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[SR-15612] Initializing NSObject inheritant with default parameter values sometimes results in crash. #57908

swift-ci opened this issue Dec 17, 2021 · 0 comments


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@swift-ci swift-ci commented Dec 17, 2021

Previous ID SR-15612
Radar None
Original Reporter VaslD (JIRA User)
Type Bug

Configuration 1 that generated dynamic init for PhoneNumberKit class in PhoneNumberKit:

MacBook Pro (Retina, 15-inch, Mid 2015)

macOS 12.1 (21C52)

Xcode 13.2 (13C90)

Apple Swift version 5.5.2 (swiftlang-1300.0.47.5 clang-1300.0.29.30)

Configuration 2 that generated dynamic init for SessionDelegate class in Alamofire:

MacBook Pro (16-inch, 2019)

macOS 11.4 (20F71)

Xcode 13.0 (13A233)

Apple Swift version 5.4 (swiftlang-1205.0.26.9 clang-1205.0.19.55)

Additional Detail from JIRA
Votes 0
Component/s Compiler
Labels Bug, RunTimeCrash
Assignee None
Priority Medium

md5: ab097cb122fe08360ca130db3553a09b

Issue Description:

If a class inheriting NSObject declares their own inits without overriding super's parameter-less init, and any one of these inits has default values for all parameters, calling the init with default parameter values may result in a runtime crash.

Basically, if I have:

class SomeObject: NSObject {
     var someValue: String

     init(value: String = "SomeObject") {
         self.someValue = value

Somewhere the app crashes at a call site SomeObject() with:

Fatal error: Use of unimplemented initializer 'init()'...

Many third-party libraries do this, for example:

Alamofire: SessionDelegate.swift @ Line 38

PhoneNumberKit: PhoneNumberKit.swift @ Line 24

I cannot reproduce this in a brand-new project, but at least two iOS apps I wrote had encountered this problem. The same project that is compiled several times on different machines may get different results. I think I've found some clues to why this is happening, and a way to reproduce it although not entirely straightforward.

When BUILD_LIBRARY_FOR_DISTRIBUTION is turned on for Alamofire, build that crashes has the following Swift Interface generated:

@objc open class SessionDelegate : ObjectiveC.NSObject {
  public init(fileManager: Foundation.FileManager = .default)
  @objc override dynamic public init()
  @objc deinit

While the build that doesn't crash is missing the dynamic init in Swift Interface:

@objc open class SessionDelegate : ObjectiveC.NSObject {
 public init(fileManager: Foundation.FileManager = .default)
 @objc deinit

So to reproduce, download or write a framework that has a class with all-default-values init. Then archive and generate an XCFramework of it. For Alamofire 5.5.0 the command to create XCFramework from its source directory is:

(Note that you need to turn Build Library for Distribution ON and Skip Intall OFF first for the intended Alamofire target.)

xcodebuild archive -project "Alamofire.xcodeproj" -scheme "Alamofire iOS" -sdk iphoneos -archivePath ./iOS.xcarchive

xcodebuild archive -project "Alamofire.xcodeproj" -scheme "Alamofire iOS" -sdk iphonesimulator -archivePath ./Simulator.xcarchive

xcodebuild -create-xcframework -archive ./Simulator.xcarchive -framework "Alamofire.framework" -debug-symbols "$(pwd)/Simulator.xcarchive/dSYMs" -archive ./iOS.xcarchive -framework "Alamofire.framework" -debug-symbols "$(pwd)/iOS.xcarchive/dSYMs" -output "./Alamofire.xcframework"

Observe if any *.swiftinterface has

@objc override dynamic public init()

for SessionDelegate declaration. If it does, integrating this framework and call

_ = SessionDelegate()

somewhere in the app will crash at runtime.

If the generated framework doesn't have that line, try running the command again on another machine (or at some other time). I have not found exactly what is causing this and how to reproduce it consistently. But since the exactly same code generates different interfaces, I'm fairly certain this is compiler's wrong-doing.

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
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