Segmentation fault: 11 when trying to resolve generic function with KeyPath

Originator:anton.siliuk
Number:rdar://50271944 Date Originated:April 27 2019
Status:Open Resolved:-
Product:Xcode, swift Product Version:10.2.1, 5.0
Classification:Bug Reproducible:Always
 
Summary:
In comment you can see an example of generic function with KeyPath. And Compiler fails to compile it.
This reproduces on lates swift 5 and on older swift 4.2 and Xcode 10.1

Can be fixed by making `label` a `var` property

Steps to Reproduce:
1. Open example project
2. Try to run it

Expected Results:
Example project compiles

Actual Results:
Compilation segfaults with error

Version/Build:
Xcode 10.2.1 swift 5

Comments

Code that produces compile error

class ViewController: UIViewController { 

override func viewDidLoad() {
    super.viewDidLoad()
    Style<ViewController>.myStyle.apply(self)

    label.text = "Hello world"
    label.translatesAutoresizingMaskIntoConstraints = false
    NSLayoutConstraint.activate([
        label.centerXAnchor.constraint(equalTo: view.centerXAnchor),
        label.centerYAnchor.constraint(equalTo: view.centerYAnchor)
    ])
}

fileprivate let label = UILabel()

}

struct Style { let apply: (V) -> V }

extension Style where V: UILabel { 

static func textColor(_ color: UIColor) -> Style {
    return Style { $0.textColor = color; return $0 }
}

}

extension Style { 

static func substyle<V2: AnyObject>(_ keyPath: KeyPath<V, V2>, style: Style<V2>) -> Style {
    return Style { _ = style.apply($0[keyPath: keyPath]); return $0 }
}

}

extension Style where V: ViewController { 

static var myStyle: Style {
    return substyle(\.label, style: .textColor(.red))
}

}

By anton.siliuk at April 27, 2019, 6:44 p.m. (reply...)

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