Improve yield from inference for unions of generators #16717
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Diff from mypy_primer, showing the effect of this PR on open source code: rich (https://github.com/Textualize/rich)
+ rich/segment.py:607: error: No return value expected [return-value]
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New error in rich is a true positive |
| # Supertype of Generator (Iterator, Iterable, object): tr is any. | ||
| return AnyType(TypeOfAny.special_form) | ||
| # We have a supertype of Generator (Iterator, Iterable, object) | ||
| # Treat `Iterator[X]` as a shorthand for `Generator[X, Any, None]`. |
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Why? Intuitively Any makes more sense to me here.
This affects code like this, right?
x: Iterator[T]
y = yield from x|
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| class T: pass | ||
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| def foo(arg: Union[Generator[int, None, T], Iterable[str]]) -> Generator[Union[int, str], None, Optional[T]]: |
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This is unsound and should arguably error. For example, I could pass a Generator[str, None, str] and get a different type out.
Possibly we should allow it for pragmatic reasons, but then again I'm not sure how often people use yield from with values typed as just Iterable.
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Fixes #15141, closes #15168
Tests written by omarsilva1