[SR-8125] Swift 4.2 exhaustivity checker regression

[sharplet]

Previous ID	SR-8125
Radar	rdar://problem/41525746
Original Reporter	@sharplet
Type	Bug
Status	Closed
Resolution	Done

Environment

Xcode Version 10.0 beta 2 (10L177m)

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug, 4.2Regression
Assignee	@belkadan
Priority	Medium

md5: 151824427e3aec5ee74b46aec98a0730

is duplicated by:

• SR-8197 REGRESSION: Switch exhaustiveness handles Never separately from other no-valued types

Issue Description:

The following code compiles in Swift 4.1, but fails with an exhaustivity error in Swift 4.2:

extension Signal where Value: ResultProtocol, Error == NoError {
    func dematerializeResults() -> Signal<Value.Value, Value.Error> {
        return .init { observer, lifetime in
            lifetime += self.observe { event in
                switch event {
                case let .value(value):
                    value.result.analysis(
                        ifSuccess: { value in
                            observer.send(value: value)
                        }, ifFailure: { error in
                            observer.send(error: error)
                        }
                    )
                case .completed:
                    observer.sendCompleted()
                case .interrupted:
                    observer.sendInterrupted()
                }
            }
        }
    }
}

The Event enum has a failure case which in this case has an associated value of type NoError, and thus is impossible to construct.

Reproduced on this branch in the ReactiveSwift repository: https://github.com/ReactiveCocoa/ReactiveSwift/tree/as-exhaustivity-bug

[belkadan]

I wonder if this is fallout from unknown case.

@swift-ci create

[belkadan]

#17680

[belkadan]

4.2: #17690

[AnnaZaks]

@sharplet, Could you verify if the problem is fixed and if so move the JIRA to "Closed"?
Thanks!
Anna

[sharplet]

This compiled for me on the latest Xcode beta, thanks!