token.hpp

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// Copyright (C) 2020-2024 Jonathan Müller and lexy contributors
// SPDX-License-Identifier: BSL-1.0
 
#ifndef LEXY_TOKEN_HPP_INCLUDED
#define LEXY_TOKEN_HPP_INCLUDED
 
#include <climits>
#include <cstdint>
#include <lexy/_detail/assert.hpp>
#include <lexy/_detail/config.hpp>
#include <lexy/_detail/detect.hpp>
#include <lexy/_detail/integer_sequence.hpp>
#include <lexy/grammar.hpp>
#include <lexy/lexeme.hpp>
 
namespace lexy
{
template <typename TokenKind, typename... Tokens>
struct _tk_map
{
    TokenKind _data[sizeof...(Tokens)];
 
    template <std::size_t... Idx>
    LEXY_CONSTEVAL explicit _tk_map(lexy::_detail::index_sequence<Idx...>, const TokenKind* data,
                                    TokenKind new_kind)
    // Add new kind at the end.
    : _data{data[Idx]..., new_kind}
    {}
 
    template <TokenKind Kind, typename Token>
    LEXY_CONSTEVAL auto map(Token) const
    {
        static_assert(lexy::is_token_rule<Token>, "cannot map non-token to token kind");
        return _tk_map<TokenKind, Tokens..., Token>(lexy::_detail::index_sequence_for<Tokens...>{},
                                                    _data, Kind);
    }
 
    template <typename Token>
    LEXY_CONSTEVAL auto lookup(Token) const
    {
        constexpr auto idx = [] {
            // There is an easier way to do it via fold expressions but clang 6 generates a bogus
            // warning about sequence points.
            // As such, we do the less fancy version of looking for the index in an array.
            bool is_same[]
                = {std::is_same_v<typename Token::token_type, typename Tokens::token_type>...};
 
            for (std::size_t idx = 0; idx != sizeof...(Tokens); ++idx)
                if (is_same[idx])
                    return idx;
 
            return sizeof...(Tokens);
        }();
        if constexpr (idx == sizeof...(Tokens))
            return unknown_token_kind;
        else
            return _data[idx];
    }
};
 
struct _tk_map_empty
{
    template <typename Token>
    static LEXY_CONSTEVAL auto lookup(Token)
    {
        return unknown_token_kind;
    }
 
    template <auto TokenKind, typename Token>
    LEXY_CONSTEVAL auto map(Token) const
    {
        static_assert(lexy::is_token_rule<Token>, "cannot map non-token to token kind");
        return _tk_map<LEXY_DECAY_DECLTYPE(TokenKind), Token>(lexy::_detail::index_sequence_for<>{},
                                                              nullptr, TokenKind);
    }
};
 
inline constexpr auto token_kind_map = _tk_map_empty{};
 
template <typename TokenKind>
constexpr auto token_kind_map_for = token_kind_map;
 
// Prevent user-defined specialization for void.
template <>
inline constexpr auto token_kind_map_for<void> = token_kind_map;
} // namespace lexy
 
namespace lexy
{
template <typename TokenRule>
constexpr auto _has_special_token_kind = [] {
    using kind = LEXY_DECAY_DECLTYPE(lexy::token_kind_of<TokenRule>);
    return !std::is_same_v<kind, lexy::predefined_token_kind> && std::is_enum_v<kind>;
}();
 
template <typename TokenKind = void>
class token_kind
{
    static_assert(std::is_void_v<TokenKind> || std::is_enum_v<TokenKind>,
                  "invalid type for TokenKind");
    using _underlying_type = lexy::_detail::type_or<TokenKind, int>;
 
    template <typename T>
    static constexpr bool _is_compatible_kind_type()
    {
        using type = std::remove_cv_t<T>;
        if constexpr (std::is_same_v<type, lexy::predefined_token_kind>)
            // Always compatible.
            return true;
        else if constexpr (std::is_void_v<TokenKind>)
            // We neeed an integer for our token kind.
            return std::is_integral_v<T>;
        else
            // We need the same enumeration type.
            return std::is_same_v<type, TokenKind>;
    }
 
public:
    //=== constructors ===//
    constexpr token_kind() noexcept : token_kind(unknown_token_kind) {}
 
    constexpr token_kind(predefined_token_kind value) noexcept : _value(value) {}
 
    constexpr token_kind(_underlying_type value) noexcept
    : _value(static_cast<std::uint_least16_t>(value))
    {
        LEXY_PRECONDITION(_underlying_type(0) <= value
                          && value < _underlying_type(_smallest_predefined_token_kind));
    }
 
    template <typename TokenRule, typename = std::enable_if_t<lexy::is_token_rule<TokenRule>>>
    constexpr token_kind(TokenRule) noexcept
    // We initialize it according to the external mapping.
    : token_kind(token_kind_map_for<TokenKind>.lookup(TokenRule{}))
    {
        // If unknown, override it by internal mapping.
        if (!*this)
        {
            constexpr auto token_rule_kind = lexy::token_kind_of<TokenRule>;
            if constexpr (_is_compatible_kind_type<decltype(token_rule_kind)>())
            {
                // The token has an associated kind of the same type.
                *this = token_kind(token_rule_kind);
            }
        }
    }
 
    //=== access ===//
    constexpr explicit operator bool() const noexcept
    {
        return _value != unknown_token_kind;
    }
 
    constexpr bool is_predefined() const noexcept
    {
        return _value >= _smallest_predefined_token_kind;
    }
 
    constexpr bool ignore_if_empty() const noexcept
    {
        return _value == unknown_token_kind || _value == error_token_kind
               || _value == whitespace_token_kind;
    }
 
    constexpr const char* name() const noexcept
    {
        if (is_predefined())
            return token_kind_name(static_cast<predefined_token_kind>(_value));
        else
            return token_kind_name(get()); // ADL
    }
    friend constexpr const char* token_kind_name(token_kind kind) noexcept
    {
        return kind.name();
    }
 
    constexpr _underlying_type get() const noexcept
    {
        return static_cast<_underlying_type>(_value);
    }
 
    //=== comparision ===//
    friend constexpr bool operator==(token_kind lhs, token_kind rhs) noexcept
    {
        return lhs._value == rhs._value;
    }
    friend constexpr bool operator!=(token_kind lhs, token_kind rhs) noexcept
    {
        return lhs._value != rhs._value;
    }
 
    //=== raw access ===//
    static constexpr std::uint_least16_t to_raw(token_kind<TokenKind> kind) noexcept
    {
        return kind._value;
    }
    static constexpr token_kind<TokenKind> from_raw(std::uint_least16_t kind) noexcept
    {
        return token_kind<TokenKind>(kind);
    }
 
private:
    constexpr explicit token_kind(std::uint_least16_t kind) noexcept : _value(kind) {}
 
    std::uint_least16_t _value;
};
 
template <typename TokenKind, typename = std::enable_if_t<std::is_integral_v<TokenKind>>>
token_kind(TokenKind) -> token_kind<void>;
template <typename TokenKind, typename = std::enable_if_t<std::is_enum_v<TokenKind>>>
token_kind(TokenKind) -> token_kind<TokenKind>;
template <typename TokenRule, typename = std::enable_if_t<_has_special_token_kind<TokenRule>>>
token_kind(TokenRule) -> token_kind<LEXY_DECAY_DECLTYPE(lexy::token_kind_of<TokenRule>)>;
} // namespace lexy
 
namespace lexy
{
template <typename Reader, typename TokenKind = void>
class token
{
public:
    using encoding  = typename Reader::encoding;
    using char_type = typename encoding::char_type;
    using iterator  = typename Reader::iterator;
 
    explicit constexpr token(token_kind<TokenKind> kind, lexy::lexeme<Reader> lex) noexcept
    : _lexeme(lex), _kind(kind)
    {
        LEXY_PRECONDITION(lex.begin() != iterator());
    }
    explicit constexpr token(token_kind<TokenKind> kind, iterator begin, iterator end) noexcept
    : token(kind, lexy::lexeme<Reader>(begin, end))
    {}
 
    constexpr token_kind<TokenKind> kind() const noexcept
    {
        return _kind;
    }
 
    constexpr const char* name() const noexcept
    {
        return _kind.name();
    }
 
    constexpr iterator position() const noexcept
    {
        return _lexeme.begin();
    }
 
    constexpr auto lexeme() const noexcept
    {
        return _lexeme;
    }
 
private:
    lexy::lexeme<Reader>  _lexeme;
    token_kind<TokenKind> _kind;
};
 
template <typename TokenKind, typename Reader>
token(token_kind<TokenKind>, lexy::lexeme<Reader>) -> token<Reader, TokenKind>;
template <typename TokenKind, typename Reader,
          typename = std::enable_if_t<std::is_integral_v<TokenKind>>>
token(TokenKind, lexy::lexeme<Reader>) -> token<Reader, void>;
template <typename TokenKind, typename Reader,
          typename = std::enable_if_t<std::is_enum_v<TokenKind>>>
token(TokenKind, lexy::lexeme<Reader>) -> token<Reader, TokenKind>;
template <typename TokenRule, typename Reader,
          typename = std::enable_if_t<_has_special_token_kind<TokenRule>>>
token(TokenRule, lexy::lexeme<Reader>)
    -> token<Reader, LEXY_DECAY_DECLTYPE(lexy::token_kind_of<TokenRule>)>;
 
template <typename Input, typename TokenKind = void>
using token_for = token<lexy::input_reader<Input>, TokenKind>;
} // namespace lexy
 
#endif // LEXY_TOKEN_HPP_INCLUDED