llvm/flang/lib/parser/token-parsers.h

#ifndef FORTRAN_PARSER_TOKEN_PARSERS_H_
#define FORTRAN_PARSER_TOKEN_PARSERS_H_

// These parsers are driven by the Fortran grammar (grammar.h) to consume
// the prescanned character stream and recognize context-sensitive tokens.

#include "basic-parsers.h"
#include "characters.h"
#include "idioms.h"
#include "provenance.h"
#include <cstring>
#include <functional>
#include <limits>
#include <list>
#include <optional>
#include <string>

namespace Fortran {
namespace parser {

class CharPredicateGuardParser {
public:
  using resultType = char;
  constexpr CharPredicateGuardParser(
      const CharPredicateGuardParser &) = default;
  constexpr CharPredicateGuardParser(bool (*f)(char), MessageFixedText t)
    : predicate_{f}, text_{t} {}
  std::optional<char> Parse(ParseState *state) const {
    auto at = state->GetLocation();
    if (std::optional<char> result{nextChar.Parse(state)}) {
      if (predicate_(*result)) {
        return result;
      }
    }
    state->PutMessage(at, text_);
    return {};
  }

private:
  bool (*const predicate_)(char);
  const MessageFixedText text_;
};

constexpr CharPredicateGuardParser digit{
    IsDecimalDigit, "expected digit"_en_US};

constexpr auto letter = applyFunction(ToLowerCaseLetter,
    CharPredicateGuardParser{IsLetter, "expected letter"_en_US});

template<char good> class CharMatch {
public:
  using resultType = char;
  constexpr CharMatch() {}
  static std::optional<char> Parse(ParseState *state) {
    auto at = state->GetLocation();
    std::optional<char> result{nextChar.Parse(state)};
    if (result && *result != good) {
      result.reset();
    }
    if (!result) {
      state->PutMessage(at, MessageExpectedText{good});
    }
    return {result};
  }
};

constexpr struct Space {
  using resultType = Success;
  constexpr Space() {}
  static std::optional<Success> Parse(ParseState *state) {
    std::optional<char> ch{nextChar.Parse(state)};
    if (ch) {
      if (ch == ' ' || ch == '\t') {
        return {Success{}};
      }
    }
    return {};
  }
} space;

constexpr auto spaces = skipMany(space);

class TokenStringMatch {
public:
  using resultType = Success;
  constexpr TokenStringMatch(const TokenStringMatch &) = default;
  constexpr TokenStringMatch(const char *str, size_t n)
    : str_{str}, bytes_{n} {}
  constexpr TokenStringMatch(const char *str) : str_{str} {}
  std::optional<Success> Parse(ParseState *state) const {
    auto at = state->GetLocation();
    if (!spaces.Parse(state)) {
      return {};
    }
    const char *p{str_};
    std::optional<char> ch;  // initially empty
    for (size_t j{0}; j < bytes_ && *p != '\0'; ++j, ++p) {
      const auto spaceSkipping{*p == ' '};
      if (spaceSkipping) {
        if (j + 1 == bytes_ || p[1] == ' ' || p[1] == '\0') {
          continue;  // redundant; ignore
        }
      }
      if (!ch.has_value() && !(ch = nextChar.Parse(state))) {
        return {};
      }
      if (spaceSkipping) {
        // medial space: 0 or more spaces/tabs accepted, none required
        // TODO: designate and enforce free-form mandatory white space
        while (*ch == ' ' || *ch == '\t') {
          if (!(ch = nextChar.Parse(state))) {
            return {};
          }
        }
        // ch remains full for next iteration
      } else if (IsSameApartFromCase(*ch, *p)) {
        ch.reset();
      } else {
        state->PutMessage(at, MessageExpectedText{str_, bytes_});
        return {};
      }
    }
    return spaces.Parse(state);
  }

private:
  const char *const str_;
  const size_t bytes_{std::numeric_limits<size_t>::max()};
};

constexpr TokenStringMatch operator""_tok(const char str[], size_t n) {
  return TokenStringMatch{str, n};
}

template<class PA, std::enable_if_t<std::is_class<PA>::value, int> = 0>
inline constexpr SequenceParser<TokenStringMatch, PA> operator>>(
    const char *str, const PA &p) {
  return SequenceParser<TokenStringMatch, PA>{TokenStringMatch{str}, p};
}

template<class PA, std::enable_if_t<std::is_class<PA>::value, int> = 0>
inline constexpr InvertedSequenceParser<PA, TokenStringMatch> operator/(
    const PA &p, const char *str) {
  return InvertedSequenceParser<PA, TokenStringMatch>{p, TokenStringMatch{str}};
}

template<class PA>
inline constexpr SequenceParser<TokenStringMatch,
    InvertedSequenceParser<PA, TokenStringMatch>>
parenthesized(const PA &p) {
  return "(" >> p / ")";
}

template<class PA>
inline constexpr SequenceParser<TokenStringMatch,
    InvertedSequenceParser<PA, TokenStringMatch>>
bracketed(const PA &p) {
  return "[" >> p / "]";
}

// Quoted character literal constants.
struct CharLiteralChar {
  struct Result {
    Result(char c, bool esc) : ch{c}, wasEscaped{esc} {}
    static Result Bare(char c) { return Result{c, false}; }
    static Result Escaped(char c) { return Result{c, true}; }
    char ch;
    bool wasEscaped;
  };
  using resultType = Result;
  static std::optional<Result> Parse(ParseState *state) {
    auto at = state->GetLocation();
    std::optional<char> och{nextChar.Parse(state)};
    if (!och.has_value()) {
      return {};
    }
    char ch{*och};
    if (ch == '\n') {
      state->PutMessage(at, "unclosed character constant"_en_US);
      return {};
    }
    if (ch != '\\') {
      return {Result::Bare(ch)};
    }
    if (!(och = nextChar.Parse(state)).has_value()) {
      return {};
    }
    ch = *och;
    if (ch == '\n') {
      state->PutMessage(at, "unclosed character constant"_en_US);
      return {};
    }
    if (std::optional<char> escChar{BackslashEscapeValue(ch)}) {
      return {Result::Escaped(*escChar)};
    }
    if (IsOctalDigit(ch)) {
      ch -= '0';
      for (int j = (ch > 3 ? 1 : 2); j-- > 0;) {
        static constexpr auto octalDigit = attempt(CharPredicateGuardParser{
            IsOctalDigit, "expected octal digit"_en_US});
        if ((och = octalDigit.Parse(state)).has_value()) {
          ch = 8 * ch + *och - '0';
        }
      }
    } else if (ch == 'x' || ch == 'X') {
      ch = 0;
      for (int j = 0; j++ < 2;) {
        static constexpr auto hexDigit = attempt(CharPredicateGuardParser{
            IsHexadecimalDigit, "expected hexadecimal digit"_en_US});
        if ((och = hexDigit.Parse(state)).has_value()) {
          ch = 16 * ch + HexadecimalDigitValue(*och);
        }
      }
    } else {
      state->PutMessage(at, "bad escaped character"_en_US);
    }
    return {Result::Escaped(ch)};
  }
};

template<char quote> struct CharLiteral {
  using resultType = std::string;
  static std::optional<std::string> Parse(ParseState *state) {
    std::string str;
    static constexpr auto nextch = attempt(CharLiteralChar{});
    while (std::optional<CharLiteralChar::Result> ch{nextch.Parse(state)}) {
      if (ch->ch == quote && !ch->wasEscaped) {
        static constexpr auto doubled = attempt(CharMatch<quote>{});
        if (!doubled.Parse(state).has_value()) {
          return {str};
        }
      }
      str += ch->ch;
    }
    return {};
  }
};

// Parse "BOZ" binary literal quoted constants.
// As extensions, support X as an alternate hexadecimal marker, and allow
// BOZX markers to appear as synonyms.
struct BOZLiteral {
  using resultType = std::uint64_t;
  static std::optional<std::uint64_t> Parse(ParseState *state) {
    std::optional<int> shift;
    auto baseChar = [&shift](char ch) -> bool {
      switch (toupper(ch)) {
      case 'B': shift = 1; return true;
      case 'O': shift = 3; return true;
      case 'Z': shift = 4; return true;
      case 'X': shift = 4; return true;
      default: return false;
      }
    };

    if (!spaces.Parse(state)) {
      return {};
    }

    auto ch = nextChar.Parse(state);
    if (!ch) {
      return {};
    }
    if (toupper(*ch) == 'X' && state->strictConformance()) {
      return {};
    }
    if (baseChar(*ch) && !(ch = nextChar.Parse(state))) {
      return {};
    }

    char quote = *ch;
    if (quote != '\'' && quote != '"') {
      return {};
    }

    auto at = state->GetLocation();
    std::string content;
    while (true) {
      if (!(ch = nextChar.Parse(state))) {
        return {};
      }
      if (*ch == quote) {
        break;
      }
      if (!IsHexadecimalDigit(*ch)) {
        return {};
      }
      content += *ch;
    }

    if (!shift && !state->strictConformance()) {
      // extension: base allowed to appear as suffix
      if (!(ch = nextChar.Parse(state)) || !baseChar(*ch)) {
        return {};
      }
    }

    if (content.empty()) {
      state->PutMessage(at, "no digit in BOZ literal"_en_US);
      return {};
    }

    std::uint64_t value{0};
    for (auto digit : content) {
      digit = HexadecimalDigitValue(digit);
      if ((digit >> *shift) > 0) {
        state->PutMessage(at, "bad digit in BOZ literal"_en_US);
        return {};
      }
      std::uint64_t was{value};
      value <<= *shift;
      if ((value >> *shift) != was) {
        state->PutMessage(at, "excessive digits in BOZ literal"_en_US);
        return {};
      }
      value |= digit;
    }
    return {value};
  }
};

// Unsigned decimal digit string; no space skipping
struct DigitString {
  using resultType = std::uint64_t;
  static std::optional<std::uint64_t> Parse(ParseState *state) {
    static constexpr auto getDigit = attempt(digit);
    auto at = state->GetLocation();
    std::optional<char> firstDigit{getDigit.Parse(state)};
    if (!firstDigit) {
      return {};
    }
    std::uint64_t value = *firstDigit - '0';
    bool overflow{false};
    while (auto nextDigit{getDigit.Parse(state)}) {
      if (value > std::numeric_limits<std::uint64_t>::max() / 10) {
        overflow = true;
      }
      value *= 10;
      int digitValue = *nextDigit - '0';
      if (value > std::numeric_limits<std::uint64_t>::max() - digitValue) {
        overflow = true;
      }
      value += digitValue;
    }
    if (overflow) {
      state->PutMessage(at, "overflow in decimal literal"_en_US);
    }
    return {value};
  }
};

// Legacy feature: Hollerith literal constants
struct HollerithLiteral {
  using resultType = std::string;
  static std::optional<std::string> Parse(ParseState *state) {
    if (!spaces.Parse(state)) {
      return {};
    }
    auto at = state->GetLocation();
    std::optional<std::uint64_t> charCount{DigitString{}.Parse(state)};
    if (!charCount || *charCount < 1) {
      return {};
    }
    std::optional<char> h{letter.Parse(state)};
    if (!h || (*h != 'h' && *h != 'H')) {
      return {};
    }
    std::string content;
    for (auto j = *charCount; j-- > 0;) {
      std::optional<char> ch{nextChar.Parse(state)};
      if (!ch || !isprint(*ch)) {
        state->PutMessage(
            at, "insufficient or bad characters in Hollerith"_en_US);
        return {};
      }
      content += *ch;
    }
    return {content};
  }
};

struct ConsumedAllInputParser {
  using resultType = Success;
  constexpr ConsumedAllInputParser() {}
  static std::optional<Success> Parse(ParseState *state) {
    if (state->IsAtEnd()) {
      return {Success{}};
    }
    return {};
  }
} consumedAllInput;

template<char goal> struct SkipPast {
  using resultType = Success;
  constexpr SkipPast() {}
  constexpr SkipPast(const SkipPast &) {}
  static std::optional<Success> Parse(ParseState *state) {
    while (std::optional<char> ch{state->GetNextChar()}) {
      if (*ch == goal) {
        return {Success{}};
      }
    }
    return {};
  }
};

// A common idiom in the Fortran grammar is an optional item (usually
// a nonempty comma-separated list) that, if present, must follow a comma
// and precede a doubled colon.  When the item is absent, the comma must
// not appear, and the doubled colons are optional.
//   [[, xyz] ::]     is  optionalBeforeColons(xyz)
//   [[, xyz]... ::]  is  optionalBeforeColons(nonemptyList(xyz))
template<typename PA> inline constexpr auto optionalBeforeColons(const PA &p) {
  return "," >> p / "::" || "::" >> construct<typename PA::resultType>{} ||
      !","_tok >> construct<typename PA::resultType>{};
}
}  // namespace parser
}  // namespace Fortran
#endif  // FORTRAN_PARSER_TOKEN_PARSERS_H_