[ty] Simplify unions of enum literals and subtypes thereof#20324
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[ty] Simplify unions of enum literals and subtypes thereof#20324
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sharkdp
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AlexWaygood,
carljm and
dcreager
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sharkdp
commented
Sep 10, 2025
Comment on lines
-447
to
-448
| self.elements | ||
| .push(UnionElement::Type(Type::EnumLiteral(enum_member_to_add))); |
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This was the problem. Instead of just using self.elements.push, we should go through the whole simplification logic in the _ => {…} branch, which I have now moved to a separate function. Every other change in this file is just the "moving out to a separate function" part.
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Diagnostic diff on typing conformance testsNo changes detected when running ty on typing conformance tests ✅ |
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AlexWaygood
approved these changes
Sep 10, 2025
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Summary
When adding an enum literal
E = Literal[Color.RED]to a union which already contained a subtype of that enum literal(!), we were previously not simplifying the union correctly. My assumption is that our property tests didn't catch that earlier, because the only possible non-trivial subytpe of an enum literal that I can think of isAny & E. And in order for that to be detected by the property tests, it would have to randomly generateAny & E | Eand then also compare that withEon the other side (in an equivalence test, or the subtyping-antisymmetry test).closes astral-sh/ty#1155
Test Plan