Erase stray typevars in functools.partial generic #18954
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| # We should not leak stray typevars that aren't in scope: | ||
| use_int_callable(partial(func_b, b="")) | ||
| use_func_callable(partial(func_b, b="")) |
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Why does this pass? I assume the erased return type is Union[int, str] and not Never...
Also could you add some reveal_type like use_func_callable(reveal_type(partial(func_b, b="")))
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The erased return type is Any. erase_typevars replaces them with Any (special_form), not with upper bounds.
Adding reveal_type is a good idea, let's show the inferred generics explicitly. I don't even need no, let's keep both - subtype checks may do something differentuse_*_callable then...
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I think you should still have the use_*_callable to ensure things still work, at least in a few spots -- printing correctly doesn't necessarily mean the logic is right, e.g. maybe the plugin could mess up passing the partials to the use_*_callable functions (?).
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And Any is really what we want. Replacing tvars with their upper bounds will cause another bunch of false positives whenever smth like def fn[T: str | int](x: T) -> T (hope I didn't mess up this ugly syntax) is used with partial.
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According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅ |
Fixes #18953. Fixes #15215. Refs #17461.
When the function passed to
partialis generic and has generic params in the return type, we must erase them, otherwise they become orphan and cannot be used later. This only applies topartial[...]generic param and not to the underlying "exact" callable stored internally as the latter remains generic.The ultimate fix would be to implement #17620 so that we stop caring about
partial[...]generic param, but this should improve usability (but causes false negatives).