path: root/libsolidity/parsing/Scanner.cpp

/*
    This file is part of solidity.

    solidity is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    solidity is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with solidity.  If not, see <http://www.gnu.org/licenses/>.

    This file is derived from the file "scanner.cc", which was part of the
    V8 project. The original copyright header follows:

    Copyright 2006-2012, the V8 project authors. All rights reserved.
    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions are
    met:

    * Redistributions of source code must retain the above copyright
      notice, this list of conditions and the following disclaimer.
    * 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.
    * Neither the name of Google Inc. nor the names of its
      contributors may be used to endorse or promote products derived
      from this software without specific prior written permission.

    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
    OWNER 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.
*/
/**
 * @author Christian <c@ethdev.com>
 * @date 2014
 * Solidity scanner.
 */

#include <algorithm>
#include <tuple>
#include <libsolidity/interface/Exceptions.h>
#include <libsolidity/parsing/Scanner.h>

using namespace std;

namespace dev
{
namespace solidity
{

namespace
{
bool isDecimalDigit(char c)
{
    return '0' <= c && c <= '9';
}
bool isHexDigit(char c)
{
    return isDecimalDigit(c)
           || ('a' <= c && c <= 'f')
           || ('A' <= c && c <= 'F');
}
bool isLineTerminator(char c)
{
    return c == '\n';
}
bool isWhiteSpace(char c)
{
    return c == ' ' || c == '\n' || c == '\t' || c == '\r';
}
bool isIdentifierStart(char c)
{
    return c == '_' || c == '$' || ('a' <= c && c <= 'z') || ('A' <= c && c <= 'Z');
}
bool isIdentifierPart(char c)
{
    return isIdentifierStart(c) || isDecimalDigit(c);
}
int hexValue(char c)
{
    if (c >= '0' && c <= '9')
        return c - '0';
    else if (c >= 'a' && c <= 'f')
        return c - 'a' + 10;
    else if (c >= 'A' && c <= 'F')
        return c - 'A' + 10;
    else return -1;
}
} // end anonymous namespace



/// Scoped helper for literal recording. Automatically drops the literal
/// if aborting the scanning before it's complete.
enum LiteralType {
    LITERAL_TYPE_STRING,
    LITERAL_TYPE_NUMBER, // not really different from string type in behaviour
    LITERAL_TYPE_COMMENT
};

class LiteralScope
{
public:
    explicit LiteralScope(Scanner* _self, enum LiteralType _type): m_type(_type)
    , m_scanner(_self)
    , m_complete(false)
    {
        if (_type == LITERAL_TYPE_COMMENT)
            m_scanner->m_nextSkippedComment.literal.clear();
        else
            m_scanner->m_nextToken.literal.clear();
    }
    ~LiteralScope()
    {
        if (!m_complete)
        {
            if (m_type == LITERAL_TYPE_COMMENT)
                m_scanner->m_nextSkippedComment.literal.clear();
            else
                m_scanner->m_nextToken.literal.clear();
        }
    }
    void complete() { m_complete = true; }

private:
    enum LiteralType m_type;
    Scanner* m_scanner;
    bool m_complete;
}; // end of LiteralScope class


void Scanner::reset(CharStream const& _source, string const& _sourceName)
{
    m_source = _source;
    m_sourceName = make_shared<string const>(_sourceName);
    reset();
}

void Scanner::reset()
{
    m_source.reset();
    m_char = m_source.get();
    skipWhitespace();
    scanToken();
    next();
}

bool Scanner::scanHexByte(char& o_scannedByte)
{
    char x = 0;
    for (int i = 0; i < 2; i++)
    {
        int d = hexValue(m_char);
        if (d < 0)
        {
            rollback(i);
            return false;
        }
        x = x * 16 + d;
        advance();
    }
    o_scannedByte = x;
    return true;
}

bool Scanner::scanUnicode(unsigned & o_codepoint)
{
    unsigned x = 0;
    for (int i = 0; i < 4; i++)
    {
        int d = hexValue(m_char);
        if (d < 0)
        {
            rollback(i);
            return false;
        }
        x = x * 16 + d;
        advance();
    }
    o_codepoint = x;
    return true;
}

// This supports codepoints between 0000 and FFFF.
void Scanner::addUnicodeAsUTF8(unsigned codepoint)
{
    if (codepoint <= 0x7f)
        addLiteralChar(codepoint);
    else if (codepoint <= 0x7ff)
    {
        addLiteralChar(0xc0 | (codepoint >> 6));
        addLiteralChar(0x80 | (codepoint & 0x3f));
    }
    else
    {
        addLiteralChar(0xe0 | (codepoint >> 12));
        addLiteralChar(0x80 | ((codepoint >> 6) & 0x3f));
        addLiteralChar(0x80 | (codepoint & 0x3f));
    }
}

// Ensure that tokens can be stored in a byte.
BOOST_STATIC_ASSERT(TokenTraits::count() <= 0x100);

Token Scanner::next()
{
    m_currentToken = m_nextToken;
    m_skippedComment = m_nextSkippedComment;
    scanToken();

    return m_currentToken.token;
}

Token Scanner::selectToken(char _next, Token _then, Token _else)
{
    advance();
    if (m_char == _next)
        return selectToken(_then);
    else
        return _else;
}

bool Scanner::skipWhitespace()
{
    int const startPosition = sourcePos();
    while (isWhiteSpace(m_char))
        advance();
    // Return whether or not we skipped any characters.
    return sourcePos() != startPosition;
}

void Scanner::skipWhitespaceExceptUnicodeLinebreak()
{
    while (isWhiteSpace(m_char) && !isUnicodeLinebreak())
        advance();
}

Token Scanner::skipSingleLineComment()
{
    // Line terminator is not part of the comment. If it is a
    // non-ascii line terminator, it will result in a parser error.
    while (!isUnicodeLinebreak())
        if (!advance()) break;

    return Token::Whitespace;
}

Token Scanner::scanSingleLineDocComment()
{
    LiteralScope literal(this, LITERAL_TYPE_COMMENT);
    advance(); //consume the last '/' at ///

    skipWhitespaceExceptUnicodeLinebreak();

    while (!isSourcePastEndOfInput())
    {
        if (isLineTerminator(m_char))
        {
            // check if next line is also a documentation comment
            skipWhitespace();
            if (!m_source.isPastEndOfInput(3) &&
                m_source.get(0) == '/' &&
                m_source.get(1) == '/' &&
                m_source.get(2) == '/')
            {
                addCommentLiteralChar('\n');
                m_char = m_source.advanceAndGet(3);
            }
            else
                break; // next line is not a documentation comment, we are done

        }
        else if (isUnicodeLinebreak())
            // Any line terminator that is not '\n' is considered to end the
            // comment.
            break;
        addCommentLiteralChar(m_char);
        advance();
    }
    literal.complete();
    return Token::CommentLiteral;
}

Token Scanner::skipMultiLineComment()
{
    advance();
    while (!isSourcePastEndOfInput())
    {
        char ch = m_char;
        advance();

        // If we have reached the end of the multi-line comment, we
        // consume the '/' and insert a whitespace. This way all
        // multi-line comments are treated as whitespace.
        if (ch == '*' && m_char == '/')
        {
            m_char = ' ';
            return Token::Whitespace;
        }
    }
    // Unterminated multi-line comment.
    return Token::Illegal;
}

Token Scanner::scanMultiLineDocComment()
{
    LiteralScope literal(this, LITERAL_TYPE_COMMENT);
    bool endFound = false;
    bool charsAdded = false;

    while (isWhiteSpace(m_char) && !isLineTerminator(m_char))
        advance();

    while (!isSourcePastEndOfInput())
    {
        //handle newlines in multline comments
        if (isLineTerminator(m_char))
        {
            skipWhitespace();
            if (!m_source.isPastEndOfInput(1) && m_source.get(0) == '*' && m_source.get(1) == '*')
            { // it is unknown if this leads to the end of the comment
                addCommentLiteralChar('*');
                advance();
            }
            else if (!m_source.isPastEndOfInput(1) && m_source.get(0) == '*' && m_source.get(1) != '/')
            { // skip first '*' in subsequent lines
                if (charsAdded)
                    addCommentLiteralChar('\n');
                m_char = m_source.advanceAndGet(2);
            }
            else if (!m_source.isPastEndOfInput(1) && m_source.get(0) == '*' && m_source.get(1) == '/')
            { // if after newline the comment ends, don't insert the newline
                m_char = m_source.advanceAndGet(2);
                endFound = true;
                break;
            }
            else if (charsAdded)
                addCommentLiteralChar('\n');
        }

        if (!m_source.isPastEndOfInput(1) && m_source.get(0) == '*' && m_source.get(1) == '/')
        {
            m_char = m_source.advanceAndGet(2);
            endFound = true;
            break;
        }
        addCommentLiteralChar(m_char);
        charsAdded = true;
        advance();
    }
    literal.complete();
    if (!endFound)
        return Token::Illegal;
    else
        return Token::CommentLiteral;
}

Token Scanner::scanSlash()
{
    int firstSlashPosition = sourcePos();
    advance();
    if (m_char == '/')
    {
        if (!advance()) /* double slash comment directly before EOS */
            return Token::Whitespace;
        else if (m_char == '/')
        {
            // doxygen style /// comment
            Token comment;
            m_nextSkippedComment.location.start = firstSlashPosition;
            comment = scanSingleLineDocComment();
            m_nextSkippedComment.location.end = sourcePos();
            m_nextSkippedComment.token = comment;
            return Token::Whitespace;
        }
        else
            return skipSingleLineComment();
    }
    else if (m_char == '*')
    {
        // doxygen style /** natspec comment
        if (!advance()) /* slash star comment before EOS */
            return Token::Illegal;
        else if (m_char == '*')
        {
            advance(); //consume the last '*' at /**

            // "/**/"
            if (m_char == '/')
            {
                advance(); //skip the closing slash
                return Token::Whitespace;
            }
            // we actually have a multiline documentation comment
            Token comment;
            m_nextSkippedComment.location.start = firstSlashPosition;
            comment = scanMultiLineDocComment();
            m_nextSkippedComment.location.end = sourcePos();
            m_nextSkippedComment.token = comment;
            if (comment == Token::Illegal)
                return Token::Illegal;
            else
                return Token::Whitespace;
        }
        else
            return skipMultiLineComment();
    }
    else if (m_char == '=')
        return selectToken(Token::AssignDiv);
    else
        return Token::Div;
}

void Scanner::scanToken()
{
    m_nextToken.literal.clear();
    m_nextToken.extendedTokenInfo = make_tuple(0, 0);
    m_nextSkippedComment.literal.clear();
    m_nextSkippedComment.extendedTokenInfo = make_tuple(0, 0);

    Token token;
    // M and N are for the purposes of grabbing different type sizes
    unsigned m;
    unsigned n;
    do
    {
        // Remember the position of the next token
        m_nextToken.location.start = sourcePos();
        switch (m_char)
        {
        case '"':
        case '\'':
            token = scanString();
            break;
        case '<':
            // < <= << <<=
            advance();
            if (m_char == '=')
                token = selectToken(Token::LessThanOrEqual);
            else if (m_char == '<')
                token = selectToken('=', Token::AssignShl, Token::SHL);
            else
                token = Token::LessThan;
            break;
        case '>':
            // > >= >> >>= >>> >>>=
            advance();
            if (m_char == '=')
                token = selectToken(Token::GreaterThanOrEqual);
            else if (m_char == '>')
            {
                // >> >>= >>> >>>=
                advance();
                if (m_char == '=')
                    token = selectToken(Token::AssignSar);
                else if (m_char == '>')
                    token = selectToken('=', Token::AssignShr, Token::SHR);
                else
                    token = Token::SAR;
            }
            else
                token = Token::GreaterThan;
            break;
        case '=':
            // = == =>
            advance();
            if (m_char == '=')
                token = selectToken(Token::Equal);
            else if (m_char == '>')
                token = selectToken(Token::Arrow);
            else
                token = Token::Assign;
            break;
        case '!':
            // ! !=
            advance();
            if (m_char == '=')
                token = selectToken(Token::NotEqual);
            else
                token = Token::Not;
            break;
        case '+':
            // + ++ +=
            advance();
            if (m_char == '+')
                token = selectToken(Token::Inc);
            else if (m_char == '=')
                token = selectToken(Token::AssignAdd);
            else
                token = Token::Add;
            break;
        case '-':
            // - -- -=
            advance();
            if (m_char == '-')
                token = selectToken(Token::Dec);
            else if (m_char == '=')
                token = selectToken(Token::AssignSub);
            else
                token = Token::Sub;
            break;
        case '*':
            // * ** *=
            advance();
            if (m_char == '*')
                token = selectToken(Token::Exp);
            else if (m_char == '=')
                token = selectToken(Token::AssignMul);
            else
                token = Token::Mul;
            break;
        case '%':
            // % %=
            token = selectToken('=', Token::AssignMod, Token::Mod);
            break;
        case '/':
            // /  // /* /=
            token = scanSlash();
            break;
        case '&':
            // & && &=
            advance();
            if (m_char == '&')
                token = selectToken(Token::And);
            else if (m_char == '=')
                token = selectToken(Token::AssignBitAnd);
            else
                token = Token::BitAnd;
            break;
        case '|':
            // | || |=
            advance();
            if (m_char == '|')
                token = selectToken(Token::Or);
            else if (m_char == '=')
                token = selectToken(Token::AssignBitOr);
            else
                token = Token::BitOr;
            break;
        case '^':
            // ^ ^=
            token = selectToken('=', Token::AssignBitXor, Token::BitXor);
            break;
        case '.':
            // . Number
            advance();
            if (isDecimalDigit(m_char))
                token = scanNumber('.');
            else
                token = Token::Period;
            break;
        case ':':
            token = selectToken(Token::Colon);
            break;
        case ';':
            token = selectToken(Token::Semicolon);
            break;
        case ',':
            token = selectToken(Token::Comma);
            break;
        case '(':
            token = selectToken(Token::LParen);
            break;
        case ')':
            token = selectToken(Token::RParen);
            break;
        case '[':
            token = selectToken(Token::LBrack);
            break;
        case ']':
            token = selectToken(Token::RBrack);
            break;
        case '{':
            token = selectToken(Token::LBrace);
            break;
        case '}':
            token = selectToken(Token::RBrace);
            break;
        case '?':
            token = selectToken(Token::Conditional);
            break;
        case '~':
            token = selectToken(Token::BitNot);
            break;
        default:
            if (isIdentifierStart(m_char))
            {
                tie(token, m, n) = scanIdentifierOrKeyword();

                // Special case for hexadecimal literals
                if (token == Token::Hex)
                {
                    // reset
                    m = 0;
                    n = 0;

                    // Special quoted hex string must follow
                    if (m_char == '"' || m_char == '\'')
                        token = scanHexString();
                    else
                        token = Token::IllegalHex;
                }
            }
            else if (isDecimalDigit(m_char))
                token = scanNumber();
            else if (skipWhitespace())
                token = Token::Whitespace;
            else if (isSourcePastEndOfInput())
                token = Token::EOS;
            else
                token = selectToken(Token::Illegal);
            break;
        }
        // Continue scanning for tokens as long as we're just skipping
        // whitespace.
    }
    while (token == Token::Whitespace);
    m_nextToken.location.end = sourcePos();
    m_nextToken.token = token;
    m_nextToken.extendedTokenInfo = make_tuple(m, n);
}

bool Scanner::scanEscape()
{
    char c = m_char;
    advance();
    // Skip escaped newlines.
    if (isLineTerminator(c))
        return true;
    switch (c)
    {
    case '\'':  // fall through
    case '"':  // fall through
    case '\\':
        break;
    case 'b':
        c = '\b';
        break;
    case 'f':
        c = '\f';
        break;
    case 'n':
        c = '\n';
        break;
    case 'r':
        c = '\r';
        break;
    case 't':
        c = '\t';
        break;
    case 'v':
        c = '\v';
        break;
    case 'u':
    {
        unsigned codepoint;
        if (!scanUnicode(codepoint))
            return false;
        addUnicodeAsUTF8(codepoint);
        return true;
    }
    case 'x':
        if (!scanHexByte(c))
            return false;
        break;
    default:
        return false;
    }

    addLiteralChar(c);
    return true;
}

bool Scanner::isUnicodeLinebreak()
{
    if (0x0a <= m_char && m_char <= 0x0d)
        // line feed, vertical tab, form feed, carriage return
        return true;
    else if (!m_source.isPastEndOfInput(1) && uint8_t(m_source.get(0)) == 0xc2 && uint8_t(m_source.get(1)) == 0x85)
        // NEL - U+0085, C2 85 in utf8
        return true;
    else if (!m_source.isPastEndOfInput(2) && uint8_t(m_source.get(0)) == 0xe2 && uint8_t(m_source.get(1)) == 0x80 && (
        uint8_t(m_source.get(2)) == 0xa8 || uint8_t(m_source.get(2)) == 0xa9
    ))
        // LS - U+2028, E2 80 A8  in utf8
        // PS - U+2029, E2 80 A9  in utf8
        return true;
    else
        return false;
}

Token Scanner::scanString()
{
    char const quote = m_char;
    advance();  // consume quote
    LiteralScope literal(this, LITERAL_TYPE_STRING);
    while (m_char != quote && !isSourcePastEndOfInput() && !isUnicodeLinebreak())
    {
        char c = m_char;
        advance();
        if (c == '\\')
        {
            if (isSourcePastEndOfInput() || !scanEscape())
                return Token::Illegal;
        }
        else
            addLiteralChar(c);
    }
    if (m_char != quote)
        return Token::Illegal;
    literal.complete();
    advance();  // consume quote
    return Token::StringLiteral;
}

Token Scanner::scanHexString()
{
    char const quote = m_char;
    advance();  // consume quote
    LiteralScope literal(this, LITERAL_TYPE_STRING);
    while (m_char != quote && !isSourcePastEndOfInput())
    {
        char c = m_char;
        if (!scanHexByte(c))
            return Token::IllegalHex;
        addLiteralChar(c);
    }
    if (m_char != quote)
        return Token::IllegalHex;
    literal.complete();
    advance();  // consume quote
    return Token::StringLiteral;
}

// Parse for regex [:digit:]+(_[:digit:]+)*
void Scanner::scanDecimalDigits()
{
    // MUST begin with a decimal digit.
    if (!isDecimalDigit(m_char))
        return;

    // May continue with decimal digit or underscore for grouping.
    do addLiteralCharAndAdvance();
    while (!m_source.isPastEndOfInput() && (isDecimalDigit(m_char) || m_char == '_'));

    // Defer further validation of underscore to SyntaxChecker.
}

Token Scanner::scanNumber(char _charSeen)
{
    enum { DECIMAL, HEX, BINARY } kind = DECIMAL;
    LiteralScope literal(this, LITERAL_TYPE_NUMBER);
    if (_charSeen == '.')
    {
        // we have already seen a decimal point of the float
        addLiteralChar('.');
        if (m_char == '_')
            return Token::Illegal;
        scanDecimalDigits();  // we know we have at least one digit
    }
    else
    {
        solAssert(_charSeen == 0, "");
        // if the first character is '0' we must check for octals and hex
        if (m_char == '0')
        {
            addLiteralCharAndAdvance();
            // either 0, 0exxx, 0Exxx, 0.xxx or a hex number
            if (m_char == 'x')
            {
                // hex number
                kind = HEX;
                addLiteralCharAndAdvance();
                if (!isHexDigit(m_char))
                    return Token::Illegal; // we must have at least one hex digit after 'x'

                while (isHexDigit(m_char) || m_char == '_') // We keep the underscores for later validation
                    addLiteralCharAndAdvance();
            }
            else if (isDecimalDigit(m_char))
                // We do not allow octal numbers
                return Token::Illegal;
        }
        // Parse decimal digits and allow trailing fractional part.
        if (kind == DECIMAL)
        {
            scanDecimalDigits();  // optional
            if (m_char == '.')
            {
                if (!m_source.isPastEndOfInput(1) && m_source.get(1) == '_')
                {
                    // Assume the input may be a floating point number with leading '_' in fraction part.
                    // Recover by consuming it all but returning `Illegal` right away.
                    addLiteralCharAndAdvance(); // '.'
                    addLiteralCharAndAdvance(); // '_'
                    scanDecimalDigits();
                }
                if (m_source.isPastEndOfInput() || !isDecimalDigit(m_source.get(1)))
                {
                    // A '.' has to be followed by a number.
                    literal.complete();
                    return Token::Number;
                }
                addLiteralCharAndAdvance();
                scanDecimalDigits();
            }
        }
    }
    // scan exponent, if any
    if (m_char == 'e' || m_char == 'E')
    {
        solAssert(kind != HEX, "'e'/'E' must be scanned as part of the hex number");
        if (kind != DECIMAL)
            return Token::Illegal;
        else if (!m_source.isPastEndOfInput(1) && m_source.get(1) == '_')
        {
            // Recover from wrongly placed underscore as delimiter in literal with scientific
            // notation by consuming until the end.
            addLiteralCharAndAdvance(); // 'e'
            addLiteralCharAndAdvance(); // '_'
            scanDecimalDigits();
            literal.complete();
            return Token::Number;
        }
        // scan exponent
        addLiteralCharAndAdvance(); // 'e' | 'E'
        if (m_char == '+' || m_char == '-')
            addLiteralCharAndAdvance();
        if (!isDecimalDigit(m_char))
            return Token::Illegal; // we must have at least one decimal digit after 'e'/'E'
        scanDecimalDigits();
    }
    // The source character immediately following a numeric literal must
    // not be an identifier start or a decimal digit; see ECMA-262
    // section 7.8.3, page 17 (note that we read only one decimal digit
    // if the value is 0).
    if (isDecimalDigit(m_char) || isIdentifierStart(m_char))
        return Token::Illegal;
    literal.complete();
    return Token::Number;
}

tuple<Token, unsigned, unsigned> Scanner::scanIdentifierOrKeyword()
{
    solAssert(isIdentifierStart(m_char), "");
    LiteralScope literal(this, LITERAL_TYPE_STRING);
    addLiteralCharAndAdvance();
    // Scan the rest of the identifier characters.
    while (isIdentifierPart(m_char)) //get full literal
        addLiteralCharAndAdvance();
    literal.complete();
    return TokenTraits::fromIdentifierOrKeyword(m_nextToken.literal);
}

char CharStream::advanceAndGet(size_t _chars)
{
    if (isPastEndOfInput())
        return 0;
    m_position += _chars;
    if (isPastEndOfInput())
        return 0;
    return m_source[m_position];
}

char CharStream::rollback(size_t _amount)
{
    solAssert(m_position >= _amount, "");
    m_position -= _amount;
    return get();
}

string CharStream::lineAtPosition(int _position) const
{
    // if _position points to \n, it returns the line before the \n
    using size_type = string::size_type;
    size_type searchStart = min<size_type>(m_source.size(), _position);
    if (searchStart > 0)
        searchStart--;
    size_type lineStart = m_source.rfind('\n', searchStart);
    if (lineStart == string::npos)
        lineStart = 0;
    else
        lineStart++;
    return m_source.substr(lineStart, min(m_source.find('\n', lineStart),
                                          m_source.size()) - lineStart);
}

tuple<int, int> CharStream::translatePositionToLineColumn(int _position) const
{
    using size_type = string::size_type;
    size_type searchPosition = min<size_type>(m_source.size(), _position);
    int lineNumber = count(m_source.begin(), m_source.begin() + searchPosition, '\n');
    size_type lineStart;
    if (searchPosition == 0)
        lineStart = 0;
    else
    {
        lineStart = m_source.rfind('\n', searchPosition - 1);
        lineStart = lineStart == string::npos ? 0 : lineStart + 1;
    }
    return tuple<int, int>(lineNumber, searchPosition - lineStart);
}


}
}