Open Radar

 
Run the code below. Press the button once (or twice at most) is almost certain to crash the app. 

The app shows a list containing two sections, each of which have four items. When button is pressed, it inserts a new item into each section and also changes the section order.

import SwiftUI

let groupNames = (1...2).map { "\($0)" }
let groupNumber = groupNames.count

let itemValues = (1...4)
let itemNumber = itemValues.count

struct Item: Identifiable {
    var value: Int
    var id = UUID()
}

struct Group: Identifiable {
    var name: String
    var items: [Item]
    var id = UUID()
    
    // insert a random item to the group
    mutating func insertItem() {
        let index = (0..<itemNumber).randomElement()!
        items.insert(Item(value: 100), at: index)
    }
}

struct Data {
    var groups: [Group]

    // initial data: 2 sections, each having 4 items.
    init() {
        groups = groupNames.map { name in
            let items = itemValues.map{ Item(value: $0) }
            return Group(name: name, items: items)
        }
    }
    
    // multiple changes: 1) reverse group order 2) insert a random item to each group
    mutating func change() {
        groups.reverse()
        for index in groups.indices {
            groups[index].insertItem()
        }
    }
}

struct ContentView: View {
    @State var data = Data()
    
    var body: some View {
        VStack {
            List {
                ForEach(data.groups) { group in
                    Section {
                        ForEach(group.items) { item in
                            Text("\(group.name): \(item.value)")
                        }
                    }
                header: {
                        Text("Section \(group.name)")
                    }
                }
            }
            Button("Press to crash the app!") {
                withAnimation {
                    data.change()
                }
            }
            .padding()
        }
    }
}