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52 lines
1.4 KiB
Python
52 lines
1.4 KiB
Python
from pegen import grammar
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from pegen.grammar import (
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Alt,
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Cut,
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Gather,
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GrammarVisitor,
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Group,
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Lookahead,
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NamedItem,
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NameLeaf,
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NegativeLookahead,
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Opt,
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PositiveLookahead,
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Repeat0,
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Repeat1,
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Rhs,
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Rule,
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StringLeaf,
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)
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class ValidationError(Exception):
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pass
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class GrammarValidator(GrammarVisitor):
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def __init__(self, grammar: grammar.Grammar):
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self.grammar = grammar
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self.rulename = None
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def validate_rule(self, rulename: str, node: Rule):
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self.rulename = rulename
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self.visit(node)
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self.rulename = None
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class SubRuleValidator(GrammarValidator):
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def visit_Rhs(self, node: Rule):
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for index, alt in enumerate(node.alts):
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alts_to_consider = node.alts[index+1:]
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for other_alt in alts_to_consider:
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self.check_intersection(alt, other_alt)
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def check_intersection(self, first_alt: Alt, second_alt: Alt) -> bool:
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if str(second_alt).startswith(str(first_alt)):
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raise ValidationError(
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f"In {self.rulename} there is an alternative that will "
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f"never be visited:\n{second_alt}")
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def validate_grammar(the_grammar: grammar.Grammar):
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for validator_cls in GrammarValidator.__subclasses__():
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validator = validator_cls(the_grammar)
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for rule_name, rule in the_grammar.rules.items():
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validator.validate_rule(rule_name, rule)
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