[stdlib] sem_t is a nullable pointer on OpenBSD. #31853
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Platform defines sem_open in Swift that calls through to the underlying platform functions because sem_open is variadic. However, the definitions here assume sem_t is non-nullable, but this assumption only holds when the platform has nullability annotations on the semaphore type, or the semaphore type on the platform is not an opaque pointer. On OpenBSD specifically, the semaphore type is an opaque pointer without any nullability annotations. This means that the type gets inferred as UnsafeMutablePointer<sem_t?>? instead of UnsafeMutablePointer<sem_t>?. To make sure the pointer values returned and their types match, we introduce a conditional typealias. The other option is to coerce everything to UnsafeMutablePointer<sem_t>? but this would be a rather blunt instrument. While sem_open is public in stdlib, it is not so much codified stdlib API, so this is a slightly nicer approach.
compnerd
approved these changes
May 18, 2020
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@swift-ci please test |
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Platform defines sem_open in Swift that calls through to the underlying
platform functions because sem_open is variadic. However, the
definitions here assume sem_t is non-nullable, but this assumption only
holds when the platform has nullability annotations on the semaphore
type, or the semaphore type on the platform is not an opaque pointer.
On OpenBSD specifically, the semaphore type is an opaque pointer without
any nullability annotations. This means that the type gets inferred as
UnsafeMutablePointer<sem_t?>? instead of UnsafeMutablePointer<sem_t>?.
To make sure the pointer values returned and their types match, we
introduce a conditional typealias.
The other option is to coerce everything to UnsafeMutablePointer<sem_t>?
but this would be a rather blunt instrument. While sem_open is public in
stdlib, it is not so much codified stdlib API, so this is a slightly
nicer approach.