Open Radar

 
Summary:
A whole-module-optimization enabled build calls a base-class var instead of the subclassed one

Steps to Reproduce:
In happens in a specific large project and I wasn’t able to reproduce it in a test project, unfortunately.
I’ll give some code sample to explain the set up.

I have a class which includes the following code:
class BaseTransactionEditor: NSViewController, NSTextFieldDelegate {
    var commonViewModel: BaseTransactionEditorViewModel { fatalError("override!") }

override func viewDidAppear() {
// other code
        commonViewModel.newTransaction()
// other code
}

and a subclass like this:
final class PlanTransactionEditor: BaseTransactionEditor, PopoverViewController {
    let viewModel: PlanTransactionViewModel
    override var commonViewModel: BaseTransactionEditorViewModel { return viewModel }

override func viewDidLoad() {
        super.viewDidLoad()
// more code
}

When I launch a build with WMO enabled, Release configuration, upon calling viewDidLoad on the subclass, the application crashes because “fatalError("override!”) executed. I’m attaching the crash log.

Debug build or Release without WMO do not crash.

Expected Results:
Base class should access the subclassed “commonViewModel”

Actual Results:
Base class accesses its own “commonViewModel”

Regression:
Haven’t checked