ladybird/Libraries/LibJS/Lexer.cpp

/*
 * Copyright (c) 2020, Stephan Unverwerth <s.unverwerth@gmx.de>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice, this
 *    list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "Lexer.h"
#include <AK/HashMap.h>
#include <AK/StringBuilder.h>
#include <ctype.h>
#include <stdio.h>

namespace JS {

HashMap<String, TokenType> Lexer::s_keywords;
HashMap<String, TokenType> Lexer::s_three_char_tokens;
HashMap<String, TokenType> Lexer::s_two_char_tokens;
HashMap<char, TokenType> Lexer::s_single_char_tokens;

Lexer::Lexer(StringView source)
    : m_source(source)
    , m_current_token(TokenType::Eof, StringView(nullptr), StringView(nullptr))
{
    if (s_keywords.is_empty()) {
        s_keywords.set("await", TokenType::Await);
        s_keywords.set("catch", TokenType::Catch);
        s_keywords.set("class", TokenType::Class);
        s_keywords.set("const", TokenType::Const);
        s_keywords.set("delete", TokenType::Delete);
        s_keywords.set("do", TokenType::Do);
        s_keywords.set("else", TokenType::Else);
        s_keywords.set("false", TokenType::BoolLiteral);
        s_keywords.set("finally", TokenType::Finally);
        s_keywords.set("for", TokenType::For);
        s_keywords.set("function", TokenType::Function);
        s_keywords.set("if", TokenType::If);
        s_keywords.set("in", TokenType::In);
        s_keywords.set("instanceof", TokenType::Instanceof);
        s_keywords.set("interface", TokenType::Interface);
        s_keywords.set("let", TokenType::Let);
        s_keywords.set("new", TokenType::New);
        s_keywords.set("null", TokenType::NullLiteral);
        s_keywords.set("return", TokenType::Return);
        s_keywords.set("true", TokenType::BoolLiteral);
        s_keywords.set("try", TokenType::Try);
        s_keywords.set("typeof", TokenType::Typeof);
        s_keywords.set("var", TokenType::Var);
        s_keywords.set("void", TokenType::Void);
        s_keywords.set("while", TokenType::While);
        s_keywords.set("yield", TokenType::Yield);
    }

    if (s_three_char_tokens.is_empty()) {
        s_three_char_tokens.set("===", TokenType::EqualsEqualsEquals);
        s_three_char_tokens.set("!==", TokenType::ExclamationMarkEqualsEquals);
        s_three_char_tokens.set("**=", TokenType::AsteriskAsteriskEquals);
        s_three_char_tokens.set("<<=", TokenType::ShiftLeftEquals);
        s_three_char_tokens.set(">>=", TokenType::ShiftRightEquals);
        s_three_char_tokens.set(">>>", TokenType::UnsignedShiftRight);
    }

    if (s_two_char_tokens.is_empty()) {
        s_two_char_tokens.set("+=", TokenType::PlusEquals);
        s_two_char_tokens.set("-=", TokenType::MinusEquals);
        s_two_char_tokens.set("*=", TokenType::AsteriskEquals);
        s_two_char_tokens.set("/=", TokenType::SlashEquals);
        s_two_char_tokens.set("%=", TokenType::PercentEquals);
        s_two_char_tokens.set("&=", TokenType::AmpersandEquals);
        s_two_char_tokens.set("|=", TokenType::PipeEquals);
        s_two_char_tokens.set("&&", TokenType::DoubleAmpersand);
        s_two_char_tokens.set("||", TokenType::DoublePipe);
        s_two_char_tokens.set("??", TokenType::DoubleQuestionMark);
        s_two_char_tokens.set("**", TokenType::DoubleAsterisk);
        s_two_char_tokens.set("==", TokenType::EqualsEquals);
        s_two_char_tokens.set("!=", TokenType::ExclamationMarkEquals);
        s_two_char_tokens.set("--", TokenType::MinusMinus);
        s_two_char_tokens.set("++", TokenType::PlusPlus);
        s_two_char_tokens.set("<<", TokenType::ShiftLeft);
        s_two_char_tokens.set(">>", TokenType::ShiftRight);
        s_two_char_tokens.set("?.", TokenType::QuestionMarkPeriod);
    }

    if (s_single_char_tokens.is_empty()) {
        s_single_char_tokens.set('&', TokenType::Ampersand);
        s_single_char_tokens.set('*', TokenType::Asterisk);
        s_single_char_tokens.set('[', TokenType::BracketOpen);
        s_single_char_tokens.set(']', TokenType::BracketClose);
        s_single_char_tokens.set('^', TokenType::Caret);
        s_single_char_tokens.set(',', TokenType::Comma);
        s_single_char_tokens.set('{', TokenType::CurlyOpen);
        s_single_char_tokens.set('}', TokenType::CurlyClose);
        s_single_char_tokens.set('=', TokenType::Equals);
        s_single_char_tokens.set('!', TokenType::ExclamationMark);
        s_single_char_tokens.set('-', TokenType::Minus);
        s_single_char_tokens.set('(', TokenType::ParenOpen);
        s_single_char_tokens.set(')', TokenType::ParenClose);
        s_single_char_tokens.set('%', TokenType::Percent);
        s_single_char_tokens.set('.', TokenType::Period);
        s_single_char_tokens.set('|', TokenType::Pipe);
        s_single_char_tokens.set('+', TokenType::Plus);
        s_single_char_tokens.set('?', TokenType::QuestionMark);
        s_single_char_tokens.set(';', TokenType::Semicolon);
        s_single_char_tokens.set('/', TokenType::Slash);
        s_single_char_tokens.set('~', TokenType::Tilde);
        s_single_char_tokens.set('<', TokenType::LessThan);
        s_single_char_tokens.set('>', TokenType::GreaterThan);
    }
    consume();
}

void Lexer::consume()
{
    if (m_position >= m_source.length()) {
        m_position = m_source.length() + 1;
        m_current_char = EOF;
        return;
    }

    m_current_char = m_source[m_position++];
}

bool Lexer::is_eof() const
{
    return m_current_char == EOF;
}

bool Lexer::is_identifier_start() const
{
    return isalpha(m_current_char) || m_current_char == '_' || m_current_char == '$';
}

bool Lexer::is_identifier_middle() const
{
    return is_identifier_start() || isdigit(m_current_char);
}

bool Lexer::is_line_comment_start() const
{
    return m_current_char == '/' && m_position < m_source.length() && m_source[m_position] == '/';
}

bool Lexer::is_block_comment_start() const
{
    return m_current_char == '/' && m_position < m_source.length() && m_source[m_position] == '*';
}

bool Lexer::is_block_comment_end() const
{
    return m_current_char == '*' && m_position < m_source.length() && m_source[m_position] == '/';
}

void Lexer::syntax_error(const char* msg)
{
    m_has_errors = true;
    fprintf(stderr, "Syntax Error: %s\n", msg);
}

Token Lexer::next()
{
    size_t trivia_start = m_position;

    // consume whitespace and comments
    while (true) {
        if (isspace(m_current_char)) {
            do {
                consume();
            } while (isspace(m_current_char));
        } else if (is_line_comment_start()) {
            consume();
            do {
                consume();
            } while (!is_eof() && m_current_char != '\n');
        } else if (is_block_comment_start()) {
            consume();
            do {
                consume();
            } while (!is_eof() && !is_block_comment_end());
            consume(); // consume *
            consume(); // consume /
        } else {
            break;
        }
    }

    size_t value_start = m_position;
    auto token_type = TokenType::Invalid;

    if (is_identifier_start()) {
        // identifier or keyword
        do {
            consume();
        } while (is_identifier_middle());

        StringView value = m_source.substring_view(value_start - 1, m_position - value_start);
        auto it = s_keywords.find(value);
        if (it == s_keywords.end()) {
            token_type = TokenType::Identifier;
        } else {
            token_type = it->value;
        }
    } else if (isdigit(m_current_char)) {
        consume();
        while (isdigit(m_current_char)) {
            consume();
        }
        token_type = TokenType::NumericLiteral;
    } else if (m_current_char == '"' || m_current_char == '\'') {
        char stop_char = m_current_char;
        consume();
        while (m_current_char != stop_char && m_current_char != '\n' && !is_eof()) {
            if (m_current_char == '\\') {
                consume();
            }
            consume();
        }
        if (m_current_char != stop_char) {
            syntax_error("unterminated string literal");
            token_type = TokenType::UnterminatedStringLiteral;
        } else {
            consume();
            token_type = TokenType::StringLiteral;
        }
    } else if (m_current_char == EOF) {
        token_type = TokenType::Eof;
    } else {
        // There is only one four-char operator: >>>=
        bool found_four_char_token = false;
        if (m_position + 2 < m_source.length()) {
            if (m_current_char == '>'
                && m_source[m_position] == '>'
                && m_source[m_position + 1] == '>'
                && m_source[m_position + 2] == '=') {

                found_four_char_token = true;
                consume();
                consume();
                consume();
                consume();
                token_type = TokenType::UnsignedShiftRightEquals;
            }
        }

        bool found_three_char_token = false;
        if (!found_four_char_token && m_position + 1 < m_source.length()) {
            char second_char = m_source[m_position];
            char third_char = m_source[m_position + 1];
            char three_chars[] { (char)m_current_char, second_char, third_char, 0 };
            auto it = s_three_char_tokens.find(three_chars);
            if (it != s_three_char_tokens.end()) {
                found_three_char_token = true;
                consume();
                consume();
                consume();
                token_type = it->value;
            }
        }

        bool found_two_char_token = false;
        if (!found_four_char_token && !found_three_char_token && m_position < m_source.length()) {
            char second_char = m_source[m_position];
            char two_chars[] { (char)m_current_char, second_char, 0 };
            auto it = s_two_char_tokens.find(two_chars);
            if (it != s_two_char_tokens.end()) {
                found_two_char_token = true;
                consume();
                consume();
                token_type = it->value;
            }
        }

        bool found_one_char_token = false;
        if (!found_four_char_token && !found_three_char_token && !found_two_char_token) {
            auto it = s_single_char_tokens.find(m_current_char);
            if (it != s_single_char_tokens.end()) {
                found_one_char_token = true;
                consume();
                token_type = it->value;
            }
        }

        if (!found_four_char_token && !found_three_char_token && !found_two_char_token && !found_one_char_token) {
            consume();
            token_type = TokenType::Invalid;
        }
    }

    m_current_token = Token(
        token_type,
        m_source.substring_view(trivia_start - 1, value_start - trivia_start),
        m_source.substring_view(value_start - 1, m_position - value_start));

    return m_current_token;
}

}