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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.
# 99% of the code is different from pgen2, now.
#
# A fork of `parso.pgen2.grammar_parser`.
# https://github.com/davidhalter/parso/blob/master/parso/pgen2/grammar_parser.py
#
# The following changes were made:
# - Type stubs were directly applied.
# pyre-unsafe
from typing import Generator, List, Optional, Tuple
from libcst._parser.parso.python.token import PythonTokenTypes
from libcst._parser.parso.python.tokenize import tokenize
from libcst._parser.parso.utils import parse_version_string
class NFAArc:
def __init__(self, next_: "NFAState", nonterminal_or_string: Optional[str]) -> None:
self.next: NFAState = next_
self.nonterminal_or_string: Optional[str] = nonterminal_or_string
def __repr__(self) -> str:
return "<%s: %s>" % (self.__class__.__name__, self.nonterminal_or_string)
class NFAState:
def __init__(self, from_rule: str) -> None:
self.from_rule = from_rule
self.arcs: List[NFAArc] = []
def add_arc(
self, next_: "NFAState", nonterminal_or_string: Optional[str] = None
) -> None:
self.arcs.append(NFAArc(next_, nonterminal_or_string))
def __repr__(self) -> str:
return "<%s: from %s>" % (self.__class__.__name__, self.from_rule)
class GrammarParser:
"""
The parser for Python grammar files.
"""
def __init__(self, bnf_grammar: str) -> None:
self._bnf_grammar: str = bnf_grammar
self.generator = tokenize(bnf_grammar, version_info=parse_version_string("3.6"))
self._gettoken() # Initialize lookahead
def parse(self) -> Generator[Tuple[NFAState, NFAState], None, None]:
# grammar: (NEWLINE | rule)* ENDMARKER
while self.type != PythonTokenTypes.ENDMARKER:
while self.type == PythonTokenTypes.NEWLINE:
self._gettoken()
# rule: NAME ':' rhs NEWLINE
# pyre-ignore Pyre is unhappy with the fact that we haven't put
# _current_rule_name in the constructor.
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) -> None:
tup = next(self.generator)
self.type, self.value, self.begin, prefix = tup
def _raise_error(self, msg: str, *args: object) -> None:
if args:
try:
msg = msg % args
except Exception:
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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