gh-108455: peg generator: Use strict_optional=True for grammar_parser (#108629)

Author: sobolevn

Tools/peg_generator/mypy.ini

@@ -14,8 +14,5 @@ enable_error_code = truthy-bool,ignore-without-code
 warn_return_any = False
 warn_unreachable = False
 
-[mypy-pegen.grammar_parser]
-strict_optional = False
-
 [mypy-setuptools.*]
 ignore_missing_imports = True

Tools/peg_generator/pegen/grammar.py

@@ -349,7 +349,7 @@ def initial_names(self) -> AbstractSet[str]:
 
 Plain = Union[Leaf, Group]
 Item = Union[Plain, Opt, Repeat, Forced, Lookahead, Rhs, Cut]
-RuleName = Tuple[str, str]
+RuleName = Tuple[str, Optional[str]]
 MetaTuple = Tuple[str, Optional[str]]
 MetaList = List[MetaTuple]
 RuleList = List[Rule]