[SR-4552] Implicitly Unwrapped Optional after casting to Any, can't be casted to Protocol it conforms to

[swift-ci]

Previous ID	SR-4552
Radar	rdar://problem/31535455
Original Reporter	lprzytula (JIRA User)
Type	Bug
Status	Resolved
Resolution	Done

Environment

Xcode 8.3, Xcode 8.3.1

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug, Runtime
Assignee	@tbkka
Priority	Medium

md5: ef0c9e8e254e8f3add523707285a627b

relates to:

• SR-8964 Type check operator (is) fails for Any! variable holding an Error (struct) value

Issue Description:

I have a protocol, and class:

protocol MyProtocol {
    func myFunc() -> Bool
}

class MyClass: MyProtocol {
    func myFunc() -> Bool {
        return true
    }
}

Then I create an implicitly unwrapped optional of this type, and cast it to 'Any':

let myObject: MyClass! = MyClass() // MyClass
let myAny: Any = myObject // MyClass

Now trying to cast the 'myAny' instance to the protocol 'MyProtocol' that it conforms to, produces 'nil', while casting 'myObject' to the same protocol returns proper object:

NSLog("\(myAny)") // MyClass
NSLog("\(myAny is MyClass)") // true
NSLog("\(myAny is MyProtocol)") // false
NSLog("\(myObject is MyProtocol)") // true
let myCasted1 = myAny as? MyProtocol // nil
let myCasted2 = myObject as? MyProtocol // MyClass
let myCasted3 = (myObject as Any) as? MyProtocol // nil
let myCasted4 = myAny as? MyClass // MyClass

Same code works properly with Swift 3.0

[belkadan]

Hm, it does seem inconsistent to extract the class but not the protocol. Casting magister @jckarter?

[jckarter]

@swift-ci create

[tbkka]

This is similar to SR-3871, but not quite the same. SR-3871 specifically is about nested Any/AnyObject existential containers. This is similar but with Optionals in the mix. It interacts with the current `print()` implementation in complex ways, so it will take me a little while to work out a good approach here.

[tbkka]

Related: PR #28994 fixes a bug in `print()` that was being covered up by this bug.

[tbkka]

#33561 should fix this for the non-optimized case (where the cast is being handled by the runtime). There may still be issues with optimized casts, though.

[tbkka]

Protocol conformance checks of objects stored in `Any` containers has been fixed in the `main` branch.