Because people put all sorts of nonsense into @objc enums (most
reasonably, "private cases", which represent valid values that are not
API), the Swift-synthesized implementation of 'hash(into:)' needs to
not expect a switch statement to be exhaustive. And since
Swift-defined @objc enums are supposed to behave enough like C-defined
enums, they should at least handle simple method calls with an invalid
raw value, which means that 'rawValue' likewise should not use a
switch.
This patch provides alternate implementations that look like this:
extension ImportedEnum {
public var rawValue: Int {
return unsafeBitCast(self, to: Int.self)
}
public func hash(into hasher: inout Hasher) {
hasher.combine(self.rawValue)
}
}
rdar://problem/41913284
Builds on 36eae9d4f6 to emit a message instead of just trapping
when a switch over a non-frozen enum ends up not matching anything.
If the enum is known to be an @objc enum, the message is
unexpected enum case 'MyEnum(rawValue: -42)'
and if it's anything else (a Swift enum, a tuple containing enums,
whatever), it's a more opaque
unexpected enum case while switching on value of type 'MyEnum'
The reason for this is to avoid calling String(describing:) or
String(reflecting:) an arbitrary value when the enum might conform to
CustomStringConvertible and therefore /itself/ have a switch that's
going to fall off the end. By handling plain @objc enums (using a
bitcast), we've at least covered the 90% case.
rdar://problem/37728359
(both C enums and Swift enums declared @objc), because of the
"feature" in C of treating a value not declared as a case as a valid
value of an enum. No more undefined behavior here!
This bit can go in separately from all the work on exhaustive/frozen
enums, which is still being discussed and will come later.
rdar://problem/20420436
