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from typing import Optional
from pegen import grammar
from pegen.grammar import Alt, GrammarVisitor, Rhs, Rule
class ValidationError(Exception):
pass
class GrammarValidator(GrammarVisitor):
def __init__(self, grammar: grammar.Grammar) -> None:
self.grammar = grammar
self.rulename: Optional[str] = None
def validate_rule(self, rulename: str, node: Rule) -> None:
self.rulename = rulename
self.visit(node)
self.rulename = None
class SubRuleValidator(GrammarValidator):
def visit_Rhs(self, node: Rhs) -> None:
for index, alt in enumerate(node.alts):
alts_to_consider = node.alts[index + 1 :]
for other_alt in alts_to_consider:
self.check_intersection(alt, other_alt)
def check_intersection(self, first_alt: Alt, second_alt: Alt) -> None:
if str(second_alt).startswith(str(first_alt)):
raise ValidationError(
f"In {self.rulename} there is an alternative that will "
f"never be visited:\n{second_alt}"
)
def validate_grammar(the_grammar: grammar.Grammar) -> None:
for validator_cls in GrammarValidator.__subclasses__():
validator = validator_cls(the_grammar)
for rule_name, rule in the_grammar.rules.items():
validator.validate_rule(rule_name, rule)
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