Avoid erasing type objects when checking runtime cover #19320
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In particular, avoid erasing CallableType that represent type objects Helps with python#19159
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JukkaL
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Jun 21, 2025
mypy/subtypes.py
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| @@ -2106,7 +2106,8 @@ def covers_at_runtime(item: Type, supertype: Type) -> bool: | |||
| supertype = get_proper_type(supertype) | |||
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| # Since runtime type checks will ignore type arguments, erase the types. | |||
| supertype = erase_type(supertype) | |||
| if not isinstance(supertype, CallableType): | |||
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Should we only skip erase if the callable type represents a type object? What about overloaded callable types?
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I'm not sure how we would get here with other CallableType's (and we don't anywhere in the test suite). isinstance(item, CallableType) isn't really a thing that can happen at runtime.
I went ahead and restricted it to just type objects though!
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According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅ |
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In particular, avoid erasing CallableType that represent type objects
Helps with #19159