Flatten union before contracting literals when checking subtyping #18898
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According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅ |
sobolevn
approved these changes
Apr 8, 2025
A5rocks
approved these changes
Apr 9, 2025
| @@ -1069,6 +1069,8 @@ class Status(Enum): | |||
| 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