Open Radar

 
Summary:
If, in a dynamic framework, an extension to UIViewController declares a computed property such as `navigationBar`, whose name may collide with a subclass of UIViewController (UINavigationController, in this case), this will cause a crash.

Steps to Reproduce:
1. make a framework (“CrashKit”), in it, add the following code.

import UIKit

extension UIViewController {
    public var navigationBar: UINavigationBar? {
        return nil
    }
}

2. In the same Xcode project, import the framework from step 1 and make a subclass to UINavigationController, present an instance of it. For example:

import CrashKit
import UIKit

open class XX: UINavigationController {
    open override func viewDidLoad() {
        super.viewDidLoad()
        print(">>>", self.navigationBar)
    }
}

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?

    func application(_  application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
        self.window = UIWindow(frame: UIScreen.main.bounds)
        let rootVC = XX()
        self.window?.rootViewController = rootVC
        self.window?.makeKeyAndVisible()
        return true
    }
}

3. run the project, observe that a crash happens with stack trace similar to this:

2017-09-05 18:34:17.991455-0700 Crash[81376:11788976] -[Crash.XX decodeObjectForKey:]: unrecognized selector sent to instance 0x7f8922823400
2017-09-05 18:34:18.000151-0700 Crash[81376:11788976] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[Crash.XX decodeObjectForKey:]: unrecognized selector sent to instance 0x7f8922823400'
*** First throw call stack:
(
	0   CoreFoundation                      0x00000001122cf1cb __exceptionPreprocess + 171
	1   libobjc.A.dylib                     0x000000010e9a9f41 objc_exception_throw + 48
	2   CoreFoundation                      0x000000011234f914 -[NSObject(NSObject) doesNotRecognizeSelector:] + 132
	3   UIKit                               0x000000010f1967a5 -[UIResponder doesNotRecognizeSelector:] + 295
	4   CoreFoundation                      0x0000000112252178 ___forwarding___ + 1432
	5   CoreFoundation                      0x0000000112251b58 _CF_forwarding_prep_0 + 120
	6   UIKit                               0x000000010f10eb89 -[UIViewController initWithCoder:] + 311
	7   Crash                               0x000000010e0912f2 _T05Crash14ViewControllerCACSgSo7NSCoderC5coder_tcfc + 66
	8   Crash                               0x000000010e091544 _T05Crash2XXC11viewDidLoadyyF + 212
	9   Crash                               0x000000010e091664 _T05Crash2XXC11viewDidLoadyyFTo + 36
	10  UIKit                               0x000000010f113fe7 -[UIViewController loadViewIfRequired] + 1235
	11  UIKit                               0x000000010f114434 -[UIViewController view] + 27
	12  UIKit                               0x000000010efeaa8b -[UIWindow addRootViewControllerViewIfPossible] + 122
	13  UIKit                               0x000000010efeb17d -[UIWindow _setHidden:forced:] + 294
	14  UIKit                               0x000000010effe01f -[UIWindow makeKeyAndVisible] + 42
	15  Crash                               0x000000010e09228d _T05Crash11AppDelegateC11applicationSbSo13UIApplicationC_s10DictionaryVySC0E16LaunchOptionsKeyVypGSg022didFinishLaunchingWithH0tF + 589
	16  Crash                               0x000000010e09250a _T05Crash11AppDelegateC11applicationSbSo13UIApplicationC_s10DictionaryVySC0E16LaunchOptionsKeyVypGSg022didFinishLaunchingWithH0tFTo + 186
	17  UIKit                               0x000000010ef70dfa -[UIApplication _handleDelegateCallbacksWithOptions:isSuspended:restoreState:] + 267
	18  UIKit                               0x000000010ef72857 -[UIApplication _callInitializationDelegatesForMainScene:transitionContext:] + 4105
	19  UIKit                               0x000000010ef77ce5 -[UIApplication _runWithMainScene:transitionContext:completion:] + 1720
	20  UIKit                               0x000000010f325118 __111-[__UICanvasLifecycleMonitor_Compatability _scheduleFirstCommitForScene:transition:firstActivation:completion:]_block_invoke + 924
	21  UIKit                               0x000000010f6e8e57 +[_UICanvas _enqueuePostSettingUpdateTransactionBlock:] + 153
	22  UIKit                               0x000000010f324d11 -[__UICanvasLifecycleMonitor_Compatability _scheduleFirstCommitForScene:transition:firstActivation:completion:] + 249
	23  UIKit                               0x000000010f32556f -[__UICanvasLifecycleMonitor_Compatability activateEventsOnly:withContext:completion:] + 668
	24  UIKit                               0x000000010fc625b9 __82-[_UIApplicationCanvas _transitionLifecycleStateWithTransitionContext:completion:]_block_invoke + 262
	25  UIKit                               0x000000010fc62472 -[_UIApplicationCanvas _transitionLifecycleStateWithTransitionContext:completion:] + 444
	26  UIKit                               0x000000010f95f646 __125-[_UICanvasLifecycleSettingsDiffAction performActionsForCanvas:withUpdatedScene:settingsDiff:fromSettings:transitionContext:]_block_invoke + 420
	27  UIKit                               0x000000010fb54e0e _performActionsWithDelayForTransitionContext + 100
	28  UIKit                               0x000000010f95f442 -[_UICanvasLifecycleSettingsDiffAction performActionsForCanvas:withUpdatedScene:settingsDiff:fromSettings:transitionContext:] + 231
	29  UIKit                               0x000000010f6e84b4 -[_UICanvas scene:didUpdateWithDiff:transitionContext:completion:] + 392
	30  UIKit                               0x000000010ef76566 -[UIApplication workspace:didCreateScene:withTransitionContext:completion:] + 523
	31  UIKit                               0x000000010f529c8b -[UIApplicationSceneClientAgent scene:didInitializeWithEvent:completion:] + 369
	32  FrontBoardServices                  0x0000000118b9f374 -[FBSSceneImpl _didCreateWithTransitionContext:completion:] + 338
	33  FrontBoardServices                  0x0000000118ba7e69 __56-[FBSWorkspace client:handleCreateScene:withCompletion:]_block_invoke_2 + 235
	34  libdispatch.dylib                   0x000000011337643c _dispatch_client_callout + 8
	35  libdispatch.dylib                   0x000000011337baf4 _dispatch_block_invoke_direct + 592
	36  FrontBoardServices                  0x0000000118bd376e __FBSSERIALQUEUE_IS_CALLING_OUT_TO_A_BLOCK__ + 24
	37  FrontBoardServices                  0x0000000118bd3424 -[FBSSerialQueue _performNext] + 464
	38  FrontBoardServices                  0x0000000118bd3993 -[FBSSerialQueue _performNextFromRunLoopSource] + 45
	39  CoreFoundation                      0x00000001122722b1 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 17
	40  CoreFoundation                      0x0000000112311d31 __CFRunLoopDoSource0 + 81
	41  CoreFoundation                      0x0000000112256c19 __CFRunLoopDoSources0 + 185
	42  CoreFoundation                      0x00000001122561ff __CFRunLoopRun + 1279
	43  CoreFoundation                      0x0000000112255a89 CFRunLoopRunSpecific + 409
	44  GraphicsServices                    0x00000001171179c6 GSEventRunModal + 62
	45  UIKit                               0x000000010ef797d0 UIApplicationMain + 159
	46  Crash                               0x000000010e092bd7 main + 55
	47  libdyld.dylib                       0x00000001133f2d81 start + 1
	48  ???                                 0x0000000000000001 0x0 + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException


Expected Results:
There shouldn’t be a crash.

Actual Results:
There’s a crash when `navigationBar` is accessed from an `UINavigationController` subclass.

Version:
Version 9.0 beta 6 (9M214v)

Notes:
I’ve attached an sample Xcode project that demonstrates it. Just open and run and you’ll see this problem in action.