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# Copyright 2004-2005 Elemental Security, Inc. All Rights Reserved.
# Licensed to PSF under a Contributor Agreement.
# Modifications:
# Copyright David Halter and Contributors
# Modifications are dual-licensed: MIT and PSF.
from typing import Optional, Iterator, Tuple, List
from parso.python.tokenize import tokenize
from parso.utils import parse_version_string
from parso.python.token import PythonTokenTypes
class NFAArc:
def __init__(self, next_: 'NFAState', nonterminal_or_string: Optional[str]):
self.next: NFAState = next_
self.nonterminal_or_string: Optional[str] = nonterminal_or_string
def __repr__(self):
return '<%s: %s>' % (self.__class__.__name__, self.nonterminal_or_string)
class NFAState:
def __init__(self, from_rule: str):
self.from_rule: str = from_rule
self.arcs: List[NFAArc] = []
def add_arc(self, next_, nonterminal_or_string=None):
assert nonterminal_or_string is None or isinstance(nonterminal_or_string, str)
assert isinstance(next_, NFAState)
self.arcs.append(NFAArc(next_, nonterminal_or_string))
def __repr__(self):
return '<%s: from %s>' % (self.__class__.__name__, self.from_rule)
class GrammarParser:
"""
The parser for Python grammar files.
"""
def __init__(self, bnf_grammar: str):
self._bnf_grammar = bnf_grammar
self.generator = tokenize(
bnf_grammar,
version_info=parse_version_string('3.9')
)
self._gettoken() # Initialize lookahead
def parse(self) -> Iterator[Tuple[NFAState, NFAState]]:
# grammar: (NEWLINE | rule)* ENDMARKER
while self.type != PythonTokenTypes.ENDMARKER:
while self.type == PythonTokenTypes.NEWLINE:
self._gettoken()
# rule: NAME ':' rhs NEWLINE
self._current_rule_name = self._expect(PythonTokenTypes.NAME)
self._expect(PythonTokenTypes.OP, ':')
a, z = self._parse_rhs()
self._expect(PythonTokenTypes.NEWLINE)
yield a, z
def _parse_rhs(self):
# rhs: items ('|' items)*
a, z = self._parse_items()
if self.value != "|":
return a, z
else:
aa = NFAState(self._current_rule_name)
zz = NFAState(self._current_rule_name)
while True:
# Add the possibility to go into the state of a and come back
# to finish.
aa.add_arc(a)
z.add_arc(zz)
if self.value != "|":
break
self._gettoken()
a, z = self._parse_items()
return aa, zz
def _parse_items(self):
# items: item+
a, b = self._parse_item()
while self.type in (PythonTokenTypes.NAME, PythonTokenTypes.STRING) \
or self.value in ('(', '['):
c, d = self._parse_item()
# Need to end on the next item.
b.add_arc(c)
b = d
return a, b
def _parse_item(self):
# item: '[' rhs ']' | atom ['+' | '*']
if self.value == "[":
self._gettoken()
a, z = self._parse_rhs()
self._expect(PythonTokenTypes.OP, ']')
# Make it also possible that there is no token and change the
# state.
a.add_arc(z)
return a, z
else:
a, z = self._parse_atom()
value = self.value
if value not in ("+", "*"):
return a, z
self._gettoken()
# Make it clear that we can go back to the old state and repeat.
z.add_arc(a)
if value == "+":
return a, z
else:
# The end state is the same as the beginning, nothing must
# change.
return a, a
def _parse_atom(self):
# atom: '(' rhs ')' | NAME | STRING
if self.value == "(":
self._gettoken()
a, z = self._parse_rhs()
self._expect(PythonTokenTypes.OP, ')')
return a, z
elif self.type in (PythonTokenTypes.NAME, PythonTokenTypes.STRING):
a = NFAState(self._current_rule_name)
z = NFAState(self._current_rule_name)
# Make it clear that the state transition requires that value.
a.add_arc(z, self.value)
self._gettoken()
return a, z
else:
self._raise_error("expected (...) or NAME or STRING, got %s/%s",
self.type, self.value)
def _expect(self, type_, value=None):
if self.type != type_:
self._raise_error("expected %s, got %s [%s]",
type_, self.type, self.value)
if value is not None and self.value != value:
self._raise_error("expected %s, got %s", value, self.value)
value = self.value
self._gettoken()
return value
def _gettoken(self):
tup = next(self.generator)
self.type, self.value, self.begin, prefix = tup
def _raise_error(self, msg, *args):
if args:
try:
msg = msg % args
except:
msg = " ".join([msg] + list(map(str, args)))
line = self._bnf_grammar.splitlines()[self.begin[0] - 1]
raise SyntaxError(msg, ('<grammar>', self.begin[0],
self.begin[1], line))
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