Reproducing SR-10221

gistfile1.txt

import Cocoa

enum Animal {
    case aardvark(NSWindow.StyleMask)
    case bear
    case cat
}

func isNotCat(_ animal: Animal) -> Bool {
    switch animal {
    case .cat:
        return false
    default:
        return true
    }
}

var globalIsNotCat: Bool = true

func reproduceBug(_ animal: Animal) {
    //
    // This reproduces the bug when all of the following is true:
    //
    // 1. The file is compiled with `swiftc -O`
    //
    // 2. The enum Animal has a case with an associated value
    //    that is an Objective-C enum.
    //
    // 3. The variable (globalIsNotCat) that the result of
    //    isNotCat(...) is assigned to is not in the scope
    //    of the reproduceBug(...) function.
    // 
    // 4. There is an `if` that checks the variable.
    //
    // 5. There is a print("") in the `if` following the first
    //    print that prints the value.
    //
    // Change one of these things and the printed value is correct.
    //
    globalIsNotCat = isNotCat(animal)
    // Correct -> prints true, Bug -> prints false
    print(globalIsNotCat)
    if globalIsNotCat {
        print("")
    }
}

reproduceBug(.bear)