How to log a warning that shows up as a runtime issue in Xcode?

Question

Xcode 8 or 9 started displaying runtime issues. You see a purple icon at the top of the window, and a list in Issue Navigator, next to buildtime issues like compilation warn

Answer 1

Well, that's a hack, far from ideal, but can by useful to get runtime warnings without having game-over behavior like in assertions or fatal errors:

func runtimeWarning(_ message: String, file: String = #file, line: Int = #line) {
    #if DEBUG
    DispatchQueue.global(qos: .userInteractive).async {
        // If you got here, please check console for more info
        _ = UIApplication.shared.windows
        print("Runtime warning: \(message): file \(file.fileName), line \(line)")
    }
    #endif
}

fileprivate extension String {
    var fileName: String { URL(fileURLWithPath: self).lastPathComponent }
}

Unfortunately this leads to quite a big print to console from Main Thread Checker, also does not show on correct line, but at least you have all info needed in console (including line of code you should check).

Usage and result is very similar to assertionFailure or fatalError:

runtimeWarning("Hi, I'm purple")

leads to message in console:

Runtime warning: Hi, I'm purple: file MyFile.swift, line 10

and this, so you won't miss it: