[SR-6970] The flatMap() deprecation warning in Swift 4.1 doesn't specify version number

[nicklockwood]

Previous ID	SR-6970
Radar	rdar://problem/37393816
Original Reporter	@nicklockwood
Type	Bug

Additional Detail from JIRA

Votes	0
Component/s	Standard Library
Labels	Bug
Assignee	@moiseev
Priority	Medium

md5: e7313a190de8c10a8076466706410906

Issue Description:

The deprecation warning for flatMap() doesn't specify which version of Swift the change takes effect from:

@available(*, deprecated, renamed: "compactMap(_:)", message: "Please use compactMap(_:) for the case where closure returns an optional value")

This makes it impossible to write a polyfill for older Swift versions (such as the code below) without triggering the warning in Xcode 9.3:

#if !swift(>=4.1)
extension Array {
func compactMap<T>(_ transform: (Element) throws -> T?) rethrows -> [T] {
return try flatMap(transform)
}
}
#endif

[airspeedswift]

@swift-ci create

[moiseev]

#14605

[moiseev]

For 4.1 branch: #14615