FileDescriptor.open(_:_:options:permissions:retryOnInterrupt:) should print an error message when trapping on unspecified permissions

[tayloraswift]

FileDescriptor.open(_:_:options:permissions:retryOnInterrupt:) traps if options.contains(.create) and permissions is nil. since its callers can throw, why not throw an error instead?

alternatively, if this isn’t appropriate for throws, it should be a fatalError instead of a precondition, so users don’t have to hunt through source code to figure out why FileDescriptor is crashing…

[tayloraswift]

actually come to think of it, this would not be a good use of throws, since it’s a programmer error. still, it would be better to print the message in the crash dump with a fatalError