[SR-6419] `NotificationCenter.addObserver` of SCLF with trailing closure syntax cannot be used on Swift 4.0.2

[ikesyo]

Previous ID	SR-6419
Radar	None
Original Reporter	@ikesyo
Type	Bug
Status	Resolved
Resolution	Done

Additional Detail from JIRA

Votes	0
Component/s	Foundation
Labels	Bug
Assignee	@ikesyo
Priority	Medium

md5: 1cb775e2d2830c261d8a0e8e57a0fbcd

Issue Description:

In Swift 4.0.2 NotificationCenter.addObserver(forName:object:queue:usingBlock🙂 is renamed to addObserver(forName:object:queue:using🙂 and the old API is kept as an obsoleted API. The obsoleted symbol makes it ambiguous to use the API with trailing closure syntax:

self.token = self.notificationCenter.addObserver(forName: nil, object: nil, queue: nil) { [weak self] n in
    // linux-swift gets confused by .append(n)
    self?.observedNotifications.append(n)
}

This is found at Quick/Nimble#481

/home/travis/build/lvsti/MockSix/.build/checkouts/Nimble.git--3756397004363768916/Sources/Nimble/Matchers/PostNotification.swift:18:27: error: ambiguous use of 'addObserver'
        self.token = self.notificationCenter.addObserver(forName: nil, object: nil, queue: nil) { [weak self] n in
                          ^

Foundation.NotificationCenter:9:15: note: found this candidate
    open func addObserver(forName name: Foundation.NSNotification.Name?, object obj: Any?, queue: Foundation.OperationQueue?, usingBlock block: @escaping (Foundation.Notification) -> Swift.Void) -> NSObjectProtocol
              ^

Foundation.NotificationCenter:10:15: note: found this candidate
    open func addObserver(forName name: Foundation.NSNotification.Name?, object obj: Any?, queue: Foundation.OperationQueue?, using block: @escaping (Foundation.Notification) -> Swift.Void) -> NSObjectProtocol
              ^

Usually we don't keep old (pre-renamed) symbols (e.g. #1315 so the obsoleted API should be removed to make it unambiguous.

[belkadan]

@phausler There was a dup of this for macOS, right?

[ikesyo]

@available(*, obsoleted: 4.0) is not appropriate and @available(swift, obsoleted: 4.0) should be used instead.

[ikesyo]

I was requested to use @available(*, unavailable) instead of @available(swift, obsoleted: 4.0).

[ikesyo]

So the actual issue here is @available(*, obsoleted: 4.0) means iOS 4.0, macOS 4.0, tvOS 4.0, watchOS 4.0 and does not mean Swift 4.0.

[belkadan]

That's hilarious. We should definitely be rejecting that!

[alblue]

This has been merged into the master branch, which should be part of the 4.1 release.