swiftui_non_rendering_view_with_preferences.swift

// BUG: FB7569572

struct GeometrySizeKey: PreferenceKey {
  static func reduce(value: inout CGSize?, nextValue: () -> CGSize?) {
    value = nextValue()
  }
}

extension View {
  func readGeometrySize() -> some View {
    background(
      GeometryReader { proxy in
        // This view can't and won't ever be rendered. 🥳

        // ✅ Solution that works as a workaround, but isn't intuitive:

//        ZStack<Never?>
//          .init { .none }
//          .preference(key: GeometrySizeKey.self, value: proxy.size)

        // ❌ Solution that should work!
        Optional<Never>
          .none
          .preference(key: GeometrySizeKey.self, value: proxy.size)
      }
    )
  }
}

extension CGSize {
  var max: CGFloat {
    Swift.max(width, height)
  }
}

struct ContentView: View {
  @State var size: CGSize?
  var body: some View {
    let view = Text("Some Text")
      .fixedSize()
      .padding(10)
      .readGeometrySize()
      .frame(width: size?.max, height: size?.max)
      .background(Circle().fill(Color.blue))
      .onPreferenceChange(GeometrySizeKey.self) { size in
        self.size = size
      }
    return VStack { view; view }
  }
}

struct ContentView_Previews: PreviewProvider {
  static var previews: some View {
    ContentView()
  }
}