Can't use storyboard custom instantiated window controller

I am getting what feels like a bug when trying to custom instantiate a window controller from a storyboard. I am using NSStoryboard.instantiateController(identifier:creator:), which is a new function as of MacOS 10.15. The block of code in question is:

let mainWC = storyboard.instantiateController(identifier: "id") { aDecoder in  
    MainWindowController(coder: aDecoder)  
} 

I have SUCCESSFULLY used basically this exact code for custom instantiating the main view controller, and just assigning that view to a new window and a new window controller. That works fine. I can also instantiate the window controller the old fashioned way without custom initialization with instantiateController(identifier:). But when I try the above code for custom instantiation of the window controller I end up with the following error:

Assertion failure in -[NSClassSwapper _createControllerForCreator:coder:]... Custom instantiated controller must call -[super initWithCoder:]

Note that both my custom view controller class (which works) and my custom window controller class MainWindowController (which doesn't work) have implemented the trivial initializer:

required init?(coder: NSCoder) {  
    super.init(coder: coder)  
}

I know that this functionality is new as of OS 10.15, but the documentation says it should work for window controllers AND view controllers, and the error message does not make any sense to me.

I hit the same problem, I thought about it a bit and here is how I worked around it.

First, why do I need this for ? I wanted to inject some dependencies to my view controller hierarchy before it's built from the Storyboard. I guess that's what the API is intended to. But then, would that method be working, how would I pass the injection information down the view controller hierarchy ?

So, as the method is working without bug for view controllers, I decided to inject the information directly at the root view controller.

So, I have in my storyboard :

• A window controller scene named "my-window-controller", which window just points to an empty view controller.
• A view controller scene named "root-view-controller", where all the view hierarchy is described.

And wherever I want to create that view controller, I just do :

func instanciateWindowController(storyboard: NSStoryboard) -> NSWindowController {

    //  Load the (empty) window controller scene
    let wcSceneIdentifier   = NSStoryboard.SceneIdentifier("my-window-controller")
    let windowController    = storyboard.instantiateController(withIdentifier: wcSceneIdentifier)
            as! NSWindowController

    //  Load the root view controller using the creator trick to inject dependencies
    let vcSceneIdentifier   = NSStoryboard.SceneIdentifier("root-view-controller")
    let viewController      = storyboard.instantiateController(identifier: vcSceneIdentifier,
                                                               creator: { coder in
        return MyOwnViewController.init(coder: coder,
                                        text:   "Victoire !") // just pass here your injection info
    })

    //  Associate the window controller and the root view controller
    windowController.contentViewController  = viewController

    return windowController
}

with

class MyOwnViewController: MSViewController {
    init?(coder:   NSCoder,
          text:    String) { // receive here the injection information
        print(text) // use the injection information here
        super.init(coder: coder)
    }

    // Not used, but required
    required init?(coder:   NSCoder) {
        super.init(coder: coder)
    }
}