Correct line and column number in source position when raising LexingError

[michal-pawlik]

When lexer is unable to find matching token, LexingError raises. This error contains source position for further debugging, but in current implementation it only points valid index (character number), while the line and colum numbers equal -1.

This PR fixes this issue by tracking column number in next() method of LexerStream and providing both self._lineno and self._colno to SourcePosition in LexingError.

[alex]

Please move this line outside the raises block so it's clear which line raises an exception.

[michal-pawlik]

@alex good point, fixed

[alex]

Same here.

[michal-pawlik]

Fixed

[nobodxbodon]

Seems there's edge case not covered here:

    def test_error_reset_column_number(self):
        lg = LexerGenerator()
        lg.add("NEW_LINE", r"\n")
        lg.add("NUMBER", r"\d+")
        l = lg.build()
        stream = l.lex("12\nfail")
        stream.next()
        stream.next()
        with raises(LexingError) as excinfo:
            stream.next()

        assert excinfo.value.source_pos.colno == 1   # it fails with 3 instead

The same assertion works if added in test_error_line_number.

[nobodxbodon]

FYI here's a fix for colno when there's lexing error: nobodxbodon@4afbd7f , covering the edge case above.