Fix #21295: Restrict provablyDisjoint with Nothings in invariant type params.
#21891
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dwijnand
approved these changes
Nov 6, 2024
| // sjrd: I will not be surprised when this causes further issues in the future. | ||
| // This is a compromise to be able to fix #21295 without breaking the world. | ||
| def cannotBeNothing(tp: Type): Boolean = tp match | ||
| case tp: TypeParamRef => cannotBeNothing(tp.binder.paramInfos(tp.paramNum)) |
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Btw, I recently added .paramInfo to TypeParamRef, as in cannotBeNothing(tp.paramInfo).
…iant type params. If `Foo[T]` is invariant in `T`, we previously concluded that `Foo[A] ⋔ Foo[B]` from `A ⋔ B`. That is however wrong if both `A` and `B` can be (instantiated to) `Nothing`. We now rule out these occurrences in two ways: * either we show that `T` corresponds to a field, like we do in the covariant case, or * we show that `A` or `B` cannot possibly be `Nothing`. The second condition is shaky at best. I would have preferred not to include it. However, introducing the former without the fallback on the latter breaks too many existing test cases.
WojciechMazur
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backport:nominated
WojciechMazur
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backport:done
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If
Foo[T]is invariant inT, we previously concluded thatFoo[A] ⋔ Foo[B]fromA ⋔ B. That is however wrong if bothAandBcan be (instantiated to)Nothing.We now rule out these occurrences in two ways:
Tcorresponds to a field, like we do in the covariant case, orAorBcannot possibly beNothing.The second condition is shaky at best. I would have preferred not to include it. However, introducing the former without the fallback on the latter breaks too many existing test cases.