text: //===- llvm/Support/YAMLTraits.h --------------------------------*- C++ -*-===//
  //
  //                             The LLVM Linker
  //
  // This file is distributed under the University of Illinois Open Source
  // License. See LICENSE.TXT for details.
  //
  //===----------------------------------------------------------------------===//
  
  #ifndef LLVM_SUPPORT_YAMLTRAITS_H
  #define LLVM_SUPPORT_YAMLTRAITS_H
  
  #include "llvm/ADT/DenseMap.h"
  #include "llvm/ADT/DenseMapInfo.h"
  #include "llvm/ADT/Optional.h"
  #include "llvm/ADT/SmallVector.h"
  #include "llvm/ADT/StringMap.h"
  #include "llvm/ADT/StringRef.h"
  #include "llvm/ADT/StringSwitch.h"
  #include "llvm/ADT/Twine.h"
  #include "llvm/Support/Compiler.h"
  #include "llvm/Support/Regex.h"
  #include "llvm/Support/SourceMgr.h"
  #include "llvm/Support/YAMLParser.h"
  #include "llvm/Support/raw_ostream.h"
  #include <system_error>
  
  namespace llvm {
  namespace yaml {
  
  /// 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 StringRef validate(IO &io, T &fields);
    //
    // 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>
  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>
  struct ScalarBitSetTraits {
    // Must provide:
    // static void bitset(IO &io, T &value);
  };
  
  /// 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 bool mustQuote(StringRef) { return true; }
  ///    };
  template<typename T>
  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 bool 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 << Val;
  ///      }
  ///      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);
  };
  
  /// This class should be specialized by any type that needs to be converted
  /// to/from a YAML sequence.  For example:
  ///
  ///    template<>
  ///    struct SequenceTraits< std::vector<MyType> > {
  ///      static size_t size(IO &io, std::vector<MyType> &seq) {
  ///        return seq.size();
  ///      }
  ///      static MyType& element(IO &, std::vector<MyType> &seq, size_t index) {
  ///        if ( index >= seq.size() )
  ///          seq.resize(index+1);
  ///        return seq[index];
  ///      }
  ///    };
  template<typename T>
  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 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);
  };
  
  // Only used by compiler if both template types are the same
  template <typename T, T>
  struct SameType;
  
  // 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
  {
    typedef void (*Signature_enumeration)(class IO&, T&);
  
    template <typename U>
    static char test(SameType<Signature_enumeration, &U::enumeration>*);
  
    template <typename U>
    static double test(...);
  
  public:
    static bool const value =
      (sizeof(test<ScalarEnumerationTraits<T> >(nullptr)) == 1);
  };
  
  // Test if ScalarBitSetTraits<T> is defined on type T.
  template <class T>
  struct has_ScalarBitSetTraits
  {
    typedef void (*Signature_bitset)(class IO&, T&);
  
    template <typename U>
    static char test(SameType<Signature_bitset, &U::bitset>*);
  
    template <typename U>
    static double test(...);
  
  public:
    static bool const value = (sizeof(test<ScalarBitSetTraits<T> >(nullptr)) == 1);
  };
  
  // Test if ScalarTraits<T> is defined on type T.
  template <class T>
  struct has_ScalarTraits
  {
    typedef StringRef (*Signature_input)(StringRef, void*, T&);
    typedef void (*Signature_output)(const T&, void*, llvm::raw_ostream&);
    typedef bool (*Signature_mustQuote)(StringRef);
  
    template <typename U>
    static char test(SameType<Signature_input, &U::input> *,
                     SameType<Signature_output, &U::output> *,
                     SameType<Signature_mustQuote, &U::mustQuote> *);
  
    template <typename U>
    static double test(...);
  
  public:
    static bool const value =
        (sizeof(test<ScalarTraits<T>>(nullptr, nullptr, nullptr)) == 1);
  };
  
  // Test if BlockScalarTraits<T> is defined on type T.
  template <class T>
  struct has_BlockScalarTraits
  {
    typedef StringRef (*Signature_input)(StringRef, void *, T &);
    typedef void (*Signature_output)(const T &, void *, llvm::raw_ostream &);
  
    template <typename U>
    static char test(SameType<Signature_input, &U::input> *,
                     SameType<Signature_output, &U::output> *);
  
    template <typename U>
    static double test(...);
  
  public:
    static bool const value =
        (sizeof(test<BlockScalarTraits<T>>(nullptr, nullptr)) == 1);
  };
  
  // Test if MappingTraits<T> is defined on type T.
  template <class T>
  struct has_MappingTraits
  {
    typedef void (*Signature_mapping)(class IO&, T&);
  
    template <typename U>
    static char test(SameType<Signature_mapping, &U::mapping>*);
  
    template <typename U>
    static double test(...);
  
  public:
    static bool const value = (sizeof(test<MappingTraits<T> >(nullptr)) == 1);
  };
  
  // Test if MappingTraits<T>::validate() is defined on type T.
  template <class T>
  struct has_MappingValidateTraits
  {
    typedef StringRef (*Signature_validate)(class IO&, T&);
  
    template <typename U>
    static char test(SameType<Signature_validate, &U::validate>*);
  
    template <typename U>
    static double test(...);
  
  public:
    static bool const value = (sizeof(test<MappingTraits<T> >(nullptr)) == 1);
  };
  
  // Test if SequenceTraits<T> is defined on type T.
  template <class T>
  struct has_SequenceMethodTraits
  {
    typedef size_t (*Signature_size)(class IO&, T&);
  
    template <typename U>
    static char test(SameType<Signature_size, &U::size>*);
  
    template <typename U>
    static double test(...);
  
  public:
    static bool const value =  (sizeof(test<SequenceTraits<T> >(nullptr)) == 1);
  };
  
  // 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<T>::value>
  class has_FlowTraits
  {
  public:
     static const bool value = false;
  };
  
  // Some older gcc compilers don't support straight forward tests
  // for members, so test for ambiguity cause by the base and derived
  // classes both defining the member.
  template <class T>
  struct has_FlowTraits<T, true>
  {
    struct Fallback { bool flow; };
    struct Derived : T, Fallback { };
  
    template<typename C>
    static char (&f(SameType<bool Fallback::*, &C::flow>*))[1];
  
    template<typename C>
    static char (&f(...))[2];
  
  public:
    static bool const value = sizeof(f<Derived>(nullptr)) == 2;
  };
  
  // Test if SequenceTraits<T> is defined on type T
  template<typename T>
  struct has_SequenceTraits : public std::integral_constant<bool,
                                        has_SequenceMethodTraits<T>::value > { };
  
  // Test if DocumentListTraits<T> is defined on type T
  template <class T>
  struct has_DocumentListTraits
  {
    typedef size_t (*Signature_size)(class IO&, T&);
  
    template <typename U>
    static char test(SameType<Signature_size, &U::size>*);
  
    template <typename U>
    static double test(...);
  
  public:
    static bool const value = (sizeof(test<DocumentListTraits<T> >(nullptr))==1);
  };
  
  inline bool isNumber(StringRef S) {
    static const char OctalChars[] = "01234567";
    if (S.startswith("0") &&
        S.drop_front().find_first_not_of(OctalChars) == StringRef::npos)
      return true;
  
    if (S.startswith("0o") &&
        S.drop_front(2).find_first_not_of(OctalChars) == StringRef::npos)
      return true;
  
    static const char HexChars[] = "0123456789abcdefABCDEF";
    if (S.startswith("0x") &&
        S.drop_front(2).find_first_not_of(HexChars) == StringRef::npos)
      return true;
  
    static const char DecChars[] = "0123456789";
    if (S.find_first_not_of(DecChars) == StringRef::npos)
      return true;
  
    if (S.equals(".inf") || S.equals(".Inf") || S.equals(".INF"))
      return true;
  
    Regex FloatMatcher("^(\\.[0-9]+|[0-9]+(\\.[0-9]*)?)([eE][-+]?[0-9]+)?$");
    if (FloatMatcher.match(S))
      return true;
  
    return false;
  }
  
  inline bool isNumeric(StringRef S) {
    if ((S.front() == '-' || S.front() == '+') && isNumber(S.drop_front()))
      return true;
  
    if (isNumber(S))
      return true;
  
    if (S.equals(".nan") || S.equals(".NaN") || S.equals(".NAN"))
      return true;
  
    return false;
  }
  
  inline bool isNull(StringRef S) {
    return S.equals("null") || S.equals("Null") || S.equals("NULL") ||
           S.equals("~");
  }
  
  inline bool isBool(StringRef S) {
    return S.equals("true") || S.equals("True") || S.equals("TRUE") ||
           S.equals("false") || S.equals("False") || S.equals("FALSE");
  }
  
  inline bool needsQuotes(StringRef S) {
    if (S.empty())
      return true;
    if (isspace(S.front()) || isspace(S.back()))
      return true;
    if (S.front() == ',')
      return true;
  
    static const char ScalarSafeChars[] =
        "abcdefghijklmnopqrstuvwxyz"
        "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789_-/^., \t";
    if (S.find_first_not_of(ScalarSafeChars) != StringRef::npos)
      return true;
  
    if (isNull(S))
      return true;
    if (isBool(S))
      return true;
    if (isNumeric(S))
      return true;
  
    return false;
  }
  
  template<typename T>
  struct missingTraits : public std::integral_constant<bool,
                                           !has_ScalarEnumerationTraits<T>::value
                                        && !has_ScalarBitSetTraits<T>::value
                                        && !has_ScalarTraits<T>::value
                                        && !has_BlockScalarTraits<T>::value
                                        && !has_MappingTraits<T>::value
                                        && !has_SequenceTraits<T>::value
                                        && !has_DocumentListTraits<T>::value >  {};
  
  template<typename T>
  struct validatedMappingTraits : public std::integral_constant<bool,
                                         has_MappingTraits<T>::value
                                      && has_MappingValidateTraits<T>::value> {};
  
  template<typename T>
  struct unvalidatedMappingTraits : public std::integral_constant<bool,
                                          has_MappingTraits<T>::value
                                      && !has_MappingValidateTraits<T>::value> {};
  // Base class for Input and Output.
  class IO {
  public:
  
    IO(void *Ctxt=nullptr);
    virtual ~IO();
  
    virtual bool outputting() = 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 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 &, bool) = 0;
    virtual void blockScalarString(StringRef &) = 0;
  
    virtual void setError(const Twine &) = 0;
  
    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() ) {
        // FIXME: Force integral conversion to allow strong typedefs to convert.
        FBT Res = (uint64_t)Val;
        yamlize(*this, Res, true);
        Val = (uint64_t)Res;
      }
    }
  
    template <typename T>
    void bitSetCase(T &Val, const char* Str, const T ConstVal) {
      if ( bitSetMatch(Str, outputting() && (Val & ConstVal) == ConstVal) ) {
        Val = 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 = 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();
    void setContext(void *);
  
    template <typename T>
    void mapRequired(const char* Key, T& Val) {
      this->processKey(Key, Val, true);
    }
  
    template <typename T>
    typename std::enable_if<has_SequenceTraits<T>::value,void>::type
    mapOptional(const char* Key, T& Val) {
      // omit key/value instead of outputting empty sequence
      if ( this->canElideEmptySequence() && !(Val.begin() != Val.end()) )
        return;
      this->processKey(Key, Val, false);
    }
  
    template <typename T>
    void mapOptional(const char* Key, Optional<T> &Val) {
      processKeyWithDefault(Key, Val, Optional<T>(), /*Required=*/false);
    }
  
    template <typename T>
    typename std::enable_if<!has_SequenceTraits<T>::value,void>::type
    mapOptional(const char* Key, T& Val) {
      this->processKey(Key, Val, false);
    }
  
    template <typename T>
    void mapOptional(const char* Key, T& Val, const T& Default) {
      this->processKeyWithDefault(Key, Val, Default, false);
    }
  
  private:
    template <typename T>
    void processKeyWithDefault(const char *Key, Optional<T> &Val,
                               const Optional<T> &DefaultValue, bool Required) {
      assert(DefaultValue.hasValue() == false &&
             "Optional<T> shouldn't have a value!");
      void *SaveInfo;
      bool UseDefault;
      const bool sameAsDefault = outputting() && !Val.hasValue();
      if (!outputting() && !Val.hasValue())
        Val = T();
      if (this->preflightKey(Key, Required, sameAsDefault, UseDefault,
                             SaveInfo)) {
        yamlize(*this, Val.getValue(), Required);
        this->postflightKey(SaveInfo);
      } else {
        if (UseDefault)
          Val = DefaultValue;
      }
    }
  
    template <typename T>
    void processKeyWithDefault(const char *Key, T &Val, const T& DefaultValue,
                                                                  bool Required) {
      void *SaveInfo;
      bool UseDefault;
      const bool sameAsDefault = outputting() && Val == DefaultValue;
      if ( this->preflightKey(Key, Required, sameAsDefault, UseDefault,
                                                                    SaveInfo) ) {
        yamlize(*this, Val, Required);
        this->postflightKey(SaveInfo);
      }
      else {
        if ( UseDefault )
          Val = DefaultValue;
      }
    }
  
    template <typename T>
    void processKey(const char *Key, T &Val, bool Required) {
      void *SaveInfo;
      bool UseDefault;
      if ( this->preflightKey(Key, Required, false, UseDefault, SaveInfo) ) {
        yamlize(*this, Val, Required);
        this->postflightKey(SaveInfo);
      }
    }
  
  private:
    void  *Ctxt;
  };
  
  template<typename T>
  typename std::enable_if<has_ScalarEnumerationTraits<T>::value,void>::type
  yamlize(IO &io, T &Val, bool) {
    io.beginEnumScalar();
    ScalarEnumerationTraits<T>::enumeration(io, Val);
    io.endEnumScalar();
  }
  
  template<typename T>
  typename std::enable_if<has_ScalarBitSetTraits<T>::value,void>::type
  yamlize(IO &io, T &Val, bool) {
    bool DoClear;
    if ( io.beginBitSetScalar(DoClear) ) {
      if ( DoClear )
        Val = static_cast<T>(0);
      ScalarBitSetTraits<T>::bitset(io, Val);
      io.endBitSetScalar();
    }
  }
  
  template<typename T>
  typename std::enable_if<has_ScalarTraits<T>::value,void>::type
  yamlize(IO &io, T &Val, bool) {
    if ( io.outputting() ) {
      std::string Storage;
      llvm::raw_string_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(llvm::Twine(Result));
      }
    }
  }
  
  template <typename T>
  typename std::enable_if<has_BlockScalarTraits<T>::value, void>::type
  yamlize(IO &YamlIO, T &Val, bool) {
    if (YamlIO.outputting()) {
      std::string Storage;
      llvm::raw_string_ostream Buffer(Storage);
      BlockScalarTraits<T>::output(Val, YamlIO.getContext(), Buffer);
      StringRef Str = Buffer.str();
      YamlIO.blockScalarString(Str);
    } else {
      StringRef Str;
      YamlIO.blockScalarString(Str);
      StringRef Result =
          BlockScalarTraits<T>::input(Str, YamlIO.getContext(), Val);
      if (!Result.empty())
        YamlIO.setError(llvm::Twine(Result));
    }
  }
  
  template<typename T>
  typename std::enable_if<validatedMappingTraits<T>::value, void>::type
  yamlize(IO &io, T &Val, bool) {
    if (has_FlowTraits<MappingTraits<T>>::value)
      io.beginFlowMapping();
    else
      io.beginMapping();
    if (io.outputting()) {
      StringRef Err = MappingTraits<T>::validate(io, Val);
      if (!Err.empty()) {
        llvm::errs() << Err << "\n";
        assert(Err.empty() && "invalid struct trying to be written as yaml");
      }
    }
    MappingTraits<T>::mapping(io, Val);
    if (!io.outputting()) {
      StringRef Err = MappingTraits<T>::validate(io, Val);
      if (!Err.empty())
        io.setError(Err);
    }
    if (has_FlowTraits<MappingTraits<T>>::value)
      io.endFlowMapping();
    else
      io.endMapping();
  }
  
  template<typename T>
  typename std::enable_if<unvalidatedMappingTraits<T>::value, void>::type
  yamlize(IO &io, T &Val, bool) {
    if (has_FlowTraits<MappingTraits<T>>::value) {
      io.beginFlowMapping();
      MappingTraits<T>::mapping(io, Val);
      io.endFlowMapping();
    } else {
      io.beginMapping();
      MappingTraits<T>::mapping(io, Val);
      io.endMapping();
    }
  }
  
  template<typename T>
  typename std::enable_if<missingTraits<T>::value, void>::type
  yamlize(IO &io, T &Val, bool) {
    char missing_yaml_trait_for_type[sizeof(MissingTrait<T>)];
  }
  
  template<typename T>
  typename std::enable_if<has_SequenceTraits<T>::value,void>::type
  yamlize(IO &io, T &Seq, bool) {
    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);
          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);
          io.postflightElement(SaveInfo);
        }
      }
      io.endSequence();
    }
  }
  
  template<>
  struct ScalarTraits<bool> {
    static void output(const bool &, void*, llvm::raw_ostream &);
    static StringRef input(StringRef, void*, bool &);
    static bool mustQuote(StringRef) { return false; }
  };
  
  template<>
  struct ScalarTraits<StringRef> {
    static void output(const StringRef &, void*, llvm::raw_ostream &);
    static StringRef input(StringRef, void*, StringRef &);
    static bool mustQuote(StringRef S) { return needsQuotes(S); }
  };
  
  template<>
  struct ScalarTraits<std::string> {
    static void output(const std::string &, void*, llvm::raw_ostream &);
    static StringRef input(StringRef, void*, std::string &);
    static bool mustQuote(StringRef S) { return needsQuotes(S); }
  };
  
  template<>
  struct ScalarTraits<uint8_t> {
    static void output(const uint8_t &, void*, llvm::raw_ostream &);
    static StringRef input(StringRef, void*, uint8_t &);
    static bool mustQuote(StringRef) { return false; }
  };
  
  template<>
  struct ScalarTraits<uint16_t> {
    static void output(const uint16_t &, void*, llvm::raw_ostream &);
    static StringRef input(StringRef, void*, uint16_t &);
    static bool mustQuote(StringRef) { return false; }
  };
  
  template<>
  struct ScalarTraits<uint32_t> {
    static void output(const uint32_t &, void*, llvm::raw_ostream &);
    static StringRef input(StringRef, void*, uint32_t &);
    static bool mustQuote(StringRef) { return false; }
  };
  
  template<>
  struct ScalarTraits<uint64_t> {
    static void output(const uint64_t &, void*, llvm::raw_ostream &);
    static StringRef input(StringRef, void*, uint64_t &);
    static bool mustQuote(StringRef) { return false; }
  };
  
  template<>
  struct ScalarTraits<int8_t> {
    static void output(const int8_t &, void*, llvm::raw_ostream &);
    static StringRef input(StringRef, void*, int8_t &);
    static bool mustQuote(StringRef) { return false; }
  };
  
  template<>
  struct ScalarTraits<int16_t> {
    static void output(const int16_t &, void*, llvm::raw_ostream &);
    static StringRef input(StringRef, void*, int16_t &);
    static bool mustQuote(StringRef) { return false; }
  };
  
  template<>
  struct ScalarTraits<int32_t> {
    static void output(const int32_t &, void*, llvm::raw_ostream &);
    static StringRef input(StringRef, void*, int32_t &);
    static bool mustQuote(StringRef) { return false; }
  };
  
  template<>
  struct ScalarTraits<int64_t> {
    static void output(const int64_t &, void*, llvm::raw_ostream &);
    static StringRef input(StringRef, void*, int64_t &);
    static bool mustQuote(StringRef) { return false; }
  };
  
  template<>
  struct ScalarTraits<float> {
    static void output(const float &, void*, llvm::raw_ostream &);
    static StringRef input(StringRef, void*, float &);
    static bool mustQuote(StringRef) { return false; }
  };
  
  template<>
  struct ScalarTraits<double> {
    static void output(const double &, void*, llvm::raw_ostream &);
    static StringRef input(StringRef, void*, double &);
    static bool mustQuote(StringRef) { return false; }
  };
  
  // 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:
    typedef llvm::AlignedCharArrayUnion<TNorm> Storage;
  
    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)
      : io(i_o), BufPtr(nullptr), Result(Obj) {
      if ( io.outputting() ) {
        BufPtr = new (&Buffer) TNorm(io, Obj);
      }
      else {
        BufPtr = new TNorm(io);
      }
    }
  
    ~MappingNormalizationHeap() {
      if ( io.outputting() ) {
        BufPtr->~TNorm();
      }
      else {
        Result = BufPtr->denormalize(io);
      }
    }
  
    TNorm* operator->() { return BufPtr; }
  
  private:
    typedef llvm::AlignedCharArrayUnion<TNorm> Storage;
  
    Storage       Buffer;
    IO           &io;
    TNorm        *BufPtr;
    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 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 InputContent,
          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();
  
  private:
    bool outputting() 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;
    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 &, bool) override;
    void blockScalarString(StringRef &) override;
    void setError(const Twine &message) override;
    bool canElideEmptySequence() override;
  
    class HNode {
      virtual void anchor();
    public:
      HNode(Node *n) : _node(n) { }
      virtual ~HNode() { }
      static inline bool classof(const HNode *) { return true; }
  
      Node *_node;
    };
  
    class EmptyHNode : public HNode {
      void anchor() override;
    public:
      EmptyHNode(Node *n) : HNode(n) { }
      static inline bool classof(const HNode *n) {
        return NullNode::classof(n->_node);
      }
      static inline bool classof(const EmptyHNode *) { return true; }
    };
  
    class ScalarHNode : public HNode {
      void anchor() override;
    public:
      ScalarHNode(Node *n, StringRef s) : HNode(n), _value(s) { }
  
      StringRef value() const { return _value; }
  
      static inline bool classof(const HNode *n) {
        return ScalarNode::classof(n->_node) ||
               BlockScalarNode::classof(n->_node);
      }
      static inline bool classof(const ScalarHNode *) { return true; }
    protected:
      StringRef _value;
    };
  
    class MapHNode : public HNode {
      void anchor() override;
  
    public:
      MapHNode(Node *n) : HNode(n) { }
  
      static inline bool classof(const HNode *n) {
        return MappingNode::classof(n->_node);
      }
      static inline bool classof(const MapHNode *) { return true; }
  
      typedef llvm::StringMap<std::unique_ptr<HNode>> NameToNode;
  
      bool isValidKey(StringRef key);
  
      NameToNode                        Mapping;
      llvm::SmallVector<const char*, 6> ValidKeys;
    };
  
    class SequenceHNode : public HNode {
      void anchor() override;
  
    public:
      SequenceHNode(Node *n) : HNode(n) { }
  
      static inline bool classof(const HNode *n) {
        return SequenceNode::classof(n->_node);
      }
      static inline bool classof(const SequenceHNode *) { return true; }
  
      std::vector<std::unique_ptr<HNode>> Entries;
    };
  
    std::unique_ptr<Input::HNode> createHNodes(Node *node);
    void setError(HNode *hnode, const Twine &message);
    void setError(Node *node, const Twine &message);
  
  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;
  
  private:
    llvm::SourceMgr                     SrcMgr; // must be before Strm
    std::unique_ptr<llvm::yaml::Stream> Strm;
    std::unique_ptr<HNode>              TopNode;
    std::error_code                     EC;
    llvm::BumpPtrAllocator              StringAllocator;
    llvm::yaml::document_iterator       DocIterator;
    std::vector<bool>                   BitValuesUsed;
    HNode                              *CurrentNode;
    bool                                ScalarMatchFound;
  };
  
  ///
  /// The Output class is used to generate a yaml document from in-memory structs
  /// and vectors.
  ///
  class Output : public IO {
  public:
    Output(llvm::raw_ostream &, void *Ctxt = nullptr, int WrapColumn = 70);
    ~Output() override;
  
    bool outputting() 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;
    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 &, bool) override;
    void blockScalarString(StringRef &) override;
    void setError(const Twine &message) override;
    bool canElideEmptySequence() override;
  public:
    // 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 outputUpToEndOfLine(StringRef s);
    void newLineCheck();
    void outputNewLine();
    void paddedKey(StringRef key);
    void flowKey(StringRef Key);
  
    enum InState {
      inSeq,
      inFlowSeq,
      inMapFirstKey,
      inMapOtherKey,
      inFlowMapFirstKey,
      inFlowMapOtherKey
    };
  
    llvm::raw_ostream       &Out;
    int                      WrapColumn;
    SmallVector<InState, 8>  StateStack;
    int                      Column;
    int                      ColumnAtFlowStart;
    int                      ColumnAtMapFlowStart;
    bool                     NeedBitValueComma;
    bool                     NeedFlowSequenceComma;
    bool                     EnumerationMatchFound;
    bool                     NeedsNewLine;
  };
  
  /// 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() { }                                                            \
          _type(const _base v) : value(v) { }                                    \
          _type(const _type &v) : value(v.value) {}                              \
          _type &operator=(const _type &rhs) { value = rhs.value; return *this; }\
          _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;                                                           \
      };
  
  ///
  /// 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> {
    static void output(const Hex8 &, void*, llvm::raw_ostream &);
    static StringRef input(StringRef, void*, Hex8 &);
    static bool mustQuote(StringRef) { return false; }
  };
  
  template<>
  struct ScalarTraits<Hex16> {
    static void output(const Hex16 &, void*, llvm::raw_ostream &);
    static StringRef input(StringRef, void*, Hex16 &);
    static bool mustQuote(StringRef) { return false; }
  };
  
  template<>
  struct ScalarTraits<Hex32> {
    static void output(const Hex32 &, void*, llvm::raw_ostream &);
    static StringRef input(StringRef, void*, Hex32 &);
    static bool mustQuote(StringRef) { return false; }
  };
  
  template<>
  struct ScalarTraits<Hex64> {
    static void output(const Hex64 &, void*, llvm::raw_ostream &);
    static StringRef input(StringRef, void*, Hex64 &);
    static bool mustQuote(StringRef) { return false; }
  };
  
  // Define non-member operator>> so that Input can stream in a document list.
  template <typename T>
  inline
  typename std::enable_if<has_DocumentListTraits<T>::value, Input &>::type
  operator>>(Input &yin, T &docList) {
    int i = 0;
    while ( yin.setCurrentDocument() ) {
      yamlize(yin, DocumentListTraits<T>::element(yin, docList, i), true);
      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
  typename std::enable_if<has_MappingTraits<T>::value, Input &>::type
  operator>>(Input &yin, T &docMap) {
    yin.setCurrentDocument();
    yamlize(yin, docMap, true);
    return yin;
  }
  
  // Define non-member operator>> so that Input can stream in a sequence as
  // a document.
  template <typename T>
  inline
  typename std::enable_if<has_SequenceTraits<T>::value, Input &>::type
  operator>>(Input &yin, T &docSeq) {
    if (yin.setCurrentDocument())
      yamlize(yin, docSeq, true);
    return yin;
  }
  
  // Define non-member operator>> so that Input can stream in a block scalar.
  template <typename T>
  inline
  typename std::enable_if<has_BlockScalarTraits<T>::value, Input &>::type
  operator>>(Input &In, T &Val) {
    if (In.setCurrentDocument())
      yamlize(In, Val, true);
    return In;
  }
  
  // Provide better error message about types missing a trait specialization
  template <typename T>
  inline
  typename std::enable_if<missingTraits<T>::value, Input &>::type
  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
  typename std::enable_if<has_DocumentListTraits<T>::value, Output &>::type
  operator<<(Output &yout, T &docList) {
    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);
        yout.postflightDocument();
      }
    }
    yout.endDocuments();
    return yout;
  }
  
  // Define non-member operator<< so that Output can stream out a map.
  template <typename T>
  inline
  typename std::enable_if<has_MappingTraits<T>::value, Output &>::type
  operator<<(Output &yout, T &map) {
    yout.beginDocuments();
    if ( yout.preflightDocument(0) ) {
      yamlize(yout, map, true);
      yout.postflightDocument();
    }
    yout.endDocuments();
    return yout;
  }
  
  // Define non-member operator<< so that Output can stream out a sequence.
  template <typename T>
  inline
  typename std::enable_if<has_SequenceTraits<T>::value, Output &>::type
  operator<<(Output &yout, T &seq) {
    yout.beginDocuments();
    if ( yout.preflightDocument(0) ) {
      yamlize(yout, seq, true);
      yout.postflightDocument();
    }
    yout.endDocuments();
    return yout;
  }
  
  // Define non-member operator<< so that Output can stream out a block scalar.
  template <typename T>
  inline
  typename std::enable_if<has_BlockScalarTraits<T>::value, Output &>::type
  operator<<(Output &Out, T &Val) {
    Out.beginDocuments();
    if (Out.preflightDocument(0)) {
      yamlize(Out, Val, true);
      Out.postflightDocument();
    }
    Out.endDocuments();
    return Out;
  }
  
  // Provide better error message about types missing a trait specialization
  template <typename T>
  inline
  typename std::enable_if<missingTraits<T>::value, Output &>::type
  operator<<(Output &yout, T &seq) {
    char missing_yaml_trait_for_type[sizeof(MissingTrait<T>)];
    return yout;
  }
  
  } // namespace yaml
  } // namespace llvm
  
  /// Utility for declaring that a std::vector of a particular type
  /// should be considered a YAML sequence.
  #define LLVM_YAML_IS_SEQUENCE_VECTOR(_type)                                 \
    namespace llvm {                                                          \
    namespace yaml {                                                          \
      template<>                                                              \
      struct SequenceTraits< std::vector<_type> > {                           \
        static size_t size(IO &io, std::vector<_type> &seq) {                 \
          return seq.size();                                                  \
        }                                                                     \
        static _type& element(IO &io, std::vector<_type> &seq, size_t index) {\
          if ( index >= seq.size() )                                          \
            seq.resize(index+1);                                              \
          return seq[index];                                                  \
        }                                                                     \
      };                                                                      \
    }                                                                         \
    }
  
  /// 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)                            \
    namespace llvm {                                                          \
    namespace yaml {                                                          \
      template<>                                                              \
      struct SequenceTraits< std::vector<_type> > {                           \
        static size_t size(IO &io, std::vector<_type> &seq) {                 \
          return seq.size();                                                  \
        }                                                                     \
        static _type& element(IO &io, std::vector<_type> &seq, size_t index) {\
          (void)flow; /* Remove this workaround after PR17897 is fixed */     \
          if ( index >= seq.size() )                                          \
            seq.resize(index+1);                                              \
          return seq[index];                                                  \
        }                                                                     \
        static const bool flow = true;                                        \
      };                                                                      \
    }                                                                         \
    }
  
  /// 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<>                                                              \
      struct DocumentListTraits< std::vector<_type> > {                       \
        static size_t size(IO &io, std::vector<_type> &seq) {                 \
          return seq.size();                                                  \
        }                                                                     \
        static _type& element(IO &io, std::vector<_type> &seq, size_t index) {\
          if ( index >= seq.size() )                                          \
            seq.resize(index+1);                                              \
          return seq[index];                                                  \
        }                                                                     \
      };                                                                      \
    }                                                                         \
    }
  
  #endif // LLVM_SUPPORT_YAMLTRAITS_H
  