AST: Add new implementation of getOpenedExistentialSignature() #76206
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This will replace all existing usages of the old implementation.
…dExistentialTypeShape()
…straintsWithExistentialBase()
…veUnfulfillableConstraintsWithExistentialBase()
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| // Specifically ignore parameterized protocols and existential | ||
| // metatypes because we can erase them to the upper bound. | ||
| if (type->is<ParameterizedProtocolType>() || | ||
| type->is<ExistentialMetatypeType>()) { |
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@slavapestov I think we need to be more careful with this sort of loosening. The more sophisticated erasure we support, the harder it will be for everyone to get off of it once we come up with something better. The non-metatype case was never supported, so I think the same should hold for an existential metatype:
class C<T> {}
protocol P {
associatedtype A
func f() -> any P & C<A>
func fMeta() -> any (P & C<A>).Type
}
do {
let p: any P
let _ = p.f() // error
let _ = p.fMeta() // crash
}The call to fMeta() used to miscompile and now crashes, so we can still make it an error.
This was referenced Feb 10, 2025
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This new mechanism allows type variables to appear in the existential type. It will eventually replace the old variant that takes a parent generic signature.