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from pegen import grammar
from pegen.grammar import (
Alt,
Cut,
Gather,
GrammarVisitor,
Group,
Lookahead,
NamedItem,
NameLeaf,
NegativeLookahead,
Opt,
PositiveLookahead,
Repeat0,
Repeat1,
Rhs,
Rule,
StringLeaf,
)
class ValidationError(Exception):
pass
class GrammarValidator(GrammarVisitor):
def __init__(self, grammar: grammar.Grammar):
self.grammar = grammar
self.rulename = None
def validate_rule(self, rulename: str, node: Rule):
self.rulename = rulename
self.visit(node)
self.rulename = None
class SubRuleValidator(GrammarValidator):
def visit_Rhs(self, node: Rule):
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) -> bool:
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):
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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