Swift 5.7 crash in iOS 15 or lower with -Osize optimisation level.

[mikhailmulyar]

Describe the bug This code crashes in iOS 15 or lower simulator or device when optimisation level is set to -Osize. It is crashing with EXC_BAD_ACCESS.

import SwiftUI

protocol SomeProto: AnyObject {
    var proto: any SomeGenericProto<Int> { get set }
    func getElements() -> [Int]
}

class SomeImpl: SomeProto {
    var proto: any SomeGenericProto<Int> = SomeGenericImpl(elements: [1,2,3])

    func getElements() -> [Int] {
        proto.getElements()
    }
}

protocol SomeGenericProto<Element> {
    associatedtype Element

    func getElements() -> [Element]
}

final class SomeGenericImpl<Element>: SomeGenericProto {

    private let elements: [Element]

    init(elements: [Element]) {
        self.elements = elements
    }

    func getElements() -> [Element] {
        elements
    }
}

struct ContentView: View {

    var someValue: any SomeProto = SomeImpl()

    var body: some View {
        VStack {
            Text("Hello, world!" + "\(someValue.getElements().last ?? 0)")
        }
        .padding()
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}

Steps To Reproduce Steps to reproduce the behavior:

1. Create simple app project in Xcode 14 beta and paste this code into ContentView.swift.
2. Set SWIFT_OPTIMIZATION_LEVEL to -Osize.
3. Run app in iOS simulator 15.5 or lower.

Expected behavior App should not crash

Environment (please fill out the following information)

• OS: [iOS 15.5]
• Xcode Version: 14.0 beta 5 (14A5294e)

Additional context Possible workaround for crash is to conform SomeGenericProto to AnyObject

protocol SomeGenericProto<Element>: AnyObject

[vrutberg]

FWIW we just hit this bug at my job, where our iOS app would crash on iOS 15.x.

[tbkka]

To diagnose crashes like this, we need a backtrace of the crashing app and ideally a small project that reproduces the crash.

[AnthonyLatsis]

Reduced example:

protocol P<A> {
  associatedtype A
}
func foo(_: any P<Never>) {}

This should be rejected with Runtime support for parameterized protocol types is only available in ... or newer when targeting OSs with 5.6 or older runtimes.