I'm getting this warning in Xcode 10.2:
Conversion to Swift 5 is available
When I click this error, it's opening this window:
When we click Next what will happen?
the current version of swift is swift5 which is only supported in Xcode 10.2 and you are using another version like swift4 or swift4.2 in xcode 10.2. This warning means that a new version of Swift is available if you click this warning you will receive a pop up and will ask for permission to convert your code to latest version of swift (which is now swift5). if you click yes to the pop up Xcode automatically convert your code to newest version of swift(which is swift5 in your case)