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JukkaLJukkaL
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[mypyc] Fix TypeError in lambda argument to overloaded function (#12780)
Previously we could export an invalid type for a lambda passed to an overloaded function. We find the matching overload variant by type checking the arguments against all overload items. We exported types for lambdas always from the final potential overload item, even if that wasn't the matching one. This could result in mypyc adding invalid type coercions that could result in bogus TypeErrors. The fix is to store types inferred when looking for matching overload items into temporary type maps, and only the type map from the matching item gets merged into the exported types. This doesn't fully solve the problem -- if there are Any types in the arguments, we can still export invalid types. This should be enough to unblock syncing typeshed (#12766). Typeshed started triggering the issue in compiled mypy when re.sub was changed to an overloaded function. Work on #12773.
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‎mypy/build.py‎

Lines changed: 4 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -2217,7 +2217,10 @@ def type_checker(self) -> TypeChecker:
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return self._type_checker
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def type_map(self) -> Dict[Expression, Type]:
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return self.type_checker().type_map
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# We can extract the master type map directly since at this
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# point no temporary type maps can be active.
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assert len(self.type_checker()._type_maps) == 1
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return self.type_checker()._type_maps[0]
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def type_check_second_pass(self) -> bool:
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if self.options.semantic_analysis_only:

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