SwiftUI/AttributeGraph bug?

SwiftUIMinimalPickerBugSampleApp.swift

import SwiftUI
import SwiftData

@Model
final class Container {
    var box: BoxInstance?
    var shape: ShapeInstance?

    init(box: BoxInstance?, shape: ShapeInstance?) {
        self.box = box
        self.shape = shape
    }
}

@Model
final class BoxInstance {
    var name: String
    var fixedShape: ShapeInstance?

    var shapeType: String?

    var hasFixedShape: Bool {
        return shapeType == nil && fixedShape != nil
    }

    @Relationship(deleteRule: .nullify, inverse: \Container.box)
    var currentContainer: Container? = nil

    #Index<BoxInstance>([\.shapeType])

    init(name: String, fixedShape: ShapeInstance?, shapeType: String?) {
        self.name = name
        self.fixedShape = fixedShape
        self.shapeType = shapeType
    }
}

@Model
final class ShapeInstance {
    var name: String
    var shapeType: String?

    @Relationship(deleteRule: .nullify, inverse: \Container.shape)
    var currentContainer: Container? = nil

    #Index<ShapeInstance>([\.shapeType])

    init(name: String, shapeType: String?) {
        self.name = name
        self.shapeType = shapeType
    }
}

struct ContainerView: View {
    private var boxes: [BoxInstance]
    private var shapes: [ShapeInstance]

    @State var container: Container

    init(container: Container, boxes: [BoxInstance], shapes: [ShapeInstance]) {
        self.container = container
        self.boxes = boxes.filter { box in
            box.currentContainer == nil || box.currentContainer == container
        }
        if let shapeType = container.box?.shapeType {
            self.shapes = shapes.filter { shape in
                    shapeType == shape.shapeType
            }
        } else {
            self.shapes = shapes.filter { shape in shape.shapeType == nil }
        }
    }

    var body: some View {
        // Defensive: reset shape if not in current valid options
        if !(container.box?.hasFixedShape ?? false) {
            if container.shape != nil && !shapes.contains(where: { $0 === container.shape }) {
                container.shape = nil
            }
        }

        return GroupBox {
            ControlGroup {
                Picker(selection: $container.box) {
                    Text("NA").tag(nil as BoxInstance?)
                    ForEach(boxes, id: \.self) { box in
                        Text(box.name).tag(box as BoxInstance?)
                    }
                } label: {
                    Label("", systemImage: "archivebox")
                }
                      .pickerStyle(.navigationLink)

                if !(container.box?.hasFixedShape ?? false) {
                    Divider()
                    Picker(selection: $container.shape) {
                        Text("NA").tag(nil as ShapeInstance?)
                        ForEach(shapes, id: \.self) { shape in
                            Text(shape.name).tag(shape as ShapeInstance?)
                        }
                    } label: {
                        Label("", systemImage: "dot.squareshape")
                    }
                      .pickerStyle(.navigationLink)
                }
            } label: {
                Text("Box")
            }
        }
    }
}

struct ContentView: View {
    private var containers: [Container]
    private var boxes: [BoxInstance]
    private var shapes: [ShapeInstance]

    init() {
        let fixedShape = ShapeInstance(name: "Fixed", shapeType: nil)
        let otherShape1 = ShapeInstance(name: "Round", shapeType: "Round")
        let otherShape2 = ShapeInstance(name: "Circular", shapeType: "Round")
        let box1 = BoxInstance(name: "Box A", fixedShape: nil, shapeType: "Round")
        let box2 = BoxInstance(name: "Box B", fixedShape: fixedShape, shapeType: nil)

        let container1 = Container(box: box1, shape: otherShape1)

        self.containers = [container1]
        self.boxes = [box1, box2]
        self.shapes = [otherShape1, otherShape2, fixedShape]
    }


    var body: some View {
        NavigationStack {
            List {
                ForEach(containers, id: \.self) { c in
                    ContainerView(container: c, boxes: boxes, shapes: shapes)
                }
            }
        }
    }
}


@main
struct SwiftUIMinimalPickerBugSampleApp: App {
    var body: some Scene {
        WindowGroup {
            ContentView()
        }
    }
}