lexer.py

# Parser for C code
# Originally by Mark Shannon (mark@hotpy.org)
# https://gist.github.com/markshannon/db7ab649440b5af765451bb77c7dba34

import re
from dataclasses import dataclass

def choice(*opts):
    return "|".join("(%s)" % opt for opt in opts)

# Regexes

# Longer operators must go before shorter ones.

PLUSPLUS = r'\+\+'
MINUSMINUS = r'--'

# ->
ARROW = r'->'
ELLIPSIS = r'\.\.\.'

# Assignment operators
TIMESEQUAL = r'\*='
DIVEQUAL = r'/='
MODEQUAL = r'%='
PLUSEQUAL = r'\+='
MINUSEQUAL = r'-='
LSHIFTEQUAL = r'<<='
RSHIFTEQUAL = r'>>='
ANDEQUAL = r'&='
OREQUAL = r'\|='
XOREQUAL = r'\^='

# Operators
PLUS = r'\+'
MINUS = r'-'
TIMES = r'\*'
DIVIDE = r'/'
MOD = r'%'
NOT = r'~'
XOR = r'\^'
LOR = r'\|\|'
LAND = r'&&'
LSHIFT = r'<<'
RSHIFT = r'>>'
LE = r'<='
GE = r'>='
EQ = r'=='
NE = r'!='
LT = r'<'
GT = r'>'
LNOT = r'!'
OR = r'\|'
AND = r'&'
EQUALS = r'='

# ?
CONDOP = r'\?'

# Delimiters
LPAREN = r'\('
RPAREN = r'\)'
LBRACKET = r'\['
RBRACKET = r'\]'
LBRACE = r'\{'
RBRACE = r'\}'
COMMA = r','
PERIOD = r'\.'
SEMI = r';'
COLON = r':'
BACKSLASH = r'\\'

operators = { op: pattern for op, pattern in globals().items() if op == op.upper() }
for op in operators:
    globals()[op] = op
opmap = { pattern.replace("\\", "") or '\\' : op for op, pattern in operators.items() }

# Macros
macro = r'# *(ifdef|ifndef|undef|define|error|endif|if|else|include|#)'
MACRO = 'MACRO'

id_re = r'[a-zA-Z_][0-9a-zA-Z_]*'
IDENTIFIER = 'IDENTIFIER'

suffix = r'([uU]?[lL]?[lL]?)'
octal = r'0[0-7]+' + suffix
hex = r'0[xX][0-9a-fA-F]+'
decimal_digits = r'(0|[1-9][0-9]*)'
decimal = decimal_digits + suffix


exponent = r"""([eE][-+]?[0-9]+)"""
fraction = r"""([0-9]*\.[0-9]+)|([0-9]+\.)"""
float = '(((('+fraction+')'+exponent+'?)|([0-9]+'+exponent+'))[FfLl]?)'

number_re = choice(octal, hex, float, decimal)
NUMBER = 'NUMBER'

simple_escape = r"""([a-zA-Z._~!=&\^\-\\?'"])"""
decimal_escape = r"""(\d+)"""
hex_escape = r"""(x[0-9a-fA-F]+)"""
escape_sequence = r"""(\\("""+simple_escape+'|'+decimal_escape+'|'+hex_escape+'))'
string_char = r"""([^"\\\n]|"""+escape_sequence+')'
str_re = '"'+string_char+'*"'
STRING = 'STRING'
char = r'\'.\''  # TODO: escape sequence
CHARACTER = 'CHARACTER'

comment_re = r'//.*|/\*([^*]|\*[^/])*\*/'
COMMENT = 'COMMENT'

newline = r"\n"
invalid = r"\S"  # A single non-space character that's not caught by any of the other patterns
matcher = re.compile(choice(id_re, number_re, str_re, char, newline, macro, comment_re, *operators.values(), invalid))
letter = re.compile(r'[a-zA-Z_]')

kwds = (
    'AUTO', 'BREAK', 'CASE', 'CHAR', 'CONST',
    'CONTINUE', 'DEFAULT', 'DO', 'DOUBLE', 'ELSE', 'ENUM', 'EXTERN',
    'FLOAT', 'FOR', 'GOTO', 'IF', 'INLINE', 'INT', 'LONG', 'OVERRIDE',
    'REGISTER', 'OFFSETOF',
    'RESTRICT', 'RETURN', 'SHORT', 'SIGNED', 'SIZEOF', 'STATIC', 'STRUCT',
    'SWITCH', 'TYPEDEF', 'UNION', 'UNSIGNED', 'VOID',
    'VOLATILE', 'WHILE'
)
for name in kwds:
    globals()[name] = name
keywords = { name.lower() : name for name in kwds }


def make_syntax_error(
    message: str, filename: str, line: int, column: int, line_text: str,
) -> SyntaxError:
    return SyntaxError(message, (filename, line, column, line_text))


@dataclass(slots=True)
class Token:
    kind: str
    text: str
    begin: tuple[int, int]
    end: tuple[int, int]

    @property
    def line(self):
        return self.begin[0]

    @property
    def column(self):
        return self.begin[1]

    @property
    def end_line(self):
        return self.end[0]

    @property
    def end_column(self):
        return self.end[1]

    @property
    def width(self):
        return self.end[1] - self.begin[1]

    def replaceText(self, txt):
        assert isinstance(txt, str)
        return Token(self.kind, txt, self.begin, self.end)

    def __repr__(self):
        b0, b1 = self.begin
        e0, e1 = self.end
        if b0 == e0:
            return f"{self.kind}({self.text!r}, {b0}:{b1}:{e1})"
        else:
            return f"{self.kind}({self.text!r}, {b0}:{b1}, {e0}:{e1})"


def tokenize(src, line=1, filename=None):
    linestart = -1
    for m in matcher.finditer(src):
        start, end = m.span()
        text = m.group(0)
        if text in keywords:
            kind = keywords[text]
        elif letter.match(text):
            kind = IDENTIFIER
        elif text == '...':
            kind = ELLIPSIS
        elif text == '.':
            kind = PERIOD
        elif text[0] in '0123456789.':
            kind = NUMBER
        elif text[0] == '"':
            kind = STRING
        elif text in opmap:
            kind = opmap[text]
        elif text == '\n':
            linestart = start
            line += 1
            kind = '\n'
        elif text[0] == "'":
            kind = CHARACTER
        elif text[0] == '#':
            kind = MACRO
        elif text[0] == '/' and text[1] in '/*':
            kind = COMMENT
        else:
            lineend = src.find("\n", start)
            if lineend == -1:
                lineend = len(src)
            raise make_syntax_error(f"Bad token: {text}",
                filename, line, start-linestart+1, src[linestart:lineend])
        if kind == COMMENT:
            begin = line, start-linestart
            newlines = text.count('\n')
            if newlines:
                linestart = start + text.rfind('\n')
                line += newlines
        else:
            begin = line, start-linestart
        if kind != "\n":
            yield Token(kind, text, begin, (line, start-linestart+len(text)))


__all__ = []
__all__.extend([kind for kind in globals() if kind.upper() == kind])


def to_text(tkns: list[Token], dedent: int = 0) -> str:
    res: list[str] = []
    line, col = -1, 1+dedent
    for tkn in tkns:
        if line == -1:
            line, _ = tkn.begin
        l, c = tkn.begin
        #assert(l >= line), (line, txt, start, end)
        while l > line:
            line += 1
            res.append('\n')
            col = 1+dedent
        res.append(' '*(c-col))
        text = tkn.text
        if dedent != 0 and tkn.kind == 'COMMENT' and '\n' in text:
            if dedent < 0:
                text = text.replace('\n', '\n' + ' '*-dedent)
            # TODO: dedent > 0
        res.append(text)
        line, col = tkn.end
    return ''.join(res)


if __name__ == "__main__":
    import sys
    filename = sys.argv[1]
    if filename == "-c":
        src = sys.argv[2]
    else:
        src = open(filename).read()
    # print(to_text(tokenize(src)))
    for tkn in tokenize(src, filename=filename):
        print(tkn)