is duplicated by:

• SR-4697 Damned if you do... (access control)

Issue Description:

With the following code, the Swift compiler complains that func test() in the extension of Y needs to be public because it implements public protocol X, but also want it to be private because protocol Y is private. I think the correct thing to do is to allow public visibility in the extension when it implements a method from a public protocol.

public protocol X {
    func test()
}
private protocol Y: X {
}
extension Y {
    public func test() {}
}
public class Z: X, Y {
}

Below: the two error messages from a playground in Xcode 7.2.1 (7C1002) for the code above. Note that applying the first fix-it causes a new error accompanied by a new fix-it proposing a return to the version above (creating a loop). The second fix-it below generates invalid code with two public attributes before func.

...playground364.swift:7:2: warning: declaring a public instance method for a private protocol
        public func test() {}
        ^~~~~~
        private
...playground364.swift:7:14: error: method 'test()' must be declared public because it matches a requirement in public protocol 'X'
        public func test() {}
                    ^
               public