Flatten union before contracting literals when checking subtyping#18898
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sobolevn merged 1 commit intopython:masterfrom Apr 9, 2025
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According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅ |
sobolevn
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Apr 8, 2025
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LGTM! Let's wait a bit for some extra feedback.
A5rocks
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Apr 9, 2025
| def try_contracting_literals_in_union(types: Sequence[Type]) -> list[ProperType]: | ||
| """Contracts any literal types back into a sum type if possible. | ||
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| Requires a flattened union and does not descend into children. |
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Maybe it's better to add an assert or transparently handle this correctly? Both usages of this in mypy seem fine but I think preventing misuse is good.
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I'd rather not - this function is called twice in the whole codebase, one of them in a rather hot function (subtyping check). While failure to pass a flattened union may result in some false positives, it isn't dangerous and can't cause any errors down the road.
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Fixes #18896