Swift: missing _OBJC_CLASS_$_RvmProduct_PurchaseOption case

issue#813 was reported as an issue with storekit2 bindings.

Terminating app due to uncaught exception ‘NSInvalidArgumentException’, reason: ‘+[missing_RvmProduct_PurchaseOption appAccountToken:]: unrecognized selector sent to class 0x1332748a0’

With comments that simulator works but app fails on real device.
Lets investigate.

Background

First if all RvmProduct_PurchaseOption is ObjectiveC wrapper around pure swift class Product.PurchaseOption and it looks like bellow:

@available(iOS 15.0, macOS 12.0, tvOS 15.0, watchOS 8.0, visionOS 1.0, *)
extension RvmProduct {
    @objc(RvmProduct_PurchaseOption)
    public class PurchaseOption : NSObject {
        let raw: Product.PurchaseOption
        init(raw: Product.PurchaseOption) {
            self.raw = raw
        }
        ....
    }
}

It has all required @objc annotations and should be available.

missing_RvmProduct_PurchaseOption

Exception report class with missing_ prefix, means that objc_getClass was not able to resolve RvmProduct_PurchaseOption and stub was added instead(it’s a workaround for missing intermediate classes]). objc_getClass its ObjectiveC runtime API that returns pointer to class by its name. Class is available to runtime if:

• from _OBJC_CLASS_$_ClassName structure that compiler stores in binary;
• or class is created runtime using objc_allocateClassPair API.

Class should be available in binary, checking both iphone and simulator versions:

nm -g StoreKitRvm.xcframework/ios-arm64/StoreKitRvm.framework/StoreKitRvm | grep 'OBJC_CLASS_$_RvmProduct_PurchaseOption'
nm -g StoreKitRvm.xcframework/ios-arm64_x86_64-simulator/StoreKitRvm.framework/StoreKitRvm | grep 'OBJC_CLASS_$_RvmProduct_PurchaseOption'
0000000000049ba0 S _OBJC_CLASS_$_RvmProduct_PurchaseOption

Symbol is missing in iphone version but is present in simulator’s that matches initial issue description.

Tracking down the issue

Long story short. It was isolated to following minimal conditions to reproduce the issue:

• targeting iphoneos;
• targeting ios12 -target arm64-apple-ios12 (targeting ios13 doesn’t have an issue);
• class contains property of type that belongs to higher iOS version than compilation target;

Minimal code to reproduce:

import Foundation
import StoreKit

@available(iOS 15.0, *)
@objc(RvmProduct_PurchaseOption) public class RvmProduct_PurchaseOption: NSObject  {
     let raw: Product.PurchaseOption
     init(raw: Product.PurchaseOption) {
        self.raw = raw 
     }
}

And command lines for demonstration:

swiftc -c test.swift -sdk `xcrun --sdk iphoneos --show-sdk-path` -target arm64-apple-ios12 -o arm64-iphone-12.o 
swiftc -c test.swift -sdk `xcrun --sdk iphoneos --show-sdk-path` -target arm64-apple-ios13 -o arm64-iphone-13.o 
swiftc -c test.swift -sdk `xcrun --sdk iphonesimulator --show-sdk-path` -target arm64-apple-ios12.0-simulator -o arm64-sim.o
nm ./arm64-iphone-12.o | grep _OBJC_CLASS_  
nm ./arm64-iphone-13.o | grep _OBJC_CLASS_  
                 U _OBJC_CLASS_$_NSObject
0000000000001758 S _OBJC_CLASS_$_RvmProduct_PurchaseOption
nm ./arm64-sim.o | grep _OBJC_CLASS_  
                 U _OBJC_CLASS_$_NSObject
0000000000001728 S _OBJC_CLASS_$_RvmProduct_PurchaseOption

Bottom line

It is looks like a bug of swift compiler. It is big question from other side why target ios12 when using ios15.
As a fix it is enough to target more recent version.

Opened a topic on forum.swift.org to see if there will be any insights.

Happy coding