duplicates:

• SR-7884 Overload resolution picks optional variant even when value is not optional

Issue Description:

Consider the following program:

import Foundation

let sequence: NSArray? = nil
if let url = sequence?.lazy.compactMap({ $0 as? NSURL }).first {
    print(url)
}

The swiftc that comes with Xcode 9.4 chooses type NSURL for the url variable.

The swiftc that comes with Xcode 10 beta chooses type ((NSURL) throws -> Bool) throws -> NSURL? for the url variable. (It's using the type of the first(where: ) method instead of the first property.)