Self-contained example:

import CoreText
func test(name: CFTypeRef, fontSize: CGFloat) {
  var font = name
  font = CTFontCreateWithName(font as! CFString, fontSize, nil)
}

Output:

<stdin>:4:36: warning: treating a forced downcast to 'CFString' as optional will never produce 'nil'
  font = CTFontCreateWithName(font as! CFString, fontSize, nil)
                                   ^
<stdin>:4:38: note: use 'as?' to perform a conditional downcast to 'CFString'
  font = CTFontCreateWithName(font as! CFString, fontSize, nil)
                                     ^
                                     ?
<stdin>:4:31: note: add parentheses around the cast to silence this warning
  font = CTFontCreateWithName(font as! CFString, fontSize, nil)
                              ^
                              (                )

I'm not entirely sure this is wrong. It's not unlikely that in an optional context you'd want to pass through nil if the downcast failed, and the warning tells you how to silence it if that's not what you meant to do.

But "forced downcast will never produce 'nil'" is just the normal and expected behavior of the Swift language. It is a known fact that will never be false. Why should we get a "this fact will never be false" warning?

As to the fix-it suggestions, you will find the 1st one is just wrong if you try it because:

Conditional downcast to CoreFoundation type 'CFString' will always succeed.

That's true, we don't have a way to do conditional downcasts for CF types right now. We could check for that before emitting the first note.

Warnings aren't always meant to catch mistaken intent. Sometimes they're meant to catch likely typos, especially if they're the sort that could easily be missed in a code review. I'd put this in that category.