llvm/flang/lib/parser/characters.h

// Copyright (c) 2018-2019, NVIDIA CORPORATION.  All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#ifndef FORTRAN_PARSER_CHARACTERS_H_
#define FORTRAN_PARSER_CHARACTERS_H_

// Define some character classification predicates and
// conversions here to avoid dependences upon <cctype> and
// also to accomodate Fortran tokenization.

#include <cstddef>
#include <optional>
#include <string>

namespace Fortran::parser {

// We can easily support Fortran program source in any character
// set whose first 128 code points correspond to ASCII codes 0-127 (ISO/IEC646).
// The specific encodings that we can handle include:
//   LATIN_1: ISO 8859-1 Latin-1
//   UTF_8: Multi-byte encoding of Unicode (ISO/IEC 10646)
enum class Encoding { LATIN_1, UTF_8 };

inline constexpr bool IsUpperCaseLetter(char ch) {
  return ch >= 'A' && ch <= 'Z';
}

inline constexpr bool IsLowerCaseLetter(char ch) {
  return ch >= 'a' && ch <= 'z';
}

inline constexpr bool IsLetter(char ch) {
  return IsUpperCaseLetter(ch) || IsLowerCaseLetter(ch);
}

inline constexpr bool IsDecimalDigit(char ch) { return ch >= '0' && ch <= '9'; }

inline constexpr bool IsHexadecimalDigit(char ch) {
  return (ch >= '0' && ch <= '9') || (ch >= 'A' && ch <= 'F') ||
      (ch >= 'a' && ch <= 'f');
}

inline constexpr bool IsOctalDigit(char ch) { return ch >= '0' && ch <= '7'; }

inline constexpr bool IsLegalIdentifierStart(char ch) {
  return IsLetter(ch) || ch == '_' || ch == '@' || ch == '$';
}

inline constexpr bool IsLegalInIdentifier(char ch) {
  return IsLegalIdentifierStart(ch) || IsDecimalDigit(ch);
}

inline constexpr char ToLowerCaseLetter(char ch) {
  return IsUpperCaseLetter(ch) ? ch - 'A' + 'a' : ch;
}

inline constexpr char ToLowerCaseLetter(char &&ch) {
  return IsUpperCaseLetter(ch) ? ch - 'A' + 'a' : ch;
}

inline std::string ToLowerCaseLetters(const std::string &str) {
  std::string lowered{str};
  for (char &ch : lowered) {
    ch = ToLowerCaseLetter(ch);
  }
  return lowered;
}

inline constexpr char ToUpperCaseLetter(char ch) {
  return IsLowerCaseLetter(ch) ? ch - 'a' + 'A' : ch;
}

inline constexpr char ToUpperCaseLetter(char &&ch) {
  return IsLowerCaseLetter(ch) ? ch - 'a' + 'A' : ch;
}

inline std::string ToUpperCaseLetters(const std::string &str) {
  std::string raised{str};
  for (char &ch : raised) {
    ch = ToUpperCaseLetter(ch);
  }
  return raised;
}

inline constexpr bool IsSameApartFromCase(char x, char y) {
  return ToLowerCaseLetter(x) == ToLowerCaseLetter(y);
}

inline constexpr char DecimalDigitValue(char ch) { return ch - '0'; }

inline constexpr char HexadecimalDigitValue(char ch) {
  return IsUpperCaseLetter(ch)
      ? ch - 'A' + 10
      : IsLowerCaseLetter(ch) ? ch - 'a' + 10 : DecimalDigitValue(ch);
}

inline constexpr std::optional<char> BackslashEscapeValue(char ch) {
  switch (ch) {
  case 'a': return std::nullopt;  // '\a';  PGF90 doesn't know \a
  case 'b': return '\b';
  case 'f': return '\f';
  case 'n': return '\n';
  case 'r': return '\r';
  case 't': return '\t';
  case 'v': return '\v';
  case '"':
  case '\'':
  case '\\': return ch;
  default: return std::nullopt;
  }
}

inline constexpr std::optional<char> BackslashEscapeChar(char ch) {
  switch (ch) {
  case '\a': return std::nullopt;  // 'a';  PGF90 doesn't know \a
  case '\b': return 'b';
  case '\f': return 'f';
  case '\n': return 'n';
  case '\r': return 'r';
  case '\t': return 't';
  case '\v': return 'v';
  case '"':
  case '\'':
  case '\\': return ch;
  default: return std::nullopt;
  }
}

struct EncodedCharacter {
  static constexpr int maxEncodingBytes{6};
  char buffer[maxEncodingBytes];
  int bytes{0};
};

template<Encoding ENCODING> EncodedCharacter EncodeCharacter(char32_t ucs);
template<> EncodedCharacter EncodeCharacter<Encoding::LATIN_1>(char32_t);
template<> EncodedCharacter EncodeCharacter<Encoding::UTF_8>(char32_t);

EncodedCharacter EncodeCharacter(Encoding, char32_t ucs);

template<Encoding ENCODING, typename STRING>
std::string EncodeString(const STRING &);
extern template std::string EncodeString<Encoding::LATIN_1, std::string>(
    const std::string &);
extern template std::string EncodeString<Encoding::UTF_8, std::u32string>(
    const std::u32string &);

// EmitQuotedChar drives callbacks "emit" and "insert" to output the
// bytes of an encoding for a codepoint.
template<typename NORMAL, typename INSERTED>
void EmitQuotedChar(char32_t ch, const NORMAL &emit, const INSERTED &insert,
    bool backslashEscapes = true, Encoding encoding = Encoding::UTF_8) {
  auto emitOneChar{[&](std::uint8_t ch) {
    if (ch < ' ' || (backslashEscapes && (ch == '\\' || ch >= 0x7f))) {
      insert('\\');
      if (std::optional<char> escape{BackslashEscapeChar(ch)}) {
        emit(*escape);
      } else {
        // octal escape sequence; always emit 3 digits to avoid ambiguity
        insert('0' + (ch >> 6));
        insert('0' + ((ch >> 3) & 7));
        insert('0' + (ch & 7));
      }
    } else {
      emit(ch);
    }
  }};
  if (ch <= 0x7f) {
    emitOneChar(ch);
  } else {
    EncodedCharacter encoded{EncodeCharacter(encoding, ch)};
    for (int j{0}; j < encoded.bytes; ++j) {
      emitOneChar(encoded.buffer[j]);
    }
  }
}

std::string QuoteCharacterLiteral(const std::string &,
    bool backslashEscapes = true, Encoding = Encoding::LATIN_1);
std::string QuoteCharacterLiteral(const std::u16string &,
    bool backslashEscapes = true, Encoding = Encoding::UTF_8);
std::string QuoteCharacterLiteral(const std::u32string &,
    bool backslashEscapes = true, Encoding = Encoding::UTF_8);

int UTF_8CharacterBytes(const char *);

struct DecodedCharacter {
  char32_t codepoint{0};
  int bytes{0};  // signifying failure
};

template<Encoding ENCODING>
DecodedCharacter DecodeRawCharacter(const char *, std::size_t);
template<>
DecodedCharacter DecodeRawCharacter<Encoding::LATIN_1>(
    const char *, std::size_t);

template<>
DecodedCharacter DecodeRawCharacter<Encoding::UTF_8>(const char *, std::size_t);

// DecodeCharacter optionally handles backslash escape sequences, too.
template<Encoding ENCODING>
DecodedCharacter DecodeCharacter(
    const char *, std::size_t, bool backslashEscapes);
extern template DecodedCharacter DecodeCharacter<Encoding::LATIN_1>(
    const char *, std::size_t, bool);
extern template DecodedCharacter DecodeCharacter<Encoding::UTF_8>(
    const char *, std::size_t, bool);

DecodedCharacter DecodeCharacter(
    Encoding, const char *, std::size_t, bool backslashEscapes);

template<typename RESULT, Encoding ENCODING>
RESULT DecodeString(const std::string &, bool backslashEscapes);
extern template std::string DecodeString<std::string, Encoding::LATIN_1>(
    const std::string &, bool);
extern template std::u16string DecodeString<std::u16string, Encoding::UTF_8>(
    const std::string &, bool);
extern template std::u32string DecodeString<std::u32string, Encoding::UTF_8>(
    const std::string &, bool);
}
#endif  // FORTRAN_PARSER_CHARACTERS_H_