[SR-4451] type(of:) behaviour change from Swift 3.0.2 to Swift 3.1.

[swift-ci]

Previous ID	SR-4451
Radar	rdar://problem/31404284
Original Reporter	razvandub (JIRA User)
Type	Bug

Attachment: Download

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug, StarterBug, TypeChecker
Assignee	None
Priority	Medium

md5: 59a922e46e7486ff5d399c2af0e0d2d8

Issue Description:

It seems that the behaviour of "type(of: )" has changed from Swift 3.0.2 to Swift 3.1 w.r.t. optional Any? closure parameters referenced as Any.

"type(of: oItem) as? T.Type" below returns "__NSCFString.Type" when using Swift 3.0.2 compiler and "nil" when using Swift 3.1 compiler.

import Foundation

internal extension Set where Element: NSObject {
    
    internal func items <T: NSObject> (ofType itemType: T.Type) -> Set<T>? {
        return NSSet(set: self).filtered(using: NSPredicate { (oItem: Any /* Note Any instead of Any? */, _) -> Bool in
            return nil != (type(of: oItem) as? T.Type)  // Swift 3.0.2 => true, Swift 3.1 => false.
            //                        return oItem is T // Swift 3.0.2 => true, Swift 3.1 => true.
        }) as? Set<T>
    }
}

let stringsOfTypeNSObject = (["1", "2"] as Set<NSString>).items(ofType: NSObject.self)

print(stringsOfTypeNSObject ?? []) // Swift 3.0.2 => [1, 2], Swift 3.1 => [].

[swift-ci]

Comment by Razvan Popescu (JIRA)

Attached playground.

[belkadan]

I suspect it is our boxing behavior that's changed. @jckarter, thoughts?

[jckarter]

If oItem contains an Optional then type(of: oItem) would give Optional<T>, which is never an NSObject.Type. Is that what's going on?

[swift-ci]

Comment by Razvan Popescu (JIRA)

@belkadan, @jckarter, thanks for the replies. @jckarter, yes, I would have expected that as well yet, however, if "NSPredicate" is constructed with

[jckarter]

Yeah, it seems to me like that warning ought to fire here.

[jckarter]

@swift-ci create

[rudkx]

razvandub (JIRA User), if I understand correctly, the concern is that we do not emit a warning for the function conversion in something like this:

struct P {
  init(_ fn: (Any?, [String : Any]?) -> Bool) {}
}

let p = P { (a: Any, _) -> Bool in }

is that correct?

[swift-ci]

Comment by Razvan Popescu (JIRA)

@rudkx, the core issue was the change in type(of: oItem) behaviour/output when switching from Swift 3.0.2 to Swift 3.1+. Based on @jckarter's reply above, it looks like it may have been a Swift 3.0.2 bug. If that's the case and the Swift 3.1+ type(of: oItem) behaviour is correct, then yes, I would have expected a warning there. Thanks.