Rxswift: Crash in MergeBasicSink with Xcode 11.2

[akolov]

Short description of the issue:

I'm getting crashes when using merge() with Xcode 11.2. Same code with 11.1 works fine.

What actually happens:

EXC_BAD_ACCESS (code=1, address=0x0)

``* thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0x0) frame #0: 0x00007fff5132ba49 libswiftCore.dylib_swift_initClassMetadataImpl(swift::TargetClassMetadata, swift::ClassLayoutFlags, unsigned long, swift::TypeLayout const const, unsigned long, bool) + 1337
frame #1: 0x0000000106c0bc46 Testtype metadata completion function for MergeSink at <compiler-generated>:0 frame #2: 0x00007fff51332ced libswiftCore.dylibswift::MetadataCacheEntryBase<(anonymous namespace)::GenericCacheEntry, void const>::doInitialization(swift::ConcurrencyControl&, swift::MetadataCompletionQueueEntry, swift::MetadataRequest) + 285
frame #3: 0x00007fff51329767 libswiftCore.dylibswift_getGenericMetadata + 1527 frame #4: 0x0000000106c0bc90 Testtype metadata accessor for MergeSink at :0
frame #5: 0x00007fff513420e1 libswiftCore.dylib(anonymous namespace)::DecodedMetadataBuilder::createBoundGenericType(swift::TargetContextDescriptor<swift::InProcess> const*, llvm::ArrayRef<swift::TargetMetadata<swift::InProcess> const*>, swift::TargetMetadata<swift::InProcess> const*) const + 257 frame #6: 0x00007fff51340e7e libswiftCore.dylibswift::Demangle::TypeDecoder<(anonymous namespace)::DecodedMetadataBuilder>::decodeMangledType(swift::Demangle::Node) + 3726
frame #7: 0x00007fff5133e32b libswiftCore.dylibswift_getTypeByMangledNodeImpl(swift::MetadataRequest, swift::Demangle::Demangler&, swift::Demangle::Node*, void const* const*, std::__1::function<swift::TargetMetadata<swift::InProcess> const* (unsigned int, unsigned int)>, std::__1::function<swift::TargetWitnessTable<swift::InProcess> const* (swift::TargetMetadata<swift::InProcess> const*, unsigned int)>) + 411 frame #8: 0x00007fff5133e132 libswiftCore.dylibswift::swift_getTypeByMangledNode(swift::MetadataRequest, swift::Demangle::Demangler&, swift::Demangle::Node, void const* const, std::__1::function const (unsigned int, unsigned int)>, std::__1::function const* (swift::TargetMetadata const, unsigned int)>) + 482
frame #9: 0x00007fff5133e6bb libswiftCore.dylibswift_getTypeByMangledNameImpl(swift::MetadataRequest, llvm::StringRef, void const* const*, std::__1::function<swift::TargetMetadata<swift::InProcess> const* (unsigned int, unsigned int)>, std::__1::function<swift::TargetWitnessTable<swift::InProcess> const* (swift::TargetMetadata<swift::InProcess> const*, unsigned int)>) + 779 frame #10: 0x00007fff5133c1c2 libswiftCore.dylibswift::swift_getTypeByMangledName(swift::MetadataRequest, llvm::StringRef, void const const, std::__1::function const (unsigned int, unsigned int)>, std::__1::function const* (swift::TargetMetadata const, unsigned int)>) + 482
frame #11: 0x00007fff51330d7a libswiftCore.dylibgetSuperclassMetadata(swift::TargetClassMetadata<swift::InProcess>*, bool) + 330 frame #12: 0x00007fff5132b53b libswiftCore.dylib_swift_initClassMetadataImpl(swift::TargetClassMetadata, swift::ClassLayoutFlags, unsigned long, swift::TypeLayout const* const, unsigned long, bool) + 43
frame #13: 0x0000000106c0b905 Testtype metadata completion function for MergeBasicSink at <compiler-generated>:0 frame #14: 0x00007fff51332ced libswiftCore.dylibswift::MetadataCacheEntryBase<(anonymous namespace)::GenericCacheEntry, void const>::doInitialization(swift::ConcurrencyControl&, swift::MetadataCompletionQueueEntry, swift::MetadataRequest) + 285
frame #15: 0x00007fff51329767 libswiftCore.dylibswift_getGenericMetadata + 1527 frame #16: 0x0000000106c0b4b0 Testtype metadata accessor for MergeBasicSink at :0

• frame #17: 0x0000000106c09e24 TestMerge.run<SourceSequence>(observer=0x0000600002b249c0, cancel=0x0000600002421260, self=0x0000600000f3cea0) at Merge.swift:580:20 frame #18: 0x0000000106c2e535 TestProducer.subscribe(observer=0x0000600002b249c0, self=0x0000600000f3cea0) at Producer.swift:18:44
  frame #19: 0x0000000106bfa690 TestMap.run<SourceType>(observer=0x000060000017a640, cancel=0x0000600002420f50, self=0x000060000017a4f0) at Map.swift:99:41 frame #20: 0x0000000106c2ee28 Testclosure #1 in Producer.subscribe(_0=() @ scalar, self=0x000060000017a4f0, observer=0x000060000017a640) at Producer.swift:26:48
  frame #21: 0x0000000106c2ef3c Testpartial apply for closure #1 in Producer.subscribe<A>(_:) at <compiler-generated>:0 frame #22: 0x0000000106bcc1cc Testthunk for @escaping @callee_guaranteed () -> (@out Disposable) at :0
  frame #23: 0x0000000106c2ef91 Testpartial apply for thunk for @escaping @callee_guaranteed () -> (@out Disposable) at <compiler-generated>:0 frame #24: 0x0000000106bb875f TestCurrentThreadScheduler.schedule(state=() @ 0xffffffffffffffff, action=0x0000000106c2ef80 Testpartial apply forwarder for reabstraction thunk helper from @escaping @callee_guaranteed () -> (@out RxSwift.Disposable) to @escaping @callee_guaranteed (@in_guaranteed ()) -> (@out RxSwift.Disposable) at <compiler-generated>, self=0x0000600000d282b0) at CurrentThreadScheduler.swift:101:30 frame #25: 0x0000000106c2e714 TestProducer.subscribe(observer=0x000060000017a640, self=0x000060000017a4f0) at Producer.swift:24:52
  frame #26: 0x0000000106c1633d TestObservableType.subscribe(on=0x0000000106d122b0 Testpartial apply forwarder for closure #1 (RxSwift.Event) -> () in (extension in RxCocoa):RxSwift.ObservableType.(bind in _F14B11F29E4023218E8359F9EC4A42AD)(to: Swift.Array) -> RxSwift.Disposable at , self=0x000060000017a4f0) at ObservableType+Extensions.swift:25:40
  frame #27: 0x0000000106d11983 TestObservableType.bind<Self>(observers=1 value, self=0x000060000017a4f0) at Observable+Bind.swift:42:21 frame #28: 0x0000000106d118bd TestObservableType.bind(observers=1 value, self=0x000060000017a4f0) at Observable+Bind.swift:20:21
  frame #29: 0x0000000106b3dafc TestAppDelegate.application(application=0x00007fcb08c00080, launchOptions=nil, self=0x0000600000d08150) at AppDelegate.swift:27:6 frame #30: 0x0000000106b3e4b4 Test@objc AppDelegate.application(_:didFinishLaunchingWithOptions:) at :0
  frame #31: 0x00007fff478467a8 UIKitCore-[UIApplication _handleDelegateCallbacksWithOptions:isSuspended:restoreState:] + 232 frame #32: 0x00007fff478481b7 UIKitCore-[UIApplication _callInitializationDelegatesWithActions:forCanvas:payload:fromOriginatingProcess:] + 3980
  frame #33: 0x00007fff4784dd06 UIKitCore-[UIApplication _runWithMainScene:transitionContext:completion:] + 1281 frame #34: 0x00007fff46f84422 UIKitCore-[_UISceneLifecycleMultiplexer completeApplicationLaunchWithFBSScene:transitionContext:] + 179
  frame #35: 0x00007fff4784a2a6 UIKitCore-[UIApplication _compellApplicationLaunchToCompleteUnconditionally] + 59 frame #36: 0x00007fff4784a5a5 UIKitCore-[UIApplication _run] + 754
  frame #37: 0x00007fff4784fb68 UIKitCoreUIApplicationMain + 1621 frame #38: 0x0000000106b3eaeb Testmain at AppDelegate.swift:14:7
  frame #39: 0x00007fff51a1dc25 libdyld.dylibstart + 1 frame #40: 0x00007fff51a1dc25 libdyld.dylibstart + 1

**Self contained code example that reproduces the issue**:

```swift
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
    let aBinder = Binder<String>(self) { _, str in
      print(str)
    }

    _ = Observable.of(
      NotificationCenter.default.rx.notification(UIApplication.willResignActiveNotification),
      NotificationCenter.default.rx.notification(UIApplication.didBecomeActiveNotification)
    )
    .merge()
    .map { _ in "test" }
    .bind(to: aBinder)

    return true
}

Sample project is attached: Test.zip

RxSwift/RxCocoa/RxBlocking/RxTest version/commit

5.0.1

Platform/Environment

• [x] iOS
• [ ] macOS
• [ ] tvOS
• [ ] watchOS
• [ ] playgrounds

How easy is to reproduce? (chances of successful reproduce after running the self contained code)

• [x] easy, 100% repro
• [ ] sometimes, 10%-100%
• [ ] hard, 2% - 10%
• [ ] extremely hard, %0 - 2%

Xcode version:

Version 11.2 (11B52)

Installation method:

• [x] SPM
• [ ] CocoaPods
• [ ] Carthage
• [ ] Git submodules

I have multiple versions of Xcode installed:
(so we can know if this is a potential cause of your issue)

• [ ] yes (which ones)
• [x] no

Level of RxSwift knowledge:
(this is so we can understand your level of knowledge
and formulate the response in an appropriate manner)

• [ ] just starting
• [ ] I have a small code base
• [x] I have a significant code base

[achernoprudov]

Related to #2094

[tcldr]

As mentioned in other issue thread – caused by SR-11564. (https://bugs.swift.org/browse/SR-11564)

[freak4pc]

🤦‍♂

[kzaher]

Usually when somebody says

Xcode 11.2. Same code with 11.1 works fine.

that means it's not our bug :)

[RamblinWreck77]

Temporary workaround that fixes it:

-Go to Project Target/Build Settings
-"Dead Code Stripping" to NO

[akolov]

Confirming that setting Dead Code Stripping to NO works. Otherwise crashes happen even when compiled with Xcode 11.1 after submitting to TestFlight.

[sree127]

I'm not able to run XCTests on Xcode 11.1,11.2 as it crashes from debounce with Thread 1: EXC_BAD_ACCESS (code=1, address=0x0)

Dead Code Stripping is set to NO
Anyone else experiencing the same issue or any work around for this case? (It works in Xcode 10.3)

[brooksdubois]

Seeing this issue with a very simple code sample built using Carthage

Dead Code Stripping set to No

var updateString = BehaviorRelay<String>(value: "")

@IBOutlet weak var fetchButton: UIButton!
@IBOutlet weak var outputLabel: UILabel!

@IBAction func buttonTapped(_ sender: UIButton) {
  updateString.accept("Updated")
}
override func viewDidLoad() {
  super.viewDidLoad()
  updateString.bind(to: outputLabel.rx.text).disposed(by: disposeBag)
}

Crashes me immediately while initializing the Binder

[freak4pc]

Unfortunately this is a bug with SPM. People already filed a bug and I hope it would be fixed soon, but there's nothing much we can do as a framework.