[SR-10337] Swift 5 regression: Incorrect type cast from AnyObject to incompatible NSObject subclass.

[swift-ci]

Previous ID	SR-10337
Radar	rdar://problem/49698830
Original Reporter	Leitch (JIRA User)
Type	Bug
Status	Closed
Resolution	Done

Environment

Xcode 10.2 (10E125)

Apple Swift version 5.0 (swiftlang-1001.0.69.5 clang-1001.0.46.3)
Target: x86_64-apple-darwin18.5.0

Additional Detail from JIRA

Votes	0
Component/s
Labels	Bug, 5.0Regression, Runtime
Assignee	None
Priority	Medium

md5: 115bba5912ffd2e281835116b906c630

Issue Description:

The following code crashes in Xcode 10.2 as the model is incorrectly cast to an NSManagedObject instance:

Unrecognized selector -[__lldb_expr_52.MyModel objectID]

This is not a problem in Xcode 10.1.

import CoreData

public protocol MyProtocol: class {}
public class MyModel: MyProtocol {}

let model: AnyObject = MyModel()

func perform() {
    guard let managedModel = model as? (NSManagedObject & MyProtocol) else { return }
    print(managedModel.objectID)
}

perform()

[swift-ci]

Comment by Ian Leitch (JIRA)

Actually this doesn't appear to be unique to just NSManagedObject, it's an issue for any NSObject subclass.

[swift-ci]

Comment by Ian Leitch (JIRA)

AnyObject appears to be the culprit, the snippet works as expected when using just Any.

[theblixguy]

Reproduced on 5.1 as well:

2019-04-08 16:22:52.727 swift[75171:9957983] *** NSForwarding: warning: object 0x7fc281d4e2a0 of class 'whats_wrong.MyModel' does not implement methodSignatureForSelector: -- trouble ahead
Unrecognized selector -[whats_wrong.MyModel objectID]

[belkadan]

cc @mikeash

[mikeash]

Most curious! Thank you for the small reproducer.

[swift-ci]

Comment by Ian Leitch (JIRA)

This is also an issue when running 4.2 compatibility mode.

[belkadan]

Yeah, that's a compilation-time setting. You're still running with a Swift 5.0 runtime and standard library in that case.

[swift-ci]

Comment by Ian Leitch (JIRA)

@belkadan Thanks for pointing that out, I didn't realize it was a compile-time only setting.