val, const char *Str, const uint32_t ConstVal) {
    if (matchEnumScalar(Str, outputting() && Val == static_cast<T>(ConstVal))) {
      Val = ConstVal;
    }
  }
 
  template <typename FBT, typename T> void enumFallback(T &Val) {
    if (matchEnumFallback()) {
      EmptyContext Context;
      // FIXME: Force integral conversion to allow strong typedefs to convert.
      FBT Res = static_cast<typename FBT::BaseType>(Val);
      yamlize(*this, Res, true, Context);
      Val = static_cast<T>(static_cast<typename FBT::BaseType>(Res));
    }
  }
 
  template <typename T>
  void bitSetCase(T &Val, const char *Str, const T ConstVal) {
    if (bitSetMatch(Str, outputting() && (Val & ConstVal) == ConstVal)) {
      Val = static_cast<T>(Val | ConstVal);
    }
  }
 
  // allow anonymous enum values to be used with LLVM_YAML_STRONG_TYPEDEF
  template <typename T>
  void bitSetCase(T &Val, const char *Str, const uint32_t ConstVal) {
    if (bitSetMatch(Str, outputting() && (Val & ConstVal) == ConstVal)) {
      Val = static_cast<T>(Val | ConstVal);
    }
  }
 
  template <typename T>
  void maskedBitSetCase(T &Val, const char *Str, T ConstVal, T Mask) {
    if (bitSetMatch(Str, outputting() && (Val & Mask) == ConstVal))
      Val = Val | ConstVal;
  }
 
  template <typename T>
  void maskedBitSetCase(T &Val, const char *Str, uint32_t ConstVal,
                        uint32_t Mask) {
    if (bitSetMatch(Str, outputting() && (Val & Mask) == ConstVal))
      Val = Val | ConstVal;
  }
 
  void *getContext() const;
  void setContext(void *);
 
  template <typename T> void mapRequired(const char *Key, T &Val) {
    EmptyContext Ctx;
    this->processKey(Key, Val, true, Ctx);
  }
 
  template <typename T, typename Context>
  void mapRequired(const char *Key, T &Val, Context &Ctx) {
    this->processKey(Key, Val, true, Ctx);
  }
 
  template <typename T> void mapOptional(const char *Key, T &Val) {
    EmptyContext Ctx;
    mapOptionalWithContext(Key, Val, Ctx);
  }
 
  template <typename T, typename DefaultT>
  void mapOptional(const char *Key, T &Val, const DefaultT &Default) {
    EmptyContext Ctx;
    mapOptionalWithContext(Key, Val, Default, Ctx);
  }
 
  template <typename T, typename Context>
  void mapOptionalWithContext(const char *Key, T &Val, Context &Ctx) {
    if constexpr (has_SequenceTraits<T>::value) {
      // omit key/value instead of outputting empty sequence
      if (this->canElideEmptySequence() && Val.begin() == Val.end())
        return;
    }
    this->processKey(Key, Val, false, Ctx);
  }
 
  template <typename T, typename Context>
  void mapOptionalWithContext(const char *Key, std::optional<T> &Val,
                              Context &Ctx) {
    this->processKeyWithDefault(Key, Val, std::optional<T>(),
                                /*Required=*/false, Ctx);
  }
 
  template <typename T, typename Context, typename DefaultT>
  void mapOptionalWithContext(const char *Key, T &Val, const DefaultT &Default,
                              Context &Ctx) {
    static_assert(std::is_convertible<DefaultT, T>::value,
                  "Default type must be implicitly convertible to value type!");
    this->processKeyWithDefault(Key, Val, static_cast<const T &>(Default),
                                false, Ctx);
  }
 
private:
  template <typename T, typename Context>
  void processKeyWithDefault(const char *Key, std::optional<T> &Val,
                             const std::optional<T> &DefaultValue,
                             bool Required, Context &Ctx);
 
  template <typename T, typename Context>
  void processKeyWithDefault(const char *Key, T &Val, const T &DefaultValue,
                             bool Required, Context &Ctx) {
    void *SaveInfo;
    bool UseDefault;
    const bool sameAsDefault = outputting() && Val == DefaultValue;
    if (this->preflightKey(Key, Required, sameAsDefault, UseDefault,
                           SaveInfo)) {
      yamlize(*this, Val, Required, Ctx);
      this->postflightKey(SaveInfo);
    } else {
      if (UseDefault)
        Val = DefaultValue;
    }
  }
 
  template <typename T, typename Context>
  void processKey(const char *Key, T &Val, bool Required, Context &Ctx) {
    void *SaveInfo;
    bool UseDefault;
    if (this->preflightKey(Key, Required, false, UseDefault, SaveInfo)) {
      yamlize(*this, Val, Required, Ctx);
      this->postflightKey(SaveInfo);
    }
  }
 
private:
  void *Ctxt;
};
 
namespace detail {
 
template <typename T, typename Context>
void doMapping(IO &io, T &Val, Context &Ctx) {
  MappingContextTraits<T, Context>::mapping(io, Val, Ctx);
}
 
template <typename T> void doMapping(IO &io, T &Val, EmptyContext &Ctx) {
  MappingTraits<T>::mapping(io, Val);
}
 
} // end namespace detail
 
template <typename T>
std::enable_if_t<has_ScalarEnumerationTraits<T>::value, void>
yamlize(IO &io, T &Val, bool, EmptyContext &Ctx) {
  io.beginEnumScalar();
  ScalarEnumerationTraits<T>::enumeration(io, Val);
  io.endEnumScalar();
}
 
template <typename T>
std::enable_if_t<has_ScalarBitSetTraits<T>::value, void>
yamlize(IO &io, T &Val, bool, EmptyContext &Ctx) {
  bool DoClear;
  if (io.beginBitSetScalar(DoClear)) {
    if (DoClear)
      Val = T();
    ScalarBitSetTraits<T>::bitset(io, Val);
    io.endBitSetScalar();
  }
}
 
template <typename T>
std::enable_if_t<has_ScalarTraits<T>::value, void> yamlize(IO &io, T &Val, bool,
                                                           EmptyContext &Ctx) {
  if (io.outputting()) {
    SmallString<128> Storage;
    raw_svector_ostream Buffer(Storage);
    ScalarTraits<T>::output(Val, io.getContext(), Buffer);
    StringRef Str = Buffer.str();
    io.scalarString(Str, ScalarTraits<T>::mustQuote(Str));
  } else {
    StringRef Str;
    io.scalarString(Str, ScalarTraits<T>::mustQuote(Str));
    StringRef Result = ScalarTraits<T>::input(Str, io.getContext(), Val);
    if (!Result.empty()) {
      io.setError(Twine(Result));
    }
  }
}
 
template <typename T>
std::enable_if_t<has_BlockScalarTraits<T>::value, void>
yamlize(IO &YamlIO, T &Val, bool, EmptyContext &Ctx) {
  if (YamlIO.outputting()) {
    std::string Storage;
    raw_string_ostream Buffer(Storage);
    BlockScalarTraits<T>::output(Val, YamlIO.getContext(), Buffer);
    StringRef Str(Storage);
    YamlIO.blockScalarString(Str);
  } else {
    StringRef Str;
    YamlIO.blockScalarString(Str);
    StringRef Result =
        BlockScalarTraits<T>::input(Str, YamlIO.getContext(), Val);
    if (!Result.empty())
      YamlIO.setError(Twine(Result));
  }
}
 
template <typename T>
std::enable_if_t<has_TaggedScalarTraits<T>::value, void>
yamlize(IO &io, T &Val, bool, EmptyContext &Ctx) {
  if (io.outputting()) {
    std::string ScalarStorage, TagStorage;
    raw_string_ostream ScalarBuffer(ScalarStorage), TagBuffer(TagStorage);
    TaggedScalarTraits<T>::output(Val, io.getContext(), ScalarBuffer,
                                  TagBuffer);
    io.scalarTag(TagStorage);
    StringRef ScalarStr(ScalarStorage);
    io.scalarString(ScalarStr,
                    TaggedScalarTraits<T>::mustQuote(Val, ScalarStr));
  } else {
    std::string Tag;
    io.scalarTag(Tag);
    StringRef Str;
    io.scalarString(Str, QuotingType::None);
    StringRef Result =
        TaggedScalarTraits<T>::input(Str, Tag, io.getContext(), Val);
    if (!Result.empty()) {
      io.setError(Twine(Result));
    }
  }
}
 
namespace detail {
 
template <typename T, typename Context>
std::string doValidate(IO &io, T &Val, Context &Ctx) {
  return MappingContextTraits<T, Context>::validate(io, Val, Ctx);
}
 
template <typename T> std::string doValidate(IO &io, T &Val, EmptyContext &) {
  return MappingTraits<T>::validate(io, Val);
}
 
} // namespace detail
 
template <typename T, typename Context>
std::enable_if_t<validatedMappingTraits<T, Context>::value, void>
yamlize(IO &io, T &Val, bool, Context &Ctx) {
  if (has_FlowTraits<MappingTraits<T>>::value)
    io.beginFlowMapping();
  else
    io.beginMapping();
  if (io.outputting()) {
    std::string Err = detail::doValidate(io, Val, Ctx);
    if (!Err.empty()) {
      errs() << Err << "\n";
      assert(Err.empty() && "invalid struct trying to be written as yaml");
    }
  }
  detail::doMapping(io, Val, Ctx);
  if (!io.outputting()) {
    std::string Err = detail::doValidate(io, Val, Ctx);
    if (!Err.empty())
      io.setError(Err);
  }
  if (has_FlowTraits<MappingTraits<T>>::value)
    io.endFlowMapping();
  else
    io.endMapping();
}
 
template <typename T, typename Context>
bool yamlizeMappingEnumInput(IO &io, T &Val) {
  if constexpr (has_MappingEnumInputTraits<T, Context>::value) {
    if (io.outputting())
      return false;
 
    io.beginEnumScalar();
    MappingTraits<T>::enumInput(io, Val);
    bool Matched = !io.matchEnumFallback();
    io.endEnumScalar();
    return Matched;
  }
  return false;
}
 
template <typename T, typename Context>
std::enable_if_t<unvalidatedMappingTraits<T, Context>::value, void>
yamlize(IO &io, T &Val, bool, Context &Ctx) {
  if (yamlizeMappingEnumInput<T, Context>(io, Val))
    return;
  if (has_FlowTraits<MappingTraits<T>>::value) {
    io.beginFlowMapping();
    detail::doMapping(io, Val, Ctx);
    io.endFlowMapping();
  } else {
    io.beginMapping();
    detail::doMapping(io, Val, Ctx);
    io.endMapping();
  }
}
 
template <typename T>
std::enable_if_t<has_CustomMappingTraits<T>::value, void>
yamlize(IO &io, T &Val, bool, EmptyContext &Ctx) {
  if (io.outputting()) {
    io.beginMapping();
    CustomMappingTraits<T>::output(io, Val);
    io.endMapping();
  } else {
    io.beginMapping();
    for (StringRef key : io.keys())
      CustomMappingTraits<T>::inputOne(io, key, Val);
    io.endMapping();
  }
}
 
template <typename T>
std::enable_if_t<has_PolymorphicTraits<T>::value, void>
yamlize(IO &io, T &Val, bool, EmptyContext &Ctx) {
  switch (io.outputting() ? PolymorphicTraits<T>::getKind(Val)
                          : io.getNodeKind()) {
  case NodeKind::Scalar:
    return yamlize(io, PolymorphicTraits<T>::getAsScalar(Val), true, Ctx);
  case NodeKind::Map:
    return yamlize(io, PolymorphicTraits<T>::getAsMap(Val), true, Ctx);
  case NodeKind::Sequence:
    return yamlize(io, PolymorphicTraits<T>::getAsSequence(Val), true, Ctx);
  }
}
 
template <typename T>
std::enable_if_t<missingTraits<T, EmptyContext>::value, void>
yamlize(IO &io, T &Val, bool, EmptyContext &Ctx) {
  char missing_yaml_trait_for_type[sizeof(MissingTrait<T>)];
}
 
template <typename T, typename Context>
std::enable_if_t<has_SequenceTraits<T>::value, void>
yamlize(IO &io, T &Seq, bool, Context &Ctx) {
  if (has_FlowTraits<SequenceTraits<T>>::value) {
    unsigned incnt = io.beginFlowSequence();
    unsigned count = io.outputting() ? SequenceTraits<T>::size(io, Seq) : incnt;
    for (unsigned i = 0; i < count; ++i) {
      void *SaveInfo;
      if (io.preflightFlowElement(i, SaveInfo)) {
        yamlize(io, SequenceTraits<T>::element(io, Seq, i), true, Ctx);
        io.postflightFlowElement(SaveInfo);
      }
    }
    io.endFlowSequence();
  } else {
    unsigned incnt = io.beginSequence();
    unsigned count = io.outputting() ? SequenceTraits<T>::size(io, Seq) : incnt;
    for (unsigned i = 0; i < count; ++i) {
      void *SaveInfo;
      if (io.preflightElement(i, SaveInfo)) {
        yamlize(io, SequenceTraits<T>::element(io, Seq, i), true, Ctx);
        io.postflightElement(SaveInfo);
      }
    }
    io.endSequence();
  }
}
 
template <> struct ScalarTraits<bool> {
  LLVM_ABI static void output(const bool &, void *, raw_ostream &);
  LLVM_ABI static StringRef input(StringRef, void *, bool &);
  static QuotingType mustQuote(StringRef) { return QuotingType::None; }
};
 
template <> struct ScalarTraits<StringRef> {
  LLVM_ABI static void output(const StringRef &, void *, raw_ostream &);
  LLVM_ABI static StringRef input(StringRef, void *, StringRef &);
  static QuotingType mustQuote(StringRef S) { return needsQuotes(S); }
};
 
template <> struct ScalarTraits<std::string> {
  LLVM_ABI static void output(const std::string &, void *, raw_ostream &);
  LLVM_ABI static StringRef input(StringRef, void *, std::string &);
  static QuotingType mustQuote(StringRef S) { return needsQuotes(S); }
};
 
template <> struct ScalarTraits<uint8_t> {
  LLVM_ABI static void output(const uint8_t &, void *, raw_ostream &);
  LLVM_ABI static StringRef input(StringRef, void *, uint8_t &);
  static QuotingType mustQuote(StringRef) { return QuotingType::None; }
};
 
template <> struct ScalarTraits<uint16_t> {
  LLVM_ABI static void output(const uint16_t &, void *, raw_ostream &);
  LLVM_ABI static StringRef input(StringRef, void *, uint16_t &);
  static QuotingType mustQuote(StringRef) { return QuotingType::None; }
};
 
template <> struct ScalarTraits<uint32_t> {
  LLVM_ABI static void output(const uint32_t &, void *, raw_ostream &);
  LLVM_ABI static StringRef input(StringRef, void *, uint32_t &);
  static QuotingType mustQuote(StringRef) { return QuotingType::None; }
};
 
template <> struct ScalarTraits<uint64_t> {
  LLVM_ABI static void output(const uint64_t &, void *, raw_ostream &);
  LLVM_ABI static StringRef input(StringRef, void *, uint64_t &);
  static QuotingType mustQuote(StringRef) { return QuotingType::None; }
};
 
template <> struct ScalarTraits<int8_t> {
  LLVM_ABI static void output(const int8_t &, void *, raw_ostream &);
  LLVM_ABI static StringRef input(StringRef, void *, int8_t &);
  static QuotingType mustQuote(StringRef) { return QuotingType::None; }
};
 
template <> struct ScalarTraits<int16_t> {
  LLVM_ABI static void output(const int16_t &, void *, raw_ostream &);
  LLVM_ABI static StringRef input(StringRef, void *, int16_t &);
  static QuotingType mustQuote(StringRef) { return QuotingType::None; }
};
 
template <> struct ScalarTraits<int32_t> {
  LLVM_ABI static void output(const int32_t &, void *, raw_ostream &);
  LLVM_ABI static StringRef input(StringRef, void *, int32_t &);
  static QuotingType mustQuote(StringRef) { return QuotingType::None; }
};
 
template <> struct ScalarTraits<int64_t> {
  LLVM_ABI static void output(const int64_t &, void *, raw_ostream &);
  LLVM_ABI static StringRef input(StringRef, void *, int64_t &);
  static QuotingType mustQuote(StringRef) { return QuotingType::None; }
};
 
template <> struct ScalarTraits<float> {
  LLVM_ABI static void output(const float &, void *, raw_ostream &);
  LLVM_ABI static StringRef input(StringRef, void *, float &);
  static QuotingType mustQuote(StringRef) { return QuotingType::None; }
};
 
template <> struct ScalarTraits<double> {
  LLVM_ABI static void output(const double &, void *, raw_ostream &);
  LLVM_ABI static StringRef input(StringRef, void *, double &);
  static QuotingType mustQuote(StringRef) { return QuotingType::None; }
};
 
// For endian types, we use existing scalar Traits class for the underlying
// type.  This way endian aware types are supported whenever the traits are
// defined for the underlying type.
template <typename value_type, llvm::endianness endian, size_t alignment>
struct ScalarTraits<support::detail::packed_endian_specific_integral<
                        value_type, endian, alignment>,
                    std::enable_if_t<has_ScalarTraits<value_type>::value>> {
  using endian_type =
      support::detail::packed_endian_specific_integral<value_type, endian,
                                                       alignment>;
 
  static void output(const endian_type &E, void *Ctx, raw_ostream &Stream) {
    ScalarTraits<value_type>::output(static_cast<value_type>(E), Ctx, Stream);
  }
 
  static StringRef input(StringRef Str, void *Ctx, endian_type &E) {
    value_type V;
    auto R = ScalarTraits<value_type>::input(Str, Ctx, V);
    E = static_cast<endian_type>(V);
    return R;
  }
 
  static QuotingType mustQuote(StringRef Str) {
    return ScalarTraits<value_type>::mustQuote(Str);
  }
};
 
template <typename value_type, llvm::endianness endian, size_t alignment>
struct ScalarEnumerationTraits<
    support::detail::packed_endian_specific_integral<value_type, endian,
                                                     alignment>,
    std::enable_if_t<has_ScalarEnumerationTraits<value_type>::value>> {
  using endian_type =
      support::detail::packed_endian_specific_integral<value_type, endian,
                                                       alignment>;
 
  static void enumeration(IO &io, endian_type &E) {
    value_type V = E;
    ScalarEnumerationTraits<value_type>::enumeration(io, V);
    E = V;
  }
};
 
template <typename value_type, llvm::endianness endian, size_t alignment>
struct ScalarBitSetTraits<
    support::detail::packed_endian_specific_integral<value_type, endian,
                                                     alignment>,
    std::enable_if_t<has_ScalarBitSetTraits<value_type>::value>> {
  using endian_type =
      support::detail::packed_endian_specific_integral<value_type, endian,
                                                       alignment>;
  static void bitset(IO &io, endian_type &E) {
    value_type V = E;
    ScalarBitSetTraits<value_type>::bitset(io, V);
    E = V;
  }
};
 
// Utility for use within MappingTraits<>::mapping() method
// to [de]normalize an object for use with YAML conversion.
template <typename TNorm, typename TFinal> struct MappingNormalization {
  MappingNormalization(IO &i_o, TFinal &Obj)
      : io(i_o), BufPtr(nullptr), Result(Obj) {
    if (io.outputting()) {
      BufPtr = new (&Buffer) TNorm(io, Obj);
    } else {
      BufPtr = new (&Buffer) TNorm(io);
    }
  }
 
  ~MappingNormalization() {
    if (!io.outputting()) {
      Result = BufPtr->denormalize(io);
    }
    BufPtr->~TNorm();
  }
 
  TNorm *operator->() { return BufPtr; }
 
private:
  using Storage = AlignedCharArrayUnion<TNorm>;
 
  Storage Buffer;
  IO &io;
  TNorm *BufPtr;
  TFinal &Result;
};
 
// Utility for use within MappingTraits<>::mapping() method
// to [de]normalize an object for use with YAML conversion.
template <typename TNorm, typename TFinal> struct MappingNormalizationHeap {
  MappingNormalizationHeap(IO &i_o, TFinal &Obj, BumpPtrAllocator *allocator)
      : io(i_o), Result(Obj) {
    if (io.outputting()) {
      BufPtr = new (&Buffer) TNorm(io, Obj);
    } else if (allocator) {
      BufPtr = allocator->Allocate<TNorm>();
      new (BufPtr) TNorm(io);
    } else {
      BufPtr = new TNorm(io);
    }
  }
 
  ~MappingNormalizationHeap() {
    if (io.outputting()) {
      BufPtr->~TNorm();
    } else {
      Result = BufPtr->denormalize(io);
    }
  }
 
  TNorm *operator->() { return BufPtr; }
 
private:
  using Storage = AlignedCharArrayUnion<TNorm>;
 
  Storage Buffer;
  IO &io;
  TNorm *BufPtr = nullptr;
  TFinal &Result;
};
 
///
/// The Input class is used to parse a yaml document into in-memory structs
/// and vectors.
///
/// It works by using YAMLParser to do a syntax parse of the entire yaml
/// document, then the Input class builds a graph of HNodes which wraps
/// each yaml Node.  The extra layer is buffering.  The low level yaml
/// parser only lets you look at each node once.  The buffering layer lets
/// you search and interate multiple times.  This is necessary because
/// the mapRequired() method calls may not be in the same order
/// as the keys in the document.
///
class LLVM_ABI Input : public IO {
public:
  // Construct a yaml Input object from a StringRef and optional
  // user-data. The DiagHandler can be specified to provide
  // alternative error reporting.
  Input(StringRef InputContent, void *Ctxt = nullptr,
        SourceMgr::DiagHandlerTy DiagHandler = nullptr,
        void *DiagHandlerCtxt = nullptr);
  Input(MemoryBufferRef Input, void *Ctxt = nullptr,
        SourceMgr::DiagHandlerTy DiagHandler = nullptr,
        void *DiagHandlerCtxt = nullptr);
  ~Input() override;
 
  // Check if there was an syntax or semantic error during parsing.
  std::error_code error() override;
 
private:
  bool outputting() const override;
  bool mapTag(StringRef, bool) override;
  void beginMapping() override;
  void endMapping() override;
  bool preflightKey(const char *, bool, bool, bool &, void *&) override;
  void postflightKey(void *) override;
  std::vector<StringRef> keys() override;
  void beginFlowMapping() override;
  void endFlowMapping() override;
  unsigned beginSequence() override;
  void endSequence() override;
  bool preflightElement(unsigned index, void *&) override;
  void postflightElement(void *) override;
  unsigned beginFlowSequence() override;
  bool preflightFlowElement(unsigned, void *&) override;
  void postflightFlowElement(void *) override;
  void endFlowSequence() override;
  void beginEnumScalar() override;
  bool matchEnumScalar(const char *, bool) override;
  bool matchEnumFallback() override;
  void endEnumScalar() override;
  bool beginBitSetScalar(bool &) override;
  bool bitSetMatch(const char *, bool) override;
  void endBitSetScalar() override;
  void scalarString(StringRef &, QuotingType) override;
  void blockScalarString(StringRef &) override;
  void scalarTag(std::string &) override;
  NodeKind getNodeKind() override;
  void setError(const Twine &message) override;
  bool canElideEmptySequence() override;
 
  class HNode {
  public:
    HNode(Node *n) : _node(n) {}
 
    static bool classof(const HNode *) { return true; }
 
    Node *_node;
  };
 
  class EmptyHNode : public HNode {
  public:
    EmptyHNode(Node *n) : HNode(n) {}
 
    static bool classof(const HNode *n) { return NullNode::classof(n->_node); }
 
    static bool classof(const EmptyHNode *) { return true; }
  };
 
  class ScalarHNode : public HNode {
  public:
    ScalarHNode(Node *n, StringRef s) : HNode(n), _value(s) {}
 
    StringRef value() const { return _value; }
 
    static bool classof(const HNode *n) {
      return ScalarNode::classof(n->_node) ||
             BlockScalarNode::classof(n->_node);
    }
 
    static bool classof(const ScalarHNode *) { return true; }
 
  protected:
    StringRef _value;
  };
 
  class MapHNode : public HNode {
  public:
    MapHNode(Node *n) : HNode(n) {}
 
    static bool classof(const HNode *n) {
      return MappingNode::classof(n->_node);
    }
 
    static bool classof(const MapHNode *) { return true; }
 
    using NameToNodeAndLoc = StringMap<std::pair<HNode *, SMRange>>;
 
    NameToNodeAndLoc Mapping;
    SmallVector<std::string, 6> ValidKeys;
  };
 
  class SequenceHNode : public HNode {
  public:
    SequenceHNode(Node *n) : HNode(n) {}
 
    static bool classof(const HNode *n) {
      return SequenceNode::classof(n->_node);
    }
 
    static bool classof(const SequenceHNode *) { return true; }
 
    std::vector<HNode *> Entries;
  };
 
  Input::HNode *createHNodes(Node *node);
  void setError(HNode *hnode, const Twine &message);
  void setError(Node *node, const Twine &message);
  void setError(const SMRange &Range, const Twine &message);
 
  void reportWarning(HNode *hnode, const Twine &message);
  void reportWarning(Node *hnode, const Twine &message);
  void reportWarning(const SMRange &Range, const Twine &message);
 
  /// Release memory used by HNodes.
  void releaseHNodeBuffers();
 
public:
  // These are only used by operator>>. They could be private
  // if those templated things could be made friends.
  bool setCurrentDocument();
  bool nextDocument();
 
  /// Returns the current node that's being parsed by the YAML Parser.
  const Node *getCurrentNode() const;
 
  void setAllowUnknownKeys(bool Allow) override;
 
private:
  SourceMgr SrcMgr; // must be before Strm
  std::unique_ptr<llvm::yaml::Stream> Strm;
  HNode *TopNode = nullptr;
  std::error_code EC;
  BumpPtrAllocator StringAllocator;
  SpecificBumpPtrAllocator<EmptyHNode> EmptyHNodeAllocator;
  SpecificBumpPtrAllocator<ScalarHNode> ScalarHNodeAllocator;
  SpecificBumpPtrAllocator<MapHNode> MapHNodeAllocator;
  SpecificBumpPtrAllocator<SequenceHNode> SequenceHNodeAllocator;
  document_iterator DocIterator;
  llvm::BitVector BitValuesUsed;
  HNode *CurrentNode = nullptr;
  bool ScalarMatchFound = false;
  bool AllowUnknownKeys = false;
};
 
///
/// The Output class is used to generate a yaml document from in-memory structs
/// and vectors.
///
class LLVM_ABI Output : public IO {
public:
  Output(raw_ostream &, void *Ctxt = nullptr, int WrapColumn = 70);
  ~Output() override;
 
  /// Set whether or not to output optional values which are equal
  /// to the default value.  By default, when outputting if you attempt
  /// to write a value that is equal to the default, the value gets ignored.
  /// Sometimes, it is useful to be able to see these in the resulting YAML
  /// anyway.
  void setWriteDefaultValues(bool Write) { WriteDefaultValues = Write; }
 
  bool outputting() const override;
  bool mapTag(StringRef, bool) override;
  void beginMapping() override;
  void endMapping() override;
  bool preflightKey(const char *key, bool, bool, bool &, void *&) override;
  void postflightKey(void *) override;
  std::vector<StringRef> keys() override;
  void beginFlowMapping() override;
  void endFlowMapping() override;
  unsigned beginSequence() override;
  void endSequence() override;
  bool preflightElement(unsigned, void *&) override;
  void postflightElement(void *) override;
  unsigned beginFlowSequence() override;
  bool preflightFlowElement(unsigned, void *&) override;
  void postflightFlowElement(void *) override;
  void endFlowSequence() override;
  void beginEnumScalar() override;
  bool matchEnumScalar(const char *, bool) override;
  bool matchEnumFallback() override;
  void endEnumScalar() override;
  bool beginBitSetScalar(bool &) override;
  bool bitSetMatch(const char *, bool) override;
  void endBitSetScalar() override;
  void scalarString(StringRef &, QuotingType) override;
  void blockScalarString(StringRef &) override;
  void scalarTag(std::string &) override;
  NodeKind getNodeKind() override;
  void setError(const Twine &message) override;
  std::error_code error() override;
  bool canElideEmptySequence() override;
 
  // These are only used by operator<<. They could be private
  // if that templated operator could be made a friend.
  void beginDocuments();
  bool preflightDocument(unsigned);
  void postflightDocument();
  void endDocuments();
 
private:
  void output(StringRef s);
  void output(StringRef, QuotingType);
  void outputUpToEndOfLine(StringRef s);
  void newLineCheck(bool EmptySequence = false);
  void outputNewLine();
  void paddedKey(StringRef key);
  void flowKey(StringRef Key);
 
  enum InState {
    inSeqFirstElement,
    inSeqOtherElement,
    inFlowSeqFirstElement,
    inFlowSeqOtherElement,
    inMapFirstKey,
    inMapOtherKey,
    inFlowMapFirstKey,
    inFlowMapOtherKey
  };
 
  static bool inSeqAnyElement(InState State);
  static bool inFlowSeqAnyElement(InState State);
  static bool inMapAnyKey(InState State);
  static bool inFlowMapAnyKey(InState State);
 
  raw_ostream &Out;
  int WrapColumn;
  SmallVector<InState, 8> StateStack;
  int Column = 0;
  int ColumnAtFlowStart = 0;
  int ColumnAtMapFlowStart = 0;
  bool NeedBitValueComma = false;
  bool NeedFlowSequenceComma = false;
  bool EnumerationMatchFound = false;
  bool WriteDefaultValues = false;
  StringRef Padding;
  StringRef PaddingBeforeContainer;
};
 
template <typename T, typename Context>
void IO::processKeyWithDefault(const char *Key, std::optional<T> &Val,
                               const std::optional<T> &DefaultValue,
                               bool Required, Context &Ctx) {
  assert(!DefaultValue && "std::optional<T> shouldn't have a value!");
  void *SaveInfo;
  bool UseDefault = true;
  const bool sameAsDefault = outputting() && !Val;
  if (!outputting() && !Val)
    Val = T();
  if (Val &&
      this->preflightKey(Key, Required, sameAsDefault, UseDefault, SaveInfo)) {
 
    // When reading an std::optional<X> key from a YAML description, we allow
    // the special "<none>" value, which can be used to specify that no value
    // was requested, i.e. the DefaultValue will be assigned. The DefaultValue
    // is usually None.
    bool IsNone = false;
    if (!outputting())
      if (const auto *Node =
              dyn_cast<ScalarNode>(((Input *)this)->getCurrentNode()))
        // We use rtrim to ignore possible white spaces that might exist when a
        // comment is present on the same line.
        IsNone = Node->getRawValue().rtrim(' ') == "<none>";
 
    if (IsNone)
      Val = DefaultValue;
    else
      yamlize(*this, *Val, Required, Ctx);
    this->postflightKey(SaveInfo);
  } else {
    if (UseDefault)
      Val = DefaultValue;
  }
}
 
/// YAML I/O does conversion based on types. But often native data types
/// are just a typedef of built in intergral types (e.g. int).  But the C++
/// type matching system sees through the typedef and all the typedefed types
/// look like a built in type. This will cause the generic YAML I/O conversion
/// to be used. To provide better control over the YAML conversion, you can
/// use this macro instead of typedef.  It will create a class with one field
/// and automatic conversion operators to and from the base type.
/// Based on BOOST_STRONG_TYPEDEF
#define LLVM_YAML_STRONG_TYPEDEF(_base, _type)                                 \
  struct _type {                                                               \
    _type() = default;                                                         \
    _type(const _base v) : value(v) {}                                         \
    _type(const _type &v) = default;                                           \
    _type &operator=(const _type &rhs) = default;                              \
    _type &operator=(const _base &rhs) {                                       \
      value = rhs;                                                             \
      return *this;                                                            \
    }                                                                          \
    operator const _base &() const { return value; }                           \
    bool operator==(const _type &rhs) const { return value == rhs.value; }     \
    bool operator==(const _base &rhs) const { return value == rhs; }           \
    bool operator<(const _type &rhs) const { return value < rhs.value; }       \
    _base value;                                                               \
    using BaseType = _base;                                                    \
  };
 
///
/// Use these types instead of uintXX_t in any mapping to have
/// its yaml output formatted as hexadecimal.
///
LLVM_YAML_STRONG_TYPEDEF(uint8_t, Hex8)
LLVM_YAML_STRONG_TYPEDEF(uint16_t, Hex16)
LLVM_YAML_STRONG_TYPEDEF(uint32_t, Hex32)
LLVM_YAML_STRONG_TYPEDEF(uint64_t, Hex64)
 
template <> struct ScalarTraits<Hex8> {
  LLVM_ABI static void output(const Hex8 &, void *, raw_ostream &);
  LLVM_ABI static StringRef input(StringRef, void *, Hex8 &);
  static QuotingType mustQuote(StringRef) { return QuotingType::None; }
};
 
template <> struct ScalarTraits<Hex16> {
  LLVM_ABI static void output(const Hex16 &, void *, raw_ostream &);
  LLVM_ABI static StringRef input(StringRef, void *, Hex16 &);
  static QuotingType mustQuote(StringRef) { return QuotingType::None; }
};
 
template <> struct ScalarTraits<Hex32> {
  LLVM_ABI static void output(const Hex32 &, void *, raw_ostream &);
  LLVM_ABI static StringRef input(StringRef, void *, Hex32 &);
  static QuotingType mustQuote(StringRef) { return QuotingType::None; }
};
 
template <> struct ScalarTraits<Hex64> {
  LLVM_ABI static void output(const Hex64 &, void *, raw_ostream &);
  LLVM_ABI static StringRef input(StringRef, void *, Hex64 &);
  static QuotingType mustQuote(StringRef) { return QuotingType::None; }
};
 
template <> struct ScalarTraits<VersionTuple> {
  LLVM_ABI static void output(const VersionTuple &Value, void *,
                              llvm::raw_ostream &Out);
  LLVM_ABI static StringRef input(StringRef, void *, VersionTuple &);
  static QuotingType mustQuote(StringRef) { return QuotingType::None; }
};
 
// Define non-member operator>> so that Input can stream in a document list.
template <typename T>
inline std::enable_if_t<has_DocumentListTraits<T>::value, Input &>
operator>>(Input &yin, T &docList) {
  int i = 0;
  EmptyContext Ctx;
  while (yin.setCurrentDocument()) {
    yamlize(yin, DocumentListTraits<T>::element(yin, docList, i), true, Ctx);
    if (yin.error())
      return yin;
    yin.nextDocument();
    ++i;
  }
  return yin;
}
 
// Define non-member operator>> so that Input can stream in a map as a document.
template <typename T>
inline std::enable_if_t<has_MappingTraits<T, EmptyContext>::value, Input &>
operator>>(Input &yin, T &docMap) {
  EmptyContext Ctx;
  yin.setCurrentDocument();
  yamlize(yin, docMap, true, Ctx);
  return yin;
}
 
// Define non-member operator>> so that Input can stream in a sequence as
// a document.
template <typename T>
inline std::enable_if_t<has_SequenceTraits<T>::value, Input &>
operator>>(Input &yin, T &docSeq) {
  EmptyContext Ctx;
  if (yin.setCurrentDocument())
    yamlize(yin, docSeq, true, Ctx);
  return yin;
}
 
// Define non-member operator>> so that Input can stream in a block scalar.
template <typename T>
inline std::enable_if_t<has_BlockScalarTraits<T>::value, Input &>
operator>>(Input &In, T &Val) {
  EmptyContext Ctx;
  if (In.setCurrentDocument())
    yamlize(In, Val, true, Ctx);
  return In;
}
 
// Define non-member operator>> so that Input can stream in a string map.
template <typename T>
inline std::enable_if_t<has_CustomMappingTraits<T>::value, Input &>
operator>>(Input &In, T &Val) {
  EmptyContext Ctx;
  if (In.setCurrentDocument())
    yamlize(In, Val, true, Ctx);
  return In;
}
 
// Define non-member operator>> so that Input can stream in a polymorphic type.
template <typename T>
inline std::enable_if_t<has_PolymorphicTraits<T>::value, Input &>
operator>>(Input &In, T &Val) {
  EmptyContext Ctx;
  if (In.setCurrentDocument())
    yamlize(In, Val, true, Ctx);
  return In;
}
 
// Provide better error message about types missing a trait specialization
template <typename T>
inline std::enable_if_t<missingTraits<T, EmptyContext>::value, Input &>
operator>>(Input &yin, T &docSeq) {
  char missing_yaml_trait_for_type[sizeof(MissingTrait<T>)];
  return yin;
}
 
// Define non-member operator<< so that Output can stream out document list.
template <typename T>
inline std::enable_if_t<has_DocumentListTraits<T>::value, Output &>
operator<<(Output &yout, T &docList) {
  EmptyContext Ctx;
  yout.beginDocuments();
  const size_t count = DocumentListTraits<T>::size(yout, docList);
  for (size_t i = 0; i < count; ++i) {
    if (yout.preflightDocument(i)) {
      yamlize(yout, DocumentListTraits<T>::element(yout, docList, i), true,
              Ctx);
      yout.postflightDocument();
    }
  }
  yout.endDocuments();
  return yout;
}
 
// Define non-member operator<< so that Output can stream out a map.
template <typename T>
inline std::enable_if_t<has_MappingTraits<T, EmptyContext>::value, Output &>
operator<<(Output &yout, T &map) {
  EmptyContext Ctx;
  yout.beginDocuments();
  if (yout.preflightDocument(0)) {
    yamlize(yout, map, true, Ctx);
    yout.postflightDocument();
  }
  yout.endDocuments();
  return yout;
}
 
// Define non-member operator<< so that Output can stream out a sequence.
template <typename T>
inline std::enable_if_t<has_SequenceTraits<T>::value, Output &>
operator<<(Output &yout, T &seq) {
  EmptyContext Ctx;
  yout.beginDocuments();
  if (yout.preflightDocument(0)) {
    yamlize(yout, seq, true, Ctx);
    yout.postflightDocument();
  }
  yout.endDocuments();
  return yout;
}
 
// Define non-member operator<< so that Output can stream out a block scalar.
template <typename T>
inline std::enable_if_t<has_BlockScalarTraits<T>::value, Output &>
operator<<(Output &Out, T &Val) {
  EmptyContext Ctx;
  Out.beginDocuments();
  if (Out.preflightDocument(0)) {
    yamlize(Out, Val, true, Ctx);
    Out.postflightDocument();
  }
  Out.endDocuments();
  return Out;
}
 
// Define non-member operator<< so that Output can stream out a string map.
template <typename T>
inline std::enable_if_t<has_CustomMappingTraits<T>::value, Output &>
operator<<(Output &Out, T &Val) {
  EmptyContext Ctx;
  Out.beginDocuments();
  if (Out.preflightDocument(0)) {
    yamlize(Out, Val, true, Ctx);
    Out.postflightDocument();
  }
  Out.endDocuments();
  return Out;
}
 
// Define non-member operator<< so that Output can stream out a polymorphic
// type.
template <typename T>
inline std::enable_if_t<has_PolymorphicTraits<T>::value, Output &>
operator<<(Output &Out, T &Val) {
  EmptyContext Ctx;
  Out.beginDocuments();
  if (Out.preflightDocument(0)) {
    // FIXME: The parser does not support explicit documents terminated with a
    // plain scalar; the end-marker is included as part of the scalar token.
    assert(PolymorphicTraits<T>::getKind(Val) != NodeKind::Scalar &&
           "plain scalar documents are not supported");
    yamlize(Out, Val, true, Ctx);
    Out.postflightDocument();
  }
  Out.endDocuments();
  return Out;
}
 
// Provide better error message about types missing a trait specialization
template <typename T>
inline std::enable_if_t<missingTraits<T, EmptyContext>::value, Output &>
operator<<(Output &yout, T &seq) {
  char missing_yaml_trait_for_type[sizeof(MissingTrait<T>)];
  return yout;
}
 
template <bool B> struct IsFlowSequenceBase {};
template <> struct IsFlowSequenceBase<true> {
  static const bool flow = true;
};
 
template <typename T>
using check_resize_t = decltype(std::declval<T>().resize(0));
 
template <typename T> struct IsResizableBase {
  using type = typename T::value_type;
 
  static type &element(IO &io, T &seq, size_t index) {
    if constexpr (is_detected<check_resize_t, T>::value) {
      if (index >= seq.size())
        seq.resize(index + 1);
    } else {
      if (index >= seq.size()) {
        io.setError(Twine("value sequence extends beyond static size (") +
                    Twine(seq.size()) + ")");
        return seq[0];
      }
    }
    return seq[index];
  }
};
 
template <typename T, bool Flow>
struct SequenceTraitsImpl : IsFlowSequenceBase<Flow>, IsResizableBase<T> {
  static size_t size(IO &io, T &seq) { return seq.size(); }
};
 
// Simple helper to check an expression can be used as a bool-valued template
// argument.
template <bool> struct CheckIsBool {
  static const bool value = true;
};
 
// If T has SequenceElementTraits, then vector<T> and SmallVector<T, N> have
// SequenceTraits that do the obvious thing.
template <typename T>
struct SequenceTraits<
    std::vector<T>,
    std::enable_if_t<CheckIsBool<SequenceElementTraits<T>::flow>::value>>
    : SequenceTraitsImpl<std::vector<T>, SequenceElementTraits<T>::flow> {};
template <typename T, size_t N>
struct SequenceTraits<
    std::array<T, N>,
    std::enable_if_t<CheckIsBool<SequenceElementTraits<T>::flow>::value>>
    : SequenceTraitsImpl<std::array<T, N>, SequenceElementTraits<T>::flow> {};
template <typename T, unsigned N>
struct SequenceTraits<
    SmallVector<T, N>,
    std::enable_if_t<CheckIsBool<SequenceElementTraits<T>::flow>::value>>
    : SequenceTraitsImpl<SmallVector<T, N>, SequenceElementTraits<T>::flow> {};
template <typename T>
struct SequenceTraits<
    SmallVectorImpl<T>,
    std::enable_if_t<CheckIsBool<SequenceElementTraits<T>::flow>::value>>
    : SequenceTraitsImpl<SmallVectorImpl<T>, SequenceElementTraits<T>::flow> {};
template <typename T>
struct SequenceTraits<
    MutableArrayRef<T>,
    std::enable_if_t<CheckIsBool<SequenceElementTraits<T>::flow>::value>>
    : SequenceTraitsImpl<MutableArrayRef<T>, SequenceElementTraits<T>::flow> {};
 
// Sequences of fundamental types use flow formatting.
template <typename T>
struct SequenceElementTraits<T, std::enable_if_t<std::is_fundamental_v<T>>> {
  static const bool flow = true;
};
 
// Sequences of strings use block formatting.
template <> struct SequenceElementTraits<std::string> {
  static const bool flow = false;
};
template <> struct SequenceElementTraits<StringRef> {
  static const bool flow = false;
};
template <> struct SequenceElementTraits<std::pair<std::string, std::string>> {
  static const bool flow = false;
};
 
/// Implementation of CustomMappingTraits for std::map<std::string, T>.
template <typename T> struct StdMapStringCustomMappingTraitsImpl {
  using map_type = std::map<std::string, T>;
 
  static void inputOne(IO &io, StringRef key, map_type &v) {
    io.mapRequired(key.str().c_str(), v[std::string(key)]);
  }
 
  static void output(IO &io, map_type &v) {
    for (auto &p : v)
      io.mapRequired(p.first.c_str(), p.second);
  }
};
 
} // end namespace yaml
} // end namespace llvm
 
#define LLVM_YAML_IS_SEQUENCE_VECTOR_IMPL(TYPE, FLOW)                          \
  namespace llvm {                                                             \
  namespace yaml {                                                             \
  static_assert(                                                               \
      !std::is_fundamental_v<TYPE> && !std::is_same_v<TYPE, std::string> &&    \
          !std::is_same_v<TYPE, llvm::StringRef>,                              \
      "only use LLVM_YAML_IS_SEQUENCE_VECTOR for types you control");          \
  template <> struct SequenceElementTraits<TYPE> {                             \
    static const bool flow = FLOW;                                             \
  };                                                                           \
  }                                                                            \
  }
 
/// Utility for declaring that a std::vector of a particular type
/// should be considered a YAML sequence.
#define LLVM_YAML_IS_SEQUENCE_VECTOR(type)                                     \
  LLVM_YAML_IS_SEQUENCE_VECTOR_IMPL(type, false)
 
/// Utility for declaring that a std::vector of a particular type
/// should be considered a YAML flow sequence.
#define LLVM_YAML_IS_FLOW_SEQUENCE_VECTOR(type)                                \
  LLVM_YAML_IS_SEQUENCE_VECTOR_IMPL(type, true)
 
#define LLVM_YAML_DECLARE_MAPPING_TRAITS(Type)                                 \
  namespace llvm {                                                             \
  namespace yaml {                                                             \
  template <> struct LLVM_ABI MappingTraits<Type> {                            \
    static void mapping(IO &IO, Type &Obj);                                    \
  };                                                                           \
  }                                                                            \
  }
 
#define LLVM_YAML_DECLARE_MAPPING_TRAITS_PRIVATE(Type)                         \
  namespace llvm {                                                             \
  namespace yaml {                                                             \
  template <> struct MappingTraits<Type> {                                     \
    static void mapping(IO &IO, Type &Obj);                                    \
  };                                                                           \
  }                                                                            \
  }
 
#define LLVM_YAML_DECLARE_ENUM_TRAITS(Type)                                    \
  namespace llvm {                                                             \
  namespace yaml {                                                             \
  template <> struct LLVM_ABI ScalarEnumerationTraits<Type> {                  \
    static void enumeration(IO &io, Type &Value);                              \
  };                                                                           \
  }                                                                            \
  }
 
#define LLVM_YAML_DECLARE_BITSET_TRAITS(Type)                                  \
  namespace llvm {                                                             \
  namespace yaml {                                                             \
  template <> struct LLVM_ABI ScalarBitSetTraits<Type> {                       \
    static void bitset(IO &IO, Type &Options);                                 \
  };                                                                           \
  }                                                                            \
  }
 
#define LLVM_YAML_DECLARE_SCALAR_TRAITS(Type, MustQuote)                       \
  namespace llvm {                                                             \
  namespace yaml {                                                             \
  template <> struct LLVM_ABI ScalarTraits<Type> {                             \
    static void output(const Type &Value, void *ctx, raw_ostream &Out);        \
    static StringRef input(StringRef Scalar, void *ctxt, Type &Value);         \
    static QuotingType mustQuote(StringRef) { return MustQuote; }              \
  };                                                                           \
  }                                                                            \
  }
 
/// Utility for declaring that a std::vector of a particular type
/// should be considered a YAML document list.
#define LLVM_YAML_IS_DOCUMENT_LIST_VECTOR(_type)                               \
  namespace llvm {                                                             \
  namespace yaml {                                                             \
  template <unsigned N>                                                        \
  struct DocumentListTraits<SmallVector<_type, N>>                             \
      : public SequenceTraitsImpl<SmallVector<_type, N>, false> {};            \
  template <>                                                                  \
  struct DocumentListTraits<std::vector<_type>>                                \
      : public SequenceTraitsImpl<std::vector<_type>, false> {};               \
  }                                                                            \
  }
 
/// Utility for declaring that std::map<std::string, _type> should be considered
/// a YAML map.
#define LLVM_YAML_IS_STRING_MAP(_type)                                         \
  namespace llvm {                                                             \
  namespace yaml {                                                             \
  template <>                                                                  \
  struct CustomMappingTraits<std::map<std::string, _type>>                     \
      : public StdMapStringCustomMappingTraitsImpl<_type> {};                  \
  }                                                                            \
  }
 
LLVM_YAML_IS_FLOW_SEQUENCE_VECTOR(llvm::yaml::Hex64)
LLVM_YAML_IS_FLOW_SEQUENCE_VECTOR(llvm::yaml::Hex32)
LLVM_YAML_IS_FLOW_SEQUENCE_VECTOR(llvm::yaml::Hex16)
LLVM_YAML_IS_FLOW_SEQUENCE_VECTOR(llvm::yaml::Hex8)
 
#endif // LLVM_SUPPORT_YAMLTRAITS_H