gitmirror/lark/lexer.py

## Lexer Implementation

import re
import sre_parse

from .utils import Str, classify
from .common import is_terminal, PatternStr, PatternRE, TokenDef

class LexError(Exception):
    pass

class UnexpectedInput(LexError):
    def __init__(self, seq, lex_pos, line, column):
        context = seq[lex_pos:lex_pos+5]
        message = "No token defined for: '%s' in %r at line %d" % (seq[lex_pos], context, line)

        super(UnexpectedInput, self).__init__(message)

        self.line = line
        self.column = column
        self.context = context

class Token(Str):
    def __new__(cls, type_, value, pos_in_stream=None, line=None, column=None):
        inst = Str.__new__(cls, value)
        inst.type = type_
        inst.pos_in_stream = pos_in_stream
        inst.value = value
        inst.line = line
        inst.column = column
        return inst

    @classmethod
    def new_borrow_pos(cls, type_, value, borrow_t):
        return cls(type_, value, borrow_t.pos_in_stream, line=borrow_t.line, column=borrow_t.column)

    def __repr__(self):
        return 'Token(%s, %r)' % (self.type, self.value)

    def __deepcopy__(self, memo):
        return Token(self.type, self.value, self.pos_in_stream, self.line, self.column)

class Regex:
    def __init__(self, pattern, flags=()):
        self.pattern = pattern
        self.flags = flags

def _regexp_has_newline(r):
    return '\n' in r or '\\n' in r or ('(?s)' in r and '.' in r)

def _create_unless_callback(strs):
    def unless_callback(t):
        if t in strs:
            t.type = strs[t]
        return t
    return unless_callback

def _create_unless(tokens):
    tokens_by_type = classify(tokens, lambda t: type(t.pattern))
    assert len(tokens_by_type) <= 2, tokens_by_type.keys()
    embedded_strs = set()
    callback = {}
    for retok in tokens_by_type.get(PatternRE, []):
        unless = {}
        for strtok in tokens_by_type.get(PatternStr, []):
            s = strtok.pattern.value
            m = re.match(retok.pattern.value, s)
            if m and m.group(0) == s:
                embedded_strs.add(strtok.name)
                unless[s] = strtok.name
        if unless:
            callback[retok.name] = _create_unless_callback(unless)

    tokens = [t for t in tokens if t.name not in embedded_strs]
    return tokens, callback


class Lexer(object):
    def __init__(self, tokens, ignore=()):
        assert all(isinstance(t, TokenDef) for t in tokens), tokens

        self.ignore = ignore
        self.newline_char = '\n'
        tokens = list(tokens)

        # Sanitization
        for t in tokens:
            try:
                re.compile(t.pattern.to_regexp())
            except:
                raise LexError("Cannot compile token %s: %s" % (t.name, t.pattern))

            width = sre_parse.parse(t.pattern.to_regexp()).getwidth()
            if width[0] == 0:
                raise LexError("Lexer does not allow zero-width tokens. (%s: %s)" % (t.name, t.pattern))

        token_names = {t.name for t in tokens}
        for t in ignore:
            if t not in token_names:
                raise LexError("Token '%s' was marked to ignore but it is not defined!" % t)

        # Init
        self.newline_types = [t.name for t in tokens if _regexp_has_newline(t.pattern.to_regexp())]
        self.ignore_types = [t for t in ignore]

        tokens, self.callback = _create_unless(tokens)
        assert all(self.callback.values())

        tokens.sort(key=lambda x:(x.pattern.priority, len(x.pattern.value)), reverse=True)

        self.tokens = tokens

        self.mres = self._build_mres(tokens, len(tokens))


    def _build_mres(self, tokens, max_size):
        # Python sets an unreasonable group limit (currently 100) in its re module
        # Worse, the only way to know we reached it is by catching an AssertionError!
        # This function recursively tries less and less groups until it's successful.
        mres = []
        while tokens:
            try:
                mre = re.compile(u'|'.join(u'(?P<%s>%s)'%(t.name, t.pattern.to_regexp()) for t in tokens[:max_size]))
            except AssertionError:  # Yes, this is what Python provides us.. :/
                return self._build_mres(tokens, max_size//2)

            mres.append((mre, {i:n for n,i in mre.groupindex.items()} ))
            tokens = tokens[max_size:]
        return mres

    def lex(self, stream):
        lex_pos = 0
        line = 1
        col_start_pos = 0
        newline_types = list(self.newline_types)
        ignore_types = list(self.ignore_types)
        while True:
            for mre, type_from_index in self.mres:
                m = mre.match(stream, lex_pos)
                if m:
                    value = m.group(0)
                    type_ = type_from_index[m.lastindex]
                    if type_ not in ignore_types:
                        t = Token(type_, value, lex_pos, line, lex_pos - col_start_pos)
                        if t.type in self.callback:
                            t = self.callback[t.type](t)
                        yield t

                    if type_ in newline_types:
                        newlines = value.count(self.newline_char)
                        if newlines:
                            line += newlines
                            col_start_pos = lex_pos + value.rindex(self.newline_char)
                    lex_pos += len(value)
                    break
            else:
                if lex_pos < len(stream):
                    raise UnexpectedInput(stream, lex_pos, line, lex_pos - col_start_pos)
                break


class ContextualLexer:
    def __init__(self, tokens, states, ignore=(), always_accept=()):
        tokens_by_name = {}
        for t in tokens:
            assert t.name not in tokens_by_name, t
            tokens_by_name[t.name] = t

        lexer_by_tokens = {}
        self.lexers = {}
        for state, accepts in states.items():
            key = frozenset(accepts)
            try:
                lexer = lexer_by_tokens[key]
            except KeyError:
                accepts = set(accepts) | set(ignore) | set(always_accept)
                state_tokens = [tokens_by_name[n] for n in accepts if is_terminal(n) and n!='$end']
                lexer = Lexer(state_tokens, ignore=ignore)
                lexer_by_tokens[key] = lexer

            self.lexers[state] = lexer

        self.root_lexer = Lexer(tokens, ignore=ignore)

        self.set_parser_state(None) # Needs to be set on the outside

    def set_parser_state(self, state):
        self.parser_state = state

    def lex(self, stream):
        lex_pos = 0
        line = 1
        col_start_pos = 0
        newline_types = list(self.root_lexer.newline_types)
        ignore_types = list(self.root_lexer.ignore_types)
        while True:
            lexer = self.lexers[self.parser_state]
            for mre, type_from_index in lexer.mres:
                m = mre.match(stream, lex_pos)
                if m:
                    value = m.group(0)
                    type_ = type_from_index[m.lastindex]
                    if type_ not in ignore_types:
                        t = Token(type_, value, lex_pos, line, lex_pos - col_start_pos)
                        if t.type in lexer.callback:
                            t = lexer.callback[t.type](t)
                        yield t

                    if type_ in newline_types:
                        newlines = value.count(lexer.newline_char)
                        if newlines:
                            line += newlines
                            col_start_pos = lex_pos + value.rindex(lexer.newline_char)
                    lex_pos += len(value)
                    break
            else:
                if lex_pos < len(stream):
                    print("Allowed tokens:", lexer.tokens)
                    raise UnexpectedInput(stream, lex_pos, line, lex_pos - col_start_pos)
                break